Direct Photocatalytic Anaerobic Conversion of Methane and Water to Acetone over RhPd Alloy-Modified TiO2

Abstract Direct upgrading of methane into high-value C2+ oxygenates is severely constrained by conventional oxidative protocols, which inevitably favor over-oxidation to CO and CO2. Herein, we report an anaerobic photocatalytic strategy to directly upgrade CH4 and water into acetone (C3) over a RhPd alloy-engineered TiO2 catalyst without external CO or chemical oxidants. At 90 °C and 15 bar of CH4, this system delivers an acetone production rate of 873 μmol gcat–1 h–1 with an 85% liquid-phase selectivity, demonstrating maximized photon utilization alongside efficient H2 evolution. Mechanistic tracking reveals that hole-mediated H2O oxidation generates active hydroxyl radicals (•OH) that primarily drive methane homolysis to sequentially yield adsorbed carbonyl (*CO) equivalents. Crucially, the electronically coupled RhPd co-catalyst acts as an efficient extraction hub to divert photogenerated electrons via a continuous hydrogen-evolution relief channel to optimize charge separation, while concurrently utilizing its enhanced adsorption affinity to pool these in situ formed *CO species and migrating methyl fragments for relay carbonylation toward exclusive C3 acetone synthesis. This orchestrated harmony establishes a mild, anaerobic strategy for methane conversion, offering a pristine paradigm for controlling complex multi-carbon coupling trajectories in solar-to-chemical conversions.