Design of Active Photocatalytic System for Removal of NOx

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The characterization of the Cu^+/ZSM-5 catalyst prepared from the ion-exchanged Cu^<2+>/ZSM-5 sample by the evacuation at higher temperatures has been undertaken by in situ photoluminescence, EPR,and FT-IR spectroscopy. EPR measurements of the Cu^<2+> signal indicate that the evacuation of the Cu^<2+>/ZSM-5 system at temperatures higher than 373 K leads to a decrease in the intensity of the EPR signal, suggesting that Cu^<2+> is chemically reduced to Cu^+ by this thermal vacuum treatment. Only the reduced Cu^+/ZSM-5 catalysts exhibit photoluminescence spectra at around 420-550 nm, attributed to the radiative decay from excited Cu^+ ions within the ZSM-5. The decrease in the intensity of EPR signal due to Cu^<2+> is closely related to the increase in the photoluminescence intensity due to Cu^+. The addition of NO onto the Cu^+/ZSM-5 catalyst leads to the formation Cu^<+delta+>--NO^<delta-> adducts and dynamic quenching of the photoluminescence, suggesting that Cu^+ reacts with NO mot only in the ground state but also in the excited state. UV-irradiation of the Cu^+/ZSM-5 catalyst in the presence of NO leads to the photocatalytic decomposition of NO into N_2 and O_2 at temperatures as low as 275 K.In situ photoluminescence, EPR,and FT-IR measurements suggest that a local charge separation involving electron transfer from the excited Cu^+ ion to the pi-anti-bonding orbital of NO is involved in the decomposition of NO on the catalyst under UV-irradiation.