Probing the Nature of the Active Phase of Molybdenum-Supported Catalysts for the Direct Synthesis of Methylmercaptan from Syngas and H₂S

Abstract

Alumina supported K-, Mo-, and K-Mo-based catalysts prepared from different precursors (ammonium heptamolybdate + KNO 3, K 2 MoO 4, K 2 MoS 4 ) with the same loading were used to produce CH 3 SH by the simple syngas/H 2 S route. The simultaneous presence of Mo and K in the catalytic system allows the achievement of higher CO conversions and CH 3 SH selectivity and a decrease in CO 2 selectivity. Through XPS analysis of sulfided catalysts, the presence of a new phase (named K x MoS 2 ) with an unusual Mo 3d binding energy in which potassium cations are intercalated between the MoS 2 layers is evidenced. The amount of this phase was well correlated with the catalytic performances of the corresponding catalysts in the reaction of methyl mercaptan production. Indeed, it was found that the higher the amount of K x MoS 2 phase in the catalyst, the higher the CH 3 SH productivity. On the basis of these statements K x MoS 2 is proposed as the active phase acting in the reaction of thiolation of syngas.