1634
J. Phys. Chem. B 2004, 108, 1634-1645
The Room Temperature Decomposition Mechanism of Dimethyl Methylphosphonate (DMMP) on Alumina-Supported Cerium Oxide - Participation of Nano-Sized Cerium Oxide Domains Mark B. Mitchell,* Viktor N. Sheinker, Woodrow W. Cox, Jr., Enid N. Gatimu, and Aron B. Tesfamichael Department of Chemistry and the Center for Surface Chemistry, Clark Atlanta UniVersity, Atlanta, Georgia 30314 ReceiVed: June 5, 2003; In Final Form: September 19, 2003
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 (
