Dehydroaromatization of methane over Sn–Pt modified Mo/H-ZSM-5 zeolite catalysts: Effect of preparation method

Abstract

The effect of different catalyst preparation methods to make tin–platinum modified Mo/H-ZSM-5 zeolite catalysts for methane dehydroaromatization at 700°C was investigated. The catalysts were prepared by both incipient wetness co-impregnation and sequential impregnation and calcined at 500°C for 6h. Catalysts prepared by the co-impregnation method showed a good platinum dispersion (10.8%), higher than found for the Pt/Sn and Sn/Pt sequentially impregnated catalysts (5.6% and 1.4%, respectively). Successive calcination treatments influenced the location of both tin and platinum in the catalyst and a decrease in platinum dispersion after reduction was evident from CO chemisorption studies. The order of sequentially loading platinum before or after tin had an effect on the electronic and structural properties of platinum as shown by XPS and FTIR studies. Different catalytic activities and aromatic selectivities were observed for the Pt/Sn and Sn/Pt catalysts. The co-impregnated Sn–Pt and the sequentially impregnated Pt/Sn catalysts showed high aromatic selectivity (>70%) and low coke selectivity (<20%). The decrease in coke selectivity is mainly dependent on the availability of platinum sites for hydrogenation of carbonaceous species.