Catalytic decomposition of methanethiol to hydrogen sulfide over TiO2

• Direct decomposition of methanethiol was examined over various metal oxide catalysts.
• Various metal oxides decompose methanethiol into hydrogen sulfide directly.
• Carbon species accumulate on the catalyst at high temperature.
• Dimethyl sulfide is produced as a by-product over titania at low temperature.
• Methanethiol is decomposed in either of two reaction paths depending on temperature.

As a new desulfurization process for fuel cell systems, catalytic direct decomposition of methanethiol into hydrogen sulfide on various metal oxides without hydrogen addition has been examined. Methanethiol was decomposed into hydrogen sulfide over several metal oxide catalysts at 300 °C. Major metal oxide catalysts used in this study decomposed methanethiol completely at 500 °C. However they would be sulfurized immediately by the decomposed products. Among them, titania (TiO2) catalyst exhibited a remarkable methanethiol decomposition activity and it was hardly sulfurized. The methanethiol conversion of TiO2 catalyst depended on the specific surface area. Hydrogen sulfide and dimethyl sulfide were produced with the same amount at below 250 °C. The methanethiol seems to be decomposed by the following equation at low temperature range: 2CH3SH → H2S + (CH3)2S. In contrast, hydrogen sulfide and methane were produced as gas phase products and carbon species were also formed on TiO2 surface above 400 °C. The methanethiol seems to be decomposed by the following equation at high temperature range: 2CH3SH → 2H2S + CH4 + C. We conclude that the direct decomposition of methanethiol on TiO2 surface proceeds via different reaction pathways depending on the reaction temperatures.

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