Synthesis, characterization and catalytic activity in the reduction of NO by CO on alumina-zirconia sol-gel derived mixed oxides

The synthesis and characterization of Al2O3-ZrO2 mixed oxides of 5, 10 and 20 wt% zirconia contents was carried out. Aluminum tri-sec-butoxide and zirconium n-butoxide were used as chemical precursors. Gelation of the alkoxides was obtained in basic (pH 9) medium using NH4OH as hydrolysis catalyst. Zirconia-alumina mixed oxides were obtained as the final materials. The oxides showed higher specific surface area (283-354 m(2)/g) and large pore size diameters (195-222 Angstrom). FT-IR absorption bands assigned to Zr-O-Al bonds were observed in the mixed oxides. Acidity and basicity were determined by ammonia and CO2 TPD thermodesorption. Low crystallinity was observed by XRD spectra, however, incipient monoclinic and tetragonal zirconia phases were identified. The solids were found active for the reduction of NO by CO. The formation of alumina-zirconia mixed oxides in which an important dilution of the alumina matrix by zirconia was inferred. (C) 1999 Elsevier Science B.V. All rights reserved.