Understanding the vacuum autoreduction behavior of Cu species in CuCl/NaY adsorbent for CO/N2 separation

Abstract

CuCl/NaY is the most representative π-complexation adsorbent, prepared by solid thermal dispersion followed by vacuum thermal activation. However, determining the autoreduction behavior of Cu species for CuCl/NaY adsorbent in vacuum thermal activation has rarely been researched. This study characterized the valence state, location, and types of Cu species during thermal dispersion and vacuum activation. During the thermal dispersion, Cu species were uniformly dispersed into NaY micropores. Under vacuum activation at 100 °C, the location of Cu species changed, migrating from supercages to near the plane (toward the sod cage or the supercage side) of the 6-membered ring connecting the supercage and sod cage. However, by activating at 150 °C, vacuum autoreduction occurred: (Cu2+–O−)Cl− species evolved into Cu+Cl− species. This was accompanied by the migration of Cu(I) species to the appropriate CO adsorption site on the plane center of the six-membered ring connecting the supercage and sod cage in the NaY framework, which achieved confined dispersion. The CO adsorption capacity of CuCl/NaY activated at 150 °C was 2.75 mmol/g, significantly higher than when activated at 100 °C. When activated at 200 °C, Cu(II) species was further reduced to Cu(I) slightly, which had not migrated to an effective adsorption site. Our results show the Cu species’ evolution and autoreduction behavior for CuCl/NaY adsorbent under vacuum thermal activation, and they can serve as a reference to guide the preparation of π-complex adsorbents.