Adsorptive denitrogenation of model fossil fuels with Lewis acid-loaded metal–organic frameworks (MOFs)

Abstract

A metal–organic framework (MOF), MIL-100(Fe), was impregnated with a Lewis acidic salt, AlCl3, in order to prepare an acidic adsorbent. The adsorbent was used in adsorptive denitrogenation (ADN) of model fuels to investigate the effect of the Lewis acidity of the composite adsorbent. To provide more in-depth understanding of the interaction/adsorption mechanism, a basic quinoline (QUI) and a neutral indole (IND) were utilized as adsorbates. A sulfur-containing compound, benzothiophene (BT), was also used along with the two nitrogen-containing compounds (NCCs) in order to investigate the selectivity of the adsorption of the NCCs. The maximum adsorption capacity of AlCl3/MIL-100(Fe) for QUI was 17% higher than that of the pristine MIL-100(Fe), despite an 8% reduction of the surface area upon loading the MOF with AlCl3. In contrast, the performance of the AlCl3/MIL-100(Fe) adsorbents in the adsorption of neutral IND decreased with the content of AlCl3 due to little interaction between the acidic adsorbent and neutral IND and the low porosities of the modified adsorbents. Therefore, the investigation shows that MOFs impregnated with Lewis acidic materials such as AlCl3 can be effectively used for adsorptive removal of basic NCCs by means of an acid–base interaction. It can also be concluded that MOFs, when modified suitably with specific functional materials, can be used for specific and improved adsorption.