Chemisorption Properties Research Articles

Effects of Organic Modifiers on a Palladium Catalyst in the Competitive Hydrogenation of 1‐Octene Versus Octanal: An Evaluation of Solid Catalysts with an Ionic Liquid Layer

AbstractThe competitive hydrogenation between 1‐octene and octanal has been investigated with a ≈5 % palladium on alumina catalyst prepared in situ with the following organic modifiers: pyridine, 1‐methylimidazole, 1,3‐dimethylimidazole methylsulfate, 1,3‐dimethylimidazole bis(trifluoromethylsulfonyl)imide and methyltri‐sec‐butylphosphonium methylsulfate. The results of these investigations indicate that the ionic liquid modifiers have significant and specific effects on catalytic performance, for example, certain systems can completely suppress octanal conversion. In addition, analytical techniques reveal that the matrix and quantity of organic species on the used catalysts are different if different ionic liquids are used as modifiers. Surface studies also reveal that the modifiers have a noticeable effect on the crystallite size and chemisorption properties of the catalysts.

Oxidized graphene as an electrode material for rechargeable metal-ion batteries – a DFT point of view

In line with a growing interest in the use of graphene-based materials for energy storage applications and active research in the field of rechargeable metal-ion batteries we have performed a DFT based computational study of alkali metal atoms (Li, Na and K) interaction with an oxidized graphene. The presence of oxygen surface groups (epoxy and hydroxyl) alters the chemisorption properties of graphene. In particular, we observe that the epoxy groups are redox active and enhance the alkali metal adsorption energies by a factor of 2 or more. When an alkali metal atom interacts with hydroxyl-graphene the formation of metal-hydroxide is observed. In addition to a potential boost of metal ion storage capability, oxygen functional groups also prevent the precipitation of the metal phase. By simulating lithiation/de-lithiation process on epoxy-graphenes, it was concluded that the oxidized graphene can undergo structural changes during battery operation. Our results suggest that the content and the type of oxygen surface groups should be carefully tailored to maximize the performance of metal-ion batteries. This is mainly related to the control of the oxidation level in order to provide enough active centers for metal ion storage while preserving sufficient electrical conductivity.

Computational study of the adsorption of benzene and hydrogen on palladium–iridium nanoalloys

The preferred chemisorption sites on a variety of palladium–iridium nanoalloys are determined for benzene and hydrogen molecules. Available sites on the surface of the nanoalloys are explored using a random-search method, directly at the density functional level of theory. These searches successfully reveal the site preference for benzene and significant nanosize effects in the chemisorption of hydrogen. It is hoped that through the study of the chemisorption properties of Pd–Ir nanoalloys, complex catalytic processes, such as tetralin hydroconversion and the preferential oxidation of CO, can be better understood.

Structure, chemisorption properties and electrocatalysis by Pd3Au overlayers on tungsten carbide – A DFT study

Tungsten carbide (WC) is in the focus of current research as a suitable electrocatalyst support. Typically, supported monometallic system are investigated, in spite the fact that practice in catalysis shows that multimetallic systems can have significantly better performance compared to monometallic counterparts. In this work, WC-supported Pd3Au overlayers were studied theoretically using periodic Density Functional Theory calculations and compared to bulk-like Pd3Au and pure Pd. Stability of studied surfaces and the electronic structures were analyzed. Chemisorption properties were probed using atomic H and CO molecule. Electrocatalytic activities of studied surfaces were estimated using hydrogen binding energy as catalytic activity descriptor for hydrogen electrode reactions. The connection between H binding energy and CO adsorption energy enabled us to establish the link between catalytic activity and CO tolerance of studied surfaces. It is considered that formation of bimetallic layers on WC opens a new perspective in designing new core-shell electrocatalysts with high performance and significantly reduced content of noble metals.

Periodic, vdW-corrected density functional theory investigation of the effect of Al siting in H-ZSM-5 on chemisorption properties and site-specific acidity

Twelve crystallographically distinct Al substitution sites of H-ZSM-5 are modeled by periodic density functional theory using the vdW-DF functional. While the stability of Al substitution and Brønsted acid OH bond length at different active site positions are similar, the OH stretch frequency, SiOAl bond angle, and adsorption energies of various probe molecules differ notably without observable correlations between these properties. Comparison of adsorption energy values with and without van der Waals corrections demonstrates the significance of the inclusion of dispersion interactions. Our data indicate that theoretical investigations of H-ZSM-5 require a careful selection of the location of the active site.

Effect of Rhenium on Ruthenium Dispersion in the Ru–Re/γ-Al2O3 Catalysts

Ru–Re/γ-Al2O3 catalysts were prepared by the incipient wet co-impregnation method and characterized by ICP-AES, BET, H2-TPR, XRD, SEM, TEM and H2 chemisorption. Structure and chemisorption properties of these catalysts were compared with monometallic (Ru, Re) catalysts synthesized by using the same Ru(NO)(NO3)3 or RuCl3 and NH4ReO4 precursors. Results showed that Ru–Re/γ-Al2O3 catalysts consist primary of bimetallic nanoparticles with small sizes (<3 nm), while the larger particles were monometallic Re, especially for the bimetallic catalyst at the Ru/Re atomic ratio of 50:50. Chemisorption data revealed that Re modifies the interaction of hydrogen with ruthenium surface sites. In the chlorine-free Ru–Re catalysts, dispersion of ruthenium increased with the rise of the Re loading. The mean particle size decrease from 1.3 to 0.9 nm by change of the Ru/Re ratio from 90:10 to 50:50. Ruthenium particle size calculated from H2 uptake agreed well with XRD and TEM data. Ruthenium dispersion of the chlorine-containing bimetallic Ru–Re catalyst (Ru/Re = 75:25) was significantly lower and comparable with the Ru(Cl) catalyst. Also, the large discrepancies between the mean particle size obtained from H2 chemisorption (3.9 nm) and TEM (1.1 nm) were observed what is explained by the contamination of Ru surface by the Cl− ions.

Dehydrocyclization of n-heptane over Pt catalysts supported on Al- and Si-promoted TiO2

The effect of content of Si- and Al-promoted TiO2 catalysts in the dehydrocyclization of n-heptane was studied. The sol–gel method was used to prepare pure TiO2 and mixed oxides with 1%, 3% and 10% of Al2O3 and SiO2. The structure and surface characterization (XRD, N2 sorption, H2 chemisorption, NH3 uptake) revealed that the promoted cations were dispersed in the TiO2 lattice, modifying structural and surface properties of catalysts. Dehydrocyclization activity and toluene yields were useful test reaction to detect the effect of content of cations in both acidic and catalytic properties of promoted catalysts. Increase in the TOF was observed as a function of cation content, hand in hand with the increase of overall reaction rate and supported Pt dispersion. The effects in both catalytic activity and deactivation resistance could be explained by the metal-support contact theory, which relates the atomic coordination of promoters with changes in catalytic activity and chemisorption properties of Pt supported on TiO2.

Carbon-supported Ru catalyst with lithium promoter for ammonia synthesis

Abstract The electronegativity of Li is much higher than that of Na or K, but the ammonia synthesis activities of Li-promoted Ru/AC catalysts were comparable to the values of Ru catalyst promoted with K, which were much higher than those over Ru catalyst with Na promoter. The presence of Li increased the catalytic activity by changing the chemisorption properties such as hydrogen adsorption and nitrogen adsorption for carbon-supported Ru catalysts, rather than affecting the sizes of Ru particles or the electron density of Ru metal.

Electrocatalytic oxidation of small organic molecules in acid medium: Enhancement of activity of noble metal nanoparticles and their alloys by supporting or modifying them with metal oxides

Different approaches to enhancement of electrocatalytic activity of noble metal nanoparticles during oxidation of small organic molecules (namely potential fuels for low-temperature fuel cells such as methanol, ethanol and formic acid) are described. A physical approach to the increase of activity of catalytic nanoparticles (e.g. platinum or palladium) involves nanostructuring to obtain highly dispersed systems of high surface area. Recently, the feasibility of enhancing activity of noble metal systems through the formation of bimetallic (e.g. PtRu, PtSn, and PdAu) or even more complex (e.g. PtRuW, PtRuSn) alloys has been demonstrated. In addition to possible changes in the electronic properties of alloys, specific interactions between metals as well as chemical reactivity of the added components have been postulated. We address and emphasize here the possibility of utilization of noble metal and alloyed nanoparticles supported on robust but reactive high surface area metal oxides (e.g. WO3, MoO3, TiO2, ZrO2, V2O5, and CeO2) in oxidative electrocatalysis. This paper concerns the way in which certain inorganic oxides and oxo species can act effectively as supports for noble metal nanoparticles or their alloys during electrocatalytic oxidation of hydrogen and representative organic fuels. Among important issues are possible changes in the morphology and dispersion, as well as specific interactions leading to the improved chemisorptive and catalytic properties in addition to the feasibility of long time operation of the discussed systems.

Poly(N-isopropylacrylamide-co-acrylic acid) hydrogels for copper ion adsorption: Equilibrium isotherms, kinetic and thermodynamic studies

Hydrogel was successfully synthesised by incorporating acrylic acid (AA) as copper ion (Cu2+) chelator into the thermo-responsive poly(N-isopropylacrylamide) (PNIPAM) via emulsion polymerisation. The stimuli-responsive properties and the Cu2+ adsorption capacity of the cross-linked PNIPAM-co-AA hydrogels were evaluated. The hydrodynamic diameter of the PNIPAM-co-AA hydrogel particles was studied using dynamic light scattering (DLS) method. It was found that the volume phase transition temperature (VPTT) of hydrogels shifted from 32°C to 27°C after Cu2+ adsorption and the hydrodynamic diameter decreased with increasing temperature. The size of the PNIPAM-co-AA hydrogel particles and the incorporation of AA functional group were confirmed by transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR), respectively. Equilibrium isotherms, kinetic and thermodynamic studies have also been evaluated for its copper ions adsorption. The adsorption capacity (qm) of PNIPAM-co-AA hydrogels for Cu2+ was found to be 67.25mgg−1 with best fit to Langmuir isotherm and the adsorption mechanism follows the pseudo-second-order model. Gibbs free energy analysis shows that the adsorption was spontaneous and it exhibited endothermic chemisorption properties. Adsorption of copper ions on PNIPAM-co-AA hydrogels was found to be more thermodynamically driven.

A first-principles study of structure, orbital interactions and atomic oxygen and OH adsorption on Mo-, Sc- and Y-doped nickel bimetallic clusters

Abstract Density functional theory (DFT) has been used to study the stability, orbitals interactions and oxygen and hydroxyl chemisorption properties of Ni n M (1 ⩽ n ⩽ 12) clusters. A single atom doped-nickel clusters increase the stability, and icosahedral Ni 12 Mo cluster is the most stable structure. Molybdenum atom prefers to exhibit center at the cluster ( n ⩾ 10) rather than edge, while Sc and Y atom remain at the edge. The Ni–Mo bond lengths are smaller than the Ni–Sc and Ni–Y. The pDOS results show that the d – d orbitals interactions are mainly dominating on the stability of clusters, while p orbitals have a small effect on the stability. The Mo-doped nanoclusters have the highest oxygen and OH chemisorption energy, and the most favorable adsorption site is on the top Mo site. The larger cluster distortion is found for the Sc- and Y-doped structures compared to other clusters. The oxygen 2 p orbitals are strongly hybridizing with the Mo 4 d orbitals ( n p and Ni 3 d , 4 s and Mo 5 s orbitals. The Mo-doped clusters are significantly increased the chemisorption energies that might improve the passive film adherence of nanoalloys.

Understanding the Electronic Structures of Graphene Quantum Dot Physisorption and Chemisorption onto the TiO2 (110) Surface: A First‐Principles Calculation

We investigated the interfacial electronic structure and charge transfer properties of graphene quantum dot (GQD) physisorption and chemisorption on the TiO(2) (110) surface from density functional theory calculations. The simulations show that a slight charge transfer occurs in physisorption case while a significant charge transfer takes place in chemisorption configuration. We present a detailed comparison of the similarities and differences between the electronic structures. The similarities originate from the positive work function difference in both the physisorption and chemisorption configurations, which is able to drive electron transfer from GQD into TiO(2), leading to charge separation across the GQD-TiO(2) interface. The differences stem from the interaction between the GQD and TiO(2) substrate. For example, GQD bounds to TiO(2) surface through van der Waals interactions in the case of physisorption. In the chemisorption configuration, however, there exists strong covalent bonding between them. This leads to much more efficient charge separation for chemisorption than for physisorption. Furthermore, the GQD-TiO(2) composites show large band-gap narrowing that could extend the optical absorption edge into the visible-light region. This should imply that chemisorbed GQDs produce a composite with better photocatalytic and photovoltaic performance than composites formed through physisorption.

Study of potassium promoter effect for Ru/AC catalysts for ammonia synthesis

Ru/AC catalysts with K promoter were prepared by impregnation of the samples with different amounts of KOH. The catalysts were characterized using a variety of techniques, including X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, CO chemisorption and temperature-programmed desorption. The presence of K promoter had a limited effect on the size of Ru particles, but significantly enhanced the amount of adsorbed hydrogen, nitrogen and ammonia. A new desorption peak of nitrogen and ammonia at low temperature can be observed in their TPD profiles for Ru catalysts with K promoter. We propose that the presence of K promoter not only improved the adsorption properties of hydrogen, nitrogen and ammonia for Ru catalyst supported on activated carbon, but also weakened the adsorption strength of nitrogen and ammonia. The change in the chemisorptive properties of reactant gases including hydrogen, nitrogen and ammonia may be responsible for K promoter enhanced ammonia synthesis activity of Ru/AC catalyst, more than just the electronic properties of K promoter.

Effect of Platinum Incorporation on the Energetics and Oxygen Chemisorption Properties of the Ni(1 1 1) Surface

Pt makes it sustainable: Ni oxidation is an important cause of deactivation of Ni catalysts in Oxidative Steam reforming (OSR). Oxygen chemisorption is weakened on the Ni(1 1 1) surface after platinum substitution, which provides the sustainability of the Pt–Ni catalyst in OSR via preventing oxidation of Ni during the reaction

Hydrogen Chemisorption on Co(0001) Surface: A DFT Study

In this work the total energy calculations on the atomic geometry and chemisorption properties of Co(0001)/H surface are performed by using the density-functional theory in the approach of the projector-augmented wave (PAW) method. For a clean Co(0001) surface the atomic relaxations of the top three Co(0001) layers are obtained. The adsorptions of atomic Hydrogen have been investigated in the surface periodicities of p(1×1), p(1×2), p(2×2), and (  )R30º combined with hcp hollow and fcc hollow sites. For the cases studied in this work, the atomic hydrogen occupies fcc hollow site preferably drawn from the total energies. In these surface structures the perpendicular distances between the adsorbate and the first layer of substrate (DH-Co) range from 0.93 Å to 0.99 Å. The calculations on the surface vibrational modes proved the frequencies of atomic hydrogen along substrate surface displayed strong dependence on the adsorption geometries.

Structural, electronic and adsorption properties of V–Rh(111) subsurface alloy

V–Rh(111) bimetallic systems were prepared by deposition of 0.4 and 2.5ML of vanadium on Rh(111) surface at 823K and by annealing up to 1023K. Subsurface alloys of similar composition and electronic structure were formed. On the latter one, (2×2) surface reconstruction was observed. Electronic structure of the V–Rh(111) subsurface alloys was studied by photoelectron spectroscopy utilizing synchrotron radiation. Atomic structure was studied by means of LEED and X-ray photoelectron diffraction. Chemisorption properties were probed by CO and O2 adsorption. The topmost atomic layer with (2×2) reconstruction consisted exclusively of Rh atoms. The obtained results indicate formation of alloy with Rh3V composition and L12-type structure. Changes observed in the electronic structure were correlated with lower reactivity towards CO adsorption. The photoemission data indicate that the CO saturation coverage at 300K is reduced to less than half on the alloy surface as compared to clean Rh(111). Oxygen adsorbed on the alloy surface strongly interacted with the subsurface vanadium and induced formation of a surface vanadium oxide.

Geometry, Orbital Interaction, and Oxygen Chemisorption Properties of Chromium-Doped Nickel Clusters

Density functional theory (DFT) for generalized gradient approximation calculations has been applied to study the stability and orbital structures of Ni and Cr-doped nickel clusters varying in the range 2 ≤ n ≤ 13. Moreover, chemisorption of the oxygen atom has also been studied to understand the oxygen reactivity on Ni and Cr-doped nickel clusters. The binding energy per atom gradually increases with the increase of number of atoms for pure nickel and Cr-doped nickel clusters. The icosahedral Ni12Cr cluster is the most stable structure with binding energy of 2.87 eV per atom. This calculation noticed that the chromium atom prefers to exhibit center at the cluster (n ≥ 10) rather than edge. Furthermore, cluster stability has been gradually decreased with the increase of chromium concentration. Icosahedron structures containing more than four chromium atoms are less stable than the Ni13 cluster. Metal atom 3d orbitals have a strong influence on the overall structure stability of these clusters. The interac...

Theory of orthogonal interactions of CO molecules on a one-dimensional substrate

A minimal model based on density-functional theory is proposed and solved to explain the unusual chemisorption properties of carbon-monooxide (CO) molecules on Cu(110)-(2 $\ifmmode\times\else\texttimes\fi{}$ 1)-O quasi-one-dimensional (1D) surface reported in Feng et al. [ACS Nano 5, 8877 (2011)]. The striking features of CO adsorption include (1) the strong lifting of the host Cu atom by 1 \AA{}, and (2) the highly anisotropic CO-CO interaction leading to self-assembly into a nanograting structure. Our model implies that the 1D nature of the surface band is the key to these two features. We illustrate how formation of a chemical bond through specific orbital interactions between an adsorbate and 1D dispersive states of the substrate can impact the surface geometrical and electronic structure.

Chemisorption properties of calcium hydrogen phosphate with respect to Cu(II) and Zn(II) ions in mono- and bicomponent solutions

Chemisorption properties of calcium hydrogen phosphate dihydrate CaHPO4·2H2O with respect to Cu(II) and Zn(II) ions in Me(NO3)2 mono- and bicomponent solutions were considered.

Model oxide-supported metal catalysts – comparison of ultrahigh vacuum and solution based preparation of Pd nanoparticles on a single-crystalline oxide substrate

Using single-crystalline Fe(3)O(4)(111) films grown over Pt(111) in UHV as a model-support, we have characterized the nucleation behaviour and chemical properties of Pd particles grown over the film using different deposition techniques with scanning tunnelling microscopy and X-ray photoelectron spectroscopy. Comparison of Pd/Fe(3)O(4) samples created via Pd evaporation under UHV conditions and those resulting from the solution deposition of Pd-hydroxo complexes reveals that changes in the interfacial functionalization of such samples (i.e. roughening and hydroxylation) govern the differences in Pd nucleation behavior observed over pristine oxides relative to those exposed to alkaline solutions. Furthermore, it appears that other differences in the nature of the Pd precursor state (i.e. gas-phase Pd in UHV vs. [Pd(OH)(2)](n) aqueous complexes) play a negligible role in Pd nucleation and growth behaviour at elevated temperatures in UHV, suggesting facile decomposition of the Pd complexes deposited from the liquid phase. Applying temperature programmed desorption and infrared spectroscopy to probe the CO chemisorption properties of such samples after reduction in different reagents (CO, H(2)) shows the formation of bimetallic PdFe alloys following reduction in H(2), but monometallic Pd particles after CO reduction.