Adsorption energy decreases across the period with increasing metal-carbon bondlength as depicted in SI Fig. . Thus, methane-SAC interactions are dominated by the size, electronegativity, and empty d-states of the dopant atom. Methane is physisorbed on late-transition metal-doped SACs, whereas it is chemisorbed on early-transition and midtransition metal-doped SACs. Within this range of chemisorption, methane interacts relatively strongly with SACs doped with early-transition metals. This can be attributed to their less electronegativity, more empty d-bands, and large atomic size of the dopant atom.