Chloride poisoning of water-gas shift activity in nickel catalysts during steam reforming

This Letter reports preliminary findings on the role of chloride poisoning during steam reforming of chlorocarbons over nickel catalysts. When conversions of chlorocarbon are very high and thermal pyrolysis absent, the principal effect of chloride is to decrease water-gas shift and CH₄-steam reforming activity. Product carbon dioxide/carbon monoxide ratios are then far from equilibrium and methane remains unconverted when introduced into the feed. These results are linked to previously published surface science studies.     

Catalytic steam reforming of methane using Rh supported on Sr-substituted hexaaluminate

This paper reports the synthesis, characterization, and performance of steam-reforming catalysts based upon dispersed Rh particles on Sr-substituted hexaaluminate supports. As confirmed by electron microscopy and X-ray diffraction, the Sr-substituted hexaaluminate provides a plate-like support structure that resists sintering and occlusion of the Rh. The hexaaluminate is synthesized using an alumoxane process, with the cation substitution accomplished by exchange with metal acetylacetonates. The Rh is dispersed using impregnation with metal-nitrate salts. A stagnation-flow reactor is used to measure catalytic activity. In these experiments, the catalyst is applied to a flat surface that is held at a fixed temperature. Reactive gases (methane, steam, and diluent) impinge on the catalytic stagnation surface. Microprobe mass spectrometry is used to measure gas-phase species profiles in the boundary layer normal to the catalyst surface. The experiments are interpreted using a chemically reacting flow model, including an elementary heterogeneous chemical reaction mechanism. Results confirm that the Rh on Sr-substituted hexaaluminate is a highly stable and active reforming catalyst.     

Catalytic activity of atomized Ni3Al powder for hydrogen generation by methane steam reforming

The catalytic activity of Ni₃Al for methane steam reforming was investigated for the first time using its atomized powder. It was found that the activity was significantly enhanced by the combined pretreatment of acid and alkali leaching, while it was quite low for the as-received powder. The high activity was attributed to the formation of fine Ni particles on the porous surface of the powder.     

Catalytic combustion assisted methane steam reforming in a catalytic plate reactor

A theoretical study of methane steam reforming coupled with methane catalytic combustion in a catalytic plate reactor (CPR) based on a two-dimensional model is presented. Plates with coated catalyst layers of order of micrometers at distances of order of millimetres offer a high degree of compactness and minimise heat and mass transport resistances. Choosing similar operating conditions in terms of inlet composition and temperature as in industrial reformer allows a direct comparison of CPRs with the latter. It is shown that short distance between heat source and heat sink increases the efficiency of heat exchange. Transverse temperature gradients do not exceed across the wall and across the gas-phase, in contrast to difference in temperature of outside wall and mean gas phase temperature inside the tube usually observed in conventional reformers. The effectiveness factors for the reforming chemical reactions are about one order of magnitude higher than in conventional processes. Minimisation of heat and mass transfer resistances results in reduction of reactor volume and catalyst weight by two orders of magnitude as compared to industrial reformer. Alteration of distance between plates in the range 1- does not result in significant difference in reactor performance, if made at constant inlet flowrates. However, if such modifications are made at constant inlet velocities, conversion and temperature profiles are considerably affected. Similar effects are observed when catalyst layer thicknesses are increased.     

甲烷水蒸气重整制氢反应及其影响因素的数值分析

本文通过建立包含动量、能量、质量以及化学反应的多物理场耦合数值模型, 以多孔介质模型表征催化剂层, 对工业转化炉管中的甲烷水蒸气重整制氢过程进行了详细分析。计算得到了转化炉管内甲烷重整过程反应物及产物气体的速度、温度及浓度场分布, 以此分析了甲烷重整制氢过程的反应特性, 并阐明了转化炉管的壁面温度、原料气入口水碳比以及入口速度对甲烷转化率的影响。结果表明:水蒸气重整在转化炉管的入口区域反应迅速, 沿着气体流动方向, 反应速率由于反应物浓度的不断降低而减小, 导致混合气体流动速度和温度也逐渐趋于稳定;水碳比和转化管壁面温度的增加以及原料气体入口流速的降低, 都会提高甲烷的转化率。本文所得到的结论对于优化实际生产中甲烷水蒸气重整制氢反应的工况条件具有一定的参考和借鉴意义。     

Catalytic performance and characterization of Pt-Ni bimetallic catalysts for oxidative steam reforming of methane

Effects of methane oxygen mixture addition to steam reforming of methane and subsequent removal of the methane oxygen mixture from the oxidative steam reforming of methane on catalytic performance were investigated using monometallic Ni and Pt catalysts and two Pt-Ni bimetallic catalysts. Hysteresis with respect to the addition and removal of the methane oxygen mixture was observed clearly on a Pt-Ni bimetallic catalyst prepared by co-impregnation method and the Ni catalyst. In contrast, no hysteresis was observed for a Pt-Ni catalyst that was prepared by sequential impregnation method. Combined with characterization results obtained using EXAFS analysis and FTIR of CO adsorption, Pt-Ni catalyst was prepared by sequential impregnation is formed Pt-Ni alloy particles, where Pt atoms are segregated on the surface, enhances the reducibility of Ni drastically and this is related to the behavior without hysteresis.     

Catalytic steam reforming of model biogas

Catalytic steam reforming of a model biogas (CH₄/CO₂ = 60/40) is investigated to produce H₂-rich synthesis gas. Gas engines benefit from synthesis gas fuel in terms of higher efficiency and lower NO_x production when compared to raw biogas or CH₄. The process is realized in a fixed bed reactor with a Ni-based catalyst on CaO/Al₂O₃ support. To optimize the performance, the reactor temperature and the amount of excess steam are varied. The experimental results are compared to the theoretical values from thermodynamic calculation and the main trends of CH₄ conversion and H₂ yield are analyzed and verified. Finally, optimal reactor temperature is pointed out and a range of potential steam to methane ratios is presented. The experimental results will be applied to design a steam reformer at an existing anaerobic biomass fermentation plant in Strem, Austria.     

汽车尾气催化净化过程中的水煤气反应和蒸汽转换反应

本研究主要考察了不同组成的汽车尾气净化催化剂在无氧条件下对ＣＯ水煤气反应和ＨＣ蒸汽转换反应的催化性能。结果表明,在催化剂中添加一定量的稀土金属氧化物（Ｌａ_２Ｏ_３、ＣｅＯ_２）和过渡金属氧化物（ＮｉＯ）,均有利于改善催化剂对ＣＯ水煤气反应和ＨＣ蒸汽转换反应的催化性能。此外还考察了水蒸汽含量以及空速的变化对反应的影响。     

FBD型一氧化碳高温变换催化剂催化性能研究

研究了FBD型低汽气比低铬一氧化碳高温变换催化剂的活性、抗硫性能和选择性。工业应用结果表明,FBD催化剂具有转化率高、使用汽气比低、低铬、抗硫性能强、机械强度高和使用寿命长等优点。     

Catalytic monoliths for ethanol steam reforming

Cordierite monoliths coated with Co/ZnO catalysts were prepared by washcoating, urea, and sol–gel techniques and characterized by confocal microscopy, scanning electron microscopy (SEM), transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), and adherence tests. The performance of the catalytic monoliths for practical application in the production of hydrogen through ethanol steam reforming (ESR) and water gas shift (WGS) reactions was evaluated. Monoliths prepared by the urea method exhibited excellent dispersion and adherence of catalyst coatings and performed better for the reforming of ethanol. 5.6 mol H₂/mol C₂H₅OH were obtained from a C₂H₅OH:H₂O = 1:6 gaseous mixture at 723 K and 0.33 mL min⁻¹ of C₂H₅OH. Under these conditions and total ethanol conversion the composition of the effluent stream was 73.9% H₂, 23.7% CO₂, 1.2% CO, and 1.0% CH₄. The amount of CO was kept low due to the activity of monoliths for the WGS reaction under ethanol steam reforming conditions.     

煤焦加压水蒸气催化气化反应特性及甲烷释放规律研究

以内蒙褐煤焦为研究对象,K_2CO_3为催化剂,在小型加压固定床上考察了反应温度、操作压力和水碳比对煤焦水蒸气气化反应过程中碳转化率、反应速率和甲烷浓度及其累计流量的影响。结果表明,随着反应温度的增加,碳转化率和反应速率显著增加,甲烷浓度及其累计流量也增加,表明甲烷化反应在600~700℃内仍受动力学控制。操作压力的提高,碳转化率和反应速率呈先增加后减小的变化趋势,而甲烷的浓度逐渐增加,其累计流量由常压下的2.4 mL逐渐增加至3.5 MPa下的43.2 mL。随着水碳比的增加,碳转化率和反应速率大幅增加,但是甲烷的浓度逐渐降低,甲烷的累计流量受反应速率和反应平衡的共同影响,呈先增加后减小的趋势。     

煤焦加压水蒸气催化气化反应特性及甲烷释放规律研究

以内蒙褐煤焦为研究对象,K_2CO_3为催化剂,在小型加压固定床上考察了反应温度、操作压力和水碳比对煤焦水蒸气气化反应过程中碳转化率、反应速率和甲烷浓度及其累计流量的影响。结果表明,随着反应温度的增加,碳转化率和反应速率显著增加,甲烷浓度及其累计流量也增加,表明甲烷化反应在600⁷00℃内仍受动力学控制。操作压力的提高,碳转化率和反应速率呈先增加后减小的变化趋势,而甲烷的浓度逐渐增加,其累计流量由常压下的2.4 mL逐渐增加至3.5 MPa下的43.2 mL。随着水碳比的增加,碳转化率和反应速率大幅增加,但是甲烷的浓度逐渐降低,甲烷的累计流量受反应速率和反应平衡的共同影响,呈先增加后减小的趋势。     

Catalytic activity evaluation for hydrogen production via autothermal reforming of methane

A nickel catalyst (5.75 wt.%) supported on gamma-alumina was evaluated through autothermal reforming of methane (ATR). The reforming process was pointed to hydrogen production, following thermodynamic and stoichiometric predictions. The catalyst was characterised by several methods including atomic absorption spectroscopy (AAS), B.E.T.-N₂, X-ray diffraction (XRD), scanning electron microscope (SEM) and thermal analyses (thermogravimetry, TG; derivate thermogravimetry, DTG; and differential thermal analysis, DTA). Experimental evaluations in a fixed-bed reactor (1023–1123 K, 1.00 bar, 150–400 cm³/min feed) presented methane conversions in the range of 40–65%. The effluent mixtures provided hydrogen yields in the range of 78–84%, carbon monoxide 3–14%, and carbon dioxide 5–18%. High molar H₂/CO ratios, ranging from 8 to 90, were obtained. Operating autothermal conditions (excess of steam, 1023–1123 K, 1.00 bar) provided low coke formation and high hydrogen selectivity (81%) for methane reforming.     

煤焦中灰成分对甲烷裂解的影响

利用煤焦作为催化剂,采用小型石英管固定床为反应装置,对甲烷在煤焦、脱灰煤焦、煤灰以及石英砂床层上在温度为1123 K下的裂解反应进行了较为详细的研究。甲烷在脱灰煤焦上和新鲜的褐煤焦上的转化率和氢气收率有一定的差别。煤灰作为催化剂时,甲烷初始转化率和氢气初始收率分别为9.81%和8.14%。表明煤焦中的灰成分对甲烷裂解有一定的影响。随着反应时间的增加,甲烷的转化率和氢气的收率都逐渐降低。通过扫描电子显微镜和比表面积测定仪对反应前后的褐煤焦、脱灰煤焦进行了表征。甲烷裂解后煤焦比表面积、微孔容都明显降低,平均孔径增大。说明甲烷裂解生成的积炭堵塞煤焦的微孔。SEM照片显示甲烷裂解后积炭覆盖在煤焦的表面,使煤焦的催化活性逐渐降低。     

Optimising H2 production from model biogas via combined steam reforming and CO shift reactions

H₂ production was studied through steam reforming of a clean model biogas in a fluidized-bed reactor followed by two stages of CO shift reactions (fixed-bed reactors). The steam reforming of biogas was performed over 11.5 wt.% Ni/Al₂O₃ and a molar CH₄/CO₂ ratio of 1.5 was employed as clean model biogas. Excess steam resulted in strong inhibition of carbon formation and an almost complete CH₄ (>98%) conversion was achieved.To optimise H₂ production, CO shift reactions were carried out at high (523–723 K) and low temperatures (423–523 K) using commercial catalysts, based on Cu/Fe/Cr and Cu/Zn, respectively. Increasing steam concentrations led to a lean CO, high H₂ product. The final product compositions following low temperature CO shift reaction (steam to dry gas ratio of 1.5 at 483 K) yielded H₂ at 68% and a CO concentration of 0.2% (equivalent to CO conversion of >99%).     

Catalytic performance and QXAFS analysis of Ni catalysts modified with Pd for oxidative steam reforming of methane

Pd–Ni bimetallic catalysts prepared by co-impregnation and sequential impregnation methods were compared in the catalytic performance in oxidative steam reforming of methane. The sequential impregnation was more effective to the suppression of hot spot formation. According to the structural analysis by in situ quick-scanning X-ray absorption fine structure (QXAFS) during the temperature programmed reduction, the sequential impregnation method gave the bimetallic particles with higher Pd surface composition because of the low possibility of the Pd–Ni bond formation. Higher surface composition of Pd with higher reducibility than Ni is connected to the enhancement of the catalyst reducibility and the suppression of the hot spot formation.     

Stable equilibrium shift of methane steam reforming in membrane reactors with hydrogen‐selective silica membranes

Equilibrium shifts of methane steam reforming in membrane reactors consisting of either tetramethoxysilane‐derived amorphous hydrogen‐selective silica membrane and rhodium catalysts, or hexamethyldisiloxane‐derived membrane and nickel catalysts is experimentally demonstrated. The hexamethyldisiloxane‐derived silica membrane showed stable permeance as high as 8 × 10^?8 mol m^?2 s^?1 Pa^?1 of H₂ after exposure to 76 kPa of vapor pressure at 773 K for 60 h, which was a much better performance than that from the tetramethoxysilane‐derived silica membrane. Furthermore, the better silica membrane also maintained selectivity of H₂/N₂ as high as 10³ under the above hydrothermal conditions. The degree of the equilibrium shifts under various feedrate and pressure conditions coincided with the order of H₂ permeance. In addition, the equilibrium shift of methane steam reforming was stable for 30 h with an S/C ratio of 2.5 at 773 K using a membrane reactor integrated with hexamethyldisiloxane‐derived membrane and nickel catalyst. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Production of hydrogen by unmixed steam reforming of methane

Unmixed steam reforming is an alternative method of catalytic steam reforming that uses separate air and fuel–steam feeds, producing a reformate high in H₂ content using a single reactor and a variety of fuels. It claims insensitivity to carbon formation and can operate autothermally. The high H₂ content is achieved by in situ N₂ separation from the air using an oxygen transfer material (OTM), and by CO₂ capture using a solid sorbent. The OTM and CO₂ sorbent are regenerated during the fuel–steam feed and the air feed, respectively, within the same reactor. This paper describes the steps taken to choose a suitable CO₂-sorbent material for this process when using methane fuel with the help of microreactor tests, and the study of the carbonation efficiency and regeneration ability of the materials tested. Elemental balances from bench scale experiments using the best OTM in the absence of the CO₂ sorbent allow identifying the sequence of the chemical reaction mechanism. The effect of reactor temperature between 600 and on the process outputs is investigated. Temperatures of 600 and under the fuel–steam feed were each found to offer a different set of desirable outputs. Two stages during the fuel–steam feed were characterised by a different set of global reactions, an initial stage where the OTM is reduced directly by methane, and indirectly by hydrogen produced by methane thermal decomposition, in the second stage, steam reforming takes over once sufficient OTM has been reduced. The implications of these stages on the process desirable outputs such as efficiency of reactants conversion, reformate gas quality, and transient effects are discussed.     

Catalytic steam reforming of chlorocarbons: methyl chloride

This paper reports a novel catalytic process for the destruction of chlorinated hydrocarbons. Based on CH₄-steam reforming reactions, the approach gives high levels of conversion (5-nines possible) at high space velocities (2−3 × 10⁵ h⁻¹) and temperatures (650–750°C). Products comprise CO, CO₂, H₂ and HCl and no others were identified. Rapid deactivation by parallel thermal pyrolysis reactions occurs if high conversion is not maintained. The presence of Cl species poisons CH₄-steam reforming and water gas shift activities, but the effect is only temporary and disappears when the Cl compounds are removed from the feed. Kinetic studies on methyl chloride have been carried out and show a Langmuir-Hinshelwood type behavior, from which a proposed mechanism involving dual-site surface dissociation is suggested. Comparisons with other common chlorocarbons show similarities, with the exception that 1,1,1-trichloroethane is very sensitive to thermal pyrolysis and gives faster deactivation.