Activation of Pd/SSZ-13 catalyst by hydrothermal aging treatment in passive NO adsorption performance at low temperature for cold start application

Pd/SSZ-13 catalysts after hydrothermal aging (HTA) treatment at 750 degrees C for 25 h showed enhanced passive NO adsorption performance at temperature below 120 degrees C, which will be suitable for cold start application, although those calcined at 500 degrees C did not possess good NO adsorption capacity irrespective of the preparation methods such as incipient wetness impregnation, wet impregnation, ion-exchange, and solid state ion exchange. NO adsorption ability of HTA treated Pd/SSZ-13 samples increases gradually as a function of the metal content, up to 2 wt% Pd loading, and then decreased implying that there is an optimum chemistry between the metal and zeolite support. Combined H-2-TPR and Pd XAFS results clearly demonstrate that Pd0 mainly existed over the fresh samples, whereas HTA treated samples contained ionic Pd2' species, indicating the redistribution of Pd0 into highly dispersed Pd2+ species within the SSZ-13 structure arising from HTA treatment. Such phenomenon was visually confirmed by comparative STEMEDS analysis of fresh and HTA Pd/SSZ-13 samples. DRIFT results display the formation of two nitrosyl complexes adsorbed on Pd2' ions, which are directly related to two desorption peaks of NOx at 250 and 400 degrees C. All combined results provide the unambiguous evidence about the generation of Pd ions in SSZ-13 zeolite induced by HTA treatment, which play as the active sites for NO adsorption at low temperature. (C) 2017 Elsevier B.V. All rights reserved.