EFFECT OF SIAL RATIO AND TYPE OF BINDER ON THE CATALYTIC PROPERTIES OF HZSM-5 CATALYSTS

Different HZSM-5 catalysts have been prepared by mixing and shaping de aluminated HZSM-5 zeolite samples with aerosil and boehmite as binder components. Catalytic investigations, adsorption measurements, tempera ture-programmed desorption studies and infrared spectroscopy with prob e molecules were carried out to characterize the catalyst properties. The catalysts were tested in the coupled methanol-hydrocarbon cracking (CMHC) reaction with n-butane as hydrocarbon feed. In general, the ca talytic data show inhibition of the deactivation resulting in lower co king, increased alkene yields and longer working periods with increasi ng Si : Al ratio independent of the nature of the binder. Comparing th e data obtained from the two series with different types of binder we concluded that boehmite has not only a binder function but also a prom oting effect on the catalyst properties. Thus, the catalyst activity w as maintained at a more stable level owing to higher cracking activity and reduced rate of dealumination. Temperature-programmed desorption and IR spectroscopy were applied to determine the Bronsted and Lewis a cidity of fresh and used samples. It was established that the addition of boehmite causes a partial neutralization of Bronsted sites. Moreov er, the acid sites of the admixed boehmite influence considerably the acidic and catalytic properties of the catalyst.