Enhanced adsorptive desulfurization by iso-structural amino bearing IRMOF-3 and IRMOF-3@Al2O3versus MOF-5 and MOF-5@Al2O3 revealing the predominant role of hydrogen bonding

Abstract

Desulfurization of oragnosulfur-containing fuels signify a great importance in improving the quality of fuel and is also beneficial to the environment. In this work, we report two new composites, namely, MOF-5@γ-Al₂O₃ and IRMOF-3@γ-Al₂O₃, synthesized by loading iso-structural MOF-5 and amino bearing IRMOR-3 onto the γ-Al₂O₃ beads (the loading amount of MOF-5 and IRMOF-3 are 13.4 wt% and 16.3 wt%, respectively). The composites are fully characterized by IR spectroscopy, XRD, SEM, BET and XRF. These iso-structural MOFs and their composites exhibit substantially high adsorptive desulfurization capacities for benzothiophene (BT), 3-methylthiophene (3-MT), dibenzothiophene (DBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT). The adsorption capacities of amino bearing IR-MOF-3 and IRMOF-3@γ-Al₂O₃ are significantly greater than those of MOF-5 and MOF-5@γ-Al₂O₃, e.g., the adsorption capacities for DBT of IRMOF-3@γ-Al₂O₃, IRMOF-3, MOF-5@γ-Al₂O₃ and MOF-5 are 54.9, 45.1, 31.4 and 24.1 mg S g⁻¹ MOFs, respectively, under optimal conditions (time 60 min, temperature 30 °C, MOFs@γ-Al₂O₃/M_oil = 1/40). The adsorption results revealed the predominant role of hydrogen bonding between the Lewis basic S atoms of the organo sulfurs and –NH₂ groups in IR-MOF-3 and also the π–π interactions that works well in MOF-5. The enhancement in the desulfurization capability of MOFs@γ-Al₂O₃versus the corresponding pristine MOFs shall be attributed to the advantage of the confinement effect of the γ-Al₂O₃ pores that results in larger specific surface area, much more exposed active sites, and shorter diffusion channels of the MOFs. The kinetics and thermodynamic parameters indicate that the adsorption process is spontaneous and endothermic, and the increase in entropy is the primary driving force for the desulfurization. In addition, it is found that the composites possess good reusability and can be regenerated by simple washing due to enhanced mechanical strength.