What Matters to the Adsorptive Desulfurization Performance of Metal-Organic Frameworks?

Metal organic frameworks (MOFs) show high potential in adsorptive removal of aromatic sulfur compounds; however, the crucial factors affecting the adsorption performances are scarcely clarified. In the present study, three classic aromatic sulfur compounds (i.e., thiophene, benzothiophene, and 4,6-dimethyldibenzothiophene) as well as five typical MOFs (i.e., MOF-5, HKUST-1, MIL-53(Fe), MIL-53(Cr), and MIL-101(Cr)) were selected for study. The adsorptive desulfurization performances of MOFs were investigated by using a fixed-bed adsorption system. In the case of thiophene, the adsorption capacity of MOFs decreases in the order MIL-53(Cr) > HKUST-1 > MOP-5 > MIL-53(Fe) > MIL-101(Cr). For the first time, the adsorbate-adsorbent interaction was examined in detail by using infrared spectra and temperature-programmed desorption. Such an interaction was demonstrated to be the most important factor affecting adsorption performance. When the molecular size of aromatic sulfur compounds is comparable to or smaller than the window diameter of MOFs, the influence of window diameter becomes apparent. It is surprising to find that the adsorbate-adsorbent interaction plays a major role, which is responsible for the poor adsorption performance of MIL-101(Cr) with quite high porosity. Therefore, metal sites and structure that contribute to the adsorbate-adsorbent interaction should be considered to be the most significant factor aiming to develop new MOFs for adsorptive desulfurization.