Time resolved x-ray absorption spectroscopy studies of the oxidation state and the structural environment of copper in zeolite CuNaY during hydrogen treatment

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Abstract
The copper exchanged zeolite CuNaY, a highly active catalyst for the cyclodimerisation reaction of butadiene to vinylcyclohexene, has been investigated by energy dispersive x‐ray absorption spectroscopy. This is a new, element specific method for studying the oxidation state and the local structural environment of the copper atoms on a time scale of several hundred milliseconds. In this work the time dependence of heterogeneous reactions of the dehydrated zeolite CuNaY with hydrogen and a gaseous mixture of hydrogen and water vapor is presented. Admitting pure hydrogen leads to the reduction to Cu + but not to metallic copper due to the strong interaction between copper cations and the alumosilicate framework. However, a two step reduction via Cu + to small metallic copper clusters is observed after co‐admission of hydrogen and water vapor. This demonstrates the importance of the formation and migration of copper complexes in the reduction mechanism.

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