Catalytic structure and reaction performance of PtSnK/ZSM-5 catalyst for propane dehydrogenation: influence of impregnation strategy

In this study, a series of PtSnK/ZSM-5 catalysts for propane dehydrogenation were prepared by changing the impregnation sequence of platinum and tin precursors (co-impregnation and successive impregnation). To investigate the influence of impregnation strategy on the catalyst structure and the reaction performance, the prepared samples were studied by several techniques, including XRD, nitrogen adsorption, ICP, TEM, NH3-TPD, FT-IR, hydrogen chemisorption, H2-TPR, and TPO. It was found that the prepared sample with co-impregnation method showed the highest reaction stability and selectivity when comparing with the ones prepared by the sequential impregnation. As for the co-impregnated catalyst, high metal dispersion, strong interaction of Pt with Sn oxide together with the decreased catalyst acidity were all responsible for the improved reaction properties and better catalytic capacity to resist the coke. Nevertheless, over the sequentially impregnated catalysts, the increased catalyst acidity and the relatively easy reduction of tin species were found when the Pt components were deposited first. Furthermore, the successive impregnation with inverse sequence led to the wide metallic distribution and the restricted transformation of the active sites. All of these factors were disadvantageous to the reaction to be carried out. Finally, a model for the influences of impregnation sequence was proposed based on the obtained results.