不同P与V比的Mo/VPO催化剂物相组成及其催化性能

Phase composition and catalytic performance of Mo/VPO catalysts with different P/V molar ratios

采用有机相法制备了不同P与V物质的量比的Mo掺杂VOHPO4·0.5H2O前驱体,并通过体积分数为50%空气-40%氮气-10%水蒸汽混合气氛活化得到Mo/VPO催化剂,采用固定床反应器评价其催化正丁烷氧化制顺酐的性能。结果表明,Mo/VPO催化剂催化活性随P与V物质的量比的增大而降低,但顺酐选择性与P与V物质的量比并不呈线性关系,P与V物质的量比为0.9的Mo/VPO催化剂具有最佳的催化性能。XRD分析表明,Mo/VPO催化剂催化正丁烷氧化制顺酐的主要活性物相为(VO)2P2O7和钒磷云母相,形成的主要因素不是P与V物质的量比,而是由焙烧条件决定。低P与V物质的量比的Mo/VPO中存在的少量V2O5物相能够提升催化剂的活性和顺酐选择性,但含量过高会因深度氧化降低催化性能。催化剂中存在的钒磷云母相有利于缩短催化剂稳定时间并提升催化性能。

A series of Mo doped VOHPO4 · 0. 5H2O precursors with different P/V molar ratios was prepared by organic method. Mo/VPO catalysts were obtained by calcining the precursors and then activating in the mixed gas atmosphere 50% air-40% N2-10% steam （ volume fraction）. The catalytic performance of the catalysts for the oxidation of n-butane to maleic anhydride was investigated in a fixed bed reactor. The results showed that the activity of Mo/VPO catalyst was weakened with the increase of P/V molar ratios, and the selectivity to maleie anhydride had no linear relationship with P/V molar ratios. Mo/VPO catalyst with P/V molar ratio 0.9 exhibited the best catalytic performance. The results of XRD characterization indicated that the main active phases of Mo/VPO catalyst for the oxidation of n-butane to maleic anhydride were （VO） 2 P2O7 and V/P mica phases, the formation of which were depended on the calcination conditions. A small amount of V2O5 in Mo/VPO catalyst with low P/V molar ratio was benefitial to the enhancement of catalyst activity and the selectivity to maleic anhydride. Excess V2O5 , however,lowered the selectivity to maleic anhydride because of deep oxidation. V/P mica phase existed in the catalyst had a great effect on shortening activation time and improving the selectivity to maleic anhydride according to the activation tests.