Structure, chemistry and activity of well-defined cu-ZSM-5 catalysts in the selective reduction of NOX

Richard W. Joyner, R. W. Joyne, M. Raflq H. Siddiqui, Efim S. Shpiro, Wolfgang Grünert, Galina N. Baeva

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Three types of copper species have been identified in a series of Cu/ZSM-5 catalysts which have been studied for the selective catalytic reduction (SCR) of nitric oxide by hydrocarbon in the presence of excess oxygen. Electron spectroscopy and X-ray absorption spectroscopy have been used to show the presence of isolated copper species, (referred to as Type I), and small copper/oxygen aggregates, (Type 11) in catalysts prepared by ion exchange. Larger, copper oxide like aggregates (Type III) predominate in catalysts prepared by impregnation. Interconversion between Cu(I) and Cu(II) is facile for both Types I and II. and the oxidation state observed depends on the environment. Disruption of Type III has been observed with the proton form of the zeolite, and results in the formation of Type I and II species which gradually migrate into the zeolite channels. Interestingly. a physical mixture of Cu/Na-ZSM-5 and H-ZSM-5 is much more active than the individual components. The activity is attributed to migration of copper ions into the proton form of the zeolite. In general the turnover number for NO reduction increases with copper dispersion, however the catalytic reaction may be favoured by the inter convertibility of copper species I and II, and by their interaction with the acidic centres of the zeolite.

Original languageEnglish
Pages (from-to)1483-1492
Number of pages10
JournalStudies in Surface Science and Catalysis
Issue numberC
StatePublished - 1 Jan 1994
Externally publishedYes


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