IR and TPD studies of the reaction of acetic acid in zeolites NaHY

Abstract

IR and TPD experiments have shown that the reaction of acetic acid in zeolite NaHY (at 370–470 K) consumes Si–OH–Al groups and produces acetate ions and water. This suggests that zeolitic Si–OH–Al which are strong acid sites (proton donors) may also act as proton acceptors from organic acids. Whereas acetic acid was sorbed in zeolite NaY, which did not contain OH, groups acetate ions were practically not formed. The sorption of acetic acid in zeolite NaHY dehydroxylated by calcination at high temperature (1100 K) formed acetate ions more easily (at room temperature) than in non-dehydroxylated zeolite. It suggests that the sites produced by dehydroxylation were more active in the reaction with acetic acid than Si–OH–Al groups. The possibility, that extraframework Al species, which play the role of Lewis acid sites, are so much reactive with acetic acid cannot be excluded. The extraframework Al species created in zeolite HY by steaming, as well as those present in HMCM-41 were also found to be more reactive against acetic acid than zeolitic Si–OH–Al. We also studied the adsorption of acetic acid on the surface of magnesia, alumina, and silica. In the case of magnesia and alumina the acetate ions were very easily formed at room temperature, indicating that Mg–OH, Al–OH or surface oxygens were better acceptors of protons from acetic acid than Si–OH–Al groups. Acetate ions in zeolite were found to be quite stable. They decomposed above 570 K, producing mostly CO 2, CO and ethane.