The Cu+/ZSM-5 catalyst: preparation, interaction with NO and photocatalytic decomposition of NO into N2 and O2 at 275 K. In situ photoluminescence, EPR and FT-ir spectroscopy

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 CuZ+/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+~+-NO&ad ducts 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 N2 and 02 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 a-antibonding orbital of NO is involved in the decomposition of NO on the catalyst under UV irradiation.