Surface investigation on Ce(x)Zr(1-x)O2 compounds

The surface of CexZr1-xO2 compounds has been studied by Fourier transform i nfrared (FTIR) spectroscopy using adsorbed probe species. Methoxy species, from methanol dissociative adsorption, compensate the coordinative unsatura tion of surface cations. From the nu(OC) vibration of methoxy species it wa s shown that mixed compounds are solid solutions with a surface composition equal to the nominal bulk composition. This result was confirmed by X-ray photoelectron spectroscopy (XPS). However, compared to pure compounds, an i ncrease of exposed Ce4+ cationic sites related to capping oxygen lability w as observed for mixed compounds. From the adsorption of CO and pyridine pro bes it was shown that the Lewis acidities of mixed compounds were intermedi ate between those of pure ceria and zirconia, which are weak, being slightl y higher for zirconia. Using CO2 as a probe for basicity investigation of t he surface, it was shown that the various carbonate species observed for mi xed compounds were already observed for pure ceria or zirconia with no stri king variation of the overall carbonatation. However, from a proposed inter pretation of the relative importance of various species, such as monodentat e or polydentate carbonates, it was inferred that surface oxygen species ar e more easily relaxed in ceria-rich mixed compounds than in ceria itself, a nd that the surface framework of cerium cations is stabilised by zirconium, the effect being the opposite in the case of the surface framework of zirc onium ions.