Computational study of 5-hydroxymethylfurfural electrocatalytic hydrogenation over Cu(111) and Ag(111)

One of the most interesting products formed from 5-hydroxymethylfurfural is 2,5-bishydroxymethylfuran (BHMF), that can be used in relevant industrial polymerizations. In this context, the selective electrochemical hydrogenation (ECH) of HMF to BHMF is gaining an increasing interest. Experimentally, it has been shown that using Ag electrocatalyst a higher selectivity in BHMF is achieved as compared to Cu. Still, a better understanding of the reaction network is necessary to limit the generation of side products and to limit the overpotential applied. In the last decade, ab initio modelling has proved its ability to elucidate catalytic reaction mechanisms. Using the computational hydrogen electrode (CHE) approach and the grand-canonical periodic density-functional theory (GC-DFT), with the support of experimental evidences collected at the University of Bologna, this work investigates the conversion of HMF into BHMF, and possible side routes yielding to methylfurfural (MF) and methylfurfuryl alcohol (MFA), and hydrofuroin (BHH). An extended reaction network for HMF-ECH has been explored over Cu(111) and Ag(111), and the energy profiles have been computed in both cases. Similar thermodynamic overpotentials for BHMF formation have been found for both the metals, in agreement with the experimental results, that show the same performance of the electrocatalysts in HMF-ECH. The computed energy profiles show that MFA, MF, BHH and BHMF can be formed from both the metals in these conditions as also the experimental evidences reveal. Along the path to BHMF, the formation of the intermediate I02, that is involved also in BHH formation is almost athermic on Ag(111) and exothermic on Cu(111). Basing only on thermodynamics, this evidence can explain why less BHH and humines are formed in the case of Ag(111) and a higher selectivity toward BHMF is observed. Moreover, this evidence can provide a simple criterium for in silico screening of catalysts for HMF selective ECH.