采用固定床微型反应装置,结合催化剂的原位电子自旋共振光谱、程序升温表面反应和紫外漫反射光谱等技术,研究了丙烷氧化脱氢的介孔氧化硅负载钒氧化物催化剂的性能和表面氧物种的状态及其反应性.结果表明,催化剂载体孔结构是影响钒氧物种分散状态乃至催化性能的一个重要因素.SBA-15负载钒氧化物催化剂因具有较大的比表面积和较大的孔径,不仅具有较高的丙烷氧化脱氢催化活性,而且具有较高的丙烯选择性.复合型钒氧化物催化剂表面与V离子相连的晶格氧物种是丙烷氧化脱氢牛成内烯的主要活性物种,载体表面高度分散的钒氧物种具有较高的丙烷氧化脱氢催化活性.负载型钒氧化物催化剂晶格氧物种是丙烷氧化脱氢转化为丙稀的主要活性物种,CO_2分子可以再生钒氧化物催化剂的晶格氧物种,同时它对丙烯的深度氧化作用较弱,因此在负载型钒氧化物催化剂上CO_2氧化丙烷可高选择性地生成丙烯.
The state and reactivity of surface oxygen species of mesoporous silica-supported vanadium oxide catalysts for oxidative dehy- drogenation of propane have been investigated by microreactor tests combined with in-situ electron spin resonance, tempera- ture-programmed surface reaction, and ultraviolet-visible diffuse reflectance spectroscopy. The pore diameter of the SBA-15, MCM-41, and silica gel supports exert great influences on the dispersion state of VO_x species and the catalytic properties of the supported vanadium oxide catalysts. The SBA-15-supported vanadium oxide catalyst has the highest selectivity for propylene because of its larger pore diameter and higher surface area. Surface lattice oxygen species of the VOx/SBA-15 catalyst are main active species for oxidative dehydrogenation of propane to propylene. Highly dispersed VO_x species have high catalytic reactivity for oxidative dehydrogenation of propane. CO_2 can regen-erate the lattice oxygen species of supported vanadium oxide catalysts. The high propylene selectivity for oxidative dehydrogenation of pro- pane by CO_2 on supported vanadium oxide catalysts is related to weaker oxidizing effect of CO_2, which inhibits the direct C_3H_8 oxidation and the consecutive oxidation of C_3H_6 to CO_x.
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