Toluene Oxidation: CO2 vs Benzaldehyde: Current Status and Future Perspectives

Toluene is a common and significant volatile organic compound (VOC). Although it finds extensive application in various industrial processes (chemical manufacturing, paint and adhesive production, and as a solvent), it creates a huge environmental impact when emitted freely into the atmosphere. Two solutions were found to mitigate the emission of this pollutant: the total oxidation to CO2 and H2O and the selective oxidation into benzaldehyde. This review discusses the two main alternatives for tackling this problem: converting the toluene into carbon dioxide by total oxidation or into benzaldehyde by selective oxidation. It presents new catalytic advances, new trends, and the advantages and disadvantages of both methods.

The important role of the interaction between manganese minerals and metals in environmental remediation: a review

With illegal discharge of wastewater containing inorganic and organic pollutants, combined pollution is common and needs urgent attention. Understanding the migration and transformation laws of pollutants in the environment has important guiding significance for environmental remediation. Due to the characteristics of adsorption, oxidation, and catalysis, manganese minerals play important role in the environment fate of pollutants. This review summarizes the forms of interaction between manganese minerals and metals, the environmental importance of the interaction between manganese minerals and metals, and the contribution of this interaction in improving performance of Mn-based composite for environmental remediation. The literatures have indicated that the interactions between manganese minerals and metals involve in surface adsorption, lattice replacement, and formation of association minerals. The interaction between manganese minerals and metals plays an important role in environmental behavior of element and environmental significance of manganese minerals. The synergistic or antagonistic effect resulted from the interaction influence the purification of heavy metal and organism pollutant. The synergistic effect benefited from the coordination of adsorption and oxidation, convenient electron transfer, abundant oxygen vacancies, and fast migration of lattice oxygen. Based on the synergy, Mn-based composites have been widely used for environmental remediation. The synthesize methods of Mn-based composites mainly include homogeneous coprecipitation, chemical etching route, hydrothermal, homogeneous chelating sol-gel, and ethylene glycol reduction strategy. This review is helpful to fully understand the migration and transformation process of pollutants in the environment, expand the resource utilization of manganese minerals for environmental remediation.

Balance of activation and ring-breaking for toluene oxidation over CuO-MnOx bimetallic oxides

CuMn oxides have been studied for many years to catalytic degradation of toluene, but there are still many divergences on the essence of their great catalytic activity and reaction mechanism. A series of CuMn bimetallic oxides were synthesized for the catalytic oxidation of toluene in this study. Cu₂Mn₁ exhibited the highest toluene oxidation rate per specific surface area, which was approximately 4 times that of monometallic CuO and Mn₃O₄. Benzoic acid was the only intermediates which could be observed during toluene oxidation. Between monometallic CuO and Mn₃O₄, toluene was more difficult to be activated by Mn₃O₄ to generate benzoic acid (toluene activation), whereas benzoic acid was oxidized (ring-breaking) by CuO with more difficulty. As for CuMn, the superior reducibility combined with the balance between ring-breaking of benzoic acid and activation of toluene-to-benzoic acid determined the high toluene oxidation rate. DFT simulations exhibited that in O-Cu-O-Mn-O structure, the Mn-O site was a more effective activation site for toluene-to-benzoic acid oxidation, whereas Cu-O mainly performed as an adsorption site for toluene. This work identifies the different roles of Cu and Mn entities in toluene oxidation and provides the novel design strategy for toluene removal catalysts.