整体式高温水煤气变换催化剂的初步研制

采用不同方法制备了整体式高温水煤气变换催化剂。利用经酸处理的蜂窝状堇青石作载体制备整体式催化剂，着重研究酸处理对堇青石载体结构、性能及其催化性能的影响。利用改性Al₂O₃涂层浸渍负载活性组分制备整体式催化剂，重点考察化学组成对整体式催化剂性能的影响。研究结果表明，蜂窝状堇青石经酸适当处理及表面改性后，可用作整体式催化剂的载体;K₂O、CuO及稀土氧化物对整体式催化剂的水煤气变换活性有很好的促进作用，而且多组分间存在的某种协同作用更有利于调变整体式催化剂的催化性能     

负载型铁基高温变换催化剂的制备和性能研究

分别以镁铝尖晶石和活性炭作为载体制备了负载型铁基高温变换催化剂，通过XRD、TEM和活性评价测试，考察了催化剂的结构和催化反应性能。以镁铝尖晶石负载γ-Fe₂O₃制得的催化剂，其催化活性明显高于负载α-Fe₂O₃催化剂，当催化剂组成为：Fe₂O₃ 26%，K2O 2%，MgO 0.05%，Cr₂O₃ 0.7%时，400℃下CO转化率为92%，350℃为84%（汽/气=1， 空速=2000 h^-1）；经氧化处理的活性炭作为催化剂载体时，低铬条件下也具有较好的催化活性，当负载量为40%时，相同变换反应条件下CO的转化率在400℃和350℃下分别为88%和80%。两种催化剂在低Cr₂O₃含量时都保持了与传统铁铬系变换催化剂(B117型)相当的催化活性，对于改善环境具有很大意义。     

Screening of bifunctional water-gas shift catalysts

A large number of different formulations have been recently proposed in the literature as new catalysts for the water-gas shift (WGS) reaction. These formulations typically consist of a metal deposited on a reducible support. As these catalysts have been synthesized and tested by different groups in different operating conditions, a true comparison of their activities is not really possible. The aim of this study is to screen these samples under identical conditions using a model reformate as reaction mixture. A commercial parallel reactor has been used for this task. Comparison of the data obtained for the Pt catalysts from the parallel reactor with those obtained from a single fixed bed reactor showed deviations of 20–30% in the kinetic parameters. Rh and Ru based catalysts produced significant amounts of methane. Pt/CeO₂/Al₂O₃ and Pt/TiO₂ were found to be the most active catalysts for the high temperature water-gas shift while gold and copper catalysts showed promising results for low temperature applications, but they require testing at lower CO partial pressures.     

新型无铬高变催化剂的研究开发

根据铁铬系高温变换催化剂的催化机理，对钙钛石型稀土铁复合氧化物高温变换催化剂进行了设计和制备。采用XRD、活性评价等实验技术对模型催化剂进行了测试，结果表明,钙钛石型混合稀土铁复合氧化物具有较好的高温变换催化活性，以La_0.5Ce_0.5FeO₃·K的催化活性最好，CO的转化率可达72%，其热稳定性也较好，能与传统的铁铬系催化剂相媲美，是一种具有工业开发价值的无铬高温变换催化剂。     

Iron-ruthenium catalyst for the water-gas shift reaction

Iron-ruthenium catalysts prepared by impregnation of calcination products of -, , -and -iron oxide-hydroxides with either ruthenium chloride or ruthenium red were tested for the activity for the water-gas shift reaction. The effect of support, ruthenium containing impregnation agent and thermal treatment on catalyst performance was discussed.     

Low-temperature water-gas shift reaction over Mn-promoted Cu/Al2O3 catalysts

Water-gas-shift reaction was carried our over a series of Mn-promoted Cu/Al₂O₃ catalysts in the temperature range of 448–533 K. The catalysts were characterized suitably by various techniques. The catalyst containing 8.55 wt% Mn was found to be the most active one among five catalysts tested. A maximum CO conversion of 90% was obtained over this catalyst at 513 K with a CO space-time of 5.33 h. The catalysts were found to be structure sensitive for the low-temperature water-gas shift reaction. A detailed kinetic study was performed for the reaction under investigation over the best catalyst. The kinetic data were fitted to two different models and the redox model was found to the better one than the other. From the estimated kinetic constant, the activation energy was determined to be 81 kJ/mol for the water-gas shift reaction in the temperature range of 448–463 K.     

铁基无硫无铬型CO高温变换催化剂制备条件研究

以铁和硝酸为主要原料制得铁基无硫无铬型CO高变催化剂,采用X射线粉末衍射（XRD）和BET比表面积测试对催化剂进行了表征。从助剂和工艺水平两个方面选取了比较有代表性的因素进行正交实验,通过极差和方差分析找出各个因素对催化剂活性影响的程度,从而得到较优的催化剂制备条件:铁液质量浓度235 g·L－1,氨水中w(NH3)为8%,热煮时间1 h,w(CoO)为6%。     

铜含量对Cu/CeO2水煤气变换催化剂性能的影响

采用共沉淀法制备了不同铜含量的Cu/CeO₂水煤气变换催化剂，考察了铜含量对催化活性的影响。结果表明，Cu/CeO₂催化剂呈现出良好的水煤气变换活性。铜含量对催化活性有显著影响，铜摩尔分数为50%时，催化剂的低温活性最高，在200 ℃时CO转化率达到66.1%。Cu/CeO₂与FBD型铁基高温变换催化剂相比，具有低温活性好、活性温区宽的特点。用XRD、N2吸附法、H₂-TPR和CO-TPD对催化剂进行了表征，结果表明,无定形CuO、纳米颗粒CuO等可能是催化反应的活性物种，晶粒CuO对催化活性影响不大。铜含量的催化剂在不同温度下呈现出不同的活性。     

The influence of alkali metals on the activity of supported ruthenium catalysts for the water-gas shift reaction

This paper presents the results of the studies on the influence of alkali metals on the activity of ruthenium catalysts, which were supported on the products of α- and δ-iron oxide-hydroxide calcination. Modification of these supports with alkali metals, in particular potassium, rubidium and cesium, prior to deposition of ruthenium was found to increase the activity of Ru/Fe₂O₃ catalysts in the water-gas shift reaction. It was also established that the activity and stability of catalysts prepared on iron oxide obtained from α-FeOOH increased when the latter was modified with sodium ions. The favourable effect of sodium on the activity of the catalysts was shown to appear at a certain proportion of the base to the active component, i.e. ruthenium. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparison of Cu–Ce–Zr and Cu–Zn–Al mixed oxide catalysts for water-gas shift

Cu–Zn–Al and Cu–Ce–Zr mixed oxide catalysts were prepared by two different methods, co-precipitation and flame spray pyrolysis. The performance of the catalysts was evaluated using the water-gas shift reaction with and without CO₂ and H₂ added to the feed. Cu–Ce–Zr catalysts are found not to be superior to Cu–Zn–Al catalysts in terms of initial activity and short-term stability. Their apparent activation energy appears to be less affected by increased concentrations of CO₂ and H₂.     

Chlorine-free iron-ruthenium catalyst for the water-gas shift reaction

Diffuse reflectance IR spectra of CO adsorbed on Pt/Mg(Al)O catalysts were studied at room temperature and different surface coverages of metallic Pt. They show the existence of two types of metallic Pt particles. One type has a normal behavior toward the adsorption of CO, which is probably related to the lower dispersion of Pt. The other type probably corresponds to smaller negatively charged clusters like those found for Pt-loaded alkaline and alkaline-earth forms of zeolites. They are characterized by the very low frequency of the singletone corresponding to the linear form of adsorbed CO and high thermal stability of the bridging complexes of CO with metallic Pt. Such by metal-support interaction modified platinum is likely responsible for high activity and selectivity of Pt/Mg(Al)O catalyst inn-alkanes aromatization.     

Investigation of the water-gas shift reaction using temperature-programmed desorption

The water-gas shift reaction has been investigated by the temperature-programmed desorption (TPD) of reaction components over a commercial low-temperature catalyst. It has been found that the oxidation state (and consequently the activity) of the catalyst is strongly influenced by the composition of the gaseous mixture. The adsorption capacity of catalysts decreases in the order: H₂O CO₂CO; hydrogen does not adsorb. The existence of two types of sites for carbon oxides adsorption has been found experimentally. A further type of storage (inactive) sites for water exists. On the basis of experimental results, model equations for TPD of H₂O, CO₂ and CO were derived. Models best fitting the experimental data were based on the assumption of a non-uniform heterogeneous surface of the catalyst.     

Gold nanoparticles supported on ceria-modified mesoporous titania as highly active catalysts for low-temperature water-gas shift reaction

New gold catalytic system prepared on ceria-modified mesoporous titania (CeMTi) used as water-gas shift (WGS) reaction catalyst is reported. Mesoporous titania (MTi) was synthesized using surfactant templating method through a neutral [C₁₃(EO)₆–Ti(OC₃H₇)₄] assembly pathway. Ceria modifying additive was deposited on MTi by deposition precipitation (DP) method. Gold-based catalysts with different gold content (1–5 wt.%) were synthesized by DP of gold hydroxide on mixed metal oxide support. The supports and the catalysts were characterized by powder X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), N₂ adsorption analysis and temperature-programmed reduction (TPR). The catalytic behavior of the gold-based catalysts was evaluated in WGS reaction in a wide temperature range (140–300 °C) and at different space velocities and H₂O/CO ratios. The influence of gold content and particle size on the catalytic performance was investigated. The WGS activity of the new gold/ceria-modified mesoporous titania catalysts was compared with that of gold catalysts supported on simple oxides CeO₂ and mesoporous TiO₂, as well as gold/ceria-modified titania and reference catalyst Au/TiO₂ type A (World Gold Council). A high degree of synergistic interaction between ceria and mesoporous titania and a positive modification of structural and catalytic properties by ceria has been achieved. It is clearly revealed that the ceria-modified mesoporous titania is of much interest as potential support for gold-based catalyst. The Au/ceria-modified mesoporous titania catalytic system is found to be efficient catalyst for WGSR.     

逆水煤气变换耦合乙烷脱氢反应中载体对氧化铬催化剂性能的影响

研究了在逆水煤气变换耦合乙烷脱氢反应中担载型氧化铬催化剂的活性,考察了多种载体对于催化剂反应性能的影响。结果表明,不同的载体所担载的氧化铬催化剂具有不同的催化性能。其中二氧化硅担载的氧化铬催化剂具有较高的乙烷转化率和乙烯选择性,在700℃时分别达到30.7%和96.5%。CO₂的作用是通过与H₂反应促进乙烷脱氢、并减少催化剂表面积炭。运用XRD、TPR、 XPS、UV-DRS和微量吸附量热技术对催化剂体相与表面结构、表面酸性和铬物种价态等进行了表征,结果显示催化剂表面酸中心适当的强度、数量和分布有利于乙烷的活化和催化转化,Cr³⁺和Cr⁶⁺物种是反应的活性中心。     

A catalytic membrane reactor for water-gas shift reaction

We conducted the WGS reaction on a catalytic membrane reactor consisting of a WGS catalyst bed, Pt/CeO₂ and thin, defect-free, Pd-Cu alloy membranes. The presence of CO and other gases with H₂ reduced the H₂ permeation through the membrane by more than 50% and the effect of the other gases on the permeation reduction decreased in the following order: CO>CO₂>N₂. In a catalytic membrane reactor with helium sweep gas, the CO conversion was improved by about 65% compared with the catalyst without any membrane, and the CH₄ formed from an undesirable side reaction was significantly reduced. Although the H₂ permeation was severely reduced by surface phenomena such as blocking of available H₂ dissociation sites by CO, CO₂ and steam, the CO conversion was notably improved by the membrane presence. Moreover, the CO conversion was maintained at 98% even after 60 h of reaction and our Pd-Cu-Ni alloy membrane withstood the exposure of CO and the other gases. However, for separation of pure H₂, a newly designed, catalyst-membrane system is required with better sealing and the ability to withstand the high operating pressure that drives the H₂ permeation.     

Oxalate as an intermediate in the base-catalysed water-gas shift reaction

The conversion of CO to H₂ and CO₂, in the presence of 1.0 M solutions of sodium carbonate, hydroxide and formate has been studied in the temperature range 200–350 °C. The decomposition of 1.0 M solutions of sodium formate, oxalate and carbonate under argon pressure was investigated using the same reaction conditions. It is shown that carbonate reacts readily with CO to produce oxalate, which decomposes easily to formate and CO₂. The formate is the most stable intermediate under the reaction conditions and only decomposes rapidly to carbonate and H₂ above 300 °C, making the water-gas shift reaction truly catalytic. Sodium hydroxide is not an intermediate in this reaction but first reacts with CO₂, formed during the reaction, to produce carbonate. Based on these results a new mechanism is proposed for the base-catalysed water-gas shift reaction.     

Identification of valence shifts in Au during the water-gas shift reaction

In situ X-ray absorption spectroscopy (XAS) has been performed to investigate the active site on Au-based catalysts in the water-gas shift (WGS) reaction. The surface area and hence the WGS activity is higher for AuTiO₂ catalysts supported on carbon nanofibres (CNF) than TiO₂. The WGS reaction rate depends on the Au coordination number with an apparent maximum close to eight which corresponds to a particle size of approximately 2.5–3.0 nm. A likely cause for the changes in the electronic structure of Au is the adsorption of CO on the surface, which also creates a small positive charge in the Au atoms. The catalytic activity significantly improves when titania is present compared to Au deposited directly on CNF.     

On the mechanism of methanol synthesis and the water-gas shift reaction on ZnO

Zinc oxide catalyses both methanol synthesis and the forward and ‘everse water-gas shift reaction (f- and r- WGSR). Copper also catalyses both reactions, but at lower temperatures than ZnO. Presently the combination of Cu and ZnO stabilized by Al₂O₃ is the preferred catalyst for methanol synthesis and for the f- and r- WGSR. On Cu, the mechanism of methanol synthesis is by hydrogenation of an adsorbed bidentate formate [1] (the most stable adsorbed species in methanol synthesis), while the f- and r- WGSR proceeds by a redox mechanism. The f-WGSR proceeds by H₂O oxidizing the Cu and CO, reducing the adsorbed oxide and the r-WGSR proceeds by CO₂ oxidising the Cu and H₂, reducing it [2–5]. Here we show that the mechanisms of both reactions are subtly different on ZnO. While methanol is shown to be formed on ZnO through a formate intermediate, it is a monodentate formate species which is the intermediate; the f- and r-WGS reactions also proceed through a formate – a bidentate formate - in sharp contrast to the mechanism on Cu.     

燃料电池用Cu-Ce(La)Ox变换催化剂

对采用共沉淀法制备的Cu-Ce(La)O_x高温变换催化剂进行了研究，包括中和pH值、中和温度、焙烧温度和方式以及CuO、CeO₂和LaO_x含量对催化剂性能的影响。5%CuO-CeO₂-La(10%)O_x高温变换催化剂的最佳制备工艺条件为：pH＝11，中和温度54 ℃，400 ℃焙烧4 h。催化剂的最佳质量分数配比是：CuO 为20%，CeO₂ 为70%，LaO_x 为10%。XRD晶相分析表明，5%Cu-Ce-La(10%)O_x催化剂中除了主相CeO₂以外，还出现了Cu与La形成的钙钛矿型复合氧化物CuLaO₂，且CuLaO₂高度均匀地分散在主相CeO_x中；还原态中除了CeO₂、CuLaO₂外，还出现了Cu单质。因此，这类催化剂的活性中心不可能是简单的CuLaO₂或Cu，这使得催化剂无论氧化态还是还原态都具有基本相同的活性。催化剂的活性位形态结构尚需做进一步研究。