Control over Nature and Population of Acidic Sites in MIL-100(Cr) for High Capacity Oil Denitrogenation

Despite extensive studies, metal-organic frameworks (MOFs) suffer from some challenges, like multistep synthesis, expensive raw materials, and leaching of particular components, in the adsorptive denitrogenation (ADN) of oil. These challenges limit the application of MOFs in industrial ADN. To go beyond these challenges, MIL-100(Cr) (with the formula [Cr₃O(X)(H₂O)(BTC)₂]·nH₂O, X = F^- or OH^-, H₃BTC = 1,3,5-benzene tricarboxylic acid) was selected and modified with two approaches to tune the acidic sites of the framework. First, H₂IPA (isophthalic acid) is applied as a defective linker in the presence of hydrofluoric acid (HF). Second, the HF modulator was eliminated. The results revealed that the second approach was more efficient for increasing the adsorption capacity to quinoline (748 mg g^-1) and indole (183 mg g^-1). These capacities were obtained by engineering the nature and population of the Brønsted and Lewis acidic sites of chromium inorganic nodes supported by X-ray photoelectron spectroscopy and ammonia temperature-programmed desorption techniques. Hydroxyl-terminated MIL-100(Cr) shows Brønsted acidity, improved Lewis acidity, high selectivity to nitrogen-containing compounds, and high regeneration ability. This work reveals how control over nature and population of acidic sites in MIL-100(Cr) can improve oil DN efficiency.