Mechanism Of Catalytic Oxidation Research Articles

Generation and reactivity of putative support systems, Ce-Al neutral binary oxide nanoclusters: CO oxidation and C–H bond activation

Both ceria (CeO2) and alumina (Al2O3) are very important catalyst support materials. Neutral binary oxide nanoclusters (NBONCs), CexAlyOz, are generated and detected in the gas phase and their reactivity with carbon monoxide (CO) and butane (C4H10) is studied. The very active species CeAlO4 (●) can react with CO and butane via O atom transfer (OAT) and H atom transfer (HAT), respectively. Other CexAlyOz NBONCs do not show reactivities toward CO and C4H10. The structures, as well as the reactivities, of CexAlyOz NBONCs are studied theoretically employing density functional theory (DFT) calculations. The ground state CeAlO4 (●) NBONC possesses a kite-shaped structure with an OtCeObObAlOt configuration (Ot, terminal oxygen; Ob, bridging oxygen). An unpaired electron is localized on the Ot atom of the AlOt moiety rather than the CeOt moiety: this Ot centered radical moiety plays a very important role for the reactivity of the CeAlO4 (●) NBONC. The reactivities of Ce2O4, CeAlO4 (●), and Al2O4 toward CO are compared, emphasizing the importance of a spin-localized terminal oxygen for these reactions. Intramolecular charge distributions do not appear to play a role in the reactivities of these neutral clusters, but could be important for charged isoelectronic BONCs. DFT studies show that the reaction of CeAlO4 (●) with C4H10 to form the CeAlO4H●C4H9 (●) encounter complex is barrierless. While HAT processes have been previously characterized for cationic and anionic oxide clusters, the reported study is the first observation of a HAT process supported by a ground state neutral oxide cluster. Mechanisms for catalytic oxidation of CO over surfaces of AlxOy∕MmOn or MmOn∕AlxOy materials are proposed consistent with the presented experimental and theoretical results.

Impact of Copper Complexes with α-Alanine on the Oxidation of Ethyl Oleate in Oil-in-Water Emulsions

Physiological role of copper complexes includes many functions and a special place occupies participation in lipid oxidation of biological membranes. Chain oxidation of ethyl oleate in micellar solution in the presence of copper (II) complexes with α-alanine as a catalyst were decomposed. The results obtained indicated parallel of formation and decomposition of primary and secondary products in catalytic lipid oxidation. We proposed mechanism of catalytic lipid oxidation, based on the results obtained and well-known kinetic scheme. Possibility of participation of copper (I and II) not only in the decomposition of primary hydroperoxides, but secondary oxidation products such as α, β-unsaturated carbonyl compounds are discussed. Activation energies of formation and decay of lipid peroxidation products were calculated. The results obtained were (71±1) and (58±1) kJ/mol, respectively. The assays described herein are similarity to biological systems.

Catalytic oxidative desulfurization mechanism in Lewis–Brønsted complex acid

Lewis–Brønsted complex acid, such as BF3, SnCl4, FeCl3, or ZnCl2-CH3COOH, can enhance thiophenic compound oxidation using solid oxidants. The catalytic oxidative mechanism was studied here. For the catalysis of the complex acid system, Lewis acid was the core, improving the Brønsted acidity of the system, promoting the dissolution of oxidant in the system, and finally catalyzing the oxidation of sulfur in the oil. For the oxidation of thiophenic compound, dibenzothiophene (DBT) was oxidized to its sulfone, but benzothiophene (BT) and thiophene (T) were oxidized to some unidentified products besides the sulfones or sulfoxides. These unidentified products originated from the oxidation of unsaturated bonds on thiophenic compounds. The electronic property of unsaturated bonds, which included bond order and π orbital occupancy, was used to explain the reactivity of unsaturated bonds on those compounds. On the basis of mechanism obtained, the catalysis for the oxidation of sulfur against olefins was controlled.

Water Oxidation with Mononuclear Ruthenium(II) Polypyridine Complexes Involving a Direct RuIV═O Pathway in Neutral and Alkaline Media

The catalytic water oxidation mechanism proposed for many single-site ruthenium complexes proceeds via the nucleophilic attack of a water molecule on the Ru(V)═O species. In contrast, Ru(II) complexes containing 4-t-butyl-2,6-di-1',8'-(naphthyrid-2'-yl)-pyridine (and its bisbenzo-derivative), an equatorial water, and two axial 4-picolines follow the thermodynamically more favorable "direct pathway" via [Ru(IV)═O](2+), which avoids the higher oxidation state [Ru(V)═O](3+) in neutral and basic media. Our experimental and theoretical results that focus on the pH-dependent onset catalytic potentials indicative of a PCET driven low-energy pathway for the formation of products with an O-O bond (such as [Ru(III)-OOH](2+) and [Ru(IV)-OO](2+)) at an applied potential below the Ru(V)═O/Ru(IV)═O couple clearly support such a mechanism. However, in the cases of [Ru(tpy)(bpy)(OH2)](2+) and [Ru(tpy)(bpm)(OH2)](2+), the formation of the Ru(V)═O species appears to be required before O-O bond formation. The complexes under discussion provide a unique functional model for water oxidation that proceeds by four consecutive PCET steps in neutral and alkaline media.

Efficient removal of dyes using heterogeneous Fenton catalysts based on activated carbon fibers with enhanced activity

Activated carbon fibers supported ferric ion (Fe@ACFs) have been reported as a heterogeneous Fenton catalyst for the efficient removal of dyes, including acid, reactive, and basic dyes. The catalysts presented sustained catalytic ability and in situ regeneration capability in these experiments. Moreover, the Fe@ACFs/H2O2 system also exhibited remarkable catalytic activity across a wider pH range. Importantly, compared with most reported supports, the introduction of ACFs contributed specifically to the activity enhancement of ferric ion. NaCl played a passive role in the degradation of RR M-3BE, consistent with the traditional Fenton reaction. The presence of isopropanol, as a hydroxyl radical (∙OH) scavenger, had a passive influence on RR M-3BE oxidation as well, indicating the hydroxyl radical was involved as the active species, confirmed by Electron Paramagnetic Resonance (EPR). Furthermore, the superoxide radical (HO2∙), which existed in the homogeneous Fenton system, was not detected by EPR in the Fe@ACFs/H2O2 system, suggesting better use of H2O2 for degradation of dyes. This paper discusses a possible catalytic oxidation mechanism in the Fe@ACFs/H2O2 system, which may be a feasible approach for the elimination of widely existing pollutants.

Preparation of Si–Al/α-FeOOH catalyst from an iron-containing waste and surface–catalytic oxidation of methylene blue at neutral pH value in the presence of H2O2

The tested Si–Al/α-FeOOH composite was prepared by dissolution, precipitation and aging of a high iron-containing grinding wheel ash (GWA). The obtained Si–Al/α-FeOOH composite was characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscope/energy dispersive X-ray spectrometer (SEM/EDS) analyses. The characterized composite was then evaluated for the decolorization of methylene blue (MB) in the presence of H2O2 at various pH conditions. The extent of MB decolorization was characterized using UV–Vis spectra, total organic carbon (TOC) and Fourier transform infrared spectroscopy (FTIR). The surface–catalytic oxidation mechanism was discussed and the roles of silica and alumina were also evaluated through preparation of four kinds of catalysts from analytical reagents (ARs). The results showed that α-FeOOH (75.40wt% Fe) was the predominate content in Si–Al/α-FeOOH composite with 2.26wt% Si and 1.02wt% Al. The Fenton-like process (Si–Al/α-FeOOH composite combined with H2O2) can effectively oxidize MB at pH 6.46% and 72% of TOC removal can be achieved after 60min catalytic oxidation. The surface–catalytic oxidation by Si–Al/α-FeOOH/H2O2 may proceed mainly through a non-radical mechanism. The introduction of silica played an important role in the enhancement of the α-FeOOH adsorptive capacity by the inhibition of the formation of crystalline structure of FeOOH, and the introduction of alumina might enhance the α-FeOOH catalytic activity and also prevent the iron from leaching from Si–Al/α-FeOOH catalyst.

Research Methods of Catalytic Oxidation on Methane in Conversion Process

The significance of catalytic conversion on Methane was summarized, the methods and mechanism of catalytic partial oxidation on Methane were elaborated, and the advance in catalyst application on Methane in the process of catalytic conversion was discussed and summarized.

Mechanism of Catalytic Water Oxidation by the Ruthenium Blue Dimer Catalyst: Comparative Study in D₂O versus H₂O.

Water oxidation is critically important for the development of energy solutions based on the concept of artificial photosynthesis. In order to gain deeper insight into the mechanism of water oxidation, the catalytic cycle for the first designed water oxidation catalyst, cis,cis-[(bpy)2(H2O)RuIIIORuIII(OH2)(bpy)2]4+ (bpy is 2,2-bipyridine) known as the blue dimer (BD), is monitored in D2O by combined application of stopped flow UV-Vis, electron paramagnetic resonance (EPR) and resonance Raman spectroscopy on freeze quenched samples. The results of these studies show that the rate of formation of BD[4,5] by Ce(IV) oxidation of BD[3,4] (numbers in square bracket denote oxidation states of the ruthenium (Ru) centers) in 0.1 M HNO3, as well as further oxidation of BD[4,5] are slower in D2O by 2.1–2.5. Ce(IV) oxidation of BD[4,5] and reaction with H2O result in formation of an intermediate, BD[3,4]′, which builds up in reaction mixtures on the minute time scale. Combined results under the conditions of these experiments at pH 1 indicate that oxidation of BD[3,4]′ is a rate limiting step in water oxidation with the BD catalyst.

Activation of Hydrogen Peroxide by Activated Carbon Fibers Coupled with Fe(Ⅲ)-Citrate for Degradation of Dyes at Neutral pH

The development of a pH-tolerant Fenton-like catalyst is a active and challenging project in the field of environ- mental catalysis. In this work, an efficient Fenton-like catalytic fibers (Cit-Fe@ACFs) with pH-tolerance has been prepared by an extremely simple impregnation method. First, activated carbon fibers (ACFs) were impregnated into a nitric acid solu- tion at 25 ℃ for 24 h to obtain acidified ACFs, and then immersed in a sodium citrate solution at 25 ℃ for 2 h, which was taken out to put into ferric chloride solution at 25 ℃ for 2 h. The treated ACFs were rinsed with distilled water and dried at room temperature to obtain the Cit-Fe@ACFs. Cit-Fe@ACFs exhibited efficient catalytic activity for the activation of hy- drogen peroxide at neutral pH to degrade dyes, including reactive, acid, and basic dyes, etc. The UV-vis spectroscopy showed that reactive brilliant red M-3BE (RR M-3BE) was eliminated completely in 15 min (Cit-Fe@ACFs: 12 g/L; H2O2: 60 mmol/L; RR M-3BE: 5×10 -5 mol/L; pH 7; T=50 ℃). Moreover, the catalyst presented excellent regeneration capability and sustained catalytic ability in these experiments. Importantly, the Cit-Fe@ACFs/H2O2 catalytic system exhibited remark- able catalytic activity across a wider pH range (2~10) and the values of apparent rate constant (kapp) were greater than 0.320 min −1 , which was efficient to expand the pH range for the traditional Fenton reaction. Various scavengers and probe com- pounds (n-butanol, benzoquinone) combined with electron paramagnetic resonance (EPR) spectroscopy were used to identify the active species involved in the catalytic system. The results revealed that the hydroxyl radicals (•OH) and superoxide radi- cal (HO2•) may be responsible for the degradation of dyes. This paper discusses a possible catalytic oxidation mechanism in the Cit-Fe@ACFs/H2O2 system, which may be a feasible approach for the elimination of widely existing pollutants. Keywords activated carbon fibers; ferric citrate; Fenton-like; catalytic fibers; dyes

Mechanism of Catalytic Water Oxidation by the Ruthenium Blue Dimer Catalyst: Comparative Study in D2O versus H2O

Mechanism of Catalytic Water Oxidation by the Ruthenium Blue Dimer Catalyst: Comparative Study in D2O versus H2O

Structure and Electronic Configurations of the Intermediates of Water Oxidation in a Highly Active and Robust Molecular Ruthenium Catalyst

Photosynthesis is one of the most important chemical processes on our planet. Splitting water into O2 and H2 using sunlight is a clean and sustainable proposition for addressing energy and environmental problems encountered in our society. Mimicking this reaction in a manmade device will allow for sunlight-to-energy conversion with water providing electrons and protons for production of chemical fuels. About 30 years ago Meyer and coworkers reported the first ruthenium-based catalyst for water oxidation, known as the “blue dimer”. This catalyst may be considered as an artificial analog of the oxygen-evolving complex (OEC) in Photosystem II (PS II). Recently it has been demonstrated that single-site Ru and Ir catalysts are also active in water oxidation. These single-site catalysts are attractive model compounds for both experimental and theoretical studies of mechanism of water oxidation and show improved catalytic activity compared to “blue dimer”. A better understanding of this mechanism and identification of the rate-limiting steps could pave the way to light-driven generation of molecular hydrogen by water splitting.A mononuclear ruthenium complex [Ru(bda)(pic)2] (pic=4-picoline) was found to show high catalytic activity as well as high chemical stability. EPR, Raman and XAS characterization of the electronic structure and molecular geometry of Ru(III)-OH2,Ru(IV)=O and Ru(IV)-OO-Ru(IV) are reported in the single site water oxidizing complex. Formation of metal bound peroxides as the result of O-O coupling has been implicated in the mechanism of catalytic water oxidation by Photosystem II oxygen evolving complex (OEC) and in Ru-based catalysts. However, such intermediates were never isolated and their structural and electronic characterization has not been reported. We believe that the intermediates described here are direct products of the O-O bond formation step in the studied catalyst.

The catalytic mechanism of glyceraldehyde 3-phosphate dehydrogenase from Trypanosoma cruzi elucidated via the QM/MM approach

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) has been identified as a key enzyme involved in glycolysis processes for energy production in the Trypanosoma cruzi parasite. This enzyme catalyses the oxidative phosphorylation of glyceraldehyde 3-phosphate (G3P) in the presence of inorganic phosphate (Pi) and nicotinamide adenosine dinucleotide (NAD+). The catalytic mechanism used by GAPDH has been intensively investigated. However, the individual roles of Pi and the C3 phosphate of G3P (Ps) sites, as well as some residues such as His194 in the catalytic mechanism, remain unclear. In this study, we have employed Molecular Dynamics (MD) simulations within hybrid quantum mechanical/molecular mechanical (QM/MM) potentials to obtain the Potential of Mean Force of the catalytic oxidative phosphorylation mechanism of the G3P substrate used by GAPDH. According to our results, the first stage of the reaction (oxidoreduction) takes place in the Pi site (energetically more favourable), with the formation of oxyanion thiohemiacetal and thioacylenzyme intermediates without acid-base assistance of His194. Analysis of the interaction energy by residues shows that Arg249 has an important role in the ability of the enzyme to bind the G3P substrate, which interacts with NAD+ and other important residues, such as Cys166, Glu109, Thr167, Ser247 and Thr226, in the GAPDH active site. Finally, the inhibition mechanism of the GAPDH enzyme by the 3-(p-nitrophenoxycarboxyl)-3-ethylene propyl dihydroxyphosphonate inhibitor was investigated in order to contribute to the design of new inhibitors of GAPDH from Trypanosoma cruzi.

Au-Decorated Silicene: Design of a High-Activity Catalyst toward CO Oxidation

First-principles calculations have been performed to study Au-decorated silicene (Au/silicene) as a high-activity catalyst for CO oxidation. The high binding strength of the Au/silicene system and the high diffusion-energy barrier of Au adsorbates, as well as the assisted Coulomb repulsion effect, jointly prevent the formation of Au clusters. Au/silicene transfers many more electrons to O2 than to CO, thus facilitating CO oxidation first by the Langmuir–Hinshelwood (LH) mechanism (CO + O2 → OOCO → CO2 + O) and then by Eley–Rideal (ER) mechanism (CO + O → CO2). The two reaction processes have quite low catalytic energy barriers of 0.34 and 0.32 eV, respectively. The underlying mechanism of high catalytic oxidation of CO can be attributed to electronic-state hybridization among Au d orbitals and CO and O2 2π* antibonding states around the Fermi energy. These findings enrich the applications of Si-based materials to the high-activity catalytic field.

Preparation of Carbon-Supported Zinc Ferrite and Its Performance in the Catalytic Degradation of Mercaptan

Zinc ferrite supported on porous carbon (ZFPC) was prepared by thermal conversion of a mixture of ferric nitrate, zinc chloride, and novolac resin and was used as a catalyst for the catalytic oxidation of mercaptan under alkali-free conditions. ZFPC exhibited a high butyl mercaptan removal efficiency (222.29 mg/g), fast catalytic degradation rate, stable catalytic activity, and outstanding regenerative ability. It is believed that the effective butyl mercaptan removal was achieved by the synergism between adsorption of porous carbon and catalysis of zinc ferrite. The mechanism of catalytic oxidation of mercaptan into disulfides by ZFPC was further discussed based on the contrast experiment. The results indicated that oxidation of mercaptan in the presence of ZFPC followed the Merox process, in which Zn(II) acted as basic sites and Fe(III) acted as oxidation sites.

Impact of the Catalyst/Soot Ratio on Diesel Soot Oxidation Pathways

The transition between catalytic and thermal soot oxidation mechanisms is of importance in diesel particulate filters (DPFs). The objective of this study is to develop and validate a new detailed k...

New insight into the CO formation mechanism during formic acid oxidation on Pt(111)

Density functional theory (DFT) calculations show a new concerted mechanism of formic acid (HCOOH) oxidation on Pt (111), which involves the simultaneous formation of CO 2 and CO via the HCOOH dimer in an elementary step. The newly proposed mechanism rationalizes the easy CO poisoning of Pt-based catalysts and improves our understanding for the mechanism of catalytic HCOOH oxidation. ► A new dimer model of formic acid oxidation (HCOOH) on Pt (111) surface is presented. ► The mechanism of simultaneous formation of CO 2 and CO is obtained. ► The easy CO poisoning of Pt-based catalysts is rationalized.

Electrocatalytic Oxidation of Glucose by Rhodium Porphyrin-Functionalized MWCNT Electrodes: Application to a Fully Molecular Catalyst-Based Glucose/O2 Fuel Cell

This paper details the electrochemical investigation of a deuteroporphyrin dimethylester (DPDE) rhodium(III) ((DPDE)Rh(III)) complex, immobilized within a MWCNT/Nafion electrode, and its integration into a molecular catalysis-based glucose fuel cell. The domains of present (DPDE)Rh(I), (DPDE)Rh-H, (DPDE)Rh(II), and (DPDE)Rh(III) were characterized by surface electrochemistry performed at a broad pH range. The Pourbaix diagrams (plots of E(1/2) vs pH) support the stability of (DPDE)Rh(II) at intermediate pH and the predominance of the two-electron redox system (DPDE)Rh(I)/(DPDE)Rh(III) at both low and high pH. This two-electron system is especially involved in the electrocatalytic oxidation of alcohols and was applied to the glucose oxidation. The catalytic oxidation mechanism exhibits an oxidative deactivation coupled with a reductive reactivation mechanism, which has previously been observed for redox enzymes but not yet for a metal-based molecular catalyst. The MWCNT/(DPDE)Rh(III) electrode was finally integrated in a novel design of an alkaline glucose/O(2) fuel cell with a MWCNT/phthalocyanin cobalt(II) (CoPc) electrode for the oxygen reduction reaction. This nonenzymatic molecular catalysis-based glucose fuel cell exhibits a power density of P(max) = 0.182 mW cm(-2) at 0.22 V and an open circuit voltage (OCV) of 0.64 V.

Reaction Mechanisms for CO Catalytic Oxidation by N2O on Fe-Embedded Graphene

Catalytic conversion of hazardous gases can solve many of the environmental problems caused by them. We performed a density functional theory (DFT) study with the Perdew–Burke–Ernzerhof (PBE) functional to investigate the CO oxidation by using N2O as an oxidizing agent over an iron-embedded graphene (Fe-Graphene) catalyst. The N2O molecule was first decomposed on the Fe site yielding the N2 molecule and an Fe–O intermediate, which was an active species for the CO oxidation. The activation energy for the N2O decomposition step was predicted to be 8 kcal/mol. According to the population analysis, the graphene acted as both the electron withdrawing and donating support to assist the charge transfer between the Fe atom and the probe molecules, which are important for the reaction. The reaction was found to be less facile when the Fe site was first covered by the CO which has a higher adsorption energy than that of the N2O (−10.0 vs −33.6 kcal/mol). The reaction proceeded via a concerted transition structure and required an activation energy of 19.2 kcal/mol when the CO was prior adsorbed. Thus, control of the adsorbing molecules over Fe-Graphene might be a key factor for the activity of the catalyst. With the higher catalytic activities of Fe-embedded graphene compared to other typical catalysts, this may open new avenues in searching for oxidation of CO at an economical cost.

CeO2/H2O2 system catalytic oxidation mechanism study via a kinetics investigation to the degradation of acid orange 7

Nano ceria with cubic lattice was prepared and characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. Degradation kinetics of acid orange 7 (AO7) was investigated to understand the catalytic oxidation mechanism of the CeO2 with H2O2. The degradation of AO7 relies significantly on its adsorption on the surface of CeO2 with an apparent order of 2.40. Increasing the concentration of H2O2 increases the degradation reaction rate constant of AO7 in a positive linear relationship at the initial stage, but later hinders further degradation of AO7 due to over-complexation of Ce3+ with H2O2. The catalytic kinetics of CeO2 in pre-adsorbed mode (AO7 pre-adsorbed on CeO2 before the addition of H2O2) and pre-mixed mode (CeO2 pre-mixed with H2O2 before the addition of AO7) is quite different. The pre-mixed mode is unfavorable for AO7 degradation, as almost all of surface Ce3+ are pre-oxidized into surface peroxide species with H2O2 and hence reduces adsorption of AO7 as well as the activation of AO7 degradation. Reversely, the reactivity of CeO2 can slowly be recovered by adsorption of AO7, which competitively adsorbs on the CeO2 and gradually initiates the release of the surface Ce3+ by consuming the surface peroxide species. The AO7 degradation kinetics investigation in this work verifies that the degradation of organics in CeO2/H2O2 system is adsorption-triggered and the Ce3+ in reduced state is essential for activating the catalytic oxidation activity of surface peroxide species. EPR studies show that the surface peroxide species oxidizes the organics via hydroxyl adduct route.

A B3LYP study on electronic structures of [(X)<sub>m</sub>Mn(<i>μ</i>-oxo)<sub>2</sub>Mn(Y)<sub>n</sub>]<sup><i>q</i>+</sup> (X, Y = H<sub>2</sub>O, OH and O) as a Mn cluster model of OEC

Electronic and molecular structures of [(X)mMn(μ-oxo)2Mn(Y)n]q+ (X, Y = H2O, OH and O), which are Mn cluster models at catalytic sites of OEC, were studied by broken-symmetry unrestricted B3LYP method. Two paths from the S0 to S3 states of Kok cycle were investigated. One is a path starting from [Mn(II) (μ-oxo)2Mn(III)] at the S0 state, and another is from [Mn(III) (μ-oxo)2Mn(III)] at the S0. Results found in this study are summarized as, 1) In [Mn(II), Mn(III)], it is not possible that H2O molecules coordinate to the Mn atoms with retaining the octahedral configuration. 2) The OHˉ anion selectively coordinates to Mn(IV) rather than Mn(III). 3) When the oxo atom directly bind to the Mn atom, the Mn atom must be a Mn(IV). From these results, the catalytic mechanism for four-electron oxidation of two H2O molecules in OEC is proposed. 1) The Mn4(II, III, IV, IV) at S0 is ruled out. 2) For Mn4(III, III, IV, IV) at S1, the Mn atom coordinated by OHˉ anion is a Mn(IV) not Mn(III). 3) Only Mn(III) ion which is coordinated by a H2O molecule at S0 plays crucial roles for the oxidation.