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Kinetic Isolation between Turnovers on Au₁₈ Nanoclusters: Formic Acid Decomposition One Molecule at a Time

Chen, BWJ; Stamatakis, M; Mavrikakis, M; (2019) Kinetic Isolation between Turnovers on Au₁₈ Nanoclusters: Formic Acid Decomposition One Molecule at a Time. ACS Catalysis , 9 pp. 9446-9457. 10.1021/acscatal.9b02167. Green open access

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Abstract

Formic acid (HCOOH or FA) is a clean, safe, and renewable hydrogen storage material. Although Au catalysts decompose vapor-phase FA with high activity and selectivity toward hydrogen, the active site and reaction mechanism remain unclear. Here, we show that the subnanometric Au18 cluster (0.8 nm in diameter) is likely the active species for FA decomposition. We performed coverage self-consistent, density functional theory-based kinetic Monte Carlo simulations of FA decomposition on gas-phase Au18 clusters, predicting 100% selectivity toward hydrogen and turnover frequencies close to experimentally determined values. The active site is made up of a triangular ensemble of three atoms each possessing a coordination number of 5. Although there are two active site ensembles on the Au18 cluster, their occupations are strongly correlated because of strong, stabilizing interactions between pairs of open-shell adsorbates mediated by the superatomic nature of the cluster. Because the occupation of the active sites blocks the dissociation of additional HCOOH molecules, there is kinetic isolation between turnovers: only one HCOOH molecule can dissociate on the cluster at a time. This explains the extraordinary, experimentally observed selectivity of Au catalysts toward HD during decomposition of HCOOD and DCOOH. Our work offers nanoscale insights into the reaction mechanisms of FA decomposition over Au. This represents a rare example of heterogeneous catalysis by a cluster that catalyzes reactants one molecule at a time. Our work on Au18 thus sheds light on how the unique electronic properties of subnanometric clusters can be used to design quasi-molecular catalysts with high activity and selectivity.

Type: Article
Title: Kinetic Isolation between Turnovers on Au₁₈ Nanoclusters: Formic Acid Decomposition One Molecule at a Time
Open access status: An open access version is available from UCL Discovery
DOI: 10.1021/acscatal.9b02167
Publisher version: https://doi.org/10.1021/acscatal.9b02167
Language: English
Additional information: This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: Formic acid, subnanometric clusters, gold, Au18, density functional theory, kinetic Monte Carlo, cluster expansion, triangular active sites
UCL classification: UCL
UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Chemical Engineering
URI: https://discovery.ucl.ac.uk/id/eprint/10082088
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