Surface acidic and redox properties of V-Ag-Ni-O catalysts for the selective oxidation of toluene to benzaldehyde
Surface acidic and redox properties of V-Ag-Ni-O catalysts for the selective oxidation of toluene to benzaldehyde
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DOI：
10.1016/j.apcata.2007.07.014
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发表时间：
2007-10
影响因子：
5.5
通讯作者：
Mingwei Xue;Jiazhen Ge;Hui-liang Zhang;Jianyi Shen
中科院分区：
文献类型：
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作者：
Mingwei Xue;Jiazhen Ge;Hui-liang Zhang;Jianyi Shen
V-Ag-O和V-Ag-Ni-O复合氧化物对甲苯选择氧化制苯甲醛具有良好的催化活性。为了了解每种金属在两种催化剂中的作用，制备了一系列单一和复合氧化物，包括V_2O_5，Ag_2O，NiO，V-Ni-O，Ag-Ni-O，V-Ag-O和V-Ag-Ni-O。X射线衍射（XRD）、红外光谱和激光拉曼光谱分析结果表明，样品中形成了具有银和镍钒酸盐相的复合氧化物，VO键的吸收峰发生了展宽和红移，表明形成了VOAg和VONi键，提高了钒物种的氧化还原能力。程序升温还原（TPR）和TPR-XRD联用技术的结果表明，Ag和Ni的加入促进了复合催化剂中钒物种的还原。微量吸附量热法和异丙醇在空气中的探针反应表明，表面酸性大大降低，而钒位的氧化还原循环显着增强后，添加Ag和Ni。采用固定床微反评价了催化剂的甲苯选择氧化反应活性，并与催化剂的表面酸性和氧化还原性能进行了关联。银是一种特殊的促进剂，它不仅降低了催化剂的表面酸性，而且增强了催化剂上钒中心的氧化还原循环，从而提高了甲苯的转化率和苯甲醛的选择性。当同时加入Ag和Ni时，这种效果甚至更明显。因此，本研究中所研究的V-Ag-Ni-O催化剂对甲苯选择氧化制苯甲醛表现出优异的性能。在613 K时甲苯转化率为8%，苯甲醛选择性为95%。
V-Ag-O and V-Ag-Ni-O complex oxides were found to exhibit good catalytic reactivity for the selective oxidation of toluene to benzaldehyde. In order to understand the effects of each metal in the two catalysts, a series of single and complex oxides were prepared including V2O5, Ag2O, NiO, V-Ni-O, Ag-Ni-O, V-Ag-O and V-Ag-Ni-O with the previously optimized compositions for the binary and tertiary oxides. Data from the X-ray diffraction (XRD), infrared spectroscopy and laser Raman spectroscopy showed the formation of complex oxides with phases of silver and nickel vanadates as well as the broadening and red shift of the band of VO bonds, suggesting the formation of VOAg and VONi bonds and the increased redox ability of vanadium species. The results from temperature programmed reduction (TPR) and the combined technique of TPR-XRD revealed that the addition of Ag and Ni promoted the reduction of vanadium species in the complex catalysts. Microcalorimetric adsorption of ammonia and the probe reaction of isopropanol in air demonstrated that the surface acidity was greatly decreased while the redox cycles of vanadium sites were significantly enhanced upon the addition of Ag and Ni. The reactivity for the selective oxidation of toluene was evaluated by using a fixed-bed microreactor, and was correlated with the surface acidity and redox property of the catalysts. Silver seemed to be a special promoter that not only decreased the surface acidity but also enhanced the redox cycles of vanadium sites, leading to the increased conversion of toluene and the selectivity to benzaldehyde. Such effect was even more pronounced when Ag and Ni were added simultaneously. Accordingly, the V-Ag-Ni-O catalyst studied in this work exhibited excellent performance for the selective oxidation of toluene to benzaldehyde. The conversion of toluene was found to be 8% with 95% selectivity to benzaldehyde on the V-Ag-Ni-O at 613K.