Boosting Methane Combustion over Pd/Y<sub>2</sub>O<sub>3</sub>–ZrO<sub>2</sub> Catalyst by Inert Silicate Patches Tuning Both Palladium Chemistry and Support Hydrophobicity
Yang Wu, Wenhu Yang, Hailong Zhang, Haidi Xu, Yi Jiao, Lin Zhong, Jianli Wang, Yaoqiang Chen
Abstract
Supported palladium (Pd) catalysts are widely utilized to reduce the emission of exhaust CH 4 from lean-burn engines by catalytic combustion. A large amount of water vapor in the exhaust makes hydroxyls accumulate on the catalyst surface at temperatures below 450 °C, leading to severe catalyst deactivation. Tuning palladium chemistry and inhibiting water adsorption are critical to developing active catalysts. Modifying the support surface with inert silicates would both change the palladium–support interaction and decrease water adsorption sites. This study reports an improved Pd/Y 2 O 3 –ZrO 2 catalyst by constructing silicate patches on yttria-stabilized zirconia (Y 2 O 3 –ZrO 2 ) support. The silicates hindered electron transfer from Y 2 O 3 –ZrO 2 oxygen vacancies to palladium, which optimized palladium chemistry, especially the reducibility of active PdO species, and thereby boosted CH 4 conversion under dry conditions. The temperature of 90% methane conversion ( T 90 ) over the catalyst decreased from 386 to 309 °C. Moreover, the inert silicates decreased surface oxygen vacancies of Y 2 O 3 –ZrO 2 to improve support hydrophobicity, thereby inhibiting hydroxyl accumulation. The poisoning effect of water on the active sites located on the palladium-silicate interface was alleviated. When reaction gases contained 10 vol % water, the silicate-modified catalyst still showed higher activity with T 90 of 404 °C, which is lower than T 90 of 452 °C for unmodified catalyst. This work represents a step forward in preparing high-performance palladium catalysts for low-temperature wet methane combustion.