Mechanism Of Catalytic Oxidation Research Articles

A DFT study on the sulfur resistance mechanism of elemental mercury catalytic oxidation over Mn-Mo/CNT

The strong sulfur resistance of Mn-Mo/CNT during the process of elemental mercury catalytic oxidation at low temperature has been demonstrated in experiment. However, there remains a dearth of in-depth research on the sulfur resistance mechanism. This work aims to explore the sulfur resistance mechanism through density functional theory (DFT) calculations. The results reveal that SO2 can be effectively oxidized to SO3 through lattice oxygen on the surface of Mn-Mo/CNT. The speed control step is the step of SO3 dissociation, with an energy barrier of 2.50 eV. Additionally, O2 can adsorb onto active sites to supplement the consumed lattice oxygen. The adsorbed O2 can also oxidize SO2, and the highest energy barrier of this reaction is only 0.26 eV. SO3 can further react with the adsorbed Hg0 to form HgSO4, and the speed control step is the step of Hg0 oxidation. Specifically, when Hg0 is adsorbed onto Mo active sites, its energy barrier of speed control step reaches 4.06eV. Whereas, when Hg0 is adsorbed on Mn site, the energy barrier of speed control step reduces to 3.18eV. Generally, the coupling reaction process of Hg0 oxidation and SO2/SO3 conversion over Mn-Mo/CNT is the reason of the promotion in sulfur resistance of this catalyst.

Photothermal synergistic catalytic oxidation mechanism of toluene by Ce-doped SrTiO3 via one-pot hydrothermal synthesis

Industrial volatile organic compounds (VOCs) emissions pose significant environmental and human health risks, with photothermal catalysis degradation emerging as a promising VOCs treatment technology. The light response range and catalysis degradation efficiency of photocatalysts, however, need to be improved. This study prepared Ce-doped SrTiO3 perovskite catalysts via a one-pot hydrothermal method. The synergistic photic/thermal degradation mechanism of toluene was uncovered via XPS, Uv–Vis, EPR, and in-situ DRIFTS analysis. It was found that the toluene removal rate and CO2 yield reached their maximums at 200 °C, reaching 95 % and 90 %, respectively, at a Ce doping ratio of 50 %. During the catalytic process, the prerequisite to trigger toluene oxidation, and light promote the generation of reactive oxygen species (·OH and ·O2–), which facilitates the formation of intermediates and thus accelerates the deep oxidation of toluene. The doped Ce increases surface oxygen vacancies while lowering the energy band gap of the catalyst, facilitating the separation of holes and photogenerated electrons. Furthermore, in situ DRIFTS studies demonstrated that toluene undergoes a ring-opening process, producing intermediates such as benzaldehyde and benzoic acid. This study will assist in promoting the use of photothermal synergistic catalytic degradation technology to remove VOCs from industrial sources.

Efficient degradation of methylene blue at near neutral pH based on heterogeneous Fenton-like system catalyzed by Fe2O3/MnO2

The contamination of aquatic environments by organic dye contaminants in industrial wastewater has attracted widespread global attention. The heterogeneous Fenton-like process presents an attractive method for degrading dye pollutants, especially when such reactions are conducted under neutral pH. In this study, Fe2O3/MnO2 composite was employed as a novel heterogeneous catalyst for activating hydrogen peroxide (H2O2) to oxidize and subsequently degrade methylene blue (MB) under neutral pH. Multiple characterization results have confirmed the presence of MnO2 and Fe2O3 as the primary phases of the synthesized compound catalyst. Degradation experiments have demonstrated that the degradation efficiency of MB approaches 100% under the conditions of H2O2 concentration of 0.30% and Fe2O3/MnO2 amount of 0.888 g/L. Furthermore, the Fe2O3/MnO2 catalyst exhibits consistent and outstanding catalytic activity within a broad pH range from 5 to 9 benefiting from the strong interface interaction in Fe2O3/MnO2. The investigation into the kinetics of the Fenton-like reaction indicates that the catalytic degradation of MB by Fe2O3/MnO2 in conjunction with H2O2 follows pseudo-first-order kinetics. Moreover, supplementary scavenging experiments have demonstrated the crucial role played by hydroxyl radicals (·OH) in the catalytic oxidation mechanism of MB. This study offers a promising catalyst for the treatment of dye-containing wastewater under neutral pH condition.

Adsorption–Activation Bifunctional Center of Al/Co‐Base Catalyst for Boosting 5‐Hydroxymethylfurfural Oxidation

AbstractElectrocatalytic conversion of biomass‐derived 5‐hydroxymethylfurfural (HMF) to value‐added 2,5‐furandicarboxylic acid (FDCA) is of great significance in compensating for the rapid consumption of fossil resources. However, it is a challenge to further improve the performance of HMF electrocatalytic oxidation (HMFOR) by synergistic kinetics (active sites) and thermodynamics (adsorption sites). In this work, Al(OH)3/Co(OH)2 is successfully fabricated as an efficient catalyst, and its catalytic mechanism for HMF oxidation is clarified. Extended X‐ray absorption fine structure (EXAFS) analysis demonstrate that electrochemically generated Co3+ is the main catalytic site for HMF oxidation. The HMF equilibrium adsorption capacity of Al(OH)3 reach 57.0 mg g−1, which effectively increase the initial concentration of substrate and promoted the reaction rate. The combined results, based on 24 stable cycles and an FDCA yield retention rate of 98.6% after 180 days, are the highest ever achieved. Additionally, it is shown that this system can oxidize four other biomass‐derived substrates. Therefore, this work provides insight into a hydroxide catalyst that owes its efficiency to synergy between active and adsorption sites.

Synergistic catalytic degradation of benzene and toluene on spinel MMn2O4 (M[dbnd]Co, Ni, Cu) catalysts

Owing to the complexity of multicomponent gases, developing multifunctional catalysts for synergistic removal of benzene and toluene remains challenging. The spinel MMn2O4 (MCo, Ni, or Cu) catalysts were successfully synthesized via the sol–gel method and tested for their catalytic performance for simultaneous degradation of benzene and toluene. The CuMn2O4 sample exhibited the best catalytic performance, the conversion of benzene reached 100 % at 350 °C, and toluene conversion reached 100 % at 250 °C. XRD, N2 adsorption-desorption, HRTEM-EDS, ED-XRF, Raman spectroscopy, H2-TPR, NH3-TPD, O2-TPD and XPS were used to characterize the physical and chemical properties of MMn2O4 catalysts. The excellent redox properties, high concentration of surface Mn4+, and adsorption of oxygen species over the CuMn2O4 sample facilitated the simultaneous and efficient removal of benzene and toluene. Additionally, in situ DRIFTS illustrated the intermediate species and reaction mechanism for the synergetic catalytic oxidation of benzene and toluene. Notably, as an effective catalytic material, spinel oxide exhibited excellent synergistic degradation performance for benzene and toluene, providing some insight for the development of efficient multicomponent VOC catalysts.

Anchoring PdOx clusters on defective alumina for improved catalytic methane oxidation

Evolution of the Pd active centers in size and spatial distribution leads to an irreversible deactivation in many high-temperature catalytic processes. This research demonstrates the use of a defective alumina (Al2O3-x) as catalyst support to anchor Pd atoms and suppress the growth of Pd clusters in catalytic methane oxidation. A combination of operando spectroscopy and density functional theory (DFT) calculations provide insights into the evolution of Pd species and reveals distinct catalytic methane oxidation mechanisms on Pd single atoms, clusters, and nanoparticles (NPs). Among these Pd species, the cluster active centers are found to be the most favorable participants in methane oxidation due to their high dispersion, high content of Pd2+ oxidation state, and resistance to deactivation by carbonates, bicarbonates, and water. The Pd/Al2O3-x catalyst shows increased stability with respect to a Pd/Al2O3 counterpart during simulated aging in alternating reducing and oxidizing conditions due to stronger interactions with the support. This study demonstrates that defect engineering of non-reducible supports can constrain the evolution of active centers, which holds promising potential for widespread utilization across diverse industrial catalytic processes, including various hydrogenation and oxidation reactions.

Mesopore Catalytic Activated‐Carbon to Reduce Harmful Gases Indoors: Adsorption, Catalytic Oxidation, and Prediction Mechanism

ABSTRACTModification of local bamboo‐based catalytic activated carbon with metallic Ag can produce mesopore and micropore types, with a mesopore content of 86%. One of the best ways to reduce formaldehyde concentrations is through catalytic adsorption. In combination with Ag nanoparticle catalyst, formaldehyde adsorption capacity is improved. Adsorption and oxidation reaction experiments are performed in a fixed bed column (di = 10 mm, length = 90 mm). The increase in formaldehyde adsorption associated with the reaction rate of formaldehyde oxidation by metallic Ag is 51 g/mmol. The oxidation reaction of Ag nanoparticles is a bimolecular reaction based on the Langmuir–Hinshelwood mechanism. Formaldehyde can be reduced by 59% and 41% through the role of adsorption and support of catalytic oxidation, respectively. Additionally, harmless gases such as CO2 and H2O are produced within the column.

Biochar Meets Single-Atom: A Catalyst for Efficient Utilization in Environmental Protection Applications and Energy Conversion.

Single-atom catalysts (SACs), combining the advantages of multiphase and homogeneous catalysis, have been increasingly investigated in various catalytic applications. Carbon-based SACs have attracted much attention due to their large specific surface area, high porosity, particular electronic structure, and excellent stability. As a cheap and readily available carbon material, biochar has begun to be used as an alternative to carbon nanotubes, graphene, and other such expensive carbon matrices to prepare SACs. However, a review of biochar-based SACs for environmental pollutant removal and energy conversion and storage is lacking. This review focuses on strategies for synthesizing biochar-based SACs, such as pre-treatment of organisms with metal salts, insertion of metal elements into biochar, or pyrolysis of metal-rich biomass, which are more simplistic ways of synthesizing SACs. Meanwhile, this paper attempts to 1) demonstrate their applications in environmental remediation based on advanced oxidation technology and energy conversion and storage based on electrocatalysis; 2) reveal the catalytic oxidation mechanism in different catalytic systems; 3) discuss the stability of biochar-based SACs; and 4) present the future developments and challenges regarding biochar-based SACs.

A combined experimental and theoretical study on the mechanism of catalytic oxidation of lignite to carboxylic acids by iron

The oxygen-oxidation of lignite to carboxylic acids (CAs) using environmentally friendly iron catalyst represents an efficient and clean technology for lignite utilization. However, the mechanism remains unclear due to the difficulty in observing the cleavage of chemical bonds and the challenge in capturing transient intermediates and radicals. In this work, the microscopic reaction mechanism of iron-catalytic oxidation of lignite was investigated by combining experimental and theoretical methods. Catalytic oxidation experiments revealed that water-soluble intermediates generated by solid-state lignite decomposition underwent a continuous carbon–carbon bond cleavage oxidation (including oxidative cleavage of aliphatic moieties and oxidative ring-opening of aromatic moieties) to form CAs with aldehyde moieties as the direct precursor. Based on molecular dynamics simulations and density functional theory, a reaction network from lignite to CAs was proposed. The iron catalyst was present in the form of iron-aqua complexes in the liquid phase and iron-phenyl complexes in the solid phase. These iron-aqua/iron-phenyl complexes could reduce the energies of oxidation reactions, promoting the cleavage of bridge bonds, the formation of o-quinones and the oxidation of aromatic moieties, thus accelerating elementary reactions for the formation of CAs. These findings provide a theoretical support for the oxidation of lignite and an in-depth insight into iron-catalytic mechanism.

Ultralow doping of Zr species into Co3O4 catalyst enhance the CO oxidation performance

The oxidation of carbon monoxide (CO) has garnered significant interest for its application in treating automobile exhaust. In this study, we employed the sol-gel method to synthesize a series of cobalt-zirconium oxide catalysts with various Co/Zr ratios, aiming to catalyze the oxidation of CO effectively. The findings showed that the Co90Zr10 catalyst, with a cobalt-to-zirconium ratio of 90:10, not only exhibited exceptional catalytic efficiency, achieving a 90 % conversion of CO at 94 °C, but also sustained superior thermal stability and resistance to water. The presence of both cobalt defects and oxygen vacancies significantly enhances the catalytic activity, which is attributed to the doping of zirconium. The characterization analyses indicated the incorporation of zirconium into the Co3O4 spinel lattice modifies the valence states (Co3+/Co2+) and geometries (CoOh/CoTd) of the cobalt cations. This alteration results from a variety of partial electron transfers and substitution sites. Enhanced ratios of Co3+/Co2+ and CoOh/CoTd in the CoxZry catalysts lead to improved reducibility and oxygen mobility. Consequently, this facilitates the lower-temperature oxidation of intermediates during the catalytic conversion of CO. DFT result showed that the Co3O4 after Zr doped has lower adsorption energy and revealed the reaction mechanism of CO catalytic oxidation.

Insights into catalytic oxidation mechanism of toluene by lanthanum mangan-based perovskite in wet environment based on in-situ DRIFTS

This paper investigated that the catalytic activity and CO2 selectivity of LaMnO3, La0.9Ca0.1MnO3 and 3-La0.9Ca0.1MnO3 catalysts with different oxygen vacancy concentrations were compared under wet and dry conditions. The 3-La0.9Ca0.1MnO3 catalysts had excellent water resistance. The presence of H2O had less effect on toluene conversion than on CO2 selectivity. In wet environment, the 3-La0.9Ca0.1MnO3 catalyst achieved 90 % toluene conversion at 173 °C, but less than 20 % selectivity for CO2 at this time, and reached 90 % selectivity for CO2 at 220 °C. The effect of H2O on the catalytic oxidation mechanism of toluene was analyzed by in-situ DRIFTS analysis. The presence of H2O could promote the decomposition of toluene into intermediates of benzyl alcohol, benzoic acid, benzaldehyde and maleic anhydride at low temperature (50 °C), but the intermediates were difficult to decompose into CO2 and H2O. It was suggested that surface hydroxyl group could promote the transformation of toluene to intermediate at low temperature, and suitable oxygen vacancies and surface hydroxyl group could jointly promote the transformation of toluene to ideal product. This work provided a theoretical basis for the design of water-resistant catalysts in industry.

Efficient degradation of vulcanized natural rubber into liquid rubber by catalytic oxidation

Waste tire rubber based on natural rubber (NR) represents an abundant feedstock for the production of valuable products. This study investigated an efficient approach to convert NR vulcanizates into liquid rubber with the number-average molar masses of 1.3 × 104 g/mol. Compared to the anaerobic liquefaction at 300 °C for 3 min, NR vulcanizates were liquefied efficiently at 210 °C for 3 min by thermo-oxidative degradation catalyzed by manganese (II) stearate. The apparent activation energy of the NR degradation reaction decreased from 470.8 kJ/mol to 208.2 kJ/mol with catalysis, which was attributed to the formation of a coordination complex between catalysts and peroxides via the single-electron transfer redox reaction, leading to the catalytic oxidative degradation of NR vulcanizates. The main chain scission and crosslink scission occurred simultaneously during the degradation process, and the main chain scission was the primary catalytic oxidation reaction according to the Horikx theory. In addition, the obtained liquid rubber contained carbonyls, ether linkages, and sulfoxide groups, as proved by FTIR and 13CNMR . The catalytic oxidative degradation mechanism of NR vulcanizates was proposed based on the chemical structure of products and simulation results. The efficient method was proposed to highly facilitate the recycling and valorization of NR-based waste tire rubber.

Mechanism of catalytic subcritical water oxidation of m-nitroaniline and nitrogen conversion by CuCo2O4 catalyst

Catalytic subcritical water oxidation (CSWO) of M−nitroaniline (M−NA) was investigated in a fused quartz tube reactor (FQTR) to determine the effects of reaction parameters on M−NA mineralization rate, total nitrogen (TN) removal rate and nitrogen-containing products distribution. The results indicated that the TN removal rate was only 26.36 % at 200 °C, 200 % excess oxidant and 15 min residence time, while the TN removal rate reached 67.83 % at 360 °C in SWO of M−NA. Compared with SWO of M−NA, the mineralization rate and TN removal rate of CSWO of M−NA increased by about 10 % and 17.83 %, respectively. The main reason is mainly attributed to CuCo2O4 catalyzing the preferential reaction of ·NO2 with ·NH4, hastening N2 generation. Alternatively, the CuCo2O4 catalyst may induce a direct reaction between the nitro and amino groups on M−NA within the benzene ring to form N2. Moreover, degradation pathways and nitrogen migration mechanism of M−NA under SWO/CSWO conditions were proposed. These crucial findings are expected to guide the development of environmentally sustainable catalytic technologies towards addressing significant water pollution challenges.

Quantitative sulfur poisoning of nanocrystal PtO2/KL-NY and its deactivation mechanism for benzene catalytic oxidation

The present study involved the synthesis of a kaolin-based NaY zeolite (KL-NY) supported nanocrystal PtO2 (5–10 nm) catalyst, which exhibited complete benzene conversion at 195 °C. However, a certain amount of sulfur species led to severe deactivation of the catalyst. This deactivation was mainly caused by the reduction of active lattice oxygen. XPS, H2-TPR and HRTEM results confirmed that adsorbed sulfur species competitively consumed active lattice oxygen, resulting in a transition of partial PtO2 to PtO. Generated PtO cannot actively participate in the oxidation reaction due to its weaker oxidation property, indicating a decrease of active species induced by sulfur poisoning. Furthermore, Al2O3 outside the KL-NY framework can adsorb sulfur species and form Al2(SO4)3, leading to an increase in acid sites. Due to the weak acid-tolerance of KL-NY, partial porous structure destruction occurred with a decrease in specific surface area and pore volume, thereby negatively impacting catalyst performance.

Ammonia-regulated CuCo2O4 spinel oxide embedded in Y zeolite for methanol oxidation

Morphology-controlled synthesis with a tailor-made structure is a promising approach to enhance the catalytic properties of inexpensive spinel oxides as a viable alternative to noble metals. AB2O4 spinel oxides, particularly, have garnered significant attention in mitigating volatile organic compounds (VOCs) emissions. The catalytic performance of these oxides can be improved through the modification of tetrahedrally coordinated A sites. In this study, we present a novel strategy for the preparation of CuCo2O4 spinel oxide nanoparticles embedded on Y zeolite. This involves the co-loading of Cu and Co oxides on Y zeolite, followed by successive treatment with NH3-reduction and re-oxidation. The resulting morphology-confined CuCo2O4 spinel oxides exhibit significantly higher catalytic activities and stabilities for the oxidation of CH3OH compared to their unrestrained counterparts. Our exploration into the in-situ formation of spinel oxides on Y zeolite, along with an investigation into their catalytic oxidation mechanism, lays the foundation for the rational design of non-noble metal oxide VOC catalysts.

Room Temperature Catalysts for High Effective Degradation of Formaldehyde: Research Progresses and Challenges

AbstractFormaldehyde (HCHO) is one of major pollutants in indoor air, and prolonged exposure to HCHO may result in great harm to human health. Therefore, it is crucial to remove HCHO from indoor air at room temperature. In recent years, various room temperature catalysts, which have the advantages of environmental friendliness and energy saving, were developed for high effective catalytic oxidation of HCHO. In this work, research progress and challenges on the room temperature catalytic oxidation of HCHO by using noble metal catalysts and non‐noble metal catalysts are systemically reviewed. Meanwhile, the room temperature catalytic oxidation performance, degradation conditions of HCHO, and room temperature catalytic oxidation mechanism of catalysts was also discussed.

Wet peroxide oxidation process catalyzed by Cu/Al2O3: phenol degradation and Cu2+ dissolution behavior.

Catalytic wet peroxide oxidation (CWPO) has become an important deep oxidation technology for organics removal in wastewater treatments. Supported Cu-based catalysts belong to an important type of CWPO catalyst. In this paper, two Cu catalysts, namely, Cu/Al2O3-air and Cu/Al2O3-H2 were prepared and evaluated through catalytic degradation of phenol. It was found that Cu/Al2O3-H2 had an excellent catalytic performance (TOC removal rate reaching 96%) and less metal dissolution than the Cu/Al2O3-air case. Moreover, when the organic removal rate was promoted at a higher temperature, the metal dissolution amounts was decreased. Combined with hydroxyl radical quenching experiments, a catalytic oxidation mechanism was proposed to explain the above-mentioned interesting behaviors of the Cu/Al2O3-H2 catalyst for CWPO. The catalytic test results as well as the proposed mechanism can provide better guide for design and synthesis of good CWPO catalysts.

Research into arsenic (III) effective catalytic oxidation in an aqueous solution on a new active manganese dioxide in a flow column

Groundwater in many places on Earth contains arsenic compounds. Arsenic (III) compounds must be oxidised to purify water containing arsenic effectively. The subject of this study is oxidation of arsenic (III) compounds in an aqueous solution. Today’s most common industrial arsenic oxidation method using aggressive oxidising agents such as chlorine or ozone has a number of serious disadvantages. The most problematic of these include extremely high risks to human health and the environment, the cost and overall complexity of the process. Catalytic oxidation of arsenic (III) compounds using atmospheric oxygen is an alternative free from the above disadvantages, yet, to date, no information about effective catalysts for this process has been presented in the literature. The arsenic (III) catalytic oxidation process is studied in an aqueous solution on a new active manganese dioxide (NAMD) synthesised by the author. A comparative experimental analysis is performed with other known modifications of manganese dioxide. It is shown that the new active manganese dioxide (NAMD) has high catalytic activity towards arsenic (III), this being confirmed experimentally in both a limited volume and a flow column mode. Some theoretical aspects of the mechanism for catalytic oxidation of arsenic (III) with oxygen on active manganese dioxide in an aqueous solution are also discussed on the basis of the research results. Experimental work is required at pilot plants in the field for successful industrial implementation of the technology for catalytic oxidation of arsenic (III) compounds on NAMD. Further laboratory research is necessary for developing a detailed theoretical basis for catalytic oxidation of arsenic in aqueous solutions. The results of this research are of interest to industrial companies specialising in removing arsenic compounds from water, to scientists and researchers studying catalytic oxidation of arsenic (III), as well as heterogeneous catalytic oxidation with oxygen in general.

Unraveling the H2S selective oxidation in cobalt phosphate cluster loaded polymeric carbon nitride

H2S selective catalytic oxidation via photocatalysis is a low-cost and efficient approach. Herein, we modeled a (CoP)4 cluster loaded melon-based carbon nitride to represent experimental cobalt phosphate cocatalyst adsorption on polymeric carbon nitride for revealing the mechanism of H2S selective catalytic oxidation to SO2 via the density functional theory (DFT) calculations. Due to the hydrogen bond effect, the calculated results show that H2S selective oxidation prefers to occur through the quasi Mars–van Krevelen (quasi-MvK) mechanism rather than Langmuir-Hinshelwood (LH) mechanism according to the thermodynamic perspective, in which quasi-MvK mechanism exhibits a favorable limiting potential of 0.26 V. Overall, this work offers a basic understanding for microscopic mechanism of H2S catalytic oxidation.

Cobalt enhanced (H/C-CdS)/CeO2 activity for visible light catalytic oxidation of formaldehyde at room temperature

The visible light catalytic oxidation of formaldehyde (HCHO) at room temperature is of great interest for improving the indoor air quality. Here, a cobalt (Co)-doped CdS-based catalyst ((H/C-CdS)/CeO2) with high visible light catalytic activity was successfully synthesized for HCHO removal at room temperature. Co addition enhanced the catalytic activity of (H/C-CdS)/CeO2, and the HCHO conversion rate reached 99.5 % for a 1 mg/L aqueous HCHO solution on the Co–(H/C-CdS)/CeO2 catalyst after 1 h at room temperature under visible light, which was greater than that of (H/C-CdS)/CeO2 (92.0 %). The (H/C-CdS)/CeO2 and Co–(H/C-CdS)/CeO2 catalysts were systemically characterized, and the results showed that the interfacial phase junction between the hexagonal (H) and cubic (C) phases of the CdS nanoparticles (NPs) and the synergistic effect of the type II heterojunction between the CdS NPs and CeO2 nanosheets (NSs) promoted the separation of e-/h+. Moreover, the addition of Co species strongly promoted the separation of photogenerated carriers. The excellent photocatalytic activity was attributed to the good dispersion of CdS NPs, which broadened the light absorption range, exposed more active sites, and provided close contact, decreasing the migration distance of photogenerated electron-hole pairs. After that, the visible light catalytic oxidation mechanism of HCHO on both (H/C-CdS)/CeO2 and Co–(H/C-CdS)/CeO2 followed the reaction pathway of HCHO to (CO2 + H2O).