Metal Coordination Sites in Heterogeneous Catalysts

3 Metal Coordination Sites in Heterogeneous Catalysts- EXAFS is 

Ni-O-Ni linked oligomers. Hydrogen reduction of NiY was shown cause incomplete reduction to small metal particles (mean coordination number 8). 

EXAFS and XANES have been used to probe the different effects 

More complicated problems are presented by the mixed-metal Co-Mo hydrodesulphurisation catalysts, which have been the subject of some interest. The molybdenum site of the sulphided catalyst seems to be part of a MoS2 like phase, with EXAFS results indicating 6 sulphur nearest neighbours ( 2.48) and - 4 Mo atoms at 3.28 distance. These parameters are essentially 

EXAFS data of either element s K-edge. The cobalt atoms are considered to be located on the periphery of these M0S2 particles. Analysis of the cobalt edge has indicated an environment of 5 or 6 sulphur atoms with a bond length of 2.33 or 2.238. There has also been a suggestion of a proportion of oxygen neighbours at 2.038. In this system only a small proportion ( - 10%) of the cobalt atoms are considered to be adsorption sites (as probed by NO), so it has been difficult to obtain definitive information about these centres.. 

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