XPS STUDIES OF SOLVATED METAL ATOM DISPERSED CATALYSTS - EVIDENCE FOR LAYERED COBALT MANGANESE PARTICLES ON ALUMINA AND SILICA

XPS studies of solvated metal atom dispersed (SMAD) catalysts coupled with detailed studies of reference compounds were carried out. It was shown that toluene-solvated cobalt atoms nucleate at surface OH groups, and the resultant cobalt oxide surface species serve as sites for nucleation of more cobalt atoms, leading to very small, reactive metallic clusters. The surface of these clusters/particles are partially oxidized by adventitious oxygen or water, but when cobalt loadings of over 4% are used, a major portion of the catalytic particle remains metallic. When solvated cobalt and manganese atoms are mixed together, the manganese atoms deposit first at surface OH sites, and manganese is highly dispersed in this way, but the majority ends up as surface MnO and Mn2O3. Some of the deposited manganese atoms/clusters serve as nucleation sites for cobalt atoms. In this way a layered catalytic particle is formed: support (SiO2 or Al2O3) covered by manganese oxide which in turn is covered by metallic cobalt. The manganese material serves as a gradient between the ionic support oxide and metallic cobalt, and the composite is quite stable and highly active in catalysis. Also, the manganese serves as a sacrificial metal, serving to scavenge oxidizing moieties' (mostly OH groups) on the support surface, thereby allowing cobalt to deposit and remain metallic and very highly dispersed. Sizes of the composite particles are probably 10-30 angstrom in diameter and are nearly amorphous.