Studies on molybdena catalysts XI. Oxygen chemisorption on sulfided catalysts

Abstract

Catalysts containing Mo or CoMo on various supports were prepared. Oxygen chemisorption on the sulfided catalysts was measured by a flow gravimetric technique. Activities of the catalysts were determined for thiophene hydrodesulfurization (HDS) and hexene hydrogenation in a catalytic microreacter at atmospheric pressure. Oxygen chemisorption increased with adsorption temperature. A definite adsorption was only obtained at −78 °C, adsorption at higher temperatures continuing for over 4 hr. For O2 chemisorption at −78 °C: (i) CoMo versus Mo catalysts showed only marginally higher values; (ii) O2 chemisorption did not correlate with HDS activity; and (iii) O2 chemisorption showed a reasonable correlation with hydrogenation activity. It is probable that O2 chemisorption reflects the general state of dispersion of the active Mo phase rather than specific HDS or hydrogenation sites.