Alumina supported Pt(1%)/Ce0.6Zr0.4O2 monolith: Remarkable stabilization of ceria–zirconia solution towards CeAlO3 formation operated by Pt under redox conditions

Abstract

A structured Pt(1 wt%)/ceria–zirconia/alumina catalyst and the metal-free ceria–zirconia/alumina were prepared, by dip-coating, over a cordierite monolithic support. XRD analyses and Rietveld refinements of the structural data demonstrate that in the Pt supported catalysts ceria–zirconia is present as a Ce0.6Zr0.4O2 homogeneous solid solution and that the deposition over the cordierite doesn’t produce any structural modification. Moreover no Pt sintering occurs. By comparing the XRD patterns recorded on Pt/ceria–zirconia/alumina and ceria–zirconia/alumina after three redox cycles, it results that Pt, favouring the structural reorganization of the ceria–zirconia into one cubic solid solution, prevents any CeAlO3 formation. On the contrary, such phase due to the interaction between Ce3+ and the alumina present in the washcoat is detected when redox cycles are carried out on the ceria–zirconia metal free. Transmission electron microscopy (TEM) investigations of the redox cycled Pt/ceria–zirconia/alumina catalyst detected ceria–zirconia grains with diameter between 10 and 35 nm along with highly dispersed Pt particles (2–3 nm) strongly interacting with ceria. Scanning electron microscopy (SEM) and EDX analyses, recorded on the redox cycled Pt/ceria–zirconia/alumina washcoated monolith evidence a homogeneous distribution of the active components through the channels even after redox aging. Reduction behaviour and CO oxidation activity are in good agreement with the structural modification of the solid solution induced by the redox cycles and reflect the positive effect of Pt/ceria interaction on the catalytic performances. The effect of redox aging on the NO reduction by C3H6, in lean conditions, was investigated over the Pt/ceria–zirconia/alumina monolith. The catalyst shows at low temperature (290 °C) good NO removal activity and appreciable selectivity to N2.