不同方法制备的CoMo/Al2O3加氢脱硫催化剂的表征

 采用干混法、湿混法和浸渍法制备了CoMo/Al2O3加氢脱硫催化剂. 物理性质分析、X射线光电子能谱、X射线能量色散谱和程序升温硫化表征结果表明,干混法和湿混法催化剂的孔容和比表面积相当,均大于浸渍法催化剂. 浸渍法催化剂的表面粒子明显大于两种混捏法. 两种混捏法催化剂可以在低温区硫化,浸渍法催化剂的硫化可分别在低温区和高温区进行. 干混法催化剂中Co和Mo在微区内分布不均匀,浸渍法催化剂中Co和Mo在催化剂表面的分散量明显高于催化剂内部,湿混法催化剂中Co和Mo在微区内呈均匀分布. 湿混法催化剂的Co和Mo在催化剂表面的分散状态好于干混法和浸渍法,制备方法对催化剂中Co和Mo的存在环境及价态没有影响. 石脑油加氢脱硫反应评价结果表明,湿混法催化剂的加氢脱硫活性高于浸渍法和干混法催化剂.     

钌基氨合成催化剂的制备方法

与铁催化剂相比较,钌基氨合成催化剂具有低温、低压、高活性的特点。对于不同的载体、制备方法和制备条件对催化剂性能影响较大。本文从载体的前处理、活性组分钌和助剂的加入方式等方面简要阐述了钌基氨合成催化剂制备方法的研究进展,介绍了熔融法、升华法、离子交换法、超声法、沉淀法、溶胶-凝胶法、浸渍法、微波辅助法等钌基氨合成催化剂制备方法,指出了一些制备方法的不足之处,并展望了钌基氨合成催化剂制备方法的研究方向。     

聚合物固载Co-Pd 催化剂的结构与活性

采用溶剂化金属原子浸渍(SMAI)法制备了几种不同金属含量的Co Pd催化剂,用X射线衍射、X射线光电子能谱和磁测定对催化剂进行表征,并与普通浸渍法(CI)制得的相同金属含量的催化剂进行比较.结果表明SMAI法制备的催化剂金属粒度小于CI法制备的催化剂,且前者零价金属含量高于后者.SMAI法制备的催化剂Co在表面上富集,而CI法制备的催化剂Co在表面和体相的金属含量基本相同.在二丙酮醇加氢及电催化反应中, SMAI法催化剂比相同组成的CI法催化剂具有更高的催化活性.     

不同方法制备Pt/C催化剂对燃料电池催化活性的影响

分别采用高压有机溶剂法和回流法不同的制备方法,制备了含铂20%(w)的催化剂Pt/C-HP(高压有机溶剂法)和Pt/C-Reflux(回流法)。实验发现:对于甲醇的阳极氧化过程,高压有机溶胶法制得的催化剂活性较高,催化剂Pt/C-HP甲醇氧化峰电流密度是Pt/C-Reflux的1.5倍,且远远高于商业催化剂JM3000含铂20%(w)Pt/C催化剂,催化剂Pt/C-Reflux甲醇氧化峰电流密度与商业催化剂JM3000催化剂相当。采用X射线衍射(XRD)、透射电镜(TEM)、循环伏安法(CV)等方法对催化剂进行表征的结果表明:高压有机溶胶法制得的催化剂分散性比回流法制得的催化剂好,使得前者催化剂的电化学活性比表面积得到了显著的提高。     

钴铝复合氧化物负载金催化剂的制备及催化分解N2O

分别用离子交换法和共沉淀法制备了钴铝复合氧化物负载金催化剂,用于催化分解N₂O。离子交换法制备的催化剂活性优于共沉淀法制备的催化剂。对于离子交换法制备的催化剂,考察了金负载量、HAuCl₄溶液的预处理方式、焙烧温度对催化剂活性的影响,用BET、XRD、H₂-TPR等技术对催化剂进行了表征,优化出了催化剂的最佳制备参数：金负载量1.1%、预调节HAuCl₄溶液的pH值至9.0、300℃焙烧。在钴铝氧化物中加入适量的助剂Na,提高了Co³⁺的还原性和催化剂的低温活性,在此基础上制备的1.5%Na/1.1%Au/Co-Al催化剂的低温活性优于1.1%Au/Co-Al和1.5%Na/Co-Al。     

制备方法对Mn/ZSM-5催化剂结构及低温SCR性能影响

本文探讨了采用离子交换法和浸渍法制备的Mn/ZSM-5催化剂并采用多种表征手段分析了催化剂表面性能与SCR活性之间的关系。结果表明:离子交换法制备的催化剂,其表面MnO_x物种的分散性优于浸渍法制备的催化剂,含有更多的四价Mn~(4+)物种,因而有利于催化剂表面吸附氧的富集,MnO_x物种的氧化还原性能更好,促进低温活性提高。但过高的负载量以及浸渍法易促进晶相物种生成而使分散性降低,不利于催化剂低温SCR活性。其中,利用离子交换法制备的5%Mn/ZSM-5(IE)催化剂其低温SCR性能最佳,其T_(50)起燃温度低至150℃、稳定转化率窗口可低至200℃。商用柴油车尾气国六NO转化催化剂的生产工艺应尽量采用离子交换法制备,有利于低温工况的达标排放。     

核壳结构:燃料电池中实现低铂电催化剂的最佳途径

电催化剂是决定低温燃料电池性能、寿命和成本的关键材料之一,核壳结构电催化剂由于其在降低铂载量、提高催化剂活性方面表现出的良好性质,已成为燃料电池领域的研究热点。本文综述了低温燃料电池核壳结构电催化剂的最新研究进展。首先,在概述核壳结构电催化剂总体特征的基础上,详细介绍了核壳结构电催化剂的制备方法,主要包括胶体法、热分解法、置换法、电化学法等,其中胶体法是目前应用最为广泛的一种方法,具有合成过程简单易控等优点;置换法和电化学法则是在最近几年得到了迅速的发展,并有望用于核壳结构电催化剂的批量化生产。然后,分别从二元及其他多元催化剂组成方面阐述了核壳型电催化剂体系的研究进展,核壳结构电催化剂不仅可有效提高贵金属铂的质量比活性,同时,其他金属元素与铂之间存在的相互作用可对电催化剂的活性及稳定性产生十分重要的调变作用。最后,我们对低温燃料电池核壳结构电催化剂的发展趋势作了展望。     

制备方法对CuO—Ce0．7Zr0．3O2催化剂的氧缺位和CO氧化活性的影响

采用溶胶-凝胶法和溶胶-凝胶 浸渍法两种方法制备了CuO-Ce0.7Zr0.3O2催化剂,并对催化剂进行了XRD、Raman等表征,考察了催化剂的CO氧化性能.研究结果表明,溶胶-凝胶法制备的CuO-Ce0.7Zr0.3O2催化剂的CO氧化活性明显高于溶胶-凝胶 浸渍法制备的CuO/Ce0.7Zr0.3O2催化剂,CuO-Ce0.7Zr0.3O2催化剂容易形成氧缺位和表面高分散CuO的颗粒较大,从而提高催化活性.     

分形理论在催化剂研究中的应用

介绍了分形和分形维数在催化剂研究中的应用.概述了催化剂研究中常用的分形维数测定方法,包括盒子维法、散射强度法和吸附法.从四个方面分析了近年来催化剂分形研究的方向和进展:分形维数与催化剂评定和筛选,催化剂分形孔结构,分形与反应动力学,模型建立.从分形维数的测量、催化剂分形生长模型以及多重分形研究三个方面对分形在催化剂方面的应用进行了评价和展望.     

离子交换法制备Pt-Sn_E/Mg(Al)O催化剂及其烷烃催化脱氢性能

以水滑石为载体,采用离子交换法制备了Pt-Sn_E/Mg(Al)O催化剂,并对其进行了X射线衍射、N2物理吸附、透射电镜等技术表征;考察了该离子交换法制备的Pt-SnE/Mg(Al)O催化剂对乙烷和丙烷脱氢的催化性能,并与浸渍法制备的Pt-SnI/Mg(Al)O催化剂进行了比较。结果表明,利用离子交换法制备的Pt-SnE/Mg(Al)O催化剂其反应活性和稳定性明显优于浸渍法制备Pt-SnI/Mg(Al)O催化剂的。在相同条件下反应2 h后,Pt-SnE/Mg(Al)O催化剂和Pt-SnI/Mg(Al)O催化剂的乙烷催化脱氢转化率分别为12.2%和3.1%,丙烷催化脱氢转化率分别为38.7%和26.4%。     

溶胶-凝胶法制备钯催化剂的织构与性能

采用溶胶-凝胶法制备了Pd/Al2O3催化剂，用LLS(激光光散射)、XRD和BET等技术考察了溶液pH值对所成胶体粒子流体力学半径、相应催化剂产品孔径分布及热稳定性的影响.研究发现，由pH=4.1的胶体制备的催化剂具有良好的热稳定性和CO、C3H6的氧化活性.氧化镧添加剂可抑制Al2O3载体在高温下由γ相向α相的转化，同时也促进了催化剂上Pd粒子的生长. La2O3可提高新鲜Pd催化剂的氧化活性，但对老化后催化剂活性的提高无促进作用.     

Light-off Performance of Three-Way Catalysts Before and After Accelerated Aging Test with an Engine-Dynamometer

This study demonstrates the reaction behavior during the purification of model automotive exhaust gases over Pd catalysts before and after thermal degradation. In particular, to investigate the relationship between the Pd state and the reaction behavior of Pd/Al₂O₃ and Pd/CeO₂−ZrO₂ (CZ), operando X-ray absorption spectroscopy measurements were performed during purifying exhaust gases over real and model catalysts mimicking the degradation of Pd particles and CZ supports after accelerated aging tests. The NO reduction activity of the aggregated Pd metal species was as high as that of the highly dispersed Pd species, but hydrocarbon (HC) poisoning was significantly enhanced by the aggregation of Pd metal particles caused by thermal aging. The existence of a three-phase boundary (TPB) between the CZ, the Pd particles, and the gas phase strongly affected the catalytic activity at low temperatures, and the presence of a sufficient TPB facilitated the combustion of unburned HCs owing to the oxygen storage performance of CZ. Thus, the TPB reduced the poisoning of the precious metal surface by HC species at low temperatures. Therefore, the findings of this study will facilitate the development of next-generation gas purification catalysts with high activity and durability.     

Alumina-Based Supports for Automotive Palladium Catalysts

Addition of La, Ba and Ce to Pd 3-way exhaust catalysts has been studied. The effect of these additives and temperature of calcination were studied on the activity of the catalysts stabilized in a simulated exhaust gas at 570°C (1 h), using an experimental design. The catalytic activities were measured in the simulated exhaust gas as a function of temperature. Also, the activity of the catalysts for the NO - CO - O₂ system, was measured while changing the oxygen content. The results show that La promotes the reduction of NO at temperatures below 250°C. Improved catalysts have a high thermal stability.     

Effect of cobalt oxide on performance of Pd catalysts for lean-burn natural gas vehicles in the presence and absence of water vapor

Pd-based catalysts modified by cobalt were prepared by co-impregnation and sequential impregnation methods, and characterized by X-ray powder diffraction (XRD), N_2 adsorption/desorption (Brunauer-Emmet-Teller method), CO-chemisorption and X-ray photoelectron spec-troscopy (XPS). The activity of Pd catalysts was tested in the simulated exhaust gas from lean-burn natural gas vehicles. The effect of Co on the performance of water poisoning resistance for Pd catalysts was estimated in the simulated exhaust gas with and without the presence of water vapor. It was found that the effect of Co significantly depended on the preparation process. PdCo/La-Al_2O_3 catalyst prepared by co-impregnation exhibited better water-resistant performance. The results of XPS indicated that both CoAl_2O_4 and Co_3O_4 were present in the Pd catalysts modified by Co. For the catalyst prepared by sequential impregnation method, the ratio of CoAl_2O_4/Co_3O_4 was higher than that of the catalyst prepared by co-impregnation method. It could be concluded that Co_3O_4 played an important role in improving water-resistant performance.     

CeO2-ZrO2-La2O3-Al2O3 composite oxide and its supported palladium catalyst for the treatment of exhaust of natural gas engined vehicles

Composite supports CeO2-ZrO2-Al2O3 (CZA) and CeO2-ZrO2-Al2O3-La2O3 (CZALa) were prepared by co-precipitation method. Palladium catalysts were prepared by impregnation and their purification ability for CH4, CO and NOx in the mixture gas simulated the exhaust from natural gas vehicles (NGVs) operated under stoichiometric condition was investigated. The effect of La2O3 on the physicochemical properties of supports and catalysts was characterized by various techniques. The characterizations with X-ray diffraction (XRD) and Raman spectroscopy revealed that the doping of La2O3 restrained effectively the sintering of crystallite particles, maintained the crystallite particles in nanoscale and stabilized the crystal phase after calcination at 1000 ℃. The results of N2-adsorption, H2-temperature-programmed reduction (H2-TPR) and oxygen storage capacity (OSC) measurements indicated that La2O3 improved the textural properties, reducibility and OSC of composite supports. Activity testing results showed that the catalysts exhibit excellent activities for the simultaneous removal of methane, CO and NOx in the simulated exhaust gas. The catalysts supported on CZALa showed remarkable thermal stability and catalytic activity for the three pollutants, especially for NOx. The prepared palladium catalysts have high ability to remove NOx, CH4 and CO, and they can be used as excellent catalysts for the purification of exhaust from NGVs operated under stoichiometric condition. The catalysts reported in this work also have significant potential in industrial application because of their high performance and low cost.     

(CeO_2-ZrO_2-Al_2O_3)-(La_2O_3-Al_2O_3)复合氧化物负载的Pd密偶催化剂:载体焙烧温度的影响

采用同时共沉淀法制备了(CeO2-ZrO2-Al2O3)-(La2O3-Al2O3)新型复合氧化物(CZA-LA),考察了焙烧温度对CZA-LA负载的Pd密偶催化剂的影响,并采用N2吸附-脱附法和X射线衍射对其进行了表征.结果表明,随着焙烧温度的升高,尽管CZA-LA样品的比表面积降低,但即使在1000°C焙烧5h后,其比表面积仍能保持在122m2/g左右;另外,CZA-LA样品的孔体积降低幅度不大,当在700℃及更高温度下焙烧后基本上保持稳定.以不同温度焙烧5h后的样品为载体,采用等体积浸渍法制备了一系列整体式Pd/CZA-LA密偶催化剂(Pd含量2.0g/L).催化剂对消除模拟汽油车尾气中C3H8活性测试结果表明,各新鲜催化剂的活性相差不大,均具有较低的起燃温度T50和完全转化温度T90.当催化剂经老化处理后,以1000°C焙烧的载体负载的Pd催化剂活性最高,T50和T90分别为310和341℃,ΔT仅为31℃,仅比新鲜催化剂的高7℃.可见,该催化剂表现出优异的催化活性和抗老化性能,可以满足欧Ⅳ及更高标准的用于汽油车尾气净化的密偶催化剂的性能要求.     

溶胶—凝胶法制备NiO／SiO2催化剂研究

分别以正硅酸乙酯、硝酸镍为硅源和镍源,采用溶胶－凝胶法,经超临界流体干燥和普通干燥制备了NiO-A-SiO2、NiO-G-SiO2催化剂;以气凝胶和干凝胶为载体,采用浸渍法制备了NiO/A-SiO2、NiO/G-SiO2催化剂。并用XRD、TEM、BET、TPR等手段,研究了制备方法对催化剂织构、结构和Ni物种存在形态的影响,发现NiO-A-SiO2和NiO-G-SiO2催化剂上高度分散的NiO簇团与SiO2之间有较强的相互作用,其顺酐液相选择加氢转化率低于10％;NiO/G-SiO2催化剂上,以单一物种形态存在的NiO与SiO2相互作用弱,顺酐转化率为42％;NiO/A-SiO2催化剂上,以多种形态存在的微量NiO与SiO2间的相互作用较复杂,其顺酐液相选择加氢的转化率和丁二酸酐的选择性分别可达100％和98％。     

The role of doped Fe on the activity of alumina-supported Pt and Pd diesel exhaust catalysts

Supported Pt and Pd are most commonly used for oxidation catalysts. They have similar and different characteristics for deactivation factors. The catalytic activity of Pt and Pd catalysts supported on ??-Al₂O₃ was studied in the presence and absence of H₂O and SO₂ during CO oxidation under simulated conditions of diesel exhaust gas. Without the addition of H₂O and SO₂ to the feed gas, Pd/Al₂O₃ had a superior catalytic activity compared to Pt/Al₂O₃. The addition of H₂O to the feed gas strongly and negligibly affected the activity of Pd and Pt, respectively, while the addition of SO₂ to the feed gas had a strong poisoning effect on the catalytic activity of both Pt and Pd catalysts. Although being the most active, Pd catalysts exhibited a strong sensitivity to water and sulfur-containing compounds. Fe was added to the Pt and Pd catalysts to introduce sulfur resistance. The addition of Fe enhanced the activity of the catalysts by suppressing the phase transition of Al₂O₃ to Al₂(SO₄)₃ and by hindering metal sintering.     

Properties of Cu(thd)2 as a precursor to prepare Cu/SiO2 catalyst using the atomic layer epitaxy technique

The new Cu/SiO2 catalyst is developed by the atomic layer epitaxy (ALE) method. The ALE-Cu/SiO2 catalyst with high dispersion and nanoscale Cu particles appears to have very different catalytic properties from those of the typical Cu-based catalysts, which have satisfactory thermal stability to resist the sintering of Cu particles at 773 K. Due to the formation of small Cu particles, the ALE-Cu/SiO2 can strongly bind CO and give high catalytic activity for CO2 converted to CO in the reverse water-gas-shift reaction. The catalytic activity decreases in the order of 2.4% ALE-Cu/SiO2 =... 2% Pt/SiO2 > 2% Pd/SiO2 > 10.3% IM-Cu/SiO2.     

Effect of the reduction conditions of the supported palladium precursor on the activity of Pd/C catalysts in hydrogenation of sodium 2,4,6-trinitrobenzoate

The study addresses the effect of the reduction conditions of palladium polynuclear hydroxo complexes (PHC) supported on the Sibunit carbon material on the dispersion of the metal particles and the activity of 0.5%Pd/Sibunit catalysts in the selective hydrogenation of sodium 2,4,6-trinitrobenzoate to 1,3,5-triaminobenzene in an aqueous solution (temperature of 323 or 343 K, pressure of 0.5 MPa). The palladium PHC were reduced using the most common methods pertaining to catalyst preparation: liquid-phase reduction with sodium formate and reduction in a hydrogen flow at elevated temperature. It was found that high-temperature reduction in the gas phase gives rise to Pd particles with a markedly lower dispersion compared with the sample obtained under mild liquid-phase reduction conditions. The catalytic activity of the sample containing large Pd particles proved to be higher than the activity of the catalyst obtained by reduction with sodium formate.