Adsorption Of Carbon Monoxide Research Articles

Pt-doped armchair graphene nanoribbon as a promising gas sensor for CO and CO2: DFT study

Abstract In this work, four armchair graphene nanoribbon (AGNR) based sensor materials were built using Atomistic ToolKit Virtual NanoLab (ATK-VNL) and utilized to detect carbon monoxide (CO) and carbon dioxide (CO2) gases. First, the effect of passivating AGNR on the sensing performance toward CO and CO2 gases has been investigated, where AGNR was passivated with hydrogen (H-AGNR) and nitrogen (N-AGNR). The obtained results reflected no significant changes in the adsorption parameters of CO and CO2 molecules on H-AGNR and N-AGNR. Particularly, the adsorption energies between H-AGNR and N-AGNR systems and CO were found to be −0.446 and −0.436 eV, while for the case of CO2, the adsorption energies were found to be −0.426 and −0.432 eV, respectively. To enhance the sensing performance, both H-AGNR and N-AGNR systems were doped with platinum (Pt) forming another two systems: Pt–H-AGNR, and Pt–N-AGNR. After doping, the results revealed a significant increase in the adsorption energy to almost 9 times than the non-doped systems for the cases of CO on Pt–N-AGNR as well as CO2 on both Pt–H-AGNR and Pt–N-AGNR. Moreover, an increase of almost 13 times was observed in the adsorption energy for the case of CO on Pt–H-AGNR. Besides to the adsorption energy ( E a d s ), the adsorption distance (( D ), charge transfer ( Δ Q ), the density of states (DOS), as well as the band structure have been examined to confirm the adsorption of CO and CO2 on the four systems.

Behavior of gold-enhanced electrocatalytic performance of NiPtAu hollow nanocrystals for alkaline methanol oxidation

The Pt-based catalyst tends to be poisoned by carbon monoxide (CO)-like intermediates produced in fuel cell reactions, which seriously deteriorates its catalytic performance. Herein, noble metal Au with the capacity of resistance to CO-like intermediates poisoning was employed to construct multi-element Pt-based catalysts. Two trimetallic NiPtAu hollow nanocrystals (HNCs) with different surface Au contents were synthesized to explore the role of Au in electrocatalysis for alkaline methanol oxidation reaction (MOR). The trimetallic NiPtAu-SRAu HNCs catalyst with the relative rich Au content (15.17 at%) on surface exhibits a much lower CO oxidation peak potential than the other HNCs counterpart and 20 wt% Pt/C, which indicates the more exceptional CO-resisting performance. Besides, the MOR specific activity of NiPtAu-SRAu HNCs (31.52 mA cm−2) is 7 times higher than that of 20wt% Pt/C (4.50 mA cm−2). This enhancement in catalytic activity as well as anti-CO poisoning capability for NiPtAu-SRAu HNCs can be mainly ascribed to the weakened CO adsorption due to the exposure of Au atoms on NiPt surface evidenced by the experimental data and density functional theory calculations. This study not only investigates the role of Au in MOR catalysis but also could be helpful for designing and optimizing the electrocatalysts for high-active and robust fuel cell applications.

Synthesis and characterization of Pt-HxMoO3 catalysts for CO-tolerant PEMFCs

Two relatively simple synthetic procedures were developed for the synthesis of Pt–HxMoO3 composites. The obtained materials may be of interest as CO-tolerant catalysts for hydrogen-air fuel cells with proton-exchange membranes (PEMFCs). The first step of both syntheses was to prepare hydrogen molybdenum bronzes (HxMoO3) through the addition of Zn powder to acidic solutions containing Mo(VI) species. Two types of hydrogen-containing molybdenum bronzes were synthesized, namely, red bronze (x≈1.55) and green bronze (x≈2.0). The next step was the Pt deposition in a redox reaction between HxMoO3 and potassium tetrachloroplatinate (K2PtCl4) under open-circuit conditions that resulted in composite materials defined by aPt⋅b(HxMoO3).Numerous physical methods, including XRD, STEM, SEM, and XPS, were used to determine both the composition and structure of the catalysts. Platinum clusters were distributed over the surface of catalytically active support (HxMoO3) in both cases; however, the type of molybdenum bronze used for synthesis affects the size of Pt particles.Linear sweep voltammetry (LSV) was used to determine the regularities of both adsorbed carbon monoxide electrodesorption and dissolved CO electrooxidation. CO-tolerance of prepared composites was estimated using H2/100 ppm CO mixture under conditions of both an electrochemical cell and a membrane electrode assembly (MEA).The results of this work are promising, as they provide a relatively simple method for the synthesis of CO-tolerant catalysts. The understanding of the origin of the CO-tolerance is essential for the development of electrode materials that could be used in the real fuel cells.

Tailoring the Antipoisoning Performance of Pd for Formic Acid Electrooxidation via an Ordered PdBi Intermetallic

Pd-based materials are promising electrocatalysts for the formic acid oxidation reaction (FAOR) but suffer from poor durability due to the poisoning of adsorbed carbon monoxide species (COads). In ...

CO2 methanation on Ni-Ce0.8M0.2O2 (M=Zr, Sn or Ti) catalyst: Suppression of CO via formation of bridging carbonyls on nickel

The effect of different cations (M=Zr, Sn or Ti) doping on ceria supported nickel (Ni-Ce0.8M0.2O2) catalysts and their performance in the CO2 methanation reaction has been investigated. Among the prepared catalysts, the Ni-CeO2 (CN) catalyst exhibited the best catalytic performance with a CO2 conversion of 62.9% at 400 °C. The selectivity on Ni-Ce0.8Zr0.2O2 (CZN) remained above 98.4% from 200 to 400 °C. As confirmed by in-situ DRIFTS, the dissociative adsorption of H2 mainly proceeds on Ni, by-product CO is mainly assigned to the releasing of weak-binding linearly adsorbed CO on nickel, which is from the hydrogenation of formates with adsorbed H. The CO-suppressing effect is attributed to the strong adsorption of carbon monoxide on nickel via the forming of bridging carbonyls. It was found that CO2 is adsorbed on the catalysts to form carbonate, bicarbonate and formate species. The formate species could be further hydrogenated by dissociated H and then finally release methane.

Study on the influence of the thickness of nanostructured rhodium films toward electrooxidation of adsorbed carbon monoxide

Carbon-supported rhodium thin films with various thicknesses are grown by varying the number of laser pulses, Nlp (from 5000 to 50,000) under 2 Torr of He background atmosphere using the pulsed laser deposition method. The thin films are characterized for their morphological features and structural properties. It is observed that smooth dense 2D nanosheets of Rh are obtained with 5000 Nlp, whereas higher Nlp yields to highly porous Rh films. X-ray photoelectron spectroscopy reveals that both metallic Rh and Rh3+ are present at the surface of the Rh films. Nevertheless, the amount of metallic Rh increased as the Nlp increased. The influence of the thickness of the Rh films on the tolerance to CO, a poison that strongly adsorbs on the surface of catalysts in fuel cells reactions, was investigated through anodic stripping voltammetry. It is found that Rh film deposited with 50,000 Nlp exhibits the highest electroactive surface area (27.90 cm2 vs. 1.20 cm2 of Pt), the lowest onset potential of CO electrooxidation (0.47 V vs. 0.60 V Pt), and a net charge corresponding to electrooxidation of the CO adlayer of 424 μC cm−2 (vs. 358 μC cm−2 of Pt). Such high tolerance to CO poisoning is explained on the basis of the elevated porosity and roughness of the Rh surface. Indeed, a roughness factor of 90.5 for Rh against about 3.8 for Pt grows under analogous deposition conditions of pressure and number of laser pulses.

Coverage-Induced Orientation Change: CO on Ir(111) Monitored by Polarization-Dependent Sum Frequency Generation Spectroscopy and Density Functional Theory.

Polarization-dependent sum frequency generation (SFG) spectroscopy was applied to study the adsorption of carbon monoxide (CO) on the well-ordered (annealed) Ir(111) single-crystal surface at various CO coverages. Coverage was adjusted by varying the substrate temperature (300–575 K) and/or gas pressure (10–7 to 1.0 mbar). Under all conditions investigated, only a single absorption band at 2038–2094 cm–1 was observed, characteristic of linearly bonded (on-top) CO. Using different polarizations, PPP and SSP spectra were acquired with a high signal-to-noise ratio, whereby tilt angles of CO on Ir(111) could be determined for the first time by SFG. It was found that not only the vibrational frequency of on-top CO but also the tilt angle was strongly coverage-dependent. The higher the coverage was, the larger the vibrational frequency and the tilt angle were. At about 0.7 ML coverage, a CO tilt angle of at least 20° was observed, which is in good agreement with density functional theory (DFT) calculations. In addition, the molecular hyperpolarizability ratio (R) of CO (at 0.13 ML in UHV) was determined to be 0.08. Based on the combined SFG/DFT results, it may change to 0.29 at 0.77 ML coverage.

Nanostructured shrub-like bimetallic PtxRh100-x alloys grown on carbon paper for the oxidative removal of adsorbed carbon monoxide for ethanol fuel cells reaction

Plasmas techniques are novel routes for the preparation of complex nanostructured materials for catalysis and clean hydrogen energy such as fuel cells. CBPLD technique allows enhanced interaction between the catalyst and the support and improved catalytic properties. Herein, a highly active and durable vertically aligned nanostructured shrub-like bimetallic PtxRh100-x alloys with atomic ratios close to nominal values are grown on carbon paper substrate. The tolerance to CO poisoning and ethanol electrooxidation reactions are studied over these new types of shrub-like bimetallic PtxRh100-x/CP catalysts, demonstrating that such structures effectively facilitate both processes and very low long-term poisoning rates. Such high catalytic activity accounts for two mechanisms: Rh a highly oxophilic transition metal activates water dissociation at lower potentials than Pt (bifunctional mechanism), and the ligand effect where Rh alters the electronic structure of the neighboring Pt suggesting a faster supply in OHads.

Characterization of Acid and Basic Sites on Zirconia Surfaces and Nanoparticles by Adsorbed Probe Molecules: A Theoretical Study

Acid and basic sites on monoclinic and tetragonal zirconia were investigated at the DFT level by computing IR and NMR properties of adsorbed probe molecules. Regular and stepped ZrO2 surfaces as well as stoichiometric zirconia nanoparticles have been considered. Acidity and basicity were probed by the adsorption of carbon monoxide and pyrrole, respectively. CO adsorption shows a positive shift of the C–O stretching frequency in IR spectra while the C atom of CO is shielded and 13C chemical shifts moves to higher field as a function of the strength of the acid site. For the study of basic sites we used a pyrrole molecule, but the interaction between the pyrrole ring and the surface leads to adsorption modes that cannot be used to titrate the surface basicity. On the other hand, at high coverage the molecule assumes an upright position and the formation of a hydrogen bond of the pyrrole NH group with the oxygen atoms of the surfaces provides a proxy of the basic properties of these sites. In particular, we focus on changes of the N–H IR frequency, 1H, 15N, and 17O NMR chemical shifts and their correlations with the surface basicity. Among the correlations found, that between the N–H stretching frequency of adsorbed pyrrole and the 17O NMR chemical shift of the O ion where the molecule is bound show a nice linear correlation. These two properties can provide useful information about the basic character of various O sites on the surface of zirconia.Graphic

Morphology and Adsorption Properties of Bimetallic Nanostructured Coatings on Pyrolytic Graphite

The paper presents the results of studies of coatings formed by gold, copper, nickel, and palladium nanoparticles in various combinations on the surface of highly oriented pyrolytic graphite. It was shown that the structure of the bimetallic coatings and the adsorption of hydrogen, oxygen, and carbon monoxide on them are affected by interactions between dissimilar nanoparticles.

Disclosing the Interaction between Carbon Monoxide and Alkylated Ti3+ Species: a Direct Insight into Ziegler-Natta Catalysis.

In the field of Ziegler–Natta catalysis for olefin polymerization, carbon monoxide (CO) is used in the industrial practice to quench the reaction when it proceeds too fast, approaching critical levels for the plant safety. The quenching effect is explained as due to the reversible coordination of CO to the titanium active sites, but no direct evidence has been ever reported. In this work, we designed a series of experiments to monitor CO adsorption at variable temperatures on a model Ziegler–Natta catalyst by means of FT-IR spectroscopy. For the first time, we have been able to spectroscopically detect CO coordinated to alkylated Ti3+ sites and the Ti–acyl species formed upon the subsequent insertion of CO into the Ti3+–alkyl bond, both in the absence and in the presence of the olefin monomer. In perspective, this has important implications for the characterization of the active sites in industrial Ziegler–Natta catalysts, even under working conditions.

Acetic Acid Adsorption and Reactions on Ni(110).

Acetic acid adsorption and reactions at multiple surface coverage values on Ni(110) were studied with temperature-programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS) at 90-500 K. The experimental measurements were interpreted with density functional theory (DFT) calculations that provided information on adsorbate geometries, energies, and vibrational modes. Below the monolayer saturation coverage of 0.36 ML at 90 K, acetic acid adsorbs mostly molecularly. Above this coverage, a physisorbed layer is formed with dimers and catemers, without detectable monomers. Dimers and catemers desorb as molecular acetic acid at 157 and 172 K, respectively. Between 90 and 200 K, the O-H bond in acetic acid breaks to form bridge-bonded bidentate acetate that becomes the dominant surface species. Desorption-limited hydrogen evolution is observed at 265 K. However, even after the acetate formation, acetic acid desorbs molecularly at 200-300 K due to recombination. Minor surface species observed at 200 K, acetyls or acetates with a carbonyl group, decompose below 350 K and generate adsorbed carbon monoxide. At 350 K, the surface likely undergoes restructuring, the extent of which increases with acetic acid coverage. The initial dominant bridge-bonded bidentate acetate species formed below 200 K remain on the surface, but they now mostly adsorb on the restructured sites. The acetates and all other remaining hydrocarbon species decompose simultaneously at 425 K in a narrow temperature range with concurrent evolution of hydrogen, carbon monoxide, and carbon dioxide. Above 425 K, only carbon remains on the surface.

Application of the training of density functional theory potentials within machine learning to adsorptions and reaction paths on Platinum surfaces

This study is conducted by making density functional theory (DFT) calculations within gpaw code and then trained the DFT potentials within a machine learning approaches of amp and ænet. Adsorbate molecules are chosen based on occurrences in fuel cells. The outcomes from the machine learned training of the potentials show differences in adsorption energies of only up to the order of 10−2 eV when trained sufficiently well. However, such small differences in energies do not seem to carry into a differences in electronic structures. It shows that (110) surface is better in facilitating a dissociation process of hydrogen and oxygen molecules into the respective ions with a barrier of dissociation of up to 0.75 eV and 1.91 eV, respectively. The relatively small adsorption energies of hydrogen and oxygen molecules, 0.82 eV and -0.10 eV, respectively, seem to be indicative of a favorable mobility of the respective ions within the electrolyte. Carbon monoxide adsorbs relatively stronger with adsorption energy of up to 1.80 eV. As a result, the formation of carbon dioxide and water molecules as a byproducts is strongly activated, but is exothermic, and seem to preferably take place on (100) and (111) surfaces. A weak adsorption energies of these byproduct molecules could also be indicative of a good mobility of the molecules within fuel cells, once formed. Training of the DFT potentials also appear to show differences in energies of reaction paths only to within the order of 10−1 eV.

Highly Catalytic Electrochemical Oxidation of Carbon Monoxide on Iridium Nanotubes: Amperometric Sensing of Carbon Monoxide.

The nanotubular structures of IrO2 and Ir metal were successfully synthesized without any template. First, IrO2 nanotubes were prepared by electrospinning and post-calcination, where a fine control of synthetic conditions (e.g., precursor concentration and solvent composition in electrospinning solution, temperature increasing rate for calcination) was required. Then, a further thermal treatment of IrO2 nanotubes under hydrogen gas atmosphere produced Ir metal nanotubes. The electroactivity of the resultant Ir metal nanotubes was investigated toward carbon monoxide (CO) oxidation using linear sweep voltammetry (LSV) and amperometry. The anodic current response of Ir metal nanotubes was linearly proportional to CO concentration change, with a high sensitivity and a short response time. The amperometric sensitivity of Ir metal nanotubes for CO sensing was greater than a nanofibrous counterpart (i.e., Ir metal nanofibers) and commercial Pt (20 wt% Pt loading on carbon). Density functional theory calculations support stronger CO adsorption on Ir(111) than Pt(111). This study demonstrates that metallic Ir in a nanotubular structure is a good electrode material for the amperometric sensing of CO.

Pollutant Gases Adsorption on the Surface of Iron-Containing Polyacrylonitrile

The possibility of adsorption of polluting gases (nitrogen dioxide, methane, ammonia, sulfur dioxide, hydrogen sulfide, ozone, carbon monoxide, carbon monoxide, chlorine) on the surface of iron-containing PAN was evaluated. A model of an iron-containing PAN cluster has been built. The method of molecular modeling was used to determine the thermodynamic parameters of systems: Fe-PAN cluster–gas molecule, Fe-PAN cluster–oxygen molecule, Fe-PAN cluster–water molecule, Fe-PAN cluster–oxygen molecule–gas molecule, Fe-PAN cluster – water molecule is a gas molecule and their comparison is made. The effect of oxygen on polluting gases adsorption on the iron-containing PAN cluster surface is revealed, while the influence of water molecules in the immediate vicinity of the cluster is not observed. The capability of iron-containing PAN to adsorb chlorine and carbon monoxide has been revealed in our calculations.

CO, CO2, and SO2 detection based on functionalized graphene nanoribbons: First principles study

Abstract In this study, density functional theory (DFT) has been used to build armchair graphene nanoribbon (AGNR) gas sensor and study its capacity to detect carbon monoxide (CO), carbon dioxide (CO2), and sulfur dioxide (SO2) gases. The adsorption of these gases on AGNR was confirmed based on the adsorption energy (Eads), adsorption distance (D), charge transfer (ΔQ), density of states (DOS), and band structure. In order to improve the adsorption capacity, three different modified AGNR systems have been built. AGNR was first functionalized with epoxy (-O-) group (AGNR-O), then with hydroxyl (-OH) group (AGNR-OH), and finally with (-O-) along with (-OH) groups (AGNR-O-OH). Before modification, the adsorption energies have been found to be −0.260, −0.145, and −0.196 eV due to the adsorption of CO, CO2, and SO2, respectively. After modification, the adsorption energy increased remarkably to −0.538 and −0.767 eV for the cases of AGNR-O-OH-CO2 and AGNR-O-OH-SO2, respectively. Indicating that functionalizing the surface of AGNR can improve significantly its performance for the field of gas sensing.

Elucidating the Defect-Induced Changes in the Photocatalytic Activity of TiO2

The adsorption and subsequent photo-oxidation of carbon monoxide on the anatase TiO2(101) and rutile TiO2(110) single crystal surfaces was investigated using low temperature X-ray photoelectron spectroscopy. Anatase was shown to significantly outperform rutile in terms of the rate of carbon dioxide yield on the stoichiometric surface, and further to this, the presence of defects was shown to heavily influence the photocatalytic efficiency. The oxidation rate was reduced on anatase but increased on rutile. This change is attributed to the location of defects within the crystal structure and is further discussed in this work. These findings are of significant importance and demonstrate the possibilities of defect engineering in photocatalysis.

Mixed-Metal-Oxide Based Hybrid Electrocatalytic Materials for Efficient Reduction of Carbon Dioxide

Of particular interest to the preparation of advanced catalytic materials is efficient utilization of catalytic sites (metal and metal oxide nanostructures, their stabilization and intentional activation, as well as organization into two-dimensional arrays, ultra-thin films or three-dimensional networks (e.g. through sequential deposition) on electrode surfaces. They can form nanosized materials with well-defined composition, structure and thickness that exhibit desirable electrocatalytic properties (e.g. toward reduction of CO2). We explore here the ability of polynuclear inorganic metal oxo systems to stabilize and functionalize metal (e.g. copper) nanostructures. Here certain nanostructured metal oxides of zirconium, titanium, zinc or tungsten have been demonstrated to influence supported metal centers in ways other than simple dispersion over electrode area. Evidence is presented that the support can modify activity (presumably electronic nature) of catalytic metal nanoparticles (e.g. Cu, Ag, Au, Pd, Ru) thus affecting their chemisorptive and catalytic properties. Metal oxide nanospecies can generate –OH groups at low potentials that induce proton mobility at the photo(electro)chemical interface.Our research interests concern development of systems for the electrocatalytic reduction of carbon dioxide not only in neutral but also in acid media. For example, nanosized Cu or Ru naoparticles immobilized within ultra-thin films of tungsten oxide or zirconia have been considered. Selectivity of the catalytic systems largely depends on the activing adsorptive (CO2) phenomena and the affinity of catalytic centers to the adsorbed carbon monoxide (CO) type intermediates leading to their protonation or hydrogenation. Reduction of carbon dioxide begins now at less negative potentials and is accompanied by significant enhancement of the CO2-reduction current densities relative to the competitive hydrogen evolution.

Adsorption and dissociation of CO on metal clusters

Adsorption and dissociation of carbon monoxide on metal clusters M13 (M = Ag, Co, Cu, Fe, Ni and Ru), has been studied. Structure stabilities of metal clusters, adsorption sites, adsorption energies and the activation energies for the dissociation of CO were determined using density functional theory. Cohesive and binding energies of metal atoms in M13 clusters of studied metals were calculated, showing the different strength interaction of metal atoms in each particle. Three active adsorption sites on the M13 particles studied have been identified, showing that CO adsorption with covalent nature can occur on different sites depending of the metal cluster. Charge density difference in the M13-CO interaction on all the adsorption sites of all metal clusters showed a strong accumulation of charge density in the MC bonding. Of the group of metal cluster modeled, Ru13, Cu13 and Co13 present higher adsorption energies. On the other hand, Fe13, Co13 and Ru13 present lower activation energies. In all cases, endothermic behavior of CO dissociation was observed. The initial stages of CO interaction with several metal clusters, in comparison with metal surfaces, is presented.

To the Mathematical Theory of the Temkin Adsorption Model

This study expands the mathematical theory of the Temkin adsorption model and demonstrates the way experimental data are to be additionally treated. A functional complement property of the Temkin isotherm has been studied as a particular case of the common theory of asymptotic complement. This property is shown to give rise to various analytical strategies to be employed for processing or interpretation of the experimental results, e.g. to perform mapping of data obtained in experiments onto a conjugated part of the true isotherm, to judge if presupposed energetic heterogeneity type of the surface really takes place, etc. Experimental data for adsorption of carbon monoxide on gold and of sodium oleate on steel with and without a magnetite coating have been extensively analysed.