水蒸气对Pt-Sn/Al_2O_3催化剂结构及其催化丙烷脱氢反应性能的影响

Effects of steam on the structure and catalytic performances of Pt-Sn/Al_2O_3 for propane dehydrogenation

采用分步等量浸渍法制备了不同Sn/Pt摩尔比的Pt-Sn/Al_2O_3催化剂,利用CO-DRIFTS,H_2-Chem,XPS等手段对催化剂进行表征,考察了水蒸气添加量对催化剂结构及其催化丙烷脱氢反应性能的影响,探讨了水蒸气对丙烷脱氢反应性能影响的作用机理。实验结果表明,水蒸气对低Sn/Pt摩尔比催化剂的活性具有抑制作用,而对高Sn/Pt摩尔比催化剂的活性具有促进作用,水蒸汽对催化活性的抑制作用主要是由于水在Pt表面吸附解离生成的含氧物种与脱氢物种之间存在相互作用及水蒸气会促进Pt颗粒的烧结;而水蒸气通过对Sn的氧化和分散作用暴露更多的Pt表面起到促进催化剂活性的作用;催化剂在水蒸气中反应时具有较高的失活程度,而Sn的引入提高了催化剂的稳定性。

Pt-Sn/Al2O3 catalysts with different Sn/Pt mole ratio were prepared through incipient wet impregnation and characterized by means of CO-DRIFTS,H2-Chem and XPS. The effects of steam on the structures of the catalysts and their performances in propane dehydrogenation were investigated. The results revealed that,steam could inhibit the activity of the catalysts with low Sn/Pt ratio and promote the activity of the catalysts with high Sn/Pt ratio. The inhibition was due to the interaction between dehydrogenation species and oxygenation species on the Pt surface and the sintering of Pt particles,while the oxidation and dispersion of Sn from Pt-Sn particles caused by steam would help to expose more active Pt surface,which was beneficial to improving the activity of the catalysts. So the presence of steam would lead to the catalyst deactivation,and the addition of Sn could improve the stability of the catalysts.