Billy T. Upchurch

Comparison of the performance characteristics of Pt/SnOx and Au/MnOx catalysts for low-temperature CO oxidation

Abstract Platinized tin oxide (Pt/SnO x ) and gold supported on manganese oxide (Au/MnO x ) catalysts have been shown to be good CO oxidation catalysts at low temperatures (30–100°C). The performance of these catalysts has been compared by reacting mixtures of CO and OZ and He under similar conditions. The Au/MnO x catalyst is superior to Pt/SnO x catalysts with regard to both activity and decay characteristics under the conditions examined. As expected, Au/MnO x catalysts exhibit greater activity as the reaction gas mixture becomes more oxidizing.

Effects of pretreatment conditions on a Pt/SnO2 catalyst for the oxidation of CO in C02 lasers

CO oxidation catalysts are important for long-life closed-cycle operation of CO{sub 2} lasers. The electrical discharges frequently used to excite such lasers decompose some CO{sub 2} to CO and O{sub 2} but many of their applications, including remote sensing from space vehicles, prohibit addition of makeup gas or removal of decomposition products because of volume and weight constraints. These lasers thus represent a new and important application for low-temperature CO oxidation catalysts, since for space applications, no catalyst heating is allowed to minimize power consumption. The most promising catalysts whose performance has been verified by actual laser operation consist of Pt and/or Pd on tin(IV) oxide. This paper presents results of a study of various pretreatment techniques on the activity of a commercially available Pt/SnO{sub 2} catalyst. Pretreatment with the reducing gases, CO and H{sub 2}, produces approximately equal steady-state CO{sub 2} yields which are significantly higher than those for the other pretreatment gases, although the steady-state is more rapidly attained with the H{sub 2} pretreatment. Pretreatment with O{sub 2} in He results in only slightly greater CO{sub 2} yields than pretreatment with He alone.

Au/MnOx catalytic performance characteristics for low-temperature carbon monoxide oxidation

Manganese oxide-supported gold (Au/MnOx) catalysts have been prepared and tested for low-temperature (< 100°C) carbon monoxide oxidation in stoichiometric mixtures of carbon monoxide and oxygen containing no carbon dioxide in the feed gas. Even with no pretreatment these catalysts are superior to the best, pretreated platinized tin oxide (Pt/SnOx) catalysts under the conditions tested. The very small decay observed for Au/MnOx catalysts is mostly due to carbon dioxide retention. The optimum gold content has been determined to be 10 at.-% of the manganese content, and a lithium promotor results in improved catalytic behavior over K- or Na-promoted Au/MnOx catalysts for the conditions examined in this study.

INFLUENCE OF PROMOTERS ON THE PERFORMANCE OF AU/MNOX AND PT/SNOX/SIO2 LOW-TEMPERATURE CO OXIDATION CATALYSTS

The influence of promoters on Pt/SnOx/SiO2 and Au/MnOx low-temperature CO oxidation catalysts has been investigated under stoichiometric reaction conditions with no CO2 added to the feed gas. The performance of Pt/SnOx/SiO2 catalysts is improved significantly by the addition of 1 wt.% Fe but reduced by the addition of 5 wt.%Fe, 1 wt.% Sb, 5 wt.% Sb, 1 wt.% As, 5 wt.%As and 1.8 wt.% P. The performance of Au/MnOx is improved significantly by the addition of 1 at.% Ce but reduced by the addition of 1 at.% Co. For the catalysts and conditions examined, the Au/MnOx catalysts are superior to the Pt/SnOx/SiO2 catalysts with respect to both activity and decay characteristics.

Influence of an Fe promoter on silica-supported Pt/SnOx catalysts used for low-temperature CO oxidation

Silica-supported Pt/SnOx catalysts used for low-temperature CO oxidation have been prepared without and with an Fe promoter. Reaction studies demonstrate that the addition of the Fe promoter results in higher catalytic activity in the presence of 8 at% CO2 and a lower decay rate. Ion scattering spectroscopy (ISS) has been used to examine the outermost atomic layers of the promoted and nonpromoted catalysts before and after activation by a reductive pretreatment. The nonpromoted catalyst exhibits agglomeration of the platinized tin oxide film exposing the catalytically inactive silica support. This agglomeration does not occur when Fe is present, and a large catalytically active surface area is maintained during the reduction.

New device and method for measuring thermal conductivity of thin-films

Thermal sensitive paints (TSPs) are used for global nonintrusive detection of boundary layer transition in flow over the surface of wind tunnel research models. Since the transition is a transient process, the TSP should have a fast response characteristic. A low paint thermal conductivity is required for fast response. A thin-film thermal conductivity meter (TFTCM) was designed and built to measure thermal conductivity of the TSPs, which are typically between 50 and 150 microm thick. In this paper, the design and operating features of the TFTCM are described. Measurement of the thermal conductivity with this TFTCM of three standard thin-film low conductivity specimens, Kapton, Teflon, and Borofloat glass, showed good agreement with the manufacturer quoted values, thus validating the instrument and the procedure. Consistently repeatable values for thermal conductivity (k=0.41 +/- 0.02 W/m K) were also obtained for the TSP specimen (TSB-B, 75 microm) tested.

Recent advances in CO2 laser catalysts

This paper discusses several recent advances in CO2 laser catalysts including comparisons of the activity of Au/MnO2 to Pt/SnO2 catalysts with possible explanations for observed differences. The catalysts are compared for the effect of test gas composition, pretreatment temperature, isotopic integrity, long term activity, and gold loading effects on the Au/MnO2 catalyst activity. Tests conducted to date include both long-term tests of up to six months continuous operation and short-term tests of one week or more that include isotopic integrity testing.

Recent advances in efficient long-life, eye-safe solid state and CO2 lasers for laser radar applications

There is increasing interest in the comparative roles of CO2 and the more recently developed eye-safe solid-state lasers for long-life efficient laser radar applications. This paper assesses recent technology advances in each area and their roles in laser radar and especially Doppler lidar and DIAL development. The key problems in eye-safe solid-state lasers are discussed relating to the energy transfer mechanisms between the complicated energy level manifolds of the Tm,Ho,Er ion dopants in hosts with decreasing crystal fields such as YAG or YLF. One concerns optimization of energy transfer for efficient lasing through choice of dopant concentration, power density, crystal field and temperature, with the highly practical goal of minimal cooling needs. Another key problem, specific to laser radar and lidar, involves tailoring of energy transfer times to provide efficient energy extraction for short, e.g., Q-switched pulses used in DIAL and Dopper lidar. Special emphasis is given to eye-safe lasers in the 2 μm range because of the high efficiency applications to DIAL and (windshear) Doppler lidar and because they are well suited for Optical Parametric Oscillator frequency conversion into the important ≈ 4 to 5 μm DIAL range. The discussion of CO2 lasers concerns recent advances in Pt/Sn02 oxide catalysts and other noble metal/metal oxide combinations. Emphasis is given to the dramatic effects of small quantities of H20 vapor for increasing the activity and lifetime of Pt/Sn02 catalysts and to increased lifetime operation with rare isotope 12C18O2 lasing mixtures; iL-the 12C18O2 laser wavelengths in the 9.1 μm range are of special interest for space-based Doppler lidar such as the proposed Laser Atmospheric Wind Sounder.

Platinized tin oxide catalysts for CO2 lasers - Effects of pretreatment

Platinized tin oxide surfaces used for low-temperature CO oxidation in CO2 lasers have been characterized before and after reduction in CO at 125 and 250°C using ion scattering spectroscopy (ISS) and X-ray photoelectron spectroscopy (XPS). XPS indicates that the Pt is present initially as Pt02. Reduction at 125°C converts the Pt02 to Pt(OH)2 while reduction at 250°C converts the Pt02 to metallic Pt. ISS shows that the Pt in the outermost atomic layer of the catalyst is mostly covered by substrate species during the 250°C reduction. Both the ISS and XPS results are consistent with Pt/Sn alloy formation. The surface dehydration and migration of substrate species over surface Pt and Sn appear to explain why a CO pretreatment at 250°C produces inferior CO oxidation activities compared to a 125°C CO pretreatment.

Catalytic Recombination Of Dissociation Products With Pt/SnO2 For Rare And Common Isotope Long-Life, Closed-Cycle CO2 Lasers

This paper reports results on recombination of pulsed CO2 laser dissociation products with Pt/Sn02 catalysts, and supporting studies in a surrogate laboratory catalyst reactor. The closed-cycle, pulsed CO2 laser has been continuously operated for 106 pulses with an overall power degradation of less than five percent. This operation was achieved by flowing the laser gas mixture through a 2% Pt/Sn02 catalyst bed. In the surrogate laboratory reactor experiments have been conducted to determine isotopic exchange with the catalyst when using rare-isotope gases. Some isotope exchange has been observed but a technique for minimizing such exchange has been demonstrated. The effects of catalyst pretreatment, catalyst sample weight, and catalyst composition and temperature on catalyst efficiency have also been determined.