Surface acidity and catalytic behavior of modified zirconium and titanium dioxides

Abstract

Various modified zirconium and titanium dioxides were examined as catalysts for the following test reactions: the gas phase alkylation of 1-butene with isobutane, the double bond isomerization of 1-butene and the disproportionation of dichlorodifluoromethane. The catalysts were prepared by treatment of the precipitated oxide hydrates with either fluorinating, chlorinating, sulfatizing or phosphating agents. The nature of the acid sites was determined by IR spectra of pyridine adsorption complexes and correlated with the catalytic behavior. An activation of zirconium dioxide with sulfur tetrafluoride led to the formation of a larger number of Bronsted acid sites than those obtained for sulfated zirconia. The isooctane yields during the alkylation offered a similar graduation. An enhancement of the number and strength of Lewis acid sites presupposed for the disproportionation test reaction was not observed. Samples based on titanium dioxide exhibited an overall lower catalytic activity. The reaction mechanism of the alkylation of 1-butene with isobutane was proposed.