Study On The Effects Of Ba And Na On The Hydrothermal Stability And CO Oxidation Performance Over Pd/CeO₂ Catalyst

DOC catalysts exhibit favorable performances for oxidation of CO and hydrocarbons.However,the precious metals are easy to aggregate after working for a long time at high temperature,resulting in a sharp decline of catalytic activity.Therefore,enough precious metals are used to guarantee the efficiency for exhaust purification,but it greatly rises the cost of catalysts.Thus,researches to improve the utilization of precious metals by optimizing the interaction between precious metals and support have become a hotspot.Pd/CeO₂ catalyst is one of the extensively used DOC catalysts.In this work,Pd/CeO₂ catalysts doped with different amounts of Ba or Na were prepared by impregnation method to investigate the effects of Ba or Na addition on the hydrothermal stability and CO oxidation performance of Pd/CeO₂,respectively.N₂physical adsorption,XRD and TEM experiments were carried out to characterize the physical structures of catalysts.DRIFTS,Raman and XPS experiments were conducted to characterize the chemical states of Pd.CO oxidation activities and kinetic studies were also performed.It was indicated that moderate amount of Ba addition inhibited the aging of CeO₂,improving the hydrothermal stability of Pd/CeO₂ catalyst.It inhibited the aggregation of Pd for its steric effect during hydrothermal aging,and improved the dispersion of Pd.When optimal 1.0 wt.%Ba was doped,there were more oxidized Pd²⁺remaining and the release of active oxygen from surface of CeO₂ and involvement of the oxygen in CO oxidation reaction were facilitated.The catalyst presented the best CO oxidation activity,with Pd²⁺playing an important role in the activity of Ba-doped catalysts.The addition of Na facilitated the aggregation of CeO₂,decreasing the hydrothermal stability of Pd/CeO₂.Moreover,the active sites of CO oxidation for Pd/CeO₂ varied,with the relative content of oxidized Pd²⁺decreased and even disappeared after hydrothermal treatment when Na was doped.The catalyst with 0.5wt.%Na doping presented superior CO oxidation activity after hydrothermal aging.