Unique properties of Ir/ZSM-5 catalyst for NO reduction with CO in the presence of excess oxygen

The reduction of NO with CO in the presence of excess oxygen was investigated over different noble metal catalysts for probing the relationship between catalytic properties and adsorption behaviors. Among the four precious metal catalysts investigated, Ir/ZSM-5 was found to be the only active one for NO reduction with CO under lean conditions. With the decreasing of the Ir content, higher NO conversion and CO selectivity was obtained. Temperature-programmed reaction (TPR) studies of NO/H-2/O-2 and NO/CO/O-2 showed that the Pt/ZSM-5 was active when H-2 was used as the reductant, whereas, the Ir/ZSM-5 was active when CO was the reducing agent. This difference is due to the different mechanisms of the two reactions. Temperature-programmed desorption (TPD) of NO, CO and O-2 showed that NO could dissociate more easily over the Ir/ZSM-5 than on the Pt/ZSM-5, while the oxidation of CO by O-2 proceeded more rapidly on the Pt/ZSM-5 than on the Ir/ZSM-5. The presence of excess O-2 inhibited drastically the dissociation of NO, which is considered as the key step for the NO-CO reaction. The high dissociation rate of NO over the Ir/ZSM-5 is visualized as the key factor for its superior high activity in NO reduction with CO under lean conditions. (C) 2002 Elsevier Science B.V. All rights reserved.

Preparation and optical properties of Ag/PPy composite colloids

Ag/PPy (polypyrrole) composite colloids were prepared through the reaction of silver nitrate with pyrrole solution in DNIF either in the dark, or under the irradiation of femtosecond laser (fs) pulse or UV lamp. The UV-vis spectra of the nanocomposite colloid display an intense absorption band around 620 nm, accompanied by a weak one around 470 nm. The colors and optical absorption spectra of as-synthesized colloids can be reversibly tuned between blue and red, corresponding to absorption band of 620 urn and 526 urn, within few seconds by adding base and acid solutions or gases in turn into the composite colloid suspension. In addition, excess of H+ solution enhanced the absorption band around 470 nm and, at the same time, depressed that around 620 nm. The possible mechanism for the formation and optical absorption properties of the Ag/PPy composite colloid was proposed. (C) 2006 Elsevier B.V. All rights reserved.

Structural, morphological and optical properties of ZnO thin films grown on gamma-LiAlO2 substrate by pulsed laser deposition

ZnO thin films were deposited on the substrates of (100) gamma-LiAlO2 at 400, 550 and 700 degrees C using pulsed laser deposition (PLD) with the fixed oxygen pressure of 20 Pa, respectively. When the substrate temperature is 400 degrees C, the grain size of the film is less than 1 mu m observed by Leitz microscope and measured by X-ray diffraction (XRD). As the substrate temperature increases to 550 degrees C, highly-preferred c-orientation and high-quality ZnO film can be attained. While the substrate temperature rises to 700 degrees C, more defects appears on the surface of film and the ZnO films become polycrystalline again possibly because more Li of the substrate diffused into the ZnO film at high substrate temperature. The photoluminescence (PL) spectra of ZnO films at room temperature show the blue emission peaks centered at 430 nm. We suggest that the blue emission corresponds to the electron transition from the level of interstitial Zn to the valence band. Meanwhile, the films grown on gamma-LiAlO2 (LAO) exhibit green emission centered at 540 nm, which seemed to be ascribed to excess zinc and/or oxygen vacancy in the ZnO films caused by diffusion of Li. from the substrates into the films during the deposition.

Influence of level filling on optical properties of quantum well

In a specially- designed three-barrier-double-well tunneling structure, electron injecting from the emitter in combination with escaping through a resonant-tunneling structure were used to adjust and control the filling of electrons in different subbands. It was observed that the occupation in the first-excited electron state can result in a suppression to quantum confinement Stark effect. Moreover, at very low bias, a series of intrigue photoluminescence peaks appeared as a small quantity of excess electron was filled in the ground state of the quantum well, that cannot be explained by the theory of hand-to-hand transition in the framework of single electron picture.

Excess arsenic in GaAs grown at low temperatures by molecular beam epitaxy

The structural properties of GaAs grown at low temperatures by molecular beam epitaxy (LTMBE GaAs) were studied. The excess arsenic atoms in LTMBE GaAs exist in the form of arsenic interstitial couples (i,e, two ns atoms share the one host site), and cause an increase in the lattice parameter of LTMBE GaAs. Annealing at above 300 degrees C, the arsenic interstitial couples decomposed, and As precipitates formed, resulting in a decrease in the lattice parameter.

Thermodynamic investigation on properties of gasohol

The heat capacities (C-p) of three types of gasohol (which consisted of 20 wt % ethanol and 80 wt % unleaded gasoline 93(#) (system S1), 30 wt % ethanol and 70 wt % unleaded gasoline 931 (system S2), 40 wt % ethanol and 60 wt % unleaded gasoline 930 (system S3), where "93(#)" denotes the octane number) were measured by adiabatic calorimetry in the temperature range of 80320 K. A glass transition was observed at 94.24, 95.15, and 95.44 K for system S1, S2, and S3, respectively. A solid-solid phase transition and solid-liquid phase transition were observed at 135.18 and 151.30 K for system S1, 131.82 and 152.10 K for system S2, and 121.29 and 155.09 K for S3, respectively. The polynomial equations for C, with respect to the thermodynamic temperature (T), and with respect to the content of ethanol (x), were established through the least-squares fitting. The thermodynamic functions and the excess thermodynamic functions of the three samples were derived using these thermodynamic relationships and equations.

Thermodynamic properties of ethanol and gasoline blended fuel

The heat capacities (C-p) of five types of gasohol (50 wt % ethanol and 50 wt % unleaded gasoline 93(#) (E50), 60 wt % ethanol and 40 wt % unleaded gasoline 93(#) (E60), 70 wt % ethanol and 30 wt % unleaded gasoline 93(#) (E70), 80 wt % ethanol and 20 wt % unleaded gasoline 93(#) (E80), and 90 wt % ethanol and 10 wt % unleaded gasoline 93(#) (E90), where the "93" denotes the octane number) were measured by adiabatic calorimetry in the temperature range of 78-320 K. A glass transition was observed at 95.61, 96.14, 96.56, 96.84, and 97.08 K for samples from the E50, E60, E70, E80, and E90 systems, respectively. A liquid-solid phase transition and a solid-liquid phase transition were observed in the respective temperature ranges of 118-153 and 155-163 K for E50, 117-150 and 151-164 K for E60, 115-154 and 154-166 K for E70, 113-152 and 152-167 K for E80, and 112-151 and 1581-167 K for E90. The polynomial equations of Cp and the excess heat capacities (C-p(E)), with respect to the thermodynamic temperature, were established through least-squares fitting. Based on the thermodynamic relationship and the equations obtained, the thermodynamic functions and the excess thermodynamic functions of the five gasohol samples were derived.