INTERMEDIATE SPECIES ON ZIRCONIA SUPPORTED METHANOL AEROGEL CATALYSTS.4. ADSORPTION OF CARBON-DIOXIDE

The interaction between carbon dioxide and the aerogel catalysts: pure ZrO2, ZnO/ZrO2, CuO/ZrO2 nd CuO/ZnO/ZrO2 produces very similar result s on all four catalysts. The irreversible surface species identified b y the Fourier transform IR spectra after adsorption of carbon dioxide at 25-degrees-C are (in the sequence of the increased stability when t he temperature increases): bidentate bicarbonate, bridged carbonate, b identate carbonate, unidentate carbonate (except for pure ZrO2) carbox ylate and ionic carbonate. The temperature-programmed desorption (TPD) spectrum is, in general, resolved into five peaks of carbon dioxide o nly, in contrast to that recorded after interaction with carbon monoxi de on two copperless aerogels where peaks of carbon dioxide and hydrog en were also detected [ D. Bianchi, T. Chafik, M. Khalfallah and S.J. Teichner, Appl. Catal. A, 105 (1993) 223. ] and were correlated with t he formation of the formate species. This species is not detected afte r the interaction with carbon dioxide.