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Methanol thiolation over Al2O3 and WS2 catalysts modified with cesium

Author:
Pashigreva, Anastasia V., Kondratieva, Elena, Bermejo-Deval, Ricardo, Gutiérrez, Oliver Y., Lercher, Johannes A.
Source:
Journal of catalysis 2017 v.345 pp. 308-318
ISSN:
0021-9517
Subject:
Lewis acids, Lewis bases, active sites, aluminum oxide, catalysts, cesium, dimethyl disulfide, dimethyl sulfide, dissociation, hydrogen sulfide, methane, methanethiol, methanol
Abstract:
Thiolation of methanol with H2S was studied on Al2O3, WS2/Al2O3, and the Cs-modified counterparts Cs/Al2O3, and Cs-WS2/Al2O3. On Cs-free catalysts, methanol reacts with similar rates to dimethyl ether and to methanethiol. Secondary steps yield dimethyl sulfide and trace amounts of dimethyl disulfide and methane. On Cs-containing catalysts, the dominating reaction is methanol thiolation. This drastic change in selectivity is related to the low strength and concentration of Lewis acid sites in the presence of Cs⁺. The active sites for condensation and thiolation of methanol are concluded to be Lewis or Brønsted acid-base pairs formed by dissociation of H2S on the Lewis sites. Thiolation and condensation follow Langmuir-Hinshelwood mechanisms with nucleophilic attack of SH or methoxy groups to adsorbed methanol as rate determining step. The formation of dimethyl ether on Cs⁺ Lewis acid sites is suppressed due to low coverage of methanol, whereas the rate of the nucleophilic attack of SH to methanethiol is enhanced.
Agid:
6092771