Mechanism Of Catalytic Oxidation Research Articles

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 13C-NMR. 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).

Unveiling the mechanism of thermal catalytic oxidation of HCHO from the kiln exhaust gas using Sc-decorated Cr2CO2-MXenes

Sc/Cr2CO2 is a novel efficient thermal catalyst for HCHO oxidation.

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.