An ESR Study of an Al2O3-MoO3-CoO Catalyst in a System with H2 and Thio-β-naphthol

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Abstract
This work was planned in order to determine the reaction mechanism of the catalytic, direct desulfurization of organic sulfur compounds on the surface of Al2O3-MoO3-CoO particles. The experimental method consists of quantitative ESR measurements, by means of which the paramagnetic species on the surface of Al2O3, Al203-MoO3, and Al2O3-MoO3-CoO in the presence and in the absence of H2 and thio-β-naphthol were studied. As it is expected that, in an ideal and fast-reacting catalytic reaction system, no reaction intermediate can be found because it will be immediately converted to the final product, several artificial reaction systems were investigated in which either one of the reactants, catalyst components, or reaction conditions (e. g., temperature) was deficient. In such deficient systems, the reaction cycle is cut off and some intermediates are expected to accumulate. The paramagnetic species observed were Co3+, Mo5+, thio-β-naphthol+-O*2− or RS+H–O*2−, and some species formed on the surface of Al2O3, in the temperature region of 20°C–200°C. Mo6+ is concluded to be the electron trap to facilitate the formation of RS+H–O*2−, Co3+ is concluded to oxidize the Mo5+ thus formed to Mo6+, and Co2+ is concluded to reduce the R-S+H2–O*2− species. The latter then decomposes to H2S and R·.