A study of the non-aqueous dealumination and gallium impregnation of H-mordenite by chlorinated reagents

Abstract

The in vacuo dealumination of H-mordenite by carbon tetrachloride followed by gallium impregnation using gallium(III) chloride has been studied by diffuse reflectance IR spectroscopy (DRIFTS), ⁷¹Ga, ²⁹Si, and ²⁷Al solid-state magic-angle spinning (MAS) NMR. Comparative studies of the interaction of carbon tetrachloride with silica and γ-alumina were also performed. IR and DRIFTS analyses of silica and γ-alumina samples show that the reaction of carbon tetrachloride at elevated temperatures can completely remove silanol and aluminol moieties at the surface of the respective oxides. The removal of intra-lattice aluminium ions is consistent with abstraction by Al³⁺ ion pairs. Solid state ¹H NMR data, in conjunction with IR and DRIFTS analysis of the dealuminated and gallium-impregnated H-mordenite samples confirms the formation of strong Brønsted acid protons by the reaction of carbon tetrachloride. The in vacuo probe reactions of H-mordenite, dealuminated H-mordenite and gallium impregnated H-mordenite, with methanol vapour, were studied as a function of temperature. The probe reactions show that the conversion of methanol vapour with the treated H-mordenite material is a function of the reaction temperature and the chemical modification to the H-mordenite. The activity of the treated H-mordenite to produce hydrocarbons from methanol follows the series gallium impregnated H-mordenite > dealuminated H-mordenite > H-mordenite. The product distribution supports the observation that the surface adsorbed mechanisms are consistent with a series of ionogenic intermolecular reactions occurring at dual Brønsted acid–base environments within the zeolite channels. These mechanisms account for the formation of higher alcohols from methanol by the combination of carbo-ionogenic moieties and hydrocarbons produced from the dehydration of alcohols.