A series of vanadium-substituted phosphomolybdic acid (HPA) catalysts supported on zirconia were prepared by impregnation method with varying the HPA active phase content from 10 to 50 wt% on the support. The calcined catalysts were characterized by X-ray diffraction, Raman spectroscopy, temperature-programmed desorption of NH3, FT-IR spectra of pyridine adsorption and surface area measurements. XRD results suggest that the active phase of heteropolyacid is present in a highly dispersed state at lower loadings and as a crystalline phase at higher HPA loadings and these findings are well-supported by the results of FT-IR and Raman spectra. Calcination of the samples did not affect the Keggin ion structure of HPA. The ammonia TPD results suggest that acidity of the catalysts was found to increase with increase of HPA loading up to 40 wt% and decreases at higher loadings. FT-IR spectra of pyridine adsorption show that the Brønsted acidic sites increase with increase of HPA loadings up to 40 wt% catalyst. However, Lewis acid sites decrease with increase of HPA loading. Catalytic properties were evaluated during vapour phase dehydration of glycerol to acrolein. The catalyst with 40 wt% HPA has exhibited excellent selectivity towards acrolein formation with complete conversion of glycerol at 225°C under atmospheric pressure. Catalytic performances during dehydration of glycerol are well-correlated with acidity of the catalysts.
采用浸渍法制备了一系列负载在
氧化锆上的
钒取代
磷钼酸(HPA)催化剂,通过在载体上改变HPA活性相含量从10到50 wt%。焙烧后的催化剂通过X射线衍射、拉曼光谱、程序升温
氨气脱附、
吡啶吸附FT-IR光谱和比表面积测量进行表征。XRD结果表明,在较低负载量时,杂多酸的活性相处于高度分散状态,而在较高HPA负载量时则呈结晶态,这些发现得到了FT-IR和拉曼光谱结果的良好支持。样品的焙烧并未影响HPA的Keggin离子结构。
氨气
TPD结果表明,催化剂的酸度随着HPA负载量的增加至40 wt%而增加,在更高负载量时则降低。
吡啶吸附FT-IR光谱显示,Brønsted酸性位点随着HPA负载量的增加至40 wt%催化剂而增加。然而,Lewis酸位点随着HPA负载量的增加而减少。催化性能在气相
甘油脱
水制
丙烯醛的过程中进行了评估。含40 wt% HPA的催化剂在225°C、常压下对
丙烯醛的生成表现出优异的选择性,
甘油转化率完全。
甘油脱
水过程中的催化性能与催化剂的酸度密切相关。