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Transformation from NaA to MCM-49 Zeolite and its Catalytic Alkylation Performance Enhui Xing, Yanchun Shi, Aiguo Zheng, Jin Zhang, Xiuzhi Gao, Dongyun Liu, MuDi Xin, Wenhua Xie, Fengmei Zhang, Xuhong Mu, and Xingtian Shu Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/ie5047736 • Publication Date (Web): 10 Mar 2015 Downloaded from http://pubs.acs.org on March 16, 2015

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Industrial & Engineering Chemistry Research

Transformation from NaA to MCM-49 Zeolite d4r HMI

lta

d6r

sod

Si

NaOH

NaA

mel

MWW

the gradient of SiO2/Al2O3 in the transformation from NaA to MCM-49 zeolite LTA

Point 1 2

72 h

48 h

SiO 2/Al2O3 2.0 2.0

Point 1 2 3 4 5

SiO 2/Al2O3 3.6 2.8 2.4 27.8 200

Point 1 2 3 4

96 h- MWW

SiO 2/Al2O3 18.4 3.0 2.5 2.4

ACS Paragon Plus Environment

Point 1 2 3

SiO 2/Al2O3 45.4 36.3 22.0


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Transformation from NaA to MCM-49 Zeolite and its Catalytic Alkylation Performance Enhui Xing, Yanchun Shi, Aiguo Zheng, Jin Zhang, Xiuzhi Gao, Dongyun Liu, Mudi Xin, Wenhua Xie, Fengmei Zhang*, Xuhong Mu, Xingtian Shu State Key Laboratory of Catalytic Materials and Reaction Engineering, Research Institute of Petroleum Processing, Sinopec, Beijing 100083, China *Tel: +86 010-82368698; [email protected]

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Abstract: The transformation from NaA (LTA) to MCM-49 (MWW) zeolite was achieved in the synergism of hexamethyleneimine (HMI), NaOH and SiO2, in spite of no common composite build units between LTA (lta, sod and d4r) and MWW (mel and d6r) structure. NaA (SiO2/Al2O3 = 2.0) was employed as the parent zeolite. The samples prepared at different crystallization stages were characterized by XRD, SEM, 29

Si/27Al/13C MAS NMR and STEM-EDS to investigate the intermediates during the

transformation from NaA to MCM-49. As shown in SEM and STEM-EDS images, MCM-49 was proposed to be transformed gradually from exterior to interior of NaA, which was clearly observed by the core (LTA, low SiO2/Al2O3) - shell (MWW, high SiO2/Al2O3) co-existing zeolites as intermediates. With high relative crystallinity and the uniform sizes of crystals, the final MCM-49 was featured by Si enrichment on the external surface, which was proved by the shell (SiO2/Al2O3 = 45.4) wrapping around the core (SiO2/Al2O3 = 22.0). For transformed H-MCM-49 zeolite, the uniform sizes of crystals and the increase of total acid sites contributed to better accessibility of active centers, which achieved simultaneous improvement in ethylene conversion and ethylbenzene selectivity in the liquid-phase alkylation of benzene with ethylene.

Keywords: NaA; MCM-49; SiO2/Al2O3 gradient; Liquid-phase alkylation; Ethylbenzene

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1. Introduction Ethylbenzene (EB) is an important material for plastic and rubber production. Global demand grew by about 4.1 % annually in the period of 2009-2014 and is forecast to grow by 3.3 % per year over the next decade.1,2 Compared with conventional AlCl3 process, two zeolite-based EB processes, vapor-phase (ZSM-5) and liquid-phase processes (USY, Beta, MCM-22), show easy separation, low corrosion, high activity and shape selectivity.3-8 Because of the low reaction temperature, there are obvious advantages such as high selectivity and long catalyst life in the liquid-phase process. USY zeolite is seldom used because of its relative inferior EB selectivity and quick deactivation. Owing to superior activity and selectivity, Beta and MCM-22 zeolites are the most widely used in commercial for liquid-phase alkylation of benzene with ethylene. Despite their low catalytic activity, MWW zeolites (MCM-22, MCM-49 and MCM-56) have attracted much attention because of their superior EB selectivity at lower molar ratio of benzene/ethylene with respect to energy input.9-11 MWW zeolites, represent an original zeolite with the combination of two classes of materials: zeolites and layered solids, which presents: 12-ring “cups”, 10-ring intralayer channels and 12-ring interlayer supercages through 10-ring apertures.12-16 Some reports have claimed that active centers of MWW zeolites were mainly located in 12-ring “cups” so that they were more easily accessed during liquid-phase alkylation of benzene with ethylene. 17,18 MWW zeolites including MCM-22, MCM-49, and MCM-56, are synthesized by conventional hydrothermal treatment of separated Si (solid silica gel, water glass, colloidal silica and so on) and Al (sodium aluminate, aluminum salt and so on) with hexamethyleneimine (HMI) as a structure-directing agent (SDA). Due to zeolite metastability, the thermodynamics induced phase transition is most commonly 3


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encountered in the phenomenon of reaction over-run, in which the zeolite product decomposes to form a denser phase, (FER),

20

19

for instance, MCM-49 (MWW) to ZSM-35

A (LTA) or X (FAU) to sodalite (SOD),21 ZSM-5 (MFI) to mordenite

(MOR),22 In spite of thermodynamically driven, final phase selection is controlled by the interplay of nucleation, growth and phase transformation kinetics. Therefore, zeolite-zeolite transformations in a controlled manner may offer the possibility of new and useful synthetic routes, which has attracted much attention all over the world. One of the successful zeolite-zeolite transformations is based on some connection with common composite building units (CBUs) between parent zeolites and product zeolites. Zeolitic CBUs are helpful for understanding the synthesis and transformations of zeolites. Seed-assisted synthesis of zeolites with or without SDAs, so-called a “seed-directed synthesis” (SDS) of zeolites, is believed to play a critical factor for inducing growth of zeolite crystals, by Xiao’s group.

23-25

Sano et al reported that

interzeolite conversions from FAU to LEV/CHA by adding the seed crystals of product zeolites.

26, 27

Zones and co-workers exploited unusual organic-cations as a

characteristic feature to achieve the zeolite-zeolite transformation with common d6r and adding silica to satisfy the mass balance, 28-32 for example, Y (FAU) to SSZ-13 (CHA) directed by N, N, N-trimethylammonium-1-adamantane cation; fluoride media directed by N-methylquinuclidinium cation.

29

28

FAU to LEV in

Recently, Okubo has

proposed that the seed crystals did not need to be same framework type but must contain at least one of the CBUs of the target zeolites.

33-35

In spite of difference in the

framework between seeds and target zeolites, the common CBUs are the key strategy to the success of zeolites synthesis with different seed structure and gel structure, for example, the target zeolite is ZSM-12 (MTW, CBUs: bik, jbw, mtw and cas), the seed 4



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zeolite is beta (*BEA, CBUs: bea, mtw, and mor), and the gel is for ZSM-5 (MFI, CBUs: mfi, mel and mor). However, Sano et al reported interzeolite conversion without any common CBUs between parent zeolites and product zeolites, such as “FAU to *BEA”,

36

which proceeded as following sequence: starting zeolites → amorphous

phase (XRD) → product zeolites. The dissolution of the starting zeolites was hypothesized to be the crucial factor for the interzeolite conversions, resulting in this process with complete disappearance of crystalline phase. In previous work,

37, 38

we have investigated the potential of the zeolite-zeolite

transformation and have succeeded in synthesizing MWW zeolite with FAU zeolite as the parent zeolite. With d6r as a common CBU, MWW zeolite was transformed gradually from exterior to interior of FAU zeolite, which was observed by the core (FAU) - shell (MWW) co-existing zeolites as intermediates through direct phase transformation. What’s more, size-controlled synthesis of MCM-49 zeolites was achieved via direct phase transformation from NaY zeolites with different crystal sizes. Here we intentionally examine the zeolite-zeolite transformation from NaA (LTA, d4r, sod and lta) zeolite, which has not any common CBUs, as a parent zeolite to synthesize MCM-49 zeolite (MWW, d6r and mel), and give detailed characterizations to study the mechanism of “LTA to MWW” transformation. In order to observe the gradient change of SiO2/Al2O3 more clearly, the NaA zeolite with SiO2/Al2O3 = 2.0 was selected as parent zeolite to enlarge the difference between the SiO2/Al2O3 ratio of NaA and MCM-49. Also NaA zeolite used as the parent zeolite showed uniform crystal morphology with little aggregation. Finally, the catalytic performance of MCM-49 obtained via the transformation from NaA was measured.

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2. Experimental 2.1 Synthesis of MCM-49 and preparation of H-type catalysts Transformation from NaA to MCM-49 zeolite: All materials were used as purchased. Commercial NaA (LTA, SiO2/Al2O3 = 2.0) was mixed in a conical flask with NaOH (96 wt. %), HMI (98 wt. %), solid silica gel (90 wt. % SiO2), and deionized water. The molar ratios of the batch composition were: SiO2/Al2O3 = 25, NaOH/SiO2 = 0.18, HMI/SiO2 = 0.3, H2O/SiO2 = 15. The transformation was carried out in a Teflon-lined autoclave under rotating condition at 145 oC and 30 rpm. The products were recovered by filtration, washed with deionized water and finally dried at 100 oC overnight to obtain as-synthesized samples. Conventional hydrothermal synthesis of MCM-49 zeolite: Comparison MCM-49 zeolite (sample 1 in Table 1) was synthesized in the 1 m3 demonstration unit in Hunan Jianchang Petrochemical Company, Sinopec via temperature-controlled phase transfer hydrothermal synthesis.39 The molar ratios of batch composition were: SiO2/Al2O3 = 25, NaOH/SiO2 = 0.18, HMI/SiO2 = 0.1, aniline/SiO2 = 0.2, H2O/SiO2 = 15. The synthesis was carried out at 145 oC for 72 h with stirring speed at 15 Hz. The products were recovered by filtration, washed with deionized water until pH value = 7 and dried in oven at 100 oC overnight in order to remove the physically adsorbed water molecules. H-type zeolites: H-type zeolites were prepared by twice liquid-phase ion-exchange with NH4NO3 solution at 90 oC for 2 h. The products were filtrated and dried at 100 oC overnight, and calcined at 550 oC for 6 h, to obtain the corresponding H-type zeolites with Na2O content less than 0.05 wt.%. The mass ratio composition of MCM-49 zeolites, NH4NO3, and deionized water was: 1:1:20. The products were named as H-MCM-49 via conventional hydrothermal method and HAM25 (SiO2/Al2O3 = 25) via 6



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the transformation from NaA, respectively. Catalyst preparation: The NH4-type samples (70 wt. %) and Al2O3 (30 wt. %) were mixed and extruded. Al2O3, which showed almost no activity for the liquid-phase alkylation of benzene with ethylene, was used as binder to increase the mechanical strength of catalysts. The extruded catalysts were then crushed, and the -16/+20 mesh fraction was collected and subjected to calcination at 550°C for 6 h to obtain corresponding H-type catalysts. 2.2 Characterization Intermediates characterization: X-ray diffraction (XRD) patterns of samples were collected on X’pert X-ray diffractometer (PANalytical Corporation, Netherland) with filtered Cu K α radiation at a tube current of 40 mA and a voltage of 40 kV. The scanning range of 2θ was 5 ~ 35 °. The relative crystallinity of the samples was calculated according to the sum of the peak intensities at 2θ of 14.3 o, 22.7 o, 23.7 o and 26.0 o. 29

Si MAS NMR experiments were performed on a Bruker AVANCE III 500WB

spectrometer at a resonance frequency of 99.3 MHz using a 7 mm double-resonance MAS probe. The magic-angle spinning speed was 5 kHz in all experiments, and a typical π/6 pulse length of 1.8 µs was adopted for 29Si resonance. The chemical shift of 29

Si was referenced to tetramethylsilane (TMS). 27

Al MAS NMR experiments were performed on a Bruker AVANCE III 600WB

spectrometer at a resonance frequency of 156.4 MHz using a 4 mm double-resonance MAS probe at a sample spinning rate of 13 kHz. The chemical shift of referenced to 1 M aqueous Al(NO3)3.

27

27

Al was

Al MAS NMR spectra were recorded by

small-flip angle technique using a pulse length of 0.4 µs ( 20) structure, in which the diffraction peaks of NaA rapidly decreased at 48 h, and peaks corresponding to MCM-49 emerged and increased with prolonging crystallization time from 48 to 96 h. Obviously, the LTA-MWW co-existing zeolites were the intermediates during the transformation. MCM-49 was generated gradually at the expense of NaA consumption and Si incorporation, which was described as the “LTA consumption - MWW growth” without complete disappearance of crystalline phase. With the increase of crystallization time to 72 h, there was a good agreement between samples with SiO2/Al2O3 = 20 and SiO2/Al2O3 = 25 in zeolite-zeolite transformation processes (samples 7 and 12 in Table 1) under same conditions: magadiite was generated because of high OH-/SiO2S (SiO2S: solid silica gel) molar ratio,40, 41 and finally magadiite could also be consumed as other way of silica source (Samples 8 and 14 in Table 1). At the end of zeolite-zeolite transformations, there occurred all feature diffraction peaks of pure MCM-49 without those of NaA and magadiite. However, it was interesting that there was no magadiite detected in the 11


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transformation process of SiO2/Al2O3 = 30 (sample 2 to 4 in Table 1), which may be attributed to appropriate OH-/SiO2S molar ratio in the initial reactant composition. It could be regarded as that lower SiO2/Al2O3 lead to higher OH-/SiO2S and the formation of magadiite. With feeding SiO2/Al2O3 = 25, MCM-49 was obtained via conventional hydrothermal synthesis as a reference material. However, it has been extensively proved that MCM-22P was usually synthesized under conventional hydrothermal treatment with SiO2/Al2O3 = 30. Interestingly, it was MCM-49 not MCM-22P that was obtained via the transformation. It has been clearly proved by Mobil researchers

12-14

and their

followers that MCM-22P has two dimensional MWW structure without formation of oxygen bridge bonds due to the higher HMI/Na+ and that MCM-49 has complete three dimensional of MWW structure because of the complete formation of oxygen bridge bonds between the MWW layers. It was not MCM-22P with 2D structure but MCM-49 with 3D structure that was transformed from NaA with 3D structure. We anticipate that if the 3D LTA structure was destructed, MCM-22P rather than MCM-49 would be formed with SiO2/Al2O3 = 30, which indicated that the zeolite-zeolite transformation proceeded by Si incorporation in the presence of HMI with little destruction of 3D connection. There was amorphous phase observed by XRD in the samples at 48 and 72 h. Only for the final MCM-49 and starting NaA, no amorphous phase was observed. During the transformation process, the amorphous phase was associated with solid silica gel, raw materials used to provide extra SiO2. The amount of solid silica gel accounted for majority of total feedings, surely large amount of amorphous phase could be observed. From 48 to 96 h, the amorphous phase became less and less and finally disappeared until 96 h, that is, the amorphous SiO2 was consumed and completely consumed at the end of the zeolite-zeolite transformations. TEM image and the selected 12



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area electron diffraction (SAED) pattern proved that the final product was pure MCM-49 without competing phases in Fig. 2. It is proposed that in alkaline solution, the consumption of LTA structure might be the rate determining step for the transformations from LTA to MWW structure in the presence of SiO2 and HMI before 72 h. Once LTA structure was consumed, the zeolite-zeolite transformation proceeded soon, and MWW structure was formed through Si incorporation from 72 to 96 h. Comparing the transformation of “LTA to MWW” with that of “FAU to MWW”, there were similar results of zeolite-zeolite transformations: one was direct zeolite to zeolite transformation with the process of “FAU/LTA consumption - MWW growth” by Si incorporation, the other was final transformations to ZSM-35 (FER), which was clearly observed that the peaks corresponding to the MCM-49 began to decrease as the treatment time still increased, and that the peaks corresponding to ZSM-35 emerged simultaneously. Finally, the pure ZSM-35 was formed because of thermodynamics drive in this transformation system. 3.2 Characterization of intermediates SEM images, 29Si, and 27Al MAS NMR, and liquor 27Al NMR measurements were performed to offer an insight into the transformation from NaA (LTA, lta, sod, and d4r) to MCM-49 zeolite (MWW, mel and d6r). SEM images: All the SEM images were taken to exhibitthe transformation from NaA to MCM-49 zeolite at different crystallization time (48 h, 72 h and 96 h). Firstly, Fig. 3 shows visual description of the “LTA consumption - MWW growth” during the zeolite-zeolite transformation (Fig. S1, S2, S3 and S4 in the supporting information). At 48 h, the rough morphology of NaA was preserved and the surface of NaA was corroded. With the increase of crystallization time to 72 h, some multi-layered structure of 13


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MCM-49 might be formed on the surface of NaA. The transformation was supposed to continue from the exterior to the interior, and MCM-49 was completely formed until 96 h. 38 The whole process was accompanied by Si incorporation and NaA consumption. It might be one way of transformation that the Si in mother liquor was transferred to LTA framework to accomplish the Si incorporation, and the final crystals seem to be originated from NaA. In this way, the crystal sizes of MCM-49 with a rose-like shape could be similar to that of NaA zeolite. Secondly, while for some cases, the solid silica gel did not depolymerize, which was proved by the preservation of large SiO2 blocks. As shown in Fig. 4, there were other ways of transformation besides the first way similar to “FAU to MWW”. 38 The driving force of zeolite-zeolite transformation was so dramatic that even large blocks of SiO2 could be incorporated into LTA framework with long crystallization time. It is reasonable to hypothesize that from 48 to 96 h the relative smaller NaA crystals were moved and adsorbed on the surface of larger SiO2 particles (several µm to 50 µm) to achieve Si incorporation into LTA framework for the formation of MCM-49. Additionally, magadiite was generated at high OH-/SiO2S by XRD (Fig. 1), and we intentionally select two different regions at the same crystallization time (72 h), namely 72 h-I and 72 h-II in Fig. 4. It can be seen clearly that amounts of layer-structure magadiite emerged in 72 h-I, and some layer-structure MWW zeolite was generated on the surface of magadiite in 72 h-II. Magadiite could be used as other way of silica source and be completely consumed in the end. 29

Si MAS NMR: Fig. 5 displays the

29

Si MAS NMR spectra of the zeolite-zeolite

transformation samples at various crystallization time. With SiO2/Al2O3 molar ratio of 2.0, there was only one typical peak of NaA framework Si at -88 ppm ~ Si(4Al), indicating only one kind of chemical environment.42 Framework Si of LTA structure 14



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was totally different from that of MWW structure.

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Si MAS NMR spectra of pure

MWW structure shows poorly separated peaks between -100 and -120 ppm, and the signal could be de-convoluted into up to 5 components as follows:

43

at -100 ppm ~

Si(1Al), and -105 ppm to 119 ppm ~ Si(0Al). With further crystallization time from 48 to 96 h, the peak of LTA framework Si decreased gradually and these resonances of MCM-49 zeolite at around -100, -115, -119 ppm became clear-cut. It was found that the intensity of Si (0Al) increased with increasing crystallization time, especially -105 and -119 ppm from 72 to 96 h, indicating the subsequent polymerization of the silicate species. Eventually, MWW framework was fully formed with the complete disappearance of LTA framework Si. The results clearly reveal the “LTA consumption MWW growth”, during which the hydrothermal consumption of LTA structure may be the rate determining step for the whole transformation. 27

Al MAS NMR: Since all Al source derived from NaA, the 27Al MAS NMR spectra

were performed to testify the chemical environmental changes of tetrahedral Al during the transformation from LTA to MWW structure (Fig. 6). There was no extra-framework Al during the whole transformation, and with the increase of the crystallization time, the 27

Al NMR resonances at 56 and 50 ppm (MCM-49) 43 eventually emerged at 96 h with

the decrease of peak at 60 ppm (NaA),

42

which disclosed simple fact that the

framework Al of LTA structure was transformed to that of MWW structure by Si incorporation. Also, the 27Al resonances showed almost no change in symmetry of NaA, which meant the perfect preservation of Al species during the zeolite-zeolite transformation. If there was any severe desilication or dealuminzation, the symmetry of resonances should be changed because of the change of chemical environments. In addition, the results also confirm that MCM-49 was generated at the expense of NaA 15


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consumption via the co-existing zeolites as intermediates, which was consistent with the results reported by XRD, SEM, and 29Si MAS NMR. 27

Al NMR of mother liquor:

27

Al NMR spectra of mother liquor at different

crystallization time (samples 6, 7 and 8 in Table 1) were performed with deionized water as the blank sample. Fig. 7 shows a broad resonance in the liquid NMR results. It could be deduced that 4-coordinate Al species were just overlapping with the broad band therein if without blank experiment of deionized water. However, the liquid NMR spectra of deionized water also showed a broad resonance at the same position even with the same intensity, which indicated there might be Al in the NMR probe. Therefore, the differential spectra of samples 6, 7 and 8 with deionized water as background were also provided in Fig. 7. Based on the differential spectra, it can be verified that there was no obvious detection of 27Al resonances in the mother liquor of samples 6, 7 and 8, which indicated that there was litter Al content in mother liquor to support the direct phase transformation from NaA to MCM-49. Also the yield of MCM-49 was calculated based upon Al balance and all the yields to final MCM-49 were higher than 99%. 3.3 Hypothesis on the transformation mechanism According to all results of above characterizations, it was proposed that NaA was directly transformed into MCM-49 by Si incorporation, without the new formation of amorphous phase, especially by XRD, SEM and

29

Si/27Al MAS NMR. The

zeolite-zeolite transformation would proceed with the consumption of LTA structure and the formation of MWW structure. The consumption of LTA structure was suggested as the preliminary step for the whole process. Here we try to unveil mechanism of the transformation from NaA to MCM-49. FTIR (KBr): Fig. 8 displays the FTIR spectra of the zeolite-zeolite transformation 16



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samples at various crystallization time. The band at 554 cm-1 was assigned to the presence of structural double rings (d4r), which were dominant sub-units in LTA structure.

44

With the increase of crystallization time from 48 to 72 h, the intensity of

band at 554 cm-1 (d4r) decreased significantly, demonstrating the gradual consumption of LTA structure and the consumption as the preliminary step during the whole transformation; however, there was no obvious band at 608 cm-1 (d6r) to be formed. With longer crystallization time at 96 h, the bands at 608 cm-1 and 560 cm-1 became clearer and stronger with the complete formation of d6r in MWW structure,

45

which

indicated that the d6r of MWW structure was originated from gradual change of d4r not from the silica gel. If the MWW structure was generated on silica gel with Al dissolution from LTA structure, the band at 608 cm-1 (d6r) should be clearly observed for the sample at 48 to 72 h (the bands at 608 and 560 cm-1 could be observed during the conventional hydrothermal synthesis), but it was not the case in Fig. 8. For the transformation from FAU to MWW structure, the mechanism of the transformation was proposed on the basis of the common CBUs between FAU (d6r and sod) and MWW (d6r and mel) structure. The common CBU (d6r) was considered to be a key to the direct phase transformation from FAU to MWW structure. 38 There were not any common CBUs between LTA (d4r, sod, and lta) and MWW structure (d6r and mel), however, the zeolite-zeolite transformation from low SiO2/Al2O3 LTA to high SiO2/Al2O3 MWW was successfully achieved by Si incorporation. There are should be other driving force beyond common CBUs hypothesis during the direct zeolite-zeolite transformation. 3.3.1 Synergism during the zeolite-zeolite transformation As shown in Table 2, without either HMI or NaOH, LTA structure was preserved 17


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from 24 to 72 h by XRD with supplementary SiO2 as amorphous phase. Sample 3 in Table 2 shows that no new formation of amorphous phase was generated when NaA treated by NaOH. The preservation of LTA structure in presence of NaOH was attributed to its low SiO2/Al2O3 molar ratio (only SiO2/Al2O3 = 2.0), which was more stable structure especially in alkaline solution. The results suggest that HMI and SiO2 adding should be crucial factors to the successful transformation from LTA to MWW structure in NaOH, as well as “FAU to MWW”. NaOH solution acts as alkaline source. HMI, as an effective structure-directing agent (SDA), is needed to direct the formation of MWW structure. The Additional SiO2 is needed to satisfy the mass balance to achieve the transformation from LTA (SiO2/Al2O3 = 2.0) to MWW (SiO2/Al2O3 > 20) structure. Si incorporation is proved by the increase of framework density from 14.2 T / 1000 Å3 (LTA) to 15.9 T / 1000 Å3 (MWW). Therefore, it is successful that transformation from LTA to MWW structure could be caused by the “synergism” of SiO2 adding, NaOH and HMI as co-key components. That is, the transformation from NaA to MCM-49 should be achieved via the synergism of NaA, HMI, NaOH and solid silica gel. From the view of SDAs, inorganic species (such as Na+) are taken into accounts as SDAs only in those cases where they are chemically associated to the organic compound to promote zeolite crystallization. As for the synthesis of NaA, Na+ acts as the only SDA. The transformation from NaA to MCM-49 could also be regarded as the process from sole-SDA system (Na+) to dual SDAs system (Na+, HMI and HMI+, named as “SDAs”). 13

C CP/MAS NMR: It has been shown that the

13

C CP/MAS NMR spectra of

occluded SDAs in synthetic zeolites were sensitive to the geometry of the intracrystalline void space in which they were located. According to the blank 18



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experiments, there were not any 13C resonances of HMI without Si adding in the system of NaA, HMI and NaOH (sample 3 at 48 h in Table 2) in Fig. 9A; so did in the system of solid silica gel, HMI and NaOH without NaA adding (sample 4 at 48 h in Table 2). The

13

C NMR spectra during the transformation from NaA to MCM-49 are shown in

Fig. 9B. The strong

13

C CP/MAS NMR resonances of HMI at 48 h clearly prove the

introduction of HMI into solid product in the zeolite-zeolite transformation, and it would represent HMI trapped in pockets within a gel phase that were similar to the MWW voids prior to crystallization, which also proved the synergism during the transformation from NaA to MCM-49. From 48 to 96 h, the C1 resonances of HMI occurred at 49 and 57 ppm, and the C2 and C3 resonances overlapped at 27 ppm. Moreover, it is found that the intensity of C1 resonance at 57 ppm increased with prolonging crystallization time, indicating that more and more MWW layers were formed. The observation of the two resonances for the C1 suggests that HMI may reside in two distinct environments within MCM-49 (Ref. 16). Therefore, HMI may play two important roles in the transformation from NaA to MCM-49. The one acts as a pore-filling agent, the other acts as a SDA to sustain the MWW layer structure. 3.3.2 The driving force during the zeolite-zeolite transformation STEM-EDS: According to above results, it could be clearly seen that the transformation from NaA (LTA, low SiO2/Al2O3 = 2.0) to MCM-49 (MWW, high SiO2/Al2O3 > 20) was successfully achieved by Si incorporation. MCM-49 was proposed to be generated on the surface of NaA from exterior to interior. Generally speaking, since SiO2/Al2O3 ratios of NaA and MCM-49 were around 2.0 and 25 respectively, the difference between them is sufficiently large to be observed. The gradient of SiO2/Al2O3 may provide much deeper information about the whole 19


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transformation, especially the gradient of SiO2/Al2O3 in the core-shell structure of LTA-MWW co-existing intermediates. In order to testify this, STEM-EDS analysis was designed to observe the change of SiO2/Al2O3 gradient directly. Fig. 10 displays typical results obtained from STEM-EDS analysis of samples during the transformation. Only SiO2 and Al2O3 values were calculated from the Si and Al counts to observe the SiO2/Al2O3 change of the samples, and to be compared with feeding initial SiO2/Al2O3 molar ratio of 25. NaA zeolite with uniform shape was selected as parent zeolite, and both two points were confirmed to have the identical SiO2/Al2O3 molar ratio of 2.0 from edge to middle, which was in accordance with XRF analysis. With crystallization time at 48 h, the SiO2/Al2O3 molar ratio was slightly higher than that of parent zeolite from edge to middle (point 1, 2 and3). Point 4 showed the SiO2/Al2O3 molar ratio of 27.8, which was close to the SiO2/Al2O3 molar ratio of MCM-49 and indicated the formation of little MWW structure (SiO2/Al2O3 molar ratio > 20); however, Point 5 displayed the area of almost silica source with SiO2/Al2O3 molar ratio of 200. With crystallization time at 72 h, SiO2/Al2O3 changed from 18.4 in the edge part (point 1) to 2.4 in the middle part (point 4). The STEM-EDS results (Fig. 10-72 h) show the presence of NaA core (low SiO2/Al2O3) within the outer MCM-49 shell (high SiO2/Al2O3), indicating that intermediate was a peculiar LTA-MWW core-shell co-existing zeolites, in good agreement with MCM-49 formed from exterior to interior. A further increase of the crystallization time up to 96 h led to the formation of pure MCM-49, and the decreasing SiO2/Al2O3 molar ratios as follow: 45.4 → 36.3 → 22.0. The SiO2/Al2O3 molar ratio of the shell (SiO2/Al2O3 = 45.4) was higher than that of the core (SiO2/Al2O3 = 22.0), which indicated a Si enrichment shell wrapping around the core. MCM-49 via 20



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Page 22 of 52

conventional hydrothermal synthesis hardly shows difference in SiO2/Al2O3 molar ratio between outer and inner. Maybe the transformation from NaA to MCM-49 by Si incorporation provides a new method to achieve adjustable distribution of SiO2/Al2O3 ratios. The crystal-size of MCM-49 with rose-like shape was similar to that of NaA (about 2 µm). The charge density match/mismatch: The change of SiO2/Al2O3 from exterior to interior was in good agreement with a core-shell growth mechanism, through which the core, with a low SiO2/Al2O3 ratio, was from parent zeolite NaA and the shell, with a high SiO2/Al2O3 of MCM-49. Unquestionably, the SiO2/Al2O3 ratio (45.4) on the crystal surface was much higher than that (22.0) of the middle part of pure MCM-49. The gradient of SiO2/Al2O3 molar ratio may be an interesting phenomenon during the whole zeolite-zeolite

transformation.

However,

with

SiO2 addition,

the failure of

transformation from NaA to MCM-49 in absence of HMI reminds us that there should be other driving force to decrease the gradient of SiO2/Al2O3. Based on the results of blank experiments, the decrease of SiO2/Al2O3 gradient was surely caused by HMI. Charge density match is a classic concept throughout the synthesis of zeolites. On one hand organic SDAs are successfully used to synthesize the high Si zeolite to afford a better match between SDAs and high Si zeolitic framework.46 UOP employed charge density mismatch (CDM) concept to synthesize several new zeolites first and make CDM popular all over the world,47-51 also former researchers from Exxon&Mobil reported they used charge density match theory to achieve the first synthesis of MCM-41 in their recent review.52 On the other there lie many failures of zeolites’ synthesis because of charge density mismatch between SDAs and zeolitic framework. To our great curiosity, could the charge density match/mismatch be used in the 21


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transformation between two zeolites without any common CBUs, that is, is the charge density match/mismatch persuasive enough to explain the transformation from NaA to MCM-49 beyond the common CBUs hypothesis? It is now well established that the 13C chemical shift of HMI in zeolites was very sensitive to the size of cavities inside which it became entrapped during the transformation from NaA to MCM-49. At 48 h in Fig. 9B, 13C NMR analysis exhibited two strong 13C resonances of HMI at 49 and 27 ppm respectively, which suggested HMI should be easily introduced in only co-existence of NaA, NaOH and Si adding. Charge density match between Na+ (high positive charge density) and LTA framework (high negative charge density with low Si/Al ratio = 2.0) of NaA was interrupted by the introduction of HMI (low positive charge density) in the presence of NaOH and Si adding, there lied charge density mismatch between HMI and LTA framework in the transformation system. In this paper, the only way to diminish charge density mismatch was Si incorporation. As proved by STEM-EDS analysis, Si was gradually incorporated into the LTA structure to diminish the mismatch between HMI and LTA framework in NaOH solution, until the complete formation of MWW structure, which was better match between HMI and MWW framework. The whole process could be described as follows: charge density match between Na+ and LTA framework → charge density mismatch between HMI and LTA framework → charge density match between HMI and MWW framework. The key of the zeolite-zeolite transformation may be the introduction of HMI and Si incorporation in NaOH solution to decrease the charge density of LTA framework to transform MWW framework. From the point of view, the synergism of NaA, HMI, NaOH and SiO2 could be well understood. With adding solid silica gel, obviously, Si 22



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was incorporated into NaA to transform MCM-49 in the presence of HMI and NaOH, which was proved by the increase of framework density from 14.2 T / 1000 Å3 (LTA) to 15.9 T / 1000 Å3 (MWW) with total amounts of Al unchanged. At the same time, the SiO2/Al2O3 molar ratio increased. This is the reason why it can be seen interesting phenomena of “the longer crystallization time, the more Si incorporation, the higher SiO2/Al2O3 molar ratio, and the better match between SDAs and zeolitic framework”. The transformation from NaA to MCM-49 proceeded from exterior to interior through core-shell intermediates by Si incorporation. The change of SiO2/Al2O3 gradient during the transformation is a side evidence of the mismatch between SDAs and zeolitic framework, which has been diminished by Si incorporation. Eventually, high SiO2/Al2O3 MCM-49, which is a low charge density framework, is formed completely by “synergism” of NaA, HMI, NaOH and adding SiO2. 3.4 Physicochemical properties of H-type zeolites The preservation of H-type zeolite crystallinity indicated that the transformed MCM-49 was mostly retained after NH4+ ion-exchanging and calcinations. HAM25 had almost similar micro surface area (412 m2·g-1) and micro pore volumes (0.17 cm3·g-1) to conventional H-MCM-49 (410 m2·g-1 and 0.17 cm3·g-1). Due to effective capability of HMI to form MWW layers, MWW layers were aggregated severely to form large crystals at 3 ~ 5 µm, which showed negative effects for liquid-phase alkylation. However as SEM images showed, the final transformed MCM-49 had uniform sizes (about 2 µm) similar to that of NaA (about 2 µm). The pore size distribution of conventional MCM-49 and transformed MCM-49 could be found in Fig. S5 (the supporting information). HAM25 might possess better accessibility of active centers and better catalytic performance in the liquid-phase alkylation of benzene with ethylene. 23


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Table 3 shows the number of acid sites characterized by Py-FTIR. HAM25 had slightly higher Brønsted acid sites (412 µmol·g-1) at 200 oC and (376 µmol·g-1) at 350 o

C than those of conventional H-MCM-49 (402 µmol·g-1) at 200 oC and (375 µmol·g-1 )

at 350 oC. However, Lewis acid sites of HAM25 (265 µmol·g-1) at at 200 oC and (218 µmol·g-1) at 350 oC were obviously higher than those of conventional H-MCM-49 (189 µmol·g-1) at 200 oC and (168 µmol·g-1) at 350 oC, which surely resulted in an increase in total acid sites and a decrease in B/L ratio. The increase of total acid sites means more acid sites could be accessed by pyridine during Py-FTIR experiments, which may offer more active centers to be accessed by reactants in liquid-phase alkylation of benzene with ethylene due to the same kinetic diameters at 0.58 nm of both benzene and pyridine molecules. MCM-49 transformed from NaA shows more active centers and better accessibility of active centers for liquid-phase alkylation. 3.5 Liquid-phase alkylation of benzene and ethylene over H-type catalysts Ethylene conversion and EB selectivity: As well known, the alkylation of benzene with ethylene is a consecutive reaction with EB as the target product. Therefore, the trade-off between ethylene conversion and EB selectivity must be carefully weighed and considered; usually improved ethylene conversion is accompanied by decreased EB selectivity. The catalysts HAM25 through the transformation from NaA and H-MCM-49 conventional via hydrothermal method show their alkylation performance in Fig. 11A and B. For HAM25 catalyst, it could be seen that ethylene conversion was improved from 99.0 % to 100 % with temperature ranging from 200 oC to 260 oC, but the EB selectivity was decreased from 96.3 % to 95.4 %. There is the similar pattern in conventional H-MCM-49 catalyst with temperature increasing from 200 oC to 260 oC: 24



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ethylene conversion increased from 96.6 % to 99.2 %; and meanwhile, EB selectivity decreased from 95.4 % to 94.9 %. Clearly, it is a common phenomenon that the ethylene conversion was increased with the rise of temperature, and the EB selectivity was decreased, which still fell into a rule like see-saw. On the whole, HAM25 catalyst showed better ethylene conversion and EB selectivity, that is, the trade-off between ethylene conversion and EB selectivity in a typical consecutive reaction has been broke through, which is mainly due to more acidic sites and better accessibility of active centers. DEB selectivity and DEB distributions: Fig. 12A and B show that DEB selectivity and DEB distributions over H-type catalysts in the liquid-phase alkylation of benzene with ethylene. The DEB selectivity for both H-type catalysts was increased slightly by the rise of temperature in Fig. 12A. On the whole, HAM25 catalyst yielded less DEB than conventional H-MCM-49 catalyst in the liquid-phase alkylation of benzene with ethylene, and the less DEB was produced to achieve better EB selectivity. At low temperature, it can be seen that the high degree of selectivity over both H-type catalysts for o-DEB, as shown in Fig. 12B, and that o-DEB decreased by the temperature rise from 200 oC to 260 oC. On the contrary, the low degree of selectivity for m-DEB gradually was achieved. As well known, p-DEB has the smallest molecular diameter among the three DEB isomers, while space-filling models have shown that the o-DEB has the most favorable configuration for active centers of H-type catalysts. With the temperature rising, more and more m-DEB was produced by the isomerization of o-DEB, and in the meantime, the selectivity of p-DEB was almost unchanged. Additionally, it is obvious to see the gradual trend of DEB isomers moving toward the thermodynamic equilibrium values and the quality ratios of DEB isomers were 25


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maintained as 64 (for m-DEB):30 (for p-DEB):6(for o-DEB), respectively. On the whole, with less DEBs generated, better EB selectivity could be achieved. Therefore HAM25 catalyst via the zeolite-zelite transformation by Si incorporation shows lower DEB selectivity and higher EB selectivity accompanying higher ethylene conversion. 4. Conclusion The transformation from NaA (LTA, lta, sod and d4r) to MCM-49 (MWW, d6r and mel) zeolite has been achieved in the synergism of HMI, NaOH and SiO2, in spite of no common CUBs between LTA and MWW structure. According to the results of XRD, SEM,

29

Si/27Al/13C MAS NMR, and STEM-EDS, it is clearly demonstrated that

MCM-49 was proposed to be generated gradually from exterior to interior of NaA via direct phase transformation, which was clearly observed by the core (LTA, low SiO2/Al2O3) - shell (MWW, high SiO2/Al2O3) co-existing zeolites as intermediates. It may be explained that the mismatch between HMI with low charge density and LTA framework with high charge density at low SiO2/Al2O3 could be the driving force to accomplish the transformation from LTA to MWW structure by Si incorporation. That is, the longer crystallization time, the more Si incorporation, the higher SiO2/Al2O3 molar ratio, and the better match between SDAs and zeolitic framework. Therefore, it can be seen clearly that the intermediates of “LTA to MWW” show the presence of NaA core within the out shell of MCM-49, indicating that intermediates are LTA-MWW core-shell structure co-existing zeolites, in good agreement with MWW zeolite formed from exterior to interior. The final MCM-49 is featured by Si enrichment on the external surface, which is proved by the shell (SiO2/Al2O3 = 45.4) wrapping around the core (SiO2/Al2O3 = 22.0). Additionally, transformed MCM-49 with Si enrichment on the external surface may have high catalytic property in liquid-phase alkylation of benzene 26



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with ethylene. Also as SEM images, transformed MCM-49 had uniform sizes (about 2 µm) similar to that of NaA (about 2 µm), and improved total acid sites determined by Py-FTIR, which meaned more active centers to be accessed by reactants in liquid-phase alkylation of benzene with ethylene. Because of more acid sites and better accessibility of active centers, HAM25 catalyst transformed from NaA zeolite showed higher ethylene conversion without loss of EB selectivity. Acknowledgments This work was supported by the National Basic Research Program of China (973 Program, No.2012CB224805). Special thanks to the Department of Analysis in Research Institute of Petroleum Processing, Sinopec. Supporting information Available Fig. S1, S2, S3 and S4 giving SEM images of calcined samples via the transformation from NaA at various crystallization time. Fig. S5 giving the pore size distribution of conventional MCM-49 and transformed MCM-49. This information is available free of charge via the Internet at http://pubs.acs.org/. References (1) Yilmaz, B.; Muller, U. Catalytic Applications of Zeolites in Chemical Industry. Top. Catal. 2009, 52, 888. (2) Zhang, B.; Ji, Y. J.; Wang, Z. D.; Liu, Y. M.; Sun, H. M.; Yang, W. M.; Wu, P. Liquid-Phase Alkylation of Benzene with Ethylene over Post-Synthesized MCM-56 Analogues. Appl. Catal. A: Gen. 2012, 443-444, 103.

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(33) Itabashi, K.; Kamimura, Y.; Iyoki, K.; Shimojima, A.; Okubo, T. A Working Hypothesis for Broadening Framework Types of Zeolites in Seed-Assisted Synthesis without Organic Structure-Directing Agent. J. Am. Chem. Soc. 2012, 134, 11542. (34) Iyoki, K.; Itabashi, K.; Okubo, T. Progress in Seed-Assisted Synthesis of Zeolites without Using Organic Structure-Directing Agents. Micropor. Mesopor. Mater. 2014, 189, 22. (35) Ogawa, A.; Iyoki, K.; Kamimura, Y.; Elangovan, S. P.; Itabashi, K.; Okubo, T. Seed-Directed, Rapid Synthesis of MAZ-type Zeolites without Using Organic Structure-Directing Agent. Micropor. Mesopor. Mater. 2014, 186, 21. (36) Jon, H.; Ikawa, N.; Oumi, Y.; Sano, T. An Insight into the Process Involved in Hydrothermal Conversion of FAU to *BEA Zeolite. Chem. Mater. 2008, 20, 4135. (37) Shi, Y. C.; Xing, E. H.; Gao, X. Z.; Liu, D. Y.; Xie, W. H.; Zhang, F. M.; Mu, X. H.; Shu, X. T. Topology Reconstruction from FAU to MWW Structure. Micropor. Mesopor. Mater. 2014, 222, 269. (38) Shi, Y. C.; Xing, E. H.; Xie, W. H.; Zhang, F. M.; Mu. X. H.; Shu, X. T. Size-Controlled Synthesis of MCM-49 Zeolites and their Application in Liquid-Phase Alkylation of Benzene with Ethylene. RSC Adv. 2015, 5, 13420. (39) Xing, E. H.; Gao, X. Z.; Xie, W. H.; Zhang, F. M.; Mu, X. H.; Shu, X. T. Temperature-Controlled Phase Transfer Hydrothermal Synthesis of MWW Zeolites. RSC Adv. 2014, 4, 24893. (40) Okutomo, S.; Kuroda, K.; Ogawa, M. Preparation and Characterization of Silylated-Magadiites. Appl. Clay. Sci. 1999, 15, 253. 32



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(41) Wang, Y.; Shang, Y.; Zhu, J.; Ji, S.; Meng, C. Synthesis of Magadiite Using a Natural Diatomite Material. J. Chem. Technol. Biotchenol. 2009, 84, 1894. (42) Xue, Z. T.; Ma, J. H.; Hao, W. M.; Bai, X.; Kang, Y. H.; Liu, J. H.; Li, R. F. Synthesis and Characterization of Ordered Mesoporous Zeolite LTA with High Ion Exchange Ability. J. Mater. Chem. 2012, 22, 3532. (43) Vuono, D.; Pasqua, L.; Testa, F.; Aiello, R.; Fonseca, A.; Koranyi, T. I.; Nagy, J. B. Influence of NaOH and KOH on the Synthesis of MCM-22 and MCM-49 Zeolites. Micropor. Mesopor. Mater. 2006, 97, 78. (44) Zhan, Y. Z.; Li, X. X.; Zhang, Y. G.; Li, H.; Chen, Y. L. Phase and Morphology Control of LTA/FAU Zeolites by Adding Trace Amounts of Inorganic Ions. Ceram. Int. 2013, 39, 5997. (45) Ravishankar, R.; Bhattacharya, D.; Jacob, N. E.; Sivasanker, S. Characterization and Catalytic Properties of Zeolite MCM-22. Micropor. Mater. 1995, 4, 83. (46) Cundy, C. S.; Cox, P. A. The Hydrothermal Synthesis of Zeolites: History and Development from the Earliest Days to the Present Time. Chem. Rev. 2003, 103, 663. (47) Blackwell, C. S.; Broach, R. W.; Gatter, M. G.; Holmgren, J. S.; Jan, D. Y.; Lewis, G. J.; Mezza, B. J.; Mezza, T. M.; Miller, M. A.; Moscoso, J. G.; Patton, R. L.; Rohde, L. M.; Schoonover, M. W.; Sinkler, W.; Wilson, B. A.; Wilson, S. T. Open-Framework Materials Synthesized in the TMA+/TEA+ Mixed-Template System: The New Low Si/Al Ratio Zeolites UZM-4 and UZM-5. Angew. Chem., Int. Ed. 2003, 42, 1737. 33


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(48) Park, M. B.; Cho, S. J.; Hong, S. B.

Synthesis of Aluminosilicate and

Gallosilicate Zeolites via a Charge Density Mismatch Approach and Their Characterization. J. Am. Chem. Soc. 2011, 133, 1917. (49) Park, M. B.; Lee, Y.; Zheng, A. M.; Xiao, F. S.; Nicholas, C. P.; Lewis, G. J.; Hong, S. B. Formation Pathway for LTA Zeolite Crystals Synthesized via a Charge Density Mismatch Approach. J. Am. Chem. Soc. 2013, 135, 2248. (50) Moteki, T.; Okubo, T. From Charge Density Mismatch to a Simplified, More Efficient Seed-Assisted Synthesis of UZM-4. Chem. Mater. 2013, 25, 2603. (51) Broach, R. W.; Boldingh, E. P.; Jan, D. Y.; Lewis, G. J.; Moscoso, J. G.; Bricker, J. C. Tailoring Zeolite Morphology by Charge Density Mismatch for Aromatics Processing. J. Catal. 2013, 308, 142. (52) Roth, W. J.; Nachtigall, P.; Morris, R. E.; Cejka, J. Two-Dimensional Zeolites: Current Status and Perspectives. Chem. Rev. 2014, 114(9), 4807.

34



NaA

Intensity (a.u.)

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

48h

72h

96h 5

10

15

20

25

30

35

o

2 Theta ( )

Fig. 1 XRD patterns of as-synthesized samples via the transformation from NaA at various crystallization time

35


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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


b*

48 h

Fig. 2 TEM image (left) and SAED pattern (right) of MWW structure along [001] direction via the transformation from NaA at 96 h

36



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

NaA

96 h

72 h

Fig. 3 SEM images of calcined samples via the transformation from NaA at various crystallization time (I)

37


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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


Solid silica gel

48 h

72 h-I

72 h

Magadiite

72 h-II

96 h

Fig. 4 SEM images of calcined samples via the transformation from NaA at various crystallization time (II)

38



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

-111 -105 -115 -119 -100

29

Si MAS NMR

96 h

-88

72 h 48 h

silica source NaA

-40

-60

-80

-100

-120

-140

-160

-180

Chemical shift (ppm)

Fig. 5 29Si MAS NMR spectra of as-synthesized samples via the transformation from NaA at various crystallization time

39


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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


27

56

Al MAS NMR

50

96 h

60

72 h

48 h

NaA

80

60

40

20

0


Fig. 6 27Al MAS NMR spectra of as-synthesized samples via the transformation from NaA at various crystallization time

40



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

27

liquor Al NMR The difference spectra of sample 6 The difference spectra of sample 7 The difference spectra of sample 8 blank: deionzed water sample 6 in Table 1 sample 7 in Table 1 sample 8 in Table 1 300

200

100

0

-100

-200


Fig. 7 27Al liquid NMR spectra of mother liquids obtained from samples 6, 7 and 8 in Table 1

41


Page 42 of 52

608

NaA 48 h 72 h 96 h

554

Transmittance (a.u.)

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


560

Page 43 of 52

1200

1000

800

600

400

-1

Wavenumber (cm )

Fig. 8 FTIR spectra of calcined samples via the transformation from NaA at various crystallization time

42



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

A

b-48 h (solid silica gel + HMI + NaOH)

a-48 h (NaA + HMI + NaOH)

150

100

50

0

-50


C2, C3

B C1

96 h

C1

72 h

48 h 150

100

50

0

-50


Fig. 9 13C MAS NMR spectra of blank experiments (A) and as-synthesized samples via the transformation from NaA at various crystallization time (B)

43


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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


SiO2/Al2O3 Samples Point 1

Point 2

Point 3

Point 4

Point 5

NaA (LTA)

2.0

2.0

48 h

3.6

2.8

2.4

27.8

200

72 h

18.4

3.0

2.5

2.4

96 h (MWW)

45.4

36.3

22.0

Fig. 10 STEM-EDS images and the gradient of SiO2/Al2O3 of calcined samples via the transformation from NaA at various crystallization time

44



C2=Conversion (%)

100

98

A

96

H-MCM-49 HAM25 (MCM-49) 94

200

210

220

230

240

250

260

o

Temperature ( C)

99

B

H-MCM-49 HAM25 (MCM-49)

98 97

EB Selectivity (%)

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

96 95 94 93 92

200

210

220

230

240

250

260

o

Temperature ( C)

Fig. 11 Ethylene conversion (%, A) and ethylbenzene selectivity (%, B) of H-type catalysts (Liquid-phase alkylation conditions: 8 mL catalysts, T = 200 oC to 260 oC, p = 3.5 MPa, benzene WHSV-1 = 3.0 h-1, benzene/ethylene molar ratio = 12.0)

45


Page 46 of 52

Page 47 of 52

DEB Selectivity (%)

5

4

3 A H-MCM-49 HAM25 (MCM-49)

2

200

210

220

230

240

250

260

o

Temperature ( C)

60

Distribution of DEB isomers (%)

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


B

50

H-MCM-49: m-DEB HAM25: m-DEB

40

H-MCM-49: p-DEB HAM25: p-DEB H-MCM-49: o-DEB HAM25: o-DEB

30

20

10 200

210

220

230

240

250

260

270

280

290

300

o

Temperature ( C)

Fig. 12 DEB selectivity (%, A) and distribution of DEB isomers (%, B) of H-type catalysts (Liquid-phase alkylation conditions: 8 mL catalysts, T = 200 oC to 260 oC, p = 3.5 Mpa, benzene WHSV-1 = 3.0 h-1, benzene/ethylene molar ratio = 12.0)

46



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 52

Table 1 Transformation from NaA zeolites and products obtained Parent zeolites

Conditions

Products

Sample No.

SiO2/

Na2O

SiO2/

Time

Crystalline phase

SiO2/

Yieldsa

RC.

Al2O3

(wt.%)

Al2O3

(h)

by XRD

Al2O3

(%)

(%)

25

72

MCM-49

22

>99

100

27

>99

106

22

>99

110

18

>99

108

1b 2

2.0

18.5

30

48

NaA

3

2.0

18.5

30

60

NaA+MCM-49

4

2.0

18.5

30

72

MCM-49

5

2.0

18.5

30

96

ZSM-35

6

2.0

18.5

25

48

NaA

7

2.0

18.5

25

72

8

2.0

18.5

25

96

MCM-49

9

2.0

18.5

25

108

MCM-49+ZSM-35

10

2.0

18.5

25

120

ZSM-35

11

2.0

18.5

20

48

NaA

12

2.0

18.5

20

72

13

2.0

18.5

20

96

NaA (trace) +MCM-49+Magadiite

14

2.0

18.5

20

108

MCM-49

NaA+MCM-49 +Magadiite

NaA+MCM-49 +Magadiite

a: Yields of MCM-49 zeolites was calculated based on Al2O3 b: Conventional synthesis of MCM-49 zeolites

47


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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


Table 2 Blank experiments Parent zeolites

Conditions of topology reconstruction

Products

Sample SiO2/

Na2O

SiO2/

HMI/

NaOH/

Time

Temp.

Al2O3

(wt.%)

Al2O3

SiO2

SiO2

(h)

(oC)

1

2.0

18.5

25.0

0

0.18

24-72

145

NaA+ amorphous phase

2

2.0

18.5

25.0

0.3

0

24-72

145

NaA+ amorphous phase

3

2.0

18.5

2.0

0.3

0.18

24-72

145

NaA

4

0

0

SiO2

0.3

0.18

24-72

145

amorphous phase

No.

48


XRD


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 50 of 52

Table 3 Acid properties of H-type zeolites 200 oC

350 oC

Samples Lewis acid (µmol·g-1)

Brønstedacid (µmol·g-1)

B/L

Lewis acid (µmol· g-1)

Brønstedacid (µmol· g-1)

B/L

H-MCM-49

189

402

2.13

168

375

2.23

HAM25

265

412

1.55

218

376

1.72

49


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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


Figure captions: Fig. 1 XRD patterns of as-synthesized samples via the transformation from NaA at various crystallization time Fig. 2 TEM image (left) and SAED pattern (right) of MWW structure along [001] direction via the transformation from NaA at 96 h Fig. 3 SEM images of calcined samples via the transformation from NaA at various crystallization time (I) Fig. 4 SEM images of calcined samples via the transformation from NaA at various crystallization time (II) Fig. 5

29

Si MAS NMR spectra of as-synthesized samples via the transformation from

NaA at various crystallization time Fig. 6

27

Al MAS NMR spectra of as-synthesized samples via the transformation from

NaA at various crystallization time Fig. 7

27

Al liquid NMR spectra of mother liquids obtained from samples 6, 7 and 8 in

Table 1 Fig. 8 FTIR spectra of calcined samples via the transformation from NaA at various crystallization time Fig. 9

13

C MAS NMR spectra of blank experiments (A) and as-synthesized samples via

the transformation from NaA at various crystallization time (B) Fig. 10 STEM-EDS images and the gradient of SiO2/Al2O3 of calcined samples via the transformation from NaA at various crystallization time Fig. 11 Ethylene conversion (%, A) and ethylbenzene selectivity (%, B) of H-type catalysts (Liquid-phase alkylation conditions: 8 mL catalysts, T = 200 oC to 260 oC, p = 3.5 MPa, benzene WHSV-1 = 3.0 h-1, benzene/ethylene molar ratio = 12.0) 50



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

Fig. 12 DEB selectivity (%, A) and distribution of DEB isomers (%, B) of H-type catalysts (Liquid-phase alkylation conditions: 8 mL catalysts, T = 200 oC to 260 oC, p = 3.5 Mpa, benzene WHSV-1 = 3.0 h-1, benzene/ethylene molar ratio = 12.0)

Table 1 Transformation from NaA zeolites and products obtained Table 2 Blank experiments Table 3 Acid properties of H-type zeolites

51


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Transformation from NaA to MCM-49 Zeolite and ... - ACS Publications

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