Characterization of Ga/HZSM-5 and Ga/HMOR synthesized by chemical vapor deposition of trimethylgallium

Abstract

Chemical vapor deposition (CVD) of trimethylgallium (TMG) has been studied as a method to disperse extraframework Ga in acidic ZSM-5 and mordenite zeolite. Various samples were extensively characterized by ICP, XPS, NMR, and FTIR. Silylation with tetramethyldisilazane is explored as a method for deactivating the external zeolite surface. The deposition of TMG in silylated ZSM-5 results in a gallium-to-aluminum ratio close to unity, which indicates a homogeneous metal distribution in the micropore space. However, pore blockage in the one-dimensional channels of mordenite results in a inhomogeneous distribution and a low Ga loading. Upon exposure to moistened air, the adsorbed methylgallium species decompose and alkoxy groups are formed. Subsequent oxidation or reduction leads to the complete removal of methyl groups. The reductive route is the preferred one resulting in a better dispersion of Ga, since oxidation of the methyl groups leads to water formation and hydrolysis of cationic Ga species