Adsorption of Propane and Propylene on CuBTC Metal–Organic Framework: Combined Theoretical and Experimental Investigation

Abstract

A combined experimental and theoretical investigation of propane and propylene adsorption in the metal− organic framework CuBTC is presented. The dependence of adsorption enthalpies on the adsorbed amount was determined by microcalorimetry up to 8 mmol g −1 coverage (roughly C 3 H n /Cu 2+ ratio of 1.5). Trends observed experimentally were interpreted on the basis of accurate calculations carried out at the hybrid DFT−ab initio level. Three types of adsorption sites were identified; however, qualitatively different results were obtained for propane and propylene. Propane preferentially adsorbs at the cage center sites (−ΔH°= 43 kJ mol −1 ), followed by adsorption at the cage window sites (31 kJ mol −1 ), while the interaction with the coordinatively unsaturated sites (CUS) is relatively weak (24 kJ mol −1 ). On the contrary, propylene preferentially interacts with the CUS (56 kJ mol −1 ), while the adsorption at the cage center and cage window sites was found to be only 45 and 34 kJ mol −1 , respectively. Due to the topology of CuBTC, lateral interactions are significantly more important among the adsorbates located at the cage center and cage window sites (populated in the case of propane) than among adsorbates at the CUS and cage center sites (populated in the case of propylene). Therefore, adsorption energies obtained for coverages above 6 mmol g −1 of adsorbed amount were larger for propane than for propylene. Consequently, the presence of small cages makes the CuBTC MOF less suitable for propane/propylene separation than MOFs having the Cu 2+ CUS but without small cages (e.g., CPO-27).

A computational study of the interaction of C2 hydrocarbons with CuBTC

“…It is also important to keep in mind that isosteric heat of adsorption determinations can be tricky, with large ranges in experimentally determined values not being uncommon. For example, in the case of propane in CuBTC, a variation of up to 20 kJ/mol has been reported in different studies [29][30][31]91].…”

“…Co-MOF-74 also exhibits a very high acetylene uptake capacity [27]. Cu-BTC (also known as MOF-199 or HKUST-1) exhibits preferential adsorption of propylene over propane, with a C3H6/C3H8 selectivity of about 3 [28][29][30][31], at low pressures. The same system selectively adsorbs isobutene over isobutene [32], and shows an exceptionally high acetylene uptake at room temperature, rendering it interesting for acetylene storage and, possibly, selective C2H2 adsorption [33][34][35].…”

Metal-dioxidoterephthalate MOFs of the MOF-74 type: Microporous basic catalysts with well-defined active sites

“…Probably, the LOT applied to the other M 2 dobdc materials with success, does not suit the Cu case. In this context the work of Nachtigall [72] on the role of the functional in the prediction of adsorption energies of propane and propylene on the MOF Cu 3 BTC 2 is of particular interest.…”

Functionalized metal‐organic polyhedra hybrid membranes for aromatic hydrocarbons recovery

“…Remarkably, as shown in the Table , the toluene was much more strongly adsorbed by the MOP‐SO 3 Na n H m . This might be attributed to a favorable binding interaction between the MOP and the toluene molecules through such as π–π stacking, π–Cu 2+ ion chelation, and polar groups with π‐electron clouds in the benzene ring of the toluene molecule. In addition, a selectivity trend of MOP‐SO 3 Na n H m > MOP‐OH > MOP‐ t Bu for toluene is recorded, which is consistent with the polarity of different functional groups in these MOPs.…”