The non-isothermal kinetics of zinc ferrite reduction with carbon monoxide

Journal of Thermal Analysis and Calorimetry - This study aims to reduce zinc ferrite using carbon monoxide in the temperature range of 25–1000 °C using temperature-programmed...     

The isothermal kinetics of zinc ferrite reduction with carbon monoxide

Journal of Thermal Analysis and Calorimetry - The reduction kinetics of zinc ferrite in CO was investigated under isothermal conditions at different CO concentration and roasting temperature with...     

Physicochemical properties of manganese-containing oxides with a spinel structure prepared with the use of ammonium nitrate and their catalytic activity in carbon monoxide oxidation

Oxide catalysts with the spinel structure with the molar ratios between components Co/Mn = 1: 2, Cu/Mn = 1: 2, and Cu/Co/Mn = 2: 2: 3 (samples I–III, respectively) have been prepared by the decomposition of metal nitrate hydrate solutions in an ammonium nitrate melt. Sample IV with the ratio Cu/Co/Mn = 2: 2: 3 containing 80% γ-Al₂O₃ is obtained by the addition of γ-Al₂O₃ powder to the initial melt. The catalysts are characterized using X-ray diffraction analysis, electron microscopy, and local X-ray analysis. Catalytic activity in the reaction of CO oxidation increased in the order I < II < III < IV. The proposed method is simple, and the synthesis is rapid. Oxides with the spinel structure homogeneous in composition and morphology without any impurities can be prepared by this method. These oxides exhibited high catalytic activity in the reaction of carbon monoxide oxidation.     

The mercury-sensitized oxidation of carbon monoxide

The mercury-photosensitized oxidation of CO was studied at 275°C over a wide range of [O₂]/[CO] ratios in the absence and presence of the oxygen atom scavenger 2-trifluoromethylpropene (TMP) and at 25°C at low [O₂]/[CO] ratios in the presence of TMP. By following the quantum yield of CO₂ production, Φ {CO₂}, as a function of the [O₂]/[CO] ratio, the reactions of vibrationally excited CO (v υ 9) and electronically excited O₂, probably in the c¹Σ^?_u state, were studied. At low [O₂]/[CO] ratios the predominant reactions are of vibrationally excited CO (v υ 9). Relative rate constants for chemical reaction versus deactivation of CO (v υ 9) were obtained. At higher [O₂]/[CO] ratios, the principal reactions are of electronically excited O₂. Relative rate constants for chemical reactions and deactivation of this electronically excited O₂ with CO, O₂, and TMP were obtained. From the effect of total pressure on Φ {CO₂}, it is proposed that an intermediate CO₃ is formed in the reaction of electronically excited O₂ with CO.     

Catalytic oxidation of carbon monoxide by oxygen and nitrogen oxides on a copper-chromium oxide catalyst

The kinetics of CO oxidation by O₂, NO and NO₂ has been studied on a Cu–Cr-oxide catalyst. A comparison with the kinetics of the CO–N₂O interaction has been made. In all cases the reaction rate is described by the equation:r=k p _CO ¹ P _0x ⁰ . The oxidation of CO has been studied in the presence of different oxidants in the reaction mixture.

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CO , . CO . CO . CO .

     

The oxidation of carbon monoxide on iron oxide

The oxidation of CO on α-Fe₂O₃ was studied in a flow reactor. The conversion was complete at 650–660 K. The catalytic activity of iron oxide was higher than that of the ferrite-containing xMgOyFe₂O₃ catalyst. The adsorption of CO on iron oxide and the kinetics of interaction of carbon monoxide with oxygen atomically adsorbed on the surface of α-Fe₂O₃ were studied. The kinetic parameters of the oxidation of CO are evidence of the participation of adsorbed oxygen atoms, whose binding energy on the surface of α-Fe₂O₃ is lower than that on the surface of the magnesium ferrite-containing catalyst.     

Copolymerization of carbon monoxide and norbornadiene with a palladium catalyst

Carbon monoxide (CO) and norbornadiene (NBD) with Pd(CH₃CN)₄(BF₄)₂ were copolymerized under various conditions at 50°C. Elemental analysis, infrared spectra, UV, Raman, and NMR spectra showed that the copolymers contained both ketone and unsaturated ring structures. Bidentate nitrogen ligands and phosphorus ligands proved to be more effective at stabilizing catalytic activity than monodentate arsenic ligands or phosphorus ligands. Methanol, protic acid, and an oxidant served as the coinitiator and chain transfer agent, respectively. X-ray diffraction analysis showed the copolymer to be partially crystalline. Thermogravimetric analysis showed that the TG curve for the NBD/CO copolymer has two stages with two maxima peaks at 251 and 470°C. This phenomenon was probably due to increased instability of the copolymers as CO content is increased. Hydrogenation of norbornadiene/CO copolymer with LiAlH₄ and Pd/C in THF yields a hydroxyl-containing polymer and norbornene/CO copolymer, respectively. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 1157–1166, 1997     

Alternating copolymerization of ethylene with carbon monoxide on a supported palladium catalyst

The kinetics of the alternating copolymerization of ethylene with carbon monoxide has been studied in the presence of a palladium catalyst immolized on a polymer support in various media (methanol, toluene, heptane). In the case of hydrocarbon solvents, the activity of the supported catalyst is commensurable with the activity of a homogeneous system in methanol. The melting temperature of the resulting copolymer and its molecular mass depend on the solvent nature. The IR reflectance spectra of the active palladium complex and the ethylene-carbon monoxide copolymer are measured.     

Platinum and molybdenum oxide deposited carbon electrocatalyst for oxidation of hydrogen containing carbon monoxide

Carbon-supported Pt/MoO_x catalysts for use in PEFC anodes were prepared and their catalytic activity for the oxidation of CO-contaminated H₂ was examined based on the fuel cell performance in PEFC single cell arrangements. Based on the XRD pattern and XPS measurements of the prepared Pt/MoO_x/C catalysts, it was found that the deposited MoO_x exists as an amorphous oxide phase. The MoO_x phase shows a redox peak at around 0.45 V, which was revealed by the cyclic voltammogram of the Pt/MoO_x/C in sulfuric acid solution. The PEFC performance of the cell with Pt/MoO_x/C was improved under 100 ppm CO-contaminated H₂ conditions compared to the Pt/C catalyst, and was almost comparable to the PtRu(1:1)/C catalyst.     

Copolymerization of carbon monoxide and 4-vinylcyclohexene with a palladium catalyst

In this work, carbon monoxide (CO) and 4-vinylcyclohexene (VCH) with [Pd(CH₃CN)₄](BF₄)₂ were copolymerized under various conditions at 60°C. Elemental analysis and infrared, UV, and NMR spectra indicated that copolymers containing a ketone and a cyclic structure of cyclohexyl and norbornane groups are produced. Bidentate nitrogen ligands proved to be more effective at stabilizing catalytic activity than monodentate phosphorus or nitrogen ligands. Also, the bulk substituent on the bidentate ligand led to inactive catalysts. Methanol served as the coinitiator and chain transfer agent. Increasing the concentration of 4-vinylcyclohexene caused the copolymer's CO content to be enhanced. TGA revealed that the copolymer's mass loss starts at 120°C and the maximum peak of decomposition occurs at 450°C. Moreover, X-ray diffraction analysis demonstrated the copolymer to be partially crystalline. Furthermore, reduction of 4-vinylcyclohexene/CO copolymer with LiAlH₄ in THF yields a hydroxyl-containing polymer. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2759–2768, 1997     

Influence of MgO contents on silica supported nano-size gold catalyst for carbon monoxide total oxidation

A series of nano-size gold catalysts were prepared by deposition-precipitation method using silica material promoted with different amounts of MgO as the carrier. The influences of MgO addition on the structure and property of the nano-size gold catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), O2 temperature-programmed desorption (O2-TPD), and inductively coupled with plasma atomic emission spectroscopy (ICP-AES) techniques. The total oxidation of CO was chosen as the probe reaction. The results suggest that for the gold catalysts supported on the silica material after MgO modification, the size of the gold particles is pronouncedly reduced, the oxygen mobility is enhanced, and the catalytic activity for low-temperature CO oxidation is greatly improved. The gold catalyst modified by 6 wt% MgO (Mg/SiO2 weight ratio) shows higher CO oxidation activity, over which the temperature of CO total oxidation is lower about 150 K than that over the silica directly supported gold catalyst.     

Preparation of Mg/Fe spinel ferrite nanoparticles from Mg/Fe-LDH microcrystallites under mild conditions

Mg/Fe spinel ferrite nanoparticles were prepared by aging Mg²⁺/Fe²⁺/Fe³⁺-LDH (layered double hydroxides) suspension at temperature below 100 °C. The yield of Mg/Fe spinel ferrite nanoparticles was dependent on the aging temperature and the molar ratio of ferrous ions in the LDH precursors. It was found that the majority of iron atoms was assembled into the lattice of spinel ferrite when the LDH precursors were aged at 95 °C for 18 h, and the formation of Mg/Fe spinel ferrite was favored with a higher molar ratio of ferrous ion in the LDH precursors. To the best knowledge of us, it is the first report on preparation of spinel ferrite under such a mild condition of below 100 °C from Mg²⁺/Fe²⁺/Fe³⁺-LDH microcrystallites.     

Chemisorption and oxidation of carbon monoxide on palladium alloys

Kinetic and adsorption data (programmed thermal desorption in situ) for the oxidation of carbon monoxide on palladium alloys with silver and gold have been discussed. It has been shown that the local reaction plays a determining role and that active cluster sites are best for catalysis which are monoatomic with respect to palladium, weakly binding the chemisorbed CO molecule. The role of silver is to activate the second component: oxygen. The cluster model makes it possible to predict the optimum composition of Pd-Ag catalysts for the oxidation of CO and to explain the dependence of Pd-Au activity on the composition.Kiev University. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 5, pg. 574–578 September–October, 1991. Original article submitted July 12, 1991.     

Preferential oxidation of carbon monoxide on supported gold catalysts

Catalyst precursors containing 1% Au were synthesized by the impregnation of Al₂O₃ and CeO₂-Al₂O₃ supports with an aqueous solution of HAuCl₄ followed by drying, treatment with aqueous ammonia for the removal of chlorine residues, and final drying at 90°C. The oxidation of CO in gas containing ～1 vol % O₂, ～1 vol % CO, 60 vol % H₂, and the balance N₂ on the activated catalysts was studied. In a number of experiments, to 18 vol % water was added to the gas mixture. The activation of precursors by the initial gas was studied. It was found that the prolonged storage of a precursor in air made its activation difficult to perform. The 1%Au/Al₂O₃ catalyst activated by the gas mixture stably operated in the preferential oxidation of CO at room temperature with the occurrence of the reaction in the mode of catalyst surface ignition (a hot spot at the bed inlet) under a change in the feed gas flow rate by a factor of 3. The effect of the presence of additional CO₂ (to 39 vol %) on the oxidation of H₂ was studied: the catalyst activity decreased. Because the reaction of CO₂ reduction to CO did not occur, the effect can be due to the adsorption of CO₂ on gold. The effect of the addition of water vapor to the feed gas was studied with the use of 1%Au/CeO₂-Al₂O₃ as an example. The exo/endo effects related to the adsorption/desorption of water on the catalyst surface were detected upon steam supply and shutoff at a bed temperature of 100–150°C. It was noted that the addition of water vapor to a certain level favorably affected the selectivity (decreased the residual concentration of CO). The boundary water concentration, at which the effect became negative, depended on catalyst bed temperature. The higher was the bed temperature, the greater amount of water could be added until the manifestation of a negative effect.     

Studies of carbon monoxide oxidation on carbon-supported platinum-osmium electrocatalysts

The electrocatalytic oxidation of hydrogen in the presence of carbon monoxide was studied on PtOs/C electrocatalysts prepared by the formic acid method and heat-treated under several temperatures and atmospheres. The physical properties of the metallic phase were evaluated by X-ray diffraction (XRD), energy dispersive X-ray (EDX) analysis, and in situ X-ray absorption spectroscopy (XAS). The electrochemical performance of these materials was evaluated by single-cell polarization measurements, cyclic voltammetry, and linear sweep CO stripping voltammetry. The results have shown an enhancement of the CO oxidation process for the as-prepared PtOs/C and for a material heat-treated in a reducing atmosphere (hydrogen at 500 °C), compared to Pt/C. The electrochemical data also showed that the as-prepared and hydrogen-treated PtOs/C catalysts present CO tolerance higher than Pt/C. This has been associated with the occurrence of a surface reaction of CO adsorbed on Pt and oxygenated Os sites, favored by an intimate physical contact between segregated Os and Pt phases.Dedicated to Prof. Wolf Vielstich on the occasion of his 80th birthday in recognition of his numerous contributions to interfacial electrochemistry     

The structure of a carbon monoxide adduct of zeolite 5A

The structure of Ca₅Na₂-A:5CO has been determined at room temperature using Rietveld profile refinement in space groupFm3c witha refined to 24.6558(2)A˚. The finalR_pw was 3.5%. As in the case of dehydrated zeolite 5A, the exchangeable cations are located in S1 (6-ring) sites, with Ca-O and Na-O distances of 2.32 and 2.37A˚. The carbon atoms of the carbon monoxide molecules have been located on the three-fold axis in the α-cage in a position analogous to that found in the CO complex of cobalt-exchanged zeolite A. However, the oxygen atoms are either undergoing considerable thermal motion or are disordered over several off-axis locations. The Ca-C distance is 2.83A˚. Inside the β-cage, with site occupancy approximately three-fourths, there are AlO₄H₃ tetrahedral species evenly distributed between two orientations, as has been found previously in studies of divalent exchanged samples of zeolite A. This aluminum complex bonds to the framework via Al-O-H … O(3) hydrogen bonds and there is coordination of the non-hydrogen-bearing oxygen atom to exchangeable calcium ions (Al-O … Ca).