The effects of a potassium overlayer on the reaction pathway of CH2 and C2H5 on Rh(111)

The effect of potassium on the reaction pathways of adsorbed CH₂ and C₂H₅ species on Rh(111) was investigated by means of reflection absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TDS). Hydrocarbon fragments were produced by thermal and photo-induced dissociation of the corresponding iodo compounds. Potassium adatoms markedly stabilized the adsorbed CH₂ and converted it into C₂H₄, the formation of which was not observed for K-free Rh(111). New routes of the surface reactions of C₂H₅ have been also opened in the presence of potassium, namely its transformation into butane and butene.     

Adsorption of CH3 and its reactions with CO2 over TiO2

The adsorption, decomposition of CH₃ and its reactions with CO₂ were followed by means of Fourier transform infrared spectroscopy combined with mass spectrometry. Methyl radicals were produced by the pyrolysis of azomethane. Absorption bands, observed at room temperature adsorption, were attributed to adsorbed CH₃ and CH₃O species. The decomposition of adsorbed CH₃ in vacuum started above 400 K and was accelerated by CO₂. In the study of the interaction of methane with titania, activated in different ways, we found no convincing spectroscopic evidence for the activation of methane at 300 K. This revised version was published online in July 2006 with corrections to the Cover Date.     

Formation and reactions of CH3 species over Mo2C/Mo(111) surface

The reaction pathways of adsorbed CH₃ on the Mo₂C/Mo(111) surface were investigated by means of temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and high-resolution electron energy loss spectroscopy (HREELS). CH₃ fragments were produced by the dissociation of the corresponding iodo-compound. CH₃I adsorbs molecularly on Mo₂C at 90 K and dissociates at and above 140 K. The main products of the reaction of adsorbed CH₃ are hydrogen, methane and ethylene. The coupling into ethane was not observed. The results are discussed in relevance to the conversion of methane into benzene on Mo₂C deposited on ZSM-5. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis, structure, and photovoltaic property of a nanocrystalline 2H perovskite-type novel sensitizer (CH3CH2NH3)PbI3

A new nanocrystalline sensitizer with the chemical formula (CH₃CH₂NH₃)PbI₃ is synthesized by reacting ethylammonium iodide with lead iodide, and its crystal structure and photovoltaic property are investigated. X-ray diffraction analysis confirms orthorhombic crystal phase with a = 8.7419(2) Å, b = 8.14745(10) Å, and c = 30.3096(6) Å, which can be described as 2 H perovskite structure. Ultraviolet photoelectron spectroscopy and UV-visible spectroscopy determine the valence band position at 5.6 eV versus vacuum and the optical bandgap of ca. 2.2 eV. A spin coating of the CH₃CH₂NH₃I and PbI₂ mixed solution on a TiO₂ film yields ca. 1.8-nm-diameter (CH₃CH₂NH₃)PbI₃ dots on the TiO₂ surface. The (CH₃CH₂NH₃)PbI₃-sensitized solar cell with iodide-based redox electrolyte demonstrates the conversion efficiency of 2.4% under AM 1.5 G one sun (100 mW/cm²) illumination.     

Decomposition and oxidation of CH3 13CH2OH on A12O3, Pd/Al2O3, and PdO/Al2O3 catalysts

Temperature-programmed desorption (TPD) and oxidation (TPO) were used to investigate the decomposition and oxidation of ethanol on Al₂O₃, Pd/Al₂O₃, and PdO/Al₂O₃. Ethyl--¹³C alcohol (CH₃ ¹³CH₂OH) was adsorbed on the catalysts so that reaction pathways of the two carbons could be distinguished. Alumina was mainly a dehydration catalyst, but dehydrogenation was also observed and some carbon remained on the surface. In the presence of O₂, A1₂O₃ oxidized the decomposition products and the-carbon was oxidized faster. Ethanol, which was adsorbed on A1₂O₃, decomposed much faster on Pd/A1₂O₃ by diffusing to Pd and undergoing CO elimination to form CH₄,¹³CO, H₂, and surface carbon. On PdO/A1₂O₃, the decomposition was slower than on Pd/A1₂O₃ until lattice oxygen was extracted above 450 K; the decomposition products were oxidized by lattice oxygen. In the presence of gas phase O₂, Pd/Al₂O₃ was an active oxidation catalyst at low temperature, but lattice oxygen had to be extracted from PdO/A1₂O₃ before it had significant oxidation activity.     

FT-IR spectroscopic investigation of the surface reaction of CH4 with NO x species adsorbed on Pd/WO3–ZrO2 catalyst

The interaction of methane at various temperatures with NO _x species formed by room temperature adsorption of NO + O₂ mixture on tungstated zirconia (18.6 wt.% WO₃) and palladium(II)-promoted tungstated zirconia (0.1 wt.% Pd) has been investigated using in situ FT-IR spectroscopy. A mechanism for the reduction of NO over the Pd-promoted tungstated zirconia is proposed, which involves a step consisting of thermal decomposition of the nitromethane to adsorbed NO and formates through the intermediacy of cis-methyl nitrite. The HCOO⁻ formed acts as a reductant of the adsorbed NO producing nitrogen.     

Pressure swing adsorption separation of H2S/CO2/CH4 gas mixtures with molecular sieves 4A, 5A,and 13X

Pressure swing adsorption experiments were carried out for the separation of equimolar mixtures of carbon dioxide and methane containing small amounts of hydrogen sulfide, utilizing 4A, 5A, and 13X molecular sieves. High-purity methane of zero or nearly zero hydrogen sulfide concentration was produced in the adsorption stage with 13X and 5A sieves, at high product recovery rates; high-purity carbon dioxide was obtained with the same sieves in the desorption stage. Zeolite 4A was found capable of raising considerably the hydrogen sulfide concentration in the accumulated desorption product (vs. the adsorption feed) at high recovery rates too. Adsorption selectivity values derived from the experimental results for all three gas pairs were in line with some theoretical predictions and experimental data of the literature.     

Effects of potassium on the chemisorption of CO2 and CO on the Mo2C/Mo(100) surface

The interaction of CO₂ with K-promoted Mo₂C/Mo(100) has been studied with high-resolution electron energy loss spectroscopy, work function measurements and temperature-programmed desorption. Pre-adsorbed potassium dramatically affects the adsorption behavior of CO₂ on the Mo₂C/Mo(100) surface. It increases the rate of adsorption, the binding energy of CO₂ and it induces the dissociation of CO₂ through the formation of negatively charged CO₂. Potassium adatoms also promote the dissociation of adsorbed CO over Mo₂C. This revised version was published online in July 2006 with corrections to the Cover Date.     

Theoretical investigation of ethylene adsorbed on Ni(100) surface by the multiple-scattering cluster method

In this paper the carbon K-edge near edge X-ray absorption fine structure spectra (NEXAFS) of adsorption system C₂H₄/Ni(100) are calculated using the multiple-scattering cluster method. By a comparison between the theoretical results and experimental spectra, the chemisorption geometry of this system has been determined. The result shows that the molecule is adsorbed on the perpendicular bridge site, and the distance between the C atom and the nearest Ni atom is 1.70 Å, while the molecular plane tilting to the surface is 50°. It is found that the interaction between hydrogen atom and Ni substrate plays an important role in the formation of the adsorption structure. The above results are supported by other evidences.     

Trapping of CH3O formed from CO + H2

Methoxy formed on Al₂O₃ from¹³CO and H₂ coadsorption on Ni/Al₂O₃ was trapped by C₂H₅OH adsorption and temperature-programmed reaction (TPR). The presence of excess C₂H₅OH significantly increases the rate of¹³CH₃OH and (¹³CH₃)₂O formation. The¹³CH₃OH forms by the reaction of C₂H₅OH with¹³CH₃O on Al₂O₃. In the absence of C₂H₅OH,TPR following¹³CO and H₂ coadsorption did not produce significant amounts of¹³CH₃OHor(¹³CH₃)₂O.     

TPD study of the reaction of CH3CH2SH and (CH3CH2)2S2 on ZnO(0001) and ZnO

Superior activation of on 1 wt% Pt/TiO₂ catalysts for the oxidation of CO was attained by loading a large amount of Fe-oxide (100 wt%) and TiO₂. In situ IR spectra of CO proved that the structural transformation is brought about on the Pt-sites by loading of Fe-oxide, where predominant Pt-sites giving linear CO change to highly reactive bridge CO Pt-sites. In contrast, no transformation of the linear CO sites to the bridge CO sites takes place by loading of TiO₂ but the environment of Pt-sites for linear CO is changed.     

Spectroscopic evidence for the formation of CHx species in the hydrogenation of carbidic carbon on Ni(100)

The CH _x species formed on Ni(100) by hydrogenation of carbidic carbon have been detected using high resolution electron energy-loss spectroscopy (HREELS). Exposures of carbidic carbon to 1×10^–7 Torr H₂ and D₂ at 313 K for 20 min produce CH _x and CD _x species, respectively. These species are identified by two energy-loss peaks for CH _x at 2970 and 1380 cm^–1 and only one peak for CD _x at 1980 cm^–1. Because of the existence of the intense peak at 1380 cm^–1, in the range of a scissors mode for CH₂ and a symmetric deformation mode for CH₃, the CH _x species are tentatively ascribed to CH₂ and/or CH₃. The CD _x species undergo decomposition at 330–370 K in UHV as well as in hydrogen below 10^–7 Torr. No stable CH _x species are observed above 400 K, which is lower than the normal reaction temperature of the methanation reaction (500 K).     

Adsorption and Reactions of CH2I2 on Clean and Oxygen-Modified Ag(111): a RAIRS and TPD Study

The surface chemistry of CH₂I₂ on Ag(111) in the presence and absence of pre-adsorbed O, produced by NO₂ adsorption at elevated temperature, has been examined using temperature-programmed desorption and reflection absorption infrared spectroscopy. There is good evidence for the formation of adsorbed methylene, CH₂(a), that reacts with another CH₂(a) to form and desorb ethylene, C₂H₄(g), in a reaction-limited process. Increasing the surface coverage of CH₂I₂ hinders both the dissociation and recombination processes indicated by the upward temperature shift in the formation of C₂H₄. Co-adsorbed O atoms strengthen the bonding of CH₂I₂ to the surface; the increased thermal stability is up to 60 K. The formation of C₂H₄ decreases with increasing amounts of pre-adsorbed O; the main reaction product is CH₂O produced in a reaction-limited process. CH₂O forms either on the chemisorbed or on the oxide phase with desorption peak temperatures of 225 and 270 K, respectively. The formation of gas-phase carbon dioxide suggests that a formate intermediate is involved in a secondary reaction pathway.     

Promotion through gas phase induced surface segregation: methanol synthesis from CO, CO2 and H2 over Ni/Cu(100)

We have studied the rate of methanol formation over Cu(100) and Ni/Cu(100) from various mixtures of CO, CO₂ and H₂. It is found that the presence of submonolayer quantities of Ni leads to a strong increase in the rate of methanol formation from mixtures containing all three components whereas Ni does not influence the rate from mixtures of CO₂/H₂ and CO/H₂, respectively. The influence of the partial pressures of CO and CO₂ on the rate indicates that the role of CO is strictly promoting. From temperature-programmed desorption spectra it follows that the surface concentration of Ni depends strongly on the partial pressure of CO. In this way the increase in reactivity is interpreted as a CO-induced structural promotion introduced by the stronger bonding of CO to Ni as compared to Cu. It is suggested that this type of promotional behavior will be of general importance in existent catalysts and perhaps even more relevant in the development of new or improved bimetallic catalysts. This revised version was published online in July 2006 with corrections to the Cover Date.     

Promoting Effect of Pt Addition to V2O5/ZrO2 Catalyst on Reduction of NO by C3H6

The effect of Pt addition to a V₂O₅/ZrO₂ catalyst on the reduction of NO by C₃H₆ has been studied by FTIR spectroscopy as well as by analysis of the reaction products. Pt loading promoted the catalytic activity remarkably. FTIR spectra of NO adsorbed on the catalysts doped with Pt show the presence of two different types of Pt sites, Pt oxide and Pt cluster, on the surface. The amount of these sites depends on Pt contents and the catalyst state. Pt atoms highly disperse on the surface as Pt oxide at low Pt content, being aggregated into Pt metal clusters by increasing Pt amount or reducing the catalysts. The spectral behavior of V=O bands on the surface also supports the formation of Pt clusters. It is concluded that Pt promotes the NO–C₃H₆ reaction through a reduction–oxidation cycle between its oxide and cluster form.     

Electrochemical and thermal studies of Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2 (x = 1/12, 1/4, 5/12, and 1/2)

Samples of the layered cathode materials, Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂ (x = 1/12, 1/4, 5/12, and 1/2), were synthesized at 900 °C. Electrodes of these samples were charged in Li-ion coin cells to remove lithium. The charged electrode materials were rinsed to remove the electrolyte salt and then added, along with EC/DEC solvent or 1 M LiPF₆ EC/DEC, to stainless steel accelerating rate calorimetry (ARC) sample holders that were then welded closed. The reactivity of the samples with electrolyte was probed at two states of charge. First, for samples charged to near 4.45 V and second, for samples charged to 4.8 V, corresponding to removal of all mobile lithium from the samples and also concomitant release of oxygen in a plateau near 4.5 V. Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂ samples with x = 1/4, 5/12 and 1/2 charged to 4.45 V do not react appreciably till 190 °C in EC/DEC. Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂ samples charged to 4.8 V versus Li, across the oxygen release plateau, start to significantly react with EC/DEC at about 130 °C. However, their high reactivity is similar to that of Li_0.5CoO₂ (4.2 V) with 1 μm particle size. Therefore, Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂ samples showing specific capacity of up to 225 mAh/g may be acceptable for replacing LiCoO₂ (145 mAh/g to 4.2 V) from a safety point of view, if their particle size is increased.     

Infrared spectroscopic study and characteristics of SnO2-based thick film for CH3CN detection

The SnO₂/Al₂O₃/Nb₂O₅/ISiO₂ thick film devices were fabricated by screen printing and dipping methods, and their sensing characteristics to CH₃CN gas was investigated. The oxidation products of CH₃CN on the thick film were analyzed by FT-IR using a heatable gas cell. The IR results showed that the products formed by oxidation of CH₃CN at 300 ‡C on the SnO₂/Al₂/Nb₂O₅ thick film without SiO₂ were mainly CO₂, H₂O, and NH₃, while on the SnO₂/Al₂O₃/Nb₂O₅/SiO₂ thick film products such as CO₂, H₂O, N₂O, HNO₃, and HNO₂ were observed. The thick film devices containing SiO₂ showed high selectivity and negative sensitivity to CH₃CN due to the presence of nitrogen compounds produced by oxidation of CH₃CN. Optimum amount of Nb₂O₅ and operating temperature were 1. 0 wt% and 300 ‡C, respectively.     

The permeability characteristics of non-porous membrane by C7H5F3/SiH4, plasma polymeric membrane

Low temperature rf-plasma was used to test the changes in the chemical and physical properties of a plasma-treated polymeric membrane made from C₇H₅F₃ and SiH₄, two materials that are very thermally, chemically, and mechanically stable. C₇H₅F₃ and SiH₄, plasma polymers were efficiently deposited to an aluminum oxide substrate with a pore size of 0.02μ. Even though the amount of the monomer C₇H₅F₃ increased, there was no significant change in the permeability of oxygen. However, selectivity of oxygen over nitrogen increased noticeably. Also, when the plate distance of the supporter from the cathode head within the reactor was 4 cm, the concentration gradients of C₇H₅F₃ and SiH₄ were the greatest. This resulted in the maximum value of permeability and selectivity and allowed the creation of a plasma-treated polymeric membrane with such characteristics when the composite permeation coefficient ranged from 4,500-7,500 GJ.s/kg.     

Pressure-Swing Adsorption Separation of H2S from CO2 with Molecular Sieves 4A, 5A,and 13X

The separation of bulk quantities of H₂S from CO₂ was investigated through a series of pressure-swing adsorption experiments utilizing 4A, 5A, and 13X molecular sieves. High selectivity of H₂S over CO₂ was encountered for all sieves, particularly for the 13X and 5A. Practically pure CO₂ was produced in the adsorption stage with fresh 5A and 13X sieves, at high product recovery rates. Efficient H₂S purification was obtained with fresh 5A and regenerated 4A zeolites. The experimental results were in line with theoretical predictions of the literature.     

Ionic Conductivity and Discharge Characteristic Studies of PVA-Mg(CH3COO)2 Solid Polymer Electrolytes

Ion conducting solid polymer electrolytes based on a polymer polyvinyl alcohol (PVA) complexed with magnesium acetate (Mg(CH₃COO)₂) were prepared by solution cast technique. Various experimental techniques, such as XRD, DSC, composition-dependent conductivity, temperature-dependent conductivity, and transport number measurements are used to characterize these polymer electrolyte films. The transference number data indicated the dominance of ion-type charge transport in these polymer electrolyte systems. An electrochemical cell with the configuration Mg/(80PVA + 20Mg(CH₃COO)₂)/(I₂ + C + electrolyte) has been fabricated and its discharge characteristics were studied. The Open Circuit Voltage (OCV) is 1.84 V.