Low temperature NO adsorption over hydrothermally aged Pd/CeO₂ for cold start application

Pd/CeO₂ catalyst hydrothermally aged at 750 °C for 25 h was employed for NO adsorption at low temperature (80–160 °C). For comparison, Pt or Pt-Pd supported on CeO₂ or Al₂O₃ catalysts were also applied. Analysis of the hydrothermally aged catalysts clearly indicates that PGM (Pt and/or Pd) on CeO₂ is more resistant to sintering than that on Al₂O₃ support. Reducibility test of Pd/CeO₂ by H₂-TPR exhibits H₂ spillover from Pd to CeO₂ support, attributed to the strong interaction between Pd and CeO₂. NO adsorption/desorption results demonstrate that CeO₂-based catalysts exhibit superior NO adsorption ability than Al₂O₃-based catalysts. In addition, PGM/CeO₂ catalysts shows the desirable desorption temperature for cold start application. The influence of reactant in stream, NO adsorption time, and temperature on low temperature NO adsorption over Pd/CeO₂ is also examined to advance the understanding of NO adsorption/desorption behavior. DRIFT results of adsorbed NO_x species on Pd/CeO₂ during NO adsorption/desorption prove that NO_x desorption peaks at 250, 300, and 450 °C originate from weakly bound nitrite, nitro-nitrito species, and nitrate species, respectively. In Pd/CeO₂ catalyst, Pd plays a role in providing additional NO adsorption site arising from the intimate interaction between Pd and CeO₂ and promoting the oxidation from adsorbed nitrite to nitrate. It can be summarized that Pd/CeO₂ can be a good candidate as low temperature NO adsorption catalyst for cold start application.