We are trying to produce accurate carbon monoxide in air gas standards with an uncertainty < 1 ppb. We are having difficulty purifying the air to remove the residual carbon monoxide. The lowest concentration of our proposed standards is 40ppb, so the uncertainty of the impurity is considerable.
Wikipedia entry- for Hopcalite (http://en.wikipedia.org/wiki/Hopcalite)
Hopcalite is a mixture of copper and manganese oxides used as catalyst to convert carbon monoxide into carbon dioxide when exposed to the oxygen in air. A variety of composition for are known, "Hopcalite II" is approximately 3:1 manganese dioxide : copper oxide. Hopcalite I is a mixture of 50% MnO, 30% CuO, 15% "Co2O3", and 5% Ag2O.
My concern is to not add other impurities and leave the matrix as intact as possible. So I would rather remove the carbon monoxide than convert it. Of course converting less than 10 ppb CO to CO2 would not impact much, so that could be the answer. We have tried another catalyst, however that did not do a good job and instead increased the nitrous oxide in the air. My next concern is that we need to do this under high pressure (>1500 psi) in order to fill our cylinders during preparation.
A Pt or Pt-Pd catalyst monolith electrically heated to ~250 deg C would oxidize the CO to CO2 fairly efficiently. If you are trying to preserve SO2 in the mixture, you may need to use Pd or a combination of Pt-Pd and adjust the temperature somewhat to avoid oxidation of SO2 to sulfate. Emitec used to make resistively heated metal monoliths that could be washcoated with alumina/ceria/platinum-group-metal coatings. Something similar could probably be fabricated.
You could use gas purification cartridges such as:
http://www.discoverysciences.com/uploadedFiles/Home/ChromAccessories_GCAcc_GasPurifiersNTraps_p268to275.pdf
Maybe you could purify the air through a column alumina and Pd-Pt catalysts packed
run the zero air through a catalytic converter; platinum or other catalytic sponge material, don't know what temperature is necessary for CO absorption or catalysis
We used a 7.5 cm x 1 cm column of 1% platinum on 3 mm alumina beads (Aldrich Co.) to remove ambient CO. It was supposed to need heating, but even at room temperature it removed CO down to undetectable levels (in our case, 0.2 ppm). I don't know if it will scrub all the way down to
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