Effect of a Single Platinum Atom within a Small Metal Oxide Cluster: Reaction of DMMP with Size-Selected Pt₁Zr₂O₇ Supported on HOPG

Abstract

Chemical warfare agents (CWAs) are a persistent threat facing civilians and military personnel across the modern geopolitical landscape. The development of the next generation of protective and sensing materials stands to benefit from an improved fundamental understanding of the interaction of CWA molecules with the active components of such candidate materials. The use of model systems in well-controlled environments offers a route to glean such information and has been applied here to investigate the fundamental interaction of a nerve agent simulant molecule, dimethyl methylphosphonate (DMMP), with a small cluster model of a single atom catalyst (SAC) active site. The cluster models, Pt1Zr2O7, were prepared by depositing mass-selected cluster anions synthesized in the gas phase onto a 100 K highly oriented pyrolytic graphite (HOPG) substrate surface prepared in ultra-high vacuum (UHV) at sub-monolayer coverage. Upon deposition, the cluster anions lost their charge to the electrically conductive surface to yield free-standing neutral clusters. The HOPG-supported clusters were characterized by X-ray photoelectron spectroscopy (XPS) to determine the oxidation states and chemical environment of the metal atoms present within the clusters. The reactivity of the clusters with DMMP was investigated via temperature-programmed desorption/reaction (TPD/R) and XPS experiments in which the clusters were exposed to DMMP and incrementally heated to higher temperatures. In contrast to two other HOPG-supported clusters, (ZrO2)3 and Pt1Ti2O7, recently investigated in our laboratory, Pt1Zr2O7 decomposed DMMP to primarily evolve a methane species, which was completely absent for the other clusters.

Electronic Structure of Heteronuclear Cerium-Platinum Clusters

“…Spectroscopy of small molecule or cluster models can provide a back-door approach to understanding the fundamental electronic structure of these materials. Small clusters, 43,44 even diatomics, 45 provide an insight into bonding and atomicscale interactions 46−49 within the materials; they are also effective models of edges, corners, and defect sites. 50−54 A previous study from our group characterized several platinum-cerium oxide binary clusters, which gave insights into the strong support-catalyst interactions reported for ceria supported platinum and its impact on the water gas-shift reaction.…”

“…Spectroscopy of small molecule or cluster models can provide a back-door approach to understanding the fundamental electronic structure of these materials. Small clusters, , even diatomics, provide an insight into bonding and atomic-scale interactions − within the materials; they are also effective models of edges, corners, and defect sites. − …”