Selective Switching Hydrogenation Products of 5-hydroxymethylfurfural at High Substrate Concentrations by Regulating Pd-MgO Interactions

Abstract

Controlling the selective activation of one or some functional groups as desired is still a challenge in hydrogenation, especially at high substrate concentrations. Herein, Pd-MgO interfaces over Al2O3 were finely regulated for efficiently selective hydrogenation of furan ring in 5-hydroxymethylfurfural (HMF) to produce 5-hydroxymethyltetrahydro-2-furaldehyde (5-HMTHFF) or total hydrogenation to 2,5-bis(hydroxymethyl)tetrahydrofuran (BHMTHF), also inhibiting side reaction. The Pd-MgO/Al2O3 with 12.0wt % of MgO selectively hydrogenates the furan rings with a 5-HMTHFF yield of 82.4% while that with 2.0wt % of MgO totally hydrogenates HMF with a DHMTHF yield of 96.2% at high substrate concentrations (400mM). Characterizations and DFT calculations demonstrated that oligomeric MgO species suppress the agglomeration of Pd nanoparticles and strengthen HMF adsorption, consequently promoting total hydrogenation. Furthermore, Pdδ+-MgO1-x sites between the crystallized MgO and Pd metal favored tilted adsorption on the interface and weakened the activation of the C=O bond, consequently selectively producing 5-HMTHFF.