Publication costs assisted by the Petroleum Research Fund Optical absorption and emission spectra have been used to study the reduction of Cu(II) and Cu(I) exchanged zeolites by hydrogen. The emission of Cu(I) was identified as a spin-forbidden transition *Ai (JS0) -3E (3D3). Additional intermediates were found spectroscopically, possibly involving copper hydride and isolated copper atoms. The final product is metallic copper in various states of agglomeration, characterized by an absorption edge at 17 000 cm"1.
Publication costs assisted by the National Science Foundation (USA) and the National Fonds voor Wetenschappelijk Onderzook (Belgium)The reduction of Cu(II) ions in CuNaY zeolites occurs via a two-step mechanism in which Cu(I) is first formed and then reduced to metallic copper. The first step in the reduction may be carried out by using relatively mild conditions, e.g., H2 at 200°C for 1 hr, and it is completely reversible. Reduction in H2 at 400°C results in the formation of copper crystallites, some of which grow to a size of 300 Á after 20 hr of reduction. The copper in these larger crystals may be reoxidized slowly to CuO. The smaller metal particles, which are postulated to reside within the zeolite cages, may be readily reoxidized to Cu(II), located at exchange sites within the zeolite. Approximately half of the metallic copper is in the form of the larger crystallites and half is present in small clusters. The reduction and reoxidation was followed by quantitatively observing the H2 or O2 consumption and H2O produced in the reaction, while the amount of Cu(II) was determined by EPR spectroscopy. The presence of Cu(I) was detected by the ir and EPR spectra of the Cu+-CO and Cu+-NO complexes, respectively.
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