Effect of K Promoter on the Performance of Pt-Sn-K/gamma-Al2O3 Catalyst for n-Hexadecane Dehydrogenation

A Pt-Sn-K/gamma-Al2O3 catalyst was prepared by complex impregnation under vacuum. The effect of the K promoter on the catalytic properties of the Pt-Sn-K/gamma-Al2O3 catalyst for the dehydrogenation of long-chain paraffins to mono-olefins was investigated using n-hexadecane dehydrogenation as a test reaction. The catalyst was characterized by infrared spectroscopy of pyridine adsorption, CO pulse chemisorption, temperature-programmed reduction with H-2, thermogravimetric analysis, and temperature-programmed oxidation with O-2. The results show that the addition of K decreases the interaction of SnOx and Al2O3, promotes the reduction of SnOx species, and suppresses the catalyst activity for dehydrogenation. The K promoter also neutralizes the acidity and decreases the amount of strong acidic centers of the catalyst. Thus, the side reactions on the catalyst are inhibited, and the selectivity for monoolefins is increased. The stability of the catalyst is slightly enhanced with the addition of K because of the increased resistance to coke formation on the catalyst. However, the synergistic effect of active sites and acidic sites is weakened by the excess addition of the K promoter, which results in a great decrease in the activity and a low stability of the catalyst.