If the above case is correct (which I have seen in a few papers), in case of synthesis of Ru-Pt bimetal on mesoporous silica, the CO-chemisorption will give the dispersion of both the metals without even giving any difference. If it is incorrect, then by changing the ratio of Pt-Ru in the bimetal, there can be a correlation between the ratio of the metal (say, Pt is kept constant and Ru varied) with the dispersion. I would like to know exactly which one makes more sense.
The issue with CO chemisorption is the understanding of the metal:gas ratio as there is both a linear and bridged chemisorbed form possible. This ratio is not constant as it is likely to change as one metal is diluted with another.
I agree with Alan F Rawle, the stoichiometry is unknown, you can even for Ru°(CO)2 (see this article about the adsorption of CO on Ru° followed by FTIR:
Article FTIR studies of CO adsorption on Al2O3- and SiO2-supported R...
H2 is probably a safer probe for the estimation of the dispersion of Ru° nanoparticles.
Regarding your question about bimetallic nanoparticles, again, if you want to study CO chemisorption on Pt-Ru, you should use FTIR. Moreover, you must keep in mind that CO chemisorption on a sample containing both Pt and Ru may vary significantly depending whether you form an alloy, or core shell nanoparticles or if your two metals remain into separate particles.
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