Copper clusters, reactions with hydrogen

The oxidation state of Cu ions in zeolite Y depends on the pretreatment procedure. After activation for more than 8 hours at 675 K phases similar to CuO occur. Admitting hydrogen at 575 K, a reduction to Cu(I) but not to Cu(0) metallic clusters is observed. Probably a reaction with extraframework oxygen takes place. However, a reduction to rather small metallic copper clusters is observed after co-addition of water vapour and hydrogen. This demonstrates the important role of strong ligands like water in the reduction mechanism, enabling a controlled formation of copper clusters. 

DEXAFS has, for example, been used to follow the dehydration of (Ni +, Na+)-loaden zeolite Y [84]. In another study, the reactions of partially Cu-exchanged Na-zeolite Y with pure H2 or with a mixture of H2/H2O have been investigated [85]. Pure hydrogen leads to the reduction of Cu + to Cu+,but not to metallic copper due to the strong interaction of the Cu(I) cations with the aliuninosilicate framework. After admission of additional water vapor, however, the Cu(I) cations become mobile and are reduced to Cu(0), forming small metallic copper clusters. 

The nse of polysnlfide complexes in catalysis has been discnssed. Two major classes of reactions are apparent (1) hydrogen activation and (2) electron transfers. For example, [CpMo(S)(SH)]2 catalyzes the conversion of nitrobenzene to aniline at room temperature, while (CpMo(S))2S2CH2 catalyzes a number of reactions snch as the conversion of bromoethylbenzene to ethylbenzene and the rednction of acetyl chloride, as well as the rednction of alkynes to the corresponding cw-alkenes. Electron transfer reactions see Electron Transfer in Coordination Compounds) have been studied because of their relevance to biological processes (in, for example, ferrodoxins), and these cluster compounds are dealt with in Iron-Sulfur Proteins. Other studies include the use of metal polysulfide complexes as catalysts for the photolytic reduction of water by THF and copper compounds for the hydration of acetylene to acetaldehyde. ... 

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