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Synthesis of Embryonic Zeolites and Their Use to Process Bulky Molecules Kok-Giap HAW, Jean-Pierre Gilson, Nikolai Nesterenko, Mariame Akouche, Hussein El Siblani, Jean-Michel Goupil, Baptiste Rigaud, Delphine Minoux, Jean-Pierre Dath, and Valentin Valtchev ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.8b01936 • Publication Date (Web): 25 Jul 2018 Downloaded from http://pubs.acs.org on July 25, 2018
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Synthesis of Embryonic Zeolites and Their Use to
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Process Bulky Molecules
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Kok-Giap Haw, †, § Jean-Pierre Gilson, † Nikolai Nesterenko, ‡ Mariame Akouche, † Hussein El
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Siblani, † Jean-Michel Goupil, † Baptiste Rigaud, † Delphine Minoux, ‡ Jean-Pierre Dath, ‡
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Valentin Valtchev †,*
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†
Normandie Univ, ENSICAEN, UNICAEN, CNRS, Laboratoire Catalyse et Spectrochimie,
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14000 Caen, France ‡
Total Research and Technology Feluy (TRTF), Zone Industrielle C, 7181 Feluy, Belgium
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Abstract
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X-ray
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tetrapropylammonium (TPA+) hydroxide as a structure directing agent. Their physicochemical
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properties are compared to those of a highly crystalline ZSM-5. Embryonic zeolites contain
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fewer acid sites, but their micropore volume and SBET area are higher than crystalline MFI-type
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material synthesized with TPA+. They can be introduced in the mesopores of a shaped silica-
amorphous
zeolite
precursors,
embryonic
zeolites,
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prepared
using
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doped alumina matrix by two procedures: i) impregnation of externally bred embryos, ii) in-situ
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growth of embryos to prepare composite catalysts. Their catalytic performances in the
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dealkylation of 1,3,5-triisopropylbenzene (TiPBz), a bulky molecule hardly penetrating the
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micropores of most zeolites, are superior to their highly crystalline ZSM-5 counterpart and the
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silica doped alumina support. This is attributed to the highly accessible active sites of embryonic
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zeolites, located in an open microporosity leading to shorter diffusion pathlengths. They offer
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interesting prospects to process bulky molecules in fields such as oil refining, petrochemistry,
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biomass upgrading.
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Keywords: embryonic zeolites, ZSM-5, composite, catalysis, bulky molecules processing,
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dealkylation
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1. INTRODUCTION
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Molecular sieve zeolites have proved exceptionally useful as heterogeneous catalysts in a
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number of industrial processes.1,2 They typically offer high specific surface area located in
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ordered micropores of molecular dimensions (ca. 0.25 – 1 nm) and active sites promoting
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superior shape selectivity in catalytic transformations.3-5 However, the downside for catalysis in
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such a confined environment is some often severeoften-severe transport limitations of reactants
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and products. Due to their limited pore sizes (< 1.0 nm), current zeolites cannot be applied to
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significantly process molecules with kinetic diameters much larger than 1.0 nm.5 Thus tTheir
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only active sites accessibility accessibile to bulky molecules is limited toare those located on the
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surface of the zeolite crystals and their pore mouths of zeolites. This handicap is particularly
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pronounced in the conversion of heavy fractions of crude and bio-sourced oils.
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Zeolites based catalysts are for instancehowever very efficient to transform convert heavy
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gasoil fractions or residues to olefins and gasoline (FCC) or middle distillates (Hydrocracking),
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but because they are engineered as composite catalysts where other components (e.g. amorphous
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silica alumina) first reduce somewhat the molecular weight of the feeds. The ongoing
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“whitening” of the oil barrel (ever heavier fractions to be converted in transportation fuels and
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petrochemicals) and biomass conversion will require extra-large pore zeolites.6 A number of
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zeolite structures possess extra-large pores, but none of them reached the commercial stage due
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to their limited (hydro)thermal stability.7 The quest for alternative materials combining zeolite-
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type of activity with better accessibility to their active sites is one of the top priorities of in
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zeolite chemistscatalysis. Since their first commercial use, much work has been expandedwas
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devoted to prepare hierarchical or mesoporous zeolites to improve the catalytic performance of
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purely microporous zeolites.8-10 A mesoporous network connected to the native micropores in
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zeolite crystals decreases the impact of mass transport limitations, but it does not change affect
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the intrinsic limited ability of hierarchical zeolites to process bulky molecules. Decreasing the
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zeolite crystal size leads to a largermore (active) external surface accessible to bulky molecules
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and is also an very effective way to reduce diffusion pathlengths.
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Advances in understanding zeolite nucleation and growth lead to more rational zeolite
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synthesis, especially to control their crystal size.9-17 This Such newly acquired knowledge
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allowed to control better the crystallization of zeolites and tune their physicochemical
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properties.18 For instance, ultra-small non-aggregated FAU- and EMT-type zeolites were
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produced with narrow particle size distribution.19,20 Such A dramatic decrease of crystal size to
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10 – 20 nm resulted in materials with external surface areas up to 250 m2 g-1. These crystals
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contain between 5 and 10 unit cells. Such drastic reduction ina crystal size is also beneficial for
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on the mass transport of small molecules. However, with these nanozeolites, and any other type
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of hierarchical zeolites, the major portion of the active sites remains inaccessible for molecules
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with size larger than the pore openings.
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A further reduction of thein crystal size is a promising alternative that wouldto combine zeolite
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activity with and more accessible surfaces. However, the preparation of zeolitic units with a size
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below 8 – 10 nm results in X-ray amorphous materials and brings difficulties in their
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identification. Some earlier works reported the preparation of X-ray amorphous materials under
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condition typical for zeolite formation. Manton and Davitz used tetraalkylammonium cations,
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largely usedubiquitous in the synthesis of high silica zeolites, to prepare amorphous
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aluminosilicates (ASA).21 They found reported a relationship between the size of the cation and
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the median size of the pores. The A solid synthesized with tetrapropylammonium (TPA+)
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showed the highest catalytic activity in the cracking of n-heptane. Shortly after this
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studythereafter, Jacobs et al. reported that precursors of ZSM-5 exhibit catalytic activities similar
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to their crystalline counterpart.22 This was attributed to zeolite units with a size below their
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detection limit by X-ray diffraction (XRD); they resorted to Infrared (IR) spectroscopy to
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evaluate the crystallinity of XRD amorphous materials. Corma and Pérez-Pariente also studied
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the physicochemical properties of amorphous silica-alumina prepared from tetraalkylammonium
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solutions in the presence of sodium and potassium.23 Their goal was to obtain amorphous
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matrices with a controlled porosity and acid site density. They paid particular attention to the
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(hydro)thermal stability of the resulting materials: upon severe steaming, their zeolite precursors
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dealuminated and their micropores collapsed. A ZSM-5 precursor prepared in the presence of
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TPA·OH was used for the synthesis of amorphous mesoporous silica-alumina (MSA) by Bellussi
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et al.24 They highlighted the occurrence of some order in the zeolite precursor species, by a
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combined combining IR and
Al MAS NMR spectroscopy characterization. Such MSA
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materials showed outstanding performance in propene oligomerization, attributed to their a
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peculiar pore system combined with remarkable superior acidity. They same group further
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performed a more detailed study on the impact of the ratio between the silica source, TPA·OH
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content and the type of solvent (methanol, ethanol, 1-propanol) on the pore structure of their
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MSA.25 Pinnavaia and co-workers studied the preparation of mesopousres materials from zeolite
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precursor systems. Their materials were substantially more (hydro)thermally stable and
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displayed a high catalytic activity.26,27 Corma and co-workers prepared amorphous zeolite
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precursors of ZSM-12, Beta, NU-87, ITQ-7 and -21 and showed that they are stable for under
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steaming calcination up to 923 K.28 The same group reported the room temperature synthesis of
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micro-mesoporous material by dual templating, i.e., combining TPA with simple molecules as
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tromethamine, cysteamine and ethanolamine.29 Recently, FAU-type zeolite precursors were used
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as basic catalysts for in the Knoevenagel condensation of benzaldehyde with ethyl
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cyanoacetate.30 The product, ethyl α-cyanoacetate, can be formed in the super cage of the FAU-
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type structure, but it is too big to be released through the 12-member ring (12MR) window. The
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crystal growth kinetics of the zeolite was used to control improve their catalystic performances.
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A sample taken at the end of the induction period, i.e. just before the appearance of a X-Ray
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crystalline phase showed displayed the highest catalytic activity. A combined Raman-HEXRD-
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solid-state NMR analysis revealed that substantial changes in the ring structure of the
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aluminosilicate precursor occurred. Thus, their high catalytic activity was attributed to a
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combination of zeolite type basic sites combined with a more open structure of semi- crystalline
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zeolite units.
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Recently we developed an advanced catalyst based on ultra-small zeolite crystals, the so-called
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embryonic zeolites, supported on a shaped (microspheres and extrudates) silica-doped alumina
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matrix providing the necessary mechanical resistance for such a composite catalyst.31 The goal of
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the present study is to shed more light on the structure, properties and catalytic potential of
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embryonic zeolites in bulky hydrocarbons conversion. Two catalyst preparation procedures are
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used in this study: i) the deposition, by nano-casting, of externally bred embryonic zeolites on a
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silica-doped alumina matrix (Siralox 30), ii) the in-situ growth of embryonic zeolites on a silica-
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doped alumina matrix (Siralox 30. Their catalysts catalystic performances are evaluated in the
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dealkylation of a model bulky molecule, 1,3,5-triisopropylbenzene (1,3,5-TiPBz, kinetic
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diameter, 0.95 nm) hardly penetrating the micropores of any industrially relevant zeolite.
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2. EXPERIMENTAL SECTION
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2.1 Preparation of ZSM-5 precursor suspension
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ZSM-5 precursors were prepared using the following reagents: tetrapropylammonium
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hydroxide (TPA·OH 20% in water, Alfa Aesar) solution, distilled water, aluminum sulfate (98%,
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Aldrich), and tetraethylorthosilicate (TEOS 98%, Aldrich). After mixing the reactants, the
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solution was allowed to hydrolyze at room temperature for 4 h in a closed bottle. A complete
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hydrolysis was confirmed by the appearance of a monophasic clear solution. The composition of
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the initial clear solution was: 4.5(TPA)2O:0.25Al2O3:25SiO2:430H2O:100EtOH, where EtOH is
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the side product of TEOS hydrolysis. The following series of zeolite precursor (ZP) solutions
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was prepared:
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ZP-1: SiO2/Al2O3=100, hydrolyzed at room temperature for 4 h followed by hydrothermal treatment at 100 °C for 12 h.
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ZP-2: SiO2/Al2O3=100, hydrolyzed at room temperature for 4 h.
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As prepared zZeolite precursor suspensions, without any any further purification, were further
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used for theto prepareation of the catalysts (see below). In order tTo study the physicochemical
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properties of the ZP-1 and ZP-2 solids, their suspensions were freeze dried. The calcination was
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performed at 550 °C (at 2 °C·min-1 ramp rate) in air flow. As mentioned, the obtained the parent
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zeolite precursor suspensions were not subjected to purificationpurified, thus the SiO2/Al2O3 was
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similar to the initial gel and the solid yield was close to 100 %.
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Reference samples: A commercial ZSM-5 sample (MFI90) with Si/Al ratio of 45 was provided
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by Sud-ChimieChemie (now Clariant). A highly crystalline nano-sized ZSM-5 prepared from the
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same initial suspension described above at 100 °C for 29 h was used as a reference sample. A
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highly crystalline micron-sized ZSM-5 prepared from an initial suspension with the molar
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composition 4.5(TPA)2O:0.07Al2O3:25SiO2:1500H2O:100EtOH at 160 °C for 24 h was also
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used for comparative purposes.
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2.2 Catalyst carrier
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A commercial silica-doped alumina microsphere, Siralox 30 (γ-Al2O3 doped with 30 % SiO2,
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Sasol - Germany) was used as a catalyst carrier. The initial (green) matrixIt was calcined under
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air at 600 °C for 10 h. A cationic polymer, PDDA (poly(diallyldimethylammonium) chloride, 20
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wt. % in water, Aldrich) diluted to 0.5 wt. % with distilled water was used to reverse the negative
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surface charge of Siralox 30. The pH of the 0.5 wt. % PDDA solution was adjusted to 8 – 9 by
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using a 0.1 M ammonia solution. A weight ratio Siralox 30/PDDA ratio of 0.3 follows by drying
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at 60 °C overnight.
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2.3 Preparation of Embryonic ZSM-5/Siralox 30 composites by impregnation
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In a typical experiment, the Siralox 30 was impregnated with thea pre-ageda clear suspension
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containing externally bred embryonic zeolites. The weight ratio of aged precursor/Siralox 30 was
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2 for the 1st first impregnation. The sample was then dried at 60 °C for 24 h and subsequently
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dried at 100 °C for 12 h. The impregnation step was repeated twice with a suspension/carrier
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ratio of 1.5 and 1 for the 2nd second and 3rd third impregnations, respectively. After a drying step,
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both organic template and the cationic polymer were decomposed by air calcination from room
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temperature toat 550 °C (2 °C·min-1 ramp rate) and heldfor 4 h under airat this final temperature.
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The calcination temperature was reached with a 2 °C·min-1 ramp. The calcined composite was
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ion-exchanged with 0.3 M NH4NO3 solution (solid:liquid=1:100, wt./wt.). The H-form of the
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ZSM-5/Siralox 30 composites was obtained by calcination at 550 °C (at 2 °C·min-1 ramp) in air
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flow. Samples prepared by Impregnation (WI) with ZP-1 and ZP-2 are denoted WI-1 and WI-2,
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respectively.
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2.4 In-situ preparation of Embryonic ZSM-5/Siralox 30 composites by hydrothermal treatment
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The Siralox 30 matrix was mixed with ZP-1 precursor suspension at solid/liquid ratio of 0.5/25
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and homogenized on a shaker at a speed of( 125 rpm) for 2 h. The crystallization was then
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performedproceeded under hydrothermal conditions at 100 °C and samples were taken every 12
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h up to 192 h (8 days). The samples prepared by hydrothermal treatment are denoted HT-x,
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where x is the duration (days) of the hydrothermal treatment. The composite was separated from
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its mother liquor and treated in distilled water under ultrasonic radiation for 5 min to disperse
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any loosely attached particles, followed by washing under vacuum filtration until pH 8 – 9 and
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dried at 100 °C. The composites were calcined at 550 °C (at 100 °C·h-1 ramp rate) in air flow for
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4 h, subjected to ion- exchanged with 0.3 M NH4NO3 solution (solid:liquid=1:100, wt./wt.),
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washed, dried and calcined at 550 °C (at 2 °C·min-1 ramp rate) in air flow.
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2.5 Characterization
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All materials were characterized by X-ray diffraction (XRD) using a PANalytical X’Pert Pro
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diffractometer with Cu Kα radiation (λ = 1.5418 Å). The samples diffractograms were scanned
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recorded in the 2θ range of 3-50° with a step size of 0.02°. Electron micrographs were taken on a
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TESCAN Mira scanning electron microscope (SEM) operated at 30 kV. To improve the
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electrical conductivity of the sample, they were sputtered with gold or platinum. Nitrogen
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adsorption measurements were carried out on a Micromeritics ASAP 2020 surface area analyzer.
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The calcined samples were analyzed after degassing at 300 °C. The isotherms were recorded
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using ASAP 2020 analysis program. The microporous volume (Vmic / cm3 g-1) and external
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surface area (Sext / m2 g-1) were obtained from t-plot based on the Harkins-Jura equation. The
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macro-mesopores size distribution was obtained from the desorption branch using the Barrett
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Joyner Halenda algorithm assuming cylindrical pores. For refined analysis, micro-mesopores
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size distribution was extracted from Density Functional Theory modelling of the adsorption
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branch. Particles size analysis was performed by dynamic light scattering (DLS) with a Malvern
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ZetaSizer Nano Series instrument. Before transferring samples into the test cells, the zeolite
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precursor particles were stabilized in water at 25 °C. TG-DSC measurements of different
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samples were carried out on a SETSYS evolution instrument (SETARAM). About 10 mg of each
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sample was introduced in an alumina crucible and that is loaded in the analyzer chamber. The
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samples was were heated from 30 °C to 800 °C with a heating ramp of 5 °C·min-1 under air (flow
2
rate: 40 mL·min-1). Prior to the analysis the physisorbed TPA+ was eliminated by ion exchange.
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Each sample was exchanged two times with 1.0 M sodium sulfate solution (composite/liquid =
4
1/50 wt./wt.) at ambient temperature under agitation on a shaker at a speed of 175 rpm for 3 h.
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After that, tThe composite was recovered from the solution, washed with distilled water and
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dried. A Siralox 30 that has been impregnated by with a TPA·OH solution (4.5TPA2O:430H2O)
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was used as a reference sample. It was also exchanged two times with Na+ before subjected toits
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TG-DSC analysis.
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All NMR measurements were done with 4-OD mm zirconia rotors and with a spinning (speed
10
rate of 12 kHz) at the magic angle. The solid state {1H}-13C CP-MAS NMR spectra were
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recorded on a Bruker Avance 400 spectrometer operating at (100.6 MHz for
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pulse program, a π/2 pulse of 3.7 µs on 1H, a contact time of 2 ms and a recycle delay of 2 s were
13
used.
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MHz for. 27Al) and MAS NMR spectra was obtained with a π/12 pulse and a recycle delay of 1 s.
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The amount of non-tetrahedral Al was estimated by the integration of peak area using the Dm-fit
16
program.32,33 The results were verified employing with the Top Spin program. The sSolid state
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29
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T) operating at 99.3 MHZ, using zirconia rotors of 4 mm outer diameter spun at 12 KHZ. A
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single pulse excitation (30° flip angle) is was used with a recycle delay of 30s. TMS was used
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asthe reference for 29Si and 13C, while a 1M Al(NO3)3 solution was employed as athe reference
21
for 27Al.
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C). During the
Al MAS NMR was recorded on a Bruker Avance 500 spectrometer operating at( 130.3
Si NMR (1pulse) was were recorded also on a Brucker Avance III-HD 500 spectrometer (11.7
129
Xe NMR experiments were performed on a Bruker AV III 400 wide bore spectrometer
equipped with a 10 mm BBO probe, operating at a frequency of 110.64 MHz for 129Xe. Prior to
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each experiment, the sample was introduced into a home-designed (10 mm O.D.) NMR tube and
2
dehydrated under high-vacuum overnight at 573K. For thermally polarized (TP)
3
experiments, xenon gas (99% enriched
4
by varying the pressure from the lower to the higher value. For hyperpolarized (HP) 129Xe NMR
5
experiments, the hyperpolarized xenon gas was obtained using a home-built xenon polarizer34
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based on the spin-exchange optical pumping (SEOP) technique.35,36 HP 129Xe NMR spectra were
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acquired under a continuous re-circulating flow at 150 mL·min-1 of a gas mixture containing 96
8
% He, 2 % N2 and 2 % of natural abundance xenon, with a 129Xe partial pressure of ~20 torr. For
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all variable temperature (VT) measurements and after each temperature change performed at a
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speed of 5 K·min-1, a waiting delay of about 20 min was generally necessary to ensure a
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homogeneous temperature all over the sample, and this stability was checked by directly
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monitoring the xenon chemical shifts. All spectra are were referenced to free xenon gas at 0 ppm.
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The IR spectra of ZP-1, ZP-2 and highly crystalline ZSM-5 reference samples were recorded
14
on a SHIMADZU IRAffinity-1 Fourier Transform Infrared Spectrophotometer using the KBr
15
pellet technique. Pyridine adsorption was used to evaluate their acidity of the samples. The study
16
was performed using a standard in-situ FTIR set-up. These Infrared IR spectra were recorded on
17
a Nicolet Magna 550 FTIR spectrometer equipped with a DTGS detector at 4 cm-1 optical
18
resolution, with one level of zero-filling for the Fourier transform. Prior to the measurement,
19
sample was grinded and pressed into a self-supporting disc (diameter: 2 cm, approx. 5 mg cm-2)
20
and activated in vacuum (ca. 10-6 hPa) at 460 °C for 2 h at 2 °C·min-1. After cooling to room
21
temperature, the spectrum of the sample was recorded for further use as a reference. Then, a
22
pressure of 1.33 hPa of pyridine was established in the cell at ambient temperature to reach
23
saturation. The wafer was heated at 100 °C for 15 min to facilitate diffusion of pyridine into
129
129
Xe NMR
Xe isotope) was directly adsorbed into on the sample
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throughout the sample. Successive evacuations were performed at 25 °C, 50 °C, 100 °C, 150 °C,
2
200 °C, 250 °C, 300 °C, and 350 °C at 15 min intervals. All spectra were normalized to 2.5 mg
3
cm-2 wafer. Quantification of the acid sites was performed on the difference spectra (spectra of
4
pyridine - coveredadsorbed on a sample - reference spectra). The amounts of acidic Lewis site
5
(L) and Brønsted site (B) were determined using the band area from the coordinated pyridine at
6
1450 cm-1 and that of the adsorbed pyridinium at 1545 cm-1 respectively. The molar extinction
7
coefficients (Ɛ) used for quantification were taken from Khabtou et al.37: Ɛ1545 (B-pyridine) = 1.8
8
cm µmol-1 and Ɛ1455 (L-pyridine) = 1.5 cm µmol-1. The OMNIC version 7.3 SP1 program was
9
used for data processing.
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Inductively coupled plasma–atomic emission spectroscopy (ICP-AES) on an OPTIMA 4300
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DV (Perkin–Elmer) was used for theto determineination of theall chemical composition by using
12
an OPTIMA 4300 DV (Perkin–Elmer) instrument.compositions
13 14
2.6 Catalytic testing
15
The performances of the cCatalystsic performances were evaluated in the dealkylation of a
16
model bulky molecule, 1,3,5-triisopropylbenzene (TiPBz) in a down flow atmospheric reactor.
17
Its kinetic diameter (0.95 nm), is well above the pore openings of the MFI-type zeolite (0.56 nm)
18
and TiPBz is therefore commonly used to study the external surface properties of zeolites,
19
including the large pores (12 MR) ones. In a typical catalytic test, 20 mg of catalyst were loaded
20
at the center of a stainless-steel tubular reactor (internal diameter of 1/2'') and activated in-situ at
21
460 °C (ramping from room temperature at 5 °C·min-1) under air flow (50 ml·min-1) for 1 h and
22
then under a dry nitrogen flow (50 ml·min-1) for 0.5 h. The temperature was subsequently
23
lowered to 300 °C, the nitrogen flow diverted to a saturator (maintained at operated at 70 °C)
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filled with TiPBz (Alfa Aesar, 97%), generating aand the resulting TiPBz partial pressure of (170
2
Pa) . sentfed to the reactor. The WHSV (Weight Hourly Space Velocity) was held constant at 8
3
h-1 for all tests. The conversions were measured at 300 °C over a period of 180 min. The online
4
analysis of the products and unconverted reactant, transferred via a heated line heated at (150 °C)
5
to a gas sampling valve, were monitored by a Varian CP-3800 Gas Chromatograph equipped
6
with a flame ionization detector (FID) detector and a HP-PONA cross-linked methyl siloxane
7
column, 50 m (L) x 0.2 mm (ID) x 0.5 µm (film thickness). The temperature of the column
8
temperature was kept constant at 160 °C,
9
temperature was maintained at 200 °C while and the detection temperature was maintained at
10
250 °C.
11
3.0 RESULTS
throughout the measurement. Tthe injection
12
We reported elsewhere the synthesis of pure embryonic zeolites.38 The impact of Si/Al ratio,
13
temperature and time on their formation of embryonic zeolitic units were screened. In the present
14
study we employed use an optimized system (SiO2/Al2O3=100) to prepare embryonic zeolites at
15
100 °C (ZP-1) and room temperature (ZP-2) and proceed to their loading on a shaped silica-
16
doped alumina matrix, Siralox 30.
17 18
3.1 Physicochemical characterization
19
All synthesized materials are X-ray amorphous (Figure S1). However, the IR spectra (KBr
20
pellet) of ZP-1 and ZP-2 exhibit absorption bands characteristic of pentasil type zeolites.39 More
21
precisely, the 1225 cm-1 (external asymmetric stretching) and 550 cm-1 (double five-membered
22
rings) bands from the MFI structure are clearly present (Figure S2). These bands are larger and
23
less intense than those of the highly crystalline reference sample. Although not intense, they
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1
illustrate that some elements of a zeolite structure are already present in the X-ray amorphous
2
precursors. According to DLS, the particle size of both samples, ZP-1 and ZP-2, is 3 – 4 nm
3
(Figure S3). The material synthesized at 100 °C (ZP-1) contains small amounts of a second
4
population of larger (ca. 18 nm) particles. TEM inspection of zeolite embryos shows highlights a
5
uniform mass of apparently amorphous particles (Figures S4a). Upon drying the solid product
6
agglomerates and form large particles with straight edges (Figure S4b). The TEM inspection of
7
the large particles showed shows identical features identical with to the freeze dried ZP-1
8
suspension (Figure S4c). No morphological differences are observed between ZP-1 and ZP-2. N2
9
adsorption analysis of calcined ZP-1 and ZP-2 indicates that they are essentially microporous
10
(Figure 1). They display a type Ib isotherm,40 characteristic of extra-large microporous materials
11
with pores ranging between 1 and 2.5 nm. Such characteristics are substantially different from
12
highly crystalline MFI-type zeolites. The ZP-1 and ZP-2 BET specific surface area and
13
micropore volume are respectively 627 and 640 cm2 g-1 and 0.31 and 0.30 cm3 g-1. This suggests
14
a microporous structure more open than the crystalline material obtained with the same template.
15
For the sake of comparison, the isotherm of a highly crystalline nano- and micron-sized ZSM-5
16
zeolite synthesized with TPA+ is included in Figure 1.
17 18 19 20 21 22 23
500
ZP-1 ZP-2
Vads / mL (STP) g-1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 14 of 49
400
Nano-sized ZSM-5 Micron-sized ZSM-5
300 200 100 0 0.0
0.2
0.4
0.6
0.8
1.0
P / P°
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Figure 1. N2 adsorption/desorption isotherms of ZP-1, ZP-2 and highly crystalline micron- and
2
nano-sized ZSM-5 samples.
3 4
The state of aluminum in as-synthesized and calcined zeolite embryos is studied by 27Al MAS
5
NMR (Figure S5). The spectra of as-synthesized embryonic zeolites exhibit a single peak
6
centered at 53 ppm. This peak is characteristic of tetrahedral aluminum in low aluminum silicon
7
rich zeolites frameworks. After calcination at 550 °C a decrease in intensity suggests that part of
8
the Al leaves this tetrahedral coordination. Indeed, a second peak at 0 ppm, typical of
9
octahedrally coordinated Al, is observed in calcined samples. A large peak below 0 ppm reveals
10
the presence of other aluminum species, their nature is difficult to be specified at this stage. The
11
amount of nnon tetrahedralnon-tetrahedral Al is estimated to be about 30 % in ZP-1 and ZP-2
12
samples. and The their 53 ppm peak broadens indicating some distorted tetrahedral units. The
13
amount of Al leaving the tetrahedral coordination is substantially higher than in the ZSM-5
14
zeolite, where the extra framework Al formed upon calcination is usually below 10 %. However,
15
the amount of Al remaining in tetrahedral coordination is substantially higher than what is
16
observed for many commercial amorphous silica-aluminas, indicating an excellent retention of
17
potential active sites.41
18
The
29
Si NMR spectra of Asas-synthesized and calcined ZP-1 and ZP-2 samples were 29
19
subjected to
20
and Q4, were observed. Their positions of the peaks match well with theose already literature
21
date reported for the ZSM-5 intermediates.42-44 Based on tThe deconvolution of the spectra by
22
using the dm-fit program (SI), ) yields the relative fraction of each of the observed species was
23
determined (Table S1). As can be expected, the number of Q2 and Q3 environments was is larger
Si NMR analysis (Figure S6). shows The different silicon environments, Q2, Q3
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1
in ZP-1 and ZP-2 samples in respectthan in to fully crystalline ZSM-5. These two chemical shifts
2
retained their positionare unchanged after calcination, while their peak areas decreaseed. This
3
The latter decreased wais coupled with an increase of in Q4 species. and indicates Later result is
4
related with thethe dealumination of ZP-1 and ZP-2 samples (cf., revealed by
5
spectra), and condensation of silica species upon during calcination.
27
Al NMR
6 7 8
9 10 11
Table 1. Physical properties of the ZP-1, ZP-2 and highly crystalline ZSM-5. Samples
SBET/ m2g-1
a
ZP-1
627
9
0.31
0.33
ZP-2
640
9
0.30
0.31
Nano-sized ZSM-5
525
108
0.20
0.40
Micron-sized ZSM-5
369
6
0.18
0.19
a
Sext/ m2g-1
a
Vmicro/ cm3g-1
Vt/ cm3g-1
Sext and Vmic were determined by t-plot. Thermogravimetry (TG/DSC) and
13
C NMR spectroscopy provide valuable insights in the
12
interaction of organic structure directing agents with zeolites.50 TG analysis of highly crystalline
13
ZSM-5 nanocrystals shows a weight loss of about 2 wt. % (water), below 130 °C (Figure S7) and
14
its associated endotherm in DSC. A second peak (weight loss of about 9 wt. %) in the
15
temperature range 250 – 450 °C associated with a DSC exotherm is due to the decomposition of
16
TPA+ cations. The TPA+ release exhibits a low temperature shoulder at about 280 °C,
17
characteristic of loosely attached cations probably located on the surface of zeolitic units. The
18
peak centered at 340 °C is typical of TPA+ cations at the intersection of straight and zig-zag
19
channels. No weight loss or other changes are observed at temperatures higher that 500 °C
20
(Figure S8). ZP-1 and ZP-2 show higher weight losses and somewhat different TG profile than
21
the reference ZSM-5. ZP-2 contains a small amount (ca. 7 wt. %) of surface water released at
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about 100 °C. A much larger release (ca. 13 wt. %) takes place between 180 °C and 280 °C and
2
the associated endotherm suggests it is due to water release, located in a more confined space or
3
strongly bound to the aluminosilicate structure. It cannot be excluded, however, that some
4
loosely attached TPA+ is also released within this temperature range. An exothermic weight loss
5
(6 wt. %) is recorded between 280 and 380 °C and signals the thermal degradation of TPA+. A
6
similar peak appears inis observed on ZP-1, synthesized at 100 °C. The larger release (ca. 40 wt.
7
%) in the temperature range 50 to 280 °C is attributed to loosely adsorbed water and TPA+
8
species. Again, a peak typical of the combustion of TPA+ interacting with the aluminosilicate
9
matrix is observed at about 340 °C.
10
In the 13C CP MAS NMR spectrum of TPA+ occluded in zeolite ZSM-5, Figure 2, the C1, C2
11
and C3 signals are characteristic of the TPA+ carbons in an MFI-type structure. The splitting of
12
the C3 peak, visible solely in the spectrum of ZSM-5, was previously attributed to methyl groups
13
in two different environments.45-47 The central nitrogen atom is positioned at the channel
14
intersections and two propyl groups are located in the linear channels (all-trans conformation)
15
while the two remaining propyls chains occupy the zig-zag elliptical channels (V-shape
16
conformation). In addition, the methyl groups of adjacent TPA+ ions are in close contact in the
17
linear channels, leading to a higher field chemical shift. Such a phenomenon splitting is not
18
observed in the spectra of the zeolite precursors (ZP-1 and ZP-2), indicating a higher mobility
19
and a looser fit of the TPA+ cations.
20
129
Xe NMR is very useful to characterize the pore structure of calcined embryonic zeolite
21
units.48 ZP-1 exhibits a sharp peak at 113 ppm with a small shoulder at about 123 ppm (Figure
22
3a). A peak at 153 ppm is observed on the (reference) nanosized ZSM-5 (MFI90) (Figure 3b).
23
The higher chemical shift of the latter points to Xe located in a more confined environment. This
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Page 18 of 49
1
again indicates, again, tthat the embryonic zeolite units possess pores larger than a typical MFI-
2
type material. The relatively narrow linewidth of the embryonic zeolites peak reveals is
3
indicative of a more open structure allowing a faster exchange than in the case of fully
4
crystallized zeolites.
5 6 7 8 9 10 11 13
C CP MAS NMR spectra of TPA+ in nanosized ZSM-5, ZP-1and ZP-2. Inset:
12
Figure 2.
13
tetrapropylammonium cation with the positions of carbon atoms.
14 15 16 17 18 19 20
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Figure 3. 129Xe NMR spectrum of ZP-1 (a) and ZSM-5 (b) acquired under a pressure of 150 kPa
2
at ambient temperature.
3
3.2 Composite catalyst preparation
4
The very small size and easy sintering of zeolite embryos make their handling and shaping in a
5
form appropriate for catalytic testing difficult. We used aA mesoporous silica-doped (30 wt. %)
6
alumina matrix (Siralox 30) is used as a carrier to accommodate zeolite embryos by either
7
impregnation or in-situ growth, vide-infra. Prior to any treatment the matrix is heated at high
8
temperature to control its reactivity. We determined Screening experiments indicated that 600 °C
9
is to be the most appropriate temperature, as it provides a good balance between matrix reactivity
10
and retention of its specific surface area; higher temperatures decreasing substantially the
11
specific surface area (Table S2). The incorporation of zeolite embryos in the matrix is takes place
12
either by impregnation of pre-formed units or by in-situ synthesis under hydrothermal
13
conditions. However, both preparations routes take place in alkaline conditions where matrix and
14
embryos are negatively charged. To promote electrostatic interactions with the negatively
15
charged zeolitic embryos, the charge of the matrix is inverted inverted by adsorbing a cationic
16
polymer, PDDA-Cl (Poly(diallyldimethylammonium chloride)), as described elsewhere.49 The
17
embryos can then be nano-casted on such a modified matrix.
18
3.3 Nano-casted composites
19
ZP-1 and ZP-2 are casted on the modified Siralox 30 matrix by impregnation (WI). XRD
20
analysis indicates their amorphous nature composites are amorphous (Figure S9). The intensity
21
of the broad peak in the 2θ range 25° - 30° 2θ range increases with the number of impregnations
22
thus revealingindicating the increase amountpresence of more zeolitic embryos in the matrix, in
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1
line increases and is visualized with as athe thick layer coating on the matrix observed by SEM
2
(Figure S10).
3
The Nitrogen physisorption sorption isotherm ofon the bare pristine matrix is a combination of
4
type II and IV isotherms together with including a mesoporous contribution (Figure 4a). The
5
composites isotherms of the composites show an increased microporosity at the expense of the
6
total pore volume (Vt) (Table 1) indicating . This clearly shows that zeolite embryos occupy
7
some of the Siralox 30 mesoporosity. BJH pore size distributions show that WI-1 has smaller
8
pores than WI-2 (Figure 4b) and a lower mesopore volume. WI-1 and WI-2 are prepared in a
9
similar way from ZP-1 and ZP-2 embryonic suspensions, respectively. The difference in
10
mesopore volume is attributed to the bigger particles obtained during hydrothermal treatment
11
(ZP-1) compared to a room temperature preparation of zeolite embryos (ZP-2).
12 13
Table 1. Textural properties of the parent matrix and composites obtained after 1 and 3
14
impregnations with ZP-1 and ZP-2. Samples
Number impregnations
of SBET
Vmic
Vt
/ m2 g-1 / cm3 g-1 / cm3 g-1
Siralox 30
-
317
0.00
1.09
WI-1 (ZP-1)
1
450
0.04
0.74
3
598
0.09
0.53
1
445
0.06
0.85
3
566
0.09
0.66
WI-2 (ZP-2)
15 16
The amount of embryonic zeolite in the composite can be estimated by the oxidative
17
decomposition of the TPA+ cations occluded using thermal analysis. Prior to each measurement,
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the physisorbed TPA+ is removed by ion exchange with a 1M NaNO3 solution as TPA+
2
molecules trapped in cages or channel intersections cannot be exchanged. The TPA+ content is
3
evaluated by the weight loss between 320 °C and 550 °C where the oxidative decomposition of
4
the TPA+ is known to take place.50 The average loss, in a similar temperature range, for the pure
5
embryonic ZSM-5 (ZP-1) is about 8 wt. %.1,8 In the Siralox composites, the amount of zeolite
6
embryos was evaluated tois 18, 20 and 22 % after 1, 2 and 3 nano-castings, respectively.
7 8 9 10 11 12 13 14 15 16
Figure 4. (a) Nitrogen adsorption isotherms and (b) BJH pore size distribution of Siralox 30
17
matrix and the composites obtained after 3 impregnations with ZP-1 and ZP-2 suspensions.
18
The composite containing only strongly bound TPA+ cations is further studied by 13C CP MAS
19
NMR (Figure 5). In addition to the TPA+ peaks (Cx), four broad peaks are attributed to the
20
adsorbed PDDA (c-x); their positions are highlighted in the inset of Figure 5 and a single methyl
21
group is present on the composite, as in their parent embryos, vide supra.
22
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1 2 3 4 5 6 7 8
Figure 5. 13C CP MAS NMR spectra of WI-1 composites obtained after 1 and 3 impregnations.
9
Inset: PDDA monomer with the positions of carbon atoms.
10 11
The
27
Al MAS NMR spectrum of the pristine matrix shows signals at 6.6 and 63.4 ppm
12
attributed to octahedrally (AlVI) and tetrahedrally (AlIV) coordinated Al atoms as observed in γ-
13
Al2O3 (Figure 6). The composites spectra, WI-1 and WI-2, exhibit an additional signal at 53.4
14
ppm, indicative of aluminum atoms in tetrahedral coordination integrated in a silicate
15
framework. Tetrahedrally coordinated AlIV is the origin of Brønsted acidity in zeolites and
16
related materials. The acidity of the composites is studied by in-situ IR spectroscopy using
17
pyridine as a probe molecule. Their IR spectra after activation and before pyridine adsorption are
18
shown in Figure S11. ; The they spectrum exhibits a distinct adsorption band at 3740 cm-1 and a
19
shoulder centered around 3600 cm-1. Owing to the intense silanol band of the Siralox matrix, the
20
bridged hydroxyls (3610 cm-1) appear as a shoulder in the IR spectra. The difference spectra (the
21
spectra of the bare pristine matrix is subtracted from those after pyridine adsorption and
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evacuation), are reported in Figure S12. The higher acidity of the composite, compared to the
2
pristine matrix, is evidenced with by an increased intensity on of the protonated pyridine (B-Py)
3
peak at 1545 cm-1. The number and strength of these acid sites is further evaluated by desorbing
4
pyridine at different temperatures, Figure 7; . in particular, tThe number of Brønsted acid sites is
5
significantly higher in the composites than in their parent pristine matrix. Moreover, strong acid
6
sites remain on the WI-1 and WI-2 composites, in contrast to the Siralox matrix and illustrate
7
that their nature is probably more zeolite-like than ASA-like as discussed by Chizallet and
8
Raybaud.51
9 10 11 12 13 14 15 27
16
Figure 6.
17
reference highly crystalline nano-sized ZSM-5 sample.
Al MAS NMR spectra of parent the Siralox 30, WI-1 and WI-2 composites and the
18 19 20 21 22
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1 2 3 4 5 6 7 8 9
Figure 7. TPD of Pyridine adsorbed on embryonic units monitored by IR Analysis. The Si/Al
10
ratio of reference nanosized ZSM-5 sample (MFI90) is 45.
11
3.4 Hydrothermally prepared composites
12
In addition to the above mentioned nano-casting of embryos on a Siralox matrix, in-situ
13
growth of embryonic zeolites on Siralox 30 carrier is also considered. Preliminary experiments
14
showed a poor interaction between the matrix and the zeolite precursor suspension as no
15
substantial changes were observed in the matrix even though the precursor was fully converted to
16
zeolite in the bulk solution. Therefore, prior to the hydrothermal step, the matrix is, as above,
17
pre-treated with a cationic polymer to promote electrostatic interactions with the negatively
18
charged zeolite precursor species. A series of scouting experiments with a ZP-1 precursor (100
19
°C, ½ to 8 days) allowed to optimize the composite formation under hydrothermal conditions.
20
XRD patterns show that all samples are amorphous, including the one hydrothermally treated
21
for 192 h (Figure S13). Although no crystalline phase is detected, some changes in the XRD
22
patterns of the composites are observed. The peaks characteristic of gamma-alumina (37 – 48°
23
2θ) gradually decrease with treatment time while a broad peak, centered at 23° 2θ, appears
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emerges and its intensity increases over prolonged hydrothermal treatment. The crystallization in
2
the bulk solutions of a similar composition is much faster and nanosized ZSM-5 are harvested
3
after only 24 h.
4
The nature of the materials formed on the surface of Siralox 30 is, as above, studied by
5
combining TG analysis and N2 adsorption. The amount of embryonic zeolite is calculated, vide
6
supra, on the basis of the weight loss of TPA+ (Figure S14). As for crystalline MFI-type
7
materials, the main weight loss takes place in the temperature range 300 – 550 °C and the
8
amount of zeolite embryos increases with crystallization time (Tables S2). It is worth mentioning
9
that even though the amount of TPA-containing phase in the composites is higher than the
10
detection limit of XRD, i.e. 3 – 5 wt. %, no X-ray crystalline material is found highlighting . This
11
unambiguously proves the absence lack of long range order in these composites. The fact that
12
ZSM-5 crystals are formed in the bulk solution after 24 h, while the content of embryonic units
13
in the matrix increases for up to 7 – 8 days, suggests that the formation of embryonic zeolites in
14
Siralox 30 is due to left over TPA+ cations reacting with the matrix.
15
N2 adsorption shows that external surface areas and micropore volumes gradually increase
16
with treatment time and to reach a maximum after 8 days of treatment (Table 2). Further
17
extension of theLonger crystallization times leads to a decrease of the SBET area (data not
18
presented). The gradual increase in micropore volume indicates the formation of microporous
19
materials in the matrix. In contrast to the impregnation, zeolitization on the matrix does not
20
decrease the total pore volume (Vt); in fact, a slight increase in the total pore volume (Vt) is
21
observed. The most plausible explanation is that the growth of zeolite embryos comes at the
22
expense of a partial dissolution of the matrix; this explains also the slow formation of the
23
microporosity, vide supra.
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1
Table 2. Textural properties of the parent matrix and the X-ray amorphous composites obtained
2
after different treatment time. Samples
SBET
Vmic
Vt
/m2 g-1
/cm3 g-1
/cm3 g-1
Siralox 30
322
0.00
1.04
HT-0.5
317
0.03
1.20
HT-1.5
328
0.03
1.10
HT-3
342
0.03
0.98
HT-6
397
0.04
1.12
HT-7
414
0.04
1.17
HT-8
419
0.05
1.12
3
To better understand the phenomenon taking place during these hydrothermal treatments, we
4
studied the chemical compositions of the solid and liquid phases harvested are measured. The
5
molar SiO2/Al2O3 ratio in the solid phase (composites) and mother liquor are shown in Figure 8.
6
The temporal changes of silica to alumina molar ratio of the solid are inversely proportional to
7
those of the mother liquor. They This are related toindicates a partial leaching of alumina from
8
the Siralox 30 and the incorporation of some silica species from the ZP-1 precursor. The
9
abundant presence of reactive aluminum species may also cause a slow crystallization of zeolite
10
units. The lowest known SiO2/Al2O3 ratio for ZSM-5 synthesized with TPA+ is 24. Thus, after
11
the rapid bulk crystallization of pre-aged ZP-1 precursor solution, the process slows down,
12
particularly in the pores of the matrix where the mismatch between zeolite stoichiometry and
13
available silica and alumina species hinders the further crystallization process.
14 15
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Figure 8. Changes in SiO2/Al2O3 mole ratio in the solid (a) and liquid (b) phase during the hydrothermal synthesis of composite catalysts.
11 12
Although the formation of the zeolite phase is partially inhibited, a constant increase in the
13
amount of TPA-occluded in the solid phase is observed. N2 adsorption also indicates changes in
14
the pore structure of the material. In the absence of clear XRD evidence for ZSM-5 formation,
15
the existence of embryonic ZSM-5 units is again studied by a combination of
16
NMR39 and
17
in ZSM-5 typically shows peaks at 62.6, 16.3, and a doublet at 10.1/11.3 ppm for C1, C2, and C3
18
carbons, respectively. As mentioned above, a splitting of the C3 is due to different confinements
19
of the terminal methyl carbon in the straight and zig-zag channels. As in the TG-DSC study, the
20
TPA+ impregnated Siralox 30 is used as a reference sample and any physisorbed TPA+ is
21
removed by sodium exchange; the observed NMR spectra represents only TPA+ confined in an
22
aluminosilicate environment.
129
13
C CP MAS
Xe NMR.52 The peak assignments of TPA+ is shown in Figure 9. TPA+ occluded
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1 13
C CP MAS NMR spectra on of the C2 and C3 of TPA+ in the
2
Figure 9. Close-up of on the
3
composites (solid line) and nano-sized ZSM-5 (dashed line). From bottom to top the treatment
4
time is increased in the following sequence: 24 (HT-1), 60 (HT-2.5), 72 (HT-3), 96 (HT-4), 144
5
(HT-6), and 192 (HT-8) h.
6
The intensity of the C2 and C3 of TPA+ cations in the embryonic composites increases with
7
time indicating that more TPA+ is occluded; at the same time, their positions also gradually shift
8
to lower fields. This indicates that the structure of embryonic units is increasingly organized
9
upon prolonged hydrothermal treatment but never reaches the configuration of a fully crystalline
10 11
MFI type zeolite (ZSM-5). 129
Xe NMR provides additional information since xenon is a probe very sensitive to confined
12
spaces.53 Low chemical shift peaks, close to 0 ppm indicate large (meso-)pores, while high
13
chemical shifts indicate more confined space (micro-)pores. Figure S15 compares the
14
NMR spectra of xenon adsorbed on a 1:1 wt. ratio mechanical mixture of nanosized ZSM-5 and
15
Siralox 30, a nanosized ZSM-5, a pristine Siralox 30 matrix and an X-ray amorphous composite
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Xe
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obtained after 6 days hydrothermal treatment (HT-6). The last sample is selected because of its
2
high catalytic activity (vide infra). All spectra are acquired under a pressure of 150 kPa at
3
ambient temperature with enough scans to enhance signal/noise ratio. The 129Xe NMR spectrum
4
of the composite shows a single resonance at 108 ppm, between typical micropore (ZSM-5, 158
5
ppm) and mesopore (pristine matrix, 57 ppm) peaks. The most plausible explanation is that the
6
micro- and mesopores in the composites are in close proximity promoting a fast exchange and
7
thus a single resonance. Such an observation on the intermediate exchange regime is further
8
confirmed by NMR spectra of thermal polarized 129Xe (≈ 99% enriched isotope) adsorbed on the
9
mechanical mixture at different pressure and at room temperature (Figure S16). Each spectrum
10
consists of 3072 scans, using a single 90◦ excitation pulse with a pulse length of 15 µs and a
11
recycle delay of 5 s. The pressure is variatedvaries from the lower lowest to higher highest value.
12
At a pressure of 20 kPa, the 129Xe NMR spectrum shows two resonances: the first, centered at
13
82 ppm, is assigned to xenon adsorbed in the mesopores of the matrix while the second, centered
14
at 127 ppm, corresponds to xenon atoms in the micropores of ZSM-5. The difference between
15
these two resonances increases with the pressure, as the chemical shifts of the first peak
16
decreases (red line) while the second one increases (green line) when pressure increases. The
17
coalescence of both peaks at lower pressure indicates that xenon atoms exchange rapidly
18
between micro and mesopores. When the pressure increases, the exchange is rate slower slows
19
and the single peak evolves in two distinct resonances. It is worth nothing that the intensity of the
20
first resonance increases strongly with the pressure while the increase of intensity is less
21
significant in the case of the second resonance. This is a strong proof that the xenon atoms
22
preferentially adsorb on in the ZSM-5 micropores.
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1
To shed more light on the intimate structure of the composite, both the pristine Siralox 30
2
matrix and the X-ray amorphous HT-6 composite are further investigated with the highly
3
sensitive hyperpolarized (HP)
4
between these two different porous environments. The spectrum of Siralox 30 recorded at 245 K
5
displays a wide
6
reflects a wide distribution of mesopores in the matrix. The chemical shift and intensity of the
7
peaks increase with decreasing temperatures. Below 200 K, a new peak appears at a much higher
8
chemical shift and persists even after the xenon polarization is turned off, possibly due to
9
adsorption of
129
129
129
Xe NMR, at different temperatures to vary the exchange rate
Xe resonance between 50 and 100 ppm (Figure 10a); such a wide resonance
Xe on Al2O3.54 Figure 10b shows the HP
129
Xe NMR spectrum of the X-ray
10
amorphous HT-6 composite. The spectrum acquired at 290 K shows a single peak at 88.2 ppm.
11
As the temperature decreases, the peak shifts to higher values, a behavior typical of
12
adsorbed in porous materials due to more Xe – surface and Xe – Xe interactions. A second peak
13
at a much lower chemical shift (~110 ppm chemical shift) is detectedappears at 170 K and its
14
intensity increases in intensity at 150 K. This indicate two types of pores in the HT-6 composite
15
at 150 K: i) the 110 ppm resonance is already attributed to the mesopores of the Siralox 30
16
matrix, ii) the 180 ppm resonance is therefore assigned to the micropores in the embryonic
17
zeolite units.
129
Xe gas
18 19 20 21 22
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1
Figure 10. Hyperpolarized
Xe NMR spectra of: (a) Siralox 30 matrix recorded at variable
2
temperature condition and (b) composite obtained after 6 days hydrothermal treatment (HT-6).
3 4
3.5 Acidity and catalytic performances of the embryonic composites
5
Figure 11a compares the TiPBz conversion, under identical T and WHSV, on Siralox 30 and
6
WI-1 and WI-2 composites obtained after 3 impregnations of ZP-1 and ZP-2 precursors,
7
respectively. The two composites are more active than the pristine matrix, as expected from the
8
presence of tetrahedrally coordinated aluminum in the embryonic zeolites. The initial
9
conversions on WI-1 and WI-2 composites are comparable. However, differences appear as a
10
function of time on stream; the deactivation rate of WI-1 is significantly lower than WI-2.
11
although they The two composites have similar micropore volume and small differences in SBET
12
and Vmic (Table 1). These Such small textural differences do notcannot explain the substantial
13
difference in their catalytic performances. One plausible cause could be the stability of the active
14
sites obtained at 100 °C (ZP-1) and 25 °C (ZP-2); namely, zeolite embryos harvested at elevated
15
temperature are more resilient due to a more locally organized network compared to their room
16
temperature counterparts.
17 18 19 20 21
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Figure 11. TiPBz conversion on composites prepared by (a) three impregnation procedures and
2
(b) hydrothermal treatment after 2 and 180 min on stream. Conditions: Treaction= 300 °C, WHSV
3
= 8 h-1. Note: errors bars are provided in (b).
4
Figure 11b compares the TiPBz conversion on Siralox 30 and HT-x composites containing
5
different levels of embryonic zeolites (x = Duration of hydrothermal treatment in day(s)). While
6
the catalytic performance of composites obtained by hydrothermal treatment is always higher
7
than the pristine matrix, those obtained during the first 48 h display relatively low conversions.
8
As discussed above, this treatment leads first to a partial dissolution of the matrix followed by a
9
slower growth of zeolite embryos in the pores of the matrix. This explains a variation in
10
performance and a maximum in activity (6 days) as a function of hydrothermal treatment time.
11
The number of Brønsted acid sites increases with crystallization time and reaches a maximum
12
after six days of synthesis (Figure 12). The catalytic impact of in-situ synthesized zeolite
13
embryos is compared with the reference nanosized ZSM-5 (MFI90) and the pristine matrix. A
14
(modest) increase in the number of Brønsted acid sites (up to 16 µmol g-1) leads to a substantial
15
increase in TiPBz conversion with no further increase in conversion up to 24 µmol g-1. With
16
nano-sized ZSM-5, MFI90, the number of Brønsted acid sites dramatically increases fivefold (up
17
to 135 µmol g-1) but most of them are now confined in a microporous network denying access to
18
bulky molecules like TiPBz: this dramatically limits the conversion to the external surface sites
19
of the zeolite crystals. This is an indirect proof that the composite containing embryonic zeolites
20
possesses a more open structure.
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Figure 12. Acidity–activity relationship of (a) Siralox 30, (b) HT-2, (c) HT-5, (d) HT-6, (e) HT-7
11
composites and (f) nano-sized ZSM-5 (MFI90).
12 13
4. DISCUSSION
14
The physicochemical characterization of zeolite precursors, the so-called embryonic zeolites,
15
highlights their amorphous nature. However, they display some structural organization (Figure
16
S2) and a well-defined pore structure (Figure 1). N2 adsorption reveals the presence of
17
micropores, templated by the TPA+ cations incorporated in their aluminosilicate matrix.
18
Combined TG – 13C MAS NMR analysis shows that the interaction between the organic template
19
and aluminosilicate species are similar with those observed in crystalline MFI-type material.
20
Indeed, only a part of TPA+ cations (ca. 8 wt. %) are strongly bound to the inorganic matrix and
21
begin their thermal degradation at temperatures similar to those of species occluded in the pores
22
of crystalline ZSM-5. On the other hand, 13C MAS NMR does not show a splitting of the (end)
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1
methyl group of TPA+. Such splitting is characteristic of the different environments found in the
2
straight and zig-zag channels of the MFI-type structure. This illustrates that the TPA+ is in a
3
local environment not possessing such a well-defined structure. The size of these pores is
4
between and 1 and 2 nm, as shown by N2 adsorption analysis. This conclusion is confirmed by a
5
129
6
aluminosilicate matrix with a very open structure. The rapid exchange is also due to the small
7
size (3 – 4 nm) of zeolite embryos. A material obtained after 4 h mixing at room temperature
8
(ZP-2) with size 3 – 4 nm exhibits an impressive micropore volume and properties similar with
9
the hydrothermally treated counterpart (ZP-1). Actually, ZP-2 possesses slightly higher
10
micropore volume than ZP-1 (Figure 1). We attribute this result to the beginning of the
11
crystallization process in ZP-1, which results in a decrease of micropore volume. The
12
hydrothermal treatment leads to an aggregation of zeolite embryos and the formation of textural
13
mesopores as revealed by the hysteresis of ZP-1 isotherm. The aggregation of primary particles
14
yields a second population of particles with a size of about 16 – 20 nm (Figure S3). In summary,
15
one can state that:
16
i) at room temperature, during hydrolysis of tetraethylortosilicate, (alumino)silicate species
17
condense around the TPA+. This is a result of electrostatic interactions between negatively
18
charged inorganic and positively charged organic components of the system. Thus, a sharp
19
distribution of 3 – 4 nm particles, incorporating TPA+ cations are formed.
Xe NMR analysis (Figure 3). The Xe atoms exchange very fast and this points to an
20
ii) upon calcination, the TPA+ is removed, leaving behind pores of 1 – 2 nm; the inorganic
21
material produced exhibits substantially higher micropore volume and specific surface area
22
compared to fully crystalline ZSM-5 obtained with the TPA+ structure directing agent.
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This indicates that tThe TPA+ trapped in the embryonic zeolite will does not fit as tightly as in
2
its corresponding zeolite, ZSM-5. This conclusion is further supported by the presence of much
3
water in the zeolite embryos and the larger micropore volume left after combustion of the
4
template.
5
For practical applications, zeolite crystals need to be shaped (beads, microspheres, extrudates)
6
as technical bodies, most of the time in the presence of a binder (amorphous silica, alumina,
7
clay) to provide thermal and mechanical resistance of the catalyst and avoid substantial pressure
8
drops. This approach, however, is difficult to apply to ultra-small embryonic particles. In
9
addition, the complex shaping process (mixing, mulling, extrusion, drying, calcination) could
10
change substantially the properties of zeolite embryos. To avoid such potential problems, we
11
used a pre-formed mesoporous matrix (Siralox 30, available as mm-sized extrudates and µm-
12
sized spheres), as a carrier for the zeolite embryos. We developed two preparation procedures,
13
impregnation and in-situ hydrothermal synthesis, to prepare composite catalysts. Both
14
procedures lead to Siralox 30 – zeolite embryos composites. In the case of impregnation, the
15
amount of zeolite embryos in the composite depends on the number of impregnation steps and
16
the content of active phase in the composite can be adjusted precisely. Besides, the properties of
17
the zeolite embryos can be set during their preparation and will remain almost unchanged after
18
deposition on the carrier. The in-situ preparation is more complex due to the interaction between
19
the zeolite synthesis solution and the Siralox 30 matrix. This process includes a partial
20
dissolution of the matrix changing the stoichiometry of the zeolite precursor. Consequently, the
21
embryos formation in the pores is slow and their composition difficult to control. We attribute
22
the slow formation of such zeolite embryos in the matrix to the presence of large quantities of
23
dissolve alumina species and therefore a stoichiometry not favorable to ZSM-5 crystallization.
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1
Longer treatment times increase the activity of the composites significantly until it reaches a
2
maximum after 6 days hydrothermal treatment (HT-6). All experimental results fully support the
3
conclusions based on the physical characterization of composites, namely that an active phase
4
comprising strong acid sites (embryonic zeolite units) is present in the composites and enhances
5
the catalytic activity of the pristine Siralox 30 matrix. The conversion of 1,3,5-TiPBz on in-situ
6
prepared composite catalysts is higher than its counterpart prepared by impregnation. We
7
underline, however, that each procedure offers certain advantages. The impregnation is rapid and
8
the number of zeolite units can be controlled by the number of impregnation steps. In addition,
9
the properties of zeolite embryos are well defined. In-situ synthesis takes time, but the amount of
10 11
active phase is higher and the mesopore structure of the carrier remains almost unchanged. 27
Al MAS NMR characterization of pre-formed embryonic zeolites shows only tetrahedrally
12
coordinated aluminum. Its position is characteristic of Al in zeolite frameworks (Figure S5).
13
Upon calcination at 550 °C a portion (ca. 30 %) of this aluminum change its coordination from
14
tetrahedral to octahedral. This is substantially higher than for ZSM-5 subjected to the same high
15
temperature treatment, but still lower than for most amorphous silica-aluminas. The lower
16
thermal stability of Al in zeolite embryos is not surprising owing to their amorphous nature and
17
very small size. Nevertheless, enough Al retains its tetrahedral coordination and provides
18
Brønsted acidity evidenced by FTIR monitoring of adsorbed pyridine (Figure 7). The composite
19
materials containing ZP-1 and ZP-2 particles showed substantially higher Brønsted acidity than
20
the pristine matrix but much fewer than a reference nanosized ZSM-5 zeolite (MFI90, Si/Al=45).
21
However, although the number of Brønsted acid in the zeolite embryos is relatively low, the
22
derived composite catalysts show high catalytic activity compared to both the reference zeolite
23
(nanosized, so with a high external surface) and the pristine matrix (Figures 11 and 12). We
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attribute the remarkable catalytic performance of embryonic zeolites in the dealkylation of TiPBz
2
(ca. 0.95 nm kinetic diameter) to their open and high accessibility structure. These results and the
3
physisorption analysis indicate that their pores are larger than 1 nm.
4
Although, the elucidation of zeolite nucleation/growth mechanism is not the goal of this study,
5
it should be addressed in order to shed more light on the formation of zeolite precursor species.
6
Our data show that TPA+ reacts with the hydrolyzed silica species and form some “cages” where
7
the interaction between the organic structure directing agent and mineral species are fairly strong
8
and close, but not identical to those in highly crystalline zeolites. We attribute this interaction to
9
the charge balancing function of TPA+ compensating the negative charge of an Al tetrahedra
10
surrounded by four silica tetrahedra. The cages contain relatively large amount of water, which is
11
not typical of MFI-type materials synthesized with TPA+. This shows, first that the cages are
12
large enough to accommodate a TPA+ cation and water molecules and second that the
13
aluminosilicate matrix does not fit tightly to the morphology of the structure directing agent. The
14
Ar analysis of ZP-1 and ZP-1 confirmed that the embryonic zeolites exhibit type Ib isotherms
15
characteristic of materials with extra-large micro- or small mesopores (Figure S17). The pore
16
size distribution is presented in Figure 13. As can be seen both sample contain pore larger than
17
0.83 nm, including a fraction of pore centered at 1.42 and 2.25 nm. This finding is in
18
disagreement with nanoslab hypothesis, where the structure of zeolite precursor units is
19
described as fully formed MFI-type framework.55,56 Our results unambiguously show that TPA+
20
cation is situated in a cage, where the four propyl chains are in similar environment. Therefore,
21
the channel system of MFI-type materials is not yet formed, although structural elements as 5-
22
member rings were detected by infrared spectroscopy (Figure S2). Thus, the most adequate
23
description of zeolite embryos as highly hydrated (alumino)silicate cages, formed around
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1
hydrated TPA+ cation and does not contain long range order. This study indicates that first cage-
2
type units forms around the TPA and later evolve to a MFI-type structure. These units are
3
isometric as the Si-O-Si shell is not following tightly the geometry of TPA cation. The curvature
4
of the embryonic zeolites is thus different from the crystalline MFI-type zeolite and their T-O-T
5
angles are most probably larger than in the crystalline MFI-type zeolite channels leading to the
6
relatively low acid strength observed in the zeolite embryos. A graphical presentation (Scheme
7
S1) highlights this conclusion.
9 10 11 12 13 14
(a)
0.83 nm
1.42 nm 2.25 nm
0
2
4
6
8 10 12 14 16 18 20 Pore width / nm
(b)
0.83 nm
Incrementral pore volume / cm3 g-1
8
Incrementral pore volume / cm3 g-1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 38 of 49
1.42 nm 2.25 nm
0
2
4
6
8 10 12 14 16 18 20 Pore width / nm
15
Figure 13. DFT pore size distribution of (a) ZP-1 and (b) ZP-2, obtained from Argon sorption at
16
87K.
17 18
5. CONCLUSIONS
19
X-ray amorphous zeolite precursors, embryonic zeolites, are formed with TPA+ cation as an
20
organic structure directing agent. Their micropore volume and specific surface area are higher
21
than that of the crystalline material (MFI-type) prepared with the same structure directing agent.
22
This is due to the very open structure of cage-like units formed in the early stage of reaction
23
between the TPA+ and (alumino)silicate species. Upon calcination, part of the Al atoms leaves
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the tetrahedral coordination, but the majority of the aluminum remains however tetrahedral to
2
provide Brønsted acidity.
3
We used such embryonic zeolite units as the active phase of composite catalysts where a
4
mesoporous silica-doped alumina matrix is used as carrier. Two preparation procedures, nano-
5
casting of pre-formed zeolite embryos and their in-situ formation under hydrothermal conditions,
6
were developed. Both procedures provide catalysts with high activity in the dealkylation of
7
1,3,5-TiPBz. Thus, depending on the particular demand or application, a preparation procedure
8
meeting the desired catalytic properties could be selected. Substantially improved catalytic
9
activity with respect to the pristine matrix and highly crystalline ZSM-5 is due embryonic
10
zeolites units with active sites in a relatively open structure able to process bulky molecules.
11
The preparation procedure could be extended to other systems/structure directing agent thus
12
providing a wide array of embryonic zeolites with different pore openings and surface properties.
13
The methodology developed in this study offers highly accessible composite material for bulky
14
molecules processing. In petroleum refining and petrochemistry, one could cite for instance i)
15
the catalytic hydrocracking function of slurry-based residue upgrading processes (eg. EST from
16
ENI, UNIFLEX from Honeywell UOP)57 where the cracking function is still thermal, ii)
17
hydrocracking of very long linear molecules (from the Fisher-Tropsch process), iii)
18
hydroisomerization of waxes (synthetic or mineral) to optimize their viscosity (viscosity index)
19
and cold flow properties. Finally, as most bio sourced feedstocks can be quite bulky and very
20
polar due to the presence of oxygen, they would probably benefit from the advantages of
21
embryonic zeolites.
22 23
ASSOCIATED CONTENT
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1
AUTHOR INFORMATION
2
Corresponding Author
3
*
[email protected] 4
ORCID
5
Valentin Valtchev: 0000-0002-2341-6397
6
Kok-Giap Haw: 0000-0002-9791-0611
7
Present Addresses
8
Kok-Giap Haw
9
§
10
Page 40 of 49
State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University,
Changchun 130012, P. R. China.
11 12 13 14 15
SUPPORTING INFORMATION The Supporting Information is available free of charge on the ACS Publications website at DOI: Characterization data: XRD, FTIR, DLS, SEM, TGA-DSC, N2 sorption,
129
Xe NMR,
27
Al
16
MAS NMR (PDF).
17
ACKNOWLEDGMENT
18
The financial supports from Total Research & Technology Feluy TOTAL Raffinage Marketing
19
is and ANR-17-CHIN-005-01 are highly appreciated.
20
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Notes
2
The authors declare no competing financial interest.
3 4
References
5
(1) Flanigen, E. M.; Broach, R. W.; Wilson, S. T. In Zeolites in Industrial Separation and
6
Catalysis; Kulprathipanja, S., Ed., Wiley-VCH: Weinheim, 2010, pp 1–26.
7
(2) Bellussi, G.; Carati, A.; Millini, R. In Zeolites and Catalysis: Synthesis, Reactions and
8
Applications; Cejka, J., Corma, A., Zones, S., Eds., Wiley-VCH: Weinheim, 2010, pp 449–
9
491.
10 11 12 13
(3) Marcilly, C. Where and how shape selectivity of molecular sieves operates in refining and petrochemistry catalytic processes. Top. Catal. 2000, 13, 357–366. (4) Vermeiren, W.; Gilson, J.-P. Impact of Zeolites on the Petroleum and Petrochemical Industry. Top. Catal. 2009, 52, 1131–1161.
14
(5) Martinez, C.; Corma, A. Inorganic molecular Molecular sievesSieves: Preparation,
15
modification Modification and industrial application in catalytic processes. Coord. Chem.
16
Rev. 2011, 255, 1558–1580.
17
(6) Landau, M. V.; Vradman, L.; Valtchev, V.; Lezervant, J.; Liubich, E.; Talinker, M.
18
Hydrocracking of Heavy Vacuum Gas Oil with a Pt/H-beta−Al2O3 Catalyst: Effect of
19
Zeolite Crystal Size in the Nanoscale Range. Ind. Eng. Chem. Res. 2003, 42, 2773–2782.
20
(7) Jiang, J.; Yu, J.; Corma, A. Extra-Large-Pore Zeolites: Bridging the Gap between Micro
21
and Mesoporous Structures. Angew. Chem. Int. Ed. 2010, 49, 3120–3145.
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Page 42 of 49
1
(8) Perez-Ramirez, J.; Christensen, C. H.; Egeblad, K.; Christensen, C. H.; Groen, J. C.
2
Hierarchical zeolites: enhanced utilization of microporous crystals in catalysis by advances
3
in materials design. Chem. Soc. Rev. 2008, 37, 2530–2542.
4 5 6 7
(9) Valtchev, V.; Majano, G.; Mintova, S.; Perez-Ramirez, J. Tailored crystalline microporous materials by post-synthesis modification. Chem. Soc. Rev. 2013, 42, 263–290. (10) Wei, Y.; Parmentier, T. E.; de Jong, K. P.; Zacevic, J. Tailoring and visualizing the pore architecture of hierarchical zeolites. Chem. Soc. Rev. 2015, 44, 7234–7261.
8
(11) Liang, D.; Follens, L. R. A.; Aerts, A.; Martens, J. A.; Van Tendeloo, G.; Kirschhock, C.
9
E. A. TEM observation of aggregation steps in room-temperature silicalite-1 zeolite
10
formation. J. Phys. Chem. C. 2007, 111, 14283–14285.
11
(12) Wakihara, T.; Kohara, S.; Sankar, G.; Saito, S.; Sanchez-Sanchez, M.; Overweg, A. R.;
12
Fan, W.; Ogura, M.; Okubo, T. A new approach to the determination of atomic-architecture
13
of amorphous zeolite precursors by high-energy X-ray diffraction technique. Phys. Chem.
14
Chem. Phys. 2006, 8, 224–227.
15
(13) Davis, T. M.; Drews, T. O.; Ramanan, H.; He, C.; Dong, J. S.; Schnablegger, H.;
16
Katsoulakis, M. A.; Kokkoli, E.; McCormick, A. V.; Penn, R. L.; Tsapatsis, M.
17
Mechanistic principles of nanoparticle evolution to zeolite crystals. Nat. Mater. 2006, 5,
18
400–408.
19 20
(14) Smaihi, M.; Gavilan, E.; Durand, J. O.; Valtchev, V. Colloidal functionalized calcined zeolite nanocrystals. J. Mater. Chem. 2004, 14, 1347–1351.
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ACS Catalysis
(15) Lupulesku, A. I.; Rimer, J. D. In Situ Imaging of Silicalite-1 Surface Growth Reveals the Mechanism of Crystallization. Science. 2014, 344, 729–732.
3
(16) Anderson, M. W.; Gebbie-Rayet, J. T.; Hill, A. R.; Farida, N.; Attfield, M. P.; Cubillas,
4
P.; Blatov, V. A.; Proserpio, D. M.; Akporiaye, D.; Arstad, B.; Gale, J. D. Predicting
5
crystal growth via a unified kinetic three-dimensional partition model. Nature. 2017, 544,
6
456–459.
7
(17) Melinte, G.; Georgieva, V.; Springuel-Huet, M.-A.; Nossov, A.; Ersen, O.; Guenneau, F.;
8
Gedeon, A.; Palcic, A.; Bozhilov, K. N.; Pham-Huu, C.; Qiu, S. L.; Mintova, S.; Valtchev,
9
V. 3D Study of the Morphology and Dynamics of Zeolite Nucleation. Chem. A Eur. J.
10
2015, 21, 18316–18327.
11
(18) Rimer, J. D.; Kumar, M.; Li, R.; Lupulesku, A. I.; Oleksiak, M. D. Tailoring the
12
physicochemical properties of zeolite catalysts. Catal. Sci. Technol. 2014, 4, 3762–3771.
13
(19) Ng, E.-P.; Chateigner, D.; Bein, T.; Valtchev, V.; Mintova, S. Capturing Ultrasmall EMT
14 15 16
Zeolite from Template-Free Systems. Science. 2012, 335, 70–73. (20) Awala, H.; Gilson, J.-P.; Retoux, R.; Boullay, P.; Goupil, J.-M.; Valtchev, V.; Mintova, S. Template-free nanosized faujasite-type zeolites. Nat. Mater. 2015, 14, 447 –451.
17
(21) Manton, M. R. S.; Davidtz, J. C. Controlled pore sizes and active site spacings
18
determining selectivity in amorphous silica-alumina catalysts. J. Catal. 1979, 60, 156–166.
19
(22) Jacobs, P. A.; Derouane, E. G.; Weitkamp, J. Evidence for X-Ray-amorphous Zeolites.
20
J.C.S. Chem. Commun. 1981, 591–593.
ACS Paragon Plus Environment
43
ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 44 of 49
1
(23) Corma, A.; Perez-Pariente, J.; Fornes, V.; Rey, F.; Rawlence, D. Synthesis and
2
characterization of silica-alumina prepared from tetraalkylammonium hydroxides. Applied
3
Catal. 1990, 63, 145–164.
4 5
(24) Rizzo, C.; Carati., A.; Barabino, C.; Perego, C.; Bellussi, G. Silica-aluminas: sol-gel synthesis and characterization. Stud. Surf. Sci.Catal. 2001, 140, 401–411.
6
(25) Bellussi, G.; Perego, C.; Carati, A.; Peratello, S.; Previde Massara, E.; Perego, G.
7
Amorphous mesoporous silica-alumina with controlled pore size as acid catalysts. Stud.
8
Surf. Sci. Catal. 1994, 84, 85–92.
9 10
(26) Liu, Y.; Zhang, W. Z.; Pinnavaia, T. J. Steam-stable aluminosilicate mesostructures assembled from zeolite type Y seeds. J. Am. Chem. Soc. 2000, 122, 8791–8792.
11
(27) Liu, Y.; Zhang, W.; Pinnavaia, T. J. Steam-stable MSU-S aluminosilicate mesostructures
12
assembled from zeolite ZSM-5 and zeolite beta seeds. Angew. Chem. Int. Ed. 2001, 40,
13
1255–1258.
14
(28) Corma, A.; Díaz-Cabañas, M. J. Amorphous microporous molecular sieves with different
15
pore dimensions and topologies: Synthesis, characterization and catalytic activity.
16
Micropor. Mesopor. Mater. 2006, 89, 39–46.
17
(29) Corma, A.; Díaz-Cabañas, M. J.; Moliner, M.; Rodríguez, G. Synthesis of micro- and
18
mesoporous molecular sieves at room temperature and neutral pH catalyzed by functional
19
analogues of silicatein. Chem. Commun. 2006, 0, 3137–3139.
ACS Paragon Plus Environment
44
Page 45 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
1
(30) Inagaki, S.; Thomas, K.; Ruaux, V.; Clet, G.; Wakihara, T.; Shinoda, S.; Okamura, S.;
2
Kubota, Y.; Valtchev, V. Crystal Growth Kinetics as a Tool for Controlling the Catalytic
3
Performance of a FAU-Type Basic Catalyst. ACS Catalysis. 2014, 4, 2333–2341.
4
(31) Haw, K. G.; Goupil, J.-M.; Gilson, J.-P.; Valtchev, V.; Nesterenko, N.; Minoux, D.;
5
Dath, J.-P. Catalyst compositions comprising small size molecular sieves crystals deposited
6
on a porous material. WIPO WO/ 2015/001004.
7
(32) Kentgens, P. M.; Scholle, K. F. M. G. J.; Veeman, W. S. Effect of hydration on the local
8
symmetry around aluminum in ZSM-5 zeolites studied by aluminum-27 nuclear magnetic
9
resonance. J. Phys. Chem. 1983, 87, 4357–4360.
10 11 12 13
(33) Klinowski, J. Nuclear magnetic resonance studies of zeolites. Progress in Nuclear Magnetic Resonance Spectroscopy. 1984, 16, 237–309. (34) El Siblani, H. Application de la RMN du
129
Xe Hyperpolarisé à l’analyse de matériaux
poreux. Ph.D. thesis, Normandie Univ, February 2016.
14
(35) Happer, W. Optical pumping. Rev. Mod. Phys. 1972, 44, 169–249.
15
(36) Happer, W.; Miron, E.; Schaefer, S.; Schreiber, D.; van Wijngaarden, W. A.; Zeng, X.
16
Polarization of the nuclear spins of noble-gas atoms by spin exchange with optically
17
pumped alkali-metal atoms. Phys. Rev. A. 1984, 29, 3092–3110.
18
(37) Khabtou, S.; Chervreau, T.; Lavalley, J. C. Quantitative infrared study of the distinct
19
acidic hydroxyl groups contained in modified Y zeolites. Micropor. Mater. 1994, 3, 133 –
20
148.
ACS Paragon Plus Environment
45
ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 46 of 49
1
(38) Haw, K. G.; Goupil, J.-M.; Gilson, J.-P; Nesterenko, N.; Minoux, D.; Dath, J.-P.;
2
Valtchev, V. Embryonic ZSM-5 zeolites: zeolitic materials with superior catalytic activity
3
in 1,3,5-triisopropylbenzene dealkylation. New J. Chem. 2016, 40, 4307–4313.
4 5
(39) Jansen, J. C.; van der Gaag, F. J.; van Bekkum, H. Identification of ZSM-type and other 5 ring containing zeolites by i.r spectroscopy. Zeolites. 1984, 4, 369−372.
6
(40) Thommes, M.; Kaneko, K.; Neimark, A. V.; Olivier, J. P.; Rodriguez-Reinoso, F.;
7
Rouquerol, J.; Sing, K. S. W. Physisorption of gases, with special reference to the
8
evaluation of surface area and pore size distribution (IUPAC Technical Report). Pure Appl.
9
Chem. 2015, 87, 1051−1069.
10 11 12 13
(41) Welsh, L. B.; Gilson J. -P; Gattuso M. J. High resolution 27Al NMR of amorphous silicaaluminas. Appl. Catal. 1985, 15, 327-331. (42) Boxhoorn, G.; Kortbeek, A.; Hays, G.R.; Alma, N.C.M.; A high-resolution solid state 29Si NMR study of ZSM-5 type zeolites. Zeolites, 1984, 4, 15-21.
14
(43) Yang, H.; Walton, R.I.; Antonijevic, S.; Wimperis, S.; Local order of amorphous zeolite
15
precursors from 29Si{1H} CPMAS and 27Al and 23Na MQMAS NMR and evidence for
16
the nature of medium-range order from neutron diffraction. J. Phys. Chem. B, 2004, 108,
17
8208-8217.
18
(44) Scholle, K.F.G.M.J.; Veemna, W.S.; Frenken, P.; Van der Velden, G.P.M.;
19
Characterization of intermediate TPA-ZSM-5 type structures during crystallization.
20
Applied catalysis, 1985, 17, 233-259.
ACS Paragon Plus Environment
46
Page 47 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
1
(45) a) Boxhoorn G.; van Santen, R.; van Erp, W. A.; Hays, G. R.; Huis R.; Clague D. An
2
investigation into the structure and position of organic bases in ZSM-5-type zeolites by
3
high-resolution solid-state
4
264-265. b) Nagy, J. B.; Gabelica, Z.; Derouane, E. G. Position and configuration of the
5
guest organic molecules within the framework of the ZSM-5 and ZSM-11 zeolites.
6
Zeolites. 1983, 3, 43–49.
13
C NMR spectroscopy. J. Chem. Soc., Chem. Commun. 1982,
7
(46) Asswad, J. E. H.-A.; Dewaele, N.; Nagy, J. B.; Hubert, R. A.; Gabelica, Z.; Derouane, E.
8
G. Identification of different tetrapropylammonium cations occluded in ZSM-5 zeolite by
9
combined thermal analysis (TG-DTA) and 13C-NMR. spectroscopy. Zeolites. 1988, 8, 221–
10
227.
11
(47) Gabelica, Z.; Nagy, J. B.; Debras, G. Characterization of X-Ray amorphous ZSM-5
12
zeolites by high resolution solid state 13C-NMR spectroscopy. J. Catal. 1983, 84, 256–260.
13
(48) Hyperpolarized Xenon-129 Magnetic Resonance: Concepts, Production, Techniques and
14
Applications; Meersmann, T., Brunner, E., Eds.; The Royal Society of Chemistry:
15
Cambridge, 2015.
16 17
(49) Valtchev, V. Preparation of regular macroporous structures built of intergrown silicalite-1 nanocrystals. J. Mater. Chem. 2002, 12, 1914–1918.
18
(50) Gabelica, Z.; Nagy, J. B.; Derouane, E. G.; Gilson, J. -P. The use of combined thermal
19
analysis to study crystallization, pore structure catalytic activity and deactivation of
20
synthetic zeolites. Clay Minerals. 1984, 19, 803-824.
ACS Paragon Plus Environment
47
ACS Catalysis 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
Page 48 of 49
1
(51) Chizallet, C.; Raybaud, P. Density functional theory simulations of complex catalytic
2
materials in reactive environments: beyond the ideal surface at low coverage. Catal. Sci.
3
Technol. 2014, 4, 2797-2813.
4
(52) Do, T. O.; Nossov, A.; Springuel-Huet, M. A.; Schneider, C.; Bretherton, J. L.; Fyfe, C.
5
A.; Kaliaguine, S. Zeolite nanoclusters coated onto the mesopore walls of SBA-15. J. Am.
6
Chem. Soc. 2004, 126, 14324–14325.
7
(53) Chen, F.; Chen, C. L.; Ding, S. W.; Yue, Y.; Ye, C. H.; Deng, F. A new approach to
8
determination of micropore size by 129Xe NMR spectroscopy. Chem. Phys. Lett. 2004, 383,
9
309−313.
10
(54) Weiland E.; Springuel-Huet, M.-A.; Nossov, A.; Guenneau F.; Quoineaud A.-A.;
11
Gédéon, A.Erika, W.; Marie-Anne, S.-H.; Andrei, N.; Flavien, G.; Anne-Agathe, Q.;
12
Antoine, G. Exploring the Complex Porosity of Transition Aluminas by
13
Spectroscopy. J. Phys. Chem. C 2015, 119, 15285-15291.
129
Xe NMR
14
(55) Kirschhock, C. E. A.; Ravishankar, R.; Van Looveren, L.; Jacobs, P. A.; Martens, J. A.
15
Mechanism of Transformation of Precursors into Nanoslabs in the Early Stages of MFI and
16
MEL Zeolite Formation from TPAOH−TEOS−H2O and TBAOH−TEOS−H2O Mixtures. J.
17
Phys. Chem. B 1999, 103, 4972−4978.
18
(56) Kirschhock, C. E. A.; Ravishankar, R.; Jacobs, P. A.; Martens, J. A. Aggregation
19
Mechanism of Nanoslabs with Zeolite MFI-Type Structure. J. Phys. Chem. B 1999, 103,
20
11021−11027.
ACS Paragon Plus Environment
48
Page 49 of 49 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60
ACS Catalysis
1
(57) Bellussi, G.: Rispoli, G.; Molinari, D.; Landoni, A.; Pollesel, P.; Panariti, N.; Millini, R.;
2
Montanari, E. The role of MoS2 nano-slabs in the protection of solid cracking catalysts for
3
the total conversion of heavy oils to good quality distillates. Catal. Sci. Technol. 2013, 3,
4
176-182.
5
ACS Paragon Plus Environment
49