In recent years, zirconium hydroxide powder and zirconium-based metal organic frameworks have found promising applications as chemical warfare agent (CWA) decomposition materials. While bulk zirconium oxide (ZrO2) has proven to be relatively inactive for such purposes, well-controlled fundamental studies investigating the potential CWA decomposition propensity of subnanoscale zirconium oxide, in which undercoordinated metal centers abound, are still severely lacking. Herein, the adsorption and decomposition of the nerve agent simulant dimethyl methylphosphonate (DMMP) on size-selected zirconium oxide trimer, that is, (ZrO2)3, clusters supported on highly oriented pyrolytic graphite (HOPG), have been investigated via the combination of X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption/reaction (TPD/R). XPS measurements acquired for the DMMP-adsorbed, HOPG-supported clusters at a preparation temperature of 298 K, and also after annealing to several successively higher temperatures of 473, 573, and 673 K, elucidated the uptake of DMMP to the (ZrO2)3 clusters, with one DMMP molecule adsorbed per cluster and virtually no thermal molecular desorption observed up to 673 K. These measurements also showed dissociative adsorption of DMMP at room temperature on some clusters, likely via scission of a P–OCH3 bond in DMMP, with further decomposition accompanying an increase in temperature above 473 K. TPD/R experiments showed the evolution of methanol as a major reaction product via two distinct pathways, with desorption peaks centered around 410 and 575 K. Evolution of dimethyl ether and formaldehyde as minor reaction products was also observed with desorption peaks centered around 560 and 620 K, respectively. A second TPD/R cycle following cluster-induced DMMP decomposition resulted in no detected decomposition chemistry, showing DMMP decomposition on the (ZrO2)3 clusters to be stochiometric and non-catalytic, whereby the remaining P-containing species poisoned the clusters.

The selective dehydrogenation of hydrocarbons and their functionalized derivatives is a promising pathway in the realization of endothermic fuel systems for powering important technologies such as hypersonic aircraft. The recent surge in interest in single atom catalysts (SACs) over the past decade offers the opportunity to achieve the ultimate levels of selectivity through the subnanoscale design tailoring of novel catalysts. Experimental techniques capable of investigating the fundamental nature of the active sites of novel SACs in well-controlled model studies offer the chance to reveal promising insights. We report here an approach to accomplish this through the soft landing of mass-selected, ultrasmall metal oxide cluster ions, in which a single noble metal atom bound to a metal oxide moiety serves as a model SAC active site. This method allows the preparation of model catalysts in which monodispersed neutral SAC model active sites are decorated across an inert electrically conductive support at submonolayer surface coverage, in this case, Pt 1 Zr 2 O 7 clusters supported on highly oriented pyrolytic graphite (HOPG). The results contained herein show the characterization of the Pt 1 Zr 2 O 7 /HOPG model catalyst by X-ray photoelectron spectroscopy (XPS), along with an investigation of its reactivity toward the functionalized hydrocarbon molecule, 1-propanamine. Through temperature-programmed desorption/reaction (TPD/R) experiments it was shown that Pt 1 Zr 2 O 7 /HOPG decomposes 1-propanamine exclusively into propionitrile and H 2 , which desorb at 425 and 550 K, respectively. Conversely, clusters without the single platinum atom, that is, Zr 2 O 7 /HOPG, exhibited no reactivity toward 1propanamine. Hence, the single platinum atom in Pt 1 Zr 2 O 7 /HOPG was found to play a critical role in the observed reactivity.

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.