Spectroscopic and catalytic characterization of faujasites dealuminated via the (NH<inf>4</inf>)<inf>2</inf>SiF<inf>6</inf> method

Abstract

Four dealuminated Y-type zeolites were prepared by treatment of NH4Y with (NH4)2SiF6. An in-depth characterization of the materials was carried out using XRD, TGA/DTG, i.r. spectroscopy, TPD of ammonia and pyridine, and ethyl benzene disproportionate as a catalytic test reaction. The results of i.r. spectroscopy indicate that with increasing degree of dealumination the density of Bron-sted acid sites decreases. At the same time, an enhancement of the acid strength was established by temperature programmed desorption of ammonia and pyridine. The steady state activity in the ethylbenzene disproportionation increases with decreasing aluminum content up to an Si/Al ratio of ca. 6 due to the enhancement of acid site strength. As a whole, ethylbenzene disproportionation is shown to be a sensible test reaction for the characterization of acidity of dealuminated zeolites. It was discovered that dealumination via the Skeels and Breck method brings about a sharp reduction of the induction period in the catalytic disproportionation of ethylbenzene. © Elsevier Science Publishers B.V.