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/(g_Pd·s) and the highest TOF_Pd (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, Ce_0.6Zr_0.4O₂ 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.