Biomass-derived gas and unused industrial byproducts are resources for H-2 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 H-2 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. (C) 2020 Elsevier Inc. All rights reserved.