Mechanism Of Catalytic Oxidation Research Articles

La-modified SBA-15/H2O2 systems for the microwave assisted oxidation of organosolv beech wood lignin

In this manuscript, the inuence of organosolv beech wood lignin (LOB) on its oxidative conver- sion to high added-value phenolic aldehydes is discussed. Environmental friendly and low-cost H 2 O 2 was used as the oxygen atom donor. � e catalyst was prepared by immobilizing Lanthanum com- pounds onto the periodic mesoporous channels of siliceous SBA-15. � e activity of the La/SBA-15 was investigated towards oxidation of LOB in the presence of hydrogen peroxide as oxidant with microwave irradiation. Considering the characteristics of LOB, an unexpected low syringaldehyde concentration at 10min of reaction time (1.47 g/L, corresponding to 15.66% yield) was obtained; the other major product was vanillin at 25min (0.78 g/L, i.e., 9.94% yield). � e high reactivity of syringyl nuclei may be pointed out as the main reason for the faster production and degradation of syringaldehyde in oxida- tion. Other low molecular weight phenolic products were found: vanillic acid, syringic acid and minor quantities of aceto-derivatives. � e prole of products concentration with the reaction time of catalytic oxidation with microwave irradiation are shown and discussed with reference to the investigated lignin features. � e mechanism of the microwave catalytic oxidation for LOB under alkaline conditions was proposed.

Investigation of catalytic mechanism of formaldehyde oxidation over three-dimensionally ordered macroporous Au/CeO2 catalyst

A colloidal crystal template method coupled with a precursor complexion process was developed to create three-dimensionally ordered macroporous (3DOM) Au/CeO2 catalyst. The resultant Au/CeO2 catalyst possesses well-defined 3DOM structure, and shows enhanced catalytic performance for formaldehyde (HCHO) oxidation with 100% HCHO conversion at ∼75°C. The catalytic mechanism of HCHO catalytic oxidation over 3DOM Au/CeO2 catalyst was systematically investigated by means of gas chromatograph (GC), H2-temperature programmed reduction (H2-TPR), temperature programmed surface reaction (TPSR), CO2-temperature programmed desorption (TPD), and Fourier transform infra-red (FT-IR) spectroscopy. GC results indicate that HCOOH intermediate is generated during HCHO catalytic oxidation. TPD and TPSR tests show that the weak absorption ability of CO2 over 3DOM Au/CeO2 catalyst and the existence of Au active species in ionic and metallic states in 3DOM Au/CeO2 catalyst largely improve the catalytic activity, favoring the enhanced HCHO catalytic oxidation. FT-IR tests prove that the carbonate and hydrocarbonate formed on the surface of 3DOM Au/CeO2 catalyst during HCHO catalytic oxidation may account for its deactivation. Based on the above investigation, a new catalytic mechanism of enhanced HCHO catalytic oxidation over 3DOM Au/CeO2 catalyst is proposed. The mechanism may afford the scientific guidance for preparing high efficiency oxide supported noble metal catalysts and present a solution for solving their deactivation problem.

Detection and sensing mechanism of acetone with modeling using Pd/TiO2/Si structure

A grided Pd/TiO2/Si (Pdtisin) gas sensor is fabricated to detect hydrocarbons such as acetone, ethanol and trichloroethylene. The sensitivity measurements are carried out in various ambient (O2, N2 and Ar) at room temperature which revealed that fabricated structure attains maximal response for acetone in contrast to other vapors examined. The study of ambient-effect on the device shows that it out-performs in oxygen ambient. A catalytic oxidation mechanism for detection of acetone with a model based upon Langmuir law of adsorption and Frenkel–Poole theory of electronic emission for the description of sensing behavior and vindication of experimental results have been proposed.

Mechanisms for Selective Catalytic Oxidation of Ammonia over Vanadium Oxides

Ministry of Science and Technology[2011CB808505, 2007CB815206]; National Natural Science Foundation of China[20973139, 20923004, 21033006, 21133004]; Program for Changjiang Scholars and Innovative Research Team in University[IRT1036]; Fundamental Research Funds for the Central Universities; Key Science and Technology Specific Projects of Fujian Province[2009HZ0002-1]; Natural Science Foundation of Fujian Province of China[2009J05035]

Mechanism of Catalytic Oxidation of NO over Mn–Co–Ce–Ox Catalysts with the Aid of Nonthermal Plasma at Low Temperature

NO catalytic oxidation performances have been investigated on a Mn–Co–Ce–Ox catalyst by using nonthermal plasma (NTP) reactor: the “PRFC” reactor. In the PRFC system, the plasma reactor was followe...

Direct-Coupling O2 Bond Forming a Pathway in Cobalt Oxide Water Oxidation Catalysts

We report a catalytic mechanism for water oxidation in a cobalt oxide cubane model compound, in which the crucial O–O bond formation step takes place by direct coupling between two CoIV(O) metal oxo groups. Our results are based upon density functional theory (DFT) calculations and are consistent with experimental studies of the CoPi water oxidation catalyst. The computation of energetics and barriers for the steps leading up to and including the O–O bond formation uses an explicit solvent model within a hybrid quantum mechanics/molecular mechanics (QM/MM) framework, and captures the essential hydrogen-bonding effects and dynamical flexibility of this system.

A comparative theoretical study of the catalytic activities of Au 2 - and AuAg- dimers for CO oxidation

The detailed mechanisms of catalytic CO oxidation over Au(2)(-) and AuAg(-) dimers, which represent the simplest models for monometal Au and bimetallic Au-Ag nanoparticles, have been studied by performing density functional theory calculations. It is found that both Au(2)(-) and AuAg(-) dimers catalyze the reaction according to the similar mono-center Eley-Rideal mechanism. The catalytic reaction is of the multi-channel and multi-step characteristic, which can proceed along four possible pathways via two or three elementary steps. In AuAg(-), the Au site is more active than the Ag site, and the calculated energy barrier values for the rate-determining step of the Au-site catalytic reaction are remarkably smaller than those for both the Ag-site catalytic reaction and the Au(2)(-) catalytic reaction. The better catalytic activity of bimetallic AuAg(-) dimer is attributed to the synergistic effect between Au and Ag atom. The present results provide valuable information for understanding the higher catalytic activity of Au-Ag nanoparticles and nanoalloys for low-temperature CO oxidation than either pure metallic catalyst.

Catalytic oxidation mechanism of oxy-nitrogen species (NO x) in FeSO 4 electrolyte

The effect of small concentrations of nitrite on the oxidation of ferrous ions in sulfuric acid under oxygen pressure at 25 °C was investigated. A mathematical model of the rate of chemical reaction was developed to simulate the concentration versus time trajectories of the prominent species in the system in parallel with previous thermodynamic and kinetics investigations on related systems. The simulations were performed by employing the COMSOL Reaction Engineering Lab Module to find numerical solutions for the model equations. The reaction scheme consists of eight principal reactions: three describing the oxidation of ferrous ions by oxy-nitrogen species, one the formation of the Fe(NO) 2+ complex, and four additional reactions that summarize the chemistry of oxy-nitrogen species in acidic solutions. The optimal NaNO 2 (HNO 2) concentration was determined to be 4.5 mM based on an objective function designed on the basis of two competing considerations: the cost of the nitrite reagent as manifested by the feed concentration employed in the processing scheme, and the processing costs as determined by the time needed to achieve 99.9% oxidation of ferrous ions. The simulations revealed that the concentration of NO x plays a critical role in determining t 99.9, the rate of reaction between nitric oxide and nitrate. In a sulfuric acid electrolyte, nitrous acid disproportionates to produce N 2O 3, NO, and NO 2. Ultimately, all the nitrogen species that evolved in the electrolyte from the sodium-nitrite reagent were oxidized to nitrate NO 3 - as the oxidation of ferrous ions to ferric ions proceeded to completion. The simulation revealed that a ferrous-nitrosyl complex was produced immediately. Thus, researcher postulates that the majority of the NO species were bound in solution, perhaps as Fe(NO) 2+.

Experimental study of intermediates and wave phenomena in co oxidation on platinum metal (Pt, Pd) surfaces

The mechanism of catalytic CO oxidation on Pt(100) and Pd(110) single-crystal surfaces and on Pt and Pd sharp tip (∼103 A) surfaces has been studied experimentally by temperature-programmed reaction, temperature desorption spectroscopy, field electron microscopy, and molecular beam techniques. Using the density functional theory the equilibrium states and stretching vibrations of oxygen atoms adsorbed on the Pt(100) surface have been calculated. The character of the mixed adsorption layer was established by high resolution electron energy loss spectroscopy—molecular adsorption (O2ads, COads) on Pt(100)-hex and dissociative adsorption (Oads, COads) on Pt(100)-(1×1). The origin of kinetic self-oscillations for the isothermal oxidation of CO in situ was studied in detail on the Pt and Pd tips by field electron microscopy. The initiating role of the reversible phase transition (hex) ↔ (1 × 1) of the Pt(100) nanoplane in the generation of regular chemical waves was established. The origination of self-oscillations and waves on the Pt(100) nanoplane was shown to be caused by the spontaneous periodical transition of the metal from the low-active state (hex) to the highly active catalytic state (1 × 1). A relationship between the reactivity of oxygen atoms (Oads) and the concentration of COads molecules was revealed for the Pd(110) surface. Studies using the isotope label 18Oads demonstrated that the low-temperature formation of CO2 at 150 K is a result of the reaction of CO with the highly reactive state of atomic oxygen (Oads). The possibility of the low-temperature oxidation of CO via interaction with the so-called “hot” oxygen atoms (Ohot) appearing on the surface at the instant of dissociation of O2ads molecules was studied by the molecular beam techniques.

A new oxovanadium(IV)–cucurbit[6]uril complex: Properties and potential for confined heterogeneous catalytic oxidation reactions

This work presents a new oxovanadium(IV)–cucurbit[6]uril complex, which combines the catalytic properties of the metal ion with the size-excluding properties of the macrocycle cavity. In this coordination compound, the VO 2 + ions are coordinated to the oxygen atoms located at the rim of the macrocycle in slightly distorted square-pyramidal configurations, which are in fact C 2 v symmetries. This combination results in a size-selective heterogeneous catalyst, which is able to oxidize linear alkanes like n-pentane at room temperature, but not styrene, cyclohexane or z-cyclooctene, which are too big to enter the cucurbit[6]uril cavity. The results presented here contribute to understanding the mechanism of alkane catalytic oxidation by oxovanadium(IV) complexes.

Reactant-Promoted Oxygen Dissociation on Gold Clusters

The molecular and dissociative adsorption of O2 on pure odd-size Aun (n = 1, 3, 5, 7, 9) clusters and Aun with a coadsorbed C2H4 molecule has been studied theoretically using density functional theory. It is demonstrated that catalytic activation of the adsorbed O2 on pure gold clusters in the considered size range cannot lead to O2 dissociation. Coadsorption of C2H4, however, involves an extra charge transfer from the gold cluster to O2, energetically promoting oxygen dissociation. Our finding indicates that O2 dissociation on the surface of small gold clusters is sensitive to the presence of other adsorbates, including the reactant molecule itself. This effect can be particularly important for understanding the mechanism of catalytic oxidation on gold clusters.

PREPARATION OF VISCOSE FIBER SUPPORTED-METAL TETRACABOXYPHTHALOCY ANINE AND ITS DEODORIZING ABILITY

Iron tetracaboxyphthalocyanine(Fe-CPc) and cobalt tetracaboxyphthalocyanine(Co-CPc) were synthesized and characterized by element analysis and FT-IR.The products were supported by modified cellulose fibers in acidic condition to obtain a novel deodorizing fibers.The results show that FePcF(fibers-supported Fe-CPc),CoPcF(fibers-supported Co-CPc)and CoFePcF(fibers-supported Fe-CPc and Co-CPc) can remove methanthiol,hydrogen sulfide,ammonia and trimethylamine effectively at room temperature.Methanthiol and hydrogen sulfide were removed by the mechanism of catalytic oxidation,while ammonia and trimethylamine by the mechanism of neutralization.The efficiency of these fibes in deodorizing methanthiol and hydrogen sulfide has the following order CoFePcF CoPcF FePcF.

Mechanism of catalytic oxidation of water-lipid substrate

The processes of ethyl oleate water-emulsion oxidation in the presence of copper (II) complexes with α-alanine as a catalyst were investigated spectroscopically. UV spectra of the samples revealed the competitive nature of the formation and decomposition of hydroperoxides in the course of oxidation. Vis spectra of the aqueous phase revealed the constant presence of copper (II) complex with α-alanine and the formation of a similar complex with copper (I) in organic phase. The involvement of these complexes in the reactions of chain nucleation and decay of hydroperoxides is suggested.

A DFT Study of CO Catalytic Oxidation by N2O or O2 on the Co3O4(110) Surface

AbstractThe reaction mechanisms for CO catalytic oxidation by N2O or O2 on the Co3O4(110) surface were studied by DFT slab calculations. CO chemisorbs preferably at a surface Co3+ site. After the Co3+ site is completely covered, CO adsorbs at the neighboring twofold coordinated surface oxygen atom bonded to Co2+ and Co3+ cations, resulting in the formation of CO2 and an oxygen vacancy with a low energy barrier of 0.033 eV, which rationalizes the experimental observation that Co3O4‐based systems are active for CO oxidation at low temperatures. N2O or O2 interacts with the oxygen vacancy site to regenerate the surface, leaving N2 or the activated O2− species to be attacked by the second CO to yield CO2 to proceed with the catalytic cycle. The CO oxidation reaction follows the Mars– van Krevelen mechanism.

Mechanism of selective catalytic oxidation of ammonia to nitrogen over Ag/Al 2O 3

The mechanism of selective catalytic oxidation (SCO) of NH 3 over Ag/Al 2O 3 was studied by NH 3 temperature-programed oxidation, O 2-pulse adsorption, and in situ DRIFTS of NH 3 adsorption and oxidation. The essence which affects the low temperature activity of Ag/Al 2O 3 has been elucidated through the mechanism study. Different Ag species on Ag/Al 2O 3 significantly influence O 2 uptake by catalysts; while different oxygen species affect the activity of NH 3 oxidation at low temperature. The activated –NH could react with the atomic oxygen (O) at low temperatures (<140 °C); however, the –NH could also interact with the O 2 at temperatures above 140 °C. At low temperatures (<140 °C), NH 3 oxidation follows the –NH mechanism. However, at temperatures above 140 °C, NH 3 oxidation follows an in situ selective catalytic reduction (iSCR) mechanism (two-step formation of N 2 via the reduction of an in situ-produced NO x species by a NH x species).

Isolated Seven-Coordinate Ru(IV) Dimer Complex with [HOHOH]− Bridging Ligand as an Intermediate for Catalytic Water Oxidation

With the inspiration from an oxygen evolving complex (OEC) in Photosystem II (PSII), a mononuclear Ru(II) complex with a tetradentate ligand containing two carboxylate groups has been synthesized and structurally characterized. This Ru(II) complex showed efficient catalytic properties toward water oxidation by the chemical oxidant cerium(IV) ammonium nitrate. During the process of catalytic water oxidation, Ru(III) and Ru(IV) species have been successfully isolated as intermediates. To our surprise, X-ray crystallography together with HR-MS revealed that the Ru(IV) species is a seven-coordinate Ru(IV) dimer complex containing a [HOHOH](-) bridging ligand. This bridging ligand has a short O...O distance and is hydrogen bonded to two water molecules. The discovery of this very uncommon seven-coordinate Ru(IV) dimer together with a hydrogen bonding network may contribute to a deeper understanding of the mechanism for catalytic water oxidation. It will also provide new possibilities for the design of more efficient catalysts for water oxidation, which is the key step for solar energy conversion into hydrogen by light-driven water splitting, the ultimate challenge in artificial photosynthesis.

Theoretical Investigation of the Mechanism of the Selective Catalytic Oxidation of Ammonia on H-Form Zeolites

The selective catalytic oxidation (SCO) of ammonia has been investigated on a portion of the H-ZSM5 framework which contains 5T atoms by using density functional theory, representing H-form zeolites. The mechanism was subdivided into three main blocks: (I) the direct reaction of NH3 with oxygen, leading either to HNO or to NH2OH, (II) the decay of nitroxyl (HNO), and (III) the decay of intermediately produced hydroxylamine (NH2OH). For the decay of HNO and NH2OH the catalyst is active for reactions with both NO and HNO, which leads to a reaction network with several energetically similar and accessible pathways. The initial reaction of oxygen with adsorbed ammonia exhibits the highest energy barrier in the mechanism and thus is likely to be the rate-limiting step. For all three parts, the crossing of potential energy surfaces was considered if necessary. The investigation of potential reaction pathways of N2O with NH3 and NO reveals a low activity of H-ZSM5 for them, and thus, they only have a minor relev...

Structural and Functional Insights into Sulfide:Quinone Oxidoreductase,

A sulfide:quinone oxidoreductase (SQR) was isolated from the membranes of the hyperthermoacidophilic archaeon Acidianus ambivalens, and its X-ray structure, the first reported for an SQR, was determined to 2.6 A resolution. This enzyme was functionally and structurally characterized and was shown to have two redox active sites: a covalently bound FAD and an adjacent pair of cysteine residues. Most interestingly, the X-ray structure revealed the presence of a chain of three sulfur atoms bridging those two cysteine residues. The possible implications of this observation in the catalytic mechanism for sulfide oxidation are discussed, and the role of SQR in the sulfur dependent bioenergetics of A. ambivalens, linked to oxygen reduction, is addressed.

Experimental Study of SOF Oxidation Catalysts under Plasma Discharge Conditions

Abstract Oxidative activities of eight different transition-metal oxides and two different noble metals toward the soluble organic fraction (SOF) in diesel particulate matter (PM) have been investigated under plasma discharge conditions. The oxidation rate with ZnO has shown the highest value 99% higher than that without a catalyst and has exceeded that with noble metals. A mechanism of catalytic SOF oxidation under plasma discharge conditions has been proposed.

Catalytic oxidation of CO on CuO x revisited: Impact of the surface state on the apparent kinetic parameters

Analysis of kinetic features of the copper oxides reduction by CO pulses as related to mechanism of CO catalytic oxidation by oxygen combined with monitoring the state of the surface by an electrochemical technique using a solid electrolyte—Pyrex glass and high resolution TEM data on the defect structure of CuO allowed us to suggest a partially “flexible” model of CuO surface. This model, with a due regard for the data of FTIR spectroscopy of adsorbed CO test molecules, assigns the most active surface sites able to coordinate highly reactive CO and O forms to clusters of Cu + cations located at outlets of extended defects (dislocations, twins). Variation of the number, size and structure of these clusters under the reaction medium effect allows explaining the difference between quasi-steady and true steady states of copper oxides in catalytic CO oxidation reaction as well as the difference between kinetic parameters of reaction estimated at quasi-steady and constant states of the surface following Boreskov's approach. Kinetic features of the reaction agree with the Langmuir–Hinshelwood reaction mechanism operating for clustered defect centers of CuO.