Mesoporous SnO2-MoO3 catalyst for diesel oxidative desulfurization: Impact of the SnO2/MoO3 ratio on catalytic efficiency

Vehicular SOx emissions have a huge detrimental impact on public health, catalytic converters, and the environment. Developing strategies to remove sulfur from diesel and thus safeguard the above is imperative. A series of SnO2-MoO3 mixed oxides and mono oxides MoO3 and SnO2 were prepared by soft template method, calcined at 450 °C and successfully tested in model diesel oxidative desulfurisation (ODS). The impact of the SnO2/MoO3 mole ratio (hereinafter denoted as Sn/Mo) on catalytic efficiency was investigated, among other catalytic parameters. The obtained samples were analyzed using X-ray diffraction (XRD), Raman spectrocscopy, scanning electron microscopy (SEM), N2-physisorption and titration method for acidic properties. The study demonstrates that mixing SnO2 and MoO3 improves acidic sites, crystallinity, and morphological properties of pure SnO2. The addition of MoO3 increased oxygen vacancies and the surface area of SnO2. High acidic site densities of 49.3, 47.4, and 46.7 mEqg-1 were observed for the catalysts with 2:1, 1:1, and 1:2 Sn/Mo mole ratio, respectively. The catalytic efficiency increased with an increase in Sn content with the highest catalytic efficiency of 99.8% for the dibenzothiophene (DBT) oxidation achieved in 30 min for Sn/Mo (2:1) catalyst compared to 92 and 70% for Sn/Mo 1:1 and 1:2 catalysts, respectively. The rate constant for the reaction was 0.057 min-1, which is eight times that of MoO3; 0.007 min-1 and three times that of SnO2; 0.017 min-1. The ODS mechanism utilizing the SnO2-MoO3 catalyst was proposed. The prepared SnO2-MoO3 catalyst demonstrated a high potential for industrial desulfurisation applications.

Combined Heterogeneous Catalyst Based on Titanium Oxide for Highly Efficient Oxidative Desulfurization of Model Fuels

In this work, new heterogeneous Mo-containing catalysts based on sulfonic titanium dioxide were developed for the oxidation of sulfur-containing model feed. The synergistic effect of molybdenum and sulfonic group modifiers allows for enhancing catalytic activity in dibenzothiophene oxidative transformation, and a strong interaction between support and active component for thus obtained catalysts provides increased stability for leaching. For the selected optimal conditions, the Mo/TiO₂-SO₃H catalyst exhibited 100% DBT conversion for 10 min (1 wt % catalyst, molar ratio of H₂O₂:DBT, 2:1; 80 °C). Complete oxidation of DBT in the presence of the synthesized catalyst is achieved when using a stoichiometric amount of oxidizing agent, which indicates its high selectivity. The enhanced stability for metal leaching was proved in recycling tests, where the catalyst was operated for seven oxidation cycles without regeneration with retainable activity in DBT-containing model feed oxidation with hydrogen peroxide under mild reaction conditions. In 30 min of the reaction (H₂O₂:S = 2:1 (mol), 0.5% catalyst, 5 mL of acetonitrile, 80 °C), it was possible to reduce the content of sulfur compounds in the diesel fraction by 88% (from 5600 to 600 ppm).

Hydrodesulfurization of 4,6-Dimethyldibenzothiophene and the Diesel Oil Fraction on NiMo Catalysts Supported over Proton-Exchanged AlMCM-41 and TiMCM-41 Extrudates

NiMo catalysts supported on mesoporous MCM-41 type materials shaped with binder were tested for activity in the hydrodesulfurization of 4,6-dimethyldibenzothiophene (4,6-DMDBT) and the diesel fuel fraction (0.92 wt% of sulfur). The aim of the investigation was to evaluate the effect of ion exchange with protons of Al- or Ti-substituted MCM-41 mesoporous supports. The subjected catalytic systems were NiMo/HAlMCM-41 and NiMo/HTiMCM-41, and for comparison purposes NiMo/AlMCM-41 and NiMo/TiMCM-41. The samples were characterized by N2 sorption (at 77 K), XRD, TEM, XPS, SEM and Py–IR. It was found that the functionalization of AlMCM-41 and TiMCM-41 with protons increased the conversion of 4,6-DMDBT and the pseudo-first-order rate constant. Correspondingly, 4,6-DMDBT HDS reactions over the NiMo/HTiMCM-41 catalyst proceeded to a similar extent via hydrogenation and direct desulfurization, whereas over the NiMo/HAlMCM-41 they proceeded mainly via direct desulfurization. Furthermore, the ion-exchanged catalysts displayed two-fold higher efficiency in direct desulfurization than their non-modified counterparts. The NiMo/HTiMCM-41 catalyst exhibited the highest catalytic efficiency in the HDS of 4,6-DMDBT and the diesel oil fraction. The high activity of the NiMo/HTiMCM-41 catalyst is mainly attributed to its appropriate acidity, as well as the metal–support interaction providing both the high dispersion of the active phase and the desirable multilayered stacking morphology of the active phase slabs.

A current overview of the oxidative desulfurization of fuels utilizing heat and solar light: from materials design to catalysis for clean energy

The ceaseless increase of pollution cases due to the tremendous consumption of fossil fuels has steered the world towards an environmental crisis and necessitated urgency to curtail noxious sulfur oxide emissions. Since the world is moving toward green chemistry, a fuel desulfurization process driven by clean technology is of paramount significance in the field of environmental remediation. Among the novel desulfurization techniques, the oxidative desulfurization (ODS) process has been intensively studied and is highlighted as the rising star to effectuate sulfur-free fuels due to its mild reaction conditions and remarkable desulfurization performances in the past decade. This critical review emphasizes the latest advances in thermal catalytic ODS and photocatalytic ODS related to the design and synthesis routes of myriad materials. This encompasses the engineering of metal oxides, ionic liquids, deep eutectic solvents, polyoxometalates, metal-organic frameworks, metal-free materials and their hybrids in the customization of advantageous properties in terms of morphology, topography, composition and electronic states. The essential connection between catalyst characteristics and performances in ODS will be critically discussed along with corresponding reaction mechanisms to provide thorough insight for shaping future research directions. The impacts of oxidant type, solvent type, temperature and other pivotal factors on the effectiveness of ODS are outlined. Finally, a summary of confronted challenges and future outlooks in the journey to ODS application is presented.

Assessment of the Oxidative Desulfurization of Middle Distillate Surrogate Fuels with Spectroscopic Techniques

The oxidative desulfurization of five (5) model sulfur compounds and eleven (11) surrogate blends was investigated using the hydrogen peroxide (H₂O₂)-acetic acid (CH₃COOH) system. Consequently, extractive desulfurization was carried out using conventional solvents. The model sulfur compounds, as well as the solvent, are present in petroleum middle distillates. The selection of the compounds was made so that they represent various kinds of sulfur compounds. The goal of this study was the implementation of a simple and economical oxidative and extractive system for the desulfurization of surrogate mixtures with an intermediate sulfur concentration 1% w/w, at the mild temperature of 70°C, and without the use of supplementary and assisting methods such as heterogeneous catalysis or ultrasound irradiation. The sulfur content was estimated using X-ray fluorescence. The progress of the oxidation reaction was monitored using liquid FT-IR. The solid sediments of the oxidation procedure were identified with solid-state FT-IR and ¹H NMR spectroscopy.

Amorphous Cr2WO6-Modified WO3 Nanowires with a Large Specific Surface Area and Rich Lewis Acid Sites: A Highly Efficient Catalyst for Oxidative Desulfurization

The oxidative desulfurization (ODS) of fuel oils is of great significance for environmental protection, and the development of efficient ODS heterogeneous catalysts is highly desired. Herein, we have designed and synthesized a novel material of amorphous Cr₂WO₆-modified WO₃ (a-Cr₂WO₆/WO₃) nanowires (3-6 nm) with a large specific surface area of 289.5 m²·g^-1 and rich Lewis acid sites. The formation of such a unique nanowire is attributed to the adsorption of Cr³⁺ cations on non-(001) planes of WO₃. In the ODS process, the a-Cr₂WO₆/WO₃ nanowires can efficiently oxidize benzothiophene (BT), dibenzothiophene (DBT), and 4,6-dimethyldibenzothiophene (4,6-DMDBT) to their corresponding sulfones in a quasi-microemulsion reaction system and possess the highest activity (E_a = 55.4 kJ/mol) for DBT: 99.0% of 15,000 ppm DBT with 2600 ppm S can be removed (70 °C, H₂O₂ as the oxidant). The improvement in ODS activity from most of WO₃ catalysts is owing to the sufficient active sites and enhanced adsorption of DBT on the basis of structural features of a-Cr₂WO₆/WO₃ nanowires. Combined with free radical capture experiments, a possible ODS mechanism of W(O₂) peroxotungstate route based on surface -OH groups is reasonably proposed. Moreover, the a-Cr₂WO₆/WO₃ nanowires have good stability and can be synthesized on a large scale, suggesting its potential applications as an efficient heterogeneous catalyst.

Iron and molybdenum mixed oxide supported on Al-PILC for the catalytic oxidative desulfurization of dibenzothiophene in simulated diesel fuel

In this work, three novel catalysts were prepared by 2.5, 5.0, and 10.0 wt.% facile impregnation with an iron and molybdenum mixed oxide (Fe/Mo) on an aluminum pillared clay (Al-PILC) support. These materials were characterized by scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD), temperature programed reduction (TPR), and nitrogen (N₂) physisorption at 77 K. Characterizations indicated that the metal particles were dispersed on the surface of the three catalysts, and the interlayer d₀₀₁ spacing of the pillared material remained unchanged after the impregnation process. The catalytic tests showed good results for DBT oxidation using the synthesized catalysts, with high turnover frequency (TOF) values, particularly for the material with 5.0 wt.% Fe/Mo. Theoretical calculations were carried out at the density functional theory (DFT) level, to investigate how the DBT molecules were adsorbed onto the surface of the mixed oxide. The lowest energy proposal was obtained when both Fe and Mo were present at the active sites, indicating a possible synergistic effect of the metals on catalyst activity. Reuse tests indicated that the catalysts could be employed effectively for up to 3 cycles in a row, then a decrease in activity occurred and the active sites needed to be regenerated.

Carbon nitride mediated strong metal–support interactions in a Au/TiO2 catalyst for aerobic oxidative desulfurization

Supported Au nanocatalysts have been regarded as efficient catalysts.

Effects of WO3 and SiO2 doping on CeO2–TiO2 catalysts for selective catalytic reduction of NO with ammonia

A series of CeO₂–WO₃/SiO₂–TiO₂ (CeW_xTiSi_y) catalysts with different loading amounts of WO₃ were synthesized by wet co-impregnation of ammonium metatungstate and cerium nitrate on a SiO₂–TiO₂ support, and were employed for the selective catalytic reduction (SCR) of NO by NH₃. The catalytic activity of the CeO₂/SiO₂–TiO₂ (CeSiTi) catalyst was enhanced by the addition of WO₃, and the W-containing catalysts showed higher hydrothermal stability especially between 550 and 600 °C. The introduction of WO₃ to the CeSiTi catalyst could produce more chemisorbed oxygen species, reducible subsurface oxygen species, acid sites and ad-NO_x species. Moreover, the modification of CeO₂–WO₃/TiO₂ (CeWTi) by SiO₂ could enhance the specific surface area, especially the aged specific surface area, thus improving the hydrothermal stability of the catalyst.

A series of CeO₂–WO₃/TiO₂–SiO₂ catalysts were prepared for SCR of NO_x with NH₃, and the effect of WO₃ and SiO₂ doping on the activity and stability of the catalysts were discussed.

Nanoparticle catalyzed hydrodesulfurization of diesel fuel in a trickle bed reactor: experimental and optimization study

This work focuses on the preparation, simulation, and optimization of the hydrodesulfurization (HDS) of dibenzothiophene (DBT) using a nanocatalyst. A homemade nanocatalyst (3 percent Co, 10 percent Mo/γ-Al₂O₃ nanoparticles) was used in a trickle bed reactor (TBR). The HDS kinetic model was estimated based on experimental observations over ranges of operating conditions to evaluate kinetic parameters of the HDS process and apply the key parameters. Based on these parameters, the performance of the TBR catalyzed by the nanocatalyst was evaluated and scaled up to a commercial scale. Also, the selectivity of HDS reactions was also modeled to achieve the highest yield of the desired hydrogenation product based on the desirable route of HDS. A comprehensive modeling and simulation of the HDS process in a TBR was developed and the output results were compared with experimental results. The comparison showed that the simulated and experimental data of the HDS process match well with a standard error of up to 5%. The best reaction kinetic variables obtained from the HDS pilot-plant (specific reaction rate expression, rate law, and selectivity) TBR have been utilized to develop an industrial scale HDS of DBT. The hydrodynamic key factors (effect of radial and axial dispersion) were employed to obtain the ratio of the optimal working reactor residence time to reactor diameter.

This work focuses on the preparation, simulation, and optimization of the hydrodesulfurization (HDS) of dibenzothiophene (DBT) using a nanocatalyst.