High metal-loading Ga/SiO2 and Ga/Al2O3 catalysts were synthesized to investigate the effect of support materials on the catalyst structures and catalytic performance for olefin oligomerization. XAS analysis revealed that Ga3+ ions with four Ga-O bonds interact differently with SiO2 and Al2O3 supports, with two Ga-O-Si bonds on Ga/SiO2 and four Ga-O-Al bonds on Ga/Al2O3. Pyridine IR spectra confirmed the presence of Lewis acid sites without Brønsted acid sites on both catalysts, with Ga/SiO2 exhibiting stronger Lewis acidity. While Lewis acids are not typically known to react with hydrocarbons, under coordinated Lewis acidic Ga3+ sites were found to catalyze oligomerization and secondary reactions including hydrogen transfer, olefins isomerization, and C-C bond fragmentation, leading to non-oligomer products. These non-oligomer products can further react at higher conversions, leading to the formation of other higher molecular weight non-oligomers. Thus, this work aims to elucidate the source of non-oligomer products from olefin oligomerization at elevated temperatures. Given that C6 olefins are the major primary products in both ethylene and propylene oligomerization on Lewis acidic Ga/SiO2 and Ga/Al2O3 catalysts, it is hypothesized that these C6 olefins undergo secondary reactions such as C-C bond fragmentation on Lewis acidic Ga3+ sites. Both experimental and theoretical studies will be presented to provide insight into the C–C bond fragmentation pathway on Ga3+ Lewis acid catalysts for olefin oligomerization.
