Bringing Molecules\nTogether: Synergistic Coadsorption\nat Dopant Sites of Single Atom Alloys

Bringing molecules together on a catalytic surface is\na prerequisite\nfor bimolecular and recombination reactions. However, in the absence\nof attractive interactions between reactants, such as hydrogen bonds,\nthis poses a challenge. In contrast, based on density functional theory,\nwe show that coadsorption at active sites of single-atom alloys (SAAs)\nis favored and that coadsorption is a general phenomenon observed\nfor catalytically relevant adsorbates on a broad range of SAAs under\ntemperature and pressure conditions commonly employed for catalysis.\nDopants located in both terrace sites and in step edge defects exhibit\na preference for coadsorption, displaying similar periodic trends.\nUsing kinetic Monte Carlo simulations, we compare the reactivity of\na model reaction on both a pure metal and an SAA and show that the\npreference for coadsorption significantly alters the overall reaction\nenergy profile, even when the barriers for the rate-determining elementary\nstep are identical. In our models, the coadsorption preference enhances\nthe catalytic activity of the SAA surface by several orders of magnitude\ncompared to the pure metal. We also report infrared (IR) spectroscopic\nsignatures of coadsorption, which facilitate experimental detection.\nAnalysis reveals that in these systems repulsive lateral interactions\nbetween nearby molecules are more than compensated for by the enhanced\nbinding at dopant sites. Among the broad range of systems considered,\nSAAs containing early transition metals (TMs) exhibit the strongest\ncoadsorption preference, which can be rationalized by assuming the\nexistence of an optimal number of electrons involved in binding. The\nstrong coadsorption preference, together with facile product desorption\nfrom early TMs, renders these systems attractive candidates for catalysis.\nMoreover, these SAAs could open new routes for reduction reactions\nbecause coadsorption with hydrogen is favored.