A new hypothesis explaining synergy between two phases in heterogeneous catalysis the case of hydrodesulfurization catalysts

We propose a new mechanistic model, explaining the properties of catalysts composed of sulfides of Group VI and sulfides of Group VIII metals. Spill‐over hydrogen, emitted by the latter, modulates, or controls, the catalytic centers at the surface of the former sulfide. Slightly reduced centers formed by spill‐over hydrogen would be active in hydrogenation, and deeply reduced centers, in hydrodesulfurization. The theory resting on this concept of a remote control agrees qualitatively with all the known catalytic and physico‐chemical properties of the catalysts.