(76b) Development of a Model for Carbon Monoxide Oxidation Using Reaction Data Generated By a Novel Catalyst and Packaging System in Humid Conditions at Room Temperature

Interest in Carbon Monoxide Oxidation dates back to 1922 by Irving Langmuir himself [1].  Since, a wide body of work has surfaced[2].  Commercially available catalysts work in low humidity and high CO concentrations, such as Moleculite and Carulite at temperatures above 25 °C.  Aurolite, a more recent gold based catalyst, is active all the way down to -40 °C[3].  Above room temperature and 50% relative humidity, RH, there are few options. A Pt-CeO₂ on SiO₂ catalyst has been developed to fill the gap above 50% RH.  Experimental results are obtained and modeled for a wide variety of working conditions with special attention paid to heat effects.

Oxidation of CO is widely known to display negative order kinetics.  It is also highly exothermic with an activation energy of 283 kJ/mol[4].  This combination of factors amplifies sensitivity to temperature and concentration changes.  It also muddies kinetic data with high CO concentrations or conversions[5].  Literature typically operates around 1% CO which corresponds to a 100 °C adiabatic heat rise in a packed bed[6-7].  Experiments were performed at low CO concentrations, below 1500 ppm, and will be presented and modeled using the Pt-CeO₂ on SiO₂ catalyst in excess oxygen.  The large humidity range, from 0 to 90%, demands water adsorption on the SiO₂ based packed bed also be accounted for. This has strong heat effects of its own; which are typically the domain of water/silica based adsorption chillers[8]. 

The effect of axial conductivity, k_eff, on the reaction system is shown to significantly alter reactor performance. k_eff is modified by using five different carrier gases: He, Ne, N₂, Ar and Kr. k_eff was changed from .091 W/(m*K) to .51 W/(m*K).    The results show an increase in the temperature at the front of the packed bed, and thus better CO conversion.  Finally, a comparison is made using Microfibrous media, MFM.  The MFM holds the catalyst in a copper sinter locked mesh which allows for excellent heat conduction [9].  The MFM entrapped catalyst has a k_eff of .54 W/(m*K) in flowing N₂. It exhibits an increase in catalytic performance and longevity relative to a packed bed.    

[1]I. Langmuir, "The mechanism of the catalytic action of platinum in the reactions 2CO + O2= 2CO2 and 2H2+ O2= 2H2O," Transactions of the Faraday Society, vol. 17, pp. 621 - 654, 1922.

[2]S. Royer and D. Duprez, "Catalytic Oxidation of Carbon Monoxide over Transition Metal Oxides," ChemCatChem, vol. 3, pp. 24-65, 2011.

[3]M. Haruta, N. Yamada, T. Kobayahi and S. Iijima, "Gold catalysts prepared by coprecipitation for low-temperature oxidation of hydrogen and of carbon monoxide," Journal of Catalysis, vol. 115, no. 2, pp. 301-309, February 1989.

[4] J. D. Cox, D. D. Wagman and V. A. Medvedev, CODATA Key Values for Thermodynamics, New York, New York: Hemisphere Publishing Corp, 1989.

 [5] F. Duprat, "Light-o curve of catalytic reaction and kinetics," Chemical Engineering Science, vol. 57, pp. 901-911, 2002.

[6] E. D. Park and J. S. Lee, "Effects of Pretreatment Conditions on CO Oxidation over Supported Au Catalysts," Journal of Catalysis, vol. 186, pp. 1-11, April 1999

[7] H. Imai, M. Date and S. Tsubota, "Preferential Oxidation of CO in H2-Rich Gas at Low Temperatures over Au Nanoparticles Supported on Metal Oxides," CATALYSIS LETTERS, vol. 124, no. 1-2, pp. 68-73, 2008.

[8]E.C. Boelman, B.B. Saha, T. Kashiwagi, “Experimental investigation of a silica gel-water adsorption refrigeration cycle – The influence ofoperating conditions on cooling output and COP,” ASHRAE Transactions, vol. 101,pp. 358-365 , 1995.

[9] D. Harris, D. Cahela and B. Tatarchuk, "Wet lay and sintering of metal-containing microfibrous composites for chemical processing opportunities," Composites Part A: Applied Science and Manufacturing, vol. 32, no. 8, pp. 1117-1126, 2001.