Reactivity of Single-Atom Alloy Nanoparticles: Modeling the Dehydrogenation of Propane

Physical catalysts often have multiple sites where reactionscantake place. One prominent example is single-atom alloys, where thereactive dopant atoms can preferentially locate in the bulk or atdifferent sites on the surface of the nanoparticle. However, ab initiomodeling of catalysts usually only considers one site of the catalyst,neglecting the effects of multiple sites. Here, nanoparticles of copperdoped with single-atom rhodium or palladium are modeled for the dehydrogenationof propane. Single-atom alloy nanoparticles are simulated at 400-600K, using machine learning potentials trained on density functionaltheory calculations, and then the occupation of different single-atomactive sites is identified using a similarity kernel. Further, theturnover frequency for all possible sites is calculated for propanedehydrogenation to propene through microkinetic modeling using densityfunctional theory calculations. The total turnover frequencies ofthe whole nanoparticle are then described from both the populationand the individual turnover frequency of each site. Under operatingconditions, rhodium as a dopant is found to almost exclusively occupy(111) surface sites while palladium as a dopant occupies a greatervariety of facets. Undercoordinated dopant surface sites are foundto tend to be more reactive for propane dehydrogenation compared tothe (111) surface. It is found that considering the dynamics of thesingle-atom alloy nanoparticle has a profound effect on the calculatedcatalytic activity of single-atom alloys by several orders of magnitude.