Cu催化水煤气的变换反应机理

采用密度泛函理论(DFT), 对Cu催化水煤气变换反应三种可能的微观机理进行了理论研究. 在GGA-PW91理论水平下优化了反应通道上各驻点(反应物、中间体、过渡态和产物)的几何构型, 并通过频率分析对过渡态进行了验证. 研究结果表明, 甲酸根机理的可能性最小, 羧基机理与氧化还原机理的可能性较大, 且与氧化还原机理相比, 羧基机理因在反应过程中有中间体COOH(s)生成, 且它与OH(s)发生歧化反应仅需越过3.8 kJ·mol-1的活化能垒, 所以反应更易遵循这条路径进行.     

程序升温脱附法对低变反应体系的吸-脱附研究

本文采用程序升温脱附法(TPD)研究了低变反应各组分CO、H₂O、CO₂和H₂在Cu/ZnO/A1₂O₃型低变催化剂上的吸-脱附行为,并对与Cu/ZnO/A1₂O₃具有可此相对组成的六种样品进行了类似的讨论,通过对所得TPD谱图的定性分析发现:构成Cu/ZnO/A1₂O₃型低变催化剂的各个组元对低变反应各组分的吸-脱附作用互不相同,且不同的组元具有各自的吸-脱附特征。     

三种Au(111)催化水煤气变换反应机理的比较

采用密度泛函理论对三种水煤气变换反应(WGSR)机理(氧化还原机理、羧基机理、甲酸基的生成机理)在Au(111)面上的反应历程进行详细讨论.通过对表面吸附物种(H2O、CO、OH、O、H、CO2、COOH、HCOO)的吸附行为进行研究,得到最佳活性吸附中心.对三种机理中的14个基元反应的活化能进行分析,得出WGSR在Au(111)上按照羧基机理和氧化还原机理进行的可能性较大,按照甲酸基的生成机理进行的可能性较小.相比较羧基机理和氧化还原机理,反应更有可能按照羧基机理进行,最佳反应途径为H2O-H→OH+CO→COOH+OH→CO2.     

水煤气变换反应初始微观反应动力学的模拟研究

用蒙特水罗方法对水气转移反应两种典型机理的寝反应动力学进行了研究。结果表明,Ｔｅｍｋｉｎ等人的氧化－还原机理中,无论反应物ＣＯ和Ｈ２Ｏ的相对浓度怎样变化,ＣＯ２和Ｈ２的初始生成速率总是相差很大。     

Theoretical Investigation of Reverse Water Gas Shift Reaction Catalyzed by Ruthenium Halogen Carbonyl Complexes

In this paper we present theoretical study of the reverse water gas shift (RWGS) reaction catalyzed by ruthenium halogen carbonyl complexes. Three mechanisms, including hydrogen chloride, formic acid and oxidation–reduction mechanism, have been explored by density functional theory. The calculations indicate that the oxidation–reduction mechanism contributes to the TDI and TDTS in the ESM TOF calculations. Bimetallic catalysts would be likely to be more highly active than monometallic catalyst for the RWGS reaction. Among bimetallic catalysts studied, both bimetallic catalysts [Ru(μ-Cl)Cl(CO)₃]₂ and [Ru(μ-CO)Cl(CO)₃]₂ shows higher activity than [Ru(μ-Cl)(CO)₄]₂ catalyst with [Ru(μ-CO)Cl(CO)₃]₂ considering as the most efficient catalyst for RWGS reaction.     

焙烧温度对低温水煤气变换Au/Fe2O3催化剂性能的影响

采用改性沉积-沉淀法制备了系列低温水煤气变换Au/Fe2O3催化剂,发现经300℃焙烧的样品具有较好的催化活性和稳定性.并运用N2物理吸附、原位X射线粉末衍射(in situ XRD)、程序升温还原(H2-TPR)和X射线光电子能谱(XPS)等技术,探讨焙烧温度对催化剂性能的影响机制,同时对样品的失活原因进行了分析.结果表明,催化剂性能与焙烧温度引起的金和载体氧化铁的相互作用以及载体还原性质的变化密切相关.XPS表征结果说明,尽管反应后在催化剂表面有碳酸盐或类碳酸盐物种生成,但半定量分析表明这些物种的形成不是催化剂失活的主要原因;根据在低温水煤气变换反应过程中Au/Fe2O3催化剂的比表面积明显下降,载体的结晶度也明显提高,推断Au/Fe2O3催化剂载体的结构性质的变化才是其失活的主要原因.     

Synthesis of Dimethyl Ether from CO Hydrogenation： a Thermodynamic Analysis of the Influence of Water Gas Shift Reaction

Three reactions involved in dimethyl ether (DME) synthesis from CO hydrogenation: methanol synthesis reaction (MSR), methanol dehydration reaction (MDR) and water gas shift reaction (WGSR) are studied by thermodynamic calculation. For demonstrating this process in detail, three models, MSR,MSR MDR, MSR MDR WGSR, are used. Their basic characteristics can be obtained by varying widely the ratios of H2 to CO in the feed (no CO2). Through thermodynamic analysis a chemical synergic effect obviously exists in the second and third models. By comparison between two models it is found that WGSR plays a special role in dimethyl ether synthesis. It is possible for the two models to shift one to the other by regulating CO2 concentration in feed. For Model 2, the selectivity for DME in oxygenates (DME methanol) does not change with the ratio of H2 to CO.     

Fe3O4(111)面上的水煤气变换反应机理

水煤气变换是一重要的制备氢气的反应, 采用密度泛函理论(DFT), 对水煤气变换反应在Fe₃O₄ (111)面上的催化反应作了深入研究. 结果表明: 氧化还原机理的活化能明显高于结合机理的活化能, 中间步骤应以结合机理进行|氢原子结合生成氢气为整个反应的速控步骤, 理论计算其活化能与水煤气变换实验数据一致, 高达1.29 eV, 还对迄今有关水煤气变换机理研究中的各种实验现象作了合理的解释, 并对Fe₃O₄ (111)催化剂的改性设计作了讨论.     

Harnessing the Power of the Water‐Gas Shift Reaction for Organic Synthesis

Since its original discovery over a century ago, the water‐gas shift reaction (WGSR) has played a crucial role in industrial chemistry, providing a source of H₂ to feed fundamental industrial transformations such as the Haber–Bosch synthesis of ammonia. Although the production of hydrogen remains nowadays the major application of the WGSR, the advent of homogeneous catalysis in the 1970s marked the beginning of a synergy between WGSR and organic chemistry. Thus, the reducing power provided by the CO/H₂O couple has been exploited in the synthesis of fine chemicals; not only hydrogenation‐type reactions, but also catalytic processes that require a reductive step for the turnover of the catalytic cycle. Despite the potential and unique features of the WGSR, its applications in organic synthesis remain largely underdeveloped. The topic will be critically reviewed herein, with the expectation that an increased awareness may stimulate new, creative work in the area.     

单个水分子对HO2+H2S反应主通道影响的理论研究

采用CCSD(T)/aug-cc-pVTZ//B3LYP/6-311+G(2df,2p)方法对HO2+H2S反应及单分子水参与其主通道的微观机理和速率常数进行了研究.结果表明,HO2+H2S反应主通道为生成产物为H2O2+HS的通道,其表观活化能为14.94 kJ/mol.考虑单分子水对主产物通道的影响发现,所得的势能面比无水参与的反应复杂得多,经历了H2O…HO2+H2S(RW1),HO2…H2O+H2S(RW2)和H2O…H2S+HO2(RW3)3个通道,RW1~RW6共6个路径.其中通道RW1是水分子参与HO2+H2S反应主通道的优势通道.在216.7~298.2K温度范围内通道RW1的有效速率常数呈现出正温度系数效应,在298 K时,k’RW 1/ktotal达到54.2%,表明在实际大气环境中水分子对HO2+H2S反应的主通道具有明显影响.     

Reaction of CF3 radicals with H2S

Hydrogen abstration from H₂S by CF₃ radicals, generated by the photolysis of both CF₃COCF₃ and CF₃I, has been studied in the temperature range 314–434 K. The rate constant, based on the value of 10^13.36 cm³/mol · s for the recombination of CF₃ radicals, is given by with CF₃COCF₃ as the radical source, and with CF₃I as the radical source, where k₂ is in cm³/mol · s and E is in J/mol. These results resolve a previously existing controversy concerning the values of the rate constants for this reaction. They show that CF₃ radicals are less reactive than CH₃ radicals in attacking H₂S, and this behavior indicates that polar effects play a significant role in the hydrogen transfer reactions of CF₃ radicals.     

Au负载催化剂应用于水煤气变换制氢反应的研究进展

水煤气变换反应是目前广泛应用于制氢的方法 ,应用于水煤气变换反应的催化剂成为了重要的研究热点.我们在简述传统水煤气变换催化剂的基础上,重点介绍了Au负载型催化剂应用于水煤气变换反应的相关文献,针对Au负载型催化剂的载体种类、制备方法以及催化剂活性机理做出了详细分析.强调了影响水煤气变换反应催化剂的重点参数及Au负载型催化剂的发展趋势,以便为提高催化剂催化活性、设计Au负载催化剂并应用在水煤气变换反应中的研究者提供必要的参考信息.     

Ni-Cu-Mn-K/γ-Al2O3高温变换催化剂的结构和性能表征

以γ-Al₂O₃为载体，采用二步等体积浸渍法，制备了Ni-Cu-Mn-K/γ-Al₂O₃高温水煤气变换催化剂。采用低温氮吸附-脱附，DTA，XRD，H₂-TPR等方法对催化剂进行了表征，比较了载体、单组分、双组分、以及多组分浸渍的样品结构及各物种的存在形式，探讨了催化剂的活性相组成。结果表明，所制备的催化剂具有较大的比表面积，孔径呈介孔分布结构;低温时，催化剂活性相主要为高度分散的Cu、Ni、Ni-Cu-O、xCuO·yMnO₂和xNiO·yMnO₂复合氧化物;高温时，活性相可能为 xCuO·yMnO₂和xNiO·yMnO₂等复合氧化物。经530 ℃耐热15 h后催化活性测试结果分析认为，活性相xCuO·yMnO₂和xNiO·yMnO₂等复合氧化物提高了该催化剂的热稳定性。     

铜物种对Cu/Fe2O3水煤气变换反应催化剂性能的影响

采用共沉淀法制备了系列铜负载量不同的Cu/Fe₂O₃水煤气变换(WGS)催化剂,并考察了铜负载量对催化剂结构和水煤气变换反应性能的影响. 结果表明,Cu/Fe₂O₃催化剂呈现出良好的水煤气反应性能,当CuO质量分数为20%时,催化剂的WGS性能最优,250 ℃时CO转化率高达97.2%,同时热稳定性也最好. 运用X射线粉末衍射(XRD)、N₂物理吸脱附和H₂程序升温还原(H₂-TPR)等手段对Cu/Fe₂O₃催化剂的物相、织构特征及还原性能进行了表征,结果表明,CuFe₂O₄物种的存在极大地改善了催化剂的还原性能和WGS反应活性. 这是由于CuFe₂O₄特殊的尖晶石结构有利于Cu微晶的稳定;同时,CuFe₂O₄在低温下即被还原为单质铜,有利于促进催化剂体系中电子的转移. 此外,通过(NH₄)₂CO₃溶液处理,研究了独立相CuO对Cu/Fe₂O₃催化剂WGS反应性能的影响,结果发现,独立相CuO的存在,有利于H原子在各组分传递,从而促进催化剂的CuFe₂O₄的还原,改善Cu/Fe₂O₃催化剂的WGS反应性能.     

Homogeneous Catalysis of the Water Gas Shift Reaction by Bridged Dinuclear Pyrazolate Rhodium Complexes. FT-IR, 1H and 13C NMR In Situ Studies

Homogeneous catalysts for the water gas shift reaction prepared from Rh₂(-Pz)₂(COD)₂ (Pz = pyrazolate ion and COD = 1,5-cyclooctadiene) in aqueous organic solvent media (pyridine, 4-picoline or 2-ethoxyethanol) and Rh₂(-Pz)₂(CO)₂(TPPMS)₂ (TPPMS = meta-sulfonatophenyl-diphenyldiphosphine) in acidic aqueous media under mild conditions are described. In situ FT-IR, ¹H and ¹³C NMR spectroscopic studies of the Rh₂(-Pz)₂(COD)₂ catalytic system reveal the presence of hydrido-Rh complexes with linear and bridging carbonyls. These complexes also catalyze the reduction of nitrobenzene to aniline.     

以ZrO_2-Al_2O_3为载体的Co-Mo-K耐硫水煤气变换催化剂

采用沉淀法和浸渍法分别制备了 Zr O2 - Al2 O3复合载体和 Co- Mo- K耐硫变换催化剂 .研究了 Zr O2 对 Co- Mo- K耐硫变换催化剂活性及热稳定性的影响 .利用 XRD、BET、TG、XPS等手段对催化剂及其载体的结构、吸硫吸水性能和氧化还原性能进行了表征 .结果表明以 Zr O2 - Al2 O3代替传统的 γ- Al2 O3作为 Co- Mo- K耐硫变换催化剂的载体 ,可提高催化剂的活性 ,尤其是低温活性 ,并可改善催化剂的热稳定性、氧化还原性、吸硫和吸水性能     

CH3CH2S自由基H迁移异构化及裂解反应的理论研究

采用密度泛函方法(B3LYP)在6-311+G(d,p)基组水平上研究了CH3CH2S自由基H迁移异构化以及裂解反应的微观动力学机理. 在QCISD(T)/6-311++G(d,p)//B3LYP/6-311+G(d,p)+ZPE水平上进行了单点能校正. 利用经典过渡态理论(TST)与变分过渡态理论(CVT)分别计算了在200~2000 K温度区间内的速率常数kTST和kCVT, 同时获得了经小曲率隧道效应模型(SCT)校正后的速率常数kCVT/SCT. 研究结果表明, CH3CH2S自由基1,2-H迁移、1,3-H迁移、C—C键断裂和β-C—H键断裂反应的势垒ΔE≠分别为149.74, 144.34, 168.79和198.29 kJ/mol. 当温度低于800 K时, 主要发生1,2-H迁移反应, 高于1800 K时, 主要表现为C—C键断裂反应, 在1300—1800 K范围内, 1,3-H迁移反应是优势通道, 在计算的整个温度段内, β-C—H键断裂反应可以忽略.