Conversion of furan over gallium and zinc promoted ZSM-5: The effect of metal and acid sites

Abstract

The addition of gallium or zinc to ZSM-5 increases the aromatic selectivity and decreases the olefin selectivity for furan conversion. Both the benzene and naphthalenes selectivities increase with small amounts of gallium or zinc addition. At 5 wt% metal loading this effect is more pronounced with zinc promoted ZSM-5 having about 25% higher benzene selectivity than the gallium promoted ZSM-5. Additionally, the decarbonylation and methane formation reactions were both increased by adding zinc or gallium to the catalyst. As zinc or gallium loading is increased, the amount of Brønsted acid sites decrease, while the quantity of Lewis acid sites increase. This effect was more pronounced with zinc, as a result of its greater effectiveness to exchange with protons at the Brønsted acid sites. The aromatic yield appears to correlate with this increase in Lewis acidity. The addition of zinc to ZSM-5 also altered the reaction chemistry occurring during the hydrolysis of furan, lowering propylene and increasing methane yields as zinc loading increased.