Prussian blue analogues (PBAs) have attracted broad attention for various applications because they are relatively cheap, environmentally friendly and can easily be scaled-up. One such application is as CO2 gas adsorbers. They have been found to have CO2 capacities of ca. 3.0 mmol/g, which is in close range with other well established CO2 adsorbents. We have studied in detail the PBA copper hexacyanoferrate (CuHCF) with and without inserted K. The aim of this study is to investigate: (i) at what sites are CO2 molecules adsorbed in CuHCF?, (ii) is the site preference dependent on the loading of CO2, i.e., the amount of CO2 adsorbed, (iii) how does the site preference depend on temperature, (IV) is the site preference dependent on the presence of K, (V) is it possible to determine diffusion paths for CO2 using Reverse Monte Carlo (RMC) modelling, (VI) at what sites are N2 molecules locate