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

Tzia Ming Onn, Shuyi Zhang, Lisandra Arroyo-Ramirez, Yu-Chieh Chung, George W. Graham, Xiaoqing Pan, Raymond J. Gorte, 2015
Pd/Al203 modified via atomic layer deposition
Image courtesy of ACS Catal.

Abstract

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.

Impact Statement

Nanoparticle catalysts for automotive exhaust applications must remain thermally stable for optimal efficiency. This paper introduces a method to thermally stabilize Pt nanoparticles on alumna using a thin layer of zirconia deposited via ALD. In situ TEM measurements with Atmosphere were used to confirm the thermal stability under typical calcination conditions. The authors found that the thin zirconia layers form nanoparticles at surprisingly low temperatures, and confirmed the behavior seen in ex situ analysis.