Hexagonal close-packed Ni (101) facets boost furan ring activation for selective total hydrogenation of biomass-derived 5-hydroxymethylfurfural over carbon-encapsulated Ni catalysts

Selective total hydrogenation of biomass-derived 5-hydroxymethylfurfural (HMF) to 2,5-bis(hydroxymethyl)tetrahydrofuran (BHMTHF) under mild condition is crucial in biomass refining, yet dauntingly challenging with non-precious metal catalysts. Herein, the hexagonal-close-packed (hcp) Ni dominated carbon-encapsulated Ni-based catalyst (Ni@C-3) was fabricated via a facile citric acid induced carbonization strategy, which exhibited an outstanding catalytic performance toward the hydrogenation of HMF, achieving a high BHMTHF yield of 95.4% under 70 °C and 2 MPa H₂. Additionally, even at high HMF concentrations (2500 mM), it maintained an high BHMTHF yield of 89.7%. The carbon layer, derived from the thermal decomposition of citric acid, effectively prevents the agglomeration of Ni nanoparticles and suppresses the phase transition of hcp-Ni to fcc-Ni. The carbon-encapsulated structure ensures the excellent storage stability and reusability of catalysts. Structure-activity relationship studies demonstrated that the hcp-Ni (101) crystal facets effectively reduce the reaction energy barrier of the rate-determining step (furan ring hydrogenation) during the reaction process, thereby promoting the hydrogenation of HMF to BHMTHF. Furthermore, the Ni@C-3 exhibited excellent catalytic activity in the hydrogenation of compounds containing various functional groups. Notably, furfural can also be hydrogenated to tetrahydrofurfuryl alcohol (THFA) under solvent-free conditions, and the yield of THFA can reach 91.2%. This study provides a facile strategy for designing and developing advanced hydrogenation catalysts based on crystal phase engineering, which makes it a promising alternative to noble metal catalysts in biorefineries.