Carbon Monoxide Chemisorption Research Articles

Pd−W and Pd−Co Bimetallic Catalysts' Sulfur Resistance for Selective Hydrogenation

The effect of cobalt and tungsten addition to a Pd/Al2O3 catalyst on its catalytic activity, selectivity, and sulfur resistance during styrene selective hydrogenation at 353 K, 20 kg cm-2 hydrogen pressure, and W/V = 0.002 g cm-3 has been studied. Catalysts were characterized by XPS, XRD, TEM, and hydrogen and carbon monoxide chemisorption. An increase in activity and sulfur resistance was observed after both cobalt and tungsten addition, which is ascribed to the formation of very active Pd−Co and Pd−W interfaces. A decorative effect of cobalt and tungsten on palladium is suggested.

97/01758 Microbial attack on sulfur-containing hydrocarbons: implications for the biodesulfurization of oils and coals

Hydrogenation of carbon monoxide (F-T synthesis) was investigated using titania-supported Ru catalysts in a comparison with alumina-supported catalysts. Ru catalysts supported on titania, especially on rutile found high activity for F-T synthesis and low selectivity for methanation compared with alumina-supported catalysts. This trend was more remarkable at elevated pressures. Reduction of the rutile-supnorted catalyst at higher temperatures such as 873K increased the catalytic activity, which was decreased by an exposure of the catalyst to oxygen. The high activity for F-T synthesis and low selectivity for methanation exhibited by titania-supported catalysts were elucidated by the reduced chemisorption of carbon monoxide and hydrogen, probably caused by a strong metal-support interaction (SMSI).

Reactivity of niobium cluster anions with nitrogen and carbon monoxide

Reactions of small niobium cluster anions, Nb n −( n = 2–7), with CO and N 2 are investigated using a flow tube reactor (flowing afterglow) apparatus. Carbon monoxide chemisorption on niobium cluster anions occurs with faster reaction rates than nitrogen chemisorption on corresponding cluster sizes. N 2 addition to niobium cluster anions is much more size-selective than is CO addition. These general trends follow those reported in the literature for reactions of neutral and cationic niobium clusters with CO and N 2. Extensive fragmentation of the clusters is observed upon chemisorption. A small fraction of the larger clusters survive and sequentially add multiple CO or N 2 units without fragmentation. However, chemisorption saturation is not reached at the experimentally accessible pressure and reagent concentration ranges. The thermochemistry of the adsorption processes and the nature of the adsorbed species, molecular or dissociated, are discussed.

Crotonaldehyde hydrogenation over bimetallic PtSn catalysts supported on pregraphitized carbon black. Effect of the preparation method

The effect of the preparation method on the catalytic behavior of bimetallic Pt Sn C catalysts in the vapor phase hydrogenation of crotonaldehyde has been determined. Nine Pt Sn C bimetallic catalysts have been prepared by coimpregnation and by successive impregnations of the support with solutions of the metal precursors, with Sn Pt atomic ratios ranging from 0 to 1.43. The effect of these variables on the surface characteristics of the catalysts has been analyzed by hydrogen and carbon monoxide chemisorption at room temperature and by X-ray photoelectron spectroscopy (XPS), and they have been related to the catalytic behavior in the title reaction. Results show that both metallic and oxidized tin species are present in the reduced catalysts (hydrogen, 623 K, 12 h) and their relative amounts depend on the preparation method and on the Sn Pt ratio. The overall activity for the title reaction increases with tin content, with a maximum for Sn Pt of about 0.8, and then decreases for higher tin loadings. The selectivity for the hydrogenation of the carbonyl bond in competition with the reduction of the olefinic CC bond seems to be related to the relative amount of oxidized surface tin species. The best results in terms of activity and selectivity are achieved with catalysts in which the tin precursor has been loaded first.

Requirements for activation of surface oxygen atoms in MgO using the Laplacian of the electron density

This paper demonstrates that the Laplacian of the electron density, the quantity ∇ 2 ϱ( r), can be used to determine the conditions required for activation of a surface atom and thus guides one in determining surface adsorption sites. It also predicts the geometry of approach of the substrate relative to the surface site and whether the interaction will correspond to physi- or chemisorption. The topology of the electron density and its Laplacian distribution for bulk MgO, its (100), (110) and (140) surfaces, as well as of embedded clusters that model these and other structural features of the surface, are studied to determine the conditions required for chemisorption of carbon monoxide. The unreactive nature of five-coordinated oxygen in the (100) surface is retained when its coordination is decreased to four in a step or to three in a corner. It is shown that electronic excitation can activate a surface oxygen atom towards reaction with a Lewis base through the creation of a “hole” in its valence shell of charge concentration, as defined by the topology of the Laplacian distribution. The results determine the site responsible for the formation of the CO − 2 radical anion on the surface of thermally activated MgO in the presence of CO gas. It also shown how a neighbouring activated oxygen atom in a stepped surface can lead to the formation of carbonate ion.

Crotonaldehyde hydrogenation over bimetallic PtSn catalysts supported on pregraphitized carbon black. Effect of the Sn/Pt atomic ratio

Three bimetallic PtSn/C catalysts have been prepared by successive impregnation of pregraphitized carbon black with an aqueous solutions of hexachloroplatinic acid and tin(II) chloride. One monometallic Pt/C sample was also prepared and studied for comparison. All catalysts were characterized by hydrogen and carbon monoxide chemisorption at room temperature and X-ray photoelectron spectroscopy and their behaviour in the gas phase hydrogenation of crotonaldehyde, at atmospheric pressure, determined. The amount of surface platinum is greatly reduced by the addition of tin, as deduced from chemisorption measurements and XPS. Both Pt 0 and Pt II are detected by XPS in the fresh bimetallic catalysts; after reduction in flowing hydrogen at 623 K platinum is completely reduced to the metallic state and, although a high proportion of tin remains in an oxidized state, a relatively important amount is reduced to Sn 0, this allowing the possibility of PtSn alloys formation. The catalytic activity in the gas phase hydrogenation of crotonaldehyde is greatly improved by the presence of tin, in spite of the fact that the amount of surface platinum is reduced. Tin has also a very important effect on the selectivity towards the hydrogenation of the CO bond, increasing the production of crotyl alcohol in respect to the hydrogenation of the CC bond that would lead to the production of butyraldehyde. The observed results are explained on the basis of a promoting effect of oxidized tin species for the hydrogenation of the CO group, whereas the formation of a PtSn alloy or the dilution of surface platinum by metallic tin would hinder the hydrogenation of the olefinic CC bond.

Application of breakthrough curves to investigate the chemisorption of carbon monoxide and hydrogen gases on platinum/silica catalysts

A study has been made on the consecutive adsorption of CO H 2 gases on Pt SiO 2 catalysts at 523 K using breakthrough measurements. The criteria for dispersion, diffusion and change in the pore size is evaluated and discussed as well as the equilibrium kinetic curves, which show to what extent the rates of sorption of one of the gases is affected by the presence of the other. The changes in average pore radii, surface areas and pore volume were very well estimated and correlated well with the breakthrough data.

Structural Study of the Ni{100}−(2 × 2)-C Surface by Time-of-flight Scattering and Recoiling Spectrometry

The structure of the Ni{100}−(2 × 2)-C surface has been investigated by time-of-flight scattering and recoiling spectrometry (TOF-SARS), low-energy electron diffraction (LEED), and classical scattering simulations. The surface was prepared by chemisorption of either carbon monoxide, benzene, or aniline onto a Ni{100} surface at 600 °C. The scattering flux from 4 keV of Ne+ and the recoiling flux of carbon from 4 keV of Ar+ were monitored as a function of the crystal azimuthal angle. An efficient simulation method, which is based on the binary collision approximation and shadowing and blocking effects, has been developed and applied to simulation of the TOF-SARS azimuthal scans. Quantitative values for the geometrical parameters were obtained by using a reliability (R) factor to compare the experimental and simulated azimuthal scans. The results are consistent with a surface structure which consists of 80% of a clock reconstructed (2 × 2)p4g phase and 20% of an unreconstructed (2 × 2) phase. For the recons...

Early days in the infrared study of adsorbed molecules

The early efforts in the development of infrared spectroscopy in studies of molecules adsorbed on catalyst surfaces are described. The effect of research atmosphere on conducting basic studies in an industrial laboratory is included. Specific examples include the chemisorption of ammonia to determine whether catalyst acidity is due to Lewis or Brønsted acids, the chemisorption of carbon monoxide on platinum, the chemisorption of nitrogen on nickel, the oxidation of carbon monoxide on nickel, and the adsorption of strongly electronegative adsorbates on impure zinc oxide which produce chemical changes within the bulk of the zinc oxide.

Evidence for kinetic and oxidative stabilization of Rh on Mo-promoted [formula omitted

Carbon monoxide hydrogenation studies on silica- and alumina-supported Rh catalysts conducted in our laboratories as well as those reported in the literature suggest that the addition of early transition-metal oxides to the catalyst surface exerts a promotional influence on active Rh centers. This promotion leads to enhanced oxygenate selectivity. Explanations of the promotional influence of the early transition-metal oxides fall into three categories: (i) kinetic stabilization of small Rh aggregates, (ii) wetting and spreading of the transition-metal oxide, leading to decoration of the surface of Rh crystallites, and (iii) oxidative stabilization of Rh aggregates, altering Rh interactions with sub-carbonyls during reaction. Characterization of the RhMo γ- Al 2O 3 system provides supporting evidence for both kinetic stabilization and oxidative stabilization of Rh aggregates and suggests that these processes contribute to the enhanced oxygenate selectivity of these materials. Hydrogen and carbon monoxide chemisorption results provide evidence for highly dispersed and oxidatively stabilized Rh aggregates. Even after extended on-stream testing (> 10 h), where metal aggregation is unavoidable, high-resolution transmission electron microscopy, associated energy dispersive spectroscopy, and the use of fast-Fourier transform post-processing to produce optical diffractograms highlight differences in the metal-aggregate morphology.

Studies of high surface area [formula omitted] and [formula omitted] catalysts for selective hydrogenation reactions I. Preparation and characterization of catalysts by X-ray diffraction, transmission electron microscopy, hydrogen consumption and carbon monoxide chemisorption

Ultrafine MoO 3 and WO 3 particles have been prepared in a flame reactor. Optimizations of reactor parameters allowed one to obtain high surface area (≥40 m 2 g −1) orthorhombic MoO 3 and monoclinic pseudo-orthorhombic WO 3, after a calcination in air at 673 K to eliminate residual chlorine. Platinum loaded (0.1–0.2 wt.−%) catalysts supported on these oxides were characterized by volumetric measurements of H 2 consumption, CO chemisorption, transmission electron microscopy and X-ray diffraction (XRD). In the presence of H 2, hydrogen bronzes of MoO 3 and MO 3 were formed by the so-called hydrogen spillover process. In the range 298–673 K, the value of x in H x MoO 3 bronzes lay between 1.44 and 2.10 whereas that of y in H y WO 3 ranged from 0.44 to 0.58. Platinum was well dispersed on MoO 3 or WO 3 and a partial reduction of the supports as a result of H 2 treatments at 673–773 K was shown by XRD.

Infrared spectroscopy of model electrochemical interfaces in ultrahigh vacuum: some implications for ionic and chemisorbate solvation at electrode surfaces

The utility of infrared reflection-absorption spectroscopy (IRAS) for examining structure and bonding for model electrochemical interfaces in ultrahigh vacuum (UHV) is illustrated, focusing specifically on the solvation of cations and chemisorbed carbon monoxide on Pt(111). These systems were chosen partly in view of the availability of IRAS data (albeit limited to chemisorbate vibrations) for the corresponding in-situ metal-solution interfaces, enabling direct spectral comparisons to be made with the “UHV electrochemical model” systems. Kelvin probe measurements of the metal-UHV surface potential changes (ΔΦ) attending alterations in the interfacial composition are also described: these provide the required link to the in-situ electrode potentials as well as yielding additional insight into surface solvation. Variations in the negative electronic charge density and, correspondingly, in the cation surface concentration (thereby mimicking charge-induced alterations in the electrode potential below the potential of zero charge) are achieved by potassium atom dosage onto Pt(111). Of the solvents selected for discussion here — deuterated water, methanol, and acetonitrile — the first two exhibit readily detectable vibrational bands which provide information on the ionic solvation structure. Progressively dosing these solvents onto Pt(111) in the presence of low potassium coverages yields marked alterations in the solvent vibrational bands which can be understood in terms of sequential cation solvation. Comparison between these spectra for methanol with analogous data for sequential methanol solvation of gas-phase alkali cations enables the influence of the interfacial environment to be assessed. The effects of solvating chemisorbed CO are illustrated for acetonitrile; the markedly larger shifts in CO frequencies and binding sites for dilute CO adlayers can be accounted for in terms of short-range coadsorbate interactions in addition to longer-range Stark effects. The differing degrees of selective solvation of cations versus CO for water and acetonitrile are also explored. While the former solvent removes all specific effects of K + upon CO, these short-range interactions partly remain upon acetonitrile solvation. The close connections between the UHV-based findings and the behavior of the in-situ electrochemical systems are also discussed.

Heat-Treated Carbon-Blacks as Supports for Platinum Catalysts

The effect of the degree of graphitization of the support on the dispersion, sintering resistance, and catalytic activity of a series of platinum catalysts supported on heat-treated carbon blacks has been determined. The supports were prepared by heat treatment of a furnace carbon black in an inert atmosphere at temperatures up to 2473 K. The resulting samples were characterized by physical adsorption (nitrogen at 77 K and carbon dioxide at 273 K), X-ray diffraction, and surface acidity measurements. Platinum catalysts were prepared by impregnating the supports with aqueous hexachloroplatinic acid; metal dispersions were measured by hydrogen and carbon monoxide chemisorption at room temperature and by transmission electron microscopy. Benzene hydrogenation was used as a test reaction to assess the possible effect of the support on the catalytic behavior of platinum. Platinum dispersions as high as 0.99 were achieved, and they can be well correlated with the surface acidity characteristics of the supports. The only sample not following the observed trend is the catalyst prepared with the less pregraphitized support. On the other hand, the highest resistance to sintering was found for the catalyst supported on the carbon black with the highest degree of graphitization, and this is attributed to an interaction between the metal particles and the π sites on the support. However, this interaction is not strong enough to affect the catalytic behavior for benzene hydrogenation. Thus, the metallic dispersion seems to be the result of, at least, two factors: (a) an adequate metal precursor support interaction during the impregnation step and (b) a high sintering resistance under the reduction conditions which hinders the metal particle growth during this stage of the catalyst preparation.

Electronic structures of large, extended, nonperiodic systems by using the elongation method: Model calculations for the cluster series of a polymer and the molecular stacking on a surface

AbstractThe elongation method based on the molecular orbital (MO) theory, which enables us to extend a polymer with any molecular fragments theoretically, has recently been developed by our group. As the next step, we introduced an approach based on the crystal orbital (CO) theory into above treatment. In the present work, the elongation method was developed at the Hartree–Fock level with CNDO/2 parameters and applied to model systems composed of the cluster series of a polymer and the molecular stacking on a surface. In the cluster‐series calculations, the hydrogen molecule [(H2)n], hydrogen fluoride [(HF)n], polyethylene, and polyacetylene were created successively to approximate their one‐dimensional periodic polymers by using the MO‐based elongation method. In the molecular‐stacking models, we described the hypothetical surface of crystal as periodically arranged hydrogen molecules by the COs, and several hydrogen molecules were stacked up on the surface one after another with the elongation procedure. Furthermore, the lattice defect on surface in which a part of stacked layer is lacking was dealt with by our approach. We also treated carbon monoxide chemisorption on a periodic magnesium chain as a more realistic model. Results for these systems support the applicability of our method for nonperiodic interactions in one‐ and two‐dimensional large systems. © 1995 John Wiley & Sons, Inc.

Interaction between ruthenium and molybdenum in RuMo/Al 2O 3 catalysts

RuMo/Al 2O 3 catalysts with various molybdenum loadings (0.15–0.6 wt.-%) and 0.6wt.-% ruthenium were prepared and characterized by hydrogen and carbon monoxide chemisorption. n-Hexane hydrogenolysis and cyclohexane dehydrogenation were performed over the reduced catalysts. Cyclohexene dehydrogenation was also carried out over the sulfided catalysts. The results suggest an electron transfer from molybdenum to ruthenium sites.

Origins of low-temperature three-way activity in Pt/CeO 2

The ability of Pt/CeO 2 to exhibit three-way catalytic activity at low temperatures results from a strong metal-support interaction, which is induced by activating the catalyst under a reducing atmosphere. Carbon monoxide chemisorption measurements show that a loss of exposed metal area occurs during the activation procedure, even though the conditions do not favour platinum sintering. Following activation (and subsequent exposure to air at ambient temperature), the surface ceria is left in a highly reducible state, which is characterised by a subambient peak during temperature-programmed reduction. We envisage that the strong interaction arises according to a traditional SMSI model, by the migration of partially reduced ceria over the surface of the platinum particles (at ⩾ 600°C). The resultant high degree of contact between the metal (with high work-function) and the metal oxide (with high band gap) promotes the formation of oxygen vacancies on the ceria surface. Although the presence of this highly reducible ceria-covering blocks conventional three-way sites on the platinum, it provides new sites that are active even at low temperatures. Therefore, unlike most previous explanations of promotion caused by a strong interaction, we propose that the ‘support’ becomes the active phase. Re-oxidation at elevated temperatures causes the ceria covering to coalesce, leading initially to its partial thinning, and subsequently to the re-exposure of the platinum particles.

Influence of chemisorption on the magnetic properties of metallic iron nanoparticles

Nano-sized α-Fe particles on a carbon support have been studied by Mössbauer spectroscopy. It is found that chemisorption of CO results in formation of a diamagnetic surface component. The magnetic anisotropy energy constant is only slightly affected by chemisorption of carbon monoxide and hydrogen.

Pd-Au/SiO2: Characterization and Catalytic Activity

A series of Pd-Au/SiO2 catalysts was prepared by incipient wetness coimpregnation of silica with respective chloride solutions, followed by calcination in air and reduction in hydrogen at 380°C for 15 h. A variety of techniques, chemisorption of hydrogen and carbon monoxide, temperature-programmed reduction, X-ray diffraction, X-ray photoelectron spectroscopy, and neopentane conversion as a catalytic probe, were employed to characterize metal dispersion and interaction between two metal components and the support. It has been discovered that the prepared materials are not uniform: a palladium-rich phase of very high metal dispersion (particle size ∼ 1.3 nm) coexists with much less dispersed gold-rich phase (particle size ∼ 15 nm). X-ray photoelectron spectroscopy revealed some presence of Si<IV species (as reduced silicon or ex-palladium silicide) in reduced silica-supported Pd-Au catalysts. Because the amount of Si<IV positively correlates with metal dispersion it is suggested that these species are in a close vicinity to the highly dispersed Pd (Pd-rich) material, forming a kind of "chemical glue" between metal and support. In contrast to other Pd-based systems (e.g., Pd-Cu and Pd-Zn), coimpregnation of silica with aqueous solutions of palladium and gold chlorides does not produce well-homogenized bimetallic material.

Improved activity of a silica supported ruthenium catalyst by carbon monoxide pretreatment

Abstract Silica supported ruthenium catalysts have been prepared by incipient wetness impregnation with RuCl3 (aq). After drying and reduction these catalysts were additionally treated with carbon monoxide or CO/H2 at 250°C. Due to this treatment the catalyst's carbon monoxide chemisorption capacity significantly increased compared to normal reduction. At the same time the intrinsic reactivity for carbon monoxide dissociation is enhanced. These effects are attributed to the structural changes of the catalysts. A model, based on TPR, XPS, IR and TEM measurements, is proposed. The carbon monoxide treatment results in a catalyst that is better reducible and has larger metal ensembles.

Mo-promoted Fe/activated carbon catalysts for carbon monoxide hydrogenation

Iron and molybdenum mono- and bimetallic catalysts supported on activated carbon have been prepared using iron pentacarbonyl and molybdenum hexacarbonyl as metal precursors. They have been characterized by temperature programmed reduction (TPR) and carbon monoxide chemisorption at 195 K and 298 K, and their catalytic activity for carbon monoxide hydrogenation at atmospheric pressure was studied under differential conditions, after reduction in hydrogen at several temperatures. Carbon monoxide chemisorption on the monometallic molybdenum catalyst was found to be strongly temperature dependent. On the other hand, the irreversible carbon monoxide chemisorption was largely decreased in the bimetallic catalyst in relation to the monometallic iron sample. The effect of molybdenum on the catalytic activity of FeMo/C is very important, producing an increase in catalytic activity which is very dependent on the reduction temperature. The selectivity of the monometallic iron catalyst is strongly modified by molybdenum addition, which produces a great increase in the yield to methane and a decrease in the alkenes to alkanes (C 2 + C 3) ratio.