An operando optical fiber UV–vis spectroscopic study of the catalytic decomposition of NO and N2O over Cu-ZSM-5

The role of the bis(μ-oxo)dicopper core, i.e., [Cu2(μ-O)2]2+, in the decomposition of NO and N2O by the Cu-ZSM-5 zeolite has been studied with combined operando UV–vis monitoring of the catalyst and on-line GC analysis. An optical fiber was mounted on the outer surface of the quartz wall of the plug-flow reactor and collected the UV–vis diffuse reflectance spectra under true catalytic conditions. Measurement under transient reaction conditions indicated that [Cu2(μ-O)2]2+ is formed by O abstraction of N2O, which is an intermediate in the NO decomposition. This conversion of N2O to N2 and O2 is strongly retarded below 673 K. Above 673 K, the produced [Cu2(μ-O)2]2+ fulfills the role of O2 release, guaranteeing the self-reduction of the catalytic site. Studying the NO decomposition as a function of the O2 content in the feed strongly suggested that O2 release from [Cu2(μ-O)2]2+ is rate limiting in the NO decomposition at 773 K.