(67a) Effect of Oxide Supports on Activity of Pdo Catalysts during Hydrothermal Aging in CH4 Oxidation
The present study compares the effect of hydrothermal aging (HTA) of PdO dispersed on high surface area supports (γ-Al2O3 and SiO2) versus low area supports (α-Al2O3 and SnO2) for CH4 oxidation at conditions relevant to natural gas vehicle exhaust gas converters. Pd supported catalysts, prepared by incipient wetness impregnation, with similar Pd loadings were hydrothermally aged at 973 K in air/H2O for various periods of time and tested using Temperature-programmed CH4 oxidation. The catalyst performance before and after HTA is compared and possible deactivation mechanisms are discussed. A comparison of catalyst properties reveals that the PdO catalysts sinter during HTA and PdO crystallites are occluded by the support as confirmed by XPS and HRTEM studies. PdO occlusion by the support plays a key role in deactivating the PdO/SiO2 catalysts during HTA but does not significantly affect the performance of PdO on other supports. The deactivation of PdO/γ-Al2O3 and PdO/SnO2 catalysts is mostly related to PdO sintering and PdO to Pd0 transformation. XRD and XPS results confirm the coexistence of PdO and Pd0 after HTA in these catalysts, associated with the presence of H2O. PdO/α-Al2O3 was found to have the highest catalyst stability during HTA at 973 K for up to 65 h. Less PdO sintering and absence of a Pd0 phase in PdO/α-Al2O3 suggests stronger Pd-support interactions, leading to higher catalyst stability during HTA.
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