V_2O_5/TiO_2催化剂的表面结构和酸碱性及氧化还原性

Structure,Surface Acidity/Basicity and Redox Properties of V_2O_5/TiO_2 Catalysts

研究了一系列锐钛矿担载的钒氧化物催化剂的表面性质 .X射线衍射和Raman光谱表明 ,8%V2 O5/TiO2 催化剂上的V2 O5处于单层分散状态 .程序升温还原研究表明 ,单层分散的钒物种较易被还原 ,而形成多聚态和晶态后钒物种的还原温度升高 .NH3 吸附量热结果表明 ,在钒物种达到单层分散前 ,催化剂的表面酸性随钒担载量的增加而减弱 ,超过单层分散后 ,表面酸位的数目和强度基本不变 .异丙醇脱氢 /脱水反应结果表明 ,有O2 时V2 O5/TiO2 催化剂显示出很强的氧化还原性 ,无O2时催化剂的脱水选择性较高 .通过异丙醇的脱氢 /脱水反应 ,将V2 O5/TiO2

The TiO 2 (anatase) supported vanadia catalyst with different vanadia loadings has been prepared and characterized by X ray diffraction (XRD), Raman spectroscopy, temperature programmed reduction (TPR), and NH 3 microcalorimetric adsorption. XRD and Raman spectroscopy show that a monolayer coverage of vanadia is formed over the 8%V 2O 5/TiO 2 catalyst. TPR profiles reveal that the monolayer dispersed vanadia species are easier to be reduced than the polymeric and crystalline species formed when the vanadia loading exceeds the monolayer coverage. Microcalorimetric adsorption of NH 3 indicates that the acidity of the V 2O 5/TiO 2 catalyst decreases with the increase in V 2O 5 loading up to the monolayer coverage and remains unchanged above the monolayer coverage. The reaction behavior of the V 2O 5/TiO 2 catalyst in the dehydrogenation and dehydration of isopropanol is correlated with their surface properties. The V 2O 5/TiO 2 catalyst exhibits mainly redox properties when the reaction is carried out at the presence of O 2. The selectivity for acetone is greater than 95%, which is almost independent of the vanadia loading. When the reaction is carried out in N 2 (without O 2) the catalyst shows both acidity and redox properties. In this case, the selectivity for acetone increases and the selectivity for propylene decreases with increasing vanadia loading. Over the 10%V 2O 5/TiO 2 catalyst, the selectivity for acetone is almost equal to the selectivity for propylene. As the surface acidity is concerned, the results of the isopropanol dehydrogenation and dehydration correlate well with those of the microcalorimetric adsorption of NH 3. This indicates that the reaction can be used as a proper probe reaction for the characterization of the surface acidity and redox properties of metal oxide catalysts.