Adsorption Properties of Hydrogen and Carbon Dioxide in Prussian Blue Analogues M₃[Co(CN)₆]₂, M = Co, Zn

H 2 and CO 2 adsorption were studied in dehydrated Prussian blue analogues M 3 [Co(CN) 6 ] 2 (M = Co, Zn) using volumetric isotherm measurements. Both materials adsorbed 1.2−1.3 wt % of H 2 at 77 K and 760 Torr with isosteric heats of adsorption ranging from 5.9 to 6.8 kJ/mol. High-pressure H 2 isotherms at 77 K showed that Co 3 [Co(CN) 6 ] 2 started to saturate well above 6 atm with a saturation coverage of ∼1.9 wt %. These materials adsorbed approximately 17.6−19.7 wt % of CO 2 at 253 K and 760 Torr with isosteric heats of adsorption of ∼25−28 kJ/mol. The CO 2 saturation coverages from high-pressure isotherms at 263 K and 15 atm were ∼27.4−29.0 wt %. The displacement of CO 2 by H 2 in these compounds was investigated with Fourier transform infrared spectroscopy (FTIR). The FTIR experiments showed that CO 2 physisorption at cryogenic temperatures produced an infrared peak at 2335 cm -1 . Co-adsorption experiments revealed that H 2 was able to displace preadsorbed CO 2 if the P H2 / P CO2 ratio was well above 100. The infrared results from the co-adsorption experiments also showed that H 2 and CO 2 competed for adsorption in the same pores under these conditions.