ChemInform Abstract: Structure of Surface Species on Alumina Supported Cobalt-Molybdena Catalysts.
Abstract
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ChemInform Abstract
The Co-Mo/Al2O3 catalyst (prepared by coimpregnation followed by calcination in oxygen atmosphere at 500 °C) as well as its reduced and sulfided forms are characterized by XRD, DTA, EPR, magnetic susceptibility measurements, and spectroscopic methods ( diffuse reflectance, IR, laser Raman). The surface of the calcined catalyst is found to contain octahedrally coordinated Mo6+ ions linked via oxygen bridges to dimeric or polymeric species. No evidence for the formation of Al2(MoO4)3 containing tetrahedrally coordinated Mo(VI) is found. Co2+ is present in tetrahedral and octahedral structures. Octahedrally coordinated Co2+ ions form structures similar to that of aand b-CoMoO4. Spinel-type compounds are observed in subsurface-layers. Thermal activation of the catalysts in H2 at 400 °C results in partial reduction of Mo(VI) to Mo(V), the latter being present in structures with C4v symmetry. The CoMoO4-like structures are found to be not easily reduced due to the stabilizing effect of the support. The spinels also show high resistance to reduction.
