High-efficiency adsorption of aromatic sulfur-containing compounds from liquid hydrocarbon fuels over metal-organic frameworks (MOFs) is challenging because of inert metal sites. A new method, the Ce-enhanced modulation of MOFs’ microenvironment, is proposed to modulate the –COO···Cu(II)– coordination microenvironment of Hong Kong University of Science and Technology (HKUST-1) using Ce(III) as a molecular scalpel for fabricating abundant high-efficiency Cu(I) and Cu-coordination-unsaturated sites and improving the pore structures around adsorptive sites. The optimal CH-250 thus exhibits adsorptive capacities for 20.2, 28.0, and 58.3 mg S g –1 of thiophene, benzo-thiophene, and dibenzothiophene, respectively, which are superior to most reported MOFs, zeolites, and nanoporous carbons. The constructed Cu(I) sites show stronger affinity for dibenzothiophene (−0.86 eV) than the initial Cu(II) (−0.74 eV) for out-of-plane adsorption. Further, they are far stronger in-plane adsorption interactions in DBT/CH-250 (−0.90 eV) than those in DBT/HKUST-1 (−0.37 eV). Thus, molecular engineering for modulating the coordination microenvironment of MOFs shows great potential for adsorption desulfurization.
Yu-Xia Li,Shuai-Shuai Li,Ding-Ming Xue,Xiao-Qin Liu,Meng-Meng Jin,Lin-Bing Sun
Cu(I)-containing materials have great potential in various applications such as in CO adsorption; however, development of an efficient and controllable method to produce Cu(I) sites remains a significant challenge; herein, a two-step double-solvent (DS) strategy is reported for the first time to fabricate Cu(I) sites in a representative metal–organic framework, MIL-101(Cr); this strategy ensures that both introduction of the Cu(II) precursor and its reduction to Cu(I) occur inside the pores and significantly minimizes the aggregation of Cu species. This is difficult to realize through conventional methods used for Cu(II) introduction (wet impregnation) or reduction (liquid-phase reduction). The two-step DS strategy involves selective reduction of Cu(II) to form Cu(I) without the formation of any Cu(0). The obtained Cu(I)-containing materials exhibit an excellent CO adsorption capacity (up to 2.42 mmol g−1) at 298 K and 1 bar, much better than that of the benchmark adsorbents including CuCl/γ-Al2O3 (1.0 mmol g−1), CuCl/MCM-41 (0.57 mmol g−1), and CuZSM-5 (0.11 mmol g−1).
Selective oxidation of methane to organic oxygenates over metal–organic frameworks (MOFs) catalysts at low temperature is a challenging topic in the field of C1 chemistry because of the inferior stability of MOFs. Modifying the surface of Cu-BTC via hydrophobic polydimethylsiloxane (PDMS) at 235 °C under vacuum not only can dramatically improve its catalytic cycle stability in a liquid phase but also generate coordinatively unsaturated Cu(I) sites, which significantly enhances the catalytic activity of Cu-BTC catalyst. The results of spectroscopy characterizations and theoretical calculation proved that the coordinatively unsaturated Cu(I) sites made H2O2 dissociative into •OH, which formed Cu(II)-O active species by combining with coordinatively unsaturated Cu(I) sites for activating the C−H bond of methane. The high productivity of C1 oxygenates (CH3OH and CH3OOH) of 10.67 mmol gcat.−1h−1 with super high selectivity of 99.6% to C1 oxygenates was achieved over Cu-BTC-P-235 catalyst, and the catalyst possessed excellent reusability.
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