Abstract
ZrO2 nH2O (hydrogel) impregnated with transition metals (Cu, Co, and Ni) was studied in this work as a precursor for the synthesis of CuO/ZrO2 (CuZ), CoOx/ZrO2 (CoZ), and NiO/ZrO2 (NiZ) catalysts, employed in the naphthalene oxidation reaction. Fresh and catalytically used materials were characterized by different physicochemical techniques, to compare the bulk and surface behavior, with particular attention to the effect of the supported metal species’ properties on the catalytic activity. Techniques such as X-ray diffraction (XRD), temperature programmed reduction (TPR), differential scanning calorimetry (DSC), Brunauer–Emmett–Teller (BET) surface area analyzer, diffuse reflectance spectroscopy (DRS UV–vis), and Raman spectroscopy, allow for establishing structural and textural aspects of the support, as well as the surface coordination and the accessibility of supported species. Results were in agreement with the CuZ > CoZ > NiZ sequence for the activity in naphthalene oxidation reaction. Electronic properties, ionic sizes, oxide phase deposition on the support surface, reducibility, metal–support interaction, and local site symmetry of metals seem to be decisive factors for the catalytic interaction with the gaseous phase.
Highlights
Volatile organic compounds (VOCs), emitted to the atmosphere by industrial and anthropic processes, are chemically associated to products derived from petrochemical processes and fuel combustion
All catalysts based on transition metal oxide supported on zirconia are active for total oxidation of naphthalene, increasing significantly, the activity of pure zirconia
A set of factors determine the catalytic efficiency, such as surface area, crystallite size, the surface dispersion of metal oxide, similarity between Zr(IV) and metal ionic radii, number of vacancies generated by cationic substitution, mobility of oxygen vacancies from the bulk to sub-surface, local symmetry of metal, stabilization of zirconia tetragonal phase, and metal reducibility
Summary
Volatile organic compounds (VOCs), emitted to the atmosphere by industrial and anthropic processes, are chemically associated to products derived from petrochemical processes and fuel combustion (e.g., automobile exhaust gas). They become hazardous for the environment, and for the human health. The high cost of these metals and the easy of deactivation by sintering or poisoning limit industrial application [9] Catalytic oxidation to carbon dioxide and water is one of the most promising methods for removing VOCs to carbon dioxide and water, since this process occurs at temperatures lower than those adopted by other non-catalytic processes, and can be used for effluent streams containing low VOC concentration [1,2,3,4,5,6,7,8].
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