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Applied Catalysis A, General (v.337, #2)
Continuous hydrogen production by sequential catalytic cracking of acetic acid by Thomas Davidian; Nolven Guilhaume; Hélène Provendier; Claude Mirodatos (pp. 111-120).
The mechanism of sequential cracking of acetic acid (AA) over Ni-based catalysts was investigated using18O2 isotopic labelling experiments. Both thermal and catalytic reactions take place during AA cracking. During the regeneration, the Ni is fully oxidized. Physico-chemical characterisations of catalysts after AA cracking and after regeneration under oxygen revealed important structural changes induced by the redox cycling. ▪In this study, the mechanism of sequential cracking of acetic acid (AA) over Ni-based catalysts was investigated. During AA cracking, both thermal and catalytic reactions take place. Acetic acid is thermally decomposed into CH4, CO, CO2 and H2, which further react on Ni through WGS and steam reforming reactions, whereas some coke accumulates on the catalyst. The statistical distribution of labelled C*O2 species suggests fast isotopic exchange between CO2 and surface carbonates. During the regeneration, the coke deposited during cracking is fully burnt, and carbonates are thermally decomposed.18O2 isotopic labelling experiments coupled with physico-chemical characterisations of catalysts, after cracking and regeneration steps, reveal that the nickel is reduced by cracking products at the beginning of each cracking step, and oxidized during the regeneration. This redox cycling progressively extracts metallic Ni, initially present as Ni2+ species incorporated in spinel-type structures.
Keywords: Acetic acid; Cracking; Regeneration; Mechanism; Isotopic labelling; Ni catalyst; Redox cycling
Nanosized NiO particles wrapped into uniformly mesocaged silica frameworks as effective catalysts of organic amines by Sherif A. El-Safty; Yoshimichi Kiyozumi; Takaaki Hanaoka; Fujio Mizukami (pp. 121-129).
Nanosized NiO-doped cage cubic Pm3 n mesoporous silica materials with high Ni/Si contents (∼1) were fabricated via a simple and reproducible one-step synthetic route. Control over the large particle-like monoliths and 3D cage nanostructures was provided by applying an instant preformed liquid crystalline phase of Brij 78 (C18H35(OCH2CH2)20OH; C18EO20) surfactant as a template. The solid NiO–silica catalysts were characterized by means of various techniques including XRD, N2 isotherms, TEM, SEM, XPS and EDX. Results, in general, show the formation of ordered cage NiO–silica matrices even at high amounts of nickel contents to the composition domains. The NiO-supported cage monoliths afforded catalysts that were more active than the free-support NiO and NiO-supported amorphous silicas. The catalytic activity was assessed in the model oxidation reaction of organic amines using batch contact-time experiments over various temperature ranges. Among all catalysts used, the ordered cage catalyst with open, uniform pore architectures, high surface area and large pore volumes allowed efficient adsorption and diffusion of organic amines to the active site of NiO clusters, leading to a high degree of conversion and a high reaction rate. A practically important issue was developing the recyclable catalysts using NiO-doped cage monoliths; however, these catalysts retained their functionalities toward the oxidation of organic amines even after extended regeneration and recycle uses.The fabrication of nanomaterials with the active network sites has led to efficient transport and easier diffusion of guest species in some catalytic applications. In this regard, nanosized NiO-doped cage cubic Pm3 n mesoporous silica with high Ni/Si contents (∼1) was fabricated via a simple and reproducible one-step synthetic route. The NiO-supported cage monoliths can act as effective catalysts toward the oxidation of organic amines.▪
Keywords: Brij 78 template; Organic amines; NiO clusters; Supported cage silica; Catalytic activity
Hydrocarbon oxidation and three-way catalytic activity on a single step directly coated cordierite monolith: High catalytic activity of Ce0.98Pd0.02O2− δ by Sudhanshu Sharma; M.S. Hegde; Ratindra Nath Das; Manish Pandey (pp. 130-137).
Catalytic activity of cordierite honeycomb by a completely new coating method for the oxidation of major hydrocarbons in exhaust gas is reported here. The new coating process consists of (a) dipping and growing γ-Al2O3 on cordierite by combustion of monolith dipped in the aqueous solution of Al(NO3)3 and oxalyldihydrazide (ODH) (or glycine) at 600°C and active catalyst phase Ce0.98Pd0.02O2− δ on γ-Al2O3-coated cordierite again by combustion of monolith dipped in the aqueous solution of ceric ammonium nitrate, ODH and 1.2×10−3M PdCl2 solution at 500°C. Weight of active catalyst can be varied from 0.02wt% to 2wt% which is sufficient but can be loaded even up to 12wt% by repeating dip dry combustion. Adhesion of catalyst to cordierite surface is via oxide growth, which is very strong. ‘HC’ oxidation over the monolith catalyst is carried out with a mixture having the composition, 470ppm of both propene and propane and 870ppm of both ethylene and acetylene with the varying amount of O2. Three-way catalytic test is done by putting hydrocarbon mixture along with CO (10000ppm), NO (2000ppm) and O2 (15000ppm). Below 350°C full conversion is achieved. In this method, handling of nano-material powder is avoided.By a unique solution combustion method, washcoat and active catalyst phase has been directly grown on cordierite surface. Oxidation of major hydrocarbons, two-way and three-way catalytic performances with Ce0.98Pd0.02O2− δ-coated cordierite monolith are very good. We find that below 350°C all the pollutants can be converted fully.▪
Keywords: Hydrocarbon; Monolith; Cordierite; Active phase; Three-way catalyst
Preparation, characterization and activities of the nano-sized Ni/SBA-15 catalyst for producing CO x-free hydrogen from ammonia by Hongchao Liu; Hua Wang; Jianghan Shen; Ying Sun; Zhongmin Liu (pp. 138-147).
Ni/SBA-15 catalysts that are used in ammonia decomposition to produce CO x-free hydrogen have been prepared by a deposition–precipitation (DP) method. The results show that the samples with nano-sized nickel particles (4–7nm) and narrow nickel particle distribution could be obtained easily and exhibit high catalytic efficiency and stability for ammonia decomposition. ▪Ni/SBA-15 catalysts that are used in ammonia decomposition to produce CO x-free hydrogen were prepared by a deposition–precipitation (DP) method and investigated by N2 adsorption/desorption, XRD, TEM and H2-TPR techniques. The results show that not only the nano-sized nickel particles with narrow distribution could be obtained, but also the ordered mesostructures of the Ni/SBA-15 catalysts could be achieved during the preparation process. The amount of formed nickel phyllosilicate increases with prolonging the DP time, while surface areas and pore sizes of samples decrease relatively. These Ni/SBA-15 catalysts exhibit higher performance than other Ni-based catalysts and even some supported Ru catalysts. Ammonia conversion is more than 96% at 873K withGHSVNH3 of 46,000ml/hg-cat. Additionally, the Ni/SBA-15 catalyst is very stable during catalytic evaluation operation due to the strong interactions between nickel grains and SBA-15 support.
Keywords: Deposition–precipitation method; Ni/SBA-15; CO; x; -free hydrogen; Ammonia decomposition
Promoting effects of doping ZnO into coprecipitated Ni-Al2O3 catalyst on methane decomposition to hydrogen and carbon nanofibers by Jiuling Chen; Yuanhua Qiao; Yongdan Li (pp. 148-154).
Direct decomposition of methane is an attractive route to produce CO/CO2-free hydrogen and solid carbon. Compared with steam reforming of methane, the process is significantly simple and energy-saving and gives real zero emission of CO2. Coprecipitated nickel-rich Ni-Al2O3 catalysts are highly active, however, the catalysts are inevitably deactivated owing to encapsulation of the catalyst particles by the solid carbon produced. The doping of ZnO to promote the stability of coprecipitated Ni-Al2O3 catalyst was investigated.▪ZnO was doped into coprecipitated Ni-Al2O3 catalyst to promote the activity and the stability in methane decomposition to hydrogen and carbon nanofibers. The promoting effects were examined with XRD, TPR, XPS and TEM, using an in situ thermal balance reactor and a tubular fixed-bed reactor. The results showed that there was a strong interaction between Ni-Al2O3 and the doped ZnO, which may result in the formation of ZnAl2O4 spinel-like structure. The doping of ZnO could improve both the activity and the stability of nickel particles in methane decomposition. Such promotion effects became more pronounced with the increase of ZnO content. The evolution of the morphologies of the carbon produced and of the catalyst particles with the reaction temperature suggested that the doping of ZnO may delay the appearance of the quasi-liquid state of the catalyst particles to the range of higher temperatures and may weaken the interfacial wetting effect between catalyst particles and the growing carbon layers to delay the encapsulation process of the catalyst particles.
Keywords: Coprecipitated Ni-Al; 2; O; 3; catalyst; Methane decomposition; Promoting effect; ZnO; Quasi-liquid state
Assessment and optimization of the mass-transfer limitation in a metal foam methanol microreformer by Hongqing Chen; Hao Yu; Yong Tang; Minqiang Pan; Feng Peng; Hongjuan Wang; Jian Yang (pp. 155-162).
The external and internal mass transfer of a methanol steam microreformer, constructed of CuZn metal foam coated by CuZnAlZr catalyst, was assessed by variation of temperature, catalyst thickness and superficial velocity. The improved external and internal mass transfer resulted in a methanol conversion increase of about 10% in microreformer compared with packed-bed. ▪The performances of a methanol steam microreformer, constructed of CuZn metal foam coated by CuZnAlZr catalyst, were compared with those of a conventional packed-bed reactor. By variation of temperature, catalyst thickness and superficial velocity, the external and internal mass transfer in the microreformer was investigated. The external mass transfer can be ignored due to the high mass transfer coefficient of the metal foam. The internal diffusion resistance of the catalyst depends on the calcination temperature and catalyst/Al2O3 binder ratio of catalyst layer over metal foam, due to the development of catalyst pores. With optimum preparation conditions, the critical thickness to eliminate internal mass transfer limitation is about 8μm. The improved external and internal mass transfer resulted in a methanol conversion increase of about 10% in microreformer compared with packed-bed.
Keywords: Mass transfer; Microreactor; Metal foam; Methanol; Steam reforming
Synthesis of cinnamyl ethyl ether in the hydrogenation of cinnamaldehyde on Au/TiO2 catalysts by C. Milone; M.C. Trapani; S. Galvagno (pp. 163-167).
From the hydrogenation of cinnamaldehyde, on the Au/TiO2 catalysts, under mild conditions, three main products were obtained: cinnamylalcohol, hydrocinnamaldehyde, and the asymmetric ether 3-ethoxyprop-1-enylbenzene (C6H5CHCH–CH2–O–C2H5) or cinnamyl ethyl ether (CEE). The behavior of Au/TiO2 catalyst in the hydrogenation of cinnamaldehyde is of particular interest because it is the first time, as far as we know, that the formation of the allyl ether is observed during this reaction. The maximum selectivity (conversion=50%) towards the formation of CEE was 33%. The mechanism of the formation of the cinnamyl ethyl ether is proposed.▪In this paper, we report the results of a study on the hydrogenation of hydrocinnamaldehyde (CA) carried out in ethanol under mild conditions ( T=333K,PH2=1atm), on the Au/TiO2 reference catalyst, supplied by the World Gold Council. The reaction was carried out on the as received and on the catalyst reduced at 473K (LTR) and 773K (HTR). From the hydrogenation of cinnamaldehyde three main products were obtained: cinnamylalcohol (UA) and hydrocinnamaldehyde (HCA), formed from the hydrogenation of the conjugated CC and CO bond, respectively, and the asymmetric ether 3-ethoxyprop-1-enylbenzene (C6H5CHCH–CH2–O–C2H5) or cinnamyl ethyl ether (CEE).The behavior of Au/TiO2 catalyst in the hydrogenation of cinnamaldehyde is of particular interest because it is the first time, as far as we know, that the formation of the allyl ether is observed during this reaction. The selectivity towards the formation of the CEE, measured at 50% of conversion, increases from 19%, on the as received catalysts, up to 33% on the catalysts reduced at 473K. A further increase of the reduction temperature does not influence the selectivity to CEE. The mechanism of the formation of the cinnamyl ethyl ether is proposed.
Keywords: Cinnamaldehyde hydrogenation; Cinnamyl ethyl ether; Au/TiO; 2
One-pot synthesis of ethylene trithiocarbonate from ethylene carbonate by Hoon Sik Kim; Dinh Quan Nguyen; Minserk Cheong; Honggon Kim; Hyunjoo Lee; Nan Hee Ko; Je Seung Lee (pp. 168-172).
Ethylene trithiocarbonate (ETTC) was synthesized in good to excellent yields and selectivities from a one-pot catalytic reaction of ethylene carbonate (EC) and CS2 in the presence of a lithium halide by using EC as a source of ethylene oxide (EO). The selectivity of ETTC was strongly affected by the rate of EC decomposition into EO and CO2. Lithium chloride, the least active catalyst for the EC decomposition, showed the highest yield and selectivity.Ethylene trithiocarbonate (ETTC) was selectively synthesized from ethylene carbonate and CS2 in the presence of LiX (X=Cl, Br, I). The selectivity of ETTC was strongly affected by the rate of EC decomposition into EO and CO2. Lithium chloride, the least active catalyst for the EC decomposition, showed the highest yield and selectivity.▪
Keywords: Ethylene carbonate; Ethylene trithiocarbonate; Cyclic trithiocarbonate; Cyclic carbonate; Ethylene oxide; Ionic liquids
Nitrogen and sulphur poisoning in alkene oligomerization over mesostructured aluminosilicates (Al-MTS, Al-MCM-41) and nanocrystalline n-HZM-5 by R. Van Grieken; J.M. Escola; J. Moreno; R. Rodríguez (pp. 173-183).
The oligomerization of 1-hexene in presence of model poisons such as thiophene and n-butylamine over mesostructured Al-MCM-41 and Al-MTS, and nanocrystalline n-HZSM-5 have been investigated. n-HZSM-5 was heavily deactivated by a concentrated poison mixture whereas Al-MTS and Al-MCM-41 retained almost completely their activity. Oligomerization of a true FCC effluent over Al-MTS led to 58% conversion with oligomer selectivity above 90% (32% C13–C18). ▪Oligomerization of 1-hexene in the presence of model poisons such as thiophene (700–7000ppm of sulphur) and n-butylamine (25–250ppm of nitrogen), either alone or in combination, were tested at 200°C, 50bar and using n-octane as solvent, over three catalysts: two uniformly mesostructured silica–alumina (Al-MTS, Al-MCM-41) and a nanocrystalline HZSM-5 zeolite. A content of 700ppm of sulphur (adding thiophene) or/and 25ppm of nitrogen (adding n-butylamine) after a TOS=240min led towards roughly 10–20% decrease in conversion over nanocrystalline HZSM-5, without significant changes in selectivity. On the contrary, a feeding of 1-hexene with 7000ppm of sulphur and 250ppm of nitrogen showed a drastic drop of conversion (from 90 to 27%) over n-ZSM-5 zeolite with a significant increase in the selectivity towards lighter oligomers (dimers, C7–C8 isomers). This fact suggests that the strong acid sites of the zeolite are deactivated by poison adsorption and heavy oligomers/coke deposition both inside the micropores and over the external surface. In contrast, neither Al-MTS nor Al-MCM-41 catalysts were meaningfully affected by the poisons (especially Al-MTS), even for high concentration conditions, due to its high surface area, mesoporosity and medium acid strength distribution. TG analyses of the mesoporous catalysts indicate weight losses of ∼20–25%, with a contribution of 6–8% at 400–500°C, assigned to the removal of deposited coke. Oligomerization of a FCC effluent under the same conditions over Al-MTS catalyst leads to a remarkable 58% conversion with a oligomer selectivity over 90% (32% of them C13–C18).
Keywords: Poisoning; Oligomerization; n-ZSM-5; Al-MTS; 1-Hexene