Liquid phase oxidation of dibenzothiophene with alumina-supported vanadium oxide catalysts: An alternative to deep desulfurization of diesel

Performance of V-Fe based catalysts on the oxidation of dibenzothiophenes

To obtain fossil fuels with ultra-low S levels at friendly conditions, different V oxides formulations on alumina modified with Fe were characterized and selected to oxidize dibenzothiophene (DBT), 4-methyl DBT and 4,6-dimethyl DBT prevailing in diesel fuel. V-Fe based catalysts (5 or 10 wt% of V) were obtained by impregnation of ammonium metavanadate solutions on Fe-modified alumina, obtained by impregnation of Mohr salt on pseudoboehmite (2 wt% of Fe). The catalysts were calcined in air atmosphere, and after were partially reduced with H2 flux to obtain a mix of several oxidation states of V and Fe species, to evaluate the interaction of Fe in VOx/Al2O3 catalysts and determine its effect on the oxidation processes. The structural and optical properties, as well as surface species, were determined by SEM-EDS, TPR, XRD, Raman, ATR-FTIR, photoluminescence, UV-Vis diffuse reflectance, and XPS spectroscopy. The catalytic performance was evaluated in oxidative desulfurization (ODS) and photocatalytic ODS (PODS) processes. The experimental results showed the addition of Fe promoted the catalytic activity of both ODS and PODS reactions. ODS activities of V-Fe catalysts increase up to 7.5 times with respect to V catalysts without Fe, and the most active catalyst (V5Fer) presents a characteristic oxidation time of 50 min for 4,6-DMDBT. The PODS activity of V10Fec was like ODS activity, showing it is possible to oxidize the dibenzothiophenes under friendly conditions to obtain lower S levels. The promoting effect of Fe was due to the interaction of Fe2+ and Fe3+ with the catalytic support, favoring the distribution of surface V3+ and V4+ species. Additionally, Fe improved the optical properties of the catalysts since the bandgap energy decrease and low recombination rate of the electron-hole pair were observed. Therefore, V-Fe based catalysts are photocatalytically actives to be used in PODS processes.

Exploring the impact of competitive compounds and catalyst synthesis method in DBT oxidative desulfurization using MoO3-V2O5/Al2O3 catalyst

This research endeavors to address the pressing challenge of reducing sulfur content in fuels, an environmental imperative. It does so by employing bimetallic catalysts to enhance the efficiency of oxidative desulfurization (ODS) processes. This involves utilizing successive impregnation and co-impregnation methods to prepare a MoO3-V2O5/Al2O3. The catalysts underwent characterization using various techniques including X-ray diffraction (XRD), N2 adsorption-desorption, UV-vis (DRS), temperature-programmed desorption (NH3-TPD), Raman, Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FE-SEM), and energy dispersive spectrum (EDS). The catalyst was utilized for the evaluation of the ODS process of dibenzothiophene (DBT). The effects of oxidants, namely H2O2 and t-butyl hydroperoxide (TBHP), were studied in the ODS. The catalyst prepared using the co-impregnation method (5M-15V-co) demonstrated significant acidic sites and exhibited remarkable efficiency in oxidative desulfurization. Remarkably, this catalyst achieved 100% oxidation of sulfur components within 30 min (min). To assess the catalyst's performance further, competitive compounds including nitrogen-containing compounds (NCCs) and saturated and unsaturated hydrocarbon compounds (HCs) were employed in the ODS. Initially, the introduction of NCCs led to a decrease in the sulfur removal rate; however, the catalyst successfully oxidized DBT completely within 60 min. When cyclohexene was present as an olefinic hydrocarbon compound, the catalyst oxidized DBT by approximately 75%, whereas DBT oxidation reached 100% within 20 min when p-xylene was introduced to the catalytic reactor. Additionally, as the O/S ratio increased from 2/5 to 10, the sulfur removal rate improved from 30 to 90%, indicating that HCs and NCCs compete with sulfur in terms of oxidant consumption.

Experimental and theoretical study of deep oxidative desulfurization of Dibenzothiophene using Oxalate-Based catalyst

The present study reports the experimental and theoretical investigation for production of ultra-low sulfur liquid fuels through estimation of various reactive species formed during the reaction with the help of simulation. All the experiments were performed using an ultrasound bath which operates at a frequency of 37 kHz and a theoretical power of 95 W. The presented oxalate-based technique is found to be more efficient with > 93% DBT oxidation within 15 min of reaction time at 25 °C due to formation of reactive species like Fe^IIC₂O₄ and [Formula: see text] which accelerate the reaction kinetics. Moreover, we have also investigated the influence of process parameters such as molar ratio of C₂O₄^2-/Fe^{2 +}, oxidant concentration, volume ratio of organic to aqueous phase, sulfur concentration, and activation methods of oxidant. The results revealed that catalyst can be reused for several runs without decrease in catalytic activity. The experimental and simulation of cavitation bubble dynamics results revealed that sonochemical effect assists to accelerate the reaction kinetics through formation of free radicals (^•O, ^•H, ^•OH and HO₂^∙) and other reactive species like O₃ and H₂O₂ generated during transient cavitation. The sono-physical effects of cavitation help to create a fine emulsion in the liquid-liquid heterogeneous system leading to enhanced mass transfer rate by providing more interfacial surface area for occurring chemical reaction.

Confined Heteropoly Blues in Defected Zr-MOF (Bottle Around Ship) for High-Efficiency Oxidative Desulfurization

The Keggin-type polyoxometalates (POMs) are effective catalysts for oxidative desulfurization (ODS) and confining these POMs in metal-organic frameworks (MOFs) is a promising strategy to improve their performances. Herein, postsynthetic modification of POMs confined in MOFs by adding thiourea creates more unsaturated metal sites as defects, promoting ODS catalytic activity. Additional modification by confining 1-butyl-3-methyl imidazolium POMs in MOFs is performed to obtain higher ODS activity, owing to the affinity between electron-rich thiophene-based compounds and electrophilic imidazolium compounds. The ODS catalytic activities of four Zr-MOF-based composites (bottle around ship) including phosphomolybdate acid (PMA)/UiO-66, [Bmim]₃ PMo₁₂ O₄₀ /UiO-66, PMA/Thiourea/UiO-66, and [Bmim]₃ PMo₁₂ O₄₀ /Thiourea/UiO-66 are therefore investigated in detail. In order to explore the catalytic mechanism of these MOF composites, their microstructures and electronic structures are probed by various techniques such as X-ray diffraction, thermogravimetric analysis, Fourier transform infrared, Raman, scanning electron microscope, transmission electron microscope, BET, X-ray photoelectron spectroscopy, EPR, UV-vis, NMR spectra, and H₂ -temperature-programmed reduction. The results reveal that phosphomolybdate blues and imidazolium phosphomolybdate blues with different Mo⁵⁺ /Mo⁶⁺ ratios with the Keggin structure are confined in defected UiO-66 for all four composites. This approach can be applied to design and synthesize other POMs/MOFs composites as efficient catalysts.

Polyoxometalate as an effective catalyst for the oxidative desulfurization of liquid fuels: a critical review

In order to meet the stringent environmental and industrial legislation on fuel specifications, sulfur compounds have to be removed efficiently from fuels. The requirement to produce ultralow-sulfur fuels (S < 10 ppm) has stimulated many works in the area of conventional hydro-desulfurization (HDS) method. Oxidative desulfurization (ODS), as an alternative or complementary technology to HDS for deep desulfurization, is conducted with high selectivity and reactivity to sterically hindered S compounds under mild reaction conditions. In the ODS process, using an appropriate oxidant in the presence of a catalyst, organic sulfur compounds can be oxidized selectively to their corresponding sulfoxides and sulfones, which can be easily removed by different separation methods. Having great catalytic characteristics, polyoxometalate materials have been utilized as a vital class of catalysts for deep desulfurization of fuels. In the past few decades, ODS of fuels using polyoxometalate as catalyst has drawn much attention, and various studies have been carried out in this area. Here, we give a critical review for the removal of sulfur compounds from liquid fuels (mostly from diesel and model fuels) by ODS via homogeneous and heterogeneous polyoxometalate catalysts.

Synthesis and crystal structures of a copper(ii) dinuclear complex and zinc(ii) coordination polymers as materials for efficient oxidative desulfurization of dibenzothiophene

Dinuclear copper(ii) complex [Cu₂(BAc)₄(QX)₂], and 2D zinc(ii) coordination polymer, [Zn(TDPA)₂(TMPy)₂]_n, presented high oxidation and adsorption thermodynamics for dibenzothiophene sulfoxide (DBTO).

Ultrasound-assisted oxidative desulfurization of bunker-C oil using tert-butyl hydroperoxide

This work investigated the ultrasonic assisted oxidative desulfurization of bunker-C oil with TBHP/MoO3 system. The operational parameters for the desulfurization procedure such as ultrasonic irradiation time, ultrasonic wave amplitude, catalyst initial concentration and oxidation agent initial concentration were studied. The experimental results show that the present oxidation system was very efficient for the desulfurization of bunker-C oil and ~35% sulfur was removed which was dependent on operational parameters. The application of ultrasonic irradiation allowed sulfur removal in a shorter time. The stronger the solvent polarity is, the higher the sulfur removal rate, but the recovery rate of oil is lower. The sulfur compounds in bunker-C oil reacted with TBHP to produce corresponding sulfoxide, and further oxidation produced the corresponding sulfone.