Metal halide screening for high adsorption capacity on carbon monoxide via DFT calculation

Abstract

Refinery of byproduct gases from many industries is essential to reduce greenhouse gas and wasted energy source. Especially, carbon monoxide (CO) should be separated from byproduct gases, not only for environmental issue but also for value-added material as synthesis gas. In this study, a porous adsorbent material (i.e., activated carbon) impregnated with metal halide compound, which consisted of highly electronegative metal cation and halogen anion, was investigated for high adsorption preference on CO. Through density functional theory (DFT) calculations, various metal halide structures were screened to find the structure showing the best CO-selective adsorption. Initially, the most stable spin configuration and Hubbard U parameters for each metal atom were investigated. The candidates were further scrutinized by investigating surface energies of the structures based on Bravais-Friedel-Donnay-Harker (BFDH) theory. Furthermore, the adsorption energies of CO and CO2 on the metal halide surface were calculated to confirm the adsorption strength and CO/CO2 selectivity. Based on local density of states (LDOS) analysis, it was confirmed that the stronger CO adsorption in metal halide with high CO selectivity, the more d-band shift of metal atoms in surface region occurred, implying that larger amount of electron was transferred from the p-orbital of CO to the d-orbital of metal atoms exposed on the metal halide surface. With these study, the optimal metal halide for CO-selective adsorption on activated carbon was identified.