The adsorption and decomposition of ethylene on Ni(100)

The adsorption behavior of ethylene on Ni(100) at a variety of temperatures has been studied using temperature programmed desorption, and X-ray and UV photoemission. The adsorption of ethylene at 98 K results in molecular adsorption with a saturation C/Ni ratio of 0.76. Heating this surface to any temperature between 213 and 683 K reduces the C/Ni ratio to 0.5. Exposure to ethylene at 300 K leads to decomposition producing surface carbide, adsorbed hydrogen atoms and an adsorbed C_xH_2x species. A comparison with other work on Ni(111) indicates that ethylene adsorption processes are structure sensitive.     

Vibrational studies of the solid imidazole and pyridine adducts of metal(II) saccharinates I. The OH/OD and NH/ND stretching regions of the cobalt(II) and nickel(II) complexes

FT-IR spectra of both protiated and deuterated analogues of the complexes [M(HIm)₄(H₂O)₂](sac)₂ and [M(H₂O)₄(py)₂](sac)₂·4H₂O (M=Co, Ni) in the region of the water stretching modes, at room temperature down to the liquid-nitrogen boiling temperature, are recorded and discussed. The regions of the NH/ND stretchings in the spectra of the imidazole saccharinates are also studied. The appearance of the bands that are mainly due to the OH, OD, NH and ND stretchings is discussed in connection with the crystallographic data. The appearance of the NH stretching region in the spectra of the studied imidazole adducts is partly explained as a result of Evans-type Fermi resonance of the NH stretchings with non-fundamental modes. In spite of the existence of single type of asymmetrically bonded water molecules in the structures of the studied imidazole complexes, an unexpected ratio 1:2 of the integral intensities of the two isotopically isolated ν(OD) stretchings in their spectra was found.     

In Situ and Theoretical Studies for the Dissociation of Water on an Active Ni/CeO2 Catalyst: Importance of Strong Metal–Support Interactions for the Cleavage of O–H Bonds

Water dissociation is crucial in many catalytic reactions on oxide‐supported transition‐metal catalysts. Supported by experimental and density‐functional theory results, the effect of the support on O? H bond cleavage activity is elucidated for nickel/ceria systems. Ambient‐pressure O 1s photoemission spectra at low Ni loadings on CeO₂(111) reveal a substantially larger amount of OH groups as compared to the bare support. Computed activation energy barriers for water dissociation show an enhanced reactivity of Ni adatoms on CeO₂(111) compared with pyramidal Ni₄ particles with one Ni atom not in contact with the support, and extended Ni(111) surfaces. At the origin of this support effect is the ability of ceria to stabilize oxidized Ni²⁺ species by accommodating electrons in localized f‐states. The fast dissociation of water on Ni/CeO₂ has a dramatic effect on the activity and stability of this system as a catalyst for the water‐gas shift and ethanol steam reforming reactions.     

The Adsorption and Thermal Decomposition of CH2CO (CD2CO) on Si(111)-7 × 7

The adsorption and thermal decomposition of ketene on Si(l 11)-7 × 7 were investigated using various surface analysis techniques. When the surface was exposed to ketene at 120 K, two CO stretching modes at 220 and 273 meV appeared in HREELS, corresponding to two adsorbed ketene states. After the sample was annealed at ?250 K, the 273 and the 80 meV peaks vanished, indicating the disappearance of one of the adsorption states by partial desorption of the adsorbate. In a corresponding TPD measurement, a desorption peak for ketene species was noted at 220 K. Annealing the sample at 450 K caused the decomposition of the adsorbate, producing CH_x and O adspecies. Further annealing of the surface at higher temperatures resulted in the breaking of the CH bond, the desorption of H and O species and the formation of Si carbide. The desorption of H at 800 K was confirmed by the appearance of the D₂ (m/e = 4) TPD peak at that temperature when CD₂CO was used instead of CH₂CO.     

Energetics and mechanism for hydroxyl radical production from the Pt-catalyzed decomposition of water

The catalytic decomposition of H₂O over a polycrystalline platinum surface has been studied in a low pressure flow system. Hydroxyl radicals were detected in gaseous decomposition products above about 820 K by laser-induced fluorescence at 300 nm. The activation energy for the HO desorption process, HO* → HO(g)+*, was determined to be 30 ± 1 kcal/mol, which is in excellent agreement with the values reported previously for the Pt-catalyzed oxidation of H₂ by O₂ and N₂O. The effects of added H₂, D₂ and O₂ on HO formation were also investigated and the observed data can be satisfactorily accounted for by a mechanism which involves chemically adsorbed H, O and HO species. A similar but brief experiment was carried out for the catalytic decomposition of NH₃ over the same catalyst. However, no NH or NH₂ radicals were detected in gaseous decomposition products up to 1100 K.     

Interaction of water with clean and oxygen precovered nickel surfaces

The adsorption of water on a Ni(111) single crystal surface, clean as well as precovered with oxygen, has been investigated with thermal desorption spectroscopy (TDS) and measurements of the adsorption-desorption equilibrium combined with XPS (X-ray photoelectron spectroscopy). The measurements have been carried out with water pressures up to 10^–5 mbar on surfaces, which have been either clean or precovered with oxygen. On the clean Ni(111) surface the first adsorbate layer with a maximum coverage of 0.42 ML (monolayers) has a desorption energy of 52 kJ/mol and a preexponential factor of desorption of 10¹⁶s^–1. A second water layer adsorbs with the desorption energy of the ice multilayer but with first order kinetics. On Ni(111) precovered with chemisorbed oxygen an additional state of molecular, more strongly bound water is found, but no dissociation. For higher oxygen precoverages where NiO islands are formed on the surface, also the water dissociation product OH is found adsorbed. On a sample covered with a closed NiO layer, adsorbed OH and molecular water in an energetically not well-defined state are found. High doses of water on oxygen-precovered Ni(111) induce a slow surface modification leading to water dissociation.     

Mechanisms for H2O decomposition on the Si(111)‐7 × 7 surface: A DFT cluster model study

The mechanisms for the complete decomposition of water molecules on the Si (111)‐7 × 7 surface were investigated theoretically. The reaction pathways for dissociation of four water molecules over the adatom and rest atom sites were calculated using the density functional theory (DFT) in conjunction with the B3LYP functional. The calculated results demonstrated that the initial O? H bond dissociation from the first H₂O to form the adsorbed OH species is more preferential on the adatom site (Si_a) than the rest atom site (Si_r) of Si (111)‐7 × 7. Four water molecules dissociate successively over the adatom site, backbonds of adatoms which are saturated by OH species can reasonably be the place of insertion of oxygen atoms, yielding a tetrahedral SiO₄ structure with one on top and three inserted oxygen atoms. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Preparation and photopatterning of Langmuir–Blodgett (LB) films of a novel copolymer containing swallow‐tailed double naphthalene groups

A new series of copolymer poly(N‐hexadecylmethacrylamide‐co‐dinaphthalen‐2‐yl 2‐allylmalonate) poly(HDMA‐co‐DNAM)s containing swallow‐tailed double naphthyl groups and long alkyl group were designed and synthesized. The behavior of copolymer molecular arranging on water surface, patterning properties of copolymer LB films, and photochemical reactions in ultrathin film were investigated. The poly(HDMA‐co‐DNAM)s could form a stable, well‐defined molecular orientation Langmuir monolayer at air/water interface. The polymer main chain was lying flat on water surface and the side chains attached to the main chain stretching out at the angle of about 50°. The results obtained showed that a well‐ordered layer‐by‐layer structure was successfully controlled in LB films, in which most of naphthyl groups in poly(HDMA‐co‐DNAM)s LB films were in dimer and the copolymer LB films were decomposed hardly upon irradiation of deep UV light. We found that the exposed and unexposed regions of the poly(HDMA‐co‐DNAM)s copolymer LB films had solubility differentiation in gold etchant, which is a mixed solution of I₂/NH₄I/C₂H₅OH/H₂O. Therefore, we could obtain gold photopattern with the maximal resolution of the employed mask without any development process. Copyright © 2011 John Wiley & Sons, Ltd.     

Electrochemical Quartz Crystal Impedance Study of Glucose Oxidation on a Nickel Hydroxide Modified Au Electrode in Alkaline Solution

The electrochemical quartz crystal impedance (EQCI) technique has been applied to investigate glucose oxidation on bare and Ni(OH)₂‐modified Au electrodes in 0.2 mol L^?1 KOH aqueous solution. The EQCI responses suggest different contributions of H⁺‐release and OH^?‐incorporation reactions of the Ni(OH)₂‐film redox process in 0.2 mol L^?1 aqueous KOH at different potentials. Glucose adsorption on the Ni(OH)₂‐modified Au electrode was studied. A mechanism for potential cyclic redox process of glucose at Ni(OH)₂‐modified Au electrode is suggested, mainly based on a comparative EQCI analysis with direct glucose oxidation on bare gold and glucose ad‐/desorption on Ni(OH)₂ film.     

Spectroscopic Monitoring of the Acidity of Water Films on Ru(0001): Orientation‐Specific Acidity of Adsorbed Water

We examined the acid–base properties of water films adsorbed onto a Ru(0001) substrate by using surface spectroscopic methods in vacuum environments. Ammonia adsorption experiments combined with low‐energy sputtering (LES), reactive ion scattering (RIS), reflection–absorption infrared spectroscopy (RAIRS) and temperature‐programmed desorption (TPD) measurements showed that the adsorbed water is acidic enough to transfer protons to ammonia. Only the water molecules in an intact water monolayer and water clusters larger than the hexamer exhibit such acidity, whereas small clusters, a thick ice film or a partially dissociated water monolayer that contains OH, H₂O and H species are not acidic. The observations indicate the orientation‐specific acidity of adsorbed water. The acidity stems from water molecules with H‐down adsorption geometry present in the monolayer. However, the dissociation of water into H and OH on the surface does not promote but rather suppresses the proton transfer to ammonia.     

Adsorption of water on sulfur dioxide pre‐exposed Zircaloy‐4 surfaces

We investigate the interaction of water (H₂O) with sulfur dioxide (SO₂) pre‐exposed Zircaloy‐4 (Zry‐4) surfaces. Adsorption of SO₂ shifts the Zr(MNN) Auger electron feature by 3.0 eV, whereas subsequent water adsorption attenuates the sulfur Auger signal and results in the development of a zirconium oxide, Zr(MNV)_o, feature. No further shift in the Zr(MNN) transition is observed with increasing H₂O exposures. Following higher H₂O exposures on SO₂‐saturated Zry‐4 surfaces, linear heating results in water desorption near 500 K. This temperature is more than 200 K lower than the desorption temperature of water from clean Zry‐4 surfaces. Copyright © 2006 John Wiley & Sons, Ltd.     

The influence of preadsorbed hydrogen and CO on adsorption of ethylene on the Pd(111) surface

The coadsorption of C₂H₄ with H₂ and CO on Pd(111) has been investigated at 300 and 330 K At 300 K two forms of adsorbed ethylene coexist on the surface in the presence of ethylene gas: a molecular form desorbing as C₂H₄ at 330 K and a dissociatively adsorbed form (giving only hydrogen in desorption spectra) which is stable both in vacuum and in hydrogen at 10^?8 Torr. The molecular form seems to be a precursor state for hydrogenation and for dissociative adsorption. Both processes are controlled by the amount of coadsorbed hydrogen which in turn is controlled by CO coverage.     

Retracted: Acid‐Catalyzed Aquation of Ni(II)‐Hydrazone Complexes: Kinetics and Solvent Effect

Complexes of the type [Ni(L)(H₂O)]Cl₂·nH₂O, where L = 2‐pyridyl‐3‐isatinbishydrazone ligands, have been synthesized and characterized on the bases of elemental analysis, molar conductance, IR, electronic spectra, and thermal analysis (TGA and DTA). Acid‐catalyzed aquation of the Ni(II) isatin‐bishydrazone complexes was followed spectrophotometrically in various water–methanol and water–acetone mixtures at temperature 298 K. Kinetic behavior of the acid aquation is a linear rate law, indicating that the acid‐catalyzed aquation of these complexes in water–methanol and water–acetone mixtures follows a rate law with k_obs = k₂[H⁺]. The effect of the mole fraction of the ganic solvent, i.e., methanol and acetone, on the acid aquation has been analyzed; the decrease in the rate constant values with increasing of the methanol or acetone ratios is attributable to the effect of the co‐organic solvent on the initial states of the acid aquation by the destabilization of the H⁺ ion.     

An infrared study of the stretching modes of the water molecules in ZnF2·4H2O

The IR spectra of ZnF₂·4H₂O and its deuterated analogues are reported at ambient and liquid-nitrogen temperatures. The OH and OD stretching and bending vibrations of the water molecules are analysed in detail. The two types of water molecules give rise to different absorption peaks in the OH and OD stretching regions in samples that contain isotopically dilute HDO groups. The strongly hydrogen-bonded water molecules H₂O(1) and H₂O(4) show four broad OH and OD stretching modes at lower frequencies, while the weaker hydrogen-bonded ones H₂O(2) and H₂O(3) give rise to four narrow bands at higher frequencies. The ν_OD frequencies of isotopically dilute HDO groups correlate very well with the known R(H---F) and R(H---O) distances in the crystals and the assignment of these modes was done on this basis. It was also found that the ratio ν_OH/ν_OD decreases with decreasing values of R(H---O) or R(H---F) in ZnF₂·4H₂O.     

Poly[[di‐μ2‐aqua‐di‐μ5‐croconato(2–)‐nickel(II)dipotassium(I)] tetra­hydrate]

In the title compound, {[K₂Ni(C₅O₅)₂(H₂O)₂]·4H₂O}_n, the Ni atom lies on an inversion centre. Two inversion‐related croconate [4,5‐dihydroxy‐4‐cyclo­pentene‐1,2,3‐trionate(2−)] ligands and an Ni^II ion form a near‐planar symmetrical [Ni(C₅O₅)₂]²⁻ moiety. The near‐square coordination centre of the moiety is then extended to an octa­hedral core by vertically bonding two water mol­ecules in the [Ni(C₅O₅)₂(H₂O)₂]²⁻ coordination anion. The crystal structure is characterized by a three‐dimensional network, involving strong K⋯O⋯K binding, K⋯O—Ni binding and hydrogen bonding.     

Reaction heat-driven CO2 desorption during CO oxidation on Au(997) at low temperatures

Adsorption and reaction of CO and CO₂ were studied on oxygen-covered Au(997) surfaces by means of temperatureprogrammed desorption/reaction spectroscopy. Oxygen atoms (O(a)) on Au(997) enhances the CO₂ adsorption and stabilizes the adsorbed CO₂(a), and the stabilization effect also depends on the CO₂(a) coverage and involved Au sites. CO₂(a) desorption is the rate-limiting step for the CO+O(a) reaction to produce CO₂ on Au(997) at 105 K and exhibits complex behaviors, including the desorption of CO₂(a) upon CO exposures at 105 K and the desorption of O(a)-stabilized CO₂(a) at elevated temperatures. The desorption of CO₂(a) from the surface upon CO exposures at 105 K to produce gaseous CO₂ depends on the surface reaction extent and involves the reaction heat-driven CO₂(a) desorption channel. CO+O(a) reaction proceeds more easily with weakly-bound oxygen adatoms at the (111) terraces than strongly-bound oxygen adatoms at the (111) steps. These results reveal complex rate-limiting CO₂(a) desorption behaviors during CO+O(a) reaction on Au surfaces at low temperatures which provide novel information on the fundamental understanding of Au catalysis.     

Synthesis,characterization and crystal structure of the new pentahydrate of bis(2,2′‐bipyridine‐κ2N,N′)(oxalato‐κ2O1,O2)nickel(II)

The reaction of NiCl₂, K₂C₂O₄·H₂O and 2,2′‐bipyridine (bpy) in water–ethanol solution at 281 K yields light‐purple needles of the new pentahydrate of bis(2,2′‐bipyridine)oxalatonickel(II), [Ni(C₂O₄)(C₁₀H₈N₂)₂]·5H₂O or [Ni(ox)(bpy)₂]·5H₂O, while at room temperature, deep‐pink prisms of the previously reported tetrahydrate [Ni(ox)(bpy)₂]·4H₂O [Román, Luque, Guzmán‐Miralles & Beitia (1995), Polyhedron, 14 , 2863–2869] were gathered. The asymmetric unit in the crystal structure of the new pentahydrate incorporates the discrete molecular complex [Ni(ox)(bpy)₂] and five solvent water molecules. Within the complex molecule, all three ligands are bonded as chelates. The complex molecules are involved in an extended system of hydrogen bonds with the solvent water molecules. Additionally, π–π interactions also contribute to the stabilization of the extended structure. The dehydration of the pentahydrate starts at 323 K and proceeds in at least two steps as determined by thermal analysis.     

Kristallstruktur,Infrarot‐ und Ramanspektren von Kupfertrihydrogenperiodatmonohydrat,CuH3IO6 · H2O

Crystal Structure, Infrared and Raman Spectra of Copper Trihydrogenperiodate Monohydrate, CuH₃IO₆ · H₂O The hitherto unknown compound CuH₃IO₆ · H₂O was studied by X‐ray, IR‐ and Raman spectroscopic methods. The crystal structure was determined by X‐ray single‐crystal studies (space group P2₁2₁2₁, Z = 4, a = 532.60(10), b = 624.00(10), c = 1570.8(3) pm, R1 = 1.85%, 1559 unique reflections (I > 2σ(I))). Isolated, meridionally configurated H₃IO₆^2– ions are coordinated to the copper ions forming double‐ropes in [100]. These ropes are connected in [010] and [001] by hydrogen bonds. The copper ions possess a square pyramidal co‐ordination with the hydrate H₂O on top. The infrared and Raman spectra as well as group theoretical treatment are presented and discussed with respect to the strength of the hydrogen bonds and the co‐ordination of the CuO₅₍₊₁₎ polyhedra and the H₃IO₆^2– ions at the C₁ lattice sites. The hydrogen bonds of the H₂O molecules and H₃IO₆^2– ions (HO–H…O–IO₅H₃ and H₂IO₅O–H…O–IO₅H₃) greatly differ in strength, as shown from both the respective O…O distances: 282.6 and 298.6 pm (H₂O), and 258.8, 259.7, and 270.9 pm (H₃IO₆^2–) and the OD stretching modes of isotopically dilute samples: 2498 and 2564 cm^–1 (90 K) (HDO), and 1786, 2024, and 2188 cm^–1 (H₂DIO₆^2–). The IO stretching modes of the H₃IO₆^2– ions (696–788 cm^–1 and 555–658 cm^–1, 295 K) display the different strength of the respective I–O and I–O(H) bonds (r_I–O: 181.1–188.3 pm and 189.2–194.5 pm).     

Syntheses,Crystal Structures,and Magnetic Properties of Two Mononuclear Nickel‐Nitronyl Nitroxide Radical Compounds

Two nickel(II) complexes were synthesized and structurally as well as magnetically characterized by using two positional isomeric nitronyl nitroxide radical ligands and H₃cda as co‐ligand: [Ni(NIToPy)(cda)]H₂O · CH₃OH ( 1 ) and [Ni(IM4Py)₂(cda)H₂O] ( 2 ) [NIToPy = 2‐(3′‐pyridinyl)‐4,4,5,5‐tetramethyl‐4,5‐dihydro‐1H‐imidazolyl‐1‐oxyl‐3‐oxide; IM4Py = 2‐(4′‐pyridinyl)‐4,4,5,5‐tetramethylimidazoline‐l‐oxyl; H₃cda = 4‐hydroxypyridine‐2,6‐dicarboxylic acid]. Single‐crystal structures analyses show that both complexes have similar mononuclear structures, in which the central Ni^II ions are hexacoordinated with a distorted octahedral arrangement. The magnetic properties of 1 and 2 were studied, and antiferromagnetic interactions between Ni^II ion and radicals are observed.     

Cysteine SH and Glutamate COOH Contributions to [NiFe] Hydrogenase Proton Transfer Revealed by Highly Sensitive FTIR Spectroscopy

A [NiFe] hydrogenase (H₂ase) is a proton‐coupled electron transfer enzyme that catalyses reversible H₂ oxidation; however, its fundamental proton transfer pathway remains unknown. Herein, we observed the protonation of Cys546‐SH and Glu34‐COOH near the Ni–Fe site with high‐sensitivity infrared difference spectra by utilizing Ni‐C‐to‐Ni‐L and Ni‐C‐to‐Ni‐SI_a photoconversions. Protonated Cys546‐SH in the Ni‐L state was verified by the observed SH stretching frequency (2505 cm^?1), whereas Cys546 was deprotonated in the Ni‐C and Ni‐SI_a states. Glu34‐COOH was double H‐bonded in the Ni‐L state, as determined by the COOH stretching frequency (1700 cm^?1), and single H‐bonded in the Ni‐C and Ni‐SI_a states. Additionally, a stretching mode of an ordered water molecule was observed in the Ni‐L and Ni‐C states. These results elucidate the organized proton transfer pathway during the catalytic reaction of a [NiFe] H₂ase, which is regulated by the H‐bond network of Cys546, Glu34, and an ordered water molecule.