Mechanism and kinetics of catalytic ozonation for elimination of organic compounds with spinel-type CuAl2O4 and its precursor

CuAl2O4 based mixed oxides were used as heterogeneous catalysts for ozone activation to degrade organics in aqueous solution. The solids were thoroughly characterized by SEM/EDS, N-2 physisorption, XRD, FTIR, Pyridine-FTIR, TEM and XPS. We demonstrated that the solid precursor calcined at 300 degrees C exhibited the best catalytic ozonation activitywith respect to CuAl2O4 spinel phase obtained at higher temperatures. Such performance was attributed to the better textural properties and a higher density of active sites (hydroxyl groups and Lewis acidity). Specifically, the mixed oxide/O-3 process allows to reach a near complete color removal of the dye solution (100 mg L-1) in 25 min at neutral pH. Corresponding reaction rate value was measured at 0.112 min(-1) and was clearly higher compared with the single oxide ozonation process (0.071 min(-1) for CuO/O-3 and 0.074 min(-1) for Al2O3/O-3). Then, we proposed that such catalytic performance was related to a synergistic function between = Cu2+ and = Al3+, which took part of a mechanism of radical formation. In such mechanism, present = Al3+ could act as a reservoir for surface active sites such as hydroxyl groups and Lewis acid sites, while = Cu2+ could provide the possibility of electron transfer with ozone for the enhancement of radical generation. We suggested that the interaction between chemisorbed ozone and surface hydroxyl groups initially stabilized on = Al3+ initiated the generation of reactive radical species. This interaction led as well to the formation of surface adsorbed HO center dot and few O-2(center dot-) on Cu2+ Lewis acid sites. Besides, the interfacial redox reaction with ozone is favored by the presence of Cu2+ following the sequence of Cu2+/ Cu+/ Cu2+ redox cycle. (C) 2018 Elsevier B.V. All rights reserved.