A sealed 100-Hz CO2TEA laser using high CO2concentrations and ambient-temperature catalysts

Surface Structure - Catalytic Function in Nanophase Gold Catalysts

Catalysts consisting of ultra-fine gold particles supported on iron oxide have been synthesized by the coprecipitation method. Subsequent to preparation, each sample was heat treated in air at four different temperatures, ranging from 473 K to 773 K. Steady state carbon monoxide oxidation was carried out over each sample. Upon extended reaction, catalyst deactivation took place over three of the catalysts whose respective surface compositions (e.g., gold to iron atomic ratio) were altered appreciably from their initial state. Surface structure analyses performed on all the unreacted catalysts have revealed variations in physical properties (e.g., degree of crystallinity and particle size). In addition, lattice parameters of gold were observed to increase up to 20 % from the bulk value. In contrast, XPS showed both gold and iron to be in essentially the same chemical states for all catalysts, irrespective of heat treatment temperatures. The importance of surface sensitive parameters to catalytic function are discussed.

Performance Characteristics of Low-Temperature Co Oxidation Catalysts

A series of Au/MnOx catalysts with the Au content ranging from 0 to 10 at%, a 19.5 wt% Pt/SnOx catalyst and a commercially available 2 wt% Pt/SnOx catalyst have been examined for activity toward low-temperature CO oxidation. A 1 atm, 10 sccm stoichiometric mixture of CO (1 vol.%) and O2 in He were reacted at 55°C over 100 mg of each catalyst for time periods as long as 20,000 min. Under these conditions a 10 at% Au/MnOx catalyst exhibits the highest activity and the lowest decay. Outgassing experiments indicate that CO2 retention is primarily responsible for the activity decay of the Pt/SnOx catalysts and that the 10 at% Au/MnOx catalyst is not significantly affected by this process.

A Study of Water Influence on Carbon Monoxide Adsorption and Oxidation on Nanocrystals of: γ-Fe2O3, Au/Fe2O3 and MnxZn1-xFe2O4

In this paper the adsorption and oxidation of CO on nanocrystalline Au/γ-Fe2O3, Au/α- Fe2O3, γ-Fe2O3 and a series of mixed ferrite with MnxZn1-xFe2O4 composition are investigated. The catalysts were prepared by co-precipitation method and characterized using X-ray diffraction (XRPD), specific surface (BET), transition electron spectroscopy (TEM) and magnetization measurements. A temperature programmed desorption (TPD) study of the water and CO interaction with nanocrystalline adsorbents is presented. The catalytic activities towards CO oxidation increased in the following order: γ-Fe2O3 < MnxZn1-xFe2O4 < Au/γ-Fe2O3 .

Chemical State Study of Palladium Powder and Ceria-Supported Palladium during Low-Temperature CO Oxidation

The chemical state of Pd at the surfaces of two sizes of Pd powders and ceria-supported Pd during low-temperature CO oxidation has been studied using X-ray photoelectron spectroscopy (XPS). During oxidation in O(2), metallic Pd powder is converted into PdO, and the thickness of the PdO layer increases with increasing reaction temperature. A similar Pd oxidation process occurs during the catalytic CO oxidation reaction, but the extent of the Pd oxidation is less due to the presence of CO which is a reducing agent. The reaction rate data indicate that the larger size Pd powder is about three times more active than the smaller size Pd powder on a surface area basis at 160 degrees C. Catalytic CO oxidation data obtained from 10 wt % Pd supported on nanocrystalline ceria powder indicate that there is a strong chemical interaction between the ceria and the supported Pd. The Pd is present as PdO on the fresh catalyst. During reaction, small amounts of Pd metal and PdO(2) are formed at 50 degrees C while less Pd metal and only a small amount of PdO(2) are present after running the reaction at 110 degrees C. At 50 degrees C, the catalytic activity decays rapidly due to accumulation of carbonate or bicarbonate species on the surface. This decay does not occur at 110 degrees C due to decomposition of the bicarbonate species.

High speed tuning mechanism for CO2 lidar systems

A method for rapidly tuning lasers is presented. The system utilizes a rotating eight-sided mirror and a fixed grating. It is demonstrated that the entire CO2 lasing spectrum can be tuned at effective rates of up to 400 Hz. It is shown that, although the pulse energy is diminished as the tuning rate is increased, the loss comes from the tail of the pulse, and the peak power is almost unchanged. In addition, the tuning method preserves the spatial beam profile while contributing a minimum of beam steering.