LAUSR

ABSTRACT Bifunctional catalysts that contain both metal and acidic functions have been widely used in renewable biomass conversions. The bifunctionality closely depends on the distance between the metal and acid sites. However, the metal–acid proximity effect has rarely investigated in biomass conversions. In this work, we precisely deposited a porous Al 2 O 3 overcoat onto a Pt/Al 2 O 3 catalyst using atomic layer deposition to improve the proximity between the Pt metal and the alumina acid sites by increasing the area of the metal–acid interface. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of pyridine chemisorption confirmed that the overall catalyst acidity did not change considerably after applying the alumina overcoat. In the aqueous-phase, hydrogenolysis of glycerol was used to demonstrate that the alumina overcoat significantly improved the activity approximately 2.8-fold, as well as the selectivity to 1,2-propanediol (1,2-PD) at high conversions. DRIFTS measurements of CO chemisorption indicated that the Pt-alumina interface had greater area for alumina coated Pt/Al 2 O 3 than for the uncoated analog. Moreover, we used the hydrogenation of acetol, the key reaction intermediate in glycerol hydrogenolysis, as a control experiment to confirm that the observed activity improvement in the hydrogenolysis of glycerol could be attributed to the enhancement of the dehydration reaction step, which requires acidic function. In brief, our work provides solid evidence that close metal–acid proximity enhances bifunctionality, thus improving the catalytic activity.