Mechanistic Insights into Methanol Steam Reforming on PdCu(111) and PtCu(111) Bimetallic Catalysts

• • PdCu(111) exhibits superior catalytic performance with water dissociation as the rate-determining step, featuring an activation energy of only 0.74 eV, enabling efficient hydrogen production at lower energy input. • • PtCu(111) is limited by the initial O–H bond cleavage of methanol with a higher activation barrier of 0.93 eV, indicating a trade-off between activity and selectivity that must be managed in catalyst design. • • Cu sites stabilize OH and CH2O species, while Pd/Pt sites preferentially bind CO, creating a spatial site separation that promotes the formate pathway and suppresses CO formation, achieving high methanol conversion with high CO2 selectivity. • • Electronic structure analyses (PDOS, charge density difference, COHP) confirm that Pt's 5d orbitals show stronger orbital overlap and π back-donation with CO's 2π* orbital, rendering CO more stably adsorbed on PtCu(111), which may increase CO poisoning risk in fuel cell applications.