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N-doped Food-grade derived 3D Mesoporous Foams as Metal-Free Systems for Catalysis Housseinou Ba, Yuefeng Liu, Lai Truong-Phuoc, Cuong Duong-Viet, Jean-Mario Nhut, Dinh Lam Nguyen, Ovidiu Ersen, Giulia Tuci, Giuliano Giambastiani, and Cuong Pham-Huu ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.6b00101 • Publication Date (Web): 19 Jan 2016 Downloaded from http://pubs.acs.org on January 25, 2016

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N-doped Food-grade derived 3D Mesoporous Foams as Metal-Free Systems for Catalysis Housseinou Ba,ξ Yuefeng Liu,ξ,* Lai Truong-Phuoc,ξ Cuong Duong-Viet,ξ,† Jean-Mario Nhut,ξ Dinh Lam Nguyen,φ Ovidiu Ersen,‡ Giulia Tuci,§ Giuliano Giambastiani,§,ψ,* and Cuong Pham-Huuξ,* ξ

† φ

‡

§

ψ

Institut de Chimie et Procédés pour l’Energie, l’Environnement et la Santé (ICPEES), UMR 7515 CNRSUniversity of Strasbourg (UdS), 25, rue Becquerel, 67087 Strasbourg Cedex 02, France Ha-Noi University of Mining and Geology, 18 Pho Vien, Duc Thang, Bac Tu Liem, Ha-Noi, Vietnam The University of Da-Nang, University of Science and Technology, 54, Nguyen Luong Bang, Da-Nang, Vietnam Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), UMR 7504, CNRS-University of Strasbourg (UdS), 23, rue du Loess, 67034 Strasbourg Cedex 02, France Institute of Chemistry of OrganoMetallic Compounds, ICCOM-CNR and Consorzio INSTM, Via Madonna del Piano, 10 – 50019, Sesto F.no, Florence, Italy Kazan Federal University, 420008 Kazan, Russian Federation.

ABSTRACT A challenging task of modern and sustainable catalysis is to re-think key-processes at the heart of renewable energy technology in light of metal-free catalytic architectures designed and fabricated from cheap and easily accessible building blocks. This contribution describes the synthesis of highly N-doped, carbon nanotube (CNT)-netting composites from cheap raw materials. Starting from physical mixtures of CNTs and food-grade components, their thermal treatment generates foamy, N-doped carbon-based architectures. The mesoporous nature of the N-doped carbon phase grown around intertwined carbon-nanotube networks together with the easy control of the final material 3D shape, make the protocol highly versatile for its full

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exploitation in the production of materials for catalysis. Besides offering unique advantages with respect to the classical N-doped CNT powders, the 3D metal-free composites are highly versatile systems for a number of liquid-phase and gas-phase catalytic processes, under a wide operative temperature range. In this paper we demonstrate their excellent and to some extent unique catalytic performance in two fundamental and catalyst-demanding processes: i) the electrochemical oxygen reduction reaction (ORR) and ii) the direct, steam-free dehydrogenation of ethylbenzene (EB) to styrene (ST).

KEYWORDS Nitrogen-doped carbon composites, Metal-free catalysts, 3D shaped mesoporous materials, Oxygen Reduction Reaction, Steam-free Ethylbenzene Direct Dehydrogenation.

Introduction Scientists agree that carbon-based materials represent one of the liveliest topic in the current fundamental and applied materials science. The unique chemical versatility of carbon, that allows for a rational control of its chemical connectivity, together with the high electronic and heat conductivity of its more common allotropic forms, are fundamental assets that largely drive the research activity in the field since the last decades. The substitutional doping of carbon materials with light hetero-elements offers a powerful tool for tuning their electronic structure/transport properties, expanding their application field remarkably.1-19 Since the pioneering works by Gong4 and Wang,5 several studies have demonstrated how the inclusion of light heteroelements in the honeycomb structure of mono- (1D) or bi-dimensional (2D) carbon nanomaterials (CNMs), generates effective metal-free systems capable of promoting a number of catalytic processes at the heart of renewable energy technology.1-20 To this purpose, nitrogen and


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boron have been widely scrutinized as electron donating and electron accepting doping-atoms, respectively.1-20 At odds with their ability to replace critical materials in several industrial key processes,1-3, 16-18

serious technological limitations still affect the widespread exploitation in catalysis of this

class of compounds. Their large-scale production in the form of porous and homogeneously doped materials featured by high surface areas and high dopant concentration still remains a great challenge for material scientists. Furthermore, the classical powdery texture of many CNMs strongly limits their application field, particularly with respect to their use in gas- and liquid phase catalytic processes. Moreover, tricky and scarcely atom-efficient synthetic protocols often represent a challenging bottleneck for the convenient material scale-up production and use in key technological fields. So far, a number of synthetic protocols including thermal pyrolysis of organic compounds,21-25 arc-discharge methods,26-28 laser ablation,29, 30 and chemical vapor deposition,3133

have been developed for the preparation of doped CNMs with different sizes, shapes, and

chemical composition. Despite their general feasibility, all these methods typically suffer from several limitations: from the employment of toxic reagents (often in their gaseous form), to the need of sophisticated equipments up to the use of harsh (if not severe) reaction conditions. In addition, the scarce atom efficiency of these synthetic methods (also affected by the partial thermal decomposition of reagents into waste and toxic by-products) hampers their widespread exploitation on an industrial scale. Milder approaches [i.e. the reduction/doping of pre-oxidized CNMs with N-containing reducing agents (top-down doping approach),34 or the chemical functionalization of pre-formed CNMs with tailored N-containing functional groups35, 36] offer useful paradigms to the comprehension (at a molecular level) of the role of the N-dopants on the


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materials catalytic performance. Nevertheless, none of these methods provides an exhaustive answer to the urgent quest for cheap and environmentally friendly techniques to the easy material upscale synthesis. The recent renaissance of hydrothermal carbonization (HTC) offers new perspectives, as it involves the use of renewable resources (e.g., cellulose) at moderately low temperatures (130– 250 °C) in aqueous medium under self-generated pressure.37-44 However, a full control on the macroscopic shape and size of the as prepared N-CNMs as well as on their graphitization degree, are still far to be fully accomplished. Nowadays, the use of easily accessible and non-toxic feedstock, the exploitation of less energy demanding and environmentally benign procedures and the achievement of a good material morphology control (both on micro- and macroscopic level) are all mandatory prerequisites for proposing new synthetic strategies finalized to the large-scale production of N-CNMs. To tackle these fundamental issues, herewith we report a new methodology for the largescale production of N-doped and hierarchically structured carbon nanotube-based composites (NC/CNT) through the controlled thermal treatment of physical mixtures of pristine multi-walled carbon nanotubes (MWCNTs) and food-processing components under solvent-free conditions. Such an approach generates 3D self-standing and shape-controllable open-cell mesoporous foams, where a highly N-doped carbon-phase is grown around a deeply intertwined MWCNTs network.45 As a result, 3D-mesoporous materials of different shape and size ranging from millimeters to several centimeters are synthesized. Ammonium carbonate [(NH4)2CO3], citric acid (C6H8O7) and D-glucose are the cheap and non-toxic naturally occurring precursors of the N-doped carbon-phase. Two successive thermal


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treatments in air at 130 and 450 °C allow for condensation/polymerization reactions to occur thus creating open-cell foam structures. A subsequent annealing at 900 °C under inert atmosphere is occasionally employed (depending on the material downstream application) with the aim of improving the electrical and thermal conductivity of the final composite. We have recently reported a related approach based on a water solution (soaking phase) of the same foodgrade components. In that case, highly shape-adaptable protocols for the tight coating of a number of macroscopic and porous host matrices are described.46 Unlike the classically prepared N-CNMs, the N-C/CNT composites list a number of remarkable advantages which make them ideal catalysts for a number of key industrial processes: i) 3D shaped, open-cell structures (foams) with low mass transfer limitation and relatively high surface area (vide infra); ii) high thermal and electrical conductivity ensured by the deeply intertwined MWCNT-based framework; iii) high density of surface-exposed N-sites due to the coating of the MWCNTs backbone by the N-C phase; iv) remarkable thermal stability of the N-C active phase even under harsh reaction conditions; v) highly homogeneous distribution of the light-heteroelement dopants (N) within the composite; vi) easy, cost-effective and environmentally safe material upscale syntheses; vii) safe handling and transport of the 3D composites; viii) synthetic procedures featured by a high atom efficiency.

Results and Discussion N-C/CNT Synthesis and properties Figure 1 summarizes the adopted strategy towards a model N-C/CNT foam material. A solid mixture of ammonium carbonate [(NH4)2CO3], citric acid, [(HO)C(COOH)(CH2COOH)2]


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D-glucose and MWCNTs (Figure 1A) is mechanically crushed to get a homogeneous dark powder (Figure 1B) before being heated at 130°C in air for 2 h (“shaping phase”).

Figure 1. Sequential steps (A → D) for the preparation of N-doped 3D self-standing composites (N-C/CNT) (D); from a physical mixture (wt./wt.) of commercially available food-grade components and pristine MWCNTs (A), their physical crushing (B) up to their thermal treatment in a selected shape-inducing sample holder (C). Thermal phases comprise a pre-heating (“shaping phase”) at 130 °C for 2 h in air, followed by the material calcination at 450 °C for 3h. A final thermal annealing at 900 °C under inert atmosphere (Ar) for 2 h is occasionally applied, depending on the material downstream application. The model N-C/CNT composite in Figure 1D is prepared from a finely crushed solid mixtures composed of D-Glucose (2g, 11.1 mmol), citric acid (3g, 15.6 mmol), MWCNTs (0.5 g) and (NH4)2CO3 (1 g, 10.4 mmol).

The first thermal phase initiates a complex series of chemical transformations (condensations, acid-base reactions, thermal decompositions) which trap the MWCNTs into a self-standing organic matrix, where D-glucose serves as the main carbon source and the mixture holder controls the foam shape and size (Figure 1C, S1 and S2). These conditions allow for the complete ammonium carbonate decomposition [(NH4)2CO3 → 2NH3 + CO2 + H2O] and the subsequent trapping of ammonia (NH3) in the form of basic ammonium citrate (tri-, di- or monobasic, depending on the ammonium carbonate/citric acid molar ratio used – see also Figure S3)46; the CO2 evolution is the main responsible for the generation of the foamy structure at the final composite during the thermal treatments. The successive thermal treatment (Figure 1C and S1) at


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450 °C under air (calcination) consolidates the foamy self-standing structure (Figure 1D) through a tight and interconnected coating of the MWCNT skeleton with a mesoporous, highly N-doped carbonaceous phase (N-C). The last thermal treatment (annealing at 900 °C under inert atmosphere) strengthens the adhesion of the N-C phase to the MWCNT scaffold while ensuring an improved electrical and thermal conductivity to the composite. The latter thermal phase is occasionally pursued depending on the chemico-physical properties required to the composite in light of its ultimate downstream application (vide infra). The presence of MWCNTs as a scaffold allows for the processing and control of the final composite shape into disks, monoliths or pellets (Figure S2) besides acting as a structural reinforce of the 3D foamy structures. The carbon nanofillers play a key role on the control of the final material morphology on both a macro- and microscopic level. The thermal heating of a plain mixture of the food-grade components (D-glucose, citric acid and ammonium carbonate) in the absence of MWCNTs leads to fragile “blobby” structures of undefined shape (Figure S4A vs. S4B) made of smooth carbon sheets (Figure S5). On the other hand, the combined action of the CNT network with that of the sample holder translates into foamy composites with a perfectly controllable shape. As SEM pictures show (Figure 2A, B), the N-C/CNT materials appear as a spongy phase (Figure 2A) made of highly entangled MWCNTs homogeneously covered by a thin N-C layer (Figure 2B). The N-content in the N-C phase growths asymptotically (Figure 3) with the increase of the (NH4)2CO3/citric acid mass ratio. The maximum value achievable equals 19.5 N at. %, roughly corresponding to a five-fold excess of ammonium carbonate with respect to the stoichiometric amount required for the complete conversion of citric acid into the corresponding ammonium citrate tri-basic (Table 1).


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Figure 2. Digital photo of a model N-C/CNT foam composite and SEM micrographs (A and B) at various magnifications.

Such an excess is required because of the solid nature of the starting mixture, where part of ammonium carbonate is invariably lost during the first aerobic thermal treatment, before that ammonia is captured and stored in the form of ammonium citrate.

Figure 3. (A) Asymptotic growth of the N (at. %) content in the N-C/CNT foams prepared at increased (NH4)2CO3/citric acid mass ratios after material heating at 450 °C. (B) High resolution XPS N1s core region recorded on the model composite N-C/CNTN15.3 and its relative peak deconvolution.


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Table 1. XPS characterization of the N-C/CNT-foam composites.a c

Entry

Sampleb

1

CNTs

2

C/CNT

3 4

N14.4

N-C/CNT N-C/CNTN15.3 A

N-C/CNTN15.3

XPS analysis (NH4)2CO3 SSA 2 (g) (m /g) C (at. %) O (at. %) N (at. %) N/C ratio -

145

90.68

9.32

-

-

-

279

83.02

16.98

-

-

0.5 1

358 423

76.84 74.63

8.71 10.09

14.45 15.28

0.19 0.20

1

249

93,7

3,46

2,75

0.03

N-C/CNT

N17.2

3

412

73.38

9.43

17.19

0.23

N-C/CNT

N18.2

8

N-C/CNT

N18.9

4 5

516 506

68.05 68.33

13.77 12.80

18.18 18.87

0.27 0.28

9

N-C/CNTN19.5

10

501

72.43

8.07

19.50

0.26

N18.8

15

476

73.19

7.97

18.84

0.26

5* 6 7

10

N-C/CNT

a

All N-C/CNT composites are prepared from finely crushed solid mixtures of D-Glucose (2g, 11.1 mmol), citric acid (3g, 15.6 mmol), MWCNTs (0.5 g) and variable amounts of (NH4)2CO3 (from 0.5 to 15 g, from 5.2 to 156 mmol); unless otherwise stated, all data refer to samples prepared after thermal heating at 450 °C. b Composites are designated as follows: AN-C/CNTNXX.X where “N-C/CNT” indicates the composite; the superscript “NXX.X” refers to the N at. % as measured for the N-C phase by XPS analysis and the superscript “A” is quoted for the annealed samples (900 °C, Ar atm., 2h) only! c Brunauer-Emmett-Teller (BET) specific surface area (SSA). *Annealed sample (900 °C, Ar atm., 2h)

Figure 4A illustrates the nitrogen adsorption isotherms (T = 77 K) of representative CNTcomposite samples prepared at variable (NH4)2CO3 contents along with the respective pore size distributions (Figure 4B). Both N-C/CNT samples present a Type IV isotherm with a distinctive H2 hysteresis loop in the range of 0.4–1.0 P/Po, typical of mesoporous structures featured by complex pore networks of ill-defined shape.47 Finally, the pore-size distribution curves (Figure 4B) show an excellent control on the material porosity with a prevailing mesopore density in the narrow 3 - 5 nm range. The BET value measured on the model composite N-C/CNTN15.3 (Table 1, entry 4) reveals a SSA over 430 m2/g, three times higher than that measured on the pristine MWCNT fillers (145 m2/g) (Figure S6A and Table 1, entry 1). A five-fold excess of (NH4)2CO3 (Table 1, entry 9 vs. entry 4) translates into an increased N-content (from 15.3 % to 19.5 %, respectively) along with an only moderate growth of the material SSA (from 433 m2/g to 501


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m2/g). Higher (NH4)2CO3 excesses (> six fold – Table 1, entry 10) compromise the mechanical resistance of the final composites leading to more fragile 3D structures. For this reason, the NC/CNTN15.3 composite (Table 1, entries 4 and 5) and its annealed counterpart are selected as the most suitable for running catalytic trials (vide infra). They appear as regularly shaped solid cylinders (Figure S1 and S2) with a calculated density (ρ) of 0.61 ± 0.09 and 0.52 ± 0.05 g/cm3, respectively (Experimental section). The role of (NH4)2CO3 on the final material texture has finally been addressed through the synthesis and characterization of a blank (NH4)2CO3-free CNT-composite (C/CNT, Figure 4, blue curve). Notably, the C/CNT presents a Type-II isotherm47 with an almost completely suppressed hysteresis loop (typical of disordered mesoporous carbons). The collapse of the smaller mesoporous structure in favor of larger meso- and macro-pores translates into a significant reduction of the overall SSA (Figure 4A and 4B, blue curves). These results unambiguously demonstrate the double role of (NH4)2CO3 as primary nitrogen source for the material N-doping and “leavening” agent (throughout the material thermal phases) for the control of the composite porosity and SSA. The higher the (NH4)2CO3 content, the higher the N2 adsorptions at low partial pressure ( 1500 m2g-1). Figure 7B illustrates the specific reaction rates (λ) for different catalytic materials as the amount of styrene produced per gram of catalyst per h under steam- and oxygen-free DH conditions (550 °C, 2,8 vol. % EB diluted in He, total flow rate: 30 mL/min). In line with recent findings in the field,101, 102, 104-107, 109-112 the material doping with light hetero-elements translates into favorable effects on the DH performance, at least in terms of reaction rate (λ). Indeed, the N-doping changes the electronic properties of the carbon-based materials and generates highly defective surface sites with enhanced catalytic properties.113,

114


The increased basicity at N-

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doped material surface finally holds beneficial effects on the overall DDH activity also thank to the inhibition/suppression of the surface material acid character (typically originated from the presence of oxygenated Brønsted acid edge-site defects) responsible for the occurrence of EB cracking side-reactions.101,

102, 104, 105, 110, 115-117

This aspect is confirmed on our samples by

comparing the λ values measured for the N-C/CNT foam with that of the N-free C/CNT sample (Figure 7B; λN-C/CNTN15,3 = 2.22; λC/CNT = 1.46). Other differences in terms of catalyst performance can be ascribed to variations of the material SSA (BET) and porosity (BJH), although whatever rationalization of these contributions still remains difficult to be addressed. At a first glance, samples featured by high values of SSA and micropore density show only limited beneficial effects on both catalyst activity and selectivity (Table 1 and Table S2, C/CNT foam vs. activated charcoal). On the other hand, mesoporous samples seem to warrant a higher control on the process selectivity. N-C/CNT samples show unique morphological properties owing to the use of “leavening” components (i.e. [(NH4)2CO3]) that play a tight control on the material mesoporous size distribution (Figure S6 and Table S2). Aimed at shedding light on the role of mesopores on the DDH selectivity, a comparative study with a benchmark class of mesoporous carbon nanomaterials - nanodiamonds (NDs), has been undertaken for the sake of completeness. NDs rank among the most effective and selective metal-free systems for the steam-free EB DDH reported in the literature so far.99, 100 Despite the higher SSA of the N-C/CNT foams compared to NDs (Table S2, entries 3-7 vs. 11), both materials are essentially mesoporous with a prevailing pore density in the lower mesopore region (62-71 % of incremental pore volume measured in the 3-20 nm range - Figure S6 and Table S2 entries 3-7 vs. 11).


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Notably, NDs and N-C/CNTN15,3 show comparable performance in terms of EB conversion with a higher ST selectivity measured for the foam catalyst at the steady-state conditions (>99 % vs. 98 % - Figure 7B). This remarkable outcome is directly related to the morphological similarities (particularly at the mesoporous level) of the two catalytic materials. If major differences in terms of material SSAs and microporous area contribute marginally to the selectivity of the DDH process (Figure 7B, Table S2 entries 3-7 and 11 vs. 10), a high density of small mesopores (particularly in a narrow nm range) seems to play a key control on the ST selectivity of the carbon-based catalysts. (Table S2, entries 3-7 vs. 11 and Figure S6 entries 3 vs. 10). Finally, the N-C/CNTN15.3 foam and the K-promoted Fe2O3 catalyst were also evaluated under harsh DDH reaction conditions, close to those used in industrial plants (i.e. 600 °C, 10 vol % EB in He). The higher the reaction temperature (from 550 to 600 °C) the higher the EB conversion (from 34 to 55 % at the steady-state conditions – Figure 7A vs. Figure S18A). Notably, at 600 °C the EB conversion on the foam catalyst remains extremely stable as a function of time on stream. Under these conditions (600 °C, 2,8 vol. % EB in He), the ST selectivity slightly decreases down to 93 % (Figure 7A vs. Figure S18A) while it turns to increase close to 96 % once the EB in He increases to 10 vol. % (Figure S18A vs. S18A’). From a comparison with the benchmark K-Fe catalyst under identical reaction conditions (Figure S18B and S18C), the metal-free N-C/CNTN15,3 foam shows remarkably higher catalytic performance both in terms of specific reaction rate (λ) and ST selectivity. These unique outcomes confirm metal-free systems as ideal catalysts for exploiting the steam-free DDH reaction in industrial plants.


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Conclusion In summary, a highly N-doped carbon-phase (N-C) is grown around a deeply intertwined MWCNTs network starting from physical mixtures of cheap raw materials and pristine carbon nanotube fillers. 3D self-standing and shape-controllable open-cell foams with relatively high SSAs and mesopore density control in a narrow nm range are prepared by means of moderate thermal treatments in air (typically up to 450 °C). An additional thermal phase at 900 °C under He atmosphere is only occasionally applied, depending on the material downstream application. These single-phase systems act as metal-free heterogeneous catalysts for a series of industrially relevant liquid- and gas-phase processes, showing excellent and to some extent unique catalytic performance. On this ground, the presence of a highly intertwined network of MWCNTs in the composite backbone ensures an ideal electrical and thermal conductivity to the final material. In ORR under alkaline environment, they offer almost superimposable electrochemical profiles to the benchmark Pt/C catalyst, with a markedly higher catalytic performance in long-term stability tests. In the steam-free DDH of EB to ST, they offer unique outcomes in terms of both Specific Reaction Rate (λ) and ST selectivity, even under operative conditions close to those of industrial plants. Noteworthy, the mesopore density in the final composites plays a key role on the catalyst selectivity control; the high N-site density at the topmost surface of the N-C phase finally strengthens the process reaction rate (λ). This finding adds another key tile to the complex puzzle of chemico-physical and morphological properties of carbon nanomaterials in catalysis, paving the way to the design and synthesis of more selective catalysts to be exploited in industrial key processes like the EB DDH. Moving far beyond the benchmark K-Fe catalyst, the N-C/CNT foam, with a ST selectivity higher than 98 %, a λ values close to 11 (under industrial steady-state conditions; 600°C and 10 vol.% of EB in He) and an easy and effective regeneration and reuse,


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unambiguously ranks as the most active and selective system reported in the literature so far. Overall, the excellent catalytic performance of our metal-free composites along with their easy and cheap upscale synthesis, open new perspectives to the development of alternative and sustainable catalytic materials with a range of practical applications even beyond the targeted reactions of this study.

Experimental Section General procedure for the synthesis of N-C/CNT foams. In a typical procedure, 2 g (11.1 mmol) of D-glucose, 3 g (15.6 mmol) of citric acid, 0.5 g of multi-walled carbon nanotubes (MWCNTs) and a proper amount (from 0.5 to 15 g) of ammonium carbonate (from 5.2 mmol to 156 mmol) are physically mixed and mechanical crushed as to obtain a homogeneous darkbrown solid mixture. The powder undergoes successive thermal heatings to get the final foam composite: Two successive thermal treatments in air at 130 °C for 2 h (shaping phase) and 450 °C (2 °C/min) for 3h (calcination) generate the foam structures. A subsequent annealing at 900 °C in He for 2 h is occasionally employed (depending on the material downstream application) with the aim at improving the electrical and thermal conductivity of the final composite. Material characterization. Thermogravimetric analyses (TGA/DTG) were performed under air (25 mL/min) on a SETARAM Analyzer (TGA/DTG) using a thermo-program between 40 and 1000 °C at the heating rate of 10 °C/min. X-ray Photoelectron Spectroscopy (XPS) analyses were performed on a MULTILAB 2000 (THERMO VG) spectrometer equipped with a


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monochromatic Al Kα X-ray source (1486.6 eV) with a spot size of 300 μm, corresponding to a power of 70 W and at a take-off angle of 53° relative to the sample normal. Survey spectra (0 1300 eV) were acquired at a pass energy of 200 eV with an energy step size of 1 eV. High resolution spectra were recorded at a pass energy of 100 eV with a step size of 0.05 eV. In the set conditions the overall energy resolution was 0.9 eV. XPS analysis was repeated on three different spots for each sample. The C1s peak at 284.6 eV was used to correct charging effects. Shirley backgrounds were subtracted from the raw data to obtain the area of the C1s peak. The high resolution spectra were fitted with mixed Gaussian-Lorentzian peaks after a Shirley background subtraction. The determined standard deviation in the peak position was ± 0.2 eV. Raman spectra were recorded using a LabRAM ARAMIS Horiba Raman spectrometer equipped with a peltier cooled CCD detector. Spectra were recorded over the range of 200 - 3200 cm-1 using the 532 nm/100 mW emission of a YAG laser source with laser quantum MPC600 PSU. The beam profile was cleaned by a spatial filter and Rayleigh scattering was filtered out using EDGE filters. The spectral resolution was 1 cm-1. Samples were analyzed by registering the spectra for each sample randomly on 3 different positions. All recorded curves were baseline and fitted using Lorentzian line-shapes and the D- and G-peak intensities were used for the calculation of the ID/IG ratios. Transmission electron microscopy (TEM) measurements were performed using a JEOL 2100F operating at 200 kV, equipped with GATAN Tridiem imaging filter and an aberration-corrected condenser. Energy-filtered TEM (EFTEM) measurements were performed at the C and N K edges and the corresponding elemental maps were calculated by using the three-window method. Scanning electron microscopy (SEM) was used to investigate the material morphology. Analyses were conducted on a JEOL F-6700 FEG with an accelerating voltage of 10 kV. The Brunauer-Emmett-Teller (BET) specific surface area (SSA) and porosity


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(based on either BJH and t-plot methods) were measured on an ASAP 2020 Micromeritics instrument, using N2 as absorbent at the liquid N2 temperature. All samples were completely degassed/activated at 250 °C for 14 h. Temperature-programmed oxidation (TPO) analyses were conducted on a Micromeritics ASAP-2100 setup equipped with a multi-channel mass spectrometer. In a typical procedure, 5 mg of the sample are loaded in the reactor and then flushed with 1% O2/He mixture (25 ml/min) at room temperature (RT) for 30 min. Afterwards, the temperature was raised from RT to 900 oC at a heating rate of 10 oC/min. The evolved species were monitored with m/e intensities for 2 (H2), 18 (H2O), 28 (CO) and 44 (CO2), respectively. Density calculation (ρ) of the foam materials is performed as ratio of foam weight (mass expressed in g) to bulk volume (V expressed in cm3): ρ = mass (g) / Vbulk (cm3). Since the composites are prepared as regularly shaped solid cylinders, their volumes (cm3) are calculated from their measured dimensions using the formula: V = πr2h (h = cylinder height, r = cylinder radius). For the representative sample N-C/CNT15,3 a bulk volume of 4.99 ± 0.62 cm3 (h = 1.47 ± 0.05 cm; r = 1.04 ± 0.05 cm) for a weight of 3.027 g, corresponds to a ρ value of 0.61 ± 0.09 g/cm3. For the annealed counterpart (AN-C/CNT15,3) a bulk volume of 12.87 ± 1.19 cm3 (h = 2.06 ± 0.05 cm; r = 1.41 ± 0.05 cm) and a mass of 6.716 g, translate into a ρ value of 0.52 ± 0.05 g/cm3. Oxygen Reduction Reaction (Electrochemical study). Electrochemical studies were performed at 25 °C in a three-electrode cell in 0.1 M KOH supporting electrolyte, using an Autolab PGSTAT30 (Eco Chemie, The Netherlands) potentiostat equipped with an analogue linear sweep generator at the sweep rate of 10 mV s-1. Mercury oxide (Hg/HgO) and Pt-wire electrodes were used as reference and counter electrodes, respectively. Unless otherwise stated, all potentials


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reported are referred to the reversible hydrogen electrode (RHE). Impedance spectroscopy is used to determine the resistance of the electrolyte solution. For RRDE tests, the working electrode (PINE AFE6R2GCPT, glassy carbon disk: 5.5 mm diameter and 0.2376 cm2 geometrical area, Pt ring: 0.234 cm2 geometrical area) was prepared by loading 50 µL of catalyst ink onto the pretreated glassy carbon and dried at room temperature. For these measurements the AN-C/CNT15,3 sample was finely crushed before being used for the preparation of the catalyst ink. This latter was prepared as follows: 10.0 mg of finely crushed catalyst, 5 mL isopropanol and 50 µL Nafion solution (5 wt.% in alcohols) ultrasonically mixed to form a homogenous catalyst ink. The reference Pt data were recorded with a 20 wt% Pt/C (Sigma) catalyst at a loading of 25 µgPt cm-2. All aqueous solutions were prepared using ultrapure water [(18 MΩcm, < 3 ppb Total Organic Carbon (TOC)] and supra-pure KOH (Sigma-Aldrich). During ORR experiments O2 was constantly bubbled through the solution in order to maintain the saturation level while the ring potential was set at 1.2 V vs. RHE. Collection efficiency (N) was calculated from the experimental data obtained in 10 mM K3Fe(CN)6 in 0.1 M NaOH at standard measurement conditions (potential sweep rate 10 mV s-1, 25 °C). The collection efficiency for the 20 wt% Pt/C Vulcan electrode was found to be 37 %. The catalysts four-electron selectivity was evaluated on the basis of the amount of H2O2 % produced, calculated from equation (1): H2O2(%) = 200(JR/N)/(JR/N-JD) (1)


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where JD and JR are the disk and ring currents density respectively and N is the ring collection efficiency. The number of electrons transferred (n) per O2 molecule was calculated in two different ways. Following the first method, n was calculated from the ring and the disk currents according to equation (2): n = -4JD/(JR/N-JD) (2) As for the second way to calculate n, the first-order Koutecky-Levich equation (3) was employed: 1/JD = 1/jk + 1/jd

(3)

where jk is the kinetic current density and jd is the diffusion-limited current density through the expression jd = Bf1/2 = 0.62nFγ-1/6DO2 2/3CO2f1/2. Here n is the average electron transfer number; F is the Faraday constant; γ is the kinematic viscosity of the electrolyte; DO2 is the oxygen diffusion coefficient (1.15 × 10-5 cm2/s); CO2 is the bulk oxygen concentration in the electrolyte (1.4 × 10-6 mol/cm3); and f is the angular velocity of the electrode. The kinetic current density (jk) and the Koutecky-Levich slope (1/B) can be obtained from a plot of 1/j versus 1/f1/2. The effect of methanol poisoning on the foam electrocatalyst (AN-C/CNTN15,3) as well as on the 20 wt% Pt/C reference electrode has been measured by chronoamperometric responses in O2saturated 0.1 M KOH electrolyte solution (0.7 V vs. RHE, 1600 rpm). Steam-free direct dehydrogenation (DDH) of ethylbenzene (EB) to styrene (ST). The reaction is carried out in a fixed-bed continuous flow reactor under atmospheric pressure. The


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catalyst in the form of cylindrical grains [overall 300 mg of grains (≈ 4 x 4 mm and 2 x 2 mm (diameter x height))] is loaded into a quartz fritted disk located inside a tubular quartz reactor (∅ x L: 8 x 800 mm). Helium gas was fed into the reactor at a flow rate of 30 mL·min−1 through a mass flow controller (BROOKS MFC) and passed through a glass evaporator filled with liquid EB maintained at constant temperature using a thermal regulated bath. The reaction system was heated to 550 oC or 600 °C and kept for 2 h under He. The reactant flow (2.8 or 10 vol. % EB diluted in helium, total flow rate of 30 mL·min-1) was then fed to the reactor. The reactant and the products [styrene (ST), benzene (BZ) and toluene (TOL)] exit from the reactor and are analyzed on–line with a PERICHROM (PR 2100) gas chromatography equipped with a flame detector (FID) and CP WAX S2CB column which was previously calibrated. In order to avoid any possible condensation of the reactant or the products all the tube lines are wrapped with a heating wire kept at 110 °C. The ethylbenzene conversion (XEB) and styrene selectivity (SST) were evaluated using equations (4) and (5):

X EB =

SST =

F0C EB,inlet - FC EB,outlet × 100% F0C EB,inlet

CST ,outlet

CST ,outlet × 100% + CTOL,outlet + C BZ ,outlet

(4)

(5)

where F and F0 are the flow rates of the outlet and inlet, respectively, and CEB, CST, CTOL and CBZ represent the concentration of ethylbenzene, styrene, toluene and benzene. The carbon balances


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amounted to around 100 % in all investigations. The results are obtained after more than 30 h on stream with stable catalytic performance at testing conditions. Associated Content Supporting Information Additional Figures; SEM images; proposed mechanism for N-C/CNT formation; Nitrogen adsorption-desorption isotherm linear plots; XPS and Raman spectra; TGA analyses; Linear sweep voltammograms, current-potential ring curves and ORR stability test; TPO analyses; additional DDH test and cycling DH reaction. This material is available free of charge via the Internet at http://pubs.acs.org.

Author Information Corresponding Authors * E-mail: [email protected] * E-mail: [email protected] * E-mail: [email protected] Notes The authors declare no competing financial interest.

Acknowledgements


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Thanks are due to the European FP7 project Freecats (contract n° NMP3-SL-2012-280658) and SATT-Conectus (DECOrATE project n° I14-033) for supporting this research activity.

References and Notes 1.

Su, D. S.; Perathoner, S.; Centi, G., Chem. Rev. 2013, 113, 5782-5816.

2.

Wang, D.-W.; Su, D., Energy Environ. Sci. 2014, 7, 576-591.

3.

Dreyer, D. R.; Bielawski, C. W., Chem. Sci. 2011, 2, 1233-1240.

4.

Gong, K.; Du, F.; Xia, Z.; Durstock, M.; Dai, L., Science 2009, 323, 760-764.

5.

Wang, X.; Li, X.; Zhang, L.; Yoon, Y.; Weber, P. K.; Wang, H.; Guo, J.; Dai, H., Science 2009, 324, 768-771.

6.

Li, X.-H.; Chen, J.-S.; Wang, X.; Sun, J.; Antonietti, M., J. Am. Chem. Soc. 2011, 133, 8074-8077.

7.

Gao, Y.; Hu, G.; Zhong, J.; Shi, Z.; Zhu, Y.; Su, D. S.; Wang, J.; Bao, X.; Ma, D., Angew. Chem. Int. Ed. 2013, 52, 2109-2113.

8.

Chizari, K.; Deneuve, A.; Ersen, O.; Florea, I.; Liu, Y.; Edouard, D.; Janowska, I.; Begin, D.; Pham-Huu, C., ChemSusChem 2012, 5, 102-108.

9.

Ge, X.; Sumboja, A.; Wuu, D.; An, T.; Li, B.; Goh, F. W. T.; Hor, T. S. A.; Zong, Y.; Liu, Z., ACS Catal. 2015, 5, 4643-4667.

10.

Paraknowitsch, J. P.; Thomas, A., Energy Environ. Sci. 2013, 6, 2839-2855.

11.

Wang, S.; Iyyamperumal, E.; Roy, A.; Xue, Y.; Yu, D.; Dai, L., Angew. Chem. Int. Ed. 2011, 50, 11756-11760.

12.

Wang, S.; Zhang, L.; Xia, Z.; Roy, A.; Chang, D. W.; Baek, J.-B.; Dai, L., Angew. Chem. Int. Ed. 2012, 51, 4209-4212.

13.

Wu, Z.-S.; Winter, A.; Chen, L.; Sun, Y.; Turchanin, A.; Feng, X.; Müllen, K., Adv. Mater. 2012, 24, 5130-5135.

14.

Ci, L.; Song, L.; Jin, C.; Jariwala, D.; Wu, D.; Li, Y.; Srivastava, A.; Wang, Z. F.; Storr, K.; Balicas, L.; Liu, F.; Ajayan, P. M., Nat. Mater. 2010, 9, 430-435.

15.

Qu, L.; Liu, Y.; Baek, J.-B.; Dai, L., ACS Nano 2010, 4, 1321-1326.


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

16.

Yu, D.; Nagelli, E.; Du, F.; Dai, L., J. Phys. Chem. Lett. 2010, 1, 2165-2173.

17.

Shui, J.; Wang, M.; Du, F.; Dai, L., Sci. Adv. 2015, 1, e1400129.

18.

Su, D. S.; Centi, G., J. Energy Chem. 2013, 22, 151-173.

19.

Long, J.; Xie, X.; Xu, J.; Gu, Q.; Chen, L.; Wang, X., ACS Catal. 2012, 2, 622-631.

20.

Zhang, J.; Dai, L., ACS Catal. 2015, 5, 7244-7253.

21.

Tang, J.; Liu, J.; Li, C.; Li, Y.; Tade; M. O.; Dai, S.; Yamauchi, Y., Angew. Chem. Int. Ed.

Page 32 of 38

2015, 54, 588-593. 22.

Wang, X.; Zhang, Y.; Zhi, C.; Wang, X.; Tang, D.; Xu, Y.; Weng, Q.; Jiang, X.; Mitome, M.; Golberg, D.; Bando, Y., Nat. Commun. 2013, 4, 2905-2912.

23.

Zhang, S.; Miran, M. S.; Ikoma, A.; Dokko, K.; Watanabe, M., J. Am. Chem. Soc. 2014, 136, 1690-1693.

24.

Lee, J. H.; Lee, H. J.; Lim, S. Y.; Kim, B. G.; Choi, J. W., J. Am. Chem. Soc. 2015, 137, 7210-7216.

25.

Lee, J. S.; Wang, X.; Luo, H.; Dai, S., Adv. Mater. 2010, 22, 1004-1007.

26.

Li, N.; Wang, Z.; Zhao, K.; Shi, Z.; Gu, Z.; Xu, S., Carbon 2010, 48, 255-259.

27.

Thess, A.; Lee, R.; Nikolaev, P.; Dai, H.; Petit, P.; Robert, J.; Xu, C.; Lee, Y. H.; Kim, S. G.; Rinzler, A. G.; Colbert, D. T.; Scuseria, G. E.; Tománek, D.; Fischer, J. E.; Smalley, R. E., Science 1996, 273, 483-487.

28.

Glerup, M.; Steinmetz, J.; Samaille, D.; Stéphan, O.; Enouz, S.; Loiseau, A.; Roth, S.; Bernier, P., Chem. Phys. Lett. 2004, 387, 193-197.

29.

Rusop, M.; Mominuzzaman, S. M.; Tian, X. M.; Soga, T.; Jimbo, T.; Umeno, M., Appl. Surf. Sci. 2002, 197, 542-546.

30.

Guo, T.; Nikolaev, P.; Rinzler, A. G.; Tomànek, D.; Colbert, D. T.; Smalley, R. E., J. Phys. Chem. 1995, 99, 10694-10697.

31.

Eftekhari, A.; Jafarkhani, P.; Moztarzadeh, F., Carbon 2006, 44, 1343-1345.

32.

Wu, J.; Yadav, R. M.; Liu, M.; Sharma, P. P.; Tiwary, C. S.; Ma, L.; Zou, X.; Zhou, X.-D.; Yakobson, B. I.; Lou, J.; Ajayan, P. M., ACS Nano 2015, 9, 5364-5371.

33.

Shan, C.; Zhao, W.; Lu, X. L.; O'Brien, D. J.; Li, Y.; Cao, Z.; Elias, A. L.; Cruz-Silva, R.; Terrones, M.; Wei, B.; Suhr, J., Nano Lett. 2013, 13, 5514-5520.


Page 33 of 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

ACS Catalysis

34.

Park, S.; Hu, Y.; Hwang, J. O.; Lee, E.-S.; Casabianca, L. B.; Cai, W.; Potts, J. R.; Ha, H.W.; Chen, S.; Oh, J.; Kim, S. O.; Kim, Y.-H.; Ishii, Y.; Ruoff, R. S., Nat. Commun. 2012, 3, 638-645.

35.

Tuci, G.; Zafferoni, C.; D’Ambrosio, P.; Caporali, S.; Ceppatelli, M.; Rossin, A.; Tsoufis, T.; Innocenti, M.; Giambastiani, G., ACS Catal. 2013, 3, 2108-2111.

36.

Tuci, G.; Zafferoni, C.; Rossin, A.; Milella, A.; Luconi, L.; Innocenti, M.; Truong Phuoc, L.; Duong-Viet, C.; Pham-Huu, C.; Giambastiani, G., Chem. Mater. 2014, 26, 3460-3470.

37.

Fang, Y.; Gu, D.; Zou, Y.; Wu, Z.; Li, F.; Che, R.; Deng, Y.; Tu, B.; Zhao, D., Angew. Chem. Int. Ed. 2010, 49, 7987-7991.

38.

Fellinger, T.-P.; White, R. J.; Titirici, M.-M.; Antonietti, M., Adv. Funct. Mater. 2012, 22, 3254-3260.

39.

Hu, B.; Wang, K.; Wu, L.; Yu, S.-H.; Antonietti, M.; Titirici, M.-M., Adv. Mater. 2010, 22, 813-828.

40.

Liang, H.-W.; Guan, Q.-F.; Chen, L.-F.; Zhu, Z.; Zhang, W.-J.; Yu, S.-H., Angew. Chem. Int. Ed. 2012, 51, 5101-5105.

41.

Zhang, P.; Yuan, J.; Fellinger, T.-P.; Antonietti, M.; Li, H.; Wang, Y., Angew. Chem. Int. Ed. 2013, 52, 6028-6032.

42.

Kubo, S.; White, R. J.; Yoshizawa, N.; Antonietti, M.; Titirici, M.-M., Chem. Mater. 2011, 23, 4882-4885.

43.

White, R. J.; Yoshizawa, N.; Antonietti, M.; Titirici, M.-M., Green Chem. 2011, 13, 24282434.

44.

Yu, L.; Falco, C.; Weber, J.; White, R. J.; Howe, J. Y.; Titirici, M.-M., Langmuir 2012, 28, 12373-12383.

45.

For a recent example of 3D free-standing monolithic carbon foams with absorbent and catalytic properties see: Zhu, L. L.; Tan, C. F.; Gao, M. M.; Ho, G. W., Adv. Mater. 2015, 27, 7713-7719.

46.

Ba, H.; Liu, Y.; Truong-Phuoc, L.; Duong-Viet, C.; Mu, X.; Doh, W. H.; Tran-Thanh, T.; Baaziz, W.; Nguyen-Dinh, L.; Nhut, J.-M.; Janowska, I.; Begin, D.; Zafeiratos, S.; Granger, P.; Tuci, G.; Giambastiani, G.; Banhart, F.; Ledoux, M. J.; Pham-Huu, C., Chem. Commun. 2015, 51, 14393-14396.


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

47.

Page 34 of 38

Sing, K. S. W.; Everett, D. H.; Haul, R. A. W.; Moscou, L.; Pierotti, R. A.; Rouquérol, J., Pure Appl. Chem. 1985, 57, 603-619.

48.

Zhao, Y.; Nakamura, R.; Kamiya, K.; Nakanishi, S.; Hashimoto, K., Nat. Commun. 2013, 4, 2390-2396.

49.

Kundu, S.; Nagaiah, T. C.; Xia, W.; Wang, Y.; Van Dommele, S.; Bitter, J. H.; Santa, M.; Grundmeier, G.; Bron, M.; Schuhmann, W.; Muhler, M., J. Phys. Chem. C 2009, 113, 14302-14310.

50.

Liu, S.; Tian, J.; Wang, L.; Zhang, Y.; Qin, X.; Luo, Y.; Asiri, A. M.; Al-Youbi, A. O.; Sun, X., Adv. Mater. 2012, 24, 2037-2041.

51.

Ferrari, A. C.; Robertson, J., J. Phys. Rev B 2001, 64, 075414-075426.

52.

Ferrari, A. C.; Robertson, J., J. Phys. Rev. B 2000, 61, 14095-14107.

53.

Lucchese, M. M.; Stavale, F.; Martins Ferreira, E. H.; Vilani, C.; Moutinho, M. V. O.; Capaz, R. B.; Achete, C. A.; Jorio, A., Carbon 2010, 48, 1592-1597.

54.

Florea, I.; Ersen, O.; Arenal, R.; Ihiawakrim, D.; Messaoudi, C.; Chizari, K.; Janowska, I.; Pham-Huu, C., J. Am. Chem. Soc. 2012, 134, 9672-9680.

55.

Daems, N.; Sheng, X.; Vankelecom, I. F. J.; Pescarmona, P. P., J. Mater. Chem. A 2014, 2, 4085-4110.

56.

Dai, L.; Xue, Y.; Qu, L.; Choi, H.-J.; Baek, J.-B., Chem. Rev. 2015, 115, 4823-4892.

57.

Zheng, Y.; Jiao, Y.; Jaroniec, M.; Jin, Y. G.; Qiao, S. Z., Small 2012, 8, 3550-3566.

58.

Zhu, C. Z.; Dong, S. J., Nanoscale 2013, 5, 1753−1767.

59.

Leon y Leon, C. A.; Solar, J. M.; Calemma, V.; Radovic, L. R., Carbon 1992, 30, 797-811.

60.

Ikeda, T.; Boero, M.; Huang, S.-F.; Terakura, K.; Oshima, M.; Ozaki, J.-I., J. Phys. Chem. C 2008, 112, 14706-14709.

61.

Zhang, L.; Niu, J.; Dai, L.; Xia, Z., Langmuir 2012, 28, 7542-7550.

62.

Lai, L.; Potts, J. R.; Zhan, D.; Wang, L.; Poh, C. K.; Tang, C.; Gong, H.; Shen, Z.; Lin, J.; Ruoff, R. S., Energy Environ. Sci. 2012, 5, 7936-7942.

63.

Kaukonen, M.; Kujala, R.; Kauppinen, E., J. Phys. Chem. C 2012, 116, 632-636.

64.

Zhao, A.; Masa, J.; Muhler, M.; Schuhmann, W.; Xia, W., Electrochim. Acta 2013, 98, 139-145.

65.

Biddinger, E. J.; Ozkan, U. S., J. Phys. Chem. C 2010, 114, 15306-15314.


Page 35 of 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

ACS Catalysis

66.

Chokai, M.; Taniguchi, M.; Moriya, S.; Matsubayashi, K.; Shinoda, T.; Nabae, Y.; Kuroki, S.; Hayakawa, T.; Kakimoto, M.-A.; Ozaki, J.-I.; Miyata, S., J. Power Sources 2010, 195, 5947-5951.

67.

Geng, D.; Chen, Y.; Chen, Y.; Li, Y.; Li, R.; Sun, X.; Ye, S.; Knights, S., Energy Environ. Sci. 2011, 4, 760-764.

68.

Morozan, A.; Jégou, P.; Pinault, M.; Campidelli, S.; Jousselme, B.; Palacin, S., ChemSusChem 2012, 5, 647-651.

69.

Park, K.-Y.; Jang, J.-H.; Hong, J.-E.; Kwon, Y.-U., J. Phys. Chem. C 2012, 116, 1684816853.

70.

Sharifi, T.; Hu, G.; Jia, X.; Wågberg, T., ACS Nano 2012, 10, 8904-8912.

71.

Zheng, B.; Wang, J.; Wang, F.-B.; Xia, X.-H., Electrochem. Commun. 2013, 28, 24-26.

72.

Jeyabharathi, C.; Venkateshkumar, P.; Rao, M. S.; Mathiyarasu, J.; Phani, K. L. N., Electrochim. Acta 2012, 74, 171-174

73.

Li, H.; Kang, W.; Wang, L.; Yue, Q.; Xu, S.; Wang, H.; Liu, J., Carbon 2013, 54, 249-257.

74.

Niwa, H.; Horiba, K.; Harada, Y.; Oshima, M.; Ikeda, T.; Terakura, K.; Ozaki, J.-I.; Miyata, S., J. Power Sources 2009, 187, 93-97.

75.

Rao, C. V.; Cabrera, C. R.; Ishikawa, Y., J. Phys. Chem. Lett. 2010, 1, 2622-2627.

76.

Subramanian, N. P.; Li, X.; Nallathambi, V.; Kumaraguru, S. P.; Colon-Mercado, H.; Wu, G.; Lee, J.-W.; Popov, B. N., J. Power Sources 2009, 188, 38-44.

77.

Guo, C.; Liao, W.; Li, Z.; Suna, L.; Chen, C., Nanoscale 2015, 7, 15990-15998.

78.

Tan, Y. M.; Xu, C. F.; Chen, G. X.; Zheng, N. F.; Xie, Q. J., Energy Environ. Sci. 2012, 5, 6923-6927.

79.

Jiang, Y.; Lu, Y.; Wang, X.; Bao, Y.; Chena, W.; Niu, L., 2014, 6, 15066–15072.

80.

Kim, D.-W.; Liab, O. L.; Saito, N., Phys. Chem. Chem. Phys. 2015, 17, 407-413.

81.

He, W.; Jiang, C.; Wang, J.; Lu, L., Angew. Chem. Int. Ed. 2014, 53, 9503-9507.

82.

Liang, H.-W.; Wu, Z.-Y.; Chen, L.-F.; Li, C.; Yu, S.-H., Nano Energy 2015, 11, 366-376.

83.

Sa, Y. J.; Park, C.; Jeong, H. Y.; Park, S.-H.; Lee, Z.; Kim, K. T.; Park, G.-G.; Joo, S. H., Angew. Chem. Int. Ed. 2014, 53, 4102-4106.

84.

Wen, Z.; Ci, S.; Hou, Y.; Chen, J., Angew. Chem. Int. Ed. 2014, 53, 6496-6500.

85.

Zhang, P.; Sun, F.; Xiang, Z.; Shen, Z.; Yun, J.; Cao, D., Energy Environ. Sci. 2014, 7, 442-450.


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

86.

Page 36 of 38

Panomsuwan, G.; Chiba, S.; Kaneko, Y.; Saito, N.; Ishizaki, T., J. Mater. Chem. A 2014, 2, 18677-18686.

87.

Bautista, F. M.; Campelo, J. M.; Luna, D.; Marinas, J. M.; Quirós, R. A.; Romero, A. A., Appl. Catal., B 2007, 70, 611-620.

88.

Vislovskiy, V. P.; Chang, J.-S.; Park, M.-S.; Park, S.-E., Catal. Commun. 2002, 3, 227231.

89.

PRLog,

http://www.prlog.org/11727607-styrene-global-markets-to-2020-substitution-of-

polystyrene-by-polypropylene. Accessed on Sept. 19, 2014. 90.

Meyers, R. A., Handbook of petrochemicals production processes. New York NY: McGraw-Hill Handbooks 11.3-11.34: 2005.

91.

Mimura, N.; Takahara, I.; Saito, M.; Hattori, T.; Ohkuma, K.; Ando, M., Catal. Today 1998, 45, 61-64.

92.

Macià-Agullò, J. A.; Cazorla-Amoròs, D.; Linares-Solano, A.; Wild, U.; Su, D. S.; Schlögl, R., Catal. Today 2005, 102-103, 248-253.

93.

Su, D.; Maksimova, N. I.; Mestl, G.; Kuznetsov, V. L.; Keller, V.; Schlögl, R.; Keller, N., Carbon 2007, 45, 2145-2151.

94.

Su, D. S.; Maksimova, N.; Delgado, J. J.; Keller, N.; Mestl, G.; Ledoux, M. J.; Schlögl, R., Catal. Today 2005, 102-103, 110-114.

95.

Wang, L.; Zhang, J.; Su, D. S.; Ji, Y.; Cao, X.; Xiao, F.-S., Chem. Mater. 2007, 19, 28942897.

96.

Zhang, J.; Liu, X.; Blume, R.; Zhang, A.; Schlögl, R.; Su, D. S., Science 2008, 322, 73-77.

97.

Zhang, J.; Wang, X.; Su, Q.; Zhi, L.; Thomas, A.; Feng, X.; Su, D. S.; Schlögl, R.; Müllen, K., J. Am. Chem. Soc. 2009, 131, 11296-11297.

98.

Zhang, J.; Su, D.; Zhang, A.; Wang, D.; Schlögl, R.; Hébert, C., Angew. Chem. Int. Ed. 2007, 46, 7319-7323.

99.

Ba, H.; Liu, Y.; Mu, X.; Doh, W.-H.; Nhut, J.-M.; Granger, P.; Pham-Huu, C., Appl. Catal., A 2015, 499, 217-226.

100. Zhang, J.; Su, D. S.; Blume, R.; Schlögl, R.; Wang, R.; Yang, X.; Gajović, A., Angew. Chem. Int. Ed. 2010, 49, 8640-8644. 101. Zhao, Z.; Dai, Y.; Lin, J.; Wang, G., Chem. Mater. 2014, 26, 3151-3161. 102. Zhao, Z.; Dai, Y., J. Mater. Chem. A 2014, 2, 13442-13451.


Page 37 of 38

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ACS Catalysis

103. Zhao, Z.; Dai, Y.; Ge, G.; Wang, G., Chemcatchem 2015, 7, 1135-1144. 104. Zhao, Z.; Dai, Y.; Ge, G.; Guo, X.; Wang, G., Green Chem. 2015, 17, 3723-3727. 105. Zhao, Z.; Y., D.; Ge, G., Catal. Sci. Technol. 2015, 5, 1548-1557. 106. Liu, H.; Diao, J.; Wang, Q.; Gu, S.; Chen, T.; Miao, C.; Yang W.; Su, D., Chem. Commun. 2014, 50, 7810-7812. 107. Wang, R.; Sun, X.; Zhang, B.; X., S.; Su, D., Chem. Eur. J. 2014, 20, 6324-6331. 108. Zhao, Z.; Dai, Y.; Ge, G.; Wang, G., AIChE Journal 2015, 61, 2543-2561. 109. Tran Thanh, T.; Ba, H.; Truong-Phuoc, L.; Nhut, J.-M.; Ersen, O.; Begin, D.; Janowska, I.; Nguyen, D. L.; Granger, P.; Pham-Huu, C., J. Mater. Chem. A 2014, 2, 11349-11357. 110. Zhao, Z.; Dai, T.; Ge, G.; Mao, Q.; Rong, Z.; Wang, G., Chemcatchem 2015, 7, 10701077. 111. Liu, L.; Deng, Q.-F.; Agula, B.; Zhao, X.; Ren, T.-Z.; Yuan, Z.-Y., Chem. Commun. 2011, 47, 8334-8336. 112. Wang, J.; Liu, H.; Diao, J.; Gu, X.; Wang, H.; Rong, J.; Zong B.; Su, D. S., J. Mater. Chem. A 2015, 3, 2305-2313. 113. Zheng, Y.; Jiao, Y.; Ge, Y. L.; Jaroniec, M.; Qiao, S. Z., Angew. Chem. Int. Ed. 2013, 52, 3110-3116. 114. Zhao, Y.; Yang, L.; Chen, S.; Wang, X.; Ma, Y.; Wu, Q.; Jiang, Y.; Qian, W.; Hu, Z., J. Am. Chem. Soc. 2013, 135, 1201-1204. 115. Kissin, Y. V., Catal. Rev.: Sci. Eng. 2001, 43, 85-146. 116. Jin, X.; Balasubramanian, V. V.; Selvan, S. T.; Sawant, D. P.; Chari, M. A.; Lu, G. Q.; Vinu, A., Angew. Chem. Int. Ed. 2009, 48, 7884-7887. 117. Gounder, R.; Iglesia, E., J. Am. Chem. Soc. 2009, 131, 1958–1971.

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