Single-Atom High-Temperature Catalysis on a Rh 1 O 5 Cluster for Production of Syngas from Methane

Single-atom catalysts are a relatively new type of catalyst active for numerous reactions but mainly for chemical transformations performed at low or intermediate temperatures. Here we report that singly dispersed Rh 1 O 5 clusters on TiO 2 can catalyze the partial oxidation of methane (POM) at high temperatures with a selectivity of 97% for producing syngas (CO + H 2 ) and high activity with a long catalytic durability at 650 °C. The long durability results from the substitution of a Ti atom of the TiO 2 surface lattice by Rh 1, which forms a singly dispersed Rh 1 atom coordinating with five oxygen atoms (Rh 1 O 5 ) and an undercoordinated environment but with nearly saturated bonding with oxygen atoms. Computational studies show the back-donation of electrons from the d z 2 orbital of the singly dispersed Rh 1 atom to the unoccupied orbital of adsorbed CH n ( n > 1) results in the charge depletion of the Rh 1 atom and a strong binding of CH n to Rh 1 . This strong binding decreases the barrier for activating C–H, thus leading to high activity of Rh 1 /TiO 2 . A cationic Rh 1 single atom anchored on TiO 2 exhibits a weak binding to atomic carbon, in contrast to the strong binding of the metallic Rh surface to atomic carbon. The weak binding of atomic carbon to Rh 1 atoms and the spatial isolation of Rh 1 on TiO 2 prevent atomic carbon from coupling on Rh 1 /TiO 2 to form carbon layers, making Rh 1 /TiO 2 resistant to carbon deposition than supported metal catalysts for POM. The highly active, selective, and durable high-temperature single-atom catalysis performed at 650 °C demonstrates an avenue of application of single-atom catalysis to chemical transformations at high temperatures.