The adsorption and decomposition of dimethyl methylphosphonate (DMMP) have been examined on four different metal oxide surfaces:  aluminum oxide, magnesium oxide, lanthanum oxide, and iron oxide. Aluminum, magnesium, and lanthanum oxides are observed to behave in much the same way, with initial binding of the PO species to the surface at an acid site, followed by stepwise elimination of the methoxy groups, beginning at temperatures as low as 50 °C, which combine with surface hydrogens to yield methanol that evolves from the surface. The final product observed for these oxides is a surface-bound methylphosphonate, with the P−CH3 bond intact, which is resistant to further oxidation even in the presence of 70 Torr of oxygen at 300−400 °C. Adsorption on iron oxide yields a different sequence of events, with the initial adsorption occurring again with the PO moiety binding to an acid site, although there is some indication of the formation of a second type of surface complex. The primary interaction on iron oxide appears to be much stronger than with the other oxides, and probably involves the unidentate coordination of the DMMP to a Lewis acid site on the surface. Nonselective elimination of both the methoxy and the phosphorus-bound methyl groups begins only after heating above 200 °C, but occurs with total elimination of the methyl and methoxy groups observed after heating above 300 °C in vacuum. The ease with which iron oxide cleaves the P−CH3 bond is attributed to the availability of multiple oxidation states to the iron atom. Participation of the Fe(III)/Fe(II) redox couple in the reaction provides a low-energy path for oxidative cleavage of the P−CH3 bond. The other oxide surfaces cannot provide a similar path, and on these surfaces the P−CH3 bond is resistant to cleavage. The use of infrared diffuse reflectance techniques, observing, in particular, the methyl stretch region of the infrared spectrum, has allowed the almost complete characterization of the decomposition processes which occur after DMMP adsorbs on aluminum oxide, magnesium oxide, lanthanum oxide, and iron oxide.

The adsorption and decomposition reactions of dimethyl methylphosphonate (DMMP) on a commercial γ-Al 2 O 3 , a γ-Al 2 O 3 -supported iron oxide, and a sol-gel-prepared alumina have been examined at temperatures from 25 to 400 °C. The capacities of these solids for the decomposition of DMMP have been measured, and the identities and amounts of the decomposition products determined over the entire temperature range. The alumina surfaces yield higher total amounts of decomposition products than the supported iron oxide material, with the sol-gel alumina showing very high activity. When corrected for surface area, however, the supported iron oxide material shows an activity equal to that of the γ-Al 2 O 3 support. The sol-gel alumina shows a higher activity at all temperatures up to saturation of the surface, presumably because of the presence of transitional phases that yield more reactive surface sites. At 25 °C, the commercial γ-Al 2 O 3 shows a total decomposition capacity of 117 µmol/g, the alumina-supported iron oxide material a capacity of 93 µmol/g, and the sol-gel alumina a capacity of 208 µmol/g. At 100 °C, these capacities increase by about a factor of 3, and at 200 °C and above, all of the materials show some capacity for sustained decomposition of DMMP.

The adsorption and oxidation of SO2 on alumina and sodium-impregnated alumina has been examined using thermogravimetric analysis and diffuse reflectance infrared Fourier transform spectroscopy. Sulfur dioxide chemisorbs initially at basic sites to form an adsorbed sulfite, which is quantitatively converted to sulfate on oxidation. It has been observed that at low coverages, ∼2.6 μmol/m2, sodium acts as a promoter for the formation of an adsorbed sulfite and sulfate which have structures similar to those of aluminum sulfite and sulfate, respectively. At higher sodium loadings, a second type of adsorbed SO2 is formed, similar to sodium sulfite and sulfate. The species with the aluminum sulfate structure appears to be more easily decomposed than does the sodium sulfate species and accounts for the regenerable adsorption capacity. Formation of the sodium sulfate species appears to account for the loss of adsorption capacity as the number of adsorption/regeneration cycles increases. Oxidation of the sulfite form to the sulfate form can occur in the absence of added oxygen, but it is an activated process and begins to occur in measurable amounts at temperatures between 150 and 300 °C. Partitioning of adsorbed SO2 between aluminum and sodium forms is not a function of temperature and depends on only sodium loading.

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.

The adsorption and decomposition reactions of dimethyl methylphosphonate (DMMP) on cerium and iron oxides supported on aluminum oxide have been examined at 25 °C. The capacities of these solids for the decomposition of DMMP have been measured, and the identities and amounts of the decomposition products determined. The coimpregnated oxide formulations are significantly more reactive than alumina alone, and the current formulations are 2.5× more reactive at room temperature than any other metal oxide studied previously. A series of screening experiments show that the most active formulation is one containing 5 wt % iron and 7.5 wt % cerium. At 25 °C, Al2O3 shows a decomposition capacity of 317 μmol/g, while the alumina-supported iron and cerium oxide combination shows a decomposition capacity of more than 510 μmol/g. Formulations containing similar amounts of iron oxide or cerium oxide individually are more active than the unmodified alumina but less active than the coimpregnated oxide. The results show that the three-dimensional CeO2 phase that forms when cerium oxide is impregnated on alumina by itself is inactive for decomposition, and that the increased reactivity for these materials originates with a two-dimensional cerium oxide phase. The increased activity for the materials that include iron is suggested to be due to the iron either increasing the number of defect sites in the ceria crystallites that do form, or facilitating the formation of smaller crystallites.