Heterogeneous Oxidation Reactions Research Articles

Au/C catalysts prepared by a green method towards C3 alcohol electrooxidation: A cyclic voltammetry and in situ FTIR spectroscopy study

Gold electrocatalysts seems to be an interesting material for application in Alkaline Fuel Cells (AFC) since several studies have reported the electro-catalytic activity of gold-based catalysts for various heterogeneous catalyzed oxidation reactions like oxidation of small organic molecules. In this paper, we synthesized Au nanoparticles (Au Nps) dispersed onto Vulcan carbon substrate using a straightforward glycerol method in order to study the pathway electro-oxidation of alcohols, like glycerol, 1,2-propanediol and 1-propanol in alkaline medium. TEM images showed a good dispersion of the gold nanoparticles on the carbon support and the particle mean size ranging from 3 to 14nm. The structure of gold is face centered cubic (fcc) indicated by XRD and the metal loading was 18% evaluated by EDS technique. Cyclic voltammetry was mainly used to evaluate the electrochemical activity of the Au NPs towards the oxidative transformation of alcohols. Electrochemical results proved that Au/C Nps are more active to oxidize glycerol than 1,2-propanediol and 1-propanol, while higher current density was obtained for the diol. In situ FTIR measurements showed different pathway for each alcohol. For glycerol electro-oxidation, the mean byproducts from reaction were formate and oxalate ions. It was already suggested that gold in alkaline medium oxidized glycerol more promptly than others alcohols. The electro-oxidation of 1,2-propanediol leaded to acetate ion and hydroxyacetone while the in situ FTIR spectrum for electrooxidation of 1-propanol suggests that propanoate is the only the product of 1-propanol electro-oxidation over Au/C.

Modelling non-equilibrium secondary organic aerosol formation and evaporation with the aerosol dynamics, gas- and particle-phase chemistry kinetic multilayer model ADCHAM

Abstract. We have developed the novel Aerosol Dynamics, gas- and particle-phase chemistry model for laboratory CHAMber studies (ADCHAM). The model combines the detailed gas-phase Master Chemical Mechanism version 3.2 (MCMv3.2), an aerosol dynamics and particle-phase chemistry module (which considers acid-catalysed oligomerization, heterogeneous oxidation reactions in the particle phase and non-ideal interactions between organic compounds, water and inorganic ions) and a kinetic multilayer module for diffusion-limited transport of compounds between the gas phase, particle surface and particle bulk phase. In this article we describe and use ADCHAM to study (1) the evaporation of liquid dioctyl phthalate (DOP) particles, (2) the slow and almost particle-size-independent evaporation of α-pinene ozonolysis secondary organic aerosol (SOA) particles, (3) the mass-transfer-limited uptake of ammonia (NH3) and formation of organic salts between ammonium (NH4+) and carboxylic acids (RCOOH), and (4) the influence of chamber wall effects on the observed SOA formation in smog chambers. ADCHAM is able to capture the observed α-pinene SOA mass increase in the presence of NH3(g). Organic salts of ammonium and carboxylic acids predominantly form during the early stage of SOA formation. In the smog chamber experiments, these salts contribute substantially to the initial growth of the homogeneously nucleated particles. The model simulations of evaporating α-pinene SOA particles support the recent experimental findings that these particles have a semi-solid tar-like amorphous-phase state. ADCHAM is able to reproduce the main features of the observed slow evaporation rates if the concentration of low-volatility and viscous oligomerized SOA material at the particle surface increases upon evaporation. The evaporation rate is mainly governed by the reversible decomposition of oligomers back to monomers. Finally, we demonstrate that the mass-transfer-limited uptake of condensable organic compounds onto wall-deposited particles or directly onto the Teflon chamber walls of smog chambers can have a profound influence on the observed SOA formation. During the early stage of the SOA formation the wall-deposited particles and walls themselves serve as an SOA sink from the air to the walls. However, at the end of smog chamber experiments the semi-volatile SOA material may start to evaporate from the chamber walls. With these four model applications, we demonstrate that several poorly quantified processes (i.e. mass transport limitations within the particle phase, oligomerization, heterogeneous oxidation, organic salt formation, and chamber wall effects) can have a substantial influence on the SOA formation, lifetime, chemical and physical particle properties, and their evolution. In order to constrain the uncertainties related to these processes, future experiments are needed in which as many of the influential variables as possible are varied. ADCHAM can be a valuable model tool in the design and analysis of such experiments.

Elucidating the role of stable carbon radicals in the low temperature oxidation of coals by coupled EPR–NMR spectroscopy – a method to characterize surfaces of porous carbon materials

Recently, the nature of the carbon radicals stabilized in various coals was characterized using Electron Paramagnetic Resonance (EPR) spectroscopy. It was demonstrated that introducing diamagnetic gases, such as He, CO2, or N2, under STP conditions to the coal surface induces the appearance of a new type of carbon surface radical. This interesting phenomenon was not observed for all coal types, which suggests that the use of EPR measurements can provide information on functional groups that exist on the carbon surface. In the current study coupling Nuclear Magnetic Resonance (NMR) with gas flow in situ EPR measurements significantly enhances the ability to characterize the nature of these radicals and the surface functional groups of coal samples. It was observed that the oxidative reaction with aliphatic groups leads to the increase in stable carbon centered radicals. In addition, there are some species of carbon centered radicals that show reversible binding to O2. This phenomena, however, is dependent on the coal rank, sample porosity and the degree of the coal sample to undergo structural changes under the LTO process. These findings shed new light onto the complex heterogeneous low temperature oxidation reactions occurring at the coal surface.

Model of the Plate Oxygen Cutting Taking into Account the Kinetics of Heterogeneous Oxidation Reaction

This paper presents a mathematical model of oxygen cutting of the plate. It takes into account not only possible heat losses from the treatment zone, but also the heat release doe to the oxidation reaction. In turn, the oxidation leads to plate thickness change. The model allows analyzing the temperature distribution during the cutting process for different modes. The following cutting modes are revealed in the model: surface cutting, detail splitting, kinetic and diffusion regime.

Soot formation and oxidation during bio-oil gasification: experiments and modeling

A model is proposed to describe soot formation and oxidation during bio-oil gasification. It is based on the description of bio-oil heating, devolatilization, reforming of gases and conversion of both char and soot solids. Detailed chemistry (159 species and 773 reactions) is used in the gas phase. Soot production is described by a single reaction based on C2H2 species concentration and three heterogeneous soot oxidation reactions. To support the validation of the model, three sets of experiments were carried out in a lab-scale Entrained Flow Reactor (EFR) equipped with soot quantification device. The temperature was varied from 1000 to 1400 °C and three gaseous atmospheres were considered: default of steam, large excess of steam (H2O/C = 8), and the presence of oxygen in the O/C range of 0.075–0.5. The model is shown to accurately describe the evolution of the concentration of the main gas species and to satisfactorily describe the soot concentration under the three atmospheres using a single set of identified kinetic parameters. Thanks to this model the contribution of different mechanisms involved in soot formation and oxidation in various situations can be assessed.

Synthesis of molybdovanadophosphoric acid supported hybrid materials and their heterogeneous catalytic activity

We have newly developed molybdovanadophosphoric acid (MVPA) supported nano silica ball/mesoporous carbon/SBA-15 as heterogeneous catalysts using the advanced impregnation method. Due to their potential applications in fine chemicals and pharmaceuticals, these hybrid materials are preferred for the development of clean and environmentally acceptable heterogeneous oxidation catalysts. This work illustrates the potential use of Keggin type catalysts in selective oxidation of benzaldehyde and formaldehyde along with degradation of methylene blue using hydrogen peroxide as oxidant. The activity and selectivity of the catalysts for solvent-free heterogeneous catalytic oxidation and degradation reaction revealed with excellent conversion and recyclability.

On the possible causes of enhancement of the heterogeneous catalytic liquid-phase oxidation reaction of m-xylene by microwave radiation

The contribution of the heterogeneous component of the total conversion of m-xylene to the process of its heterogeneous catalytic liquid-phase oxidation has been studied, as this contribution is most clearly manifested in the case of microwave treatment. It has been shown that microwave irradiation shortens the induction period of the reaction taken to reach a steady state. It has been suggested that the observed increase in the generation rate of free m-xylyl radicals by microwave treatment is due to the appearance at the hydrocarbons/catalyst interface of local overheating regions whose temperature can exceed the weight-average temperature in the reaction space.

Iron(iii) porphyrin supported on metahalloysite: an efficient and reusable catalyst for oxidation reactions

The raw clay minerals kaolinite and halloysite were calcined at controlled temperature and time, to obtain metakaolinite and metahalloysite, respectively. The resulting materials were used as supports for the anionic iron(III) porphyrin [Fe(TDFSPP)] (FePor) and found that only metahalloysite is adequate for FePor immobilization, although the FePor loading on this solid is low. XRPD, FTIR and solid UV-Vis spectroscopies, and textural analysis confirmed metakaolinite and metahalloysite formation and FePor immobilization on metahalloysite. The catalytic activity of the metahalloysite-supported FePor (FeMhallo) was evaluated in heterogeneous oxidation reactions using iodosylbenzene as oxidant and cyclooctene, cyclohexane, or n-heptane as substrate, obtaining expressive product yields for all the substrates. At the end of the oxidation, the catalyst was recovered from the reaction medium and used in a further reaction, which also afforded appreciable results. In competitive catalytic reactions using cyclohexane and n-heptane as substrates, FeMhallo is not significantly selective for any of the substrates.

Aerobic oxidation of 4-tert-butyltoluene over cobalt and manganese supported hexagonal mesoporous silicas as heterogeneous catalysts

Monometallic cobalt and manganese, and their bimetal-supported hexagonal mesoporous silicas (HMS) prepared by incipient-wetness impregnation using cobalt nitrate and manganese acetate as precursors, and ethanol and ethylene glycol as impregnation solvents, respectively, were examined as catalysts for partial oxidation of 4-tert-butyltoluene with dioxygen as oxidizing agent in acetonitrile solvent. The catalysts were characterized by X-ray powder diffraction, N2 adsorption–desorption isotherm, diffuse reflectance UV–vis spectroscopy and thermogravimetric and differential thermal analysis. The introduction of cobalt oxides to HMS kept complete mesostructure of HMS supports, high specific surface areas and big pore volumes. The dominant phase of Co3O4 was detected in the Co–HMS materials calcined at 550°C. A mixture of manganese oxides (MnO, Mn2O3, Mn3O4) was dispersed on the Mn–HMS catalysts after calcination at 550°C in the air. The bimetal-supported Co–Mn–HMS with loading 4wt.% of Co and Mn exhibited the best catalytic performance in the oxidation of 4-tert-butyltoluene with O2, and gave a conversion of 43.7% of 4-tert-butyltoluene and maximal yield of 27.4% of 4-tert-butylbenzaldehyde in a reaction time of 5h in liquid phase under mild condition. A high concentration and dispersion of M2+ (Co2+, Mn2+) and M3+ (Co3+, Mn3+) ions on catalysts were responsible for high catalytic performance in the oxidation reaction via a free-radical chain promoted by N-hydroxyphthalimide (NHPI). The four consecutive cycles revealed that the cobalt and manganese species supported on HMS provided a possibility for the heterogeneous oxidation reaction.

Catalysts for heterogeneous oxidation reaction based on metalloporphyrins immobilized on kaolinite modified with triethanolamine

Raw kaolinite was modified with triethanolamine (TEA), in an attempt to create a new support for the immobilization of metalloporphyrins. Anionic metalloporphyrins containing Fe3+ or Mn3+ as metallic centers were immobilized on the prepared support, and the obtained solids were characterized by Fourier-transform infrared (FTIR) spectroscopy, X-ray powder diffraction (XRPD), thermal analysis (thermogravimetric and differential thermal analyses – TGA/DTA), and scanning electron microscopy (SEM). The solids were used in heterogeneous oxidation catalysis of cyclooctene and cyclohexane. The yields from the oxidation of cyclooctene depended on the amount of TEA and/or water present in the solids. Good reaction yields were obtained for the oxidation of cyclohexane, with selectivity for the alcohol. In one specific case, a possible co-catalytic activity was verified for TEA during the oxidation of cyclohexane.

Stable radicals formation in coals undergoing weathering: effect of coal rank

Once coal is excavated it comes into contact with atmospheric oxygen and begins to undergo low temperature oxidation. The mechanism by which the molecular oxygen interacts with the coal macromolecule is suggested to occur in several steps. These steps primarily involve O(2) diffusion to the surface where physical adsorption followed by chemical adsorption takes place. The chemical adsorption forms several types of oxides that can subsequently react to form several products, primarily CO(2). It has also been suggested that some of these oxidation mechanisms might involve radical reactions. As the previous studies were conducted under conditions where significant structural changes occur it is possible that in the low temperature range (T < 100 °C) the oxidation mechanism is different. Several different rank (lignite-subbituminous-bituminous) coals were isothermally heated at 95 °C in an air atmosphere for a period of up to 6 months and samples were collected at two week intervals. The radical concentration of each sample was measured by Continuous Wave Electron Paramagnetic Resonance (CW-EPR). It is apparent that there are distinct differences between the lower rank (lignite) and the higher rank (subbituminous, bituminous) coals. The lower rank coals exhibited only carbon centered radicals with an adjacent oxygen atom and the higher rank coals exhibited only carbon centered radicals. Interestingly, the lower rank coals exhibited no change in radical concentration due to the long term oxidation treatment while the higher rank coals showed a distinct increase in the radical concentration. These findings shed new light on the complex heterogeneous low temperature oxidation reactions occurring at the coal surface.

Anionic iron(III) porphyrins immobilized on zinc hydroxide chloride as catalysts for heterogeneous oxidation reactions

This work describes the immobilization of an anionic iron(III) porphyrin (FePor) family on zinc hydroxide chloride (ZHC), a layered hydroxide salt prepared by reacting an aqueous zinc chloride solution with an ammonium hydroxide solution. The FePor immobilization was performed at room temperature under magnetic stirring, under air atmosphere, of each complex ethanol solution and the ZHC solid support suspension. The materials obtained were characterized by X-ray powder diffraction (XRPD), ultraviolet-visible spectroscopy (UV–vis) (solid samples), Fourier transform infrared spectroscopy (FTIR) and electron paramagnetic resonance (EPR). The catalytic activity of the solids was investigated in cyclooctene, cyclohexane and n-heptane heterogeneous catalytic oxidation reactions with iodosylbenzene as the oxygen donor. The solid catalyst's reutilization capacity was also investigated and the heterogeneous character of the catalytic process was confirmed. The compounds and the catalytic activity of FePor-ZHC were compared with the synthesis and catalytic activity of the same FePor immobilized on zinc hydroxide nitrate (ZHN). Though the matrixes are similar, the results obtained were exactly the opposite when the selectivity was analyzed.

Heterogeneous oxidation reaction of gas‐phase ozone with anthracene in thin films and on aerosols by infrared spectroscopic methods

AbstractIn this paper, a real‐time laboratory study of the heterogeneous oxidation reaction of gas‐phase ozone with anthracene on surface substrates by using infrared spectroscopy in two distinctly different experimental configurations is reported. One set of kinetic measurements was made by attenuated total internal reflection infrared (ATR‐IR) spectroscopy using approximately 75‐nm films of anthracene adsorbed on ZnSe, for which the reactive uptake coefficient was determined to be (2.0 ± 1.1) × 10−7. Using an aerosol flow tube coupled to an infrared spectrometer (AFT‐IR), similar measurements were made on (NH4)2SO4 (ammonium sulfate) aerosols coated with a 0.1‐μm film of anthracene. The aerosol kinetic results as a function of the ozone concentration are consistent with a Langmuir–Hinshelwood‐type mechanism, for which the ozone‐partitioning coefficient was K = (1.4 ± 1.7) × 10−16 cm3 molecule−1, and the maximum pseudo‐first‐order rate coefficient was kImax = (0.035 ± 0.016) s−1. Infrared spectroscopic and mass spectrometric analysis of the ozonolysis reaction in the bulk phase identified the main ozonolysis products as dihydroxyanthrones, 9,10‐endoperoxide–anthracene, 9,10‐anthraquinone, and anthrone. Larger products were also seen in the mass spectra, most likely the result of secondary product and oligomer formation. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 694–707, 2011

Pyrazolate‐Based Cobalt(II)‐Containing Metal–Organic Frameworks in Heterogeneous Catalytic Oxidation Reactions: Elucidating the Role of Entatic States for Biomimetic Oxidation Processes

Crystal structures of two metal-organic frameworks (MFU-1 and MFU-2) are presented, both of which contain redox-active Co(II) centres coordinated by linear 1,4-bis[(3,5-dimethyl)pyrazol-4-yl] ligands. In contrast to many MOFs reported previously, these compounds show excellent stability against hydrolytic decomposition. Catalytic turnover is achieved in oxidation reactions by employing tert-butyl hydroperoxide and the solid catalysts are easily recovered from the reaction mixture. Whereas heterogeneous catalysis is unambiguously demonstrated for MFU-1, MFU-2 shows catalytic activity due to slow metal leaching, emphasising the need for a deeper understanding of structure-reactivity relationships in the future design of redox-active metal-organic frameworks. Mechanistic details for oxidation reactions employing tert-butyl hydroperoxide are studied by UV/Vis and IR spectroscopy and XRPD measurements. The catalytic process accompanying changes of redox states and structural changes were investigated by means of cobalt K-edge X-ray absorption spectroscopy. To probe the putative binding modes of molecular oxygen, the isosteric heats of adsorption of O(2) were determined and compared with models from DFT calculations. The stabilities of the frameworks in an oxygen atmosphere as a reactive gas were examined by temperature-programmed oxidation (TPO). Solution impregnation of MFU-1 with a co-catalyst (N-hydroxyphthalimide) led to NHPI@MFU-1, which oxidised a range of organic substrates under ambient conditions by employing molecular oxygen from air. The catalytic reaction involved a biomimetic reaction cascade based on free radicals. The concept of an entatic state of the cobalt centres is proposed and its relevance for sustained catalytic activity is briefly discussed.

The Role of Reactive Reaction Intermediates in Two‐Step Heterogeneous Electrocatalytic Reactions: A Model Study

AbstractThis paper summarises the result of previous experimental investigations of heterogeneous electrocatalytic reactions performed in flow cells which provide an environment with controlled parameters. Measurements of the oxygen reduction reaction in a flow cell with an electrode consisting of an array of Pt nanodisks on a glassy carbon substrate exhibited a decreasing fraction of the intermediate H2O2 in the overall reaction products with increasing density of the nanodisks. A similar result is true for the dependence on the catalyst loading in the case of a supported Pt/C catalyst thin‐film electrode, where the fraction of the intermediate decreases with increasing catalyst loading. Similar effects have been detected for the methanol oxidation.In order to give a possible explanation to the observed effect, we present a model of multistep heterogeneous electrocatalytic oxidation and reduction reactions based on an adsorption‐reaction‐desorption scheme using the Langmuir assumption and macroscopic transport equations. A continuum based model problem in a vertical cross‐section of a rectangular flow cell is proposed in order to explain basic principles of the experimental situation. It includes three model species A, B, C, which undergo adsorption and desorption at a catalyst surface, as well as adsorbate reactions from A to B to C. These surface reactions are coupled with diffusion and advection in the Hagen Poiseuille flow in the flow chamber of the cell. High velocity asymptotic theory and a finite volume numerical method are used to obtain approximate solutions to the model. Both approaches show a behaviour similar to the experimentally observed. Working in more general situations, the finite volume scheme was applied to a catalyst layer consisting of a number of small catalytically active areas corresponding to nanodisks. Good qualitative agreement with the experimental findings is established for this case as well.

Geometric and electronic approaches to size effects in heterogeneous catalysis

The influence of electronic and geometric factors is considered in the context of the manifestation of size effects in heterogeneous catalytic oxidation and hydrogenation reactions. Both of the factors are interdependent; however, the electronic factor predominates with regard to small metal and metal oxide particles (smaller than 10 nm), for which the energies of electron transitions in an activated complex are size-dependent. Only the geometry of active component nanoparticles exerts the main effect on the catalytic properties of coarser particles. In this case, the geometric factor depends on the accessibility of the active surface to reactants. The probability of the occurrence of complex active centers including several surface atoms increases as the active component particles of a catalyst become larger. The efficiency of the approach proposed to study the activating effect of nanophase catalysts is demonstrated using the oxidation and hydrogenation reactions of carbon oxides and the hydrogenation of acetonitrile and acetone as examples.

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.

Characterization of Fine Nickel-Coated Powder as Potential Fuel Additive

M ETAL fuel additives to propellants, explosives, and pyrotechnic compositions help increase the energy density of respective formulations [1–3]. Among various metal additives, aluminum is used most widely due to its high combustion enthalpy and low cost [1,4]. Aluminum particles are coated with a thin protective oxide layer, so that the heterogeneous oxidation reaction leading to aluminum ignition is rate controlled by a relatively slow diffusion of aluminum and oxygen ions through this layer [5–8]. Respectively, extended ignition delays often present a bottleneck for the overall combustion rate of aluminum powders. In addition, the agglomeration of aluminum particles before ignition, in particular occurring in solid propellant formulations, results in further ignition delays and the incomplete combustion of metal particles [9,10]. One approach proposed to reduce ignition delays and increase the burn rate of aluminum powders is based on using nickel surface coatings [11–21]. Such coatings are produced using one of several chemical methods, including an electroless nickel plate solution for treating aluminum powder [22], using aluminum to reduce metals from solutions of its salts [23], and using a modified polyol process [24]. Limited information is currently available about the ignition and combustion processes for such nickel-coated aluminum powders. For example, it was reported that nickel-coated aluminum powders could be ignited on the surface of an electrically heated nickel– chromium filament whereas similar powders without such coating did not ignite [21]. Coated powders also exhibited a reduced ignition temperature compared to uncoated aluminum [21]. Burn rates for individual particles were reported to be unaffected by the Ni coating [21]; however, the bulk burn rates of the coated powders were reported to be greater than that of uncoated aluminum [18]. It was reported that Al–Ni intermetallic reaction is capable of supporting a flame in a cloud of coated Al–Ni powders aerosolized in inert gas [13]. Experiments with Ni-coated particles with sizes ranging from 32 m to 1 mm levitated in various oxidizing environments and ignited with a laser beam were reported in [14–16]. Those experiments established that, for Ni-coated particles with thick coatings ( 50 wt% of Ni), ignition is defined by reactions in the Ni–Al system and does not depend on the presence of an external oxidizer. A similar conclusion was made for large, 2.5 mm particles with Ni coatings comprising 29 and 58 wt% ignited under normal and microgravity conditions [19]. Forfiner particles and thinner coatings, the Ni–Al reaction was considered a critically important exothermic process assisting ignition; however, the role of selective oxidation of nickel or the effect of nickel on the oxidation of aluminum were not considered. Micron-sized particles with small bulk concentrations of Ni are expected to be used in practical energetic formulations, in which it is desirable to maximize the overall energy density of the fuel additives. Thus, heat release due to the intermetallic Al–Ni reaction may become comparable to or even smaller than the heat released due to the heterogeneous oxidation of aluminum. The rate of oxidation itself can be affected by the presence of the Ni coating instead of, or in addition to, the natural amorphous aluminum oxide coating present on surface of pure Al powders. The objective of the present study is to characterize heterogeneous reactions leading to ignition in fine Ni-coated aluminum powders. It is further desired to assess whether the presence of relatively small amounts of Ni affect ensuing particle combustion.

Using time-resolved methods to monitor and understand catalytic oxidation reactions

A number of strategies for time-resolved analysis of heterogeneous oxidation reactions are being explored. They comprise the temporal analysis of products (TAP) reactor including micro-kinetic evaluation of TAP experiments, steady-state isotopic transient kinetic analysis, and time-resolved catalyst characterization by in-situ spectroscopic techniques. The present review demonstrates the potential of these methods for elucidating mechanistic and kinetic aspects of oxidative functionalization of C 2–C 3 hydrocarbons, water–gas shift reaction, direct N 2O decomposition, and high-temperature ammonia oxidation to nitric oxide (Ostwald process). Particular emphasis will be put on the application of isotopic labels and time-resolved analysis of gas-phase and surface species for identifying true surface intermediate species. Perspectives in further developments of time-resolved methods will be also indicated.

Sorption of mercury by activated carbon in the presence of flue gas components

The purpose of the current study is to evaluate the mercury removal ability of F400 and Norit FGD activated carbons, through fixed bed adsorption tests at inert atmosphere (Hg° + N 2). Additionally, adsorption tests were realized on F400 activated carbon, in the presence of HCl, O 2, SO 2 and CO 2 in nitrogen flow. The obtained results, revealed that F400 activated carbon, with a high-developed micropore structure and increased BET area, exhibit larger Hg° adsorptive capacity compared to Norit. HCl and O 2, can strongly affect mercury adsorption, owing to heterogeneous oxidation and chemisorption reactions, which is in accordance with the assumptions of some researchers. Additionally, SO 2 presence enhances mercury adsorption, in contrast with the conclusions evaluated in other studies. The above result could be attributed to the possible formation of sulphur spaces on activated carbon surface and consist of a clarification for the role of SO 2 on mercury adsorption. On the contrary, the mercury adsorption efficiency of F400 activated carbon showed a decrease at about 25%, with increasing CO 2 concentration from 0 to 12%.