Catalytic conversion of propane to BTX over Ga, Zn, Mo, and Re impregnated ZSM-5 catalysts

A systematic study of the comparative performances of 1 wt.% and 3 wt.% Ga, 1 wt.% and 3 wt.% Zn, 3 wt.% Mo, and 3 wt.% Re impregnated ZSM-5 catalysts for propane aromatization is presented. It was found that methane, ethene, ethane, benzene, toluene, and xylene are the major products on all of these catalysts at typical propane aromatization temperature (∼550 °C). 3% Zn/ZSM-5 catalyst shows the highest propane conversion among all the tested catalysts with approximately 56% total selectivity toward benzene, toluene, and xylene (i.e., BTX) but lower selectivity to methane, ethene, and ethane (i.e., light hydrocarbons). In sharp contrast, 3% Mo/ZSM-5 catalyst shows the lowest activity with lower BTX selectivity but as high as 52% total selectivity toward methane, ethene, and ethane. Further, calculations indicate that 1% Zn/ZSM-5 catalyst displays the highest H2 and BTX formation rates (mmol/s/mol-metal), followed by 1% Ga, 3% Re, 3% Zn, and 3% Ga impregnated ZSM-5 catalysts, while 3% Mo/ZSM-5 catalyst shows remarkably lower H2 and BTX formation rates. This suggests that the addition of 1% Zn into ZSM-5 via impregnation significantly improves the dehydrogenation and subsequent chain growth reaction as well as cyclization, thereby favoring propane aromatization. However, compared to other promoters (i.e., Zn, Ga, and Re), the promotional effect of Mo over ZSM-5 is insignificant for propane aromatization, thus resulting in substantial formation of methane, ethene, and ethane.