DFT calculations for adsorption of H2S and other natural gas compounds on M-BTC MOF clusters
摘要
Desulfurization is a necessary process to reduce the corrosiveness of natural gas. In this regard, H2S adsorption on porous materials has gained attention in the development of new eco-friendly technologies. Although there are many experimental and theoretical studies about gas adsorption on MOFs, so far, there has been no theoretical work about desulfurization of natural gas or biogas through H2S adsorption on MOF BTC. Therefore, the objective of this study was to preselect by ab initio calculations which metal center M2+, such as Co2+, Ni2+, Cu2+, or Zn2+, has the highest potential for selective desulfurization of natural gas. DFT calculations were performed at B3LYP-D3/6-311++G(2d,p)+LanL2DZ level for H2O, H2S, COS, CO2, and CH4 adsorption on M-BTC MOF clusters in order to obtain adsorption complex equilibrium geometries, adsorption energies and thermodynamic properties. It was found that Zn-BTC MOF cluster has the highest potential for selective H2S removal from dry natural gas streams, since its adsorption energy is −79.4 kJ mol−1, which is 2.4 times higher than CH4. Furthermore, H2S adsorption on Zn-BTC MOF is an exothermic process and thermodynamically favorable. Through NBO and EDA analyses, it was found that d electrons transfer from adsorbate to metal center unoccupied orbitals contributes mainly to a possible H2S chemisorption on Zn-BTC and Co-BTC, while for CO2 and CH4 adsorption, non-bonded interactions predominate. Most of the gases coordinate to coordinatively unsaturated site of BTC MOF cluster at axial position, indicating a stronger interaction with metal center compared to linkers.