Multistep CO2 Activation and Dissociation Mechanisms on Pd x Pt4-x Clusters in the Gas Phase

Palladium, platinum, and their alloys are promising catalystsforelectrochemical CO2 reduction reactions (CO2RR), leading to the design of durable and efficient catalysts forthe production of useful chemicals in a more sustainable way. However,a deep understanding of the CO2RR mechanisms is still challengingbecause of the complexity and the factors influencing the system.The purpose of this study is to investigate at the atomic scale thefirst steps of the CO2RR, CO2 activation anddissociation mechanisms on Pd x Pt4-x clusters in the gas phase. To do it, we use DensityFunctional Theory (DFT)-based reaction path and ab initio moleculardynamics (AIMD) computations. Our research focuses on the descriptionof CO2 activation and dissociation processes via the computationof multistep reaction paths, providing insights into the site andbinding mode dependent reactivity. Detailed understanding of the CO2-cluster interaction mechanisms and estimating of thereaction energy barriers facilitate comprehension of why and how catalystsare poisoned and identification of the most stable activated adductsconfigurations. We show that increasing the platinum content induces fluxional behavior of the cluster structure and biases CO2 dissociation; in fact, our computations unveiled several dissociatedCO(2) isomers that are very stable and that there are variousisomerization processes leading to a dissociated structure (possiblya CO poisoned state) from an intactly bound CO2 one (activatedstate). On the basis of the comparison of the Pd x Pt4-x reaction paths, wecan observe the promising catalytic activity of Pd3Pt inthe studied context. Not only does this cluster composition favorCO(2) activation against dissociation (thereby expected tofacilitate the hydrogenation reactions of CO2), the potentialenergy surface (PES) is very flat among activated CO2 isomers.