Acid-base property of the supporting material controls the selectivity of Au catalyst for glycerol oxidation in base-free water

Abstract

Glycerol (GL) valorization by catalytic aerobic oxidation in water over Au-based catalysts usually produces a number of products. A soluble base (usually NaOH) is often added to the reaction solution to promote GL activation and affect the product distribution. We report in this study the support effect on the catalysis of Au nanoparticles (NPs) for GL oxidation in base-free water on a series of supporting MgO-Al2O3 materials. The acid-base property on the surfaces of these MgO-Al2O3 supports were systematically varied by tuning the molar Mg/Al ratio (x) before they were loaded with the catalytic Au NPs. Au NPs on the most acidic and least basic MgO-Al2O3 exhibited the highest activity for GL activation and the highest selectivity for dihydroxyacetone (DHA) production. Increasing the surface basicity or lowering the acidity of the MgO-Al2O3 support results in continuously improved selectivity for glyceric acid (GLA) but lowered the selectivity for DHA. These correlations disclose for the first time that the support acid-base property inversely affects the formation of DHA and GLA, and demonstrate that the support acidity/basicity is a key to the selectivity control of their carrying Au NPs for GL oxidation.