Solvent molecules form surface redox mediators in situ and cocatalyze O 2 reduction on Pd

Solvents forming redox mediators The role of solvents participating directly in thermal catalytic reactions is clearer for homogeneous catalysis than for heterogeneous catalysis. Adams et al. studied the formation of hydrogen peroxide from hydrogen and oxygen on palladium nanoparticles by measuring the kinetic isotope effect and performing density functional theory simulations in aqueous and organic solvents. Methanol formed chemisorbed hydroxymethyl intermediates. These surface redox mediators transferred electrons and protons to adsorbed oxygen species and were regenerated by oxidizing chemisorbed hydrogen atoms. However, water molecules heterolytically oxidized hydrogen to generate solvated protons and surface electrons that reduced oxygen. Science , this issue p. 626