Unexpected Penetration of CO Molecule into Zeolitic Micropores Almost Plugged by CuCl via π-Complexation of CO-CuCl

Abstract

Carbon monoxide (CO) is a key reactant in several Fischer–Tropsch processes, including those used in light olefin and methanol syntheses. However, it is highly toxic and causes serious poisoning of noble metal catalysts. Thus, a solid adsorbent that can selectively capture CO, especially at low concentrations, is required. In this study, zeolite Y-based adsorbents in which Cu(I) ions occupy the supercage cation sites (CuCl/Y) are prepared via solid-state ion exchange. Volumetric adsorption measurements reveal that the Cu(I) ions significantly enhance CO adsorption in the low-pressure range by π-complexation. Furthermore, unexpected molecular sieving behavior, with extremely high CO/CO2 selectivity, is observed when excess CuCl homogeneously covers the zeolite pore structures. Thus, although CO has a larger kinetic diameter, it can penetrate the zeolite supercage while smaller molecules (i.e., Ar and CO2) cannot. Density functional theory calculations reveal that CO molecules can remain adsorbed in pseudoblocked pores by CuCl, thanks to the strong interaction of C 2p and Cu 3d states, resulting in the high CO/CO2 selectivity. One of the prepared adsorbents, CuCl/Y with 50 wt % CuCl, is capable of selectively capturing 3.04 mmol g–1 of CO with a CO/CO2 selectivity of >3370.

Direct Fabrication of Cu(I)/4A Assisted with a Molecular Complex toward High-Efficiency CO-Selective Adsorption from H2

“…According to this model, the chemical potential energy in the adsorbed phase is equal to that in the gas phase at equilibrium. Previous literatures have reported that IAST theory was employed to predict the selectivity of copper ion-based adsorbents. ,− The IAST theoretical calculation formulas are given in the Supporting Information.…”