Complete Oxidation Of CO Research Articles

Single- and double-stage catalytic preferential CO oxidation in H 2-rich stream over an α-Fe 2O 3-promoted CuO–CeO 2 catalyst

Single- and double-stage catalytic preferential CO oxidation (CO-PrOx) over-Fe 2O 3-promoted CuO–CeO 2 in a H 2-rich stream has been investigated in this work. The catalyst was prepared by the urea-nitrate combustion method and was characterized by X-ray diffractometer (XRD), X-ray fluorescence (XRF), Brunauer–Emmet–Teller (BET), transmission electron microscope (TEM), and scanning electron microscope (SEM). The catalytic activity tests were carried out in the temperature range of 50–225 °C under atmospheric pressure. The results of the single-stage reaction indicated that complete CO oxidation was obtained when operating at a O 2/CO ratio of 1.5, W/ F ratio of 0.36 g s/cm 3, and at a reaction temperature of 175 °C. At these conditions, H 2 consumption in the oxidation was estimated at 58.4%. Applying the same conditions to the double-stage reaction, complete CO oxidation was found and H 2 consumption in the oxidation was reduced about 4.9%. When decreasing the double-stage reaction temperature to 150 °C, the results elucidated that CO could be converted to CO 2 completely while H 2 consumption in the oxidation was further reduced to 33.5%. A temperature blocking 2 2 factorial design has been used to describe the importance of the factors influencing the catalytic activity. The factorial design was according to the experimental results. When adding CO 2 and H 2O in feed, reduction of CO conversion for single- and double-stage reaction is obtained due to a blocking of CO 2 and H 2O at a catalytic active site. Comparing CO conversion obtained when operating with/without CO 2 and H 2O in feed for single- and double-stage reaction, less reduction is achieved when operating in double-stage reaction.

Selective CO oxidation with nano gold particles-based catalysts over Al2O3 and ZrO2

We present the preparation, characterization and catalytic evaluation of gold-based catalysts over Al2O3, ZrO2 and 10% ZrO2/Al2O3 in selective CO oxidation. Oxidation and reduction pretreatments were evaluated using in situ X-ray diffraction, and the size of gold particles was determined. All catalysts contained gold particles in the range of 2–5 nm, with as-prepared samples containing a mixture of gold species (Au3+ and Au0). The catalytic tests showed complete CO oxidation at temperatures lower than 100 °C, with Au/ZrO2 sample presenting the best performance. Both the support and pretreatment conditions were found to cause changes to gold species. In situ X-ray diffraction patterns indicated the presence of different gold phases and of nanometer-scale crystallites of gold, which was confirmed by transmission electron microscopy results. It was also found that cationic gold improved the activity of Au/ZrO2. Concerning stability, time on stream tests showed that all samples were stable to coke deposition and sintering.

CO Adsorption and Oxidation on Ceria Surfaces from DFT+U Calculations

The limiting steps of CO oxidation catalyzed by ceria via the Mars−van Krevelen reaction mechanism are identified and investigated by means of density functional theory calculations that account for the on-site Coulomb interaction via a Hubbard term (DFT+U). We address the adsorption of CO on the (111) and (110) surfaces, and its oxidation via participation of lattice oxygen leading to vacancy formation and CO2 desorption. CO physisorbs on the (111) ceria surface (Ebind 2 eV) yielding carbonate formation and surface reduction. The DFT+U energy of CO adsorption and oxidation is studied as a function of the parameter U. This analysis demonstrates that the values of U presently used in the literature (U > 4 eV) tend to overestimate the binding energy of CO to ceria surfaces. In contrast, the energy for the complete CO oxidation reaction is effectively independent of U and in good agreement with the available experimental data. The discuss...

Complete Oxidation of Harmful Organic Compounds Over Alumina Supported Cu-Mn Mixed Oxide Catalysts

The catalytic activity of mixed alumina-supported copper-manganese oxides during complete oxidation of CO, ethylacetate, toluene and benzene is investigated. The samples were prepared by impregnation of g-Al2O3 with aqueous solutions of copper and manganese formates at room temperature and subsequent calcination at 670 K .All samples have been obtained using a fixed ratio between the two components in the impregnating solutions. The use of formates as precursors permits formation of mixed formates and their decomposition without preliminary melting thus resulting in the formations of oxide phases of high dispersity. The content of supported active metals was determined by chemical analysis. The specific surface area of the samples was measured using BET method and the magnetic susceptibility depending on temperature was investigated by the Faraday method at temperatures up to 620 K. The catalytic activity of the catalysts was measured in flow reactor.

MnOx modified Co3O4-CeO2 catalysts for the preferential oxidation of CO in H2-rich gases

In this work, MnOx modified Co3O4-CeO2 catalysts were prepared and used for preferential oxidation of CO in hydrogen-rich gases. The catalytic performance tests results showed that the catalyst with Co:Ce:Mn molar ratio of 8:1:1 exhibited the best low-temperature CO oxidation activity and higher selectivity for CO-PROX reaction among tested catalysts. 100% CO conversion could be obtained over this catalyst at 80–180°C with the feeding gas of 1vol.% CO, 1vol.% O2, 50vol.% H2 and N2 balance under the space velocity of 40,000 ml h−1 gcat−1. Adding CO2 and/or water was unfavorable for CO removal, even so complete oxidation of CO was still achieved over this catalyst with the reaction stream of 20vol.% CO2, 10vol.% H2O, 1vol.% CO, 1vol.% O2, 50vol.% H2 and N2 balance under high space velocity of 80,000 ml h−1 gcat−1 at reaction temperature range of 160–180°C. The catalysts were characterized by XRD, TEM, EDX, TPR and XPS techniques and the results showed that adding MnOx into Co3O4-CeO2 led to more uniform mixing of Co3O4 and CeO2 particles and led to finely dispersed and high valence state cobalt oxides species, which contributed to high catalytic activity of Co-Ce-Mn mixed oxides catalysts.

Catalytic behavior of hydrothermally synthesized La 0.5Sr 0.5MnO 3 single-crystal cubes in the oxidation of CO and CH 4

La 0.5Sr 0.5MnO 3 single-crystal cubes and nanoparticles were synthesized by hydrothermal and citrate routes, respectively. Their catalytic properties for low-temperature CO oxidation and high-temperature CH 4 combustion were evaluated, and the effects of crystal structure and morphology on the catalytic properties of the catalysts were investigated. The activity (220 °C) of the complete oxidation of CO over the single cubes was lower than that (190 °C) over the nanoparticles. After running at 600 °C for 48 h under the reaction conditions, the surface area of the nanoparticles decreased significantly, but the cubes nearly maintained their surface area. For CH 4 combustion, the La 0.5Sr 0.5MnO 3 cubes showed a higher activity ( T 10 = 360 ° C , T 10 : the temperature at 10% conversion of CH 4) than the nanoparticles ( T 10 = 440 ° C ). The different activities were attributed to their different crystal structures and morphologies.

Growth of single phase tetragonal structure iron tantalum oxide thin films grown by sol–gel spin coating technique

For the first time, crack free, and dense tetragonalFe2Ta2O8 thin films have been prepared by sol-gel method using tantalum isopropoxide and iron oxalate. As the annealing temperature increased from 700 to 800 ◦C, we have observed the growth of rhombohedral phase of iron tantalum oxide along with Fe2Ta2O8 tetragonal phase. The complete and single phase of Fe2Ta2O8 tetragonal structure was formed on silicon (100) substrate at an annealing temperature of 900 ◦C for 5 h. Structural, morphological studies of these Fe2Ta2O8 thin films produced by sol-gel synthesis have been characterized by grazing incidence X-ray diffraction (GIXRD), and tapping mode atomic force microscopy. Iron based mixed-type oxides containing metals such as MTaO4 (M = W, Ti, Co, Cr) are well known as functional inorganic materials having a wide range of applications such as electrodes of solid oxide fuels (SOFCs) [1], metal-air barriers [2], gas sensors [3], and as high performance catalysts [4] for the complete oxidation of hydrocarbons or CO and NO2 reduction as well as magnetic oxides for recording medium. Many preparation processes with low cost and low processing temperatures, such as the malate route [5], citrate route [6], polymeric precursor route [7], propionic acid route [8] have been reported to synthesize nanocrystalline powders. These methods can easily synthesize fine powders: however, it is difficult to use them to prepare thin films, as most of these amorphous precursors used in the processes mainly consist of some organic compounds and metal nitrates which easily explode to form powders. So far, oxide thin films structure have only been prepared by dry processes such as sputtering [9] and laser ablation [10] and metal organic chemical vapor deposition [11] methods. The sol-gel technique has many advantages over other fabrication techniques, such as homogeneity, stoichiometry control, purity, ease of processing and controlling the composition and ability to coat large and complex area substrates [12]. The crystallization of sol-gel derived films has followed a development path that is similar to that which has been observed in simple metal oxides that were prepared using sol-gel technique [13]. In the present study, we have selected iron oxalate for iron source and tantalum isopropoxide for tantalum source as starting materials of a sol-gel process to synthesize iron tantalum oxide

Complete oxidation of methane and CO at low temperature over LaCoO 3 prepared by spray-freezing/freeze-drying method

Perovskite-type LaCoO 3 oxides were prepared by spray-freezing/freeze-drying method using citrate precursor. The calcination temperature for a single phase of LaCoO 3 could be lowered to 500 °C without formation of any other oxides and the product had the highest surface area of 23.7 m 2/g. Below 500 °C, this catalyst with the perovskite structure and the high surface area showed higher activity for complete oxidation of low concentration methane (2000 ppm) and CO (1%) compared to Pt/Al 2O 3 catalyst.

Ir-based additives for NO reduction and CO oxidation in the FCC regenerator: Evaluation, characterization and mechanistic studies

Ir-based additives, developed to reduce NO and CO emitted during the regeneration of spent fluid catalytic cracking (FCC) catalysts were characterized to correlate physicochemical properties with catalytic performance. Support, metal loading and the state of the metal significantly affected the catalytic performance. Increasing the Ir loading or using a Ce-promoted γ-alumina (CPBase) support results in the formation of larger Ir particles. Local reduction of iridium oxide surface in such particles leads to coexisting Ir and Ir2O phases being very beneficial for the catalytic activity.NO reduction and CO oxidation take place thermally at 700°C. Increasing the O2 concentration in the feed favors CO oxidation at the expense of NO reduction. With 500ppmIr/CPBase and 1000ppmIr/CPBase additives, complete NO reduction and CO oxidation is achieved in the presence of 40% excess oxygen. Higher oxygen excess, however, reduces or eliminates the NOx reduction activity of these materials. IR studies suggest that NO reduction by CO proceeds on Ir/alumina additives via the dissociative adsorption of NO, the formation of NCO species on Ir and their migration to the alumina support, where N2 and CO2 are formed. IR spectroscopy indicates that Ce modifies the Ir surface enhancing the CO oxidation and enabling NO reduction via the NO2 formation.

Thin films of cobalt oxides obtained by a reaction during vacuum deposition

The structure and the composition of thin films obtained by vacuum co-evaporation of Co and TeO2 are studied by scanning and transmission electron microscopy, X-ray photoelectron spectroscopy and energy dispersive spectroscopy. Carbon coated mica is used as a substrate. It is shown that during vacuum deposition a chemical reaction between both substances take place resulting in the formation of CoO and Te phases, amorphous or nanocrystalline depending on the atomic ratio RCo/Te. The reaction proceeds until the complete oxidation of Co to Co2+ in the films with RCo/Te<2 or until the complete reduction of TeO2 to elemental Te in the films with RCo/Te>2. Upon subsequent treatment at 400°C the reaction proceeds until complete consumption of excess TeO2 in the films with RCo/Te<2 or excess of Co in the films with RCo/Te>2 and the formation of nanocrystals of Co3O4, Co6Te5O16 and CoTe2. A partial evaporation of Te takes also place.

Efficient trapping of the intermediates in the photooxygenation of sulfides by aryl selenides and selenoxides

Aryl selenides and selenoxides trap efficiently the intermediates in the reaction of singlet oxygen with sulfides. In the co-photooxygenation of 1equiv of an aryl selenoxide with 1.3equiv of dimethyl sulfide, the aryl selenone is formed quantitatively. Aryl selenides require 4–5equiv of sulfide for their complete co-oxidation to selenones.

Thin films of cobalt oxides obtained by vacuum co-deposition of Co and TeO 2

The composition and structure of thin films obtained by vacuum co-deposition of Co and TeO 2 in an atomic ratio R Co/Te=1.5 are studied. It is shown that during the co-deposition a chemical reaction between both substances takes place resulting in the formation of amorphous CoO phase and elemental Te, very finely dispersed in the amorphous matrix. The reaction in as-deposited films proceeds until the complete oxidation of Co to Co 2+. It is found that the crystalline phases of CoO, Co 3O 4 and/or Te are formed upon thermal heating of the films above 300°C. In this case, the reaction proceeds until complete consumption of TeO 2 via the oxidation of Co 2+ to higher valence and the formation of mixed oxides.

Oxidation Activity and 18O-Isotope Exchange Behavior of Cu-Stabilized Cubic Zirconia

A series of Cu–ZrO2 samples with varying concentrations of Cu from 1 to 33 mol% have been prepared by sol–gel technique and calcined at 873 K. XRD characterization of the samples with a copper content of 2 to 20 mol% reveals the stabilization of zirconia into cubic (fluorite) phase. The Cu–ZrO2 samples with higher Cu content (>20 mol%) revealed the presence of bulk CuO. A linear decrease in lattice parameter with increase in Cu content up to 20 mol% indicates the possible incorporation of Cu2+ in the lattice position of Zr4+ ions. XPS data of these samples provide further evidence for the incorporation of Cu2+ ions in the ZrO2 lattice up to 5 mol%. At higher concentrations of Cu, about half of the input of Cu goes into the lattice and the remaining stays as extra lattice Cu, possibly on the surface or subsurface layer of ZrO2. The BET surface area of these samples was in the range of 2 to 8 m2 g−1. The activity of these samples in CH4 and CO oxidation was investigated by 18O-isotope exchange as well as by catalytic reaction studies in complete oxidation of CH4 and CO. The Cu–ZrO2 with 20 mol% Cu was found to be the most active sample in the series, which has the maximum amount of copper in the substitutional position. For comparison, yttrium-stabilized zirconia samples with and without Cu was also prepared following the same procedure. Yttrium-stabilized zirconia without Cu was almost inactive in complete methane oxidation, whereas Cu-containing sample was more active. This confirms that the presence of Cu species in substitutional positions along with oxygen vacancies in zirconia lattice are substantially responsible for the catalytic activity in CH4 and CO oxidation as well as in complete heterogeneous 18O exchange processes. The light-off temperature for 50% conversion of CH4 (T50) decreases with an increase in Cu content up to 20 mol% and matches well with the results of 18O exchange measurements. The shapes of the curves of T50 and Texchange follow a similar trend indicating that both CH4 oxidation and 18O exchange processes occur via a completely heterogeneous mechanism.

Growth of single phase tetragonal structure iron tantalum oxide thin films grown by sol-gel spin coating technique

For the first time, crack free, and dense tetragonalFe2Ta2O8 thin films have been prepared by sol-gel method using tantalum isopropoxide and iron oxalate. As the annealing temperature increased from 700 to 800 ◦C, we have observed the growth of rhombohedral phase of iron tantalum oxide along with Fe2Ta2O8 tetragonal phase. The complete and single phase of Fe2Ta2O8 tetragonal structure was formed on silicon (100) substrate at an annealing temperature of 900 ◦C for 5 h. Structural, morphological studies of these Fe2Ta2O8 thin films produced by sol-gel synthesis have been characterized by grazing incidence X-ray diffraction (GIXRD), and tapping mode atomic force microscopy. Iron based mixed-type oxides containing metals such as MTaO4 (M = W, Ti, Co, Cr) are well known as functional inorganic materials having a wide range of applications such as electrodes of solid oxide fuels (SOFCs) [1], metal-air barriers [2], gas sensors [3], and as high performance catalysts [4] for the complete oxidation of hydrocarbons or CO and NO2 reduction as well as magnetic oxides for recording medium. Many preparation processes with low cost and low processing temperatures, such as the malate route [5], citrate route [6], polymeric precursor route [7], propionic acid route [8] have been reported to synthesize nanocrystalline powders. These methods can easily synthesize fine powders: however, it is difficult to use them to prepare thin films, as most of these amorphous precursors used in the processes mainly consist of some organic compounds and metal nitrates which easily explode to form powders. So far, oxide thin films structure have only been prepared by dry processes such as sputtering [9] and laser ablation [10] and metal organic chemical vapor deposition [11] methods. The sol-gel technique has many advantages over other fabrication techniques, such as homogeneity, stoichiometry control, purity, ease of processing and controlling the composition and ability to coat large and complex area substrates [12]. The crystallization of sol-gel derived films has followed a development path that is similar to that which has been observed in simple metal oxides that were prepared using sol-gel technique [13]. In the present study, we have selected iron oxalate for iron source and tantalum isopropoxide for tantalum source as starting materials of a sol-gel process to synthesize iron tantalum oxide

Influence of the form of photodeposited platinum on titania upon its photocatalytic activity in CO and acetone oxidation

Specimens of titania with platinum in various oxidation states deposited by a photocatalytic method, as well as mixture of PtO 2 + TiO 2, and PtO 2 have been studied by means of XPS, TEM and UV-VIS diffuse reflectance spectroscopy. Activities of the specimens in thermal and photocatalytic complete oxidation of gaseous acetone and CO by atmospheric oxygen at 40°C have been evaluated using a flow-circulating reactor. Photocatalytic activity increases with lowering of Pt oxidation state. Possible reasons of this behavior are discussed.

Complete Oxidation of CO, Ethanol, and Ethyl Acetate over Copper Oxide Supported on Titania and Ceria Modified Titania

Titania and titania modified with 3 and 12 μmol Ce/m2surface area of the titania were prepared and were used as supports for copper oxide. Preparations with 3 and 12 μmol CuOx/m2surface area of the support were tested for the combustion of CO, ethyl acetate, and ethanol. The results show that the Ce-doped titania surface is good as support for CuOxand that the cerium not only enhances the activity of the copper species, but also stabilises the surface area of the TiO2support in the presence of copper oxide. Additions of Al, K, and La are also found to stabilise the TiO2support but, compared with Ce, these elements do not to the same extent enhance the activity of the copper species. Acetaldehyde is observed to be an intermediate in the combustion of both ethanol and ethyl acetate over Cu-Ce-Ti-O catalysts. Since acetaldehyde is more harmful than any of the reactants and also is photochemically active, it is in applications important to assure that the combustion is complete. Cu-Ce-Ti-O catalysts show good performance not only for feeds without water vapour, but also for humid feeds. Although the concentrations of intermediates are affected by the addition of water, there is little effect on the temperature required for obtaining complete conversion to carbon dioxide and water. Characterisation with XRD, FT-Raman, TPR, and XPS indicates that the dispersed copper species are in the form of patches or a bidimensional layer which interacts with the surface of the support. When the content of cerium and copper is low, other types of dispersed copper species are present, which possibly are monomers or dimers. The copper species are predominantly Cu2+species.

Studies on Indian Ocean Manganese Nodules: XI. Physicochemical Characterization and Catalytic Activity of Silver Oxide Mixed Manganese Nodules

The promoting effect of Ag2O on the physicochemical properties and catalytic activity of manganese nodules has been investigated. The surface area and surface oxygen increased with addition of Ag2O, reaching a maximum at 1 mol% of Ag, and then decreased with further addition of Ag2O. The catalytic activity of manganese nodules substantially increased with addition of Ag2O over a wide range (0.25–25 mol% Ag). Addition of only 0.25 mol% of Ag to the nodule decreased the temperature of complete CO oxidation from 350°C to as low as 100°C. This enhanced activity was explained by the concerted action of Ag and Mn, where CO was preferentially adsorbed on Ag2O and oxidized. The reduced Ag was then reoxidized rapidly by oxygen transferred from Mn. The promoting effect of Ag2O on H2O2decomposition and ketonization of acetic acid, however, was less pronounced.

An electrochemical quartz crystal microbalance investigation of the adsorption and oxidation of CO on a platinum electrode

The adsorption and electrocatalytic oxidation of carbon monoxide on platinum was studied in both acid and alkaline supporting electrolytes using an electrochemical quartz crystal microbalance. Depending on the pH of the medium, a significant influence of CO on the electrode mass was observed, particularly in the potential range preceding the complete oxidation of CO. In acid medium coupling with solvent molecules was also evidenced and was found to be potential dependent. Furthermore, the mass responses depended strongly on the way the adsorption of CO was realised. In addition, the effect of the bulk concentration of CO was investigated in the case of perchloric acid medium.

Improving the Selectivity of NH3TPD Measurements

Pt supported on ZSM-5 catalysts are important for the catalytic oxidation of CO and volatile organic compounds (VOCs) due to their extraordinary performance at low temperatures and economic purposes. However, achieving complete oxidation at low temperatures and stability under water vapor remains challenging. Herein, we report the synthesis of several loading of Pt on a ZSM-5 catalyst via a flame synthesis technique. The Pt/ZSM-5 exhibited good activity towards complete CO and C3H6 oxidation at low temperatures due to the interaction between the Pt and ZSM-5. The combined effect of the PtOx (Pt2++Pt4+) and lattice oxygen from Pt (OPtOx) as the active centers in Pt/ZSM-5 favors the complete oxidation with high reaction rates, TOFs, and low activation energies (Ea), which is well consistent with the increasing concentration of the (Pt2++Pt4+)/Pt0. Pt/ZSM-5 presents a long-time tolerance to water vapor deactivation even at temperatures below 80 °C. The distributed Pt favor the reaction occurring through the Langmuir-Hinshelwood (L-H) route. The excellent catalytic results indicate an attractive approach for designing supported Pt on ZSM-5 catalysts for automobiles and industry exhausts.

X-ray Absorption Spectroscopic Study of Brønsted, Lewis, and Redox Centers in Cobalt-Substituted Aluminum Phosphate Catalysts

The structure of acid sites in cobalt-substituted aluminophosphates (AlPOs) catalysts has been investigated, with EXAFS spectroscopy. Data obtained, using in situ methods, for the Co K-edge spectra of cobalt-substituted AlPO-5, AlPO-18, AlPO-36, and APSO-44 in as-prepared, calcined, and reduced states yield the local structure of the Co ions. Whereas the as-prepared materials clearly contain Co(II) ions in regular four-coordinated sites, complex behavior is exhibited by their calcined analogues, with essentially complete oxidation of Co(II) to Co(III) in CoAlPO-18, with the local coordination of the high-spin Co(III) being distorted. By contrast incomplete oxidation of the Co(II) is observed for CoAlPO-5 and CoAlPO-36. A combination of EXAFS data analysis with the results of computer modeling studies suggests that this behavior is interpretable in terms of the formation of oxygen vacancies by dehydroxylation which lead to undercoordinated Lewis acid, Co(II) sites. IR data of the reduced samples reveal the...