Redox and chemisorptive properties of ex-chloride and ex-nitrate Rh/Ce0.6Zr0.4O2 catalysts - 2. Effect of high-temperature redox cycling

The influences of high-temperature redox cycling and of the presence of chl oride on the textural, redox, chemisorptive, and catalytic properties of Rh /Ce0.6Zr0.4O2 were investigated by means of N-2 physisorption, volumetric h ydrogen chemisorption, temperature programmed reduction (TPR), temperature programmed desorption, and catalytic activity measurements of the reduction of NO by CO. This was achieved by conducting experiments on two samples of the material prepared from nitrate and chloride precursors. For the purpos es of comparison, some parallel investigations were also conducted on the p ure support. The results indicate that the precursor used does not affect t he extent of vacancy creation upon application of identical high-temperatur e reduction procedures. However, the high-temperature reduction procedure u sed does have a detrimental effect on the position of vacancy creation duri ng subsequent TPR profiles after mild reoxidation. Differences in behaviour due to the presence of chloride are detectable after application of such h igh-temperature reduction/mild reoxidation cycles, mainly in the chemisorpt ion behaviour at low temperature and activity measurements under pseudo-ste ady-state conditions at 473 K. Significantly, severe ageing under reaction conditions does not eliminate differences in the rates of formation of prod ucts during the reduction of NO by CO. (C) 2000 Academic Press.