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Using a combination of theory and experiments, we show that ZnO substitutionally doped with Ti or Al oxidizes CO by several parallel reaction pathways that differ from the traditional Mars-van Krevelen (MVK) mechanism. In one, the dopant atoms at the surface of the doped oxide adsorb and activate O 2 so that it reacts with CO. In the other, a surface oxygen atom from the lattice next to the dopant, D, moves onto the dopant and creates an O-D group and an oxygen vacancy. The O-D group is capable of oxidizing a reductant. To test these predictions made by theory, we have prepared Ti- and Al-doped ZnO and have shown that these compounds oxidize CO at temperatures at which pure-phase ZnO, Al 2O 3, or TiO 2 do not. The proposed mechanisms were made plausible by studying CO oxidation with 18O 2.

The gas-phase oxidation of CO catalyzed by iridium was studied under CO-rich reactant conditions over the pressure range 10 -4-10 -2 Pa to investigate the controversial size and pressure dependencies. The reactivity of iridium clusters with an average size of 3 nm was compared to macroscopic metal particles with extended single crystal facets over a range of temperatures (433-573 K), and the apparent activation energies for CO oxidation were consistent with the known activation energies for CO desorption from iridium surfaces. No size-specific dependence of the reaction kinetics was measured, and no indication of the previously reported "pressure gap" was observed. Unlike many other transition metal catalysts, iridium may be used as a model catalyst for CO oxidation in different morphological forms over a range of pressures without invoking a change in the kinetic model.

The reactivity of rutile phase TiO2 (110) and polycrystalline anatase surfaces with molecular and ionized deuterium and hydrogen was investigated. Thermal Desorption Spectroscopy (TDS), following exposure to more than 100kL of molecular deuterium, showed a D2 desorption peak at ∼440K on both single crystal rutile and polycrystalline anatase surfaces. The desorption peak was observed following exposure only at surface temperatures between 140-270K. Ionized D2 is significantly more reactive with the titania surface and two desorption peaks at 380K and ∼550K were observed together with a small D2O peak observed at ∼440K. Dosing the surfaces with hydrogen and deuterium either in succession or as a mixture showed HD desorption with no change in the desorption peaks, consistent with dissociative adsorption of both ionized and molecular species. The experimental data was compared to Density Functional Theory calculations and modeled as a two-step process of hydrogen dissociation at oxygen vacancy sites on TiO 2.

Excitation of a luminescence by highly exothermic chemical reaction on the surface of a luminophore provides a unique opportunity to separate surface luminescence from the bulk luminescence. This enables studies of the electronic properties of the semiconductor surfaces even if the surfaces are of complicate shapes. We have studied heterogeneous chemiluminescence (HCL) of ZnO powders. The luminescence was excited by a release of chemical energy, namely by catalytic recombination of hydrogen atoms. The HCL spectra were compared to the photoluminescence (PL) spectra. The HCL spectra were sensitive to the details of preparation and treatment whereas PL spectra almost did not change. HCL spectra of powder samples pretreated for enhancing “green” luminescence exhibited long-wavelength tail (up to 800 nm) and their maximum was blue-shifted as compared with PL spectra. Different HCL bands forming long-wavelength tail were isolated by changing the temperature of the samples. Additional milling of ZnO led to amplification of the HCL-specific surface bands. Pure ZnO showed neither PL nor HCL; however we were able to observe HCL surface bands with maxima at 610 nm and 730 nm after treatment of the sample in atomic hydrogen atmosphere at 570 K. Remarkably, such treatment did not cause appearance of the PL. The HCL in the presence of atomic hydrogen was steady in time and was caused by an abstraction of adsorbed hydrogen by incident hydrogen atoms, i.e. the reaction followed Eley-Rideal mechanism. The HCL can be utilized for in situ monitoring of the growth and evolution of ZnO in controlled atmosphere.

Commercial scale production of silicon carbide (SiC) nanoparticles smaller than 10 nm remains a significant challenge. In this paper, a microwave plasma reactor and appropriate reaction conditions have been developed for the synthesis of amorphous SiC nanoparticles. This continuous gas phase process is amenable to large scale production use and utilizes the decomposition of tetramethylsilane (TMS) for both the silicon and the carbon source. The influence of synthesis parameters on the product characteristics was investigated. The as-prepared SiC particles with sizes between 4 and 6 nm were obtained from the TMS precursor in a plasma operated at low temperature and low precursor partial pressure (0.001-0.02 Torr) using argon as the carrier gas (3 Torr). The carbon:silicon ratio was tuned by the addition of hydrogen and characterized by x-ray photoelectron spectroscopy. The reaction mechanism of SiC nanoparticle formation in the microwave plasma was investigated by mass spectroscopy of the gaseous products.

A low-voltage (< 2 V, three-electrode system) method for the cathodic electrodeposition of fullerol [polyhydroxylated fullerene, C-60 (OH)(n)] from an aqueous solution has been developed for the synthesis of thin films. Scanning electron microscopy of the electrodeposited fullerol films shows that the films are microscopically uniform; the film thickness was observed to vary linearly with the deposition charge. X-ray photoelectron spectroscopy of the C 1s peak indicates that the carbon constituents of the electrodeposited films are electronically similar to the fullerol precursor. Infrared spectroscopy (IRS) confirmed that the fullerol moiety is intact upon electrodeposition and that the films are thermally stable up to 150 S C. At higher temperatures IRS data suggest there is cleavage of a ketal or hemiketal group followed by hydroxyl group cleavage. The (direct) optical bandgap obtained from UV-visible spectroscopy of the electrodeposited film was 2.6 eV. (c) 2006 The Electrochemical Society.