Nano ferrites (AFe2O4, A = Zn, Co, Mn, Cu) as efficient catalysts for catalytic ozonation of toluene.

Abstract

Nano ferrites (AFe2O4, A = Zn, Co, Mn, Cu) were supported on the surface of γ-Al2O3 support by hydrothermal synthesis to prepare a series of novel composite catalysts (AFe2O4/γ-Al2O3) for catalytic ozonation for elimination of high concentration toluene at ambient temperature. The characterization results showed that the high-purity nano-AFe2O4 particles were uniformly loaded on mesoporous γ-Al2O3. Further, it was confirmed that among the several catalysts prepared, the amount of oxygen vacancies (Ovs), Lewis acid sites (LAS), and Brønsted acid sites (BAS) of the ZnFe2O4/γ-Al2O3 catalyst were the highest. This meant that the ZnFe2O4/γ-Al2O3 catalyst had a strong adsorption capacity for toluene and ozone (O3), and had a strong catalytic activity. When the temperature was 293 K and the space velocity was 1500 h−1, the mol ratio of O3 to toluene was 6, the degradation rate of toluene (600 mg m−3) can reach an optimum of 99.8%. The results of electron paramagnetic resonance (EPR) and Fourier infrared (FT-IR) proved superoxide radicals and hydroxyl radicals by catalytic ozonation. Moreover, the GC-MS analysis results indicated that the toluene degradation began with the oxidation of methyl groups on the benzene ring, eventually producing CO2 and H2O. After repeated experiments, the toluene degradation rate remained stable, and the residual content of O3 in each litre of produced gas was less than 1 mg L−1, thereby indicating that the ZnFe2O4/γ-Al2O3 catalyst had excellent reusability and showed great potential for the treatment of toluene waste gas.