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Multistep CO2 Activation and Dissociation Mechanisms on PdxPt4–x Clusters in the Gas Phase

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journal contribution
posted on 2023-05-17, 13:05 authored by Renata Sechi, Tibor Höltzl
Palladium, platinum, and their alloys are promising catalysts for electrochemical CO2 reduction reactions (CO2RR), leading to the design of durable and efficient catalysts for the production of useful chemicals in a more sustainable way. However, a deep understanding of the CO2RR mechanisms is still challenging because of the complexity and the factors influencing the system. The purpose of this study is to investigate at the atomic scale the first steps of the CO2RR, CO2 activation and dissociation mechanisms on PdxPt4–x clusters in the gas phase. To do it, we use Density Functional Theory (DFT)-based reaction path and ab initio molecular dynamics (AIMD) computations. Our research focuses on the description of CO2 activation and dissociation processes via the computation of multistep reaction paths, providing insights into the site and binding mode dependent reactivity. Detailed understanding of the CO2–cluster interaction mechanisms and estimating of the reaction energy barriers facilitate comprehension of why and how catalysts are poisoned and identification of the most stable activated adducts configurations. We show that increasing the platinum content induces fluxional behavior of the cluster structure and biases CO2 dissociation; in fact, our computations unveiled several dissociated CO2 isomers that are very stable and that there are various isomerization processes leading to a dissociated structure (possibly a CO poisoned state) from an intactly bound CO2 one (activated state). On the basis of the comparison of the PdxPt4–x reaction paths, we can observe the promising catalytic activity of Pd3Pt in the studied context. Not only does this cluster composition favor CO2 activation against dissociation (thereby expected to facilitate the hydrogenation reactions of CO2), the potential energy surface (PES) is very flat among activated CO2 isomers.

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