Adsorption and Decomposition of Dimethyl Methylphosphonate on Size-Selected Zirconium Oxide Trimer Clusters

Abstract

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.

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

“…P2p1 exhibits a 2p 3/2 binding energy of 133.9 eV, which is typical of molecularly chemisorbed DMMP. This has been observed in previous studies of ours, as well as the work of others. , P2p2 exhibits a lower 2p 3/2 binding energy of 132.9 eV, which has been previously assigned to surface-bound phosphonate or phosphate decomposition products. , This result shows that DMMP has already begun to decompose by room temperature and is similar to the results of our previous experiments involving room-temperature exposure of (ZrO 2 ) 3 clusters to DMMP …”

“…It was found that DMMP was strongly adsorbed by the clusters and proceeded to decompose with heating, evolving primarily methanol along with relatively minor amounts of dimethyl ether and formaldehyde. 28 While the use of small metal oxide particles and clusters as active decomposition species has been a research focus for some time now, a recently emerging newer focus is on the potential application of single catalytically active metal atoms supported on the surface of metal oxide particles to this problem. Over the last decade, the concept of such a single atom catalyst (SAC) was convincingly demonstrated in a seminal study by Qiao et al 29 and spawned a field that has grown exponentially in scope since.…”

“…In particular, a highly active node consisting of a partially hydroxylated zirconium oxide hexamer cluster has been shown to facilitate the hydrolysis of various nerve agent simulants when incorporated into a host of MOF structures. − Moreover, bulk zirconium hydroxide has also shown promise in the adsorption and decomposition of various nerve agent simulants and live agents as well. − This work motivated a recent study of ours in which we investigated the reactivity of even smaller ZrO 2 trimer clusters size-selected in the gas phase and soft-landed onto an HOPG substrate surface in ultra-high vacuum (UHV). It was found that DMMP was strongly adsorbed by the clusters and proceeded to decompose with heating, evolving primarily methanol along with relatively minor amounts of dimethyl ether and formaldehyde …”

Titania Nanomaterials for Sarin Decomposition: Understanding Fundamentals

“…The P 2p spectrum for the nanopowder and mesoporous samples after GB exposure (Figure a) effectively resemble each other. Only a component centered at around 133 eV appears in the P 2p spectrum, commonly observed for GB or DMMP (a simulant for GB) adsorption. ,,,− Figure b displays the F 1s spectrum. Two characteristic components appear in the F 1s region for both samples after GB dosing.…”

Ultrasmall Cluster Model for Investigating Single Atom Catalysis: Dehydrogenation of 1-Propanamine by Size-Selected Pt1Zr2O7 Clusters Supported on HOPG

“…This work was conducted using a newly constructed apparatus with substantial improvements over its predecessor, the latter of which was used in previously published work from our laboratory − and described in detail previously . The cluster ion beamline was completely redesigned, and the cluster deposition/surface analytical region of the apparatus underwent significant modification, while retaining much of the same analytical instrumentation.…”