Stabilization of unique Zr>4+ species in NiFe2O4 nanocrystals for unprecedented catalytic transfer hydrogenation reaction

Stabilization of transition metal species (like Zr>4+) with increasingly positive charge density at oxide surfaces is highly important for intrinsically improving catalytic performance for many uses like catalytic transfer hydrogenation (CTH) reaction, which however remains inaccessible. Here, we showcase a water-quenching strategy that stably achieves Zr>4+ species at surfaces of prototype spinel oxide NiFe2O4. Systematic investigation unveils that these Zr>4+species were precisely incorporated into surface octahedral Ni sites of NiFe2O4. The local electronic structure was thus regulated. As a consequence, there simultaneously appear electron depletion (Zr>4+) and accumulation (O2-) at the resulted sites, which play the distinct roles as Lewis acid-base sites in (i) facilitating O-H bond dissociation and CO bond activation, (ii) enhancing the interaction and bonding with substrate molecules, and (iii) reducing the energy barrier for hydrogen transfer process. The resulting catalysts exhibit superior catalytic performance and stability in the CTH reaction of biomass-derived carbonyls and representative aldehydes/ketones, especially the reduction of furfural to furfuryl alcohol with a yield of 90.7% under 120 ℃ for 3 h. This work provides new insights into optimizing catalytic activity in metal oxides by stabilizing transition metal species with unexpectedly positive charge density. [Display omitted] •An innovative quenching strategy precisely incorporates Zr>4+ ions onto the surface octahedral Ni sites of NiFe2O4.•Regulating electronic structure creates Lewis acid-base sites with electron depletion (Zr>4+) and accumulation (O2-).•Catalysts exhibit superior and universal performance in the CTH reaction under mild conditions.•The unique surface chemistry reduces the energy barrier for hydrogen transfer.•Direct hydrogen transfer prevailsin catalytic reaction over NiFe2O4-Zr catalysts.