Search results for "Chemisorption"
showing 10 items of 53 documents
Pd-Cu catalysts supported on anion exchange resin for the simultaneous catalytic reduction of nitrate ions and reductive dehalogenation of organochlo…
2019
International audience; The present work proposes the simultaneous removal of these classes of pollutants by a catalytic hydrotreatment processes. For this purpose, bimetallic Pd-Cu catalysts (with mass ratio Pd:Cu of 4:1) supported on macroporous strong base anion resin were prepared by different methods. The catalysts were characterized (by XRD, SEMEDX, XPS, AAS and H-2 chemisorption) and tested in a continuous flow system. The selected catalyst preparation protocol consists in a two-step method, which implies the deposition of palladium by ion exchange and the subsequent deposition of copper by controlled reaction on the surface of the pre-reduced palladium. The effectiveness of the cata…
Lithium adsorption at prismatic graphite surfaces enhances interlayer cohesion
2013
Abstract We use density functional calculations to determine the binding sites and binding energies of Li + at graphene edges and prismatic graphite surfaces. Binding is favorable at bare and carbonyl terminated surfaces, but not favorable at hydrogen terminated surfaces. These findings have implications for the exfoliation of graphitic anodes in lithium-ion batteries that happens if solute and solvent co-intercalate. First, specific adsorption facilitates desolvation of Li + . Second, chemisorption lowers the surface energy by about 1 J m −2 prismatic surface area, and gives graphite additional stability against exfoliation. The results offer an explanation for experiments that consistentl…
Effect of Pre-Reduction on the Properties and the Catalytic Activity of Pd/Carbon Catalysts: A Comparison with Pd/Al2O3
2013
The effect of pre-reduction in solution with chemical reagents on the catalytic performance and catalyst properties of Pd/carbon catalysts was systematically investigated with a multitechnique approach. The results are critically discussed in comparison to those recently obtained on analogous Pd/alumina catalysts. It was proved that the Pd phase on the carbon surface is characterized by a high mobility, opposite to what occurs on alumina. As a result, the Pd particles on carbon aggregate together during pre-reduction, with a consequent decrease in available metal surface. Pd particles remain aggregated also in reaction conditions; the decreased Pd dispersion negatively affects the catalyst …
Thermo-, piezo-, photo- and chemo-switchable spin crossover iron(II)-metallocyanate based coordination polymers
2011
Abstract The design of coordination polymers (CPs) with switch and memory functions is an important subject of current interest in the search for new advanced materials with potential applications. Implementation of CPs with electronically labile iron(II) building blocks able to undergo cooperative spin crossover (SCO) behavior is a singular approach to this end. This review provides an up to date survey of a new generation of iron(II)-metallocyanate based spin crossover coordination polymers (SCO-CPs) developed during the last decade. These new solids feature structural diversity, supramolecular isomerism, interpenetrating frameworks, structure flexibility, reversible solid-state chemical …
Fabrication of Single Cylindrical Au-Coated Nanopores with Non-Homogeneous Fixed Charge Distribution Exhibiting High Current Rectifications
2014
We have designed and characterized a cylindrical nanopore that exhibits high electrochemical current rectification ratios at low and intermediate electrolyte concentrations. For this purpose, the track-etched single cylindrical nanopore in polymer membrane is coated with a gold (Au) layer via electroless plating technique. Then, a non-homogeneous fixed charge distribution inside the Au-coated nanopore is obtained by incorporating thiol-terminated uncharged poly(N-isopropylacrylamide) (PNIPAM) chains in series to poly(4-vinyl pyridine) (PVP) chains, which are positively charged at acidic pH values. The functionalization reaction is checked by measuring the current–voltage (I–V) curves prior …
Chemical modification of Topaz surfaces
1999
In chemisorption, one is typically faced with the problem that the two-dimensional structure of the organic layer does not match the structure of the inorganic substrate. This work describes the first steps toward an induced epitaxial correlation of organic compounds on an inorganic surface. The idea of this work was to use a single crystal with a two-dimensional surface structure, Topaz (001), that matches an alkyl chain lattice better than existing substrates. X-ray reflectivity and FTIR experiments prove the surface modification of the Topaz, which is probably an etherification of the reactive OH-groups on the Topaz (001) surface.
Multilayer build-up of a reactive polymer with α,ω-functionalized chromophores
1997
Alternating multilayers with up to ten layers have been prepared by sequential reaction of a reactive polymer (poly[(1-methylvinyl isocyanate)-alt-(maleic anhydride)]) with α,ω-functionalized chromophores. For this purpose new chromophores were synthesized varying the length of the hydrophobic spacer. The analysis of the multilayer build-up shows that physisorption is more important than chemisorption for fixation of new polymer layers. Thus, a multilayer build-up is only possible with the shorter, more hydrophilic chromophore and not with the long hydrophobic spacer.
Defects and Reactivity at Oxide Surfaces: Experimental Aspects of the Interaction of Hydrogen, Co And Co2 with the Nio{001} Surface
1989
This paper summarizes some previous or more recent experimental results on chemical interaction, at moderate temperatures, of H, H2, CO and CO2 with the surfaces of nickel oxide, mainly the NiO {001} surface. These results are in a general agreement with theoretical predictions. Nearly perfect surfaces of maximal valency oxides cannot react with molecules. Dissociation of molecules is often required for chemisorption. Conversely, chemical reaction is usually observed either when molecules are predissociated or the surface has defects with an energy level high enough to enable both dissociation and chemisorption. On a nearly perfect, “in situ” cleaved, NiO {001} surface, partially atomized h…
Decomposition of nitrous oxide upon nickel oxide-magnesium oxide solid solutions
1966
The decomposition of N 2 O has been studied over MgO catalysts, doped with NiO and NiO + Li 2 O from 1 to 10% (atomic). For pure MgO, activity is low, but is enhanced by addition of Ni 2+ ions. The apparent activation energy is reduced from 35 kcal/mole for pure MgO, to about 18 kcal/mole. Oxygen acts as a poison, and it is chemisorbed on the catalyst. The presence of lithium greatly increases the apparent activation energy. The results are interpreted in terms of oxygen chemisorption and of its influence on the course of the reaction.
Study by static SIMS, XPS and UPS of the adsorption of cyanogen on (100) Ni surfaces
2000
Abstract The interaction of cyanogen with (100) Ni surfaces at room temperature was studied using secondary ion mass spectrometry in a static mode, and photoemission spectroscopies (XPS and UPS). It has been shown that cyanogen is adsorbed on this nickel surface in a dissociative mode: atomic carbon and nitrogen are present on the surface as well as CN fragments. These adsorbed species have been characterized by XPS and UPS. Increasing the temperature in the 400 K range increases the rate of the dissociation reaction of CN into atomic carbon and nitrogen. Moreover carbon is found to dissolved into the bulk for temperatures as low as 475 K. No evidence has been found of a polymerized form of…