Electrochemical promotion of RuO2 catalysts for the combustion of toluene and ethylene

The electrochemical promotion of the complete catalytic oxidation of ethylene and toluene on RuO₂Catalyst films deposited on Y₂O₃-stabilized-ZrO₂ (YSZ) has been investigated at temperatures 400 to 500°C. Anodic polarization (1.5 V), i.e. O^2– supply from the YSZ support to the catalyst, is found to enhance the rates of ethylene and toluene oxidation by a factor of 10 and 8 respectively. Cathodic polarization (–1.5 V) i.e. oxygen removal from the catalyst, enhances the oxidation rates by a factor of 3 and 4, respectively. These rate enhancements are strongly nonFaradaic. The kinetics, positive order in both reactants, and the promotional results, inverted-volcano type for both reactions, conform to the recently found rules of electrochemical promotion.*To whom correspondence should be addressed. E-mail: cat@chemeng.upatras.gr     

The effects of titania overlayers on C2H4/CO/H2 reactions over a Rh foil

The effects of submonolayer deposits of titania on the activity and selectivity of a Rh foil catalyst for C₂H₄/CO/H₂ reactions have been investigated. Reactions were carried out at 1 atm total pressure and at temperature of 488 K and 523 K. The addition of titania to the catalyst enhances the total rate of C₃-oxygenate formation. This rate enhancement is due entirely to an increase in the rate of 1-propanol formation, which reaches a maximum at a TiO _x . coverage of 0.2 ML. The rate of propanal formation, by contrast, is not enhanced. The rates of formation of methane, ethane, and C₃-hydrocarbons also exhibit rate maxima at a TiO _x . coverage of 0.2 ML. The rates of formation of C₄- and C₅-hydrocarbons, on the other hand, are suppressed by titania addition. The higher rate of 1-propanol production in the presence of titania is attributed to an interaction between Ti³⁺ ions at the edge of TiO _x . islands and the carbonyl bond of adsorbed C₃-oxygenated species. Such interactions are envisioned to facilitate hydrogenation of the carbonyl bond.     

Electrochemical modification of the catalytic activity of TiO<Subscript>2</Subscript>/YSZ supported rhodium films

The electrochemical activation of ethylene oxidation was studied over rhodium catalysts of different thickness (40, 100 and 160 nm) sputtered on top of a thin layer of TiO₂ deposited on YSZ. The strong relationship between catalytic activity and oxidation state of rhodium was confirmed. Under open-circuit operation the catalyst potential appears as a suitable indicator of the surface oxidation state of rhodium allowing a prediction of the catalytic behavior from solid electrolyte potentiometric measurements. Under closed-circuit conditions the catalyst potential was used as a tool to tune the catalytic activity of rhodium which showed increasing promotional efficiency with decreasing catalyst film thickness.     

The Partial Oxidation of CH3OH to CO2 and H2 Over a Cu/ZnO/Al2O3 Catalyst

The partial oxidation of CH₃OH to CO₂ and H₂ over a Cu/ZnO/Al₂O₃ catalyst has been studied by temperature-programmed oxidation (TPO) using N₂O and O₂ as the oxidant. Post-reaction analysis of the adsorbate composition of the surface of the catalyst was determined by temperature-programmed desorption (TPD). The temperature dependence of the composition of the mixture of products formed by TPO was shown to depend critically on the partial pressure of the oxidant, with the highest partial pressure of oxygen used (10% O₂ in He, 101 kPa—the CH₃OH partial pressure was 17% throughout), producing marked non-Arrhenius fluctuations on temperature programming. Unsurprisingly, therefore, the adsorbate composition of the catalyst revealed by post-reaction TPD was also found to be determined by the partial pressure of the oxidant. Using high partial pressures of oxidant (5% and 10% O₂ in He, 101 kPa), the only adsorbate detected was the bidentate formate species adsorbed on Cu. Lowering the oxygen partial pressure to 2% in He (101 kPa) revealed a catalyst surface on which the bidentate formate on Cu was the dominant intermediate with the formate on Al₂O₃ also being present. A further lowering of the partial pressure of the oxidant, obtained by using N₂O as the oxidant (2% N₂O in He, 101 kPa), resulted in a surface on which the formate adsorbed on ZnO was the dominant adsorbate with only a small coverage of the Cu by the bidentate formate.     

Ti(OC4H9)4水解过程的粘度控制

报道了用溶胶-凝胶法制备二氧化钛薄膜过程中钛酸丁酯[Ti(OC4H9)4]水解特性的研究结果，给出了体系的酸碱度(酸催化或者碱催化)、添加乙酰丙酮(AcAc)和硝酸银(AgNO3)对Ti(OC4H9)4-C2H5OH-H2O体系粘度变化和凝胶化时间的影响，发现AgNO3对该体系溶胶有非常明显的稳定作用.     

Preparation and characteristics of thin film with wear-resistant behavior on HDPE surface polymerized by C2H2–H2–SiH4 plasma

Plasma-polymerized deposition of an acetylene–hydrogen–silane mixture (C₂H₂–H₂–SiH₄) to obtain thin film with good wear behavior on a high-density polyethylene (HDPE) surface was present in this work. It was found that the bond between thin film and HDPE substrate was excellent and H₂ gas in system led the deposited thin film to better adhesive properties, but slower thin film deposition rate. Surface wear-resistant properties of modified HDPE were improved with the input of SiH₄. Infrared and X-ray photoelectron spectroscopy spectra suggested that there be large quantities of >CO, O H, C Si, and Si O groups in thin film and that the ratio of C to Si was increased due to the addition of SiH₄ and H₂, which inferred that the thin film structure and components lie between organic and inorganic materials. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1561–1566, 1998     

Catalytic reduction of N2O with CH4 and C3H6 over Ag–Rh/Al2O3 bimetallic catalyst in the presence of oxygen

A study of nitrous oxide (N₂O) reduction with methane (CH₄) and propene (C₃H₆) in the presence of oxygen (5%) over Ag/Al₂O₃, Rh/Al₂O₃ and Ag–Rh/Al₂O₃ catalysts, with Ag and Rh loadings of 5 wt% and 0.05 wt% respectively, has been performed. From the results, it was observed that the Ag–Rh bimetallic catalyst was the most active for both nitrous oxide removal (more than 95%) and hydrocarbon oxidation. This high activity seems to be connected with a synergistic effect between Ag and Rh. The findings from X‐ray diffraction and X‐ray photoelectron spectroscopy studies showed also, that there were no strong interactions (eg alloying) between Ag and Rh. Copyright © 2005 Society of Chemical Industry     

Enhancement of C2H6 Oxidation by O2 in the Presence of N2O over Fe Ion-Exchanged BEA Zeolite Catalyst

Selective catalytic reduction (SCR) of N₂O with C₂H₆ took place effectively over Fe ion-exchanged BEA zeolite catalyst (Fe-BEA) even in the presence of excess oxygen. The mechanism in the SCR of N₂O with C₂H₆ over Fe-BEA catalyst was studied by a transient response experiment and an in situ DRIFT spectroscopy. No oxidation of C₂H₆ by O₂ took place below 350 °C (in C₂H₆/O₂). In the N₂O/C₂H₆/O₂ system, however, it was found that the reaction of C₂H₆ with O₂ was drastically enhanced by the presence of N₂O even at low temperatures (200-300 °C). Therefore, it was concluded that N₂O played an important role in the oxidation of C₂H₆ (i.e., activation of C₂H₆ at an initial step). On the basis of these findings, the mechanism in the SCR of N₂O with C₂H₆ is discussed.     

Direct Oxidation of H2 to H2O2 and Decomposition of H2O2 Over Oxidized and Reduced Pd-Containing Zeolite Catalysts in Acidic Medium

Both the conversion and H₂O₂ selectivity (or yield) in direct oxidation of H₂-to-H₂O₂ (using 1.7 mol% H₂ in O₂ as a feed) and also the H₂O₂ decomposition over zeolite (viz. H-ZSM-5, H-GaAlMFI and H- ) supported palladium catalysts (at 22 °C and atmospheric pressure) are strongly influenced by the zeolite support and its fluorination, the reaction medium (viz. pure water, 0.016 M or 1.0 M NaCl solution or 0.016 M H₂SO₄, HCl, HNO₃, H₃PO₄ and HClO₄), and also by the form of palladium (Pd⁰ or PdO). The oxidized (PdO-containing) catalysts are active for the H₂-to-H₂O₂ conversion and show very poor activity for the H₂O₂ decomposition. However, the reduced (Pd⁰-containing) catalysts show higher H₂ conversion activity but with no selectivity for H₂O₂, and also show much higher H₂O₂ decomposition activity. No direct correlation is observed between the H₂-to-H₂O₂ conversion activity (or H₂O₂ selectivity) and the Pd dispersion or surface acidity of the catalysts. Higher H₂O₂ yield and lower H₂O₂ decomposition activity are, however, obtained when the non-acidic reaction medium (water with or without NaCl) is replaced by the acidic one.     

Electrochemical promotion of NO reduction by C2H4 in 10% O2 using a monolithic electropromoted reactor with Rh/YSZ/Pt elements

The reduction of NO by C₂H₄ in high excess of O₂ and temperatures 200−300 °C was investigated using a monolithic electropromoted reactor (MEPR) with twenty-two Rh/YSZ/Pt parallel plate elements. It was found that at 220–240 °C and 10% O₂ the selective catalytic reduction (SCR) of NO can be electropromoted by 450% with near 100% selectivity to N₂ and Λ_NO values up to 2.4. The corresponding rate enhancement ratio of complete C₂H₄ oxidation is up to 900% with Faradaic efficiency, , values up to 350. The system appears promising for practical applications.