Adsorptive desulfurization using Cu–Ce/metal–organic framework: Improved performance based on synergy between Cu and Ce

Copper and cerium oxides were synthesized via a new way within a highly porous metal–organic framework (MOF; here, MIL-101 or chromium–benzenedicarboxylate) in a consecutive manner under mild conditions for the first time. The crystal structure of MIL-101 remained intact after loading of the two metal oxides using this approach. The efficiencies of the new adsorbents in selective adsorptive removal of benzothiophene (BT) from a model liquid fuel were evaluated. Compared with that of virgin MOF, the maximum adsorption capacity (Q₀) of the modified MIL-101 increased by 57% and 188%, based on the weight and unit surface area, respectively. The increased Q₀could be explained by the synergistic effect of π-complexation (between Cu(I) and BT) and direct bond formation (between Ce(IV) and S) on BT adsorption. Moreover, Cu–Ce/MIL-101, unlike Cu/MIL-101, selectively adsorbed BT even in the presence of an aromatic additive (toluene) because Ce(IV) could effectively bind to sulfur in BT (without interacting with the aromatic ring). The adsorbent was reused in up to four cycles without significant loss of BT adsorption capacity, and it was presumed that the presence of Ce species could stabilize the +1 oxidation state of Cu via a redox phenomenon throughout the synthesis/regeneration processes.