Microwave-assisted catalytic wet peroxide oxidation. Comparison of Fe catalysts supported on activated carbon and ?-alumina

- MW affects quite differently to the performance of Fe/AC and Fe/?-Al2O3 in CWPO.
- The dielectric properties of the support are critical for MW-CWPO.
- The high MW absorption of AC explains its better performance.
- MW enhanced phenol mineralization with Fe/AC respect to conventional CWPO.
- Even the bare AC showed a better performance than Fe/?-Al2O3.

This paper studies the role of the catalytic support on microwave-assisted catalytic wet peroxide oxidation (MW-CWPO) with Fe as active phase. Experiments were carried out with and without MW using catalysts of Fe on activated carbon (Fe/AC) and gamma alumina (Fe/?-Al2O3). Phenol (100 mg·L-1) was used as target pollutant, operating at pH 3, 120 °C, 100 mg·L-1 catalyst concentration and the theoretical stoichiometric amount of H2O2 (500 mg·L-1). MW radiation promotes hot spot formation on the surface of AC, enhancing HOX generation, so that the rate of mineralization is significantly increased with respect to non-assisted CWPO. Under these conditions, phenol oxidation proceeded essentially through direct aromatic ring breakdown, yielding carboxylic acids, while the formation of the highly toxic intermediates hydroquinone and p-benzoquinone were barely detected. The Fe/AC catalyst showed a better performance than the Fe/?-Al2O3 one, which can be explained by the much higher MW absorption on AC, which, in fact, showed to be a good MW-CWPO catalyst by itself. Meanwhile, the results proved that ?-Al2O3 was basically transparent to MW, and deposition of condensation byproducts on the surface hindered the activity of the Fe/?-Al2O3 catalyst.

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