Catalytic Decomposition Of CO Research Articles

Reduction effect of α-Fe2O3 on carbon deposition and CO oxidation during chemical-looping combustion

First-principle calculations based on density functional theory (DFT) were performed to investigate the reactions between CO and the perfect and reduced Fe2O3[001] and Fe2O3[100] surfaces during chemical-looping combustion (CLC), which includes the detailed adsorption, oxidation and catalytic decomposition of CO on these surfaces. CO can chemically adsorb on all surfaces, showing a monotone increasing functional relationship between Eads and the reduction degree, which suggests that reduction of Fe2O3 favors the CO adsorption step. Potential energy profiles for CO oxidation and decomposition indicate that partial reduction of Fe2O3 into FeO rather than further reduction to Fe is more efficient for CO oxidation. After reduction of Fe2O3[001] into period around Fe2O2 and Fe2O, the reduced surface exhibits excellent catalytic activity for CO decomposition, which may lead to obvious carbon deposition and decrease CLC efficiency. By contrast, the occurrence of CO decomposition on [100] facets is more difficult. Molecular-level calculations demonstrate that rationally controlling the reduction degree and crystal surface of iron oxide OC can optimize CLC performance.

Density Functional Theory Study of Elemental Mercury Adsorption on Fe2O3[104] and Its Effect on Carbon Deposit during Chemical Looping Combustion

This study investigated the adsorption of elemental mercury (Hg0) on perfect and reduced Fe2O3[104] surfaces as well as analyzed the synergistic effect of Hg0 on the catalytic decomposition of CO on the reduced surfaces using density functional theory calculations. This study aimed to clarify the correlations among Hg0 adsorption, CO decomposition, and Fe2O3 reduction degree. Theoretical results indicated that Hg0 underwent Fe top site adsorption to Fe bridge site adsorption as Fe2O3 was reduced into iron. This phenomenon increased Eads with a local extreme of −2.063 eV for Hg0–Fe2O1.364. The adsorption of Hg0 decreased Eads for CO adsorption on the reduced Fe2O3 surfaces but promoted charge transfer from the surface to the adsorbed CO molecule. This event activated the C–O bond, favoring its decomposition. A kinetic model for catalytic CO decompositions with and without Hg0 further revealed the synergistic effect of Hg0 on carbon deposition and the relationship between the reaction rate and degree of che...

Synergetic Effect of Mercury Adsorption on the Catalytic Decomposition of CO over Perfect and Reduced Fe<sub>2</sub>O<sub>3</sub>[001] Surface

Synergetic Effect of Mercury Adsorption on the Catalytic Decomposition of CO over Perfect and Reduced Fe<sub>2</sub>O<sub>3</sub>[001] Surface

Fe particles on the tops of carbon nanofibers immobilized on structured carbon microfibers for ammonia decomposition

Fe particles on the tops of carbon nanofibers immobilized on structured carbon microfibers (Fe-CNFs/CMFs) were prepared in situ by the catalytic decomposition of CO over Fe/CMFs catalyst, and their particle sizes, shapes and crystal phases were adjusted by changing the growth time of CNFs and the partial pressure of hydrogen. The as-obtained Fe-CNFs/CMFs were used as a catalyst for ammonia decomposition, which showed higher activity when they were prepared with the longer growth time of CNFs and the higher partial pressure of hydrogen. Moreover, the behavior of the typical Fe-CNFs/CMFs catalyst was also investigated when changing the experimental conditions.

Effect of sulfur compounds on the decomposition of carbon monoxide on red mud

The utilizing of red mud via the carburization of its ferrous components by CO-containing gases of ferroalloy furnaces is investigated. As a result of our experiments, it is established that the red mud of alumina production and exhaust gases of ferroalloy furnaces are quite suitable for performing the decomposition reaction of carbon monoxide after the required preparation. It is found that the presence of hydrogen sulfide has a toxic effect on the catalytic abilities of iron oxides as catalysts of the thermal catalytic decomposition of CO. The mechanism behind the effect of sodium aluminum silicate hydrates entering the red mud on the degree to which sulfur compounds are removed from the ferroalloy gas is revealed. It is established that purification of the ferroalloy gas allows us to increase the carbon content in the final product by a factor of 5–10.

Synthesis of carbon nanofibers/mica hybrids for antistatic coatings

The use of carbon nanofibers (CNFs) as polymer additive has been impeded due to the problem associated with the dispersion of CNFs. In this study, CNFs/mica hybrids were synthesized by catalytic decomposition of CO over mica supported iron catalysts to increase their dispersity in polymer matrix. Antistatic coatings were prepared by dispersing the as-synthesized hybrids into epoxy with low shearing agitation and then casting the mixture by a coater. With the help of mica, the CNFs could be easily dispersed into the resin uniformly. The morphology of the CNFs, their distributions on mica surface and the size of mica, are discriminated to have great effect on surface resistivity of the coating.

Laser Directed Growth of Carbon-Based Nanostructures by Plasmon Resonant Chemical Vapor Deposition

We exploit the strong plasmon resonance of gold nanoparticles in the catalytic decomposition of CO to grow various forms of carbonaceous materials. Irradiating gold nanoparticles in a CO environment at their plasmon resonant frequency generates high temperatures and strong electric fields required to break the CO bond. By varying the laser power, exposure time, and gas flow rate, we deposit amorphous carbon, graphitic carbon, and carbon nanotubes. The formation of iron oxide nanocrystals catalyzes the growth of carbon nanotubes. Predefined microstructure geometries are patterned by moving the focused laser spot during the growth process, forming suspended single-walled carbon nanotube structures. Raman spectroscopy, energy dispersive X-ray spectroscopy, and transmission electron microscopy are used to characterize the resulting material. The localized nature of the plasmonic heating enables growth of these materials, while the underlying substrate remains at room temperature.

Efficient Catalytic Decomposition of CO2 to CO and O2 over Pd/Mixed-Conducting Oxide Catalyst in an Oxygen-Permeable Membrane Reactor

The thermal decomposition of CO2 to CO and O2 is a potential route for the consumption and utilization of CO2. However, this reaction is limited by both the thermodynamic equilibrium and the kinetic barrier. In this study, we reported an innovative catalytic process to decompose CO2 in an oxygen-permeation membrane reactor packed with a mixed-conducting oxide supported noble metal catalyst, or Pd/SrCo0.4Fe0.5Zr0.1O3-delta (Pd/ SCFZ), which is of high activity in the decomposition of CO2 into CO and O2. Pd/SCFZ catalyst was prepared by incipient wetness impregnation of the SCFZ powders with an aqueous solution of PdCl2, and the CO2 sorption/desorption property was examined by in situ Fourier transform infrared spectroscopy and temperature-programmed desorption-mass spectrometry technologies. It was shown that there appeared a typical of bridged carbonyls (Pd-CO) on the surface of the Pd/SCFZ catalyst formed after CO2 decomposition. Both CO2 and CO could be detected in the species desorbed from Pd/SCFZ catalyst, which implied that the Pd/SCFZ catalyst could effectively activate the CO2 molecule. During the catalytic process, furthermore, the activity of the Pd/SCFZ catalyst can self-regenerate by removing the produced lattice oxygen through the dense oxygen-permeable ceramic membrane. At 900 degrees C, this catalytic process attains 100% of CO formation selectivity at 15.8% of CO2 conversions.

PdC formation in ultra-thin Pd membranes during separation of H 2/CO mixtures

The influence of typical syngas CO concentrations (20–33%) on the stability of 3 μm thick Pd membranes was investigated between 593 and 773 K in the limit of maximum H 2 extraction. Two kinds of CO inhibition effects were observed: CO adsorption and carbon deposition resulting from catalytic decomposition of CO on the Pd surface. CO adsorption reduced the H 2 permeation rate in particular below 623 K due to reversible blocking of Pd surface sites. Carbon deposition became more severe at higher temperatures and feed gas velocities and accumulated with time. In particular, the formation of a Pd 1− x C x phase was observed above 723 K with x = 0.1. The propensity to PdC formation increased with temperature and the CO concentration in the retentate. Although the carbon incorporated into the Pd membrane could be effectively removed by H 2 and O 2 at 723 K, an irreversible increase of the N 2 flux after the removal of the carbon was observed in particular after treatment with O 2.

Self-assembling carbon filament ropes formation

The process of carbon nanotubes and filaments production via catalytic decomposition of CO on SiO 2-modified Co catalyst was investigated. It was demonstrated that variation in carbon nucleation conditions could be used for the production of different type of carbon deposits over the same catalyst. Carbon nucleation conditions were altered by varying reaction temperature and/or catalyst pretreatment procedure. The formation of carbon filament ropes was observed for the first time.

Structural characterization and diameter-dependent oxidative stability of single wall carbon nanotubes synthesized by the catalytic decomposition of CO

Low T oxidation followed by brief sonication in hot HCl has been optimized to remove Fe catalyst residues from HiPco material with minimal loss of tubes. One pass reduces Fe from 6–10 to 0.6–1.6 at.% with 60% yield, most of the loss being Fe. Raman scattering reveals a broad diameter distribution with a mean of 1.0–1.1 nm. After purification we find excellent correlation between oxidation temperature and Raman spectra whereby the oxidation rate varies inversely with tube diameter. This can be explained by the larger strain associated with greater curvature of small tubes.

Electrochemical Tuning of Electronic Structure of Single-Walled Carbon Nanotubes: In-situ Raman and Vis-NIR Study

The population of valence-band electronic states of single-walled carbon nanotubes (SWCNTs) was tuned electrochemically in acetonitrile electrolyte solution. In dry and oxygen-free solution, the electrochemistry of SWCNTs is controlled by capacitive charging. Reversible changes of intensity and frequency of the Raman spectra can be monitored during cyclic voltammetry at low scan rates. Electrochemical charging of SWCNTs can be also traced via reversible bleaching of the electronic transitions in the vis-NIR region. An aprotic medium offers a broader electrochemical window for tuning of electronic properties of SWCNTs. Electrochemical charging of SWCNTs in an aprotic electrolyte solution allows easy and precise control of the electronic structure of SWCNTs. In addition to commercial SWCNTs, a material made from gas-phase catalytic decomposition of CO by the HiPco process was also studied. Selective quenching of vis-NIR and Raman spectra is a useful tool to the analysis of tubes of varying diameter and helicity.

Applications of Carbon Nanotubes and Nanofilaments as Electrodes of Electrochemical Supercapacitors, Effect of Chemical Oxidation

Carbon nanofilaments obtained by the catalytic decomposition of CO and carbon deposit containing large amount of SWNTs (Single-Walled Carbon Nanotubes) obtained by electric-arc discharge were used as electrodes of electrochemical capacitors with 6M KOH electrolyte. The specific capacitance was estimated by cyclic voltammetry measurements and impedance spectroscopy. Acidic oxidizing treatment of nanofilaments with concentrated HNO3, mixture of H2SO4/HNO3, and fuming HNO3 allow to increase ten times the specific capacitance to reach 80 F/g. This result is attributed to both textural and structural modifications by acid treatment and the development of oxygenated surface functional group enhancing the pseudocapacitance. The capacitive property of the electric-arc discharge carbon deposit (18 F/g) is attributed mainly to SWNTs bundles. Acid treatments enable to enhance slightly their specific capacitances (30 F/g).

Controlled production of single-wall carbon nanotubes by catalytic decomposition of CO on bimetallic Co–Mo catalysts

The term `controlled production' of single-wall nanotubes (SWNT) implies the ability to control the selectivity towards SWNT by changing catalyst formulations and operating conditions, combined with a quantitative measurement of the SWNT obtained. In this contribution, a significant advancement towards the controlled production of SWNT is reported. A family of Co–Mo catalysts has been found to be able to produce SWNT with high selectivity, depending on the Co:Mo ratio, the temperature of operation, and the processing time. The optimization of the catalyst was possible by the application of a simple and direct method of quantification of the SWNT production.

Hydrogen uptake by carbon nanotubes

Multi-wall carbon nanotubes were synthesised from the catalytic decomposition of CO and CH 4 on powder Co/La 2O 3 catalysts. TEM and HR-TEM, XRD, and TGA were used to characterise carbon nanotubes. It was found that by adjusting the composition of the catalysts, the size of the nanotubes was controllable and by annealing, the crystallinity could be improved. The carbon nanotubes produced from CO were found to be able to uptake a certain amount of hydrogen under ambient conditions, whereas graphite powders were unable, which suggests that the carbon nanotubes may be a promising material that can be used for hydrogen storage under ambient conditions.

Studies on catalytic decomposition of CO over transition metal ion (TMI) doped alumina-boria catalyst systems

ESCA and ESR studies on TMI incorporating alumina-boria catalyst systems for CO conversion show the presence of carbidic phase and no valence change of the incorporated copper in the spent catalyst.

Sorption of noble gases by solids, with reference to meteorites. III. Sulfides, spinels, and other substances; on the origin of planetary gases

To simulate trapping of noble gases by meteorites, we reacted 15 FeCr or FeCrNi alloy samples with CO, H 2O or H 2S at 350–720 K, in the presence of noble gases. The reaction products, including (Fe,Cr) 2O 3, FeCr 2S 4, FeS, C, and Fe 3C, were analyzed by mass spectrometry, usually after chemical separation by selective solvents. Three carbon samples were prepared by catalytic decomposition of CO or by dehydration of carbohydrates with H 2SO 4. The spinel and carbon samples were similar to those of earlier studies (Yang et al., 1982 and Yang and Anders, 1982), with only minor effects attributable to the presence of Ni. All samples sorted substantial amounts of noble gases, with distribution coefficients of 10 −1–10 −2 cm 3 STP/g atm for Xe. On the basis of release temperature three gas components were distinguished: a generally dominant physisorbed component (20–80% of total), and two more strongly bound, chemisorbed and trapped components. Judging from the elemental pattern, the adsorbed components were acquired at the highest noble gas partial pressure encountered by the sample—atmosphere or synthesis vessel. Sulfides, particularly daubréelite, showed three distinctive trends relative to chromite or magnetite: the high- T component was larger, 30–70% of the total; Ne Xe ratios were higher, by up to 10 2, possibly due to preferential diffusion of Ne during synthesis. In one synthesis, at relatively high P, the gases were sorbed with only minimal elemental fractionation, presumably by occlusion. Most of the features of primordial noble gases can be explained in terms of the data and concepts presented in the three papers of this series. The elemental fractionation pattern of Ar, Kr, Xe in meteorites, terrestrial rocks, and planets resembles the adsorption pattern on the solids studied: carbon, spinels, Sulfides, etc. The variation in Ne Ar ratio may be explained by preferential diffusion of Ne. The high release temperature of meteoritic noble gases may be explained by transformation of physisorbed to chemisorbed gas, as observed in some experiments. The ready loss of meteoritic heavy gases on surficial oxidation (“Phase Q”) is consistent with adsorption, as is the high abundance. Extrapolation of the limited laboratory data suggests that the observed amounts of noble gases could have been adsorbed from a solar gas at 160–170 K and 10 −6–10 −5 atm, i.e. in the early contraction stages of the solar nebula. The principal unsolved problem is the origin of isotopically anomalous, apparently mass-fractionated noble gases in the Earth's atmosphere and in meteoritic carbon and chromite.

Catalytic effect of iron on decomposition of carbon monoxide: II. Effect of additions of H2, H2O, CO2, SO2 and H2S

In this work the effect of additions of H2, H2O, CO2, SO2, and H2S on the catalytic decomposition of CO by iron has been investigated at 400, 600, and 800°C and atmospheric pressure. The catalyst was porous iron formed by the reduction of hematite ore granules with hydrogen. The relative importance of carbon deposition by the reactions 2CO → C + CO2 and H2 + CO → C + H2O was determined as a function of hydrogen concentration. It was found that even low concentrations of hydrogen greatly enhanced the rate of decomposition of CO, presumably by a catalytic action of adsorbed hydrogen on iron. The presence of water vapor had a dual effect. At low concentrations of hydrogen the rate of decomposition of CO increased with the addition of H2O, apparently by a catalytic effect. At high concentrations of hydrogen, however, carbon deposition was retarded because of the effect of the reverse reaction H2O + C → H2 + CO. In CO-CO2 mixtures the rate of carbon deposition decreased with increasing CO2 content, because of the effect of the reverse reaction CO2 + C → 2CO. The presence of traces of sulfur-bearing gaseous species, such as SO2 and H2S, retarded the decomposition of CO on iron and brought about the early cessation of carbon deposition. This strong effect may be due to the retardation of the decomposition of the intermediate product, cementite, and the formation of pyrrhotite on the surface of the iron catalyst.

Inhibition of carbon deposition on iron and steel surfaces

Experiments have been carried out on the feasibility of inhibiting the deposition of carbon which takes place by catalytic decomposition of CO on iron and steel surfaces. Two distinct classes of inhibitors have been investigated: firstly, compounds exerting an irreversible effect, such as SO 2 and various silanes; and secondly, inhibitors (H 2O, N 2O, NH 3, and CO 2) which are effective only as long as they are continuously added to the reaction mixture. It is shown that—with the exception of CO 2-all the inhibitors suppress the deposition of carbon on iron and steel surfaces completely if they are present in the reaction mixture in argon in a sufficient concentration. The inhibition effect decreases in the order SO 2 > silane > H 2 O > N 2 O > NH 3 > CO 2. Measurements of the retarding influence of H 2O as a function of H 2 H 2O ratio indicate that, in High Temperature Gas-Cooled Reactors where CO and H 2 are present in the helium coolant in low and approximately equal concentrations, the deposition of carbon can be prevented on heat exchanger surfaces during normal operation if the H 2 H 2O ratio is maintained between 15 and 20. High CO partial pressures and H 2 H 2O ratios may be tolerated temporarily if a silane inhibitor is added in small doses to the helium coolant.

Untersuchung Von Oberflächenreaktionen An Kupfer Mittels Beugung Langsamer Elektronen (LEED). II

The interaction of C 2H 4, CO, and H 2O with clean (110)-, (100)-, and (111)-surfaces of copper, the subsequent adsorption of oxygen on preadsorbed layers of another surface species, and the kinetics of some surface reactions has been studied by low energy electron diffraction. Adsorption of ethylene on the (110)-surface causes the appearance of half-order streaks, corresponding to the formation of a stable chain-like adsorption layer which is of onedimensional order. A structure model is proposed which is based on geometrical considerations. Additional oxygen partially displaces the ordered C 2H 4 and leads to the formation of a partly disordered adsorption layer and small O-covered domains. With the (100)-face diffuse spots of an unstable 2 × 2-structure are visible; on the (111)-face no adsorption occurs. Adsorption of water occurs on regular lattice points without formation of new extra spots. Interaction with carbon monoxide: On the (110)-face sometimes formation of weak streaks similar to the adsorption of C 2H 4 occurs, but normally with all planes no extra spots appear at low temperatures. At higher temperatures catalytic decomposition of CO and formation of carbon takes place. This causes the appearance of a 2 × 3-structure on the (110)-face. Additional oxygen adsorbs on separate non-covered surface regions. On the (100)-face upon interaction with CO at 500 °C formation of two structures, with 2 × 2- and a more complicated symmetry, occurs. On a surface covered with carbon in the 2 × 2- structure oxygen adsorption takes place only above 200°C with formation of an “alloy”- phase, which decomposes on annealing at 450°C into separate C- or O-covered domains. The carbon is completely oxidized at 500 °C. Kinetic studies: The intensity change of an extra spot with time and temperature is a measure of the velocity of a surface reaction. The activation energy for the formation of the O 2-II-structure on the (110)-face is found to be 3.5 kcal mole , the activation energy for desorption 53 kcal mole , and therefore the heat of adsorption about 50 kcal mole . The initial activation energies for the reaction CO+O ad→CO 2 on the (110)- and (100)-face are 5 and 30 kcal mole respectively. Longer interaction with oxygen leads to a partial poisoning of the catalyst. There is some other evidence on the participation of non-periodic structure elements (structure defects, impurities) at surface reactions on single crystal planes which can play the role of “active centers”.