Tailor-Made Mesoporous Ti-SBA-15 Catalysts for Oxidative Desulfurization of Refractory Aromatic Sulfur Compounds in Transport Fuel

Stabilisation of molecular TiO4 species on the pore surface of mesoporous silica for photocatalytic H2 evolution

Although molecular tetrahedral Ti-oxo species exhibit unique electronic and photochemical properties due to their discrete energy levels, which are different from those of anatase and rutile, such Ti-oxo species are generally unstable and readily transformed to amorphous/crystalline TiO2 (bulk phases, nanoparticles and clusters) via hydrolysis and condensation. Here, molecular Ti-oxo species were immobilised within mesoporous silica SBA-15 by grafting titanium(IV) oxyacetylacetonate using the surface silanol groups of SBA-15 as a scaffold, followed by chemical etching with dilute hydrochloric acid to form molecular TiO4 species. These Ti species mainly exist as isolated tetrahedrally coordinated structures, as was confirmed by diffuse reflectance UV-vis and Raman spectroscopy. The SBA-15-immobilised molecular TiO4 exhibited higher photocatalytic activity for H2 evolution from an aqueous methanol solution than conventional Ti-incorporated mesoporous silica (Ti-MCM-41) and reference TiO2 (P25).

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).

Oxidative desulfurization of model and real fuel samples with natural zeolite-based catalysts: experimental design and optimization by Box–Behnken method

In this study, oxidative desulfurization was performed on simulated oil fraction consist of 1000 ppm dibenzothiophene. Cobalt supported on natural zeolite of Kaolin has been used as heterogeneous catalysts. 10% Co/metaKaolin with hydrogen peroxide as oxidant and acetonitrile as extraction solvent have shown excellent performance on desulfurization. Response surface methodology in experimental design and its subset Box–Benken was used to evaluate the performance of the selected catalyst in different operating conditions such as temperature, oxidant to sulfur molar ratio, time and catalyst amount. Also, optimum conditions was obtained are equal to 60 °C, O/S molar ratio (10.8 mol/mol), time (46 min) and catalyst amount 0.04 g with 97.1% sulfur removal. Oxidative desulfurization of model oil containing 1000 ppm of each sulfur component benzothiophene and thiophene was also tested at the optimum conditions, Oxidative desulfurization yield was ordered as DBT > BT > Th. In addition, after four steps consecutive recycle under optimum conditions oxidative desulfurization capacity of 10% Co/metaKaolin catalyst decreased from 97% to 92%, which is still high desulfurization capability. Finally, the performance of 10% Co/metaKaolin catalyst in oxidative desulfurization was evaluated for real oil fractions, gasoline and gasoil that was provided from regional oil refinery with sulfur content of 286 ppm and 7900 ppm, respectively. At the optimum conditions of operating variables desulfurization yield was 58% and 79% of total sulfur removal for gasoline and gasoil respectively with no significant changes in fuels properties.

Advances in Oxidative Desulfurization of Fuel Oils over MOFs-Based Heterogeneous Catalysts

Catalytic oxidative desulfurization (ODS) of fuel oils is considered one of the most promising non-hydrodesulfurization technologies due to the advantages of mild reaction conditions, low cost and easy removal of aromatic sulfur compounds. Based on this reason, the preparation of highly efficient ODS catalysts has been a hot research topic in this field. Recently, metal-organic frameworks (MOFs) have attracted extensive attention due to the advantages involving abundant metal centers, high surface area, rich porosity and varied pore structures. For this, the synthesis and catalytic performance of the ODS catalysts based on MOFs materials have been widely studied. Until now, many research achievements have been obtained along this direction. In this article, we will review the advances in oxidative desulfurization of fuel oils over MOFs-based heterogeneous catalysts. The catalytic ODS performance over various types of catalysts is compared and discussed. The perspectives for future work are proposed in this field.

Tungsten Nitride, Well-Dispersed on Porous Carbon: Remarkable Catalyst, Produced without Addition of Ammonia, for the Oxidative Desulfurization of Liquid Fuel

Polyanilines (pANIs), loaded with phosphotungstic acid (PTA), are pyrolyzed to get WO₃ or W₂ N (≈6 and ≈7 nm, respectively), which is well-dispersed on pANI-derived porous carbons (pDCs). Depending on the pyrolysis temperature, WO₃ /pDC, W₂ N/pDC, or W₂ N-W/pDCs could be obtained selectively. pANI acts as both the precursor of pDC and the nitrogen source for the nitridation of WO₃ into W₂ N during the pyrolysis. Importantly, W₂ N could be obtained from the pyrolysis without ammonia feeding. The obtained W₂ N/pDC is applied as a heterogeneous catalyst for the oxidative desulfurization (ODS) of liquid fuel for the first time, and the results are compared with WO₃ /pDC and WO₃ /ZrO₂ . The W₂ N/pDC is very efficient in ODS with remarkable performance compared with WO₃ /pDC or WO₃ /ZrO₂ , which is applied as a representative ODS catalyst. For example, W₂ N/pDC shows around 3.4 and 2.7 times of kinetic constant and turnover frequency (based on 5 min of reaction), respectively, compared to that of WO₃ /ZrO₂ . Moreover, the catalysts could be regenerated in a facile way. Therefore, W₂ N/pDC could be produced facilely from pyrolysis (without ammonia feeding) of PTA/pANI, and W₂ N, well-dispersed on pDC, can be suggested as a very efficient oxidation catalyst for the desulfurization of liquid fuel.

A new simple protocol for the synthesis of nanohybrid catalyst for oxidative desulfurization of dibenzothiophene

This study offers an investigation of the catalytic activity of TiO₂/SiO₂ during oxidative desulfurization (ODS) of a model fuel that includes dibenzothiophene (DBT), using hydrogen peroxide (H₂O₂) as a green oxidant in the absence of UV irradiation. For the first time, though a novel and simple protocol, TiO₂/SiO₂ nanohybrid was synthesized using ascorbic acid and glycerol as green complexing and polymerizing agents, respectively. The TiO₂/SiO₂ catalyst was thoroughly characterized by XRD, FT-IR, nitrogen adsorption-desorption measurements, TEM, FESEM, and TGA. Results revealed a high catalytic oxidative activity for the catalyst in the removal of DBT regarding sulfur removal up to 99.4% within 20 min under optimum reaction conditions. The main factors affecting the ODS process, including catalyst dosage, temperature, O/S molar ratio, and different oxidizing agents, were evaluated to identify optimum conditions. The desulfurization efficiency of the recoverable catalysts showed no loss in activity after four times. The present article suggests a new and green method for the synthesis and characterization of an efficient catalyst (TiO₂/SiO₂) in deep oxidative desulfurization at 25 °C and removal of refractory organosulfur compounds that yield ultra-low sulfur fuels. Also, it proved to have a much higher catalytic oxidation capacity when compared to pure TiO₂.

SBA-15 Anchored Metal Containing Catalysts in the Oxidative Desulfurization Process

Recalcitrant sulfur compounds are common impurities in crude oil. During combustion they produce SOx derivatives that are able to affect the atmospheric ozone layer, increasing the formation of acid rains, and reducing the life of the engine due to corrosion. In the last twenty years, many efforts have been devoted to develop conventional hydrodesulfurization (HDS) procedures, as well as alternative methods, such as selective adsorption, bio-desulfurization, oxidative desulfurization (ODS) under extractive conditions (ECODS), and others. Among them, the oxidative procedures have been usually accomplished by the use of toxic stoichiometric oxidants, namely potassium permanganate, sodium bromate and carboxylic and sulfonic peracids. As an alternative, increasing interest is devoted to selective and economical procedures based upon catalytic methods. Heterogeneous catalysis is of relevance in industrial ODS processes, since it reduces the leaching of active species and favors the recovery and reuse of the catalyst for successive transformations. The heterogenization of different types of high-valent metal transition-based organometallic complexes, able to promote the activation of stoichiometric benign oxidants like peroxides, can be achieved using various solid supports. Many successful cases have been frequently associated with the use of mesoporous silicas that have the advantage of easy surface modification by reaction with organosilanes, facilitating the immobilization of homogeneous catalysts. In this manuscript the application of SBA-15 as efficient support for different active metal species, able to promote the catalytic ODS of either model or real fuels is reviewed, highlighting its beneficial properties such as high surface area, narrow pore size distribution and tunable pore diameter dimensions. Related to this topic, the most relevant advances recently published, will be discussed and critically described.

Improving the Catalytic Performance of Keggin [PW12O40]3- for Oxidative Desulfurization: Ionic Liquids versus SBA-15 Composite

Different methodologies were used to increase the oxidative desulfurization efficiency of the Keggin phosphotungstate [PW₁₂O₄₀]^3- (PW₁₂). One possibility was to replace the acid proton by three different ionic liquid cations, forming the novel hybrid polyoxometalates: [BMIM]₃PW₁₂ (BMIM as 1-butyl-3-methylimidazolium), [BPy]₃PW₁₂ (BPy as 1-butylpyridinium) and [HDPy]₃PW₁₂ (HDPy as hexadecylpyridinium. These hybrid Keggin compounds showed high oxidative desulfurization efficiency in the presence of [BMIM]PF₆ solvent, achieving complete desulfurization of multicomponent model diesel (2000 ppm of S) after only 1 h, using a low excess of oxidant (H₂O₂/S = 8) at 70 °C. However, their stability and activity showed some weakness in continuous reused oxidative desulfurization cycles. An improvement of stability in continuous reused cycles was reached by the immobilization of the Keggin polyanion in a strategic positively-charged functionalized-SBA-15 support. The PW₁₂@TM⁻SBA-15 composite (TM is the trimethylammonium functional group) presented similar oxidative desulfurization efficiency to the homogeneous IL⁻PW₁₂ compounds, having the advantage of a high recycling capability in continuous cycles, increasing its activity from the first to the consecutive cycles. Therefore, the oxidative desulfurization system catalyzed by the Keggin-type composite has high performance under sustainable operational conditions, avoids waste production during recycling and allows catalyst recovery.

Probing the Catalytic Activity of Sulfate-Derived Pristine and Post-Treated Porous TiO2(101) Anatase Mesocrystals by the Oxidative Desulfurization of Dibenzothiophenes

Mesocrystals (basically nanostructures showing alignment of nanocrystals well beyond crystal size) are attracting considerable attention for modeling and optimization of functionalities. However, for surface-driven applications (heterogeneous catalysis), only those mesocrystals with excellent textural properties are expected to fulfill their potential. This is especially true for oxidative desulfuration of dibenzothiophenes (hard to desulfurize organosulfur compounds found in fossil fuels). Here, we probe the catalytic activity of anatases for the oxidative desulfuration of dibenzothiophenes under atmospheric pressure and mild temperatures. Specifically, for this study, we have taken advantage of the high stability of the (101) anatase surface to obtain a variety of uniform colloidal mesocrystals (approximately 50 nm) with adequate orientational order and good textural properties (pores around 3-4 nm and surface areas around 200 m²/g). Ultimately, this stability has allowed us to compare the catalytic activity of anatases that expose a high number of aligned single crystal-like surfaces while differing in controllable surface characteristics. Thus, we have established that the type of tetrahedral coordination observed in these anatase mesocrystals is not essential for oxidative desulfuration and that both elimination of sulfates and good textural properties significantly improve the catalytic activity. Furthermore, the most active mesocrystals have been used to model the catalytic reaction in three-(oil-solvent-catalyst) and two-phase (solvent-catalyst) systems. Thus, we have been able to observe that the transfer of DBT from the oil to the solvent phase partially limits the oxidative process and to estimate an apparent activation energy for the oxidative desulfuration reaction of approximately 40 kJ/mol in the two-phase system to avoid mass transfer limitations. Our results clearly establish that (101) anatase mesocrystals with excellent textural properties show adequate stability to withstand several post-treatments without losing their initial mesocrystalline character and therefore could serve as models for catalytic processes different from the one studied here.

Performance, kinetic, and biodegradation pathway evaluation of anaerobic fixed film fixed bed reactor in removing phthalic acid esters from wastewater

Emerging and hazardous environmental pollutants like phthalic acid esters (PAEs) are one of the recent concerns worldwide. PAEs are considered to have diverse endocrine disrupting effects on human health. Industrial wastewater has been reported as an important environment with high concentrations of PAEs. In the present study, four short-chain PAEs including diallyl phthalate (DAP), diethyl phthalate (DEP), dimethyl phthalate (DMP), and phthalic acid (PA) were selected as a substrate for anaerobic fixed film fixed bed reactor (AnFFFBR). The process performances of AnFFFBR, and also its kinetic behavior, were evaluated to find the best eco-friendly phthalate from the biodegradability point of view. According to the results and kinetic coefficients, removing and mineralizing of DMP occurred at a higher rate than other phthalates. In optimum conditions 92.5, 84.41, and 80.39% of DMP, COD, and TOC were removed. DAP was found as the most bio-refractory phthalate. The second-order (Grau) model was selected as the best model for describing phthalates removal.

Lewis acidity quantification and catalytic activity of Ti, Zr and Al-supported mesoporous silica

Water-tolerant metal supported Lewis acids were synthesized for the catalytic amidation of electron-poor and bulky amines.

Controllable synthesis of mesoporous titanosilicates for styrene oxidization using a nanocellulose template strategy

A nanocellulose-template strategy is reported for the controllable synthesis of mesoporous titanosilicates as efficient catalysts for the oxidization of styrene.

Performances, kinetics and mechanisms of catalytic oxidative desulfurization from oils

Ultra-deep desulfurization technologies are critical for cleaner oils and consequent better air quality.

Chelating agent-free, vapor-assisted crystallization method to synthesize hierarchical microporous/mesoporous MIL-125 (Ti)

Titanium-based microporous heterogeneous catalysts are widely studied but are often limited by the accessibility of reactants to active sites. Metal-organic frameworks (MOFs), such as MIL-125 (Ti), exhibit enhanced surface areas due to their high intrinsic microporosity, but the pore diameters of most microporous MOFs are often too small to allow for the diffusion of larger reactants (>7 Å) relevant to petroleum and biomass upgrading. In this work, hierarchical microporous MIL-125 exhibiting significantly enhanced interparticle mesoporosity was synthesized using a chelating-free, vapor-assisted crystallization method. The resulting hierarchical MOF was examined as an active catalyst for the oxidation of dibenzothiophene (DBT) with tert-butyl hydroperoxide and outperformed the solely microporous analogue. This was attributed to greater access of the substrate to surface active sites, as the pores in the microporous analogues were of inadequate size to accommodate DBT. Moreover, thiophene adsorption studies suggested the mesoporous MOF contained larger amounts of unsaturated metal sites that could enhance the observed catalytic activity.

Palladium nanoparticles confined in thiol-functionalized ordered mesoporous silica for more stable Heck and Suzuki catalysts

The influence of confinement of Pd nanoparticles on thiol functionalized silica structures (modified MCF, SBA-15, plugged SBA-15 and Aerosil) was explored for the Heck and the Suzuki reactions.

Novel catalyst by immobilizing a phosphotungstic acid on polymer brushes and its application in oxidative desulfurization

In the study, an HPW–PDMAEMA–SiO₂ (phosphotungstic acid (HPW); poly-N,N-dimethylaminoethyl methacrylate (PDMAEAM)) catalyst was successfully synthesized.

Efficient Mukaiyama aldol reaction in water with TiO4 tetrahedra on a hydrophobic mesoporous silica surface

A new heterogeneous catalyst, hydrophobic TiO₄-deposited mesoporous silica, exhibited high catalytic performance as a reusable catalyst for the Mukaiyama-aldol condensation in water without a surfactant.