The Room Temperature Decomposition Mechanism of Dimethyl Methylphosphonate (DMMP) on Alumina-Supported Cerium Oxide − Participation of Nano-Sized Cerium Oxide Domains

Abstract

The adsorption and decomposition reactions of dimethyl methylphosphonate (DMMP) on cerium oxide supported on aluminum oxide have been examined at 25 °C. Experiments were carried out that involved dosing the reactive adsorbent with small doses of DMMP, followed by quantitative determination of the decomposition products. The results suggest that the formation reactions of methanol and dimethyl ether are competitive processes involving the same surface intermediate, which is most likely a surface methoxy species. Based on the observed results, it is proposed that the formation of dimethyl ether is due to the combination of two surface methoxy groups, while an important, if not the dominant, reaction producing methanol involves a surface methoxy group interacting with a vapor phase or physisorbed DMMP molecule. The presence of significant amounts of methoxy fragments formed upon DMMP adsorption is supported by results from diffuse reflectance spectroscopy, which also show that those groups are primarily associated with the cerium oxide domains. FT-Raman spectroscopy shows that the most active cerium oxide domains are highly dispersed two-dimensional domains or very small (<1 nm) crystallites. Somewhat larger (<6 nm) three-dimensional crystallites add to the decomposition yield, but less strongly. The FT-Raman evidence also supports the formation of a relatively narrow particle size distribution of cerium oxide crystallites on the alumina support surface from the sample preparation method. The alumina-supported cerium oxide reactive adsorbents developed as part of this study are the most active that have been reported in the literature for ambient temperature applications, decomposing approximately 775 µmol of DMMP per gram of adsorbent at 25 °C, and strongly or irreversibly adsorbing an additional 400 µmol, for a total capacity at room temperature of 1.1-1.2 mmol of DMMP per gram.

Adsorption of dimethyl methylphosphonate and trimethyl phosphate on calcium oxide: an ab initio study

“…Several studies were carried out to understand the mechanism of the adsorption and decomposition processes on such oxides as alumina-supported cerium oxide and iron co-impregnated oxide [31], manganese oxide [32], monoclinic tungsten oxide (m-WO 3 ) [33], cerium oxide, Fe 2 O 3 , silica [34][35][36][37][38], and TiO 2 [39][40][41][42]. The thermal oxidative decomposition study of DMMP on amorphous manganese oxide and Al 2 O 3 -supported manganese oxide catalyst has shown the DMMP oxidation to CO 2 [32].…”

“…The investigation of the adsorption of DMMP on monoclinic tungsten oxide has proven that DMMP simulant adsorbs on the surface solely through the P=O functionality with the surface water layer as well as the Lewis and Brönsted acid site [33]. DMMP on the alumina-supported cerium oxide decomposes by producing methanol and dimethyl ether [34]. DMMP adsorbs on iron oxide at room temperature through cleavage of the phosphorus-carbon bond [35].…”

Tulane/Xavier Vaccine Development/Engineering Project

“…(The decomposition measurements were carried out as explained in earlier publications. 4 ) However, the observed decomposition activity is relatively short-lived due to the low surface are of the titania substrate (50 m 2 /g) compared to that of the alumina substrate (~400 m 2 /g). Also, although there is a generally increasing trend in the amount of methanol produced with amount of supported cerium, the increase is not particularly dramatic, and the increase in decomposition yield observed is not really sufficient to justify the extra costs that would be associated with the synthesis of these materials.…”

“…4 Experiments with the ozone co-reactant initially used the alumina-supported cerium oxide as the reactive adsorbent, but no significant improvements in decomposition capacity were observed. It was then decided to examine alumina-supported iron oxide as the reactive adsorbent, based on other studies that examined iron oxide in combination with an active oxygen species, typically hydrogen peroxide, to oxidize organic compounds via Fenton-like chemistry.…”

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“…On the other hand, the formed SMI when interacting with DMMP produces methanol (Scheme 4). 101 This is the most active catalyst reported in the literature so far, which decomposes 775 μmol of DMMP per gram of adsorbent, and strongly/irreversibly adsorbing an additional 400 μmol at 25°C. Thermocatalytic oxidation of DMMP was carried out on nickel, iron, copper, and vanadium oxides supported on γ‐Al 2 O 3 , and their degradation products were analyzed 130 .…”