Influence of the SMSI effect on the catalytic activity of a Pt(1%)/Ce_(0.6)Zr_(0.4)O_2 catalyst:SAXS,XRD,XPS and TPR investigations

摘要

The steady-state activity of NO reduction by C_3H_6,in lean conditions,was studied on a Pt(1%)/Ce_(0.6)Zr_(0.4)O_2 catalyst,in a plug-flow reactor,in the temperature range 100-500 degC.The influence of reductive pre-treatments on the catalytic performance at low temperature (250degC) was investigated.Enhancement of the activity was found for the catalyst pre-treated in hydrogen at 350 degC as compared to the sample pre-treated in H_2 at 800 and 1050degC.Moreover,transient reactivity tests of NO reduction by hydrogen were also carried out.As previously observed,the sample reduced at 350degC was the most active catalyst.In both types of reactions the temperature and the nature of pre-treatment had no effect on the selectivity to N_2 at the temperature of maximum NO conversion.Analyses by temperature programmed reduction (TPR),small-angle X-ray scattering (SAXS),X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) supported the occurrence of a strong metal-support interaction (SMSI) effect between plantium and ceria and the important role of the platinum in promoting the ceria-zirconia structural reorganization.Such type of interaction determined a decrease of the platinum and ceria reduction temperature and a stabilization of the platinum oxide even in reducing atmosphere at high temperature.The catalytic behavior of the Pt/ceria-zirconia catalyst was discussed in terms of the structural and electronic modifications induced by the SMSI effect.