Acetylene Adsorption on CPO-27-M Metal-Organic Frameworks (M=Fe, Co and Ni)

Acetylene is an industrially important gas. Despite its widespread use in welding technologies and fine-chemicals synthesis, there remain significant issues in gas separation (from CO2 or CH4) and storage. The latter problem arises due to the high risk of explosion at pressures above 0.2 MPa (2 atm), even in the absence of oxygen. Acetylene can be stored and/or purified using microporous materials, such as zeolites and carbons, which show, however, poor gas selectivity and can catalyze C2H2 polymerization. Metal–organic frameworks (MOFs) are likely the candidates to solve these issues due to the modular nature of the framework, which can be modified synthetically or post-synthetically to reach the desirable sorption properties. Under the relatively low pressure that has to be used for acetylene adsorption, the surface area of the MOF does not appear to be the dominant factor in the overall adsorption capacity. The energy of interaction with acetylene is more important at low pressures. As was also observed for other gases, at low pressure, MOFs with open metal sites and/or small pores store significantly more acetylene than those without open metal sites and/or large pores. In fact, neutron-diffraction studies of C2D2 adsorption evidenced the open metal sites as the preferential adsorption sites in MOFs.