Promoting effect of 2000 ppm H2S on the dry reforming reaction of CH4 over pure CeO2, and in situ observation of the behavior of sulfur during the reaction

[Display omitted] •Stable activity of pure CeO2 was demonstrated in dry reforming under 2000 ppm H2S.•No impurity phases and carbon deposition appeared after the reaction.•Catalytic activity was enhanced as the concentration of H2S increased.•DRIFT and S K-edge XANES visualized fast redox cycle of sulfur on CeO2.•The fast redox cycle of sulfur accelerated re-oxidation of CeO2-x by CO2. Biomass-derived gas and unused industrial byproducts are resources for H2 production with low CO2 emission; however, they contain > 1000 ppm H2S, which necessitates the use of H2S-tolerant catalysts. Herein, a pure CeO2 catalyst demonstrated stable and efficient H2 production via the dry reforming reaction in the presence of 2000 ppm H2S. No impurity phases and carbon deposition appeared on the catalyst after the reaction. Moreover, CeO2 catalytic activity improved with H2S concentration. The effect of H2S on CeO2 was determined by in situ infrared spectroscopy and S K-edge X-ray absorption near-edge structure studies. The re-oxidation of CeO2 by CO2, a key step of the dry reforming reaction, was accelerated by the rapid redox cycle of sulfur, which promoted CH4 activation and decreased the apparent activation energy from 125 to 101 kJ/mol. The redox cycle of S made the pure CeO2 catalyst resistant to high concentration of H2S.