Modification of Pd/CeO2 catalyst by Atomic Layer Deposition of ZrO2

Modification of a 1 wt% Pd/CeO2 catalyst by Atomic Layer Deposition of thin ZrO2 films was studied. Calcination of the unmodified Pd/CeO2, prepared by precipitation of aqueous Ce(NO3)3 solutions, with Pd added by impregnation, caused a large decrease in surface area and an increase in crystallite size between 673 K and 1073 K; however, catalysts modified by 0.4 nm ZrO2 films showed no change in either surface area or CeO2 crystallite size upon calcination to 1073 K. Methane-oxidation rates in 0.5% CH4 and 5% O2 were slightly lower on the ZrO2-covered catalyst when both materials were calcined at 673 K but the activity of the ZrO2-modified catalyst did not decrease with catalyst calcination temperature. Both catalysts showed good activity for the water–gas-shift reaction but the ZrO2 film improved sulfur tolerance by preventing formation of cerium sulfates.