Influence of SMSI effect on the catalytic activity of a Pt(1%)/ Ce0.6Zr0.4O2 catalyst: SAXS, XRD, XPS and TPR investigations

Abstract

The steady-state activity of NO reduction by C3H6, in lean conditions, was studied on a Pt(1%)/Ce0.6Zr0.4O2 catalyst, in a plug-flow reactor, in the temperature range 100–500 ◦C. The influence of reductive pre-treatments on the catalytic performance at low temperature (250 ◦C) was investigated. Enhancement of the activity was found for the catalyst pre-treated in hydrogen at 350 ◦C as compared to the sample pre-treated in H2 at 800 and 1050 ◦C. Moreover, transient reactivity tests of NO reduction by hydrogen were also carried out. As previously observed, the sample reduced at 350 ◦C was the most active catalyst. In both types of reactions the temperature and the nature of pre-treatments had no effect on the selectivity to N2 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 platinum 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.