Boosting 2,3-butanediol selective dehydrogenation over hierarchical Cu/silicalite-1 via tailoring metal-support interactions

Abstract

Herein, Silicalite-1 supported Cu catalysts were synthesized by coupling the alkaline treatment and ammonia evaporation methods to synchronously introduce the hierarchical pores and strong metal-support interaction for anaerobic 2,3-butanediol dehydrogenation to acetoin. Characterization results demonstrated that mesoporous structures of resultant Cu/S-x-T can be enhanced by tuning the ammonia dosage in the synthetic solution to boost the formation of -Cu-O-Si- structures and improve the dispersion of copper species simultaneously. The increase in the reduction temperature would induce the reduction of Cu2+ existing in the form of -Si-O-Cu-O-Si-. Highly dispersed Cu0 and abundant Cu2+ sites with an appropriate Cu2+/Cu0 ratio brought about the superior activity of Cu/S-25-300 with a conversion of 78% and selectivity of 92%. A correlation analysis on the catalytic activity and Cu0/Cu2+ site densities as well as IR spectra of adsorbed 2,3-butanediol demonstrated that the synergic catalysis of Cu0 and Cu2+ was primarily responsible for the 2,3-butanediol dehydrogenation. Distinctively, DFT calculations revealed that Cu subnanoclusters was capable of catalyzing the 2,3-butanediol dehydrogenation to acetoin, following a similar reaction mechanism to the dehydrogenation of monohydric alcohols on Cu0 sites due to the size mismatch of reactive sites in reactants and catalytic structures.