The present work studied ibuprofen degradation using titanium dioxide as a photocatalyst. Mechanistic aspects were presented and the preferred attack sites by the OH˙ radical on the ibuprofen molecule were detailed, based on experimental and simple theoretical-computational results. Although some previous studies show mechanistic proposals, some aspects still need to be investigated, such as the participation of 4-isobutylacetophenone in the ibuprofen degradation and the preferred regions of attack by OH˙ radicals. The photodegradation was satisfactory using 0.03 g of TiO₂ and pH = 5.0, reaching 100% decontamination in 5 min. The zeta potential curve showed the regions of attraction and repulsion between TiO₂ and ibuprofen, depending on the pH range and charge of the species, influencing the amount of by-products formed. Different by-products have been identified by GC-MS, such as 4-isobutylacetophenone. Ibuprofen conversion to 4-isobutylacetophenone takes place through decarboxylation reaction followed by oxidation. The proposed mechanism indicates that the degradation of ibuprofen undergoes a series of elementary reactions in solution and on the surface. Three different radicals (OH˙, O₂ ⁻˙ and OOH˙) are produced in the reaction sequence and contribute strongly to the oxidation and mineralization of ibuprofen and by-products, but the hydroxyl radical has a greater oxidation capacity. The simple study using the DFT approach demonstrated that the OH˙ radical attacks preferentially in the region of the ibuprofen molecule with high electronic density, which is located close to the aromatic ring (CC bond). The presence of the OH˙ radical was confirmed through a model reaction using salicylic acid as a probe molecule.

A polymeric precursor method was applied to synthesize catalysts of the general formula MFe₂O₄ (M = Co and Ni) in order to contribute to studies on ethylbenzene dehydrogenation in the presence of CO₂. The catalysts were characterized by TG, H₂-TPR, XRD, Mossbauer spectroscopy (MS), N₂ adsorption/desorption isotherms and TPD-CO₂. Investigations using XRD and MS revealed that the spinel structures of CoFe₂O₄ and NiFe₂O₄ phases were formed. The catalytic results suggested that materials with a spinel structure are particularly interesting for ethylbenzene dehydrogenation. Compared to the other catalysts synthesized the sample containing cobalt ferrite showed higher conversion and good styrene selectivity. The analysis of the spent catalyst (DRX) showed that the CoFe₂O₄ phase was stable under the reaction conditions and that a coke (TG) deposit was more pronounced for the NiFeSi.

The present study describes the catalytic performance of cobalt ferrite supported on MCM-41 for the oxidative dehydrogenation of ethylbenzene. The catalytic activity of cobalt ferrite was compared with that of the traditional hematite based catalyst. A mechanism is described indicating the role of the O²⁻–Fe³⁺–O²⁻ and O²⁻–Co²⁺–O²⁻ acid–base sites present in the tetrahedral and octahedral positions of the cobalt ferrite structure. The solids were characterized by X-ray diffraction (XRD), Raman spectroscopy (RS), Mössbauer spectroscopy (MS), X-ray photoelectron spectroscopy (XPS), vibrating-sample magnetometry (VSM), temperature-programmed reduction (H₂-TPR), chemical adsorption of NO and pyridine followed by infrared analysis, temperature programmed desorption of CO₂ (TPD), N₂ physisorption and transmission electronic microscopy (TEM). The catalytic tests were performed in a fixed bed reactor using a saturator containing ethylbenzene. The XRD, RS, MS and VSM results confirmed the formation of cobalt ferrite, which was classified as partially inverted ferrite. The low-angle XRD, N₂ isotherms and TEM images show the formation of the mesoporous MCM-41 support with a high surface area. The catalytic tests confirmed that the cobalt ferrite is more active and stable than the traditional hematite catalyst. The catalytic cycle for ethylbenzene dehydrogenation occurs preferentially in the O²⁻–Fe³⁺–O²⁻ octahedral sites compared to the O²⁻–Co²⁺–O²⁻ sites. A theoretical approach using density functional theory revealed a higher acidity of iron sites compared to cobalt ones on the surface of the partially inverted spinel. The adsorption of ethylbenzene takes place preferentially in the outermost FeO_x (x > 4) sites (Lewis acid) and the dehydrogenation reaction occurs predominantly in the oxygens bound to iron (Lewis base) according to the complementary electrostatic potential surface approach.