Boosting Methane Combustion over Pd/Y₂O₃–ZrO₂ Catalyst by Inert Silicate Patches Tuning Both Palladium Chemistry and Support Hydrophobicity

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.