Preparation, characterization, and activity of Al2O3-supported V2O5 catalysts
Preparation, characterization, and activity of Al2O3-supported V2O5 catalysts
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DOI：
10.1016/j.jcat.2003.07.011
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发表时间：
2004-01-01
影响因子：
7.3
通讯作者：
Varma, RS
中科院分区：
文献类型：
--
作者：
Reddy, EP;Varma, RS
采用湿法浸渍法制备了一系列V_2O_5负载量为5 ~ 25wt%的活性氧化铝负载钒氧化物催化剂。采用BET比表面积、氧化学吸附、X射线衍射（XRD）、程序升温还原（TPR）、热重分析（TGA）和傅里叶变换红外（FTIR）等物理化学方法，对钒在氧化铝表面的化学环境进行了表征。氧的吸收量在370 degreesC下测量，在相同的温度下进行预还原，这似乎产生更好的分散和氧原子位点密度的数值。XRD和FTIR结果表明，钒氧化物存在于一个高度分散的状态低于15重量%的V2 O 5负载和微晶相高于此负载水平。V_2O_5/Al_2O_3催化剂的TPR曲线在V_2O_5含量为15wt%的低温下只出现一个峰。有人建议，低温还原峰是由于表面的钒氧化物，这已被归因于四面体的配位几何的V离子的还原。TPR的V2 O 5/Al 2 O3在较高的氧化钒负载量表现出三个峰在还原温度下，表明块状的氧化钒物种存在于这些催化剂只有在较高的氧化钒负载量，与V离子的八面体协调。V_2O_5/Al_2O_3催化剂的TPR曲线表明，当V_2O_5负载量低于15%时，V_2O_5形成孤立的表面氧化钒物种，而在高负载量（> 15%V_2O_5）体系中，二维结构和V_2O_5微晶变得普遍。乙苯液相氧化为苯乙酮已被用作化学探针反应来检测催化活性。乙苯氧化实验表明，V_2O_5/Al_2O_3比V_2O_5负载量高的催化剂具有更高的活性。(C)2003年爱思唯尔公司All rights reserved.
A series of activated alumina-supported vanadium oxide catalysts with various V2O5 loadings ranging from 5 to 25 wt% have been prepared by wet impregnation technique. A combination of various physicochemical techniques such as BET surface area, oxygen chemisorption, X-ray diffraction (XRD), temperature-programmed reduction (TPR), thermal gravimetric analysis (TGA), and Fourier transform infrared (FTIR) were used to characterize the chemical environment of vanadium on the alumina surface. Oxygen uptakes were measured at 370 degreesC with prereduction at the same temperature, which appears to yield better numerical values of dispersion and oxygen atom site densities. XRD and FTIR results suggest that vanadium oxide exists in a highly dispersed state below 15 wt% V2O5 loading and in the microcrystalline phase above this loading level. TPR profiles of V2O5/Al2O3 catalysts exhibit only a single peak at low temperature up to 15 wt% V2O5. It is suggested that the low-temperature reduction peak is due to the reduction of surface vanadia, which has been ascribed to the tetrahedral coordination geometry of the V ions. TPR Of V2O5/Al2O3 at higher vanadia loadings exhibited three peaks at reduction temperatures, indicating that bulk-like vanadia species are present for these catalysts only at higher vanadia loadings, with V ions in an octahedral coordination. The TPR profiles Of V2O5/Al2O3 catalysts indicate that at loadings lower than 15% vanadia forms isolated surface vanadia species, while two-dimensional structure and V2O5 crystallites become prevalent in highly loaded (>15% V2O5) systems. Liquid-phase oxidation of ethylbenzene to acetophenone has been employed as a chemical probe reaction to examine the catalytic activity. Ethylbenzene oxidation results reveal that 15% V2O5/Al2O3 is more active than higher vanadia loading catalysts. (C) 2003 Elsevier Inc. All rights reserved.