Enhanced SO2 resistance of the Pd/Silicate-1 catalyst by rare earth oxide modification in methane combustion.

The inherent irreducibility and limited sulfur dioxide tolerance of zeolites constrain oxygen exchange efficiency in palladium/zeolite catalysts, which can adversely affect their performance in methane combustion. Herein, a novel molecular sieve (Silicate-1, denoted as S-1) catalyst functionalized with rare earth oxide sites was developed for catalytic methane combustion. Although both Pd/S-1@CeO2-30 (in which CeO2 content was 30 wt.%) and Pd/S-1 catalysts demonstrated comparable initial catalytic activities, the Pd/S-1@CeO2-30 sample achieved a methane reaction rate of 114.0 µmol/(gPd·s) and the highest TOFPd (0.033 s-1), with a 90% methane conversion at 424 °C at a space velocity of 20,000 mL/(g h). The CeO2 shell in Pd/S-1@CeO2-30 exhibited the superior long-term stability that was attributed to the redox property of CeO2, which could facilitate the provision of abundant oxygen species. As a result, the Pd/S-1@CeO2-30 catalyst maintained stable performance in 10,000-ppm CH4 methane combustion at 400 °C and retained a high CH4 conversion efficiency even under exposure to 50 ppm SO2. Similarly, Ce0.6Zr0.4O2 or Sm2O3 shell also demonstrated comparable SO2 resistance. Detailed characterization results revealed that CeO2 acted as an exceptional redox center, significantly enhanced SO2 adsorption, and effectively inhibited the poisoning of the active PdO sites by SO2, leading to a notable improvement in sulfur dioxide tolerance. These findings highlighted the critical role of the core-shell structure in enhancing catalyst resistance to SO2 poisoning during methane combustion. The present work provides valuable insights into the appropriate designing of advanced core-shell catalysts with improved durability and performance in the sulfur dioxide-containing environments.