Engineering of oxygen vacancy defect in CeO2 through Mn doping for toluene catalytic oxidation at low temperature

Ce-based three-dimensional mesoporous microspheres with Mn homogeneous incorporation for toluene oxidation

Ce-based three-dimensional (3D) mesoporous microspheres with Mn homogeneous incorporation were synthesized. The CeMn-0.4, characterized by a Ce/Mn molar ratio of 6:4, demonstrated exceptional catalytic activity and stability. The formation of CeMn solid solution strengthened the Ce-Mn interaction, yielding higher concentrations of Ce3+ and Mn4+. Mn4+ initiated toluene preliminary activation owing to its robust oxidative properties, while Ce3+ contributed to oxygen vacancy generation, enhancing the activation of gaseous oxygen and lattice oxygen mobility. Integrating experiments and Density Functional Theory (DFT) calculations elucidated the oxygen reaction mechanisms. A portion of oxygen was converted into surface reactive oxygen species (Oads) that directly oxidized toluene. Additionally, the presence of oxygen vacancies promoted the participation of oxygen in toluene oxidation by converting it into lattice oxygen, which was crucial for the deep oxidation of toluene. Diffuse Reflectance Fourier Transform Infrared Spectroscopy (DRIFTS) indicated the accumulation of benzene-ring intermediates on the catalyst surface hindered continuous toluene oxidation. Thus, the abundant oxygen vacancies in CeMn-0.4 played a pivotal role in sustaining the oxidation process by bolstering the activation of gaseous oxygen and the mobility of lattice oxygen.

Theory-guided unraveling of the mechanism underlying Cu1.0/Mn1.0-ZnO with dual reaction centers for enhanced peroxymonosulfate activation

Developing efficient catalytic systems for water contamination removal is a topic of great interest. However, the use of heterogeneous catalysts faces challenges due to insufficient active sites and electron cycling. In this study, results from first-principles calculations demonstrate that dual reaction centers (DRCs) are produced around the Cu and Mn sites in Cu1.0/Mn1.0-ZnO due to the electronegativity difference. Experimental results reveal the material with DRCs greatly enhances electron transfer efficiency and significantly impacts the oxidation and reduction of peroxymonosulfate (PMS). In addition, the self-consistent potential correction (SCPC) method was introduced to correct the energy and charge of charged periodic systems simulating a catalytic process, resulting in more precise catalytic results. Specifically, the material exhibits a preference for adsorbing negatively charged PMS anions at electron-deficient Mn sites, facilitating PMS oxidation for the generation of 1O2, and PMS reduction around the electron-rich Cu for the formation of •OH and SO4•-. The major reactive oxygen species is 1O2, showcasing effective performance in various degradation systems. Overall, our work provides novel insights into the persulfate-based heterogeneous catalytic oxidation process, paving the way for the development of high-performance catalytic systems for water purification.

Establishing efficient toluene elimination over cobalt-manganese bimetallic oxides via constructing strong Co-Mn interaction

Doping proves to be an efficacious method of establishing intermetallic interactions for enhancing toluene oxidation performance of bimetallic oxides. However, conventional bimetallic oxide catalysts are yet to overcome their inadequacy in establishing intermetallic interactions. In this work, the dispersion of Mn-Co bimetallic sites was improved by hydrolytic co-precipitation, strengthening the intermetallic interactions which improved the structural and physicochemical properties of the catalysts, thus significantly enhancing its catalytic behavior. MnCo-H catalysts fabricated by the hydrolytic co-precipitation method showed promising catalytic performance (T50 = 223 °C, T90 = 229 °C), robust stability (at least 100 h) and impressive water resistance (under 10 vol.% of water) for toluene elimination. Hydrolytic co-precipitation has been found to improve dispersion of MnCo elements and to enhance interaction between Co and Mn ions (Mn4+ + Co2+ = Mn3+ + Co3+), resulting in a lower reduction temperature (215 °C) and a weaker Mn-O bond strength, creating more lattice defects and oxygen vacancies, which are responsible for superior catalytic properties of MnCo-H samples. Furthermore, in situ DRIFTs showed that gaseous toluene molecules adsorbed on the surface of MnCo-H were continuously oxidized to benzyl alcohol → benzaldehyde → benzoate, followed by a ring-opening reaction with surface-activated oxygen to convert to maleic anhydride as the final intermediate, which further generates water and carbon dioxide. It was also revealed that the ring-opening reaction for the conversion of benzoic acid to maleic anhydride is the rate-controlling step. This study reveals that optimizing active sites and improving reactive oxygen species by altering the dispersion of bimetals to enhance bimetallic interactions is an effective strategy for the improvement of catalytic behavior, while the hydrolytic co-precipitation method fits well with this corollary.

The removal of toluene by thermoscatalytic oxidation using CeO2-based catalysts:a review

Volatile organic compounds (VOCs) pose a serious threat to human health and the ecological environment. Thermal catalytic oxidation based on cerium dioxide based (CeO2-based) catalysts is widely used in the degradation of toluene. However, new problems and challenges such as how to reduce the energy consumption during catalytic oxidation, improve the anti-poisoning performance of catalysts, and enhance the multi-species synergistic catalytic ability of catalysts continue to emerge. On this basis, we systematically summarize the current status of research progress on the thermocatalytic oxidation of toluene based on CeO2-based catalysts. Firstly, we summarized the rules on how to improve the catalytic performance and anti-poisoning performance of CeO2-based catalysts; Secondly, we discussed the effect of light reaction conditions on the thermal coupled catalytic oxidation of toluene; In addition to this, we explored the current status of synergistic multi-pollutant degradation, mainly of toluene; Finally, we summarized the mechanism of catalytic oxidation of toluene by combining theoretical simulation calculations, in-situ infrared analyses, and other means. We present the promising applications of CeO2-based catalysts in the catalytic oxidation of toluene, and hope that these summaries will provide an important reference for the catalytic treatment of VOCs.