Heterogeneous Catalytic Oxidation Research Articles

New insights into the formation and transformation of active species in nZVI/BC activated persulfate in alkaline solutions

In this study, a nanocomposite material synthesized by loading nanoscale zerovalent iron (nZVI) onto biochar (BC, gasification plant byproduct) was successfully prepared, and the nZVI/BC5 (mass ratio 1:5) exhibited oxidative resistance, reutilization and stability via COD removal experiments. The nZVI/BC5 nanocomposites was used in persulfate (PS) activation for the synergistic degradation of aromatic pollutants in alkaline wastewater. The nZVI/BC5 selectively adsorbed aromatic pollutants through π-π, π-π-metal (BCsurface-OFeO) bonding interactions in textile dyeing wastewater (TDWW), and make the free radicals easier to react to aromatic pollutants. FTIR, XPS and EPR analyses showed that some PFRs generated through the reaction between nZVI and the surface functional groups of BC, the other PFRs were transformed from the BCsurface-OFeO species. The chemisorption provided electrons for the BCsurface-O-Fe(III)O- to produce the BCsurface-Ȯ··Fe(II)-O- (persistent free radicals, PFRs). The formation and transformation of the BCsurface-OFeO species were the dominant processes in the radical pathways, they could quickly and sustainably produce SO4·- and ·OH through heterogeneous catalytic oxidation of water (mediator) and S2O82- (from 0.81 to 0.02 g/L). Finally, a favorable synergistic combined process was initiated via chemisorption and degradation of aromatic pollutants. The BCsurface-OFeO species offer a new understanding of synergistic heterogeneous degradation in alkaline solutions. The byproduct BC could be reused and applied in wastewater pretreatment by this new feasible strategy.

Heterogeneous Catalytic Oxidation of Amides to Imides by Manganese Oxides

Herein, we report a one-step peroxide mediated heterogeneous catalytic oxidation of amides to imides utilizing a series of manganese oxides. Among them, Cs/Mn2O3 was found to be the most active catalyst for the selective partial oxidation of N-benzylbenzamide to diphenyl imide. We have been able to apply an optimized oxidation method to other aromatic substrates. The feasibility of using air as an oxidant, the heterogeneous nature, inexpensive catalytic materials, respectable turnover numbers, and chemoselectivity to imides make this methodology an attractive choice for functional group transformations of amides to imides.

Influence of Catalytic Activity of CeO2/SnO2 Nanocomposites on Sensitivity to Hydrogen of Sensors on Their Base

Addition of cerium to sensor nanomaterials based on tin dioxide leads to a significant increase in their catalytic activity, which is a reason of increasing the sensitivity to H2 of obtained adsorption semiconductor sensors. Mechanism proposed for the surface heterogeneous catalytic hydrogen oxidation reaction includes both reactions involving chemisorbed oxygen at the interface between tin dioxide nanoparticles and introduced cerium dioxide and reactions involving CeO2.

Charge transfer/mass transport competition in advanced hybrid electrocatalytic wastewater treatment: Development of a new current efficiency relation

The contribution of homogeneous versus heterogeneous catalytic oxidation has been studied for the first time in a hybrid anodic oxidation (AO)/electro-Fenton (EF) batch reactor at different initial organic load in terms of chemical oxygen demand (COD) values of 1.61, 12.1 and 23.3 g-O2 L−1. The rate of three (electro)-chemical processes, e.g., (i) AO at the surface of boron-doped diamond (BDD) anode, (ii) Fenton oxidation in the bulk solution and (iii) mediated oxidation (MO) in the bulk solution, have been considered in a mathematical model. The mass transfer coefficient was depending on the concentration of the compound due to the unstationary behavior in the diffusion layer at the vicinity of the anode. After calibration and validation of the model with experimental data, it could be noticed that the competition between the mass transport and the charge transfer was evolving according to the COD load. At 1.61 g-O2 L−1, the applied current density was higher than the limiting current density all along the treatment, meaning that the process was under mass transport control. In this case, the Fenton oxidation rate had the highest contribution in the oxidation efficiency while AO oxidation rate had the lowest efficiency. Increasing the initial COD concentration up to 23.3 g-O2 L−1, made raising the influence of AO process that became predominant after a certain electrolysis time, before reaching the critical time (tcr). Finally, a new current efficiency expression has been proposed by taking into account the three reaction rates and the model could fit the experimental data, showcasing a promising approach. These results further emphasized the need to adapt the reactor design to favor either AO and/or Fenton oxidation according to the organic load of wastewater to be treated, i.e., as pre-treatment or polishing treatment.

Active site localization of methane oxidation on Pt nanocrystals

High catalytic efficiency in metal nanocatalysts is attributed to large surface area to volume ratios and an abundance of under-coordinated atoms that can decrease kinetic barriers. Although overall shape or size changes of nanocatalysts have been observed as a result of catalytic processes, structural changes at low-coordination sites such as edges, remain poorly understood. Here, we report high-lattice distortion at edges of Pt nanocrystals during heterogeneous catalytic methane oxidation based on in situ 3D Bragg coherent X-ray diffraction imaging. We directly observe contraction at edges owing to adsorption of oxygen. This strain increases during methane oxidation and it returns to the original state after completing the reaction process. The results are in good agreement with finite element models that incorporate forces, as determined by reactive molecular dynamics simulations. Reaction mechanisms obtained from in situ strain imaging thus provide important insights for improving catalysts and designing future nanostructured catalytic materials.

Enhanced heterogeneous catalytic oxidation of 2,4-dichlorophenoxyacetic acid in aqueous solution by nanoscale zero-valent iron particle@suparticlelfur/nitrogen dual-doped r-GO (nZVIPs@SN-G) composites

Herein, we reported the synthesis of nanoscale zero-valent iron particles stabilized by sulfur/nitrogen dual-doped r-GO (nZVIPs@SN-G) and their applications as the heterogeneous catalysts to the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) by combining H2O2 under varying pHs, temperatures, catalyst dosages and H2O2 concentrations, as well as in the presence of radical scavengers. The experimental results showed that this heterogeneous Fenton-like catalytic system remained effective up to 90 min of reaction time, and could reach at least 98% degradation efficiency at the optimal conditions, especially when the initial pH values were below 4.5. And the scavenging experiments revealed that 2,4-D was mainly decomposed by the attack of surface-bounded hydroxyl radicals (OH). The structure and properties of the nZVIPs@SN-G catalyst was characterized by X-ray diffraction (XRD), scanning elctron microscopy (SEM), surface area analysis (BET), Raman spectroscopy (Raman) and X-ray photoelectron spectroscopy (XPS). The SEM images indicated that nanoscale zero-valent iron particles (nZVIPs) with size of about 10–50 nm were uniformly stabilized on the surface of sulfur/nitrogen dual-doped r-GO (SN-G), and had good combination with the multilayer matrix. Additionally, the catalyst at the optimum pH could maintain effective degradation even after five cycles, and achieved 91% degradation efficiency of 2,4-D, which was indicative of a good stability. More importantly, the possible reaction mechanism and dechlorination pathway of 2,4-D by the nZVIPs@SN-G/H2O2 heterogeneous catalytic system was also illustrated in this study.

Applicability study on the degradation of acetaminophen via an H2O2/PDS-based advanced oxidation process using pyrite

H2O2- and PDS-based reactions are two typical advanced oxidation processes (AOPs) with different adaptive pH ranges. However, the underlying mechanisms that caused the distinct applicability of these two AOPs have rarely been explored. Herein, a comparative study of H2O2/PDS-based AOPs employing pyrite as a catalyst to degrade acetaminophen (ACT) was reported. The poor ACT degradation in H2O2/pyrite under alkaline conditions was proven to be caused by a lack of OH production instead of by the weaker oxidation property of OH. The continuous exposure surface behavior induced by the intense acid-production reaction between PDS and pyrite prevented the coverage of iron-containing compounds on the pyrite surface. Therefore, the adaptive pH range in PDS/pyrite could extend from 4 to 10, in contrast to the narrow effective pH range of 4–6 in H2O2/pyrite. Oxidant consumption indicated that H2O2/pyrite possesses a higher oxidation efficiency than PDS/pyrite. The homogenous catalytic effect was non-negligible in PDS/pyrite, whereas heterogeneous catalytic oxidation dominated H2O2/pyrite under acidic conditions. The quenching experiment and electron spin resonance (ESR) spectroscopy demonstrated that the dominant radical species in H2O2/PDS-based AOPs via pyrite at a pH of 4 were OH and OH/SO4-, respectively, thus causing different degradation pathways of ACT. In addition, a higher proportion of S consumption was found in H2O2/pyrite, indicating that sulfur also plays a role during the catalytic reaction. The distinct surface reactions between pyrite and H2O2/PDS led to different water treatment applications.

Ferrosilicate-Based Heterogeneous Fenton Catalysts: Influence of Crystallinity, Porosity, and Iron Speciation

Different ferrosilicate samples have been prepared with varying degrees of crystallinity, porous texture, and speciation of the Fe sites by both hydrothermal and sol–gel procedures: Fe-silicalite-1 with microcrystals (2–10 µm) and nanocrystals (180 nm), Fe-containing composite material consisting of silicalite-1 and amorphous silica, and two samples of mesoporous Fe-containing amorphous silica Fe–SiO2. The resulting solids have been tested for their potential as organic pollutants removal under Fenton-like conditions in heterogeneous catalytic wet peroxide oxidation of phenol and clarithromycin lactobionate. Our results indicate that the three aforementioned parameters show a strong interplay towards the abatement of pollutants in liquid phase. Thus, samples with high crystallinity show an improved performance in the oxidation of organic contaminants over amorphous samples in which the Fe speciation is very well controlled.

Recent developments on gas–solid heterogeneous oxidation removal of elemental mercury from flue gas

Mercury is a toxic and persistent environmental pollutant which has been recognized as a global threat to human health and our ecosystem because mercury bio-accumulates in the food chain and can be transformed into the more neurotoxic methylmercury. Among current and emerging abatement technologies for elemental mercury in flue gas, gas–solid heterogeneous oxidation is nowadays gaining increasing attention due to several inherent advantages. The catalysts and adsorbents are key materials that control the heterogeneous catalytic oxidation and adsorption of Hg0 from flue gas. Here we present a review of the recent developments on several catalysts and adsorbents, including noble metal-based catalysts, non-noble metal-based catalysts (transition metal oxides and selective catalytic reduction catalysts), activated carbon/coke-based sorbents, biochar-based sorbents, fly ash-based sorbents, mineral material-based sorbents and other novel catalysts. The key process parameters and kinetic reaction mechanisms and advantages and disadvantages of various emerging catalysts/adsorbents and technologies of Hg0 removal are described in detail.

Simultaneous removal of NO and SO2 from flue gas using vaporized H2O2 catalyzed by nanoscale zero-valent iron.

To remove NO and SO2 from flue gas simultaneously, a heterogeneous catalytic oxidation system was developed with the nanoscale zero-valent iron (nZVI), vaporized H2O2, and sodium humate (HA-Na) acting as the catalyst, oxidant, and absorbent, respectively. The experimental results indicated that the desulfurization was mainly influenced by the absorption, and the denitrification was significantly affected by the catalytic oxidation parameters. Under the optimal conditions, the simultaneous removal efficiencies of SO2 and NO were 100 and 88.4%, respectively. The presence of ·OH during the removal process was proved by the scavenger tests, and the production of ·OH with and without nZVI was indirectly evaluated by the electron paramagnetic resonance (EPR) and methylene blue experiments. Moreover, the fresh and aged nZVI were characterized by a series of techniques and the results suggested that the redox pair Fe2+/Fe3+ released by nZVI could react with H2O2 to provide the sustainable ·OH, which was important for the oxidation from NO and SO2 to NO3- and SO42-. The removal mechanism was proposed preliminarily based on the correlative experiments, characterizations, and references.

Advanced Heterogeneous Fenton Treatment of Coalbed Methane-Produced Water Containing Fracturing Fluid

This study investigated the heterogeneous Fenton treatment to process coalbed methane-produced water containing fracturing fluid and chose the development region of coalbed methane in the Southern Qinshui Basin as a research area. We synthesized the catalyst of Fe-Co/γ-Al2O3 by homogeneous precipitation method and characterized it by BET, XRD, SEM-EDS, FTIR, and XPS. Based on the degradation rate, we studied the influences of the heterogeneous Fenton method on the coalbed methane output water treatment process parameters, including initial pH, H2O2 concentration, and the catalyst concentration. We also investigated the impacts of overall reaction kinetics of heterogeneous catalytic oxidation on coalbed methane-produced water containing fracturing fluid. Results showed that Fe-Co/γ-Al2O3 as a Fenton catalyst has a good catalytic oxidation effect and can effectively process coalbed methane-produced water. This reaction also followed first-order kinetics. The optimal conditions were as follows: the initial pH of 3.5, a H2O2 concentration of 40 mol L−1, a catalyst concentration of 4 g/L, and an apparent reaction rate constant of 0.0172 min−1. Our results provided a basis to establish methods for treating coalbed methane-produced water.

Rapid microwave-hydrothermal conversion of lignin model compounds to value-added products via catalytic oxidation using metal organic frameworks

Microwave irradiation is an effective method for faster heating to shorten reaction time of oxidative valorization of lignin. However, studies using microwave irradiation for lignin oxidation all employ homogeneous catalysis. Thus, this study aims to investigate heterogeneous catalytic oxidation of lignin under microwave irradiation. Especially, metal organic frameworks (MOFs) are adopted as transition metal-containing heterogeneous catalysts for lignin oxidation. In particularly, MOFs (MIL-101 (Cr), MIL-101 (Fe), UiO-66, HKUST-1, and MOF-801) are also prepared using microwave irradiation and used as for oxidative conversion of a model lignin compound, vanillyl alcohol (VAL), to the valuable products, vanillin (VN) and vanillic acid (VAC), using H2O2 as an oxidant. While the tested MOFs all exhibit catalytic activities for VAL conversion to VN/VAC, MIL-101 and MOF-801 appear to be relatively effective. Through investigating the effect of temperature, VAL conversion to VN/VAC is less favorable at higher temperature possibly due to degradation of H2O2 at high temperatures. While a higher dosage of H2O2 increases VAL conversion, the additionally added H2O2 seems to further oxidize VN to VAC instead of converting more VAL to VN. Through the EPR analyses, the mechanism of VAL conversion to VN/VAC may be attributed to both the OH-based and non-OH• routes. The most effective MOF, MOF-801, also exhibited very similar catalytic activities over several cycles. The results indicate that MOFs can convert VAL to valuable products of VN and VAC within a very short time (10 min) under microwave irradiation. MOF-801 was also validated as a promising MOF for VAL conversion.

Highly Efficient Catalytic Oxidation of Inert C(sp3)–H Bonds by the Synergistic Effect of Copper Nanoparticles/N‐Doped Graphene

The applicability of Cu is still limited in the heterogeneous catalytic oxidation of C(sp3)–H bonds. This problem was resolved by exploiting the synergistic effect existing between Cu nanoparticles (Cu NPs) and N‐doped graphene. We demonstrate a highly efficient, green protocol for the catalytic oxidation of inert C(sp3)–H bonds with only oxygen as the oxidant catalyzed by Cu NPs/N‐doped graphene (Cu‐N‐rGO). The new composite materials were obtained through a very simple one‐pot solvothermal process. Remarkably, newly prepared Cu‐N‐rGO showed 34.5 % conversion and 89.2 % selectivity for the catalytic oxidation of cyclohexane to KA oil [mixture of cyclohexanone (K) and cyclohexanol (A)] in a single cycle and thus exhibited significantly higher efficiency than the N‐free Cu catalysts. Cu‐N‐rGO has good stability because the doped nitrogen atoms allow strong interactions between the Cu species and graphene, so that the conversion and selectivity can be maintained over five runs. The delicate relationship between the Cu NPs and nitrogen was investigated by accurate control of the ratio of nitrogen and Cu in doped graphene. A hypothesized free‐radical chain mechanism and a peroxidative oxidation process were proven and explained, and the synergistic effect of the Cu NPs and N‐doped graphene in facilitating the oxidation process was also elucidated.

Heterogeneous Fenton-like discoloration of methyl orange using Fe3O4/MWCNTs as catalyst: kinetics and Fenton-like mechanism

The kinetics and Fenton-like mechanism are two challenging tasks for heterogeneous Fenton-like catalytic oxidation of organic pollutants. In this study, three kinetic models were used for the kinetic studies of Fe3O4/MWCNTs-H2O2 Fenton-like reaction for MO degradation. The results indicated that this reaction followed the first-order kinetic model. The relationship of reaction rate constant and temperature followed the Arrhenius equation. The activation energy and frequency factor of this system were calculated as 8.2 kJ·mol-1 and 2.72 s-1, respectively. The quantifications of Fe ions dissolution and •OH radicals generation confirmed that the homogeneous and heterogeneous catalyses were involved in Fe3O4/MWCNTs-H2O2 Fenton-like reaction. The reaction rate constant was closely related with Fe ions dissolution and •OH radicals generation. Fe3O4/MWCNTs nanocomposites had typical ferromagnetic property and could be easily separated from solution by an external magnet after being used. Furthermore, Fe3O4/MWCNTs nanocomposites exhibited good stability and recyclability. Finally, the Fenton-like mechanisms on homogeneous and heterogeneous catalyses were described.

Synthesis, characterization and optimization of heterogeneous catalytic cyclohexene oxidation by tungstophospho(aqua)ruthenate via the fractional factorial design methodology

Keggin-type tungstophospho(aqua)ruthenate (PRuW) was synthesized and supported on acid activated montmorillonite under mild conditions.

Ordered nanoporous lyotropic liquid crystal polymer resin for heterogeneous catalytic aerobic oxidation of alcohols.

An ordered, nanoporous, TEMPO-based polymer resin formed from lyotropic liquid crystal monomers catalyzes the hetereogeneous oxidation of alcohols with high activity and substrate size selectivity under transition-metal-free, aerobic conditions.

Heterogeneous catalytic water oxidation controlled by coordination geometries of copper(ii) centers with thiolato donors.

Treatment of a penicillaminato platinum(ii) metalloligand with Cu2+ gave an S-bridged PtII2CuII2 complex, which reacted with Zn2+ to produce 1D and 3D (PtII2CuII2ZnII)n coordination polymers, depending on the counter anions. These compounds increased heterogeneous electrocatalytic activities for water oxidation in proportion to the number of vacant coordination sites at thiolato dicopper(ii) cores.

Co(II)-pyrophyllite as Catalyst for Phenol Oxidative Degradation: Optimization Study Using Response Surface Methodology

A cobalt supported clay catalyst was elaborated by an impregnation method. It was then tested as heterogeneous catalyst for the oxidation of phenol by hydrogen peroxide. The clay used as support is the natural local pyrophyllite. Both raw and modified clays were characterized by X-ray diffraction (XRD), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Response surface methodology (RSM), based on central composite design (CCD), was applied. Influences of three operating parameters, namely temperature, hydrogen peroxide concentration and catalyst amount were selected for the optimization of the heterogeneous catalytic oxidation reaction. Based on analysis of variance (ANOVA), the quadratic model fits well with the experimental results. The maximum oxidation efficiency was found to be 70.18% under the optimum conditions of operational parameters (T = 50 °C; [H2O2] = 6.4 mmol L−1; catalyst amount = 1.7 g L−1). After 5.5 h of reaction under the optimum conditions, it was possible to degrade the phenol totally and with 75.21% of mineralization. This time is also sufficient for detoxification of polluted solution.

Sulfidation of Iron-Based Materials: A Review of Processes and Implications for Water Treatment and Remediation.

Iron-based materials used in water treatment and groundwater remediation-especially micro- and nanosized zerovalent iron (nZVI)-can be more effective when modified with lower-valent forms of sulfur (i.e., "sulfidated"). Controlled sulfidation for this purpose (using sulfide, dithionite, etc.) is the main topic of this review, but insights are derived by comparison with related and comparatively well-characterized processes such as corrosion of iron in sulfidic waters and abiotic natural attenuation by iron sulfide minerals. Material characterization shows that varying sulfidation protocols (e.g., concerted or sequential) and key operational variables (e.g., S/Fe ratio and sulfidation duration) result in materials with structures and morphologies ranging from core-shell to multiphase. A meta-analysis of available kinetic data for dechlorination under anoxic conditions, shows that sulfidation usually increases dechlorination rates, and simultaneously hydrogen production is suppressed. Therefore, sulfidation can greatly improve the efficiency of utilization of reducing equivalents for contaminant removal. This benefit is most likely due to inhibited corrosion as a result of sulfidation. Sulfidation may also favor desirable pathways of contaminant removal, such as (i) dechlorination by reductive elimination rather than hydrogenolysis and (ii) sequestration of metals as sulfides that could be resistant to reoxidation. Under oxic conditions, sulfidation is shown to enhance heterogeneous catalytic oxidation of contaminants. These net effects of sulfidation on contaminant removal by iron-based materials may substantially improve their practical utility for water treatment and remediation of contaminated groundwater.

Organic Molecular Catalyst for Electrochemical Production of Hydrogen Peroxide

Hydrogen peroxide (H2O2) as a low cost, safe and clean disinfection agent plays an important role in providing clean water for human society. Compared with complicated industrial anthraquinone process or direct catalytic synthesis from H2 and O2, the distributed production of H2O2 in a polymer electrolyte fuel cell system (PEFC) has numerous merits, including lower financial and energy cost, safer process, use of small-scale, easily deployable device.1,2 For these reasons, there is strong interest in developing electrocatalysts with high activity and selectivity for H2O2 production via the electrochemical reduction of molecular oxygen. Up until now, H2O2 electrocatalysts have been based on precious-metal amalgams, which are costly, scarce, and difficult to handle safely due to the use of Hg.2,3 Carbon-based electrocatalysts have been considered for H2O2 production,4-6 as have been metal-free and nitrogen-containing molecular catalysts known to be selective for two-electron reduction of O2 in various media.7-9 In this presentation, we will demonstrate a new catalyst based on a small organic molecule that enables electrochemical production of H2O2 in an aqueous acidic electrolyte (0.5 M H2SO4). When adsorbed onto glassy carbon this molecular catalyst shows a high onset potential of around 0.6 V vs. RHE, and a specific current density > 1.3 mA/cm2 ECA at 0 V vs. RHE in electrochemical cell test. Rotating ring-disk electrode (RRDE) studies indicate high selectivity for H2O2 production, with H2O2 yield over 80%, and current efficiency over 67%. The durability of this molecule has been evaluated in an electrochemical cell, as well as in a PEFC. Based on experimental data and density functional theory (DFT) calculations, a two electron oxygen reduction mechanism on this molecular catalyst will be proposed. References (1) Centi, G.; Perathoner, S.; Abate, S. In Modern Heterogeneous Oxidation Catalysis; Wiley-VCH Verlag GmbH & Co. KGaA: 2009, p 253. (2) Siahrostami, S.; Verdaguer-Casadevall, A.; Karamad, M.; Deiana, D.; Malacrida, P.; Wickman, B.; Escudero-Escribano, M.; Paoli, E. A.; Frydendal, R.; Hansen, T. W.; Chorkendorff, I.; Stephens, I. E. L.; Rossmeisl, J. Nat. Mater. 2013, 12, 1137. (3) Verdaguer-Casadevall, A.; Deiana, D.; Karamad, M.; Siahrostami, S.; Malacrida, P.; Hansen, T. W.; Rossmeisl, J.; Chorkendorff, I.; Stephens, I. E. L. Nano Lett. 2014, 14, 1603. (4) Yamanaka, I.; Onizawa, T.; Takenaka, S.; Otsuka, K. Angew. Chem. Int. Ed. 2003, 42, 3653. (5) Yamanaka, I.; Onisawa, T.; Hashimoto, T.; Murayama, T. ChemSusChem 2011, 4, 494. (6) Fellinger, T.-P.; Hasché, F.; Strasser, P.; Antonietti, M. J. Am. Chem. Soc. 2012, 134, 4072. (7) Hatay, I.; Su, B.; Méndez, M. A.; Corminboeuf, C.; Khoury, T.; Gros, C. P.; Bourdillon, M.; Meyer, M.; Barbe, J.-M.; Ersoz, M.; Záliš, S.; Samec, Z.; Girault, H. H. J. Am. Chem. Soc. 2010, 132, 13733. (8) Wu, S.; Su, B. Chem. Eur. J. 2012, 18, 3169. (9) Savéant, J.-M. Chem. Rev. 2008, 108, 2348.