铌酸在催化反应中的应用

介绍了铌酸(Nb2O·5nH2O)的性质及其在酯化、水合、脱水等反应中的应用。结果表明,无论是作为固体酸催化剂还是作为载体,铌酸都表现出较高的催化活性和稳定性,具有良好的应用前景。     

Selectivity and mechanism for skeletal isomerization of alkanes over typical solid acids and their Pt-promoted catalysts

Selectivities for skeletal isomerizations of n-butane and n-pentane catalyzed by typical solid acids such as Cs_2.5H_0.5PW₁₂O₄₀ (Cs2.5), SO₄²⁻/ZrO₂, WO₃/ZrO₂, and H-ZSM-5 and their Pt-promoted catalysts were compared. High selectivities for n-butane and low selectivity for n-pentane were observed over Cs2.5 and SO₄²⁻/ZrO₂, while H-ZSM-5 was much less selective, and WO₃/ZrO₂ was highly selective for both reactions. The Pt-promoted solid acids were usually selective for these reactions in the presence of H₂ except for Pt-H-ZSM-5 for n-butane isomerization. Both the acid strength and pore structure would be factors influencing the selectivity. Mechanism of skeletal isomerization of n-butane was investigated by using 1,4-¹³C₂-n-butane over Cs2.5 and Pt–Cs2.5. It was concluded that n-butane isomerization proceeded mainly via monomolecular pathway with intramolecular rearrangement on Pt–Cs2.5, while it occurred through bimolecular pathway with intermolecular rearrangement on Cs2.5. The higher selectivity on Pt–Cs2.5 would be brought about by the monomolecular mechanism. In the skeletal isomerization of cyclohexane, Pt–Cs2.5/SiO₂ was highly active and selective, while Pt–Cs2.5 was less selective. Control in the acid strength of Cs2.5 by the supporting would be responsible for the high selectivity.     

SWA/TiO_2微球的制备及催化α-蒎烯异构化性能

采用溶胶-凝胶法和浸渍法,制备了纳米负载型H4SiW12O40（SWA）催化剂,考察了载体种类、SWA浸渍浓度对催化剂性能的影响。结果表明,用TiO2固载、8%SWA浸渍所得催化剂SWA/TiO2的催化性能较佳。利用XRD、TEM和BET比表面测定技术对其结构进行了表征。结果显示,该催化剂颗粒为圆球形,粒径为40～50 nm,具有较好的分散性。载体TiO2的引入明显增大了SWA的比表面积。将纳米SWA/TiO2用于催化α-蒎烯异构化反应,实验结果表明,该催化剂具有较好的催化活性和选择性,异构化反应的主产物是莰烯。在适宜的实验条件下,α-蒎烯的转化率达98%,莰烯的产率达58%。与其它负载型催化剂比较,SWA/TiO2具有用量少、活性高、反应时间短等特点。     

多相催化剂在生物柴油生产中的研究进展

综述了油脂酯交换反应生产生物柴油中多相催化剂的研究进展,对催化剂的性能效率做了对比,指出在以废油脂代替精制植物油生产生物柴油的发展中,多相酸催化剂较多相碱催化剂有更强的适用性和工业前景。     

多孔WC-TiC催化剂的戊烷异构化活性

以TiC和MoSi₂为基体,WO₃和仲钨酸铵为WC的前驱体,碳酸氢铵为造孔剂,采用固相合成技术, 1 560 ℃制备碳化钛基复合WC催化材料。分别通过X射线衍射仪、扫描电镜、压汞仪、气相色谱和气质谱表征催化材料的相组成、显微结构、孔径分布和对戊烷的催化性能。结果表明,碳化钛基复合WC材料的相组成为TiC、SiC、MoC、 WC 和 (Ti, Si)C;当WO₃为WC前驱体时,催化材料的孔径呈现单峰分布［（0.3~50 μm）］,350 ℃其对戊烷的转化率为16.21%,异构化选择性为5.68%;当仲钨酸铵为WC前驱体时,催化材料的孔径呈现双峰分布［（100~800） nm和（1 ~5） μm］,WC颗粒在500 nm以下,350 ℃戊烷转化率达到48.44%,异戊烷的选择性为12.91%。     

Synthesis and characterization of solid-phase super acid catalysts and their application for isomerization of n-alkanes

In the present work, first, the reference catalyst super acidic nanostructured sulfated zirconia (SZ) and super acidic nanostructured aluminum chloride impregnated sulfated zirconium oxides in mole ratios of Zr⁴⁺:Al³⁺ as 2:1 (ACSZ-1), 1:1 (ACSZ-2), and 1:2 (ACSZ-3) were synthesized by a simple precipitation method. The catalytic performance of these four catalysts were evaluated during the isomerization of n-hexane, n-heptane, and n-octane to their corresponding branched chain isomers at low temperature and pressure conditions. ACSZ-2 shows high activity toward isomerization of n-hexane, n-heptane, and n-octane into their corresponding branched chain isomers. The reference catalyst SZ was proved to be less effective compare to the other three synthesized ACSZ catalysts. Ammonia-temperature-programmed desorption of these two materials ensures that the super acidity of ACSZ-2 is higher than that of SZ. Atomic force microscopic and scanning electron microscopic pictures predict the nature of the surface of the catalysts. Transmission electron micrographic analysis indicates the presence of particle-bulks having average size 12–20?nm, presenting an amorphous nature and having no definite surface morphology of ACSZ-2. Fourier transform infrared provides an outline regarding different linkages and bond connectivities between atoms and groups in ACSZ-2 and SZ. After catalyst evaluation and characterization a probable reaction mechanism has been proposed theoretically. The reactivity and selectivity of ACSZ-2 and SZ as well as the order and activation energy of the isomerization reactions in presence of ACSZ-2 have been calculated. The use of ACSZ-2 is beneficial from the point of cost efficiency as well as its use is energy saving.     

Cis–trans isomerization of olefinic alcohols promoted by Rh(I) complexes

Homogeneous hydrogenation and isomerization reaction of cis-2-butene-1,4-diol has been investigated in ethanol by using tris(triphenylphosphine)chlororhodium(I), RhCl(PPh₃)₃, and triethylamine at 303 K and 0.01–0.1 MPa partial hydrogen pressure. Under reduced H₂ pressure, the geometric isomerization reaction occurs, to a high extent, leading to trans-2-butene-1,4-diol up to 93% selectivity at 90% conversion of the cis analogous. Effects of H₂ partial pressure as well as triethylamine, added phosphine and olefin concentrations on the rate of reaction and on the products distribution were also investigated. The results obtained can be interpreted on the basis of a proposed mechanism in which RhH(PPh₃)₃ is the active species. The high selectivity towards cis-trans isomerization of cis-2-butene-1,4-diol is attributed to steric factors of the Rh(I) coordinated triphenylphosphine groups.     

Reverse-Flow Operation in Fixed Bed Catalytic Reactors

Transition from the usual steady-state mode of continuous processes toward forced unsteady-state conditions (FUSC) has been discussed in chemical engineering literature since the beginning of the 1960s [1-12]. FUSC can be created by periodic variations of temperature, composition, or other parameters to the inlet of a chemical unit.     

正丁烯骨架异构化催化剂的研究

成功合成了YZ-2型正丁烯异构化催化剂。以醚后混合碳四为原料,无任何稀释气体,在固定床反应器装置上考察了催化剂对正丁烯异构化的催化性能,探讨了工艺条件对异构化产物分布的影响,考察了催化剂性能的稳定性。结果表明:YZ-2型催化剂在正丁烯骨架异构化上具有较好的催化性能和稳定性。     

KBrH2O2催化顺酐异构化合成富马酸

以KBr-H2O2为催化剂,在H2SO4存在下,顺酐异构化为富马酸。反应的最优条件为：顺酐15g,水30mL,H2SO4（8／5）1mL,KBr0.1g,H2O20.3mL,回流反应60min,产率达93％以上。     

膨润土固体酸催化剂的制备及性能研究

用不同酸对膨润土进行酸化处理得到活性白土,并以活性白土为栽体浸渍负载氯化铁,得到FeCl3膨润土固体酸催化剂;以四氢呋喃阳离子开环聚合为探针反应,考察酸化条件对FeCl3膨润土催化剂性能的影响;利用XRD、BET、SEM及正丁胺滴定法对催化剂进行表征.结果表明,在质量分数为25%的硝酸98℃下酸化2 h,制备的催化剂性...     

Radial profiles of solids loading and flux in a gas–solid circulating fluidized bed

An electrical-impedance tomography (EIT) system has been developed to non-invasively measure radial voidage profiles in the riser of a pilot-scale circulating fluidized bed (CFB), yielding quantitative information that is validated by comparison to a gamma-densitometry tomography (GDT) system. EIT and GDT were applied to the CFB riser (14-cm inner diameter, 5.77-m height) containing fluid catalytic cracking particles in air. For all cases, the average and near-wall voidages from EIT and GDT agreed to within 0.03 and 0.07, respectively. This good agreement suggests that, where feasible, EIT can be used in place of GDT, which is advantageous since EIT systems are often safer, less expensive, and faster than GDT systems. The results also compared well to two correlations for radial voidage profile from the literature. Finally, a procedure for determining radial solids flux profiles from radial voidage profiles using an additional correlation [M.J. Rhodes, X.S. Wang, H. Cheng, T. Hirama, B.M. Gibbs, Similar profiles of solids flux in circulating fluidized-bed risers, Chemical Engineering Science 47 (1992) 1635–1643] was investigated. It was found that the accuracy of this correlation strongly depends on the voidage and/or solids flux measurement at the riser center.     

Synthesis and Catalytic Applications of Mesoporous Polymer Colloids in Olefin Hydrosilylation

Mesoporous polymer particles (MPPs) have been synthesized by using the spherical microparticles of siliceous mesocellular foam (MCF) as a hard template. The MPPs possessed a robust structure with ultralarge mesopores, and a clean and inert surface. The surface properties of the MPPs could be tailored for various applications by using different functionalized monomers. An imidazolium‐pyrrolidine ligand was successfully immobilized onto MPPs and used as a supported platinum organometallic catalyst in olefin hydrosilylation. The MPP‐supported catalyst provided superior activity and selectivity for this reaction as compared to the MCF‐supported catalyst.     

杂多酸催化剂的组成对烷烃异构化性能影响规律分析

含固体杂多酸双功能催化剂表现出优异的催化活性,并具有催化反应条件温和、不腐蚀设备、不污染环境等优点.此外,杂多酸基催化剂具有广阔的应用前景,已成为烷烃异构化催化剂领域研究热点.该文综述了杂多酸用于轻质烷烃异构化研究进展,详细论述了负载型杂多酸的载体种类、金属活性组分种类和混合方式等对异构化性能的影响规律.分析了杂多酸基催化剂结构与异构化性能之间的构效关系.提出了今后杂多酸基异构化催化剂的研究方向.     

固体酸催化合成水杨酸甲酯进展

固体酸是一种优良的催化剂,能够替代硫酸作为酯化催化剂。评述了对甲苯磺酸、氨基磺酸、强酸性阳离子交换树脂、溴化铜、一水硫酸氢钠、固体超强酸、杂多酸和分子筛等催化合成水杨酸甲酯的方法。     

新型碳八芳烃异构化催化剂的制备及其性能

选用独特结构的分子筛材料为酸性组元,制备了新型碳八（C8）芳烃异构化催化剂,并对该催化剂的异构化能力进行了研究。选取目前工业用催化剂作为对比催化剂,采用相同的反应原料,在各自最佳的反应条件下,与新型催化剂进行比较。实验结果表明,随着原料的不同,在反应产物中,新型催化剂反应中的对二甲苯在二甲苯中的浓度为19.06%～24.14%,乙苯转化率为32.07%～41.50%,C8烃收率为97.08%～99.11%,远高于对比催化剂;同时,甲苯含量为0.26%～1.20%,重芳烃含量为0.22%～0.62%,远低于对比催化剂。同对比催化剂相比,新型催化剂具有较高的异构化活性和选择性,能在较高的空速下运行。     

A comparison of cesium-containing heteropolyacid and sulfated zirconia catalysts for isomerization of light alkanes

The heteropolyacid H₃PW₁₂O₄₀ and its cesium salts Cs_xH_3-x PW₁₂O₄₀ (x = 1, 2, 2.5, 3) were synthesized, characterized and tested as catalysts for hydrocarbon reactions. All samples were characterized by a variety of techniques including elemental analysis, X-ray diffraction, dinitrogen adsorption, thermal gravimetric analysis and ammonia sorption. Results from these methods confirmed that pure cesium salts were prepared without significant contamination by amorphous oxide phases. Incorporation of cesium into the heteropolyacid decreased the acidic protons available for catalysis, increased the specific surface area, and increased the thermal stability. The heteropolyacids were tested as catalysts for butane skeletal isomerization, pentane skeletal isomerization and 1-butene double bond isomerization. For comparison, the activity of sulfated zirconia, a well-studied strong acid catalyst, was also evaluated for the three probe reactions. On a per gram basis, the Cs₂HPW₁₂O₄₀ sample was the most active heteropolyacid, presumably due to its high surface area. This sample was more active than sulfated zirconia for pentane skeletal isomerization and 1-butene double bond isomerization. However, sulfated zirconia was more effective for butane skeletal isomerization. Since the pentane and 1-butene reactions were monomolecular in nature, whereas butane isomerization was bimolecular, restrictions inside the micropores of the heteropolyacid may inhibit the formation of long chain intermediates. Interestingly, trace butenes were required to initiate butane isomerization reactions on sulfated zirconia, whereas heteropolyacids catalyzed the reaction in the absence of butenes. This revised version was published online in June 2006 with corrections to the Cover Date.     

不同碳基磺酸化固体酸的制备及催化性能比较

以常见的碳水化合物葡萄糖、纤维素、蔗糖、医用棉为原料,采用碳化磺化法制备得到四种碳基磺酸化固体酸催化剂。采用傅里叶转换红外光谱（FT-IR）、表面酸量的测定等手段对这四种碳基磺酸化固体酸进行了表征。同时将其用在乙酸乙酯的合成中,比较了其催化效率、稳定性。此外还进行了再生实验。     

催化酯化合成丁酸正丁酯的研究进展

固体催化剂代替硫酸作为酯化的催化剂,评述了对甲苯磺酸、甲烷磺酸盐、氨基磺酸、强酸性阳离子交换树脂、三氯化铁、二氯化锡、四氯化锡、硫酸铁铵、硫酸亚铁,硫酸铈、硫酸钛、硫酸氢钠、季铵盐、固体超强酸、杂多酸、分子筛等固体催化剂和酶催化酯化合成丁酸正丁酯的方法。     

固体酸催化合成氯乙酸异辛酯

以固体酸催化合成了氯乙酸异辛酯。经实验确定的最佳反应条件为 :醇酸的量比为 1 0∶1 0 ,固体酸用量为反应物总质量的 2 0 % ,反应时间为 1～ 2h ,酯化率达 96 8%。该催化剂后处理简单 ,不腐蚀设备 ,无环境污染 ,催化活性稳定 ,无须再生处理 ,经重复使用 30次后催化效力基本不变