Dynamic catalytic adsorptive desulfurization of real diesel over ultra-stable and low-cost silica gel-supported TiO2

The single metal atom (Ni, Pd, Pt) anchored on defective hexagonal boron nitride for oxidative desulfurization

Single-atom catalysts (SACs) have attracted great attention for various chemical reactions because of their strong activity, high metal utilization ratio, and low cost. Here, by using the density functional theory (DFT) method, the stability of a single VIII-group metal atom (M = Ni, Pd, Pt) anchored on the defective hexagonal boron nitride (h-BN) sheet and its possible application in oxidative desulfurization (ODS) are investigated. Calculations show that the stability of the single M atom embedded in the h-BN surface with B and N vacancies is strikingly enhanced compared to that on the perfect h-BN surface. The catalytic activities of the defective h-BN-supported single metal atom are further studied by the activation of molecular oxygen and subsequent oxidation of dibenzothiophene (DBT). O2 is activated to the super-oxo state with large interaction energies on three M/VN surfaces. However, among the three M/VB surfaces, only Pt/VB performs efficient activation of O2. The oxidation of DBT proceeds in two steps; the rate-determining step is the initial step, in which activated O2 oxidizes DBT to produce sulfoxide. By comparing the energy barrier in the first reaction step, both Ni/VN and Pt/VB are revealed as promising candidates for the ODS reaction.

Efficient Oxidative Desulfurization of High-Sulfur Diesel via Peroxide Oxidation Using Citric, Pimelic, and α-Ketoglutaric Acids

The widespread use of diesel fuel for transportation, industry, and electricity generation causes several environmental issues via an increase in the amount of sulfur compound emissions. Commercial diesel fuel must be free of sulfur-containing compounds since they can cause several environmental problems. Considering the currently available processes to eliminate sulfur compounds, oxidative desulfurization (ODS) is one of the effective means for this purpose. This work presented a simple, low cost, and efficient ODS system of high-sulfur diesel fuels using peroxide oxidation with the aid of citric, pimelic, and α-ketoglutaric acids. The aim of the study was to investigate the potential of these acids as hydrogen peroxide (H2O2) activators for ODS and to optimize the reaction conditions for maximum sulfur removal. The results showed that citric, pimelic, and α-ketoglutaric acids were effective catalysts for the desulfurization of high-sulfur diesel with an initial sulfur content of 2568 mg L−1, achieving a sulfur removal efficiency of up to 95%. The optimized reaction conditions were found to be 0.6 g of carboxylic acid dosage and 10 mL of H2O2 at 95 °C. The desulfurization efficiency of the real diesel sample (2568 mg L−1) was shown to be 27, 34, and 84.57%, using citric acid, α-ketoglutaric acid, and pimelic acid after 1h, respectively. The effectiveness of the oxidation process was characterized by gas chromatographic pulsed flame photometric detector (GC-PFPD) and Fourier-transform infrared spectroscopy (FTIR) techniques. The experimental results demonstrated that the developed system exhibited high efficiency for desulfurization of real high-sulfur diesel fuels that could be a good alternative for commercial application with a promising desulfurization efficiency.

Process Optimization for Catalytic Oxidation of Dibenzothiophene over UiO-66-NH2 by Using a Response Surface Methodology

This research investigates the catalytic performance of a metal-organic framework (MOF) with a functionalized ligand-UiO-66-NH₂-in the oxidative desulfurization of dibenzothiophene (DBT) in n-dodecane as a model fuel mixture (MFM). The solvothermally prepared catalyst was characterized by XRD, FTIR, ¹H NMR, SEM, TGA, and MP-AES analyses. A response surface methodology was employed for the experiment design and variable optimization using central composite design (CCD). The effects of reaction conditions on DBT removal efficiency, including temperature (X ₁), oxidant agent over sulfur (O/S) mass ratio (X ₂), and catalyst over sulfur (C/S) mass ratio (X ₃), were assessed. Optimal process conditions for sulfur removal were obtained when the temperature, O/S mass ratio, and C/S mass ratio were 72.6 °C, 1.62 mg/mg, and 12.1 mg/mg, respectively. Under these conditions, 89.7% of DBT was removed from the reaction mixture with a composite desirability score of 0.938. From the results, the temperature has the most significant effect on the oxidative desulfurization reaction. The model F values gave evidence that the quadratic model was well-fitted. The reusability of the MOF catalyst in the ODS reaction was tested and demonstrated a gradual loss of activity over four runs.

Polyoxometalate/Cellulose Nanofibrils Aerogels for Highly Efficient Oxidative Desulfurization

Polyoxometalate (POM) presents great potential in oxidative desulfurization (ODS) reaction. However, the high dissolubility of POM in common solvents makes it difficult to recycle. Besides, the small specific surface area of POM also limits the interaction between them and the substrate. Depositing polyoxometalates onto three-dimensional (3D) network structured materials could largely expand the application of POM. Here, the surfaces of cellulose nanofibrils (CNFs) were modified with very few (3-Aminopropyl) trimethoxysilane (APTS) to endow positive charges on the surfaces of CNFs, and then phosphotungstic acid (PTA) was loaded to obtain the aerogel A-CNF/PTA as the ODS catalyst. FT-IR indicated the successful deposition of PTA onto aminosilane modified CNF surfaces. UV-VIS further suggested the stability of PTA in the aerogels. BET and SEM results suggested the increased specific surface area and the relatively uniform 3D network structure of the prepared aerogels. TGA analysis indicated that the thermal stability of the aerogel A-CNF/PTA50% was a little higher than that of the pure CNF aerogel. Most importantly, the aerogel A-CNF/PTA50% showed good catalytic performance for ODS. Catalysis results showed that the substrate conversion rate of the aerogel A-CNF/PTA50% reached 100% within 120 min at room temperature. Even after five cycles, the substrate conversion rate of the aerogel A-CNF/PTA50% still reached 91.2% during the dynamic catalytic process. This work provides a scalable and facile way to stably deposit POM onto 3D structured materials.

Heteroatom Bridging Strategy in Carbon-Based Catalysts for Enhanced Oxidative Desulfurization Performance

Carbon-based catalysts are found to be promising metal-free species for aerobic oxidative desulfurization of fuel oil. Thus, a proper approach to promote their catalytic performances is very much in demand. In this contribution, a heteroatom bridging strategy is proposed to enhance the catalytic activities of carbon-based catalysts. As proof of the strategy, a series of boron (B)-doped graphite catalysts were synthesized. Detailed characterizations showed that the hetero-B atoms were uniformly dispersed in graphite. More importantly, it was found that the doped B atoms functioned as a bridge for electron transfer. With the existence of the heteroatom bridge, the activation of oxygen by graphite during the catalytic oxidation process was enhanced remarkably, leading to an ultradeep oxidative desulfurization performance. Moreover, the catalyst can be readily recycled five times without a significant decrease in desulfurization performance.

Oxidative Desulfurization of Petroleum Distillate Fractions Using Manganese Dioxide Supported on Magnetic Reduced Graphene Oxide as Catalyst

In this study, oxidative desulfurization (ODS) of modeled and real oil samples was investigated using manganese-dioxide-supported, magnetic-reduced graphene oxide nanocomposite (MnO2/MrGO) as a catalyst in the presence of an H2O2/HCOOH oxidation system. MnO2/MrGO composite was synthesized and characterized by scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) analyses. The optimal conditions for maximum removal of dibenzothiophene (DBT) from modeled oil samples were found to be efficient at 40 °C temperature, 60 min reaction time, 0.08 g catalyst dose/10 mL, and 2 mL of H2O2/formic acid, under which MnO2/MrGO exhibited intense desulfurization activity of up to 80%. Under the same set of conditions, the removal of only 41% DBT was observed in the presence of graphene oxide (GO) as the catalyst, which clearly indicated the advantage of MrGO in the composite catalyst. Under optimized conditions, sulfur removal in real oil samples, including diesel oil, gasoline, and kerosene, was found to be 67.8%, 59.5%, and 51.9%, respectively. The present approach is credited to cost-effectiveness, environmental benignity, and ease of preparation, envisioning great prospects for desulfurization of fuel oils on a commercial level.

Synthesis of porous carbon via a waste tire leavening strategy for adsorptive desulfurization

Adsorptive desulfurization is an effective technology for removing harmful sulfur under mild conditions. Carbon materials have many advantages and are often used in adsorption desulfurization research, but until now have been synthesized using complicated methods and have shown limited adsorption capacity. Using an NaHCO₃-assisted leavening method, waste tires were in the current work used as raw materials to produce hierarchically porous carbon that exhibits a high specific surface area and abundant oxygen-containing functional groups. In contrast to the sulfur removal by the carbon material prepared using a commonly used method, the as-prepared carbon material shows excellent adsorption performance, and was able to achieve an ultra-deep desulfurization of pentanethiol, specifically removing up to 99.7% of the sulfur from a model fuel with an initial sulfur concentration of 28 ppm. Therefore, we have provided a simple method for synthesizing adsorbents with high adsorption performance, and we expect these adsorbents to be used for industrial adsorptive desulfurization.

Adsorptive desulfurization is an effective technology for removing harmful sulfur under mild conditions.

Kinetics of Sulfur Removal from Tehran Vehicular Gasoline by g-C3N4/SnO2 Nanocomposite

The graphitic carbon nitride/tin oxide (g-C₃N₄/SnO₂) nanocomposite synthesized under microwave irradiation was used for adsorptive removal of sulfur-containing dibenzothiophene (DBT) from Tehran vehicular gasoline. High-resolution transmission electron microscopy, X-ray powder diffraction, energy dispersive X-ray spectroscopy, Brunauer-Emmett-Teller, Fourier-transform infrared spectroscopy, and field emission scanning electron microscopy techniques determined the adsorbent characteristics, and gas chromatography with a flame ionization detector determined the DBT concentration of the samples. Application of the experimental data into the solid/fluid kinetic models indicated a chemisorption control regime that increased the removal of sulfur from the commercial samples used. A pseudo-second-order reaction with the rate constant of 0.015 (g mg^-1 min^-1) and total conversion time of 316 min described the adsorption process. Based on the real fuel results, the adsorption capacity of the g-C₃N₄/SnO₂ adsorbent reached 10.64 mg S g^-1 adsorbent at equilibrium conditions. This value was the highest adsorption capacity obtained so far for a commercial gasoline sample. The g-C₃N₄/SnO₂ nanocomposite could, therefore, be introduced as an inexpensive, easily obtainable adsorbent that can significantly remove the sulfur from the vehicular gasoline fuels.

Ionic liquid-supported 3DOM silica for efficient heterogeneous oxidative desulfurization

DBT is absorbed by IL-3DOM SiO₂ and then oxidized to DBTO₂ in the presence of H₂O₂.