Photoassisted decomposition of dimethyl methylphosphonate over amorphous manganese oxide catalysts

The gas-phase decomposition of dimethyl methylphosphonate (DMMP) has been s tudied over amorphous manganese oxide (AMO) catalysts in the presence of li ght (similar to 200-800 nm). The reaction was studied under oxidizing condi tions using air at low temperatures (40-70 degrees C). DMMP and gas-phase p roducts were studied using gas chromatography (GC). DMMP was found to adsor b strongly to the AMO surface and produce small amounts of methanol (MeOH) even in the absence of light. When AMO was irradiated with light of similar to 200-800 nm, large amounts of MeOH and CO2 were initially formed. Follow ing the initial period of high activity, strong deactivation was observed. After the reactions were performed, aqueous extracts from spent AMO were an alyzed using ion chromatography (IC). The IC analyses indicated that severa l products accumulate on the AMO surface. These products include methyl met hylphosphonate (MMP) and methylphosphonic acid (MPA). Greater amounts of MM P and MPA are produced after irradiation. Fourier transform infrared (FTIR) spectroscopy was used to examine adsorbed DMMP species on spent AMO. The I R results indicate that DMMP bonds to Mn Lewis acid sites on the AMO surfac e via the phosphoryl oxygen. On the basis of these results a mechanism is p roposed for the adsorption and photoassisted decomposition of DMMP over AMO .