Hydrogen Adsorption and Its Displacement of Carbon Dioxide in Microporous Transition Metal Cyanides

The adsorption properties of H$_{2}$ and CO$_{2}$ have been investigated in M$_{3}$[Co(CN)$_{6}$] (M = Cu, Zn) Prussian blue analogues and M[Fe(CN)$_{5}$NO] (M= Co, Ni) metal nitroprussides. Adsorption isotherms show that both materials adsorb between 1.4 to 1.7 wt {\%} of H$_{2}$ at 77 K and 1 atm. The isosteric heat of adsorption was between 6.5 to 7.5 kJ/mol. Kinetic measurements are conducted in a specially designed vacuum system which is coupled to a Fourier-Transform Infrared Spectrometer. In a typical experiment, an infrared active gas (i.e CO$_{2})$ is physisorbed in the transition metal cyanide and the system is later back-filled with H$_{2}$. The infrared intensity of the physisorbed CO$_{2}$ is monitored to deduce the kinetics and energetics associated with its displacement from the transition metal cyanide by H$_{2}$. We have identified several kinetic steps, measured the rate constants, and examined the temperature dependence of this displacement process.