Exceptionally stable sol-immobilization derived Pd/SBA-15 catalysts for methane combustion

Pd-Based catalysts are efficient for methane combustion but impractical at high temperatures due to the sintering effect. Herein, we report a thermally stable Pd/SBA-15 catalyst that was prepared by using the sol-immobilization (SI) method, instead of the conventional incipient wetness impregnation (IWI) method. Pd nanoparticles retain the small size of similar to 5 nm in the channels of SBA-15 in Pd/SBA-15-SI even after aging at 800 degrees C in air for 3 days, while those in the Pd/SBA-15-IWI samples aggregate into particles larger than 10 nm over the surface. The thermally stable Pd/SBA-15-SI indeed displays excellent catalytic activity for methane combustion at low temperatures with T-50 at similar to 300 degrees C and T-90 at similar to 350 degrees C and high stability during cyclic operations, which are much superior to those of the Pd/SBA-15-IWI catalysts. Interestingly, hydrothermal treatment of the Pd/SBA-15-SI catalysts leads to partial re-dispersion of Pd to form smaller particles of similar to 1.6 nm, while the catalytic activity decreases a bit. Steam in the reactant mixture has a negative effect on the catalytic activity of Pd/SBA-15-SI catalysts, presumably due to the competitive adsorption of H2O to O-2/CH4. Significantly, the size of Pd nanoparticles is essential to the catalytic performance and those having sizes of similar to 5 nm are the most active. Finally, the catalytic activity of the catalysts in the presence of CO2 was studied. This work might be helpful in designing stable metal catalysts using porous materials for reactions under harsh conditions.

Automated summary

A thermally stable Pd/SBA-15 catalyst prepared using the sol-immobilization method shows excellent catalytic activity and stability for methane combustion at low temperatures, with smaller nanoparticles size being essential for higher activity. The presence of water vapor in the reactant mixture negatively affects the catalytic activity of the catalyst, and hydrothermal treatment leads to partial re-dispersion of Pd nanoparticles. This work may provide insights into designing stable metal catalysts for reactions under harsh conditions using porous materials.