Relay semi-hydrogenation of acetylene via hydrogen spillover on non-reducible Al2O3-supported single-atom catalysts

Hydrogen spillover involves the migration of hydrogen atoms from metal to another component, yet it remains challenging to achieve on non-reducible supports. This paper describes the observation of hydrogen spillover on non-reducible Al2O3-supported Pd single-atom catalysts, facilitated by phosphorus−hydroxyl (P−OH) bridge sites, for acetylene semi-hydrogenation. Through in situ spectroscopy, kinetic analysis, and computational analyses, we show that Pd single atoms promote the heterolytic activation of H2, while phosphorus doping on Al2O3 lowers energy barrier for hydrogen spillover via the formation of P−OH species. Gas-phase acetylene collides and hydrogenates with as-formed P−OH, following Eley-Rideal type mechanism, making inert Al2O3 active in hydrogenation reaction. This unconventional relay pathway reduced Pd usage by one order of magnitude and improved catalytic stability, with over 95% ethylene selectivity at 99% acetylene conversion in ethylene-rich stream at 100 °C for more than 200 hours. This work elucidates the mechanism of hydrogen spillover on non-reducible Al2O3 and relay hydrogenation on supported single-atom catalysts. Hydrogen spillover involves the migration of hydrogen atoms from metal to another component and is hard to achieve on non-reducible supports. Here the authors report the hydrogen spillover on non-reducible Al2O3-supported Pd single atom catalysts, facilitated by phosphorus−hydroxyl (P−OH) bridge sites, for acetylene semi hydrogenation.