Metal-oxide boundary effects in vanadium oxide – Rh(111) inverse model catalysts: a RAIRS, STM and TPD study

The formation and the reactivity of V-oxide/Rh(111) inverse catalyst surfaces has been investigated by reflection absorption infra red spectroscopy (RAIRS), varaiable-temperature scanning tunneling microscopy (VT-STM) and thermal programed desorption (TPD), The oxidation of metallic V island structures deposited on Rh(111) at room temperature has been monitored in situ at 200 °C and 400 °C by VT-STM and RAIRS, leading to small-island and large-island morphologies, respectively. The different reactivities of the generated inverse catalyst surfaces have been probed using the adsorption and oxidation reaction of CO. It is shown that the small-island V-oxide/Rh(111) catalyst exhibits enhanced reactivity in the oxidation of CO and is more easily subjected to oxide reduction. This is ascribed to the significant influence of the metal-oxide phase boundary on the catalyst activity. This paper is dedicated to Konrad Hayek.     

Surface Chemistry Involved in Epitaxy of Graphene on 3C-SiC(111)/Si(111)

Surface chemistry involved in the epitaxy of graphene by sublimating Si atoms from the surface of epitaxial 3C-SiC(111) thin films on Si(111) has been studied. The change in the surface composition during graphene epitaxy is monitored by in situ temperature-programmed desorption spectroscopy using deuterium as a probe (D₂-TPD) and complementarily by ex situ Raman and C1s core-level spectroscopies. The surface of the 3C-SiC(111)/Si(111) is Si-terminated before the graphitization, and it becomes C-terminated via the formation of C-rich (6√3 × 6√3)R30° reconstruction as the graphitization proceeds, in a similar manner as the epitaxy of graphene on Si-terminated 6H-SiC(0001) proceeds.     

The role of Rh on Pt-based catalysts: structure sensitive NO + H2 reaction on Pt(110) and Pt(100) and structure insensitive reaction on Rh/Pt(110) and Rh/Pt(100)

The catalytic activity of the Pt(110) surface for the reaction of NO + H₂ was much less than that of the Pt(100) surface. However, the catalytic activity of the Rh deposited Pt(1l0) surface was almost equal to that of the Rh deposited Pt(100) surface. That is, the catalytic reaction of NO + H₂ on Pt(110) and Pt(100) surfaces is highly structure sensitive, but it changes to structure insensitive by the deposition of Rh atoms. These results are rationalized by formation of an active overlayer on the Pt(110) and Pt(100) surfaces, which is very analogous to the Rh-O/Pt-layer formed on Rh/Pt(100), Pt/Rh(100) and Pt-Rh(100) alloy surfaces during catalysis. The formation of the common overlayer of Rh-O/Pt-layer during catalysis is responsible for the structure insensitive catalysis of Rh deposited Pt-based catalysts, which is an important role of Rh in a three way catalyst.     

Pd deposition onto Au(111) from nitrate solution

The initial stages of palladium deposition onto Au(111) from 0.1 M HNO₃ + 0.2 mM Pd(NO₃)₂ have been studied by cyclic voltammetry and in situ scanning tunnelling microscopy. It is demonstrated that nucleation starts exclusively at surface defects such as monoatomic high steps, which is at variance with recently published work. From this and our previous work it thus appears that surface defects are the preferred nucleation sites indeed for nitrate, sulphate and chloride containing solutions.     

Infrared spectroscopic detection of Rh(1) by CO in supported Rh catalyst

The detection limit of Rh(1) in the Rh/Al₂O₃ catalyst in a form of Rh¹(CO)₂ was determined by FTIR spectroscopy. It was demonstrated that at least 0.5 g Rh, corresponding to 0.005 wt% of Rh, can be identified in this way. During synthesis gas conversion the predominant surface species is Rh _x -CO, but a detectable amount of Rh(1) exists on the catalyst up to 473 K.This laboratory is a part of the Center for Catalysis, Surface and Material Science at the University of Szeged.     

Ethylene dimerization over a model Sn/Pt(111) catalyst

The dimerization reaction of ethylene was studied over Pt(111) and (3×3)R30°-Sn/ Pt(111) model catalysts at moderate pressures (20–100 Torr). The catalyst surfaces were prepared and characterized in a UHV surface analysis system and moderate pressure catalytic reactions were conducted with an attached batch reactor. The overall catalytic activity of the (3×3)R30°-Sn/Pt(111) surface alloy for C₄ products was slightly higher than that at Pt(111). In addition to the dimerization reaction, hydrogenolysis of ethylene to propane and methane was also observed, with the (3×3)R30°-Sn/Pt(111) surface alloy less active than Pt(111). Among the C₄ products, butenes andn-butane were the major components. Carbon buildup was observed to be significant above 500 K with the (3×3)R30°-Sn/Pt(111) surface alloy much more resistant than Pt(111). The dimerization of ethylene was not eliminated by the presence of surface carbonaceous deposits and even at significant surface coverages of carbon the model catalysts exhibited significant activities. The results are discussed in terms of the surface chemistry of ethylene and the previously reported catalytic reactions of acetylene trimerization andn-butane hydrogenolysis at these surfaces.     

In/Au(111)和Ir/Au(111)面上巴豆醛选择加氢的机理研究及比较

基于巴豆醛在M/Au（111）合金表面（M=In,Ir）垂直吸附的最稳定吸附结构,采用密度泛函理论对其不完全加氢的反应机理进行探究。从不同加氢机理下各基元反应的活化能、反应热计算以及构型变化分析中可知,巴豆醛在M/Au（111）面上均优先对距离合金表面较近的C＝O进行加氢,且以C为活性中心优先进行加氢为最优机理,其中第1步加氢反应的活化能较高,是该机理的控速步骤。反应物巴豆醛的O原子与合金的掺杂原子M形成较强的化学吸附,提高了M/Au（111）面对C＝O加氢的选择性。巴豆醛按最优机理加氢的基元反应中在In/Au（111）面上最高反应能垒为0.969 eV,比在Ir/Au（111）面的最高反应能垒1.332 eV低,因此认为In/Au合金对其不完全加氢有更好的催化活性。     

Extraction and separation of Pt(IV)/Rh(III) from acidic chloride solutions using Aliquat 336

Extraction and separation of Pt(IV)/Rh(III) from chloride solutions using Aliquat 336 (Quaternary ammonium salt made by the methylation of mixed tri octyl/decyl amine) diluted in kerosene as an extractant/synergist alone and mixed with organophosphorous extractants as synergists/extractants were carried out from an aqueous feed containing 0.0005 mol L⁻¹ Pt(IV)/Rh(III).Variation of hydrochloric acid concentration of aqueous phase from 0.005 to 10.0 mol L⁻¹ increased the percentage extraction of platinum up to 5.0 mol L⁻¹ there after it decreases. Whereas in the case of rhodium, from 0.005 to 1.0 mol L⁻¹ acid range the percentage extraction was decreased from 1.0 to 10.0 mol L⁻¹ acid range is favorable for extraction. Platinum(IV)/rhodium(III) separation factor of 279.2 was obtained at 1.0 mol L⁻¹ HCl concentration with 0.005 mol L⁻¹ Aliquat 336 and separation factor of 612.3 was obtained at 3.0 mol L⁻¹ HCl concentration with 0.01 mol L⁻¹ Aliquat 336. The present study optimized the various experimental parameters like phase contact time, effect of extractant, salts, temperature, loading capacity of extractant, stripping studies with various mineral acids/bases, recycling and reusing capacity of extractant up to ten cycles.     

Light Emission from M-Type Enantiomer of 2,13-bis(hydroxymethyl)[7]-thiaheterohelicene Molecules Adsorbed on Au(111) and C60/Au(111) Surfaces Investigated by STM-LE

Light emission from the M-type enantiomer of a helicene derivative (2,13-bis(hydroxymethyl)[7]-thiaheterohelicene) adsorbed on the clean Au(111) and the C₆₀-covered Au(111) surfaces were investigated by tunneling-current-induced light-emission technique. Plasmon-originated light emission was observed on the helicence/Au(111) surface and it was strongly suppressed on the area where the helicene molecules were adsorbed at the edges of the Au(111) terraces. To avoid luminescence quenching of excited helicene molecules and to suppress strong plasmon light emission from the Au(111) surface, C₆₀ layers were used as decoupling buffer layers between helicene molecules and the Au(111) surface. Helicene molecules were adsorbed preferentially on the Au(111) surface rather than on the C₆₀ buffer layers due to the small interaction of the molecules and C₆₀ islands. This fact motivated us to deposit a multilayer of helicene molecules onto the C₆₀ layers grown on the Au(111) surface, leading to the fact that the helicene/C₆₀ multilayer showed strong luminescence with the molecules character. We consider that such strong light emission from the multilayer of helicene molecules has a plasmon origin strongly modulated by the molecular electronic states of (M)-[7]TH-diol molecules.     

Methanol synthesis by the hydrogenation of CO2 over Zn-deposited Cu(111) and Cu(110) surfaces

The hydrogenation of CO₂ over Zn-deposited Cu(111) and Cu(110) surfaces was performed at 523 K and 18 atm using a high pressure flow reactor combined with XPS apparatus. It was shown that the ZnO _x species formed on Cu(111) during reaction directly promoted the methanol synthesis. However, no such promotional effect of the Zn was observed for methanol formation on Cu(110). Thus, Zn on Cu(111) acts as a promoter, while Zn on Cu(110) acts as a poison. The activation energy and the turnover frequency are in fairly good agreement with those obtained for Cu/ZnO powder catalysts.     

Synergistic Effect in the Dehydrogenation of Cyclohexene on C/W(111) Surfaces Modified by Submonolayer Coverage Pt

The dehydrogenation and decomposition of cyclohexene on the Pt-modified C/W(111) surfaces have been studied by temperature-programmed desorption (TPD), Auger electron spectroscopy (AES) and high-resolution electron energy loss spectroscopy (HREELS). The objective of the current study is to investigate how the surface reactivity of tungsten carbide is modified by the presence of submonolayer Pt. Similar to that observed on Pt(111), Pt(100) and C/W(111) surfaces, the characteristic reaction pathway on Pt/C/W(111) is the selective dehydrogenation of cyclohexene to benzene. At a Pt coverage of 0.52 monolayer, the selectivity to the gas-phase benzene product is 86±7%, which is slightly higher than that on Pt(111) (75%) and on C/W(111) (67±7%). More importantly, the desorption of benzene on Pt/C/W(111) is a reaction-limited process that occurs at 290 K, which is much lower than the benzene desorption temperature of 400 K from Pt(111).     

The decomposition of NO on CNTs and 1 wt% Rh/CNTs

Carbon nanotubes (CNTs) and CNTs-supported rhodium were tested as catalysts for NO decomposition. For the fresh catalysts, 100% NO conversion was achieved at 600°C over CNTs; when 1 wt% Rh was loaded on CNTs, 100% NO conversion was achieved at 450°C. If the catalysts were pre-reduced in H₂ at or above 300°C, 100% NO conversions were observed at 300°C. XPS investigation indicated that there was still metallic rhodium (BE=307.2 eV) on Rh/CNTs after heating in air at 500°C for 2 h and after the NO decomposition reaction. As for a 1 wt% Rh/Al₂O₃ sample, the rhodium (BE = 308.2 eV) was completely in the form of Rh₂O₃ after similar treatments. These results suggest that compared to γ-Al₂O₃, the CNTs material is more capable of keeping the rhodium in its metallic state. The results obtained in H₂-TPR studies support this conclusion. In addition, TEM investigation revealed that the rhodium particles distributed rather evenly over CNTs with a particle diameter of around 8 nm. We propose that CNTs can be used as a material for the facilitation of NO decomposition. This revised version was published online in July 2006 with corrections to the Cover Date.     

Adsorption and desorption of copper(II) from solutions on new spherical cellulose adsorbent

An investigation was conducted on the adsorption and desorption of copper(II) from aqueous solutions with a new spherical cellulose adsorbent containing the carboxyl anionic group. Various factors affecting the adsorption were optimized. The adsorption of Cu²⁺ ions on the adsorbent was found to be dependent on the initial time and pH, the concentration, and the temperature. The adsorption process follows both Freundlich and Langmuir adsorption isotherms and was found to be endothermic (ΔH = 23.99 kJ/mol). The Cu²⁺ ions adsorbed on the adsorbent can be recovered with a NaOH or HCl aqueous solution. The maximum percentage of recovery is about 100% when 2.4 mol/L HCl solution is used. In addition, only 7.2% of the adsorption capacity is lost after 30 replications of the adsorption and desorption. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 478–485, 2002; DOI 10.1002/app.10114     

Propene Oxidation on Ag(111): Spectroscopic Evidence of Facile Abstraction of Methyl Hydrogen

Reactions of propene on an oxygen-modified Ag(111) surface were investigated by means of temperature-programmed reaction spectra and reflection--adsorption infrared spectroscopy (RAIRS) at 100 K. In the presence of oxygen adatoms, interactions of propene with the substrate are strengthened. The reaction between propene and oxygen adatoms (0.086 monolayer) produces not only total oxidation products (CO₂ and H₂O), but also partial oxidation products (CO and acetone). The formation of chemisorbed hydroxyl groups is identified by RAIRS when coadsorbed propene and oxygen adatoms are annealed to 200 K. The formation of hydroxyl is ascribed to the abstraction of methyl hydrogen by oxygen adatoms.     

Thermal degradation of poly(sulfobetaines)

Due to their interesting properties, zwitterionic polymers have been extensively studied; however, only a few reports discuss their thermal degradation. The objective of this work was to study the pattern of thermal degradation of three poly(sulfobetaines) with different lateral chain lengths and the relationship between structure and degradation mechanism of the polymers. Because the initial decomposition temperatures are not significantly different in polymers with different ethylene glycol residues, it was possible to study the thermal behavior of these polymers at the same temperature range. The apparent activation energies of the degradation for polymers, calculated by the Ozawa method, was different for each poly(sulfobetaine). A decomposition mechanism is suggested, which included a Hoffman elimination of the quaternary amine giving vinyl ethers, which in turn, decompose to carboxylic acids, which can suffer and intramolecular cyclization reaction, and finally produce a polypropylene like chain. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1409–1414, 1999     

Structure sensitivity of alcohol reactions on (110) and (111) palladium surfaces

A temperature programmed reaction/desorption (TPD) study of decomposition pathways of methanol, ethanol, 1-propanol and 2-propanol was conducted on the clean Pd(110) surface under ultra-high vacuum conditions. No alcohol underwent C-O scission. Alcohols appear to react on this clean surface via the same dehydrogenation and decarbonylation steps observed on the Pd(111) surface. In contrast to previous reports noting substantial differences in methanol chemistry on the Pt(110) and (111) surfaces, the reactions of methanol and ethanol were found to be the same on the Pd(110) and (111) surfaces, giving rise to H₂ plus CO from methanol, and H₂, CO, and CH₄ from ethanol. The C₃ alcohols, 1- and 2-propanol, did produce somewhat different products on the Pd(110) and (111) surfaces, but these differences can be accounted for by differences in the chemistry of intermediate reaction products, rather than different reaction pathways of the parent alcohols.     

生物滴滤塔处理低浓度氮氧化物

采用活性炭填料挂膜的生物滴滤塔净化低浓度氮氧化物废气,研究结果表明,生物净化效率可达99%。适宜的喷淋量为3L/h,适宜的气体流量为0.4～0.5m3/h。当气体流量在0.56m3/h,入口气体氮氧化物浓度为480mg/m3,停留时间18.4s时,氮氧化物的净化效率可达到96.67%。净化氮氧化物的反硝化菌大部分为副球菌属(Paracoccus)中的细菌,也有小部分硫杆菌属(Thiobacillus)中的细菌。活性炭生物净化氮氧化物废气主要发生在活性炭外表面,而活性炭内表面发生的生化反应很少。     

Absorption and desorption of chromium ions by poly(acrylic acid) gels

The ability of crosslinked poly(acrylic acid) gels to retain chromium species was studied as a function of pH. Chromium retention was found to increase with pH according to two mechanisms. In the low pH range where chromium species are soluble, retention occurs via ion‐binding in the whole volume of the gel. At higher pH where insoluble chromium hydroxide particles are formed, retention comes from an adsorption process at the surface of the gel. The desorption of chromium species under acidic conditions was also investigated and found to be very dependent on retention mechanism and aging time of the polymer–chromium complex. When retention occurs by ion‐binding, only partial desorption was achieved at very short aging time. In contrast, a very fast desorption was observed when retention occurs via adsorption at the surface of the polymer gel. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 455–466, 1999     

Oxidation of Cl-modified Ag(111) under UHV conditions and ethylene adsorption on the oxidized surface

Oxidation of Cl-modified Ag(111) under UHV conditions was investigated using AES, ISS and HREELS. The results showed that Cl-modified Ag(111) can be easily oxidized at 550 K by 1 × 10^–6 mbar oxygen which was also heated to 550 K. With HREELS two fundamental vibrations at 600 and 1000 cm^–1 were detected for silver oxide and the multiple losses and combination excitations as well. Ethylene adsorption on the oxide was analyzed by HREELS. Surface hydroxyl species was formed at 230 K and stable to above 300 K, which is attributed to silver oxide. Ethylidyne was suggested to form concurrently with hydroxyl species.