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/
M. Anpo et al., 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/, Journal of physical chemistry, 98(22), 1994, pp. 5744-5750
The characterization of the Cu+/ZSM-5 catalyst (1.9 wt% Cu) prepared f
rom the ion-exchanged Cu2+/ZSM-5 sample by evacuation at higher temper
atures has been undertaken by in situ photoluminescence, EPR, and FT-I
R spectroscopy. EPR measurements of the Cu2+ Signal indicate that evac
uation of the Cu2+/ZSM-5 system at temperatures higher than 373 K lead
s 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 Cuions within the ZSM-5. The decrease in the intensity of the EPR signal
due to Cu2+ is closely related to the increase in the photoluminescen
ce intensity due to Cu+. The addition of NO onto the Cu+/ZSM-5 catalys
t leads to the formation Cu-+delta+-NOdelta adducts and dynamic quench
ing of the photoluminescence, suggesting that Cu+ reacts with NO not o
nly 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 photocata
lytic decomposition of NO into N-2 and O-2 at temperatures as low as 2
75 K. In situ photoluminescence, EPR, and FT-IR measurements suggests
that a local charge separation involving electron transfer from the ex
cited Cu+ ion to the pi-antibonding orbital of NO is involved in the d
ecomposition of NO on the catalyst under UV irradiation.