Cesium Induced Changes in the Acid-Base Properties of Metal Oxides and the Consequences for Methanol Thiolation

Cs⁺-modified γ-alumina, titania anatase, and zirconia in the absence of WS₂ are active catalysts for methanol thiolation. Pyridine and CO adsorptions via IR show that Cs⁺ cations induce higher concentrations and strength of base sites. Reaction rates are similar on all three catalysts, indicating that the Cs⁺ cations are part of the dominating active sites. Methanol thiolation shows similar apparent activation energies, decreasing with Cs⁺ concentration. Reaction orders close to 0.5 for both reactants suggest that all three metal oxides and their alkali-metal-modified counterparts follow the identical base-catalyzed Langmuir-Hinshelwood mechanism. A reaction between the surface alcoholate and the corresponding sulfhydryl groups is hypothesized to be the pathway for reaction.