METAL-OXIDES AS CATALYSTS FOR THE REACTION BETWEEN METHANOL AND HYDROGEN-SULFIDE

The reaction between methanol and hydrogen sulfide leading to the form ation of methanethiol and dimethyl sulfide has been studied using diff erent H2S:CH3OH molar ratios (0.5:1, 1:1, 2:1) at 623 K on various met al oxides presenting different acidity and basicity. The correlations between activity and selectivity of catalysts and their average oxygen and cation charges as well as the strength of their acidic and basic sites, determined by adsorption of probe molecules followed by IR spec troscopy, are as follows: (i) the highest strength of basic sites and the highest negative charge on oxygen (MgO) lead to the lowest activit y and the highest selectivity toward CH3SH; (ii) the lowest strength o f basic sites (medium oxygen charge) and the highest cation charge (ga mma-Al2O3) cause the highest activity and the highest selectivity towa rd (CH3)2S. The dimethylsulfide selectivity is in the reverse order of the number of basic sites. IR measurements show that the reaction occ urs between chemisorbed methanol (methoxy species) and SH- species or/ and H2S molecules. Too strongly held methoxy speCies as on MgO and PO4 3-/SiO2 do not react with H2S. The difference in activity and selectiv ity of both titania samples (anatase and rutile) is discussed.