Experimental and DFT investigations on enhanced stability found on Re-, Rh-, and Nb-promoted Pt/WOx/γ-Al2O3 catalyst during aqueous-phase glycerol hydrogenolysis

Abstract

The aqueous-phase glycerol hydrogenolysis is one of the catalytic methods used to convert the glycerol by-product from biodiesel production to highly valuable chemicals, especially 1,3–propanediol (1,3PDO). The density functional theory (DFT) and experiments were used to study the promotional effects of third metals promoters: Re, Rh, and Nb in WOx doped Pt-based catalysts that withstand deactivation via metal leaching, sintering, and coking. The third metal promoter improves catalytic activity and 1,3PDO selectivity due to increased electron density at the Pt active site confirmed by DFT. However, improved stability was found only on re- and Rh-promoted systems, evident from sustained activity and selectivity of spent catalysts. The deactivation study revealed that Pt leaching was negligible in all cases. Still, W leaching is more concerned and can be reduced only by Re and Nb promoters, whereas Pt sintering can be prevented only in the case of Re promoter. Mitigation of coking can be realized from DFT that only the Re promoter has comparable electron donor property to Pt and can prevent active site blockage by shifting the preferable coke adsorption site from Pt to a promoter atom, as also confirmed by the lowest amount of type I coke measured by the thermal gravimetric analysis leading to a high product yield.