Influence of the Presence of Different Alkali Cations and the Amount of Fe(CN) Vacancies on CO Adsorption on Copper Hexacyanoferrates.

The CO adsorption on various Prussian blue analogue hexacyanoferrates was evaluated by thermogravimetric analysis. Compositions of prepared phases were verified by energy-dispersive X-ray spectroscopy, infra-red spectroscopy and powder X-ray diffraction. The influence of different alkali cations in the cubic 3 structures was investigated for nominal compositions Cu[Fe(CN)] with = vacant, Li, Na, K, Rb, Cs. The Rb and Cs compounds show the highest CO adsorption per unit cell, 3.3 molecules of CO at 20 C and 1 bar, while in terms of mmol/g the Na compound exhibits the highest adsorption capability, 3.8 mmol/g at 20 C and 1 bar. The fastest adsorption/desorption is exhibited by the -cation free compound and the Li compound. The influence of the amount of Fe(CN) vacancies were assessed by determining the CO adsorption capabilities of Cu[Fe(CN)] (3 symmetry, nominally 50% vacancies), KCu[Fe(CN)] (3 symmetry, nominally 25% vacancies), and CsCu[Fe(CN)] (-42 symmetry, nominally 0% vacancies). Higher adsorption was, as expected, shown on compounds with higher vacancy concentrations.