Understanding CO(2) Adsorption in CuBTC MOF: Comparing Combined DFT-ab Initio Calculations with Microcalorimetry Experiments
Abstrakt
A combined experimental and theoretical investigation of CO(2) adsorption in the metal organic framework CuBTC is presented. Adsorption enthalpies were measured as a function of coverage up to 13 mmol g(-1) adsorbed amount (corresponding roughly to CO(2)/Cu = 5:2) by a Tian-Calvet-type microcalorimeter.
Experimetal data are interpreted based on accurate calculations employing a combined DFT-ab initio computational scheme. CO(2) molecules adsorb preferentially on coordinatively unsaturated sites for coverages below CO(2)/Cu = 1:1; at higher coverages (up to CO(2)/Cu = 5:3), CO(2) adsorbs in cage window sites; and at higher coverages, the sites in cage centers and in large cages start to be occupied.
Experimental adsorption enthalpies are almost constant (-29 kJ mol(-1)) up to the CO(2)/Cu = 5:3 coverage, suggesting a homogeneity of adsorption sites. However, calculations clearly show that adsorption sites in CuBTC are rather heterogeneous.