A highly stable CuO-derived adsorbent with dual Cu(I) sites for selective CO adsorption

Abstract

Cu(I)-based adsorbents with high stability and adsorption capacity enable effective carbon monoxide separation. Starting from CuO nanoparticles, we synthesized a CO adsorbent with Cu2O and CuCl on the surface by a two-step synthesis route. The first step was a fast thermal reduction under 5 vol% flow of H2 at 673 K. CuCl was then introduced by a room temperature liquid-phase reaction between surface metallic copper and CuCl2. X-ray diffraction was used to investigate the stability of the dual-active site adsorbent under atmospheric air. Compared to single Cu(I) site counterparts, the dual-active site adsorbent has a superior adsorption capacity and selectivity for CO, making itself a promising candidate for CO-CO2 mixture separation. Site energy distribution was used to describe the heterogeneity of the adsorbent surface based on equilibrium adsorption isotherm models. Each synthesis step resulted in the formation of sites at both high and low ends of the site energy spectrum. Adsorption kinetics of CO and CO2 to the adsorbent was also investigated by fitting kinetics results to various adsorption kinetic models. We found that adventitious metallic copper reaction with air forms new active Cu2O sites. Further reaction with ambient air formed a protective layer of copper oxide and carbonate on the surface. These surface moieties enhanced adsorbent stability under atmospheric air for up to 10 days while retaining the adsorption capacity once activated. The oxygen-resistant layer can be easily removed by heating under a vacuum. This study provides a path for the design and synthesis of Cu(I)-based adsorbents with high CO adsorption capacity and stability.