The study of the active surface for CO oxidation over supported Pd catalysts

CO oxidation was investigated on various powder oxide supported Pd catalysts by temperature-programmed reaction.The pre-reduced catalysts show significantly higher activities than the pre-oxidized ones.Model studies were performed to better understand the oxidation state,reactivities and stabilities of partially oxidized Pd surfaces under CO oxidation reaction conditions using an in situ infrared reflection absorption spectrometer(IRAS).Three O/Pd(100)model surfaces,chemisorbed oxygen covered surface,surface oxide and bulk-like surface oxide,were prepared and characterized by low-energy electron diffraction(LEED)and Auger electron spectroscopy(AES).The present work demonstrates that the oxidized palladium surface is less active for CO oxidation than the metallic surface,and is unstable under the reaction conditions with sufficient CO.     

In situ Observation of the Photochromism in the Langmuir Monolayer of a Non—typical Amphiphilic Spiropyran Derivative at the Air／Water Interface

In situ photochromic process in the monolayer of aphotochromic spiropyran derivative without long alkyl chain,was investigated.The photochromism at the air/water interface under differnet surface pressures was studied by surface pressure-area isotherms,surface pressure-time curves,area-time curves and Brewster angle microscopy.Both forms of the compound were found to form monolayers at the air/water interface althouhg it does not have long alkyl chain.A large area expansion in the monolayer corresponding to a zreo^th order reaction was found at the initial stage of the UV light irradiation.A series of dynamic investigations revealed that at high pressure after phase transition in the monolayer,the surface pressure changes greatly umder alternative irradiation of UV and visible light.An obvious morphological change accompanying with the photochromism was observed in situ.     

Surface oxidation and water desorption of CdS

The surface oxidation and HP desorption of powder CdS were studied by means of X-ray photoetectron spectroscopy (XPS), quadrupole mass spectrometry (QMS) and in-situ FTIR. The results show that with the changes of surface composition and the elongation of store time of CdS there are four types of H2O thermally desorbed at different temperatures. It has also been found that through high-temperature air treatment for a short time the oxidized surface layer of CdS can prevent O2 and H2O in air from further attacking the inner CdS molecules.     

Kinetic study on hydrolysis and oxidation of formamidine disulfide in acidic solutions

Hydrolysis and oxidation of formamidine disulfide in acidic medium were investigated using high-performance liquid chromatography(HPLC) and mass spectrometry(MS) at 25 °C.By controlling the slow reaction rate and choosing appropriate mobile phase,HPLC provides the unique advantages over other methods(UV-Vis,chemical separation) in species tracking and kinetic study.In addition to thiourea and formamidine sulfinic acid,two unreported products were also detected in the hydrolysis reaction.Mass spectrometry measurement indicates these two products to be formamidine sulfenic acid and thiocyanogen with mass weights of 92.28 and 116.36,respectively.In the oxidation of formamidine disulfide by hydrogen peroxide,besides thiourea,formamidine sulfenic acid,formamidine sulfinic acid,thiocyanogen and urea,formamidine sulfonic acid and sulfate could be detected.The oxidation reaction was found to be first order in both formamidine disulfide and hydrogen peroxide.The rate constants of hydrolysis and oxidation reactions were determined in the pH range of 1.5-3.0.It was found both rate constants are increased with the increasing of pH.Experimental curves of different species can be effectively simulated via a mechanism scheme for formamidine disulfide oxidation,including hydrolysis equilibrium of formamidine disulfide and irreversible hydrolysis of formamidine sulfenic acid.     

微等离子体氧化Al2O3陶瓷膜的组织结构与形成过程

The alumina ceramic coatings were prepared on aluminum alloy using micro-plasma oxidation. The structure and morphologies of ceramic coatings were studied by X-ray diffraction (XRD) and scanning electron microscope (SEM), and then its formation process was investigated. The results of XRD reveal that with increasing oxidation time the content of γ-Al₂O₃in the ceramic coatings decreases, and in which the content of α-Al₂O₃increases. The results of SEM show that many crater-mouth like traces formed by the plasma discharge are observed on the coatings surface, it indicates when the plasma is discharging, a plasma thermal chemical reaction occurs between the aluminum from the substrate and the oxygen and other ions from the electrolyte. The reaction products then are propelled away from the inner-wall of the discharging channels. Finally, these products agglomerate in the inner-wall of the discharging channels and on the surface near the discharging channels to produce the ceramic coatings. The change of ceramic coatings thickness with increasing oxidation time divides into two stages, and the final thickness is formed in first stage. With increasing current density the final thickness of ceramic coatings increases.     

1 ,3 ,2-Oxazaphospholidine Derivatives(I)——The Synthessa of 2 - Diethylamino- 3-arylsulfonyl- 1,3,2-Oxazaphospholidine and Its 2-thiono Deiativea and Their Properties

A series of new 2-diethylamino-3-substituted phenylsulfonyl-1,3,2-oxazaphospholidine derivatives (Ⅰ) has been synthesized by the reaction of tris(diethylamino) phosphine with N-(β-hydroxyethyl) substitutedphenylsulfonamides. When was refluxed with sulfur in benzene, the 2-thiono derivatives (Ⅱ) was obtained conveniently.(Ⅰ) was easily oxidized in air and the diethylamino group could be substituted by phenoxy or other amino group giving the corresponding derivatives. Their H NMR and MS spectra have been discussed. Some of compounds (Ⅱ) have herbicidal activities.     

Surface and structural properties of pt/ceo2catalyst under preferential co oxidation in hydrogen (PROX)

Summary Preferential oxidation of CO in the presence of excess hydrogen was studied on Pt/CeO₂with 5% metal loading. Catalytic data were similar to those observed on 1% Pt/CeO₂earlier [16]. The optimum temperature region is T￡373 K; conversion and selectivity of CO oxidation strongly decreased at higher temperatures. High-pressure XPS indicated CO adsorbed on platinum particles and significant amount of water on the ceria surface. The top-most ceria surface re-oxidized as small amount of oxygen (3%) was introduced into the H₂/CO feed. Despite this surface re-oxidation, high-resolution TEM after reaction indicated oxygen deficient ceria bulk structure, in which the defects formed a super-cell, with CeO_1.695structure. The defective ceria is suggested to play an important role stabilizing the hydrogen bonded surface water, which (i) suppresses further hydrogen oxidation and (ii) reacts at the metal/support interface with linearly adsorbed CO in a low temperature water-gas-shift type reaction to produce CO₂.</o:p>     

Oxidation of Steels and HgO Growth after 5000 Hours Exposure in Mercury at 573 K

 Corrosion tests on martensitic steels, F82H and MANET-II, were conducted in static Hg at 573 K in two batches: 1) the Hg covered with air for 5000 h, and 2) the Hg covered with Ar for 2000 h. Different techniques (EPMA, SEM, RHEED, XRD, SIMS) have been applied for surface analysis. The main results show that the surfaces of the samples are oxidized and covered with large amounts of red HgO single crystals (1 μm to 1 mm) under air atmosphere. The surface layers formed in the presence of air consist of oxides of types (Fe, Cr)₂O₃, Fe₃O₄, FeCr₂O₄ and have a thickness up to 680 nm for F82H and 310 nm for MANET-II. Replacing air with Ar in the containers reduces drastically the oxidation of the steels. In this case the maximum thickness of oxide film is of 10 nm and no HgO crystals form.     

Kinetics and Mechanism of the Photo-oxidation of Thiophene by O2 Adsorbed on Molecular Sieves

Photochemical oxidation of thiophene in n-octane/water extraction system using O2 as oxidant was studied. The reaction mechanism ofthiophene oxidation was proposed. Results obtained here can be used as the reference for the oxidative desulfurization of gasoline because thiophene is one of the main components containing sulfur in fluid catalytic cracking gasoline. Thiophene dissolved in n-octane was photodecomposed and removed into the water phase at ambient temperature and atmospheric pressure. A 500 W high-pressure mercury lamp （main wave length 365 nm, 0.22 kW/m） was used as light source for irradiation, and air was introduced by a gas pump to supply O2. Thiophene can be photo-oxidized to sulfone, oxalic acid, SO4^2-, and CO2. The desulfurization yield of thiophene in n-octane is 58.9% under photo-irradiation for 5 h under the conditions of air flow at 150 mL/min and V（water）：V（n-octane）=1：1. It can be improved to 92.3% by adding 0.15 g zeoliteartificial into 100 mL reaction system, which is the adsorbent for O2 and thiophene. And under such conditions, the photo-oxidation kinetics of thiophene with O2/zeoliteartificial is first-order with an apparent rate constant of 0.5047 h^-1 and a half-time of 1.37 h. The sulfur content can be depressed from 800 μL/L to less than 62 μL/L.     

Oxidation of Carbon Monoxide over Cu/CeO_2 Catalysts Prepared by SMAI

Introduction Carbon monoxide is ubiquitous air pollutants emitted by many sources. Total oxidation of carbon monoxide to carbon dioxide is employed to meet environmental regulations in an economic way. Precious metals (Pt, Pd) are well-known oxidation catalysts with high activity and stability, and are widely used for exhaust gas emission control. However, the high cost of precious metals and their sensitivity to sulfur poisoning have long motivated the search for substitute catalysts. …     

Methane Oxidation on the Surfaces of Manganese Oxides: a First Principles Study

A comprehensive density functional theory calculation was employed to investigate the possible reaction pathways and mechanisms of methane complete oxidation(CH_4 + 2O_2 → CO_2 + 2H_2O) on different manganese oxides including a-MnO_2(100) and b-MnO_2(111) surfaces. According to a coupling of the Mars-van Krevelen and Langmuir-Hinshelwood mechanism, the activation energy barrier and the reaction energy of each elementary surface reaction were determined. Our calculated results show that the detailed processes for methane oxidation on two surfaces are different due to the differences in the surface structure. The breaking of the last C–H bond of CH_4 moleculeis the rate-determining step with an activation barrier of 0.85 eV for a-MnO_2(100) surface. By contrast, the overall reaction rate on b-Mn O_2(111) surface is limited by the dissociation of the second O_2 molecule adsorbed on the vacancy site, and re-oxidation of the reduced b-MnO_2(111) surface by the gaseous oxygen requires a much higher energy barrier of 1.44 eV. As a result, the a-Mn O_2(100) exhibits superior activity and durability in the methane oxidation reaction than b-MnO_2(111) surface. The present study provides insight into understanding the structure-catalytic activity relationship of the catalysts based on manganese oxides towards the methane oxidation reaction.     

Cluster—cracking Reaction,a New Method to Synthesize Unsymmetrical Dithiolate Complexes for the Study of Third—Order Nonlinear Optical Properties

A new coluster-cracking method to synthesize dithiolate metal complexes was reported and four unsymmetric complexes with formula(Me4N)2[M(Ln)(SPh)2](M=Cd and Zn,L1=dmit=1,3-dithiole-2-thione4-5,dithiolate,L2=dmid=1,3-dithiole-2-one-4,5-dithiolate,SPh=thiophenolate)(1-4)were characterized by elemental analysis,IR,UV NMR spectra and so on.The advantages of this method are summarized in two aspects:(1) the preparation is very convenient;(2) the reaction usually completed giving the product with high pruity.The crystal structure of 1 showed that the bond distances of Cd(Ⅱ）to the sulfur of the thiophenolate group are shorter than those of Cd(Ⅱ）to the sulfur of dmit,so that the thiophenolate group does not be replaced in the reaction and thmixed ligand complexes are the dominant produxts.The dmit complexes showed well third-order NLO properties,but not of the dmid complexes,although dmid is an analogue to dmit.     

A DFT Study of Thiophene Adsorption on the Rh（111） Surfaces

Thiophene adsorption on the Rh(111) surfaces has been investigated by density functional theory.The results show that the adsorption at the hollow and bridge sites is the most stable.The molecular plane of the thiophene ring is distorted,the C=C bond is stretched to 1.448  and the C-C bond is shortened to 1.390.The C-H bonds tilt 22～42oaway from the surface.The calculated adsorption geometries are in reasonable agreement with population analysis and density of states.The thiophene molecule obtains 0.74 electrons,reflecting the interaction between the lone pair of sulfur and the d-orbitals of metal.The reaction paths and transition states for desulfurization of the molecule have been investigated.The bridge adsorption structure of thiophene leads to a thiol via an activated reaction with an energetic barrier of 0.30 eV.This second step is slightly difficult,and dissociation into a C4H4 fragment and a sulfur atom is possible,with an energetic barrier of 0.40 eV.     

S掺杂纳米多孔碳的光催化活性:表面化学和孔隙率的重要性(英文)

This minireview summarizes our recent findings on the photoactivity of S-doped nanoporous carbons. The materials were either synthesized from the sulfur-containing polymers or obtained by heat treatment of commercial carbon with hydrogen sulfide. Their surface was extensively charac terized from the points of view of its surface chemistry, porosity, morphology, and electronic properties. The carbons showed enhanced activity towards oxidation of arsine and removal of diben-zothiophenes from model diesel fuel. The latter were oxidized to various oxygen containing intermediates and the cleavage of C–C bonds in aromatic ring was detected when carbon with adsorbed species was exposed to UV or visible light. Irradiation resulted in generation of photocurrent in a broad range of wavelength. The presence of sulfur led to the reduction of oxygen and contributed to an increased capacitive performance. We link these effects to the presence of reduced sulfur in the small pores which enhances the dispersive interactions via inducing a positive charge to carbon atoms, to sulfur in oxygenated forms which contribute to Faradaic reactions and increase the polar interactions, and to the hydrophobicity of a surface in small pores where oxygen can be reduced by excited electrons from chromophoric-like sulfur containing groups.     

Electrodeposited Pt and Pt-Sn nanoparticles on Ti as anodes for direct methanol fuel cells

Electro-oxidation of methanol was studied on titanium supported nanocrystallite Pt and Pt_x-Sn_y catalysts prepared by electrodeposition techniques. Their electro-catalytic activities were studied in 0.5mol/L H₂SO₄ and compared to those of a smooth Pt, Pt/Pt and Pt-Sn/Pt electrodes. Platinum was deposited on Ti by galvanostatic and potentiostatic techniques. X-ray diffractometer (XRD) and energy dispersive X-ray (EDX) techniques were applied in order to investigate the chemical composition and the phase structure of the modified electrodes. Scanning electron microscopy (SEM) was used to characterize the surface morphology and to correlate the results obtained from the two electrochemical deposition methods. Results show that modified Pt/Ti electrodes prepared by the two methods have comparable performance and enhanced catalytic activity towards methanol electro-oxidation compared to Pt/Pt and smooth Pt electrodes. Steady state Tafel plots experiments show a higher rate of methanol oxidation on a Pt/Ti catalyst than that on a smooth Pt.  Introduction of a small amount of Sn deposited with Pt improves the catalytic activity and the stability of prepared electrode with time as indicated from the cyclic votlammetry and the chronoamperometric experiments. The effect of variations in the composition for binary catalysts of the type Pt_x-Sn_y/Ti towards the methanol oxidation reaction is reported. Consequently, the Pt_x-Sn_y/Ti (x∶y (8∶1), molar ratio) catalyst is a very promising one for methanol oxidation.     

Influence of Surface Structure of Platinum Electrodes on Electrooxidation of CO

The oxidation of CO on platinum electrodes in an acid solution was studied with the conventional electro-chemical methods and the on-line electrochemical mass spectroscopy. It was found that this reaction is strongly determined by the surface morphology of platinum. The pretreatment of platinum electrodes can change the surface properties dramatically, in consequence it can improve the electrocatalytic activity towards the electrooxidation of CO. The existence of surface active sites on the roughened platinum electrodes can be used to explain its high electrocatalysis towards the oxidation of CO.     

Electrolessly Plated Ni-Zn（Fe）-P Alloy and Its Corrosion Resistance Properties

The autocatalytic deposition of Ni-Zn(Fe)-P alloys has been carried out on substrate of carbon steel from a bath containing nickel sulfate, zinc sulfate, sodium hypophosphite, sodium citrate and boric acid. The effects of pH and the molar ratio of NiSO4/ZnSO4 on the deposition rate and the composition of deposits have been studied. It was found that the presence of zinc sulfate in the bath has an inhibitory effect on the alloy deposition. The structure and the surface morphology of Ni-Zn(Fe)-P coatings were characterized with XRD and SEM, respectively. The alloys plated under the experimental conditions consisted of an amorphous phase coexisting with a crystalline cubic Ni phase (poly-crystalline). The surface morphology of the coating is dependent on the deposition parameters. The corrosion resistance of the Ni-Zn(Fe)-P deposits was examined via mass loss tests and anodic polarization measurements, respectively. The results show that the surface morphologies of the deposits and the corrosion resistance of the deposits have been improved. The results of mass loss tests almost accord with those of anodic polarization measurements. The corrosion mechanisms of Ni-Zn(Fe)-P alloys in NaCl and NaOH solutions were investigated by means of EDX. The deposit immersed in an NaCI or an NaOH solution contains more content of oxygen and less contents of the metals(except Fe) than that placed in air, which shows that the NaCl or NaOH solution can accelerate the oxidation of the deposit.     

ROLE OF THIOL-DISULFIDE EXCHANGE IN INSULIN BINDING TO ITS RECEPTOR

The effects of reduction by DTT, oxidation by DTNB and treatment with NEM on the thiol contents and insulin binding to its receptor in mice liver membranes were studied. Reduction with DTT leads to a parallel increase in the thiol content and the speciflc binding of insulin to the membrane. Scatchard analysis of the results shows little change in the number of binding sites but a twofold increase of the binding constant. Washing the membrane with bound insulin by a DTT containing buffer results in a more marked increase in the release of bound insulin than washing with buffer alone, suggesting that part of the insulin is bound to its receptor by covalent disulfide linkages through a thIol-disulfide exchange reaction and reduction with DTT leads to a marked increase in this "disulfide-linked" insulin. Treatment with DTNB or NEM of the DTT-reduced membrane seems to reverse the effect of DTT reduction, although the reaction of the untreated membrane with DTNB or NEM had little or no effect on the specific     

水溶性荧光CdSe量子点的合成及其在指纹显现中的应用

Water-soluble fluorescent CdSe quantum dots(QDs) were synthesized by using Se、Na₂SO₃ and CdCl₂ as precursors and mercaptoacetic acid(TGA) as modifier. The effects of refluxing time and initial pH values of the reaction on the particle size and fluorescence intensity of CdSe QDs were studied. The XRD、HRTEM and fluorescent spectroscopy were employed to characterize these samples. It is found that CdSe QDs with crystalline size of 2～3 nm are homogeneously distributed in the organic matrix. The maximum fluorescence absorption and emission peak of CdSe QDs solution are at 450 nm and 562 nm, respectively. The fingerprint details on the surface of smooth objects were clearly developed with CdSe QDs solution under irradiation of UV lights.     

In-situ UV-Raman study on soot combustion over TiO_2 or ZrO_2-supported vanadium oxide catalysts

UV-Raman spectroscopy was used to study the molecular structures of TiO2 or ZrO2-supported vana-dium oxide catalysts.The real time reaction status of soot combustion over these catalysts was de-tected by in-situ UV-Raman spectroscopy.The results indicate that TiO2 undergoes a crystalline phase transformation from anatase to rutile phase with the increasing of reaction temperature.However,no obvious phase transformation process is observed for ZrO2 support.The structures of supported va-nadium oxides also depend on the V loading.The vanadium oxide species supported on TiO2 or ZrO2 attain monolayer saturation when V loading is equal to 4(4 is the number of V atoms per 100 support metal ions).Interestingly,this loading ratio(V4/TiO2 and V4/ZrO2) gave the best catalytic activities for soot combustion reaction on both supports(TiO2 and ZrO2).The formation of surface oxygen com-plexes(SOC) is verified by in-situ UV Raman spectroscopy and the SOC mainly exist as carboxyl groups during soot combustion.The presence of NO in the reaction gas stream can promote the pro-duction of SOC.