Study Of New Catalysts Supported On ZSM-5 Zeolite For Propane Dehydrogenation

Pt/ZSM-5,PtSn/ZSM-5,PtSnNa/ZSM-5 and PtSnNaLa/ZSM-5 catalysts were prepared on ZSM-5 zeolite for propane dehydrogenation and the catalysts were characterized by several techniques.The best Pt content and suitable Si/Al ratio of ZSM-5 zeolite were confirmed on Pt/ZSM-5 catalyst. Although the initial reaction activity of Pt/ZSM-5 catalyst was high, the reaction stability and selectivity to propene were poor. Suitable addition of Sn could improve the catalytic behavior of Pt/ZSM-5 catalyst for propane dehydrogenation obviously. In order to discuss the possible reasons, several techniques including BET surface area, XRD, hydrogen chemisorption, H₂-TPD, TPR, TPO and thermogravimetric analysis were used to get their physical structure, surface character of Pt, interactions between metal and carrier and anti-coking property. Comparing with PtSn/γ-Al₂O₃ catalyst, the capacity to accommodate the coke of PtSn/ZSM-5 catalyst was much better, which resulted in the improved reaction stability. Moreover, the deactivation process of Pt/ZSM-5 catalyst was studied and the formula between the carbon amount and reaction time of Pt/ZSM-5 catalyst at the beginning of reaction and the formula about the coke velocity were obtained.The best content of Na in PtSnNa/ZSM-5 catalyst was 1.0%. In this case, the addition of Na could not only reduce the Br(o|¨)nsted acid sites and moderate/strong Lewis acid sites, but also increase the fraction of bare metallic Pt on the surface of the catalyst, thus making the matching between acid functions and metal functions stand at the best state. However, the excessive addition of Na increased the amount of Lewis acid sites and promoted the reduction of Sn species, which was disadvantageous to the reaction. Different reaction conditions could have obvious impacts on the reaction performance of PtSnNa/ZSM-5 catalyst in the dehydrogenation of propane.The addition of alumina binder in PtSnNa/ZSM-5 catalyst could increase the particle intensity obviously. The results of ²⁷Al MAS NMR indicated that some Al species from the binder could migrate into the zeolite framework in calcination so as to produce some acid sites of moderate intensity. The best content of...