Synergistic effect between Ni single atoms and acid–base sites: Mechanism investigation into catalytic transfer hydrogenation reaction

Abstract Catalytic Transfer Hydrogenation (CTH) of unsaturated functional groups to obtain high value-added products has attracted considerable attention in heterogeneous catalysis. Herein, we report a Ni single atoms (SAs) catalyst anchoring to Mg Al mixed metal oxide (MMO) based on structural topotactic transformation from hydrotalcite precursor, which displays an excellent catalytic behavior toward CTH of cinnamaldehyde (CAL) to cinnamyl alcohol (COL) (conversion: 100%; selectivity: 100%; 2 h). A combination research including AC-STEM, XAFS and in situ CO-IR demonstrates that Ni species anchored by Ni O coordination with different dispersion could be precisely obtained by tuning the reduction temperature: the Ni SAs (only Ni O coordination) were obtained below 450 °C, and the Ni Ni coordination appears and increases gradually with the rise of the reduction temperature. The selective poisoning experiment, kinetic isotope effect (KIE), in situ FT-IR measurement and DFT calculation reveal the synergistic effect between metal Ni SAs and acid–base sites toward CTH of CAL. Specifically, the Ni SAs play a crucial role in dehydrogenation reaction of 2-propanol (2-POL) to supply activated H, the base sites induce α-C H cleavage in 2-POL (the rate-determining step), and the Lewis acid sites serve as the active center for C O adsorption in CAL molecule. This work demonstrates a synergetic effect between Ni SAs and acid–base sites, which would pave the way in the rational design and synthesis of high-performance SAs materials used in CTH reactions.