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.