Abstract
A series of porous metal–organic frameworks (MOFs) of the UiO-66 family, namely UiO-66(Zr), UiO-66(Hf) and UiO-66(Hf)-NH2, prepared by solvothermal procedures were characterized, and their catalytic efficiency for oxidative denitrification (ODN) was investigated for the first time. Sustainable denitrogenation systems combining adsorption and oxidative catalytic capacity were designed using a model diesel containing two distinct nitrogen compounds (NCs) in a solvent-free medium and using an environment-friendly oxidant (H2O2). An efficient adsorptive denitrogenation process was only achieved after long reaction times (24 h): using the Hf-based MOFs, the adsorptive denitrogenation increased from 19% to 79% at 5 to 24 h, while the UiO-66(Zr) reached 76% after 24 h, although the absence of adsorption capacity after 5 h. UiO-66(Hf) and UiO-66(Hf)-NH2 also revealed superior oxidative catalytic denitrogenation than UiO-66(Zr), attaining 97% of efficiency instead of 80%. ODN processes demonstrated to be more effective than the adsorptive denitrogenation, mainly during the first hours of the process. In addition, the metal center in the MOF structure had a larger influence than the presence of the amine-functional groups. Hf-based compounds revealed higher denitrogenation efficiency than the UiO-66(Zr) for a shorter reaction time (5 h).
Highlights
Compounds 2021, 1, 3–14. https://The complex composition of crude oil containing aromatics with sulfur, nitrogen and/or oxygen compounds is a challenge when selective cleaning treatment procedures need to be applied [1]
Fourier-transform infrared (FTIR) spectra were acquired on the attenuated total reflectance (ATR) operation mode of a PerkinElmer FTIR system spectrum BX spectrometer, and the spectra representations are shown in arbitrary units of transmittance
Shown in Figure 2a,strategy the FTIR spectra of the UiO-66-type compounds reveal a plementary set of methods, such asprevious
Summary
The complex composition of crude oil containing aromatics with sulfur, nitrogen and/or oxygen compounds is a challenge when selective cleaning treatment procedures need to be applied [1]. A well-known example is the disabling behavior presented by the nitrogen compounds (NCs), which compete with sulfur species during the catalytic desulfurization treatment [2]. Several methods based on extraction, oxidation and adsorption have been investigated to remove NCs from fuels [4]. In particular, is an interesting choice since it can be used in combination with either adsorption or extraction, resulting in an efficient denitrogenation route. To improve the selectivity of the oxidant for nitrogen atoms, it is important to choose suitable catalysts that offer both good catalytic activity and selectivity and possess recycling characteristics in order to obtain an efficient and sustainable denitrogenation method.
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