Study of Hydrogen Adsorption on Pt/WO3-ZrO2 through Pt Sites

The rate determining step and the energy barrier involved in hydrogen adsorption on Pt/WO_3- ZrO_2 were studied based on the assumption that the hydrogen adsorption occurs only through Pt sites. The rate of hydrogen adsorption on Pt/WO_3-ZrO_2 was measured in the adsorption temperature range of 323-573 K and an initial hydrogen pressure of 50 Torr.The rates of hydrogen uptake were very high for the initial few minutes and the adsorption continued for more than 5 h below 523 K.The hydrogen uptake far exceeded the H/Pt ratio of unity for all adsorption temperatures,indicating that the adsorption of hydrogen involved the dissociative adsorption of hydrogen on Pt sites to form hydrogen atoms,the spillover of hydrogen atoms onto the surface of the WO_3-ZrO2 catalyst,the diffusion of spiltover hydrogen atom over the surface of the WO_3-ZrO_2 catalyst,and the formation of protonic acid site originated from hydrogen atom by releasing an electron in which the electron may react with a second hydrogen atom to form a hydride near the Lewis acid site.The rate determining step was the spillover with the activation energy of 12.3 kJ/mol.The rate of hydrogen adsorption cannot be expressed by the rate equation based on the assumption that the rate determining step is the surface diffusion.The activity of Pt/WO_3-ZrO_2 was examined on n-heptane isomerization in which the increase of hydrogen partial pressure provided positive-effect on the conversion of n-heptane and negative-effect on the selectivity towards iso-heptane.     

The First-principles Study of Hydrogen Adsorption and Diffusion on the Biaxial Strained Fe(110) Surface

Hydrogen is known to play a negative role in mechanical properties of steel due to hydrogen embrittlement. Surface strain modifies the surface reactivity. In this paper, we employed spin-polarized periodic density functional to study the atomic H adsorption and diffusion on the biaxial strained Fe(110) surface. The result shows that the adsorption of H at the Tf site is the most stable on compressive surface and tensile surface. And H atom on the top site relaxes to Tf site on the strained surface. The adsorbed hydrogen atom at all calculated adsorption sites relaxes towards the surface due to the tensile strain. Lattice compression makes the bonding strength weaker between H atom and the surface. The analysis of the partial density of states shows that H 1 s orbital hybridizes with the Fe 4 s orbital. The result of charge density difference shows electrons are transferred from Fe to H atom. Compressive strain reduces the transferred electrons and decreases the Mulliken electrons of Fe 4 s orbital, which weaken the bonding interaction between H and Fe atoms. H atom diffuses into subsurface through a distorted tetrahedron. Surface strain does not change diffusion path but affects the diffusion barrier energy. Tetrahedron gap volume in the transition state of compressive system decreases to increase the diffusion barrier. This suggests compressive strain impedes H penetrating into the Fe subsurface. The present results indicate that it is a way to control adsorption and diffusion of hydrogen on the Fe surface by surface strain.     

DFT Study on the Effect of Hydrogen-bond Formation on the Adsorption of Aminotriazines on Graphene

DFT calculations have been performed to explore the aminotriazine adsorption on graphene surfaces.Relative energies,equilibrium geometries and electronic structures of monomer and dimer of aminotriazine molecules adsorbed at the surface were investigated and analyzed in details.It was found that the hydrogen atoms in the NH2 group of aminotriazine molecules are directed toward the graphene surface,and the adsorption energy increases as the NH2 group is added.The adsorbed aminotriazine molecules facilely form a dimer through the hydrogen bonding interactions,and the two aromatic rings of optimized structure of 2-amino-1,3,5-triazine(B) dimmer(denoted by B2) and melamine(D) dimmer(denoted by D2) are parallel to the graphene sheet.The large deviation of the averaged adsorption energy of B2 and D2 compared to monor adsorption may reflect the increase of π-π repulsion and the effect of hydrogen bond formation.The electronic structure analyses reveal that the formation of hydrogen bonds in melamine dimer has great influence on the adsorption mode at the graphene surface.     

Improved electrochemical hydrogen storage properties of Mg-Y thin films as a function of substrate temperature

Pd-capped Mg_(78)Y_(22) thin films have been prepared by direct current magnetron co-sputtering system at different substrate temperatures and their electrochemical hydrogen storage properties have been investigated.It is found that rising substrate temperature to 60 ℃ can coarsen the surface of thin film,thus facilitating the diffusion of hydrogen atoms and then enhancing its discharge capacity to ~1725 mAh·g~(-1).Simultaneously,the cyclic stability is effectively improved due to the increased adhesion force between film and substrate as a function of temperature.In addition,the specimen exhibits a very long and flat discharge plateau at about —0.67 V,at which nearly 60%of capacity is maintained.The property is favorable for the application in metal hydride/nickel secondary batteries.The results indicate that rising optimal substrate temperature has a beneficial effect on the electrochemical hydrogen storage of Mg-Y thin films.     

Two New Copper(Ⅱ) Complexes with p-Cyanobenzoic Acid: Synthesis,Crystal Structures and Properties

The complexes of [Cu(bpy)(H2O)(CBA)2]n 1 and [Cu(phen)(H2O)(CBA)2]·H2O 2 based on p-cyanobenzoic acid(HCBA) have been synthesized in aqueous ethanolic solution at room temperature. The single-crystal X-ray diffraction studies demonstrated that complex 1 crystallizes in orthorhombic and complex 2 is of triclinic system. The results indicate the complex 1 shows a 1D chain structure bridged by two carboxylic oxygen atoms from CBA–, and complex 2 is a mononuclear structure. Through intermolecular hydrogen bonding and π...π stacking interactions, the complexes are assembled into supramolecular structures. Complex 1 has been characterized by magnetic measurements. The magnetic measurement indicates that weak ferromagnetic interaction(zJ= 0.038(5)) between the Cu2+ ions is dominant in the structure. The IR spectrum and results of thermal and elemental analyses are also presented.     

Influence of Pretreatment on the Interaction of Oxygen with Silver and the Catalytic Activity of Ag／SiO2 Catalysts for CO Selective Oxidation in H2

The interactions of oxygen with pre~reduced silver catalysts as well as their catalytic propertiesfor CO selective oxidation in H2 after oxygen pre-treatment are studied in this paper. It is found that the pretreatment exerts a strong influence on the activity and selectivity of the silver catalyst. A drop in activity and selectivity is observed after treating a pre-reduced catalyst with oxygen at low temperatures,whereas a converse result is obtained after an oxidizing treatment at high temperatures (T≥350℃). O2-TPD results show that surface oxygen species adsorbs on silver surface after the oxygen treatment at low temperatures. However, penetration of oxygen into the silver is enhanced by a high temperature treatment, meanwhile the surface oxygen species disappear. No other silver species except metallic silver are observed on all the catalysts by XRD, and the size of silver particle is not changed after the treatment with oxygen at low temperatures. The surface oxygen species formed by oxygen treatment can also be removed by hydrogen reduction. The strongly-adsorbed surface oxygen species prohibit the adsorption and diffusion of oxygen species in reaction gas on the surface of silver catalyst, causing the decrease in CO oxidation activity, in other words, it is important to obtain a clean silver surface for increasing the catalyst activity in CO removal from H2-rich feed gas. The differences in activity and selectivity due to the oxygen pretreatment at different temperatures axe discussed in terms of the changes in the surface/subsurface oxygen species of the silver particles.     

A voltammetric sensor for simultaneous determination of lead,cadmium and zinc on an activated carbon fiber rod

A simple, low cost and sensitive voltammetric sensor was developed for the simultaneous detection of Pb²⁺, Cd²⁺, and Zn²⁺ based on a disposable carbon fiber rod (CFR). The important factors to enhance the sensing property were creation of a clean surface by dealing with CFR at a high potential and electrochemical deposition of Bi film to improve the accumulation of heavy metal ions.     

A reaction-and-assembly approach using monoamine zinc porphyrin for highly stable large-area perovskite solar cells

Inhibiting the irreversible escape of organic cations and iodide species in perovskite films is crucial for the fabrication of efficient and stable perovskite solar cells(PSCs). Here, we develop a reaction-and-assembly approach using monoamine zinc porphyrin(ZnP) to modify methylammonium(MA~+) lead iodide perovskite film. The amine group in ZnP reacts with MA~+ and I~- ions to yield monoammonium zinc porphyrin(ZnP-H+I-). The resultant films show no escape of iodide when immersed in ether solutions. Measurements from space-charge limited currents and transient photoluminescence indicate the modified films have reduced density of defects. These results suggest the formed ZnP-H~+I~- is bound on the surface and grain boundary of perovskite film to retard migrations of ions. DFT calculations also show that the energy alignment between ZnP-H~+ and perovskite facilitates the electron transfer and reduces charge recombination at the perovskite grains. Furthermore, post-treating the Zn Pdoped film with ZnP again results in the formation of a one dimension zig-zag coordination polymer on the surface of the perovskite film. The single crystal structure of ZnP shows the polymer layer is formed through the coordination interaction between the Zn(II) metal center and a neighboring monoamine. The polymer facilitates the interfacial charge transfer, and reduces the escape of organic cations and iodide species in perovskite films, thereby keeping the excellent cell performance(20.0%) and further realizing the ion encapsulation. Finally, the modified PSCs retain over 90% of its original efficiency over2,000 h at 85 °C or AM 1.5 G continuous illumination, or over 6,000 h in 45% humidity without encapsulation. This work affords a new strategy to achieve the efficient ions immobilization and encapsulation by in situ reaction and coordination assembly of mono-amine zinc porphyrin.     

Electrochemical Metalloimmunoassay Based on Enlargement of Gold Nanoparticle Label Treated with Ag Enhancement System

A novel sensitive electrochemical immunoassay with colloidal gold as the antibody labeling tag and subse-quent signal amplification by silver enhancement is described. Colloidal gold was treated by a light-sensitive silver enhancement system which made silver deposit on the surface of colloidal gold(form Au/Ag core-shell structure), followed by the release of the metallic silver atoms anchored on the antibody by oxidative dissolu-tion of them in an acidic solution and the indirect determination of the dissolved Ag ions by anodic stripping voltamrnetry(ASV) at a carbon fiber microelectrode. The electrochemical signal is directly proportional to the amount of analyte(goat IgG) in the standard or a sample, The method was evaluated by means of a non-competitive heterogeneous immunoassay of immunoglobulin G(IgG) with a concentration as low as 0. 2 ng/mL. The high performance of the method is related to the sensitive ASV determination of silver( I ) at a car-bon fiber microelectrode and to the release of a large number of Ag^ ions from each silver shell anchored on the analyte (goat IgG).     

Photostability Study of Nanoporous TiO2 Film Electrodes in Basic Solutions

The nanoporous TiO2 film electrodes have been prepared by a sol-gel deposition process The photostability of the electrodes in basic solutions has been studied. The results show that the photostability of the electrodes decreases rapidly in strong basic solutions with or without methanol. The reaction of holes to O^2- produces active O^2- atoms and the products O^2- atomsoxidize Ti^3 to Ti^4 on TiO2 film surface and subsurface. This results in the TiO2 film electrodes unstable in basic solutions both without methanol and with too low concentration.     

Third generation biosensor based on myoglobin-TiO2/MWCNTs modified glassy carbon electrode

TiO2 nanoparticles were homogeneously coated on multi-walled carbon nanotubes by hydrothermal deposition, this nanocomposite may be a promising material for myoglobin immobilization in view of its high biocompatibility and large surface. The glassy carbon electrode modified with Mb-TiO2/MWCNTs films exhibited a pair of weU defined, stable and nearly reversible cycle voltammetric peaks. The electron transfer between Mb and electrode surface, Ks of 3.08 s^-1, was greatly facilitated in the TiO2/ MWCNTs film. The electrocatalytic reductions of hydrogen peroxide were studied, the apparent Michaelis-Menten constant is calculated to be 83.10 μmol/L, which shows a large catalytic activity of Mb in the TiO2/MWCNTs film to H2O2.     

Dispersion state of CuO on CeO_2——An incorporation model for the interaction between metal oxide and oxide support

XRD and XPS are used to study the dispersion state of CuO on ceria surface.The dispersion capacity values of CuO measured by the two methods are consistent,which are of 1.20 mmol CuO/100 m CeO2.In addition,the results reveal that highly dispersed Cu2 + ions are formed at low CuO loadings and that increasing the CuO content to a value higher than its dispersion capacity produces crystalline CuO after the surface vacant sites on CeO2 are filled.The atomic composition of the outermost layer of the CuO/CeO2 samples has been probed by using static secondary ion mass spectroscopy (SSIMS),and the ratios of Cu/Ce are found to be 0.93 and 0.46 for the 1.22 and 0 61 mmol CuO/CeO2 samples respectively.Temperature-programmed reduction (TPR) profile with two reduction peaks at 156 and 16513 suggests that the reduction of highly dispersed Cu2+ ions consists of two steps and is easier than that of CuO crystallites,in which the TPR profile has only one reduction peak at about 249℃.The above experimental results are in     

Pore size effects of nanoporous carbons with ultra-high surface area on high-pressure hydrogen storage

In this work, the morphologies and pore structures of a series of corncob-derived activated carbons and zeolite templated carbon with ultrahigh surface area were carefully investigated by SEM, HRTEM and N2-sorption characterization technologies. The high-pressure hydrogen uptake performance was analyzed using standard Pressure-Composition-Temperature apparatus in order to study the pore size effects on hydrogen uptake. These as-obtained porous carbons showed different characteristics of pore size distribution as well as specific surface area. The results indicate that the most effective pores for adsorbing hydrogen depended on the storage pressure. These ultramicropores(0.65-0.85 nm) could be the most effective pores on excess H2 uptake at 1 bar, however, micropores(0.85-2 nm) would play a more important role in excess H2 uptake at higher pressure at 77 K. At room temperature, pore size effects on H2 uptake capacity were very weak. Both specific surface area and total pore volume play more important roles than pore size for H2 uptake at room temperature, which was clearly different from that at 77 K.For applications in future, the corncob-derived activated carbons can be more available than zeolite templated carbons at 77 K. Element doping enhanced hydrogen uptake could be main research direction for improving H2 uptake capacity at room temperature.     

THEORETICAL STUDIES ON THE SUBSTITUTION EFFECT OF FLUORINE ON ETHANE

<正> The substitution effect of fluorine on ethane has been investigated by means of studying the properties of the charge distribution at the bond critical points with the theory of atoms in molecule.It is found that the major substitution effects of fluorine atom are positive a inductive and polarity effect.At the same time,fluorine atom partially provides π electrons to other chemical bonds by means of hy-perconjugation in molecules with two fluorine atoms and one or two carbon atoms in the same plane,and these effects are reflected in the quantity of bond ellipticity,Laplacian and the charge density of charge distribution at the bond critical points.The substitution of hydrogen by fluorine in ethane strengthens all the bonds in substituted ethanes.Other effects originating from the substitution of hydrogen by fluorine have also been discussed.     

Hydrogen and syngas production from two-step steam reforming of methane using CeO2 as oxygen carrier

CeO2 oxygen carrier was prepared by precipitation method and tested by two-step steam reforming of methane (SRM). Two-step SRM for hydrogen and syngas generation is investigated in a fixed-bed reactor. Methane is directly converted to syngas at a H2/CO ratio close to 2 : 1 at a high temperature (above 750 °C) by the lattice oxygen of CeO2; methane cracking is found when the reduction degree of CeO2 was above 5.0% at 850 °C in methane isothermal reaction. CeO2?δ obtained from methane isothermal reaction can split water to generate CO-free hydrogen and renew its lattice oxygen at 700 °C; simultaneously, deposited carbon is selectively oxidized to CO2 by steam following the reaction (C+2H2O→CO2+2H2). Slight deactivation in terms of amounts of desired products (syngas and hydrogen) is observed in ten repetitive two-step SRM process due to the carbon deposition on CeO2 surface as well as sintering of CeO2.     

Studies of the Methane Steam Reforming Reaction at High Pressure in a Ceramic Membrane Reactor

The effects of temperature and pressure on the steam reforming of methane 3H2+CO) were investigated in a membrane reactor (MR) with a hydrogen permeable membrane. The studies used a novel silica-based membrane prepared by using the chemical vapor deposition (CVD) technique with a permeance for H2 of 6.0×l0-8 mol·m-2·s-1·Pa-1 at 923 K. The results in a packed-bed reactor (PBR) were compared to those of the membrane reactor at various temperatures (773-923 K) and pressures (1-20 atm, 101.3-2026.5 kPa) using a commercial Ni/MgAl2O4 catalyst. The conversion of methane was improved significantly in the MR by the countercurrent removal of hydrogen at all temperatures and allowed product yields higher than the equilibrium to be obtained. Pressure had a positive effect on the hydrogen yield because of the increase in driving force for the permeance of hydrogen. The yield of hydrogen increased with pressure and reached a value of 73×10-6 mol·g-1·s-1 at 2026.5 kPa and 923 K which was higher by 108% than the value of 35×10-6 mol·g-1·s-1 obtained for the equilibrium yield. The results obtained with the silica-based membrane were similar to those obtained with various other membranes as reported in the literature.     

Quasiclassical trajectory study of the reaction NH(X~3∑~-)+H→N(~4S)+H_2

The dynamics of the NH + H→N+H2 reaction has been investigated by means of the 3D quasiclassical trajectory approach by using the LEPS potential energy surface.The calculated rate coefficient is in good agreement with the experimental value.The reaction was found to occur via a direct channel.The product H2 has a cold excitation of rotational state,but has a reverse distribution of the vibrational state with a peak at v=1.Based on the potential energy surface and the trajectory analysis,the reaction mechanism has been explained successfully.     

Size Effects for the Adsorption of Alkali Metal Atoms on the Si(001) Surface

The adsorptions of a series of alkali metal(AM) atoms, Li, Na, K, Rb and Cs, on a Si(001)-2×2 surface at 0.25 monolayer coverage have been investigated systematically by means of density functional theory calculations. The effects of the size of AM atoms on the Si(001) surface are focused in the present work by examining the most stable adsorption site, diffusion path, band structure, charge transfer, and the change of work function for different adsorbates. Our results suggest that, when the interactions among AM atoms are neglectable, these AM atoms can be divided into three classes. For Li and Na atoms, they show unique site preferences, and correspond to the strongest and weakest AM–Si interactions, respectively. In particular, the band structure calculation indicates that the nature of Li–Si interaction differs significantly from others. For the adsorptions of other AM atoms with larger size(namely, K, Rb and Cs), the similarities in the atomic and electronic structures are observed, implying that the atom size has little influence on the adsorption behavior for these large AM atoms on the Si(001) surface.     

Synthesis,crystal structures and luminescence properties of europium and terbium picolinamide complexes

The novel coordination structures of europium and terbium chloride-picolinamide complexes （EuCl3-（C6H6N2O）2.5H2O, Eu-pa and TbCl3.（C6H6N2O）2.5H2O, Tb-pa） are reported. The crystal structures in the solid state are characterized by X-ray single crystal diffraction, FTIR, Raman, FIR, THz and luminescence spectroscopy. In the crystal structures, the pyridyl nitrogen and carbonyl oxygen atoms in picolinamide are coordinated to the metal ions to form a five-membered ring structure. The experimental results indicate the similar coordination structures of Eu and Tb-pa complexes and the changes of hydrogen bonds and conformation provide models for the coordination structures of the ligands induced by complexation. The results of lanthanide ions with ligands having amide groups.     

丙炴醇聚合膜对铁在酸性溶液中的缓蚀作用

The formation of polymer film of propargyl alcohol(PA) and its protective ability against corrosion in Fe/H_2SO_4 and Fe/H_2SO_4+H_2S systems have been investigated using impedance measurement. The composition and morphology of the corrosion surface of iron, on which PA polymerized at different bines, were obtained with the aid of SEM and AFM as well as EDX. The results showed that PA polymerized into compact polymer film in Fe/H_2SO_4 and Fe/ H_2SO_4 + H_2S systems, which made iron surface smooth and have a morphologies of regular square structure in microscopic level. In Fe/H_2SO_4 system, macroscopic continuous polymer film of PA was not formed leading to local corrosion on electrode surface. In Fe/H_2SO_4 +H_2S system, the adsorption of H_2S and HS - on electrode surface slowed down the formation of polymer film of PA. However, the iron sulfide, produced after a longer time, increased the continuity of the polymer film of PA and therefore, the polymer film could perform its long-te...更多rm inhibition action.