Efficiency of Zn/TiO<Subscript>2</Subscript> catalyst operation in a microchannel reactor in methanol steam reforming

The activity of a Zn/TiO₂ catalyst deposited on metal microchannel plates in methanol steam reforming was studied. The catalyst exhibited maximum activity upon deposition on microchannel plates made of copper foam. In this case, the specific hydrogen production of a microreactor at 450°C was 78.6 l (g Cat)^?1 h^?1. The catalysts deposited on a microchannel plate of nickel foam and on corrugated brass foil exhibited lower activity because of the lower efficiency of heat transfer to the reaction zone. A correlation between the thermal conductivity of the microchannel plate material and the activity of the catalyst was observed in the following order: copper, brass, and nickel. The kinetic parameters of the process of methanol steam reforming in a microreactor were calculated with the use of a plug-flow reactor model. In this case, the calculated formal activation energy of 132 kJ/mol was independent of the microchannel plate material. A comparison of the equilibrium concentrations of reaction products at the reactor outlet, which were calculated from thermodynamic data, with the experimental data demonstrated that methanol steam reforming at a temperature higher than 400°C occurred in the nonequilibrium region. The concentration of carbon monoxide at the microreactor outlet was lower than 1 mol %, which is lower than the equilibrium concentration by one order of magnitude. This effect was attributed to the suppression of the reversed water gas shift reaction on the catalyst.     

Study on the service life and deactivation mechanism of Ti/SnO<Subscript>2</Subscript>-Sb electrode by physical and electrochemical methods

The Sb doped tin dioxide electrode (Sb-doped SnO₂) inter-layer was prepared using electroposition layer-by-layer onto a titanium plate, and the Sb-doped SnO₂ surface catalytic layer (Ti/SnO₂-Sb) was prepared using thermo-decomposition method. Accelerated service life tests were carried out in 0.5 M H₂SO₄ solution and 1.0 M NaOH solution, respectively. The deactivation mechanism of the electrodes is studied using oxygen evolution reaction (OER) as the reaction mode. Cyclic voltammetry test showed that the electrodes after accelerated life tests had no catalytic-oxidizing activity upon phenol. Electrochemical impedance spectroscopy (EIS) analysis exhibited that the membrane resistance of the deactivated electrode increases obviously in 0.5 M H₂SO₄ solution and 1.0 M NaOH solution, with the values of 1231 and 90.6 Ω, respectively. The structure, morphology and the content of the fresh and deactivated electrode were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray detector (EDX). This suggested that the Ti content on the electrode surface increases after deactivation, and TiO₂ membrane with poor conductivity is grown on the electrode surface.     

Mechanism of methanol conversion on ZrO<Subscript>2</Subscript> and 5% Cu/ZrO<Subscript>2</Subscript> according to in situ IR spectroscopic data

It is demonstrated by in situ IR spectroscopy that, in methanol conversion on ZrO₂ and 5% Cu/ZrO₂ catalysts, methoxy groups are present on the catalyst surface, which result from O-H or C-O bond breaking in the methanol molecule. Two types of formate complexes, localized on ZrO₂ and CuO, are also observed. The formate complexes form via the oxidative conversion of the methoxy groups. There are two types of linear methoxy groups. First-type linear methoxy groups condense with the formate complex located on CuO to yield methyl formate and then CO and H₂. Second-type methoxy groups appear as intermediate products in the formation of dimethyl ether. The main hydrogen formation reactions are the recombination of hydrogen atoms (which result from the interconversion of surface complexes) on copper clusters and the decomposition of methyl formate. The source of CO₂ in the gas phase is the formate complex, and the source of CO is methyl formate. The effect of water vapor and oxygen the surface reactions and product formation is discussed.     

Alkylation of isobutane with C<Subscript>4</Subscript> olefins under conventional and supercritical conditions

The solid acid alkylation of isobutane with butylenes on the ultrastable zeolite Y is studied in the temperature range from 120 to 150°C and in a pressure range of 20–120 atm. The catalyst service life becomes longer on passing from the conventional (liquid- and gas-phase) conditions of alkylation to supercritical conditions. The maximum period of complete butylene conversion at 150°C and 120 atm is 3.5 h. The composition of the reaction products is determined by the phase state of the reaction mixture, the reaction time, and the conversion of the C₄ olefins. When the alkylation is carried out under supercritical conditions, the C₈ hydrocarbon selectivity varies between 30 and 40%. Thermoanalytical data suggest that the surface of the spent catalyst contains carbon deposits indicating the formation of oligomeric and cyclic structures.     

Conversion of C<Subscript>2</Subscript>-C<Subscript>4</Subscript> alcohols over copper-containing catalysts on carbon and fluorocarbon fibers

Carbon and fluorocarbon fibers were used as carriers for the preparation of copper catalysts from copper oxalate as precursor. The catalytic properties of catalyst were studied in the reaction of the dehydrogenation of C₂-C₄ alcohols by the pulsed microcatalytic method. The effect of the copper content in the catalyst, the reaction temperature on the degree of conversion, and the relation of the reaction channels were studied. The electron microphotographs were obtained, specific surfaces were measured, and X-ray pictures and infrared spectra of catalysts were taken. The activity of the catalysts on the carbon and fluorocarbon fibers in the dehydration-dehydrogenation reactions of C₂-C₄ alcohols was comparatively estimated. It was shown that the selectivity of the products from the dehydrogenation reaction is higher for the Cu-fluorocarbon fiber catalyst.     

Formation of sulfur surface species on a commercial NO<Subscript>x</Subscript>-storage reduction catalyst

The influence of SO₂ exposure under lean (oxidizing) and rich (reducing) reaction conditions on the storage and oxidation/reduction function of a commercial NO_x storage-reduction catalyst was investigated by temperature-programmed uptake experiments and high temperature XRD. Both the storage capacity and the oxidation/reduction function of the catalyst were deactivated by SO₂ exposure under lean and rich reaction conditions. The deactivation of the storage component, i.e. the loss of the NO_x storage capacity, resulted mainly from the formation of Ba-sulfates accumulating in the bulk phase, which have a high thermal stability (>800°C) and, therefore, cannot be removed under the typical operation conditions of a NSR catalyst. For the oxidation function only a temporarily deactivation during lean reaction conditions was observed. Besides the formation of SO^2- ₄ species on the storage component at the beginning of the SO₂ exposure under rich conditions, an adsorption of SO₂ on the noble metal component was observed resulting in the formation of sulfur deposits. The oxidation of these sulfur species with a subsequent spillover of SO^2- ₄ species to the storage component during lean conditions could accelerate the deactivation of the storage capacity.     

Synthesis and Characterization of AlPO<Subscript>4</Subscript>/ZSM-5 Catalyst for Methanol Conversion to Dimethyl Ether

A catalyst based on zeolite was synthesized using the hydrothermal method, and alumina phosphate was embedded in its structure. The correspondent reactor tests were carried out to assess the synthesized catalyst where methanol with a purity of 99.9% was used. The results indicated that alumina phosphate is considerably effective on catalyst functionality. Given the results, the best performance was obtained when the ratio of alumina phosphate to alumina is 0.7 weighted in catalyst and fixed-bed reactor serves in a temperature of 300°C and WHSV of 0.8 h^?1. Structure and morphology of synthesized catalyst were characterized by BET, XRF, SEM, and XRD. The catalyst was evaluated in the process of converting methanol to dimethyl ether in a fixed-bed reactor under operating conditions of 300°C, 1 atm and 0.5 mL min^?1 of feed (pure methanol). The results of test indicated by increasing the amount of alumina phosphate to alumina, the conversion rate of methanol was increased to a constant value and does not change in ratios higher than 0.7. Moreover, the methanol conversion rate will reach temperature 300°C at 84%.     

Computational fluid dynamics study of the dry reforming of methane over Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst in a membrane reactor. Coke deposition

This work investigates the dry reforming of CH₄ as an important process for the conversion of greenhouse gases to synthesis gas. The mixture of methane and CO₂ is readily available in the greenhouse gas which makes realization of dry reforming of methane process more convenient. The paper is an attempt to numerically analyse by computational fluid dynamics (CFD) the coking and gasification mechanisms in the lab-scale membrane module with a fixed-bed supported nickel catalyst (Ni/Al₂O₃). The concentrations and molar fluxes obtained by the simulation are compared with the experimental profiles to validate the CFD model. It was found that working in a catalytic fixed-bed membrane reactor, in the case of the dry reforming of methane and under specific conditions, was not critical, from the point of view of catalyst deactivation.     

Studies on the synthesis of higher alcohol over modified Cu/ZnO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

Higher alcohol has been considered as a potential fuel additive. Higher alcohol, including C₂–C₄ alcohol was synthesized by catalytic conversion of syngas (with a ratio of CO/H₂?=?1) derived from natural gas over modified Cu/ZnO/Al₂O₃ catalyst. Modified Cu/ZnO/Al₂O₃ catalysts promoted by alkali metal (Li) for higher alcohol synthesis (HAS) were prepared at different pH (6, 6.5, 7, 8, and 9) by co-precipitation to control Cu surface area and characterized by N₂ physisorption, XRD, SEM, H₂-TPR and TPD. The HAS reaction was carried out under a pressure of 45 bar, GHSV of 4000 h^?1, ratio of H₂/CO?=?1, and temperature ranges of 240 and 280 °C. It was found that the malachite phase of copper causes the size of copper to be small, which is suitable for methanol synthesis. Methanol and HAS share a common catalytic active site and intermediate. It was also found that the productivity to higher alcohol was correlated with Cu surface area.     

Oxidative dehydrogenation of <Emphasis Type="Italic">n</Emphasis>-butenes to 1,3-butadiene over BiMoFe<Subscript>0.65</Subscript>P<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> catalysts: effect of phosphorous contents

A series of BiMoFe_0.65P _x oxide catalysts with varying phosphorous contents from 0.0 to 0.6 mol ratio were prepared by a co-precipitation method, and oxidative dehydrogenation (ODH) was carried out to produce 1,3-butadiene (BD) from n-butenes. The physico-chemical properties of the oxide catalysts were characterized by X-ray diffraction (XRD), Raman spectroscopy, N₂ sorption, and NH₃ and 1-butene temperature-programmed desorption (TPD). Among the catalysts studied here, BiMoFe_0.65P_0.1 oxide catalyst showed the highest conversion and selectivity to BD. From the result of 1-butene TPD, the higher catalytic activity is related to the amount of weakly bounded intermediate and the desorbing temperature of strongly bounded intermediates. Also, the higher catalytic activity likely originates from the acidity of the BiMoFe_0.65P_0.1 oxide catalyst; its acidity was higher than that of phosphorous-free oxide catalyst and further contained other oxide catalysts. BiMoFe_0.65P_0.1 oxide catalyst is stable and no significant deactivation for 100 h ODH reaction was shown.     

Poisoning Deactivation of Mesoporous Titanosilicate-Supported WO<Subscript>3</Subscript> During Metathesis of Butene to Propene

Deactivation by poisoning is studied in the metathesis of 2-butene to propene on mesoporous titanosilicate-supported WO₃ (WO₃/MTS–9), for which we focus on the effect of polar organic oxygenates on the activity of the catalyst. It is found that deactivation is strongly influenced by these oxygenates in feedstock, and the rate of deactivation increases with the increase of the polarity of the organic oxygenates. The deactivation by poisoning is reversible. The deactivation catalyst can be recovered by treatment in a nitrogen atmosphere at a high temperature.     

合成气一步法制备液化石油气单管实验研究

采用甲醇合成催化剂与脱水催化剂机械混合,制备了液化石油气(LPG)合成催化剂。以模拟生物质气为原料气,在固定床单管实验装置上,温度(220~330 ℃)、压力(1.2~5.1 MPa)和空速(500~3 000 h^-1)条件下考察催化剂的性能。结果表明,在325 ℃、2.1 MPa、1 500 h^-1条件下,CO转化率达到72.36%,LPG占烃类产物的71.21%。当设定温度为325 ℃、压力2.1 MPa时、空速≤2 500 h^-1时,系统可以稳定运行;空速达到3 000 h^-1时,反应器内部温度迅速升高无法控制,造成催化剂烧结失活。针对上述催化剂,采用NH₃-TPD、XRD、N₂吸附-脱附和TPO对催化剂进行了表征。结果表明,催化剂的积炭、强酸位酸性降低及比表面积的降低是导致催化剂活性降低的重要影响因素。     

用于甲醇直接气相氧化羰基化的负载铜催化剂

 采用浸渍法制备了负载型铜基催化剂,并用其催化甲醇直接气相氧化羰基化合成碳酸二甲酯(DMC), 考察了浸渍溶剂、载体、助催化剂和铜含量的影响. 结果表明,以CuCl为活性组分原料、浓氨水为浸渍溶剂和活性炭为载体制得的负载铜催化剂显示出很高的催化活性,在特定的反应条件下,该催化剂上甲醇的转化率可达27.7%, DMC选择性可达95%. 分子筛负载的铜催化剂上甲醇的转化率低于1%, 但是生成DMC的选择性高达100%. 催化剂活性随着Cu负载量的增加而增大,但负载量过高可引起甲醇的过度氧化反应,导致DMC选择性下降. 催化剂中添加KOH或钯化合物,有利于提高以CuCl2为活性组分原料制得的铜催化剂的活性,但同时也促进了副反应的发生. 随着反应时间的延长,催化剂的活性组分流失,活性下降,但是生成DMC的选择性维持在95%左右.     

Direct conversion of synthesis gas to light hydrocarbons on heterogeneous catalysts

Six catalysts consisting of mixtures of catalysts for methanol synthesis and its conversion to hydrocarbons were prepared by mechanical mixing, impregnation, and coprecipitation, followed by extrusion. Phase changes occurring during various stages of preparation and after use were followed by x-ray diffraction. The catalysts were found to be nontrivial bifunctional catalysts which selectively convert synthesis gas directly to low molecular weight hydrocarbons in the range of C₁ to C₄. Methanol and dimethylether were detected as intermediates. Olefins were formed, and their further hydrogenation yielded products with high paraffinic content. Carbon dioxide retards the conversion of synthesis gas to hydrocarbons, whereas steam retards the hydrogenation of olefins. On heating the commercial zinc chromite catalyst, dehydration, reduction, and solid-state reactions occur with the formation of ZnO-ZnCr₂O₄ solid solution. Exchanging cations within the zeolite component did not affect the space lattice, but these ions tend to occupy special sites, and during service more order was detected. Copper ions tend to diffuse in ZnO, forming a solid solution, and during service metallic copper was produced.     

Effect of supercritical fluid of CO2 drying during Cu/ZnO catalyst preparation on methanol synthesis from syngas at low temperature

A copper-based catalyst can be utilized to synthesize methanol from syngas containing carbon dioxide as well as water at low temperature and low pressure. However, the agglomeration of the metallic copper and zinc oxide decreased the catalyst surface area and the Cu-specific surface area. In order to prevent the sintering, the supercritical CO₂ was used to extract water from the catalyst precursor. Our results demonstrate that the Cu-specific surface area was the essential factor to affect the catalytic activity. A larger Cu-specific surface area would cause higher methanol synthesis activity. The optimized supercritical CO₂ drying condition was at 308?K and 8.0?MPa for 3?h when the methanol yield reached 44.8%.     

Laws of selective CO oxidation over a Ru/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst in the surface ignition regime: II. Transition states

The kinetics of selective CO oxidation (or individual CO or H₂ oxidation) over ruthenium catalysts are considerably as affected by the heat released by the reaction and specifics of the interaction of ruthenium with feed oxygen. In a reactor with reduced heat removal (a quartz reactor) under loads of ∼701 g_Cat⁻¹ h⁻¹ and reagent percentages of ∼1 vol % CO, ∼1 vol % O₂, ∼60 vol % H₂, and N₂ to the balance, the reaction can be carried out in the catalyst surface ignition regime. When catalyst temperatures are below ∼200°C, feed oxygen deactivates metallic ruthenium, the degree of deactivation being a function of temperature and treatment time. Accordingly, depending on the parameters of the experiment and the properties of the ruthenium catalyst, various scenarios of the behavior of the catalyst in selective CO oxidation are realized, including both steady and transition states: in a non-isothermal regime, a slow deactivation of the catalyst accompanied by a travel of the reaction zone through the catalyst bed along the reagent flow; activation of the catalyst; or the oscillation regime. The results of this study demonstrate that, for a strongly exothermic reaction (selective CO oxidation, or CO, or H₂ oxidation) occurring inside the catalyst bed, the specifics of the entrance of the reaction into the surface ignition regime and the effects of feed components on the catalyst activity should be taken into account.     

Oxidation of ammonia using modified TiO<Subscript>2</Subscript> catalyst and UV-VIS irradiation

The impact of UV and VIS irradiation and specific nitrogen modification on a 5%Cu/5%TiO₂/SiO₂ catalyst in the course of oxidation of ammonia was investigated. It was demonstrated that both UV and VIS irradiation increased the conversion of the reactant in the reaction studied. Due to a good distribution of titanium dioxide and copper on the surface of the support, higher ammonia conversion was achieved. Physico-chemical characterisation of the catalysts studied using methods such as BET, SEM-EDS, TPD (NH₃), and TPD (CO₂) was carried out.     

Oxidative conversion of methane and methanol on M/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/cordierite structured metal oxide catalysts (m = Ni,Cu, Zn)

A study was carried out on the properties of Ni/Al₂O₃ and Cu-ZnO/Al₂O₃ composites supported on ceramic honeycomb monoliths made from synthetic cordierite in the carbon dioxide conversion of methane and the partial oxidation of methanol. The structured nickel-alumina catalysts are significantly more efficient than the conventional granulated catalysts. The improved working stability of these catalysts was achieved by adjusting the acid-base properties of the surface by introducing sodium and potassium oxides, which leads to inhibition of surface carbonization. The hydrogen yield was close to 90% in the partial oxidation of methanol with a stoichiometric reagent ratio in the presence of the Cu-ZnO/Al₂O₃/cordierite catalyst. A synergistic effect was found, reducing the selectivity of CO formation in the presence of the Cu-ZnO catalyst relative to samples derived from the individual components Cu and ZnO. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 5, pp. 299–306, September–October, 2007.     

Methanol conversion over CuO supported on CeO<Subscript>2</Subscript>-ZrO<Subscript>2</Subscript>: An in situ IR spectroscopic study

The main reactions yielding hydrogen are the recombination of hydrogen atoms on copper clusters and methyl formate decomposition. Methyl formate results from the interaction between the linear methoxy group and the formate complex located on CuO. The source of CO₂ appearing in the gas phase is the formate complex, and the source of CO is methyl formate. The rates of methoxy group conversion and product formation over supports (ZrO₂, CeO₂, Ce_0.8Zr_0.2O₂) and copper-containing catalysts (5%Cu/CeO₂, 5%Cu/ZrO₂, 2%Cu/Ce_0.8Zr_0.2O₂, 2%Cu/Ce_0.1Y_0.1Zr_0.8) are compared. The dominant process in methoxy group conversion over the supports and copper-containing catalysts is methanol decomposition to H₂ and CO and to H₂ and CO₂, respectively. The methoxy group conversion rate is proportional to the H₂ and CO₂ formation rate and is determined by the concentration of supported copper.     

Hydrothermal preparation of CuO-ZnAl<Subscript>2</Subscript>O<Subscript>4</Subscript> catalyst for phenol <Emphasis Type="Italic">ortho</Emphasis>-alkylation with methanol: effect of the calcination temperature on the catalytic performance

The effect of heat-treatment on 10 wt% CuO-ZnAl₂O₄ catalytic activity in methylation of phenol and the degree of interaction of CuO active phase with support spinel phase were investigated. The CuO-ZnAl₂O₄ sample was subjected to heat-treatment up to 1000°C. The thermal products were characterized by X-ray diffraction (XRD) analysis, nitrogen adsorption-desorption at -196°C and temperature-programmed desorption (TPD-MS) of CO₂. Additionally, the reducibility of copper phases was investigated by temperature-programmed reduction (TPR). XRD patterns of the fresh catalyst sample (calcined at 600°C) indicated the presence of a mixture of poorly crystallized CuO and ZnAl₂O₄ spinel phase. The presence of two reducible copper species has been found on fresh CuO-ZnAl₂O₄ catalyst by TPR analysis. After subsequent calcinations in air at elevated temperatures some CuO disappeared with appearance of CuAl₂O₄ phase. The catalytic results revealed that the CuO addition to ZnAl₂O₄ increases the activity in ortho-methylation of phenol. Subsequent heat-treatment up to 900°C causes partial deactivation of copper centers, which is the result of transformation of CuO to the inactive CuAl₂O₄ phase.