Design of Highly Active Photocatalytic System for the Removal of NOx

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Reducing global air pollution caused by NOx and SOx is currently an urgent and serious challenge. Utilization of photocatalytic processes in gas-solid systems also promising. In the present project, we have studied and found that Cu^<2+> ions supported on silica (Cu^<2+>/SiO_2) and Y-Zeolite (Cu^<2+>/Y-Zeolite) prepared by an ion-exchange method are easily reduced to Cu^+ ions when the Cu^<2+>/SiO_2 and Cu^<2+>/Y-Zeolite samples are evacuated at temperatures higher than 573 K and the reduced Cu^+ ions on silica (Cu^+/SiO_2) and Y-Zeolite (Cu^+/Y-Zeolite) catalysts can decompose NO molecules photocatalytically and stoichiometrically into N_2 and O_2 at 275 K.UV irradiation ( 270 nm) of the Cu^+/SiO_2 and Cu^+/Y-Zeolite catalysts in the presence of NO molecules at 275 K was found to lead to the decomposition of NO into N_2 and O_2. Decomposition of NO proceeds linearly with UV irradiation time at 275 K. The major products of NO decomposition were N_2 and O_2 with a minor formation of N_2 … More O and NO_2. These minor products were found to be secondary products of N, O, and NO, and the overall reaction was found to be stoichiometrical. Thus, these results clearly indicate that UV irradiation of the CU^+/SiO_2 catalyst (or Cu^+/Y-Zeolite) in the presence of NO leads to the photocatalytic decomposition of NO into N_2 and O_2 at 275 K.The physicochemical and photochemical properties of Cu^+ ions anchored onto SiO_2 and Y-Zeolite have been investigated by means of ESR measurements of the copper (Cu^<2+>) ions and of NO species adsorbed on the copper ions and dynamic photoluminescence measurements of the excited state of the copper (Cu^+) ions (3d^94s^1 electronic state), as well as product analysis of photodecomposition of NO molecules. These results indicate that the excited state of copper ions (Cu^+ ions) plays a significant role in the photocatalytic decomposition of NO molecules and the photoreaction involves an electron transfer from the excited state of the Cu^+ ion into an anti-bonding orbital of NO molecule within the lifetime of its excited state.Thus, the present results obtained with the Cu^+/SiO_2 and Cu^+/Y-Zeolite catalysts imply the possibility of their utilization as a potentially promising type of photocatalysts for the direct decomposition of NOx into N_2 and O_2 at around normal temperature. Less