The gas-phase decomposition of dimethyl methylphosphonate (DMMP) has been studied over amorphous manganese oxide (AMO) catalysts in the presence of light (∼200-800 nm). The reaction was studied under oxidizing conditions using air at low temperatures (40-70 °C). DMMP and gas-phase products were studied using gas chromatography (GC). DMMP was found to adsorb 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 ∼200-800 nm, large amounts of MeOH and CO 2 were initially formed. Following the initial period of high activity, strong deactivation was observed. After the reactions were performed, aqueous extracts from spent AMO were analyzed using ion chromatography (IC). The IC analyses indicated that several products accumulate on the AMO surface. These products include methyl methylphosphonate (MMP) and methylphosphonic acid (MPA). Greater amounts of MMP and MPA are produced after irradiation. Fourier transform infrared (FTIR) spectroscopy was used to examine adsorbed DMMP species on spent AMO. The IR results indicate that DMMP bonds to Mn Lewis acid sites on the AMO surface via the phosphoryl oxygen. On the basis of these results a mechanism is proposed for the adsorption and photoassisted decomposition of DMMP over AMO.

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The decomposition of the cyanine dye, pinacyanol chloride, has been studied using hydrogen peroxide and several mixed valent manganese oxide catalysts in aqueous, alkaline solution at room temperature. These catalysts belong to a class of porous manganese oxides known as octahedral molecular sieves (OMS). The most active catalysts were those of Fe 3+ -, Cr 3+ -, and Co 2+ -doped OMS-2. Rates of reaction were found to be first-order with respect to the dye. The highest reaction rates were observed when no H 2 O 2 was present. Reactions were studied at pH ) 6-11, which caused variations in the catalytic activity. The decomposition of the dye was examined using varying amounts of the catalysts, which showed the dye decomposing activity to be proportional to the amount of catalyst. X-ray diffraction studies showed that no changes in the catalyst structure occurred, implying that these reactions are surface controlled.

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