Highly selective hydrogenation of 5-hydroxymethylfurfural to 2,5-dimethylfuran at low temperature over a Co–N–C/NiAl-MMO catalyst†
Currently there is tremendous interest in the discovery of catalysts which can selectively hydrogenate biomass-derived 5-hydroxymethylfurfural (HMF) to 2,5-dimethylfuran (DMF). Herein, a highly selective catalyst for this transformation was developed, by adsorption of a cobalt porphyrin (CoTAPP) onto a nickel–aluminium layered double hydroxide (NiAl-LDH) support, followed by a pyrolysis step at 500 °C under a N2 atmosphere. The obtained catalyst (denoted here as Co–N–C/NiAl-MMO), comprising cobalt species (Co0 and CoOx) and N-doped carbon on a NiAl mixed metal oxide support, showed outstanding initial selectivity (99.9%) for the hydrogenation of HMF to DMF at 170 °C in tetrahydrofuran (THF). This is one of the highest selectivities reported to date for this reaction, with the reaction temperature being very mild. After 3 cycles of catalytic tests, with catalyst regeneration by heating at 300 °C in N2 between tests, the HMF conversion efficiency and DMF selectivity of Co–N–C/NiAl-MMO had both decreased by >70% compared to the initial values. This deactivation resulted from the loss of surface basic sites needed for H2 activation, as well as a change in the Co speciation on the catalyst surface (i.e. Co0 oxidation to CoOx). Results guide the development of improved catalysts for the selective conversion of HMF to DMF.