PREPARATION AND CHARACTERIZATION OF THE CU+/ZSM-5 CATALYST AND ITS REACTION WITH NO UNDER UV IRRADIATION AT 275 K - IN-SITU PHOTOLUMINESCENCE, EPR, AND FT-IR INVESTIGATIONS

The characterization of the Cu+/ZSM-5 catalyst (1.9 wt% Cu) prepared from the ion-exchanged Cu2+/ZSM-5 sample by evacuation at higher temperatures has been undertaken by in situ photoluminescence, EPR, and FT-IR spectroscopy. EPR measurements of the Cu2+ Signal indicate that evacuation of the Cu2+/ZSM-5 system at temperatures higher than 373 K leads to a decrease in the intensity of the EPR signal, suggesting that Cu2+ 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 the EPR signal due to Cu2+ 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+-NOdelta adducts and dynamic quenching of the photoluminescence, suggesting that Cu+ reacts with NO not 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 suggests that a local charge separation involving electron transfer from the excited Cu+ ion to the pi-antibonding orbital of NO is involved in the decomposition of NO on the catalyst under UV irradiation.