Improved Thermal Stability and Methane-Oxidation Activity of Pd/Al2O3 Catalysts by Atomic Layer Deposition of ZrO2

The effect of modifying Pd/Al2O3 catalysts by atomic layer deposition of 1 nm ZrO2 films was studied. For deposition on oxidized, PdO/Al2O3 catalysts, TEM imaging, EDS mapping, and metal-dispersion measurements confirmed the presence of the thin ZrO2 over both the Al2O3 support and the metal particles. The ZrO2 films were surprisingly stable, forming a well-crystallized phase only above 1173 K. The ZrO2 coating over the PdO particles created a semicore-shell-like structure that stabilized the metal against sintering in air at 1073 K. Steady-state, methane oxidation rates on unmodified PdO/Al2O3 decreased with increasing catalyst calcination temperature, but rates on the ZrO2-covered surfaces increased with increasing calcination temperature.