Recent advances in catalytic systems in the prism of physicochemical properties to remediate toxic CO pollutants: A state-of-the-art review

Catalysts Prepared from Atomically Dispersed Ce(III) on MgO Rival Bulk Ceria for CO Oxidation

Atomically dispersed cerium catalysts on an inert, crystalline MgO powder support were prepared by using both Ce(III) and Ce(IV) precursors. The materials were used as catalysts for CO oxidation in a once-through flow reactor and characterized by atomic-resolution scanning transmission electron microscopy, X-ray absorption near-edge structure spectroscopy, X-ray photoelectron spectroscopy, and temperature-programmed reduction, among other techniques, before and after catalysis. The most active catalysts, formed from the precursor incorporating Ce(III), displayed performance similar to that reported for bulk ceria under comparable conditions. The catalyst provided stable time-on-stream performance for as long as it was kept on-stream, 2 days, increasing slightly in activity as the atomically dispersed cerium ions were transformed into ceria nanodomains represented as CeOx and having increased reducibility on the MgO support. The results suggest how highly dispersed supported ceria catalysts with low cerium loadings can be prepared and may pave the way for improved efficiencies of cerium utilization in oxidation catalysis.

Study on the mechanism of NOx reduction by NH3-SCR over a ZnXCu1-XFe2O4 catalyst

Experimental evidence shows that CuFe₂O₄ exhibits excellent catalytic performance in the SCR reaction. However, there is a lack of in-depth research on its specific reaction mechanism. Our study begins by computing the adsorption model of molecules like NH₃ and then goes on to examine the SCR reaction mechanism of NH₃ on CuFe₂O₄ before and after Zn doping. The results indicate that NH₃ is chemically adsorbed (-1.26 eV) on the surface and has a strong interaction with the substrate. Importantly, Zn doping provides more favorable reactive sites for NH₃ molecules. Subsequent investigation into the NH₃ dehydrogenation and SCR reaction processes showed that incorporating Zn can greatly decrease the energy barrier of the most critical step in the reaction (0.58 eV). Additionally, the study also assesses the feasibility of the reaction of adsorbed NO with surface active O atoms to form NO₂ (barrier 0.86 eV). Lastly, the sulfur resistance of the catalyst before and after doping is calculated and analyzed, and it is found that Zn doping effectively improves the sulfur resistance. Our study provides valuable theoretical guidance for the development of ferrite spinel and doping modification.

The migration of CO and PM under different working conditions of trackless rubber-tyred vehicle and health risk assessment of underground personnel

Trackless rubber-tyred vehicles are among the most widely used underground auxiliary transportation equipment in major coal mines at present. The migration of exhaust gas that threaten human health varies with the working conditions of trackless rubber-tyred vehicles. In order to better evaluate the health risks faced by underground personnel in the process of exhaust emission from underground diesel vehicles, in this paper, the migration of carbon monoxide (CO) and particulate matter (PM) emitted by trackless rubber-tyred vehicle under three working conditions was analyzed by using the method of CFD (Computational Fluid Dynamics) numerical simulation and field measurement. It can be concluded that the concentrations of CO and PM changed with the change of airflow field under different working conditions, and their distribution tended to be consistent on the whole. Although the migration of CO and PM were different under different working conditions, CO with high concentration (C ≥ 44.74 ppm) and PM with high concentration (C ≥ 89.47 mg/m³) were mainly distributed in the area near the exhaust pipe of trackless rubber-tyred vehicle. Therefore, the drivers of trackless rubber-tyred vehicle and underground personnel need to comprehensively consider the risk factors under different working conditions when carrying out personal protection.

Nano-ZrO2@C, Nano-(ZrC, ZrO2)@C and Nano-ZrC@C Composites Prepared by Plasma-Assisted Carbonization of Zr-Loaded Iminodiacetate-Functionalized Styrene-Divinylbenzene Copolymers

We have developed an easy route to prepare (nano-ZrO2,nano-ZrCx)@C composites with varying ZrO2/ZrCx content. The process consists of preparing a zirconium-loaded, iminodiacetate-functionalized styrene-divinylbenzene (STY-DVB) copolymer, and its subsequent carbonization in a tube furnace and/or a thermal plasma reactor. Depending on the zirconium salt used (zirconyl chloride, zirconyl nitrate or zirconium (IV) sulfate) in the Zr loading, the Zr-loaded resins resulted in ZrO2@C pre-pyrolizates with C to Zr molar ratios of 5.8, 6.8 and 6.60. This carbon surplus is sufficient for the partial or even complete reduction of ZrO2 into ZrC0.58 at 1400 °C. The reaction products also contain 5 to 55 mass% residual free carbon. The plasma processing of the ZrO2@C composite formed at 1000 °C in a tube furnace led to ZrC0.94@C composites. The transformation of amorphous carbon content during the plasma treatment strongly depended on the atmosphere (He or H2) in the reactor and the anion type of the Zr salt. In the presence of He, amorphous carbon could be completely transformed into graphite. In the presence of H2, amorphous carbon and graphite were found at roughly the same ratio. No ZrO2 could be detected in the plasma-treated samples, whilst different ZrO2 polymorphs were found in the samples prepared in the tube furnace, depending on the synthesis conditions.

Mechanism insights into CO oxidation over transition metal modified V2O5/TiO2 catalysts: A theoretical study

The V₂O₅/TiO₂ based selective catalytic reduction (SCR) catalysts possess not only promising capability on the denitrification of nitrogen oxides (NO_x), but also certain effects on the oxidation of carbon monoxide (CO) in the flue gas. Modification of traditional SCR catalysts with certain transition metals can further improve their catalytic oxidation ability of CO. Therefore, it is of great significance to reveal the catalytic oxidation mechanism of CO for developing modified SCR catalysts to achieve the co-removal of CO and NO_x. Theoretical calculations based on density functional theory (DFT) were performed to probe the comprehensive reaction mechanism of CO oxidation on M doped V₂O₅/TiO₂ catalysts (M = Mo, Fe, and Co). The whole CO oxidation cycles include three stages, i.e., the first CO oxidation, the re-oxidation of the surface, and the second CO oxidation. The terminal oxygen and the surface oxygen formed by the adsorbed O₂ all play vital roles in the whole CO oxidation cycles. The activation barriers of the rate-determining steps for CO oxidation on Fe-V₂O₅/TiO₂ and Co-V₂O₅/TiO₂ are much lower than that of Mo-V₂O₅/TiO₂, which indicates Fe and Co dopants can apparently promote the CO oxidation activities of the modified SCR catalysts. Meanwhile, the electronic structure analysis confirms that Fe and Co dopants can cause electron distribution change with strong oxidation ability at the active oxygen sites.

Recent Breakthroughs and Advancements in NOx and SOx Reduction Using Nanomaterials-Based Technologies: A State-of-the-Art Review

Nitrogen and sulpher oxides (NO_x, SO_x) have become a global issue in recent years due to the fastest industrialization and urbanization. Numerous techniques are used to treat the harmful exhaust emissions, including dry, traditional wet and hybrid wet-scrubbing techniques. However, several difficulties, including high-energy requirement, limited scrubbing-liquid regeneration, formation of secondary pollutants and low efficiency, limit their industrial utilization. Regardless, the hybrid wet-scrubbing technology is gaining popularity due to low-costs, less-energy consumption and high-efficiency removal of air pollutants. The removal/reduction of NO_x and SO_x from the atmosphere has been the subject of several reviews in recent years. The goal of this review article is to help scientists grasp the fundamental ideas and requirements before using it commercially. This review paper emphasizes the use of green and electron-rich donors, new breakthroughs, reducing GHG emissions, and improved NO_x and SO_x removal catalytic systems, including selective/non-catalytic reduction (SCR/SNCR) and other techniques (functionalization by magnetic nanoparticles; NP, etc.,). It also explains that various wet-scrubbing techniques, synthesis of solid iron-oxide such as magnetic (Fe₃O₄) NP are receiving more interest from researchers due to the wide range of its application in numerous fields. In addition, EDTA coating on Fe₃O₄ NP is widely used due to its high stability over a wide pH range and solid catalytic systems. As a result, the Fe₃O₄@EDTA-Fe catalyst is projected to be an optimal catalyst in terms of stability, synergistic efficiency, and reusability. Finally, this review paper discusses the current of a heterogeneous catalytic system for environmental remedies and sustainable approaches.