Aqueous phase reforming and hydrodeoxygenation of ethylene glycol on Pt/SiO₂-Al₂O₃: Effects of surface acidity on product distribution

Aqueous-phase reforming (APR) and aqueous-phase hydrodeoxygenation (APH) reactions of ethylene glycol (EG) were investigated using platinum supported solid-acid SiO₂-Al₂O₃ catalysts with different Si/Al molar ratios. The molar ratio of Si/Al on the SiO₂-Al₂O₃ mixed metal oxides largely altered the surface area due to changes to the acidity, as well as changing the reduction behavior of the supported platinum nanoparticles. The Pt/SiO₂-Al₂O₃ catalysts with a Si/Al molar ratio of 0.1 showed a higher activity for APR as well as APH. Among the various properties of Pt/SiO₂-Al₂O₃, the amount of acid sites on the SiO₂-Al₂O₃ supports changed the EG conversion and production distribution with different coke depositions. The acidic property was a more dominant factor for the catalytic activity than the affects of the platinum crystallite size on the reduction behavior. The easy and simultaneous cleavages of C-C as well as the C-O bonds in EG on the Bronsted acid sites of Pt/SiO₂-Al₂O₃ catalysts were responsible for a higher EG conversion and hydrocarbon formation. A larger number of weak acid sites was also related to the formation of larger hydrocarbons and a lower coke deposition. Compared with Pt/Al₂O₃, improved catalytic acidity with a low coke deposition was observed for Pt/SiO₂-Al₂O₃ at a Si/Al molar ratio of 0.1. This can mainly be attributed to the easy control of weak and strong acid sites with a high dispersion of platinum crystallites by simply changing the Si/Al molar ratio of the SiO₂-Al₂O₃ mixed metal oxides.