Adsorption studies of acylation reagents and products on zeolite beta catalysts

Abstract

Abstract We report in situ infrared spectroscopy of the adsorption of acetic anhydride, acetic acid and 4-methoxyacetophenone on H-BEA and Na-BEA. The results are intended to cast light on the mechanism of acylation by H-BEA and other materials, and are interpreted in the light of a temperature programmed desorption study that we have recently reported, [1]. On Na-BEA there is relatively little perturbation of the spectrum of adsorbed acetic anhydride, compared to that of the free molecule, although even here the presence of more strongly and weakly bound states can be differentiated. Even here, there is some indication that the adsorbed anhydride decomposes into adsorbed acetic acid. Much of the adsorption of acetic acid on H-BEA is molecular, but again the spectra and correlated temperature desorption results show the presence of both strongly and more weakly adsorbed states. The most complex spectra are observed for acetic anhydride adsorbed on H-BEA. The species observed initially is acetic acid rather than the anhydride, and complex spectra and desorption patterns result as the adsorption pressure is increased. 4-methoxyacetophenone is more weakly adsorbed than either the acid or the anhydride.