STRUCTURE – REACTIVITY RELATIONSHIP FOR REVERSIBLE ACTION OF WATER VAPOUR ON THE ENVIRONMENT OF COPPER IN CU-ZSM-5 CATALYST FOR THE SELECTIVE REDUCTION OF NOX GASES: AN IN-SITU X-RAY ABSORPTION FINE STRUCTURE STUDY

The effect of water vapour on the structure and oxidation state of copper in Cu-ZSM-5 catalyst has been studied by in-situ EXAFS (extended X-ray absorption fine structure) and XANES (X-ray absorption near edge structure) under reaction conditions similar to those used for NOx reduction. The EXAFS results show that there is reduction of some copper to metallic state together with the oxidation of Cu^+ to Cu^2+ when the catalyst is treated with water vapour at 350°C. The Cu^2+ is then reversibly reduced back to Cu^+ when heated in vacuum at 500° C. XANES studies also support this reversible redox process where the catalyst oxidizes to Cu^2+ at 350°C and rereduces to Cu^+ in vacuum at 500°C. Gas chromatographic studies at 500°C showed evolution of oxygen and hydrogen supporting the reversibility of catalyst by water vapour.