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1.
The adsorption of H2 and D2 on a Rh (110) surface at 100 K leads to a sequence of ordered phases, among others 1×2 phases at
H
=0.5 and at
H
=1.5 which likely involve a partial surface reconstruction consisting of a small perpendicular displacement of Rh surface atoms. The structure of the adsorbate phases is strongly correlated with the binding energy of the adsorbed phases. Three H (D) binding states (1,2 and) are populated at saturation as determined by thermal desorption spectroscopy (TDS). Whereas the peak temperature of the state is invariant with the hydrogen isotope, the D 1 state appears at a 8 Klower and theD 2 state at a 5 Khigher temperature than the respective H states. Generally the D phases exhibit a better long-range order than the H phases. The rate of adsorption is identical for the first three adsorbed phases but D2 adsorbs appreciably faster in the 1×2–3H and the final l×1–2H phases.Zero point energy effects as well as a H coverage dependent local interaction model could account for the observed effects. 相似文献
2.
S.B. Lyubchik L.P. Tikhonova O.L. Galushko I.M. Fonseca 《Applied Surface Science》2006,252(17):6084-6088
Selective adsorption of platinum group metals (PMG) on activated carbons from a multi-component model and technological solutions was proposed for the preparation of heterogeneous-supported catalysts. Activated natural anthracites and a nitrogen-containing synthetic carbon are considered as carriers for Pd-supported catalysts. Their catalytic activity was studied in the Pd-catalyzed reactions of hydrogen peroxide decomposition and chloride ions oxidation by manganese(III). On the base of the obtained results, novel high sensitive analytical methods both for direct determination of supported-metal quantity and palladium oxidation states on the surface of spent adsorbents are suggested. 相似文献
3.
The acid-base properties of native zinc oxide surfaces have been studied using X-ray photoelectron spectroscopy (XPS). The native layers of zinc oxide have been obtained by ageing mechanically polished pure zinc disks in a glass dryer for 1 month. Such a treatment lead to the formation of an unstable oxide layer and dehydroxylation has been observed during storage in vacuum. By following adsorption in ultrahigh vacuum of 1,2-diaminoethane (DAE) several types of active sites have been evidenced. Zinc cations react with the probe molecule following a Lewis acid/base interaction, while the hydroxyl and the carbonate-like species react following a Brønsted acid/base reaction. Although initial interaction via the Brønsted-like mechanisms is favoured, it has been shown that the resulting complexes are not stable. Under vacuum conditions, the adsorbed DAE molecules either partly desorb or modify their interaction mode with the surface to form additional Lewis-like bonded stable complexes. In addition, a cleaning effect of the molecule has been observed which lead to partial removal of the carbonate-like contamination. 相似文献
4.
Diffusion and desorption of platinum on the tungsten micro-crystal in the form of the W(1 1 1) oriented emitter tip has been studied using the field electron microscopy (FEM) technique. Diffusion of small dose of platinum (average thickness about 0.18 geometrical ML after spreading) on the thermally clean W emitter tip was studied at temperatures 648-742 K. Average activation energy for diffusion Ediff was found to lie between 1.16 ± 0.08 eVand 1.30 ± 0.16 eV. During annealing at the diffusion temperatures Pt-induced faceting of the emitter surface was visible in the neighbourhood of the {1 1 1} pole. The layer equilibrated in the diffusion process was stable at temperatures up to 1100 K where reduction of the high voltage at a fixed emission current, characteristic of alloying of Pt with W, was detected. Submonolayer of platinum (ΘPt = 0.18 ML) started to desorb at tip temperature ≥1780 K. The measurements of average activation energy for desorption of ‘zero coverage’ Pt (0.03 ML ≤ ΘPt ≤ 0.06 ML) from the entire W emitter surface were carried out at temperatures 1990-2170 K and yield the value of Edes = 5.19 ± 0.22 eV to 5.33 ± 0.19 eV. The results are compared with data for diffusion of individual Pt atoms and small clusters and with data for adsorption of Pt atoms on a planar W(1 1 0) surface. In discussion the atomic surface structure of the substrate, modified by the strong interaction of Pt with the W micro-crystal, is also taken into account. 相似文献
5.
J. Harris 《Applied Physics A: Materials Science & Processing》1988,47(1):63-71
Recent technological developments have made possible measurements of the distribution of internal levels of molecules desorbing from a hot surface. Such measurements provide new information concerning the desorption process and the potential energy surface (PES) that governs it. Associative, or re-combinative desorption is of particular interest because the distributions of internal levels reflect the manner in which the molecular bond is formed as the desorbing species leaves the surface. As the simplest associative desorption systems, H2 and D2 adsorbing on and desorbing from metal surfaces deserve special attention and serve as prototypes for systems with a more complex chemistry. In this note I review briefly from the theoretical point of view some features of the interaction of H2 with metals and their relevance to associative adsorption and dissociative sticking. 相似文献
6.
The thermal evolution of deuterium from thin titanium films, prepared under UHV conditions and deuterated in situ at room temperature, has been studied by means of thermal desorption mass spectrometry (TDMS) and a combination of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The observed Ti film thickness dependent morphology was found to play a crucial role in the titanium deuteride (TiDy) film formation and its decomposition at elevated temperatures. TDMS heating induced decomposition of fine-grained thin Ti films, of 10-20 nm thickness, proceeds at low temperature (maximum peak temperature Tm about 500 K) and its kinetics is dominated by a low energy desorption (ED = 0.61 eV) of deuterium from surface and subsurface areas of the Ti film. The origin of this process is discussed as an intermediate decomposition state towards recombinative desorption of molecular deuterium. The TiDy bulk phase decomposition becomes dominant in the kinetics of deuterium evolution from thicker TiDy films. The dominant TDMS peak at approx. Tm = 670 K, attributed to this process, is characterized by ED = 1.49 eV. 相似文献
7.
A detailed study of the La1−xCaxCoO3 perovskites surface by XPS was carried out since this is a potentially useful tool to identify the oxygen species involved in the catalytic reaction and discriminate them. Mainly, the concentration of surface oxygen vacancies (λ′) can be estimated from the XPS atomic ratio. 相似文献
8.
J. Deleplanque 《Applied Surface Science》2009,255(9):4897-4901
Trimethylphosphine (TMP) has been used as an NMR probe in order to determine the acidity of Keggin-type 12-tungstophosphoric heteropolyacid (HPW), pure and supported on silica, dehydrated at 473 K. Adsorption of TMP on pure dehydrated HPW leads to the formation of trimethylphosphonium ions (TMPH+) characteristic of the presence of strong Brönsted acid sites. TMP replaces the water molecules lost by dryness and allows the Keggin secondary structure to recover.Silica interacts with TMP by two kinds of acid sites: with weak acid support sites through the isolated silanol groups and with strong Brönsted acid, which lead to the formation of TMPH+, through the hydrogen-bonded silanol groups. Silica only interacts with HPW through its isolated silanol groups. 相似文献
9.
10.
Adolf Winkler 《Applied Surface Science》2009,256(4):1114-1119
The interaction of hydrogen (deuterium) with different modified Pd(1 1 1) surfaces has been investigated. The focus was put on the energy and angel dependence of the desorbing molecules from oxygen covered, potassium covered and vanadium oxide covered surfaces. Conventional adsorption/desorption as well as permeation/desorption experiments were performed. For the oxygen covered surface optimum reaction rates for water production and the energy distribution of the reaction products were determined, both for the reaction of oxygen with molecular hydrogen as well as with atomic hydrogen. Potassium on the surface enhances the activation barrier for hydrogen adsorption resulting in a hyper-thermal desorption flux and a forward focused angular distribution of desorption. Permeation/desorption of deuterium from ultra-thin vanadium oxide films yield mainly thermalized desorbing molecules or slightly hyper-thermal, depending on the oxidation state of the surface oxide. 相似文献
11.
Porous mixtures of aluminosilicate/calcium phosphate have been studied for biomaterials applications. Aluminosilicates formed with an inorganic polymeric constitution present amorphous zeolites because of their 3D network structure and present the ability to link to bone matrix. Amorphous geopolymers of the potassium-poly(sialate)-nanopolymer type were synthesised at low temperature and studied for their use as potential biomaterials. They were mixed with 13% weight of calcium phosphate like biphasic hydroxyapatite and β-tricalcium phosphate. In this study, “in vivo” experiments were monitored to evaluate the biocompatibility, the surface and the interface behaviour of these composites when used as bone implants. Moreover, it has been demonstrated using histological and physicochemical studies that the developed materials exhibited a remarkable bone bonding when implanted in a rabbit's thighbone for a period of 1 month. The easy synthesis conditions (low temperature) of this composite and the fast intimate links with bone constitute an improvement of synthetic bone graft biomaterial. 相似文献
12.
D. Mercier 《Applied Surface Science》2008,254(20):6495-6503
Interaction of propylamine (PA), 1,2-diaminoethane (DAE) or 3-aminomethyl-3,5,5-trimethylcyclohexylamine (isophorone diamine, IPDA) with native aluminium oxide layers in non-aqueous environment has been studied using time-resolved inductively coupled plasma optical emission spectroscopy (ICP-OES) and X-ray photoelectron spectroscopy (XPS). The formation of several surface complexes has been evidenced. Monodentate and bidentate metal-bond surface complexes (MBSC) result from interactions between the amine terminations of the molecule and aluminium cations by donation of the N lone electron pair to the metal ion (Lewis-like mechanism leading to OAl?N bonds). Monodentate and bidentate hydrogen-bond surface complexes (HBSC) are due to interaction of the amino group with surface hydroxyl groups by protonation of the amine termination (Brønsted-like mechanism leading to the formation of AlOH?N bonds) or interaction with carbonaceous contamination (CxOyHz?N bonds). Diamines can also form mixed complexes with one amino group forming an O-Al?N bond and the other group forming an AlOH…N or CxOyHz?N bond. AlOH?N and CxOyHz…N bonds are less stable under vacuum than OAl?N bonds, leading to partial desorption of the DAE molecules in vacuum and modification of the interaction modes. Only DAE and IPDA can lead to partial dissolution of the aluminium native (hydr)oxide films. A detailed mechanism of dissolution has been proposed based on the formation of mononuclear bidentate (chelate) MBSC by ligand exchange between the terminal η1-OH and bridged μ2-OH surface sites and the amino terminations of the molecule. The detachment of this complex from the surface is likely to be the precursor step to the formation of the interphase in epoxy-amine/metal systems. 相似文献
13.
Wincenty Turek Mieczyslaw Lapkowski Agnieszka Stolarczyk 《Applied Surface Science》2005,252(3):801-806
The goal of our studies was to determine the nature of interactions between catalytic active samples, such as polypyrrole (PPy) doped with: chloride anions, heteropolyacids such as H5PMo10V2O40, or H4SiW12O40, and oxygen particles. In order to reveal the mechanism of the linkage between the catalysts and oxygen we provided the electron paramagnetic resonance (EPR) measurements of synthesized samples in O2 and N2 flow. Moreover, the X-ray photoelectron spectroscopy (XPS) measurements were performed to show the properties of doped heteropolyacids and the state of nitrogen in polypyrrole matrix. The results of EPR studies of PPy(Cl), PPy(H4SiW12O40), PPy(H5PMo10V2O40) samples, show that the polypyrrole doped with chloride anions interacts much easier with oxygen than polypyrrole doped with heteropolyacids (in the above given order, of preference with the most active polypyrrole system first). It correlates with XPS results, which show that a molybdenium-vanadium anion is more reduced than a silicon-tungsten one. The redox reactions of heteropolyacids involve the oxidation-reduction of the conjugated polymer chain, leaving no or little place for interactions with oxygen. Polypyrrole doped with H4SiW12O40 shows some oxygen sensitivity as observed in the EPR studies, as opposed to polypyrrole doped with H5PMo10V2O40, which is in line with the XPS results. 相似文献
14.
Attenuated total reflection infrared spectroscopy (ATR-FT-IR) is employed to study the H/D-exchange of planar hydroxylated silica during ND3 and D2 dosing, and catalyzed by Rh nanoparticles. For ND3 dosing, it is observed that the H/D-exchange is about 10 times more efficient in the presence of Rh nanoparticles on the hydroxylated silica than for bare hydroxylated silica. When the Rh adsorption sites are blocked by CO, the H/D-exchange is similar to the case without Rh nanoparticles. No H/D-exchange is observed for exposure to D2 regardless of the presence of Rh nanoparticles. Hydrogen spillover, involving the decomposition of D2 on the Rh and subsequent transfer of atomic D to the oxide support, therefore does not explain the observed effects. Alternatively, we conjecture that for ND3, the exchange is through a mechanism in which ND3 adsorption on the edge of the Rh particles takes place, followed by direct H/D exchange with the hydroxyls of the support. This exchange is possibly aided by the formation of ammonium complexes with the help of hydrogen from the hydroxyls. 相似文献
15.
J. Aguado-Serrano R.M. Martín-Aranda V. Gómez-Serrano 《Applied Surface Science》2006,252(17):6075-6079
The sol-gel method has been applied for the synthesis of a series of acid metal-carbon xerogels (with M = V, Cr, Mo and Ni) by polymerisation of resorcinol with formaldehyde in the presence of metallic precursors. A blank sample was also prepared without any metal addition. The xerogels were heated in nitrogen at 1000 °C to obtain the pyrolysed products. The samples were characterised by different techniques such as thermal-mass spectrometry analysis, gas physisorption, and mercury porosimetry. In addition, the acid character of the pyrolysed products was tested by the Claisen-Schmidt condensation between benzaldehyde and acetophenone for the formation of chalcones. 相似文献
16.
E. Dietrich A. Lucas-Girot Y. Le Gal S. Jeanne G. Cathelineau 《Applied Surface Science》2008,255(2):391-395
Bioactive glasses in the system SiO2-CaO-Na2O-P2O5 were synthesized pure and doped with magnesium or zinc by melt-derived method. The bioactivity was studied during in vitro assays: the ability of hydroxycarbonate apatite (HCA) layer to form on the glass surface was examined after contact with simulated body fluid (SBF). The X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) studies were performed before and after immersion in vitro assays. The SBF solutions were also analyzed using inductively coupled plasma-optical emission spectroscopy (ICP-OES).Introduction of magnesium and zinc as trace element induces several modifications on the observed phenomena at the glass surface and in SBF solution after immersion of the samples. The chemical durability of the glasses, the formation of the silica-rich layer and the crystallization of the HCA layer were affected, but not present the same modifications as the introduced doping element. 相似文献
17.
《Applied physics. B, Lasers and optics》1977,14(1):79-87
Results on the isotope effect for total and ionic desorption cross sections in the electron impact desorption of various binding
states of CO on the (110) plane of tungsten, and of oxygen on this plane are presented and discussed. It is shown that the
observations allow a dissection of cross sections into excitation cross sections and escape probabilities, and that the latter
can be used to estimate lifetimes of excited or ionic states. It is found that excitation cross sections for total desorption
are of the order of 10−16–10−17 cm2, but seem to be significantly smaller in some cases for excitation to ionic states, suggesting that different excitations
are involved. In all cases examined here the isotope effect for total desorption is much smaller than for ion production.
This can be explained by the fact that ion lifetimes are somewhat shorter than those of excited neutrals. Lifetimes are estimated,
in the cases examined, to be of the order of 10−14s. 相似文献
18.
Rinaldo S. Araújo Débora A.S. Maia Diana C.S. Azevedo Célio L. Cavalcante Jr. E. Rodríguez-Castellón A. Jimenez-Lopez 《Applied Surface Science》2009,255(12):6205-6209
The surface acidity of mesoporous molecular sieves of aluminum and titanium was evaluated using four different techniques: n-butylamine volumetry, cyclohexylamine thermodesorption, temperature-programmed desorption of ammonia and adsorption of pyridine. The nature, strength and concentration of the acid sites were determined and correlated to the results of a probe reaction of anthracene oxidation to 9,10-anthraquinone (in liquid phase). In general, the surface acidity was highly influenced by the nature, location and coordination of the metal species (Al and Ti) in the mesoporous samples. Moderate to strong Brönsted acid sites were identified for the Al-MCM-41 sample in a large temperature range. For mesoporous materials containing Ti, the acidity was represented by a combination of weak to moderate Brönsted and Lewis acid sites. The Ti-HMS sample exhibits a higher acidity of moderate strength together with a well-balanced concentration of Brönsted and Lewis acid sites, which enhanced both conversion and selectivity in the oxidation reaction of anthracene. 相似文献
19.
Mikhail V. Lebedev 《Applied Surface Science》2008,254(24):8016-8022
These studies are focused on understanding the role played by a solvent in chemical and electronic processes occurred in the course of semiconductor surface passivation at semiconductor/electrolyte interface. It is shown that the chemical reactivity of the ionic adsorbate at a semiconductor/electrolyte interface can be changed considerably through interaction with solvent molecules. The reactivity of anions depends essentially on the solvating solvent: hydrated ions could be either slightly electrophilic or slightly nucleophilic, whereas the ions solvated by alcohol molecules are always strongly nucleophilic. Mechanism of interaction of such solvated ions with the semiconductor surface atoms depends on the solvent, as is demonstrated by the example of processes occurred at GaAs(1 0 0)/sulfide solution interfaces. It is found that on adsorption of HS− ions from different solvents the AsS bonds with solvent-dependent ionic character are formed on a GaAs(1 0 0) surface. The surface obtained in such a way possesses different ionization energy and exhibit different electronic properties dependent on the solvent. 相似文献
20.
Recently, the feasibility of butane oxidation in an electrochemical membrane reactor (EMR) using a vanadium phosphorus oxide (VPO) catalyst layer on a tubular anodic electrode has been reported. This novel application of EMR gives rise to questions about the vanadium oxidation state (Vox) under working conditions and about its spatial distribution in the catalyst layer. It has now been determined by means of position-resolved XPS measurements. In addition, model calculations on the spatial Vox distribution have been performed for the first time. The simulations reveal a non-uniform 3D distribution of Vox due to the relative rate of reduction and re-oxidation processes in the catalyst layer, in good agreement with the experimental XPS data. 相似文献