Single atom alloys 2.0: Exploiting undercoordination for stronger dissociative CH4 chemisorption

Efficient C-H bond activation is key to low temperature methane oxidation in catalytic converters of natural gas-powered vehicles. Through ab initio calculations, we investigate the potential enhancement of dissociative CH₄ chemisorption on single atom doped (211) facets of Pt and Pd, the preferred platinum group metals (PGMs) for methane oxidation. Single atom doping at undercoordinated edge sites induces surface relaxation, leading to stronger methane dissociation energies due to dopant-induced expansive lattice strain. Conversely, geometrically restricted subsurface doping imposes compressive strain, resulting in weaker chemisorption energies. Our findings indicate that the d-band model fails to capture these strain-dominated activity trends at single-atom sites. Although subsurface sites are thermodynamically stable for single atom doping under inert conditions, we demonstrate that dopant segregation to exposed edge sites becomes more favorable when dissociated methane is chemisorbed on the surface. This study adds a new dimension to the design of single-atom alloy catalysts and encourages experimental efforts to synthesize edge-doped dilute single-atom PGM alloys for enhanced CH₄ activation.