One-pot synthesized niobium-doped nickel catalysts for efficient hydrogen-free glycerol hydrogenolysis

• NiAl 2 O 4 is doped with Nb using one-pot citrate sol–gel method. • Catalysts are evaluated for 1,2-PG production via H 2 -free glycerol HDO. • Nb doping increases both the metal and acid sites densities, and oxygen vacancies. • 1 wt% Nb has balanced metallic and acid sites, yielding 39% selectivity to 1,2-PG. • Ni oxidation and leaching of metals occur throughout the 4 h reaction. Hydrogenolysis with in situ produced hydrogen is a promising route to the fabrication of bio-based chemicals such as propylene glycol from biomass-derived glycerol. This study examines the effect of doping a nickel aluminate-derived catalyst with Nb on the physicochemical properties and product distribution during the hydrogenolysis of glycerol. The catalysts were synthesized from stoichiometric nickel aluminate spinel doped with different Nb contents using the citrate sol–gel method in a one-pot synthesis approach. Catalytic runs were performed in a continuous plug flow reactor at 235 °C/45 bar for 4 h time-on-stream. Catalysts were thoroughly characterized by XRD, HRTEM, XPS, NH 3 -TPD, Py-IR, and H 2 -TPD. Results indicated that Nb doping produced Ni 0 crystallites of smaller size, increased the density of both metal and acid sites, and generated more oxygen vacancies when compared to the undoped catalyst. The nanoscale proximity of Nb to metallic nickel particles was also confirmed. The addition of Nb had a noticeable effect on the product distribution, with a marked increase in selectivity for C–O bond hydrogenolysis compared to C–C bond cleavage. The catalyst doped with 1 wt% Nb achieved a glycerol conversion of 58.1 % and a 1,2-propylene glycol yield of 37.5 %. Post-reaction characterization revealed that oxidation and leaching of surface metal species was minimum. In conclusion, the 1 wt% Nb-doped nickel aluminate-derived catalyst showed potential to facilitate the selective production of 1,2-propylene glycol in an environmentally friendly one-pot process coupling both the H 2 generation and the hydrogenolysis reactions.