Mechanism Of Catalytic Oxidation Research Articles

High catalytic performance of thermally treated Mn-rich limonite for catalytic oxidation of toluene

Abstract The development of active and low-cost transition metal oxide-based catalysts was vital for the catalytic oxidation of toluene. This study aimed to prepare Fe-Mn oxide catalysts by Mn-rich limonite, and investigate the catalytic activity and mechanism for toluene oxidation. The natural Mn-rich limonite was thermally activated at different temperatures and these thermally activated samples exhibited different oxidation activities. YL-300, obtained through thermal treatment at 300°C, exhibited excellent catalytic activity, showing 90% toluene conversion at 239°C (1000 ppm toluene) and remarkable catalytic stability even in the presence of water vapor (5 vol.%). The amount of oxygen vacancies in the catalyst was regulated by tuning the thermal treatment temperatures. Optimal thermal treatment facilitated the increase of oxygen vacancies and enhanced the oxygen mobility and redox capacity of YL-300, contributing to the complete oxidation of toluene to H2O and CO2. The oxidation of toluene was greatly influenced by the adsorbed oxygen species. This study demonstrates the potential of Mn-rich limonite as a promising catalyst for toluene oxidation, thereby promoting the utilization of natural mineral materials in the field of environmental pollution control.

The progress of research on vacancies in HMF electrooxidation.

5-Hydroxymethylfurfural (HMF), serving as a versatile platform compound bridging biomass resource and the fine chemicals industry, holds significant importance in biomass conversion processes. The electrooxidation of HMF plays a crucial role in yielding the valuable product (2,5-furandicarboxylic acid), which finds important applications in antimicrobial agents, pharmaceutical intermediates, polyester synthesis, and so on. Defect engineering stands as one of the most effective strategies for precisely synthesizing electrocatalytic materials, which could tune the electronic structure and coordination environment, and further altering the adsorption energy of HMF intermediate species, consequently increasing the kinetics of HMF electrooxidation. Thereinto, the most routine and effective defect are the anionic vacancies and cationic vacancies. In this concise review, the catalytic reaction mechanism for selective HMF oxidation is first elucidated, with a focus on the synthesis strategies involving both anionic and cationic vacancies. Recent advancements in various catalytic oxidation systems for HMF are summarized and synthesized from this perspective. Finally, the future research prospects for selective HMF oxidation are discussed.

Sulfur resistance mechanism of PdSx catalysts in catalytic oxidation of toluene

A series of catalysts were prepared by gas-phase sulfidation. The mechanism of catalytic oxidation of VOCs is the MVK mechanism.

Catalytic oxidation mechanism of ethyl acetate on O-ligand-single-atom-Ni/2-dimensional reduced graphene oxide: the essential role of the O ligand

The catalytic oxidation of ethyl acetate by SANi5-O-2DRGO is an example to display the electron transfer and detailed structural changes of the O ligand.

Catalytic Oxidation Mechanism of Toluene on the Ce0.875Zr0.125O2 (110) Surface

Aromatic volatile organic compounds (VOCs) are toxic to public health and contribute to global air pollution; thus, it is urgent to control VOC emissions. Catalytic oxidation technology has been widely investigated to eliminate aromatic VOCs; this technology exhibits high catalytic efficiency even at low temperatures. However, the reaction mechanism of aromatic VOCs’ total oxidation over metal-oxide-based catalysts, which is of great significance in the design of catalysts, is not yet clear. In this study, we systemically calculated the catalytic oxidation mechanism of toluene over the Ce0.875Zr0.125O2 catalyst using density functional theory (DFT). The results show that toluene first loses hydrogen from the methyl group via oxy-dehydrogenation and is gradually oxidized by lattice or adsorbed oxygen to benzyl alcohol, benzaldehyde, and benzoic acid following the Mars-van Krevelen (MVK) mechanism. Afterwards, there is a decarboxylation step to produce phenyl, which is further oxidized to benzoquinone. The rate-determining step then proceeds via the ring-opening reaction, leading to the formation of small molecule intermediates, which are finally oxidized to CO2 and H2O. This work may provide atomic-scale insight into the role of lattice and adsorbed oxygen in catalytic oxidation reactions.

Insights into the differences in metal anchoring mechanisms and the impact on HCN catalytic oxidation performance

Hydrogen cyanide (HCN) is often produced in various industrial processes, such as metal smelting, carbon fiber production, etc. Due to its highly toxic nature, it has significant harm to the human body and the environment. Catalytic oxidation can convert HCN into non-toxic N2, CO2 and H2O. In this study, we conducted a comparative evaluation of the catalytic oxidation of HCN using Cu, Co and Mn as catalyst active centers, and used in situ DRIFTS to explore the reaction mechanism of HCN catalytic oxidation. The difference in the anchoring state of different metals on the hydroxyl groups on the Al2O3 surface, mainly the difference in anchoring strength and hydroxyl consumption, determines the difference in the metal dispersion state, which in turn affects the oxygen activation ability and HCN oxidation performance. Under high loading conditions, compared to Co and Mn, Cu species are more fully anchored due to lower hydroxyl consumption, exhibiting higher dispersion and redox properties, so the 10Cu/Al2O3 catalyst performs well HCN oxidation activity.

Unveiling the electron-acceptor effect in selenium-doped Cu-N-C catalyst with atomically dispersed active sites for boosting Hg0 oxidation

M-N-C catalysts have considerable potential in the fields of catalysis, such as highly polluting gaseous elemental mercury (Hg0) oxidation. However, the direct application of these kinds of catalysts for mercury removal is stymied by their low catalytic efficiency. Heteroatom-doping in M-N-C catalysts has been proposed as a powerful strategy to the promote catalytic of Hg0, but the origin of boosting catalytic activity is still elusive. Herein, it is disclosed that selenium doping induces an obvious electron-acceptor effect for accelerating the Hg0 catalytic oxidation. The model selenium-doped Cu-N-C catalyst with atomically dispersed active sites was verified by various characterization methods, such as SEM-EDS and scanning transmission electron microscopy. The optimal Cu-NC-Se with Cu/Se ratio of 1:1 exhibited the best Hg0 removal performance, over 8-fold enhancement in their Hg0 oxidation capacities than raw selenium-free Cu-NC. At the optimal reaction temperature of 90 °C, Cu-NC-Se achieved an average Hg0 removal rate of 92.44% within 60 min under single pure N2 atmosphere. As for the influence of flue gas components, the presence of O2 promoted the removal of mercury in Cu-NC-Se, whereas CO2, NO and SO2 served as slight inhibitors. Even after five cycles of the experiment, the average mercury oxidization efficiency was still remained at 88.5%, showing that Cu-NC-Se can be reused with good maintenance of the catalytic activity and atomic dispersion of Cu and Se in the structure. The unsaturated Cu sites connected with pyridinic N on the carbon matrix can serve preferential adsorption to Hg0 and doped selenium. Meanwhile, the selenium doping accelerated Hg0 adsorption and accept sufficient electrons for promoting Hg0 oxidation to forming stable HgSe, which is also corroborated by the theoretical analysis results based on density functional theory. This work not only provides an alternative facile synthetic strategy for developing heteroatom-doping atomically dispersed M-N-C catalysts, but also represents a significant advance for deepening the understanding of the Hg0 catalytic oxidation mechanism on M-N-C catalyst.

La-doped macroporous carbon fiber catalytic converter for tetracycline efficient removal

Metal-organic frameworks (MOFs) show substantial potential and impressive development prospects in persulfate-based advanced oxidation (SR-AOPs) due to their exceptional structural advantages. Nevertheless, the structural characteristics, catalytic performance, and catalytic mechanism of lanthanide metal-doped MOFs (La-MOFs) remain unclear. Therefore, we prepared lanthanum-nitrogen co-doped hollow carbon nanofibers (La-HCNFs) through electrospinning and pyrolysis to study the structure, catalytic activity, and mechanism of La-MOFs. Furthermore, we analyzed the physicochemical properties of La-HCNFs with a range of characterisation techniques, and examined the catalytic oxidation mechanism with quenching experiments. Finally, this study clarifies the role of SR-AOPs in La-MOFs and indicates pathways for future research on La-MOFs materials, in order to advance the use of MOFs materials in environmental chemistry and sustainable catalysis.

Synergies of redox ability and acidity over RuMn/ZSM-5 for catalytic elimination of 1,2-dichloroethane

Ru-Mn bimetallic catalyst supported on HZSM-5 was prepared by impregnation method for catalytic oxidation of 1, 2-dichloroethane (1, 2-DCE). The 0.1Ru1Mn/ZSM-5 catalyst exhibited the lowest T90 of 241 °C and the highest yields of HCl (75%) and CO2 (57%). The products contained a small amount of dichloroethylene, trichloroethylene, and tetrachloroethylene, with a total yield of <5%. By the characterizations of various instruments, it was found that 0.1Ru1Mn/ZSM-5 exhibited the best catalytic activity because of its rich acidity, high redox property, and highly dispersed Ru and Mn nanoparticles on the surface of HZSM-5. Furthermore, due to the synergies of Ru-Mn bimetal and redox ability-acidity, 0.1Ru1Mn/ZSM-5 exhibited excellent chlorine resistance ability and good catalytic activity during long-term test. The reaction mechanism of catalytic oxidation of 1, 2-DCE was investigated using in situ DRIFTS and GC–MS techniques. Vinyl alcohol was the vital intermediates for 1, 2-DCE oxidation to CO2 and H2O. The double synergistic strategy can provide a reference for designing catalysts to remove chlorinated volatile organic compounds.

Catalytic oxidation of carbon monoxide over copper oxide with interfering gases involved for industrial buildings: An experimental and theoretical study

With the intention of thoroughly eliminating carbon monoxide (CO) from indoor environment, it is one of the most promising methods of converting it into carbon dioxide (CO2) via catalytic oxidation processes. Therefore, in this study, catalytic oxidation mechanisms of CO over copper oxide (CuO) with interfering gases involved are investigated via theoretical calculations and experimental verification, which mainly include basic catalytic oxidation processes over CuO, effects of different interfering gases and analyses of thermodynamic features. According to results, catalytic oxidation of CO over CuO can be performed in three different routes and rate-determining transition-state (TS) energy barriers vary a lot from route to route at high temperature owing to different thermal stability. In the meantime, SO2, H2O and NO are theoretically proved to affect catalytic oxidation of CO via competitive adsorption, high oxidizability and hydrogen bonds, which are accompanied with different sensitivities to changes of temperature or temperature power exponents. In experiments, it is found that impurity of lattice planes and small specific surface areas in CuO are key to restricting catalytic oxidation performances. What is more, some extra chemical reactions in experiments (e.g. SO2 + O2 + CuO → CuSO4, NO + O2 + CO → CO2 + NO) caused by interfering gases colossally affect catalytic oxidation performances of CuO. The whole study provides crucial information for indoor air purification in industrial buildings by using cheap adsorbents/catalysts.

Influence of Rare-Earth Promoters (Ce, Zr and La) on Catalytic Performance of Copper-Based Catalyst in Toluene Oxidation

ABSTRACT Copper-infused mixed metal oxides have been identified as powerful catalysts for eliminating volatile organic compounds (VOCs) due to their widespread availability and cost-effectiveness. The copper metal oxide catalysts were synthesized using the sol-gel method and promoted with rare earth elements, La, Ce, and Zr, to catalyze the oxidation of toluene. Compared to all tested catalysts, CuLaOx demonstrates the least activity igniting activity even though La appears to enhance copper dispersion and generate a large number of oxygen species on the surface. CuZrOx displays remarkable thermal stability, resulting in a minimal amount of lattice oxygen participating in toluene oxidation. The introduction of Ce into the CuCeOx catalyst enhances its activity significantly, attributed to the exceptional reducibility of copper species. Therefore, the TOF for the CuCeOx, CuLaOx and CuZrOx catalysts are 9.23–24.8 × 10−3 s−1, 1.29–6.22 × 10−3 s−1, and 1.05–10.03 × 10−3 s−1 at 200–400 °C, respectively. The infrared spectra, observed at varying temperatures during toluene oxidation, were presented. Interestingly, all catalysts demonstrated a comparable reaction pathway. The catalytic oxidation mechanism is expected to proceed via the intermediates of toluene-alkoxide-aldehydic-carboxylic acid, ultimately culminating in complete degradation to CO2 and H2O. This study establishes a theoretical foundation for the judicious selection of suitable rare earth elements as promoters, enabling the development of copper-based catalysts for efficient volatile organic compound (VOC) removal in industrial settings.

Ultrathin MnO2 with strong lattice disorder for catalytic oxidation of volatile organic compounds

Catalytic oxidation proves the most promising technology for volatile organic compounds (VOCs) abatement. Lattice disorder plays a crucial role in the catalytic activity of catalysts due to the exposure of more active sites. Inspired by this, we successfully prepared a series of ε-MnO2 with different lattice disorder defects via several simple methods and applied them to the catalytic oxidation of two typical VOCs (toluene and acetone). Various characterizations and performance tests confirm that the ultrathin (1.4–1.8 nm) structure and strong lattice disorder can enhance the low temperature reduction and reactive oxygen species, so that MnO2-R exhibits excellent toluene and acetone oxidation activities. In-situ DRIFTS tests were carried out to detect reaction intermediates in the toluene and acetone oxidation process on the catalyst surface. Moreover, we propose a possible synergistic mechanism for toluene and acetone mixtures catalytic oxidation. This work reveals the important role of lattice disorder defects in the catalytic oxidation of VOCs on Mn-based catalysts, and deepens the insights of the reaction path in toluene and acetone catalytic oxidation.

Catalytic aerobic oxidation of carbohydrates to formic acid over H5PV2Mo10O40: Rate relationships among catalyst reduction, catalyst re-oxidation and acid-catalyzed reactions and evidence for the Mars-van Krevelen mechanism

Catalytic aerobic oxidation of biomass-derived carbohydrates is a promising way to sustainably produce formic acid. Understanding the rate relationships among catalyst reduction, catalyst re-oxidation and acid-catalyzed reactions occurring in catalytic systems is significant for the revelation of catalytic mechanism and the selection of reaction conditions. Herein, the rate relationships among the multiple reactions over an excellent homogeneous catalyst, H5PV2Mo10O40 (HPA-2) were investigated. A rate matching relationship between catalyst reduction and catalyst re-oxidation was unveiled by the separate redox kinetics of catalyst, indicating that higher O2 pressures are required to maintain the activity of HPA-2 at higher temperatures. The consistency between the separate redox kinetics and the catalytic oxidation provided the first kinetic evidence of the Mars-van Krevelen mechanism for catalytic oxidation of carbohydrates. Furthermore, rate relationships among the multiple reactions at different conditions were discussed to clarify the correlation between product selectivity and reaction conditions.

Recent Advances in Co3O4-Based Composites: Synthesis and Application in Combustion of Methane.

In recent years, it has been found that adjusting the organizational structure of Co3O4 through solid solution and other methods can effectively improve its catalytic performance for the oxidation of low concentration methane. Its catalytic activity is close to that of metal Pd, which is expected to replace costly noble metal catalysts. Therefore, the in-depth research on the mechanism and methods of Co3O4 microstructure regulation has very important academic value and economic benefits. In this paper, we reviewed the catalytic oxidation mechanism, microstructure regulation mechanism, and methods of nano-Co3O4 on methane gas, which provides reference for the development of high-activity Co3O4-based methane combustion catalysts. Through literature investigation, it is found that the surface energy state of nano-Co3O4 can be adjusted by loading of noble metals, resulting in the reduction of Co-O bond strength, thus accelerating the formation of reactive oxygen species chemical bonds, and improving its catalytic effect. Secondly, the use of metal oxides and non-metallic oxide carriers helps to disperse and stabilize cobalt ions, improve the structural elasticity of Co3O4, and ultimately improve its catalytic performance. In addition, the performance of the catalyst can be improved by adjusting the microstructure of the composite catalyst and optimizing the preparation process. In this review, we summarize the catalytic mechanism and microstructure regulation of nano-Co3O4 and its composite catalysts (embedded with noble metals or combined with metallic and nonmetallic oxides) for methane combustion. Notably, this review delves into the substance of measures that can be used to improve the catalytic performance of Co3O4, highlighting the constructive role of components in composite catalysts that can improve the catalytic capacity of Co3O4. Firstly, the research status of Co3O4 composite catalyst is reviewed in this paper. It is hoped that relevant researchers can get inspiration from this paper and develop high-activity Co3O4-based methane combustion catalyst.

Process compatible desulfurization of new suspension preheater cement production: Rapid catalytic oxidation of trace SO2 over V2O5-based catalysts in preheater environment

Efficient capture of sulfur dioxide (SO2) in the preheater of the cement production system is the key to achieving process compatible flue gas desulfurization (FGD). Herein, the rapid oxidation of trace SO2 over V2O5-based catalysts in the preheater environment was realized to enhance the SO2 capture capacity of limestone in raw meal, and the catalytic efficiency was further improved by 45.2%, 56.1% and 61.9% after introducing TiO2/MnO2/CeO2 as cocatalysts, respectively. The V2O5-based catalysts had superior catalytic behavior only when the flue gas temperature exceeded 500 °C, while the composition variation of flue gas had a minor influence on SO2 oxidation. Finally, a maximum SO2 oxidation efficiency of 68.1% was achieved in the presence of 4.0% O2, 25.0% CO2 and 15.0% H2O at 600 °C. Furthermore, the mechanism of SO2 catalytic oxidation over V2O5-based catalysts was deduced based on the results of XRD, BET, XPS and Raman, and V5+ was identified as the primary vanadium species for SO2 oxidation. The results provide a deeper insight into the catalytic oxidation of SO2 in the preheater environment, and then facilitate the improvement of process compatible FGD and available dry FGD technologies for cement industry.

Catalytic Oxidation Mechanism of Toluene over CexMn1-xO2: The Role of Oxygen Vacancies in Adsorption and Activation of Toluene.

Catalytic oxidation has been extensively studied as a promising technology for the removal of toluene from industrial waste gases and indoor air. However, the debate regarding the oxidation mechanism is far from resolved. CexMn1-xO2 catalysts with different mixing ratios are prepared by the sol-gel method and found to exhibit better catalytic activities for toluene oxidation than a single oxide. Characterizations and theoretical calculations reveal that the doped Mn increases the number of oxygen vacancies and the ability of oxygen vacancies to activate aromatic rings, which promotes the rate-determining step of toluene oxidation, i.e., ring-opening reactions. The oxidation products detected by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and Vocus proton transfer reaction mass spectrometry (Vocus-PTR-MS) show that the doped Mn significantly improves the ring-opening efficiency and subsequently yields more short-chain products, such as pyruvic acid and acetic acid. A comprehensive oxidation pathway of toluene is refined in this work.

Electrospun Ce–Mn oxide as an efficient catalyst for soot combustion: Ce–Mn synergy, soot-catalyst contact, and catalytic oxidation mechanism

Increasing the contact efficiency and improving the intrinsic activity are two effective strategies to obtain efficient catalysts for soot combustion. Herein, the electrospinning method is used to synthesize fiber-like Ce–Mn oxide with a strong synergistic effect. The slow combustion of PVP in precursors and highly soluble manganese acetate in spinning solution facilitates the formation of fibrous Ce–Mn oxides. The fluid simulation clearly indicates that the slender and uniform fibers provide more interwoven macropores to capture soot particles than the cubes and spheres do. Accordingly, electrospun Ce–Mn oxide exhibits better catalytic activity than reference catalysts, including Ce–Mn oxides by co-precipitation and sol-gel methods. The characterizations suggest that Mn3+ substitution into fluorite-type CeO2 enhances the reducibility through the acceleration of Mn–Ce electron transfer, improves the lattice oxygen mobility by weakening the Ce–O bonds, and induces oxygen vacancies for the activation of O2. The theoretical calculation reveals that the release of lattice oxygen becomes easy because of a low formation energy of oxygen vacancy, while the high reduction potential is beneficial for the activation of O2 on Ce3+-Ov (oxygen vacancies). Due to above Ce–Mn synergy, the CeMnOx-ES shows more active oxygen species and higher oxygen storage capacity than CeO2-ES and MnOx-ES. The theoretical calculation and experimental results suggest that the adsorbed O2 is more active than lattice oxygen and the catalytic oxidation mainly follows the Langmuir-Hinshelwood mechanism. This study indicates that electrospinning is a novel method to obtain efficient Ce–Mn oxide.

Insights into catalytic oxidation mechanism of CO over Cu catalyst: Experimental and modeling study

Cu thin films have been synthesized using a chemical vapor deposition technique for catalytic kinetic study of CO oxidation. The obtained samples are morphologically uniform and homogeneous with porous textures. Structure analysis by X-ray diffraction indicated the formation of pure Cu metal. X-ray photoelectron spectroscopy exhibited the existence of Cu in a metallic state at the surface, in addition to a minor quantity of Cu1+ that could be formed during the deposition process. The catalytic performance was evaluated through CO oxidation at gas hourly space velocity (GHSV) of ∼300,000 mL·g−1·h−1. The results showed that the Cu catalyst is very active in CO oxidation. The CO2 effect on the CO conversion during the catalytic reaction was investigated by using different amounts of CO2 in the inlet gas mixtures. Moreover, density functional theory (DFT) calculations were performed to determine the adsorption and reaction energies, revealing the best results on Cu hollow active sites. The surface reaction mechanism of the catalytic oxidation of CO over Cu catalyst was developed with reasonable prediction against the measured results. The simulated results revealed a good correlation with the experimental data when Langmuir-Hinshelwood (LH) mechanism is followed. CO2 exhibits an inhibiting effect on the catalytic oxidation of CO. Accordingly, the findings revealed that combining experimental data and theoretical calculations could allow a better understanding of the catalytic reaction mechanism, which can pave the way to investigate other catalytic reactions.

Revealing active edge sites induced by oriented lattice bending of Co-CeO2 nanosheets for boosting auto-exhaust soot oxidation

Herein, a series of Cox-CeO2 nanosheet catalysts were elaborately synthesized by a one-step hydrothermal method. The CeO2 microsphere with crossed nanosheets can improve the soot-catalyst contact efficiency and the lattice substitution of Co ions for cerium sites in CeO2 results in the oriented lattice bending of Co-CeO2 nanosheets for improving adsorption/activation properties of NO and O2. Co2-CeO2 catalyst displays the highest H2O-tolerance activity (T50 = 334 °C, TOF = 1.32 h−1) and excellent stability during soot oxidation in the presence of H2O. Combined with characterizations and DFT calculations, the mechanism was proposed: the active edge sites located at the oriented lattice bending of Co-CeO2 nanosheets can activate surface oxygen and gaseous O2, and active oxygen species can boost NO oxidation to NO2, which is a crucial step of NOx-assistant catalytic mechanism for soot oxidation. It provides a promising way for the rational design of high-performance non-noble metal catalysts for soot oxidation in practical applications.

Adsorption-enhanced catalytic oxidation for long-lasting dynamic degradation of organic dyes by porous manganese-based biopolymeric catalyst

Improving the adsorption kinetics of metal-oxide catalysts is critical for the enhancement of catalytic performance in heterogeneous catalytic oxidation reactions. Herein, based on the biopolymer pomelo peels (PP) and metal-oxide catalyst manganese oxide (MnOx), an adsorption-enhanced catalyst (MnOx-PP) was constructed for catalytic organic dyes oxidative-degradation. MnOx-PP shows excellent methylene blue (MB) and total carbon content (TOC) removal efficiency of 99.5 % and 66.31 % respectively, and keeps the long-lasting stable dynamic degradation efficiency during 72 h based on the self-built continuous single-pass MB purification device. The chemical structure similarity and negative-charge polarity sites of the biopolymer PP improve the adsorption kinetics of organic macromolecule MB, and construct the adsorption-enhanced catalytic oxidation microenvironment. Meanwhile, the adsorption-enhanced catalyst MnOx-PP obtains lower ionization potential and O2 adsorption energy to promote the continuous generation of active substance (O2*, OH*) for the further catalytic oxidation of adsorbed MB molecules. This work explored the adsorption-enhanced catalytic oxidation mechanism for the degradation of organic pollutants, and provided a feasible technical idea for designing adsorption-enhanced catalysts for the long-lasting efficient removal of organic dyes.