Study of the supported K2MoO4 catalyst for methanethiol synthesis by one step from high H2S-containing syngas

ESR and XPS are used to study the Mo-based catalysts MoO3/K2CO3/SiO2 and K2 MoO4/SiO2 prepared with two kinds of precursors, (NH4)(6)Mo7O24. 4H(2)O and K2MoO4. The catalytic properties of the catalysts for methanethiol synthes is from high H2S-containing syngas are explored. The activity assay shows t hat the two catalysts have much the same activity for the reaction. By the ESR characterization of both functioning catalysts, the resonant signals of "oxo-Mo(V)" (g = 1.93), "thio-Mo(V)" (g = 1.98) and S (g = 2.01 or 2.04) c an be detected. In the catalyst MoO3/SiO2 modified with K2CO3, as increasin g amounts of K2CO3 are added, the content of "oxo-Mo(V)" increases, but "th io-Mo(V)" decreases. The XPS characterization indicates that Mo has mixed v alence states of Mo4+, Mo5+ and Mo6+, and that S includes three kinds of sp ecies: S2- (161.5 eV), [S-S](2-) (162.5 eV) and S6+ (168.5 eV). Adding K2CO 3 promoter to the catalysts, the Mo species of high valence state is easily sulphided and reduced to Mo2S and "oxo-M(V)", and the derivation of [S-S]( 2-) and S2- species from S is promoted simultaneously. The methanethiol syn thesis is favored if the mole ratio of (Mo6+ + Mo5+)/Mo4+ less than or equa l to 0.8 and S2-/[S-S](2-) is kept at a value of about 1.