Multi-electron oxidation of formaldehyde on a platinum electrode

The time evolution of a self-sustained potential oscillation under constant current oxidation of formaldehyde was observed on the rotating ring disk electrode assemble. Under the condition when the potential was controlled, the laser deflection voltammogram as well as the conventional cyclic voltammogram were measured. The mechanism of the multi-electron oxidationof formaldhyde on a platinum electode is discussed.     

IR spectroscopic signs of surface intermediates of partial oxidation of propane by nitrogen monoxide on Fe-ZSM-5

We have used IR spectroscopy to study adsorption of NO, propane, and their mixture on Fe-ZSM-5 in the temperature range 20-350 °C. We show that it is possible to form adsorbed nitrate ions, C-, N-, and O-containing intermediates leading to formation of partial oxidation products: oxygenates and nitrogen-containing compounds. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 2, pp. 121-124, March-April, 2009.     

Thermal stability of platinum particles embedded in mesoporous silicates

Summary The thermal stability of platinum nanoparticles immobilized in SBA-15 silicate was investigated. The Pt nanoparticles were prepared in aqueous solution using polyvinyl-pirrolidone (PVP) as shape- and size controlling agent. The appropriate pretreatment conditions of cleaning the metal surface were determined.     

IR studies of the transformations of nitrogen-containing organic intermediates during selective reduction of nitrogen oxides by hydrocarbons

Thermal transformations of nitromethane and deuterated acetonitrile adsorbed on the surface of H-ZSM-5, Cu-ZSM-5, Co-ZSM-5 has been studied by IR spectroscopy. The nature of cation has been found to greatly affect the transformation pathways of these species as possible intermediates in the NO_x selective reduction by hydrocarbons, thus explaining the different selectivities of these catalysts.     

Estimation of Surface Structure and Carbon Monoxide Oxidation Site of Shape‐Controlled Pt Nanoparticles

Surface structures of shape‐controlled Pt nanoparticles have been estimated using cyclic voltammetry (CV) and infrared reflection absorption spectroscopy (IRAS). Cubic and cuboctahedral Pt nanoparticles are prepared using a capping polymer. These nanoparticles give CVs similar to those of single crystal electrodes of Pt in sulfuric acid solution. The CV of cubic nanoparticles is similar to that of the Pt(510) [=5(100)–(110)] electrode, while the CV of cuboctahedral nanoparticles is reproduced well with the convolution of Pt(766) [=13(111)–(100)] and Pt(17 1 1) [=9(100)–(111)] electrodes. These results suggest that the planes of the cubic and cuboctahedral nanoparticles are composed of step‐terrace and atomically flat terraces, respectively. Adsorbed carbon monoxide (CO) on the shape‐controlled nanoparticles gives the IR bands that are assigned to on‐top and bridged CO. The band of on‐top CO is deconvoluted to two bands: the higher and the lower frequency bands are assigned to the CO on the plane and the edges of the nanoparticles, respectively. On‐top CO adsorbed on the edges is oxidized at more negative potential than that on the planes. Edge sites of the nanoparticles promote CO oxidation.     

Photolysis of Carbonyl Diisocyanate: Generation of Isocyanatocarbonyl Nitrene and Diazomethanone

The stepwise decomposition of carbonyl diisocyanate, OC(NCO)₂, has been studied by using IR spectroscopy in solid argon matrices at 16 K. Upon irradiation with an ArF laser (λ=193 nm), carbonyl diisocyanate split off CO and furnished a new carbonyl nitrene, OCNC(O)N, in its triplet ground state. Two conformers of the nitrene, syn and anti, that were derived from the two conformers of OC(NCO)₂ (62 % syn–syn and 38 % syn–anti) were identified and characterized by combining IR spectroscopy and quantum chemical calculations. Subsequent irradiation with visible light (λ>395 nm) caused the Curtius rearrangement of the nitrene into OCNNCO. In addition to the expected decomposition products, N₂ and CO, further photolysis of OCNNCO with the ArF laser yielded NOCN, through a diazomethanone (NNCO) intermediate. To further validate our proposed reaction mechanism, ArF‐laser photolysis of the closely related NNNNCO and cyclo‐N₂CO in solid argon matrices were also studied. The observations of NOCN and in situ CO‐trapped product OCNNCO provided indirect evidence to support the initial generation of NNCO as a common intermediate during the laser photolysis of OCNNCO, NNNNCO, and cyclo‐N₂CO.     

Conformational reorientation of immunoglobulin G during nonspecific interaction with surfaces.

To achieve a better understanding of the nonspecific adsorption process of proteins on solid surfaces, the mechanism of this interaction was investigated by a model system comprising the structurally flexible ("soft") protein goat anti-rabbit immunoglobulin G and a set of chemically defined surfaces. The thermodynamic properties of both protein and surfaces were derived from contact angle measurements by applying the Lifshitz-van der Waals acid-base approach, and the Gibbs free enthalpy of interaction was calculated. The protein shows two conformational states, one hydrophobic and the other hydrophilic. The interaction energy indicates that the hydrophobic conformation favorably adsorbs onto the surfaces. With real-time binding kinetics, measured by a supercritical angle fluorescence biosensor, we show that during the nonspecific adsorption the protein performs a reorientation in its three-dimensional amino acid structure from a hydrophilic to a hydrophobic molecular structure. Unlike the rates of adsorption and desorption, the transition rate is independent of the type of surface and only influenced by the structural reorganization of the protein.     

Catalytic effects of ruthenium and osmium spontaneous deposition on platinum surfaces toward methanol oxidation

The influence of ruthenium and osmium spontaneous deposition on polycrystalline platinum in sulfuric acid was studied by conventional electrochemical techniques. The inhibition of the hydrogen adatom voltammetric profile by the foreign adatoms was used to calculate the degree of surface coverage of ruthenium, osmium, and a mixture of both metal ions from solutions of different composition. Methanol adsorption and oxidation were compared on bare platinum, platinum/ruthenium, platinum/osmium, and ternary compounds, considering the efficiency of methanol oxidation per hydrogen adatom displaced by the foreign metal on platinum.     

Experimental and theoretical study of 2,6-difluorophenylnitrene, its radical cation, and their rearrangement products in argon matrices.

2,6-Difluorophenylnitrene was reinvestigated both experimentally, in Ar matrices at 10 K, and computationally, by DFT and CASSCF/CASPT2 calculations. Almost-pure samples of both neutral rearrangement products (the bicyclic azirine and the cyclic ketenimine) of a phenylnitrene were prepared and characterized for the first time. These samples were then subjected to X-irradiation in the presence of CH2Cl2 as an electron scavenger, which led to ionization of the neutral intermediates. Thereby, it was shown that only the phenylnitrene and the cyclic ketenimine yield stable radical cations, whereas the bicyclic azirine decays to both of these compounds on ionization. The cyclic ketenimine yields a novel aromatic azatropylium-type radical cation. The electronic structure of the title compound is discussed in detail, and its relation to those of the iso-pi-electronic benzyl radical and phenylcarbene is traced.     

An infrared study on the chemisorption of tertiary phosphines on coinage and platinum group metal surfaces

The chemisorption of dimethylphenyl-, methyldiphenyl- and triphenylphosphine on evaporated gold, silver, copper, rhodium, iridium, palladium, platinum and nickel surfaces has been studied by means of infrared reflection–absorption spectroscopy (IRAS). Multilayers of physisorbed phosphine are formed on the surfaces of all metals studied except nickel after deposition from dilute toluene solution. The deposition rate varies for different metal surfaces and it is sometimes quite slow. The standard immersion time was 20 h in this study to secure that an equilibrium between the surface and the solution is reached. Several minutes of ultrasonic treatment are required to get rid of the physisorbed phosphine, leaving a very thin layer of chemisorbed phosphine on the metal surface. Most of the absorption bands in IRAS spectra of these thin layers show significant shifts, which are especially large for dimethylphenylphosphine. It is evident that the electron distribution in the entire phosphine molecules is changed and that the chemisorption to the coinage and platinum group metal surfaces is strong. Infrared spectra of coordination compounds of gold(I), silver(I) and copper(I) with dimethylphenyl-, methyldiphenyl- and triphenylphosphine and of the corresponding phosphine oxides have served as reference material for the chemisorbed phosphines. The spectra of the coordination compounds show similar shifts and intensity changes as the IRAS spectra of tertiary phosphines chemisorbed on the coinage and platinum group metals. This suggests that the studied phosphines are as strongly bound to the coinage and platinum group metal surfaces as to the monovalent coinage metal ions known to form very stable complexes with tertiary phosphines.     

Rhenium deposition on platinum surface by reduction of perrhenic acid with methanol

It has been demonstrated that rhenium deposition onto Pt surface can be carried out by reduction of perrhenic acid with methanol and results in the same adsorbed species as its reduction either with hydrogen or with electric polarization.     

中空树枝状三氧化钨载铂催化剂对甲醇的电催化氧化性能研究

采用水热法和牺牲模板法相结合制备具有中空树枝结构的三氧化钨载体(d-WO₃),在其表面进一步负载活性成分Pt,得到纳米Pt/d-WO₃复合催化剂。采用X射线粉末衍射(XRD)、透射电镜(TEM)和比表面积和孔结构分析(BET)等对催化剂的形貌和结构进行了表征。结果表明,三氧化钨具有长6 μm和宽2 μm的中空树枝状结构,孔径分布主要集中在20~120 nm,比表面积为24 m²/g,平均粒径为7.2 nm的Pt纳米粒子均匀分布在其表面。采用循环伏安和计时电流法研究了Pt/d-WO₃催化剂在酸性溶液中对甲醇的电催化氧化性能。结果表明,Pt/d-WO₃催化剂比Pt/C和Pt/WO₃催化剂对甲醇有更高的电催化氧化活性和稳定性。d-WO₃所具有的中空介孔结构和双功能作用机理有利于甲醇在铂表面的直接脱氢氧化过程。     

Adsorption of [D2]methanol on Ru(001)--O surfaces: the influence of preadsorbed oxygen on the methoxide geometry.

The influence of oxygen precoverage on the bonding geometry of methoxide on Ru(001) was studied using the isotopically labeled molecule CHD2OH by reflection-absorption infrared spectroscopy (RAIRS). This molecule is an excellent model because the vibrational spectra of CHD2O- may be unambiguously correlated with the adsorption configuration. For Ru(001)--O layers with an effective oxygen coverage (theta0) between 0.25 and 0.6 ML (ML=monolayer), the influence of the oxygen precoverage was shown to vary with the initial methanol exposure. For an extremely low dose of [D2]methanol (0.01 L; L=Langmuir, 1 L=10(-6) torr s), at 90 K, no oxygen-coverage effects were detected on the geometry of [D2]methoxide: it adsorbs in an upright orientation (pseudo-C(3v) local symmetry), just as on clean Ru(001). An increase in the methanol exposure to 0.1 L, at the same temperature, results in the formation of a disordered layer of tilted methoxide: for theta(O)=0.25 ML, C(s)/C1 and intrinsic C1 configurations are present on the surface, whereas for theta(O)> or =0.5 ML, only the former species were identified. The thermal activation of these tilted layers to 105 K results in a lower coverage of upright methoxide for any oxygen precoverage, coadsorbed with decomposition products, as confirmed by the detection of adsorbed formaldehyde and, on the denser oxygen layer (theta(O)=0.6 ML), formate. The influence of the oxygen precoverage becomes determinant when annealing a [D2]methanol multilayer to 105 K: for theta(O)=0.25 ML, the RAIR spectrum correlates with a disordered layer of tilted methoxide and formaldehyde, whereas for theta(O)=0.6 ML upright methoxide, formate, and carbon monoxide were identified. On clean Ru(001), for methanol exposures > or =0.1 L, the C(3v) methoxide configuration was never attained upon thermal activation.