Effects of β-cyclodextrin introduction to zirconia supported-cobalt oxide catalysts: From molecule-ion associations to complete oxidation of formaldehyde

The present paper deals with the impact of the addition of beta-cyclodextrin on the genesis of cobalt active phases in zirconia-supported catalysts and on their performances in the complete oxidation of formaldehyde. With this aim, a series of cobalt catalysts supported on zirconia (5 wt.%) is prepared by wet impregnation using mixtures of Co(NO3)(2) and beta-cyclodextrin as precursors. After the impregnation step, the materials are dried and calcined under air at 400 degrees C. Different ratios of beta-cyclodextrin to cobalt have been employed to obtain insight in the role of beta-cyclodextrin, i.e. from 0.01 to 1. The ability of beta-cyclodextrin to interact with the cobalt salt is investigated in solution by UV-vis spectroscopy, ion conductivity in water and dynamic light scattering measurements. After the impregnation step, the cobalt supported materials are characterized at different stages of the preparation (before and after calcination) by means of conventional techniques including UV-vis spectroscopy, thermogravimetry, N-2 adsorption/desorption, X-ray diffraction and temperature-programmed reduction analysis. Characterization results suggest that the carbohydrate ligand bound to the cobalt species retards the decomposition of the cobalt complexes into Co3O4. Finally, these cobalt oxide catalysts prepared from beta-cyclodextrin are able to catalyze the oxidation of formaldehyde more efficiently than the control sample. The results are explained in terms of cobalt oxide dispersion and cobalt-support interactions. Indeed, the cobalt oxide particles generated by the thermal decomposition of beta-cyclodextrin-Co(II) adducts are on the one hand smaller than those formed with cobalt nitrate alone and on the other hand reducible at lower temperatures, two key factors in the catalytic oxidation reactions. (c) 2013 Elsevier B.V. All rights reserved.