X-Ray Photoelectron and Raman Spectroscopies,Comparative Studies of Supported Molybdenum Cobalt and Cobalt Molybdenum Catalysts

Laser Raman Spectroscopy is used to study catalysts : Co, Mo or Co-Mo supported on alumina. Well defined salts spectra are compared to those of these solids, which permits to establish superficial structures of cobalt, molybdenum or both.

For molybdenum catalysts, we found two structures depending upon the concentration

isolated MoO^2- ₄ molecular ions at low concentration < 4%

polymolybdate phase at higher concentration

For cobalt catalysts two structures are also observed: - tetrahedrally surrounded co ²+ ions at low concentration Co³O⁴ clusters at higher concentrations

For cobalt-molybdenum (8%) catalysts three cases occur no effect is observable at very low concentration of cobalt (0.5%)

a well defined compound appears for Co/Mo atomic ratio 0.25

when the cobalt concentration increases a third structure is observed but not identified

All these results are compared to X Ray photoelectron spectroscopic studies and are in good agreement with them.