Effects of alkali promoters on catalytic properties of alumina-supported Pt-Sn catalysts for long-chain paraffin dehydrogenation

The influence of alkali metal ion promoters on the catalytic properties of Pt-Sn/gamma -Al2O3 catalysts for the long-chain paraffin (C(10)similar toC( 13)) dehydrogenation has been studied by H-2 chemisorption, infrared spectr oscopy (IR), thermogravimetry (TG), temperature-programmed reduction (TPR) and microreactor testing. The results show that adding Li+ and Na+ to the P t-Sn/gamma -Al2O3 catalyst can improve its selectivity and stability for th e paraffin dehydrogenation by decreasing the amount of coke formed on the c atalysts and increasing the fraction of bare metallic Pt surface after carb on deposition. However, the addition of K+ and Cs' with higher basicity lea ds to a remarkable decrease in the catalytic activity of the Pt-Sn/gamma -A l2O3 catalyst. Tin oxides in the Pt-Sn-Cs/gamma -Al2O3 catalyst can be easi ly reduced to metallic tin, which might form alloy particles with Pt, so th at the H-2 uptake and the catalytic activity of the catalyst decrease drast ically.