TiO2-Containing Carbon Derived from a Metal-Organic Framework Composite: A Highly Active Catalyst for Oxidative Desulfurization

Fabrication of Unique Mixed-Valent CoICoII and CuICuII Metal-Organic Frameworks (MOFs) for Desulfurization of Fuels: A Combined Experimental and Theoretical Approach toward Green Fuel

Herein, metal-organic framework (MOF)-based adsorbents are designed with distinct hard and soft metal building units, namely, [Co2ICoII(PD)2(BP)] (Co_PD-BP) and [Cu2ICuII(PD)2(BP)] (Cu_PD-BP), where H2PD = pyrazine-1,4-diide-2,3-dicarboxylic acid and BP = 4,4'-bipyridine. The designed MOFs were characterized via spectral and SCXRD techniques, which confirm the mixed-valent states (+1 and +2) of the metal ions. Topological analysis revealed the rare ths and gwg topologies for Co MOF, while Cu-MOF exhibits a unique 8T21 topology in the 8-c net (point symbol for net: {424·64}). Moreover, severe environmental issues can be resolved by effectively removing heterocyclic organosulfur compounds from fuels via adsorptive desulfurization. Further, the developed MOFs were investigated for sulfur removal via adsorptive desulfurization from a model fuel consisting of dibenzothiophene (DBT), benzothiophene (BT), and thiophene (T) in the liquid phase using n-octane as a solvent. The findings revealed that Cu_PD-BP effectively removes the DBT with a removal efficiency of 86% at 300 ppm and an operating temperature of 25 °C, with a recyclability of up to four cycles. The adsorption kinetic analysis showed that the pseudo-first-order model could fit better with the experimental data indicating the physisorption process. Further, the studies revealed that adsorption capacity increased with the increasing initial DBT concentration with a remarkable capacity of 70.5 mg/g, and the adsorption process was well described by the Langmuir isotherm. The plausible reason behind the enhanced removal efficiency shown by Cu_PD-BP as compared to Co_PD-BP could be the soft-soft interactions between soft sulfur and soft Cu metal centers. Interestingly, density functional theory (DFT) studies were done in order to predict the mechanism of binding of thiophenic compounds with Cu_PD-BP, which further ascertained that along with other interactions, the S···π and S···Cu interactions predominate, resulting in a high uptake of DBT as compared to others. In essence, Cu_PD-BP turns out to be a promising adsorbent in the field of fuel desulfurization for the benefit of mankind.

Efficient destruction of basic organo-nitrogenous compounds in liquid hydrocarbon fuel using ascorbic acid/H2O2 system under ambient condition

Due to the limitations of the conventional refinery methods, development of a new method such as oxidative denitrogenation (ODN) is highly desirable. This study described a novel ODN to remove organo-nitrogenous compounds (ONCs) in liquid fuel by ascorbic acid (AscH2) and H2O2 redox system under ambient conditions. Seven ONCs including pyridine, quinoline, acridine, 7,8-benzoquinoline, indole, N-methylpyrrolidone (NMP), and N,N-dimethylformamide (DMF) were chosen to assess the fuel-denitrified ability of the AscH2/H2O2 system. The results showed that the basic group of ONCs (pyridine, quinoline, and acridine) can be effectively removed (removal ratio > 95 %) while the removal efficiency of water-soluble compounds (7,8-benzoquinoline, NMP, and DMF) was moderate (61-68 %) under a mild temperature (30 °C) and atmospheric pressure. Free radical quenching and electron paramagnetic resonance experiments confirmed that hydroxyl and AscH2 radicals played a major role in the degradation of ONCs. The degraded products of quinoline were analyzed by gas chromatography-mass spectroscopy and ion chromatography. Based on the identified intermediate products, a putative reaction pathway majorly involving three steps of N-onium formation, transfer hydrogenation, and free radical oxidative ring-opening was suggested for the quinoline degradation. The presented approach can be performed at a normal temperature and pressure and will live up to expectations in the pre-denitrogenation and selective removal of basic ONCs in fuel oils.

A sustainable management of polycyclic aromatic hydrocarbons to synthesize microporous organic polymers for adsorptive desulphurization of fuels

A sustainable management of carcinogenic polycyclic aromatic hydrocarbons (PAHs) to synthesize a series of high surface area (SABET of 563-1553 m2 g-1) microporous polymeric adsorbents is reported. The products with high yield (>90%) were obtained within only 30 min at a low temperature of 50 °C using a microwave-assisted approach with 400 W microwave power followed by 30 min of ageing by raising the temperature to 80 °C. The synthesized adsorbents are used for removing another category of carcinogenic pollutants i.e., polycyclic aromatic sulphur heterocycles (PASHs) from model and real fuels. Adsorptive desulphurization experiment in batch mode could reduce the sulphur from high concentrated model (100 ppm) and real (102 ppm) fuels to 8 ppm and 45 ppm respectively. Similarly, desulphurization of model and real fuels with ultralow sulphur concentrations of 10 and 9 ppm, respectively, reduced the final concentration of sulphur to 0.2 and 3 ppm, respectively. Adsorption isotherms, kinetics, and thermodynamic studies have been conducted using batch mode experiments. Adsorptive desulphurization using fixed bed column studies show the breakthrough capacities of 18.6 and 8.2 mgS g-1, for the same high concentrated model and real fuels, respectively. The breakthrough capacities of 1.1 and 0.6 mgS g-1 are estimated for the ultralow sulphur model and real fuels, respectively. The adsorption mechanism, based on the spectroscopic analysis (FTIR and XPS) demonstrates the role of π-π interactions between the adsorbate and adsorbent. The adsorptive desulphurization studies of model and real fuels from batch to fixed bed column mode would offer an in-depth understanding to demonstrate the lab-scale findings for industrial applications. Thus, the present sustainable strategy could manage two classes of carcinogenic petrochemical pollutants, PAHs and PASHs, simultaneously.

Sand-Fixation Model for Interface Engineering of Layered Titania and N/O-Doped Carbon Composites to Enhance Potassium/Sodium Storage

Layered titania (L-TiO2 ) holds great potential for potassium-ion batteries (PIBs) and sodium-ion batteries (SIBs) due to their high specific capacity. Synthesizing L-TiO2 functional materials for high-capacity and long cyclability battery remains challenging due to the unstable and poor conductivity of bare L-TiO2 . In nature, plant growth can stabilize land by preventing sands from dispersing following desertification. Inspired by nature's "sand-fixation model," Al3+ "seeds" are in situ grown on layered Ti3 C2 Tx "land." Subsequently, NH2 -MIL-101(Al) "plants" with Al as metal nodes are grown on the Ti3 C2 Tx "land" by self-assembly. After annealing and etching processes (similar to desertification), NH2 -MIL-101(Al) is transformed into interconnected N/O-doped carbon (MOF-NOC), which not only acts as a plant-like function to prevent the pulverization of L-TiO2 transformed from Ti3 C2 Tx but also improves the conductivity and stability of MOF-NOC@L-TiO2 . Al species are selected as seeds to improve interfacial compatibility and form intimate interface heterojunction. Systematic ex situ analysis discloses that the ions storage mechanism can be endowed by mixed contribution of non-Faradaic and Faradaic capacitance. Consequently, the MOF-NOC@L-TiO2 electrodes exhibit high interfacial capacitive charge storage and outstanding cycling performance. The interface engineering strategy inspired by "sand-fixation model" provides a reference for designing stable layered composites.

Heteropolyacid Ionic Liquid-Based MCF: An Efficient Heterogeneous Catalyst for Oxidative Desulfurization of Fuel

A new type of catalyst was synthesized by immobilizing heteropolyacid on ionic liquid-modified mesostructured cellular silica foam (denoted as MCF) and applied to the oxidative desulfurization of fuel. The surface morphology and structure of the catalyst were characterized by XRD, TEM, N₂ adsorption-desorption, FT-IR, EDS and XPS analysis. The catalyst exhibited good stability and desulfurization for various sulfur-containing compounds in oxidative desulfurization. Heteropolyacid ionic liquid-based MCF solved the shortage of the amount of ionic liquid and difficult separation in the process of oxidative desulfurization. Meanwhile, MCF had a special three-dimensional structure that was not only highly conducive to mass transfer but also greatly increased catalytic active sites and significantly improved catalytic efficiency. Accordingly, the prepared catalyst of 1-butyl-3-methyl imidazolium phosphomolybdic acid-based MCF (denoted as [BMIM]₃PMo₁₂O₄₀-based MCF) exhibited high desulfurization activity in an oxidative desulfurization system. The removal of dibenzothiophene could achieve levels of 100% in 90 min. Additionally, four sulfur-containing compounds could be removed completely under mild conditions. Due to the stability of the structure, sulfur removal efficiency still reached 99.8% after the catalyst was recycled six times.

Recent advances of metal-organic framework-based and derivative materials in the heterogeneous catalytic removal of volatile organic compounds

Since the environmental hazards of volatile organic compounds (VOCs) are well known, heterogeneous catalysis has become one of the most popular methods to treat VOCs due to its environmental friendliness and simplicity of operation. Although a large number of reports have reviewed the application of catalytic oxidation for the degradation of VOCs, relatively few reports are based on this direction of metal organic frameworks (MOFs) and MOF derivatives. Herein, this paper reviews the recent applications of heterogeneous catalytic technologies in the degradation of VOCs, including photocatalysis, thermal catalysis and other catalytic approaches. The applications of MOFs and their derivatives in VOCs degradation, such as the progress of MOF-derived metal oxides in the treatment of toluene, were highlighted. The mechanisms of VOCs degradation by different catalytic approaches were systematically presented. Finally, we presented the views and directions of VOCs treatment technology development. We hope that this reaction type-oriented review will provide important insights into MOFs and MOF-derived materials for VOCs pollution control.

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.

Carbon-Based Materials for Oxidative Desulfurization and Denitrogenation of Fuels: A Review

Sulfur (S) and nitrogen (N) are elements naturally found in petroleum-based fuels. S- and N-based compounds in liquid fuels are associated with a series of health and environmental issues. Thus, legislation has become stricter worldwide regarding their content and related emissions. Traditional treatment systems (namely hydrodesulfurization and hydrodenitrogenation) fail to achieve the desired levels of S and N contents in fuels without compromising combustion parameters. Thus, oxidative treatments (oxidative desulfurization–ODS, and oxidative denitrogenation-ODN) are emerging as alternatives to producing ultra-low-sulfur and nitrogen fuels. This paper presents a thorough review of ODS and ODN processes applying carbon-based materials, either in hybrid forms or as catalysts on their own. Focus is brought to the role of the carbonaceous structure in oxidative treatments. Furthermore, a special section related to the use of amphiphilic carbon-based catalysts, which have some advantages related to a closer interaction with the oily and aqueous phases, is discussed.

Metal-Organic Framework-Derived Hollow and Hierarchical Porous Multivariate Metal-Oxide Microspheres for Efficient Phosphoproteomics Analysis

Pre-enrichment of the biological samples is a crucial step in phosphoproteomics research. At present, metal-oxide affinity chromatography (MOAC) is one of the most recognized enrichment strategy. Therefore, the design and preparation of a MOAC-based affinity material with better enrichment properties will be of great significance for the phosphoproteomics study. In this work, we obtained a novel multivariate metal-oxide microsphere (NiFe₂O₄@C@TiO₂) with a hollow and hierarchical porous structure through pyrolysis of TiO_2-modified Fe/Ni-based metal-organic frameworks (MOFs). After pyrolysis, the carbon matrix derived from the MOFs provided support and porous properties. Meanwhile, multivariate metal oxides endowed the microspheres with an excellent magnetic response property and superior enrichment performance for phosphorylated biomolecules. The unique hollow and hierarchical porous structure greatly enhanced the diffusion of phosphorylated biomolecules. Therefore, the microspheres exhibited excellent enrichment performance for phosphorylated biomolecules: a large adsorption capacity (124 μmol g^-1), excellent selectivity (α-casein/BSA, 1:5000, m/m), perfect size-exclusion performance (α-casein digests/α-casein/BSA, 1:500:500), and extremely low detection limit (2 fmol). Furthermore, the microspheres showed excellent enrichment performance in a series of real biological samples, such as nonfat milk, serum, saliva, rat brain tissue, and plasma exosomes of patients with esophageal cancer, which further demonstrated its huge application potential in MS-based phosphoproteomics research.

Designing biopolymer-based artificial peroxidase for oxidative removal of dibenzothiophene from a model diesel fuel

Naturally occurring peroxidases are important for living organisms and have manifold utility in industries. However, lack of stability in harsh reaction conditions hinders wide applicability of such enzymes. Thus, suitable alternative is vital which can endure severe reaction conditions. As a substitute of natural peroxidase, herein, biopolymer-based polyelectrolyte complexes (PECs) coordinated with Feⁿ⁺ is proposed as macromolecular peroxidase mimicking systems. Three PECs were engineered via complexation of protonated chitosan and alginate with Fe²⁺ (Fe²⁺-PEC), Fe³⁺ (Fe³⁺-PEC), and Fe₃O₄ (Fe₃O₄-PEC), respectively. Computational study showed the Fe³⁺-PEC was highly stable with abundant electrostatic and intramolecular hydrogen bonding interactions. The versatility of the Fe-PECs as artificial peroxidase biocatalysts was probed by two types of peroxidase assays - ABTS oxidation in buffer systems (pH 4.0 and 7.0) and pyrogallol oxidation in organic solvents (acetonitrile, ethyl acetate and toluene). Overall, Fe³⁺-PEC showed remarkably high peroxidase activity both in aqueous buffers and in organic solvents, whereas, Fe₃O₄-PEC showed least catalytic activity. Finally, as a proof of concept, the ability of the biocatalyst to carry out deep oxidative desulphurization was demonstrated envisaging removal of dibenzothiophene from model fossil fuel in a sustainable way.

How neutral nitrogen-containing compounds are oxidized in oxidative-denitrogenation of liquid fuel with TiO2@carbon

Oxidative-denitrogenation (ODN) of indole (IND) and methyl-substituted INDs (methyl-INDs), representative neutral nitrogen-containing compounds (NCCs), was carried out with TiO₂@C and H₂O₂ as heterogeneous catalyst and oxidant, respectively, under ultrasound irradiation. The oxidation of INDs progressed through radical formation, as evidenced by electron spin resonance and radical scavenger experiments. The oxidized position of INDs in the ODN process was checked via characterization of the obtained products. It was observed that the oxidation finally occurred on the carbon rather than on the nitrogen atom of INDs, unlike the oxidation of basic NCCs (e.g., oxidation on the nitrogen atom, as respective N-oxides were formed) and sulfur-containing compounds. To understand the relative reactivity and oxidation position, electron density (ED) on the nitrogen atom of the studied INDs and relative stability of representative intermediates/products were calculated. It could be confirmed that ED on the nitrogen atom of the INDs is very important in the oxidation of INDs since the ODN reactivity of INDs was enhanced with increasing ED on the nitrogen atom of the investigated INDs. Moreover, theoretical analyses of the relative stability of substrate and intermediates/products (especially for IND) can explain the route for the observed final products in ODN. In other words, oxygen on the nitrogen atom, obtained via the first step of oxidation (electrophilic addition of an active oxygen atom on nitrogen), moves to the nearby carbon atom, because of the relative stability of the intermediates and products.

Metal organic framework-derived C-doped ZnO/TiO2 nanocomposite catalysts for enhanced photodegradation of Rhodamine B

A series of C-doped ZnO/TiO₂ composites with various molar ratios of ZnO to TiO₂ were synthesized by one-step controllable pyrolysis of Zn/Ti bimetallic metal-organic frameworks (Zn/Ti-MOF). The Zn/Ti-MOF was prepared using a facile microwave hydrothermal method. Electron microscopic analysis proved that the composites presented regularity cubic morphology with an edge length of about 1 μm and the C atoms were successfully doped into ZnO/TiO₂ composites. X-ray photoelectron spectroscopy (XPS) measurement results confirmed the C-doping in the ZnO/TiO_2. Comparative experimental studies showed that 2% ZnO/TiO₂ composites prepared with the calcination temperature of 600℃ displayed the best photocatalytic degradation efficiency (94%) of RhB under the simulated sunlight irradiation. Cyclical experiment indicated the high stability and reusability of 2% ZnO/TiO₂ composites. Electron spin resonance (ESR) and trapping experiments illustrated that the produced O₂^- served as the main active species for the efficient RhB removal. This work provides an efficient way for preparing C-doped bimetal oxides composites, which would have an important application prospect in the photocatalytic degradation of organic pollutants in environmental water.

Metal-Organic Frameworks in Oxidation Catalysis with Hydrogen Peroxide

In recent years, metal–organic frameworks (MOFs) have received increasing attention as selective oxidation catalysts and supports for their construction. In this short review paper, we survey recent findings concerning use of MOFs in heterogeneous liquid-phase selective oxidation catalysis with the green oxidant–aqueous hydrogen peroxide. MOFs having outstanding thermal and chemical stability, such as Cr(III)-based MIL-101, Ti(IV)-based MIL-125, Zr(IV)-based UiO-66(67), Zn(II)-based ZIF-8, and some others, will be in the main focus of this work. The effects of the metal nature and MOF structure on catalytic activity and oxidation selectivity are analyzed and the mechanisms of hydrogen peroxide activation are discussed. In some cases, we also make an attempt to analyze relationships between liquid-phase adsorption properties of MOFs and peculiarities of their catalytic performance. Attempts of using MOFs as supports for construction of single-site catalysts through their modification with heterometals will be also addressed in relation to the use of such catalysts for activation of H2O2. Special attention is given to the critical issues of catalyst stability and reusability. The scope and limitations of MOF catalysts in H2O2-based selective oxidation are discussed.

Synergistic Effect between Zr-MOF and Phosphomolybdic Acid with the Promotion of TiF4 Template

Metal-Organic Framework (MOF) materials are often modified or functionalized, and then the crystal size and morphology of MOF materials are changed. In the process of preparing UiO-66 confined phosphomolybdic acid (PMA) composites (PU), the TiF₄-modified PU (PMA + UiO-66) composite catalyst (TiF₄-PU) was successfully synthesized by adding titanium tetrafluoride, and the catalytic desulfurization activity was excellent. Similarly, the reaction mechanism was investigated by means of infrared spectroscopy, Raman spectroscopy, XPS, and UV/Vis spectroscopy. The results show that the addition of TiF₄ not only changes the appearance and color of the catalyst, but also changes the valence distribution of the elements in the catalyst. The number of oxygen vacancies in the MOF increases due to the addition of TiF₄, and more electrons are transferred from the Zr-MOF to PMA to form more Mo⁵⁺, which improved the performance of oxidative desulfurization in comparison. Thus, a stronger strong metal-support interaction (SMSI) effect is observed for TiF₄-modified PU catalysts. In addition, the quenching experiment of free radicals shows that ·OH radical is the main active substance in the oxidative desulfurization reaction over TiF₄-PU catalyst.

Titanium-Modified MIL-101(Cr) Derived Titanium-Chromium-Oxide as Highly Efficient Oxidative Desulfurization Catalyst

A titanium-chromium-oxide catalyst was prepared by a facile calcination of titanium-modified MIL-101(Cr). The resulting material, possessing a surface area of 60 m2 g−1 and a titania content of 50.0 wt%, can be directly used as the catalyst for oxidative desulfurization (ODS) reaction of dibenzothiophene (DBT). This novel ODS catalyst can remove 900 ppm sulfur-containing compounds in a reaction time of 30 min at 60 °C. The experimental results showed that the specific activity increased with the titanium content. The specific activity of the catalyst with 50%Ti reached 129 μmol/m2, which was much higher than that of reported Ti-based catalysts.

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.

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.

Lattice-Refined Transition-Metal Oxides via Ball Milling for Boosted Catalytic Oxidation Performance

Surface oxygen vacancy can greatly affect the properties of transition-metal oxides. However, engineering oxygen vacancy-abundant transition-metal oxides with high specific surface area (SSA) remains challenging. At present, the generation of oxygen vacancies in metal oxides is time-consuming and less environmentally friendly by chemical leaching methods that usually require additional waste treatment. Herein, a series of oxygen vacancy-abundant transition-metal oxides with high SSA are constructed via a lattice refining strategy. This strategy is realized by urea-assisted ball milling pyrolysis and is green, efficient, and universal. The oxygen vacancies promote the mobility of oxygen, leading to a boosted catalytic oxidation performance of aromatic sulfides. Such a strategy provides an efficient approach to manufacturing oxygen vacancies on transition-metal oxides, which may be beneficial for various related applications as an effective catalytic material.

Poly(dimethylsilylene)diacetylene-Guided ZIF-Based Heterostructures for Full Ku-Band Electromagnetic Wave Absorption

Zeolitic imidazolate frameworks (ZIFs), a group of metal-organic frameworks (MOFs), hold promise as building blocks in electromagnetic (EM) wave absorbing/shielding materials and devices. In this contribution, we proposed a facile strategy to synthesize three-dimensional ZIF-67-based hierarchical heterostructures through coordinated reaction of a preceramic component, poly(dimethylsilylene)diacetylene (PDSDA) with ZIF-67, followed by carbonizing the PDSDA-wrapped ZIF at high temperature. The introduction of PDSDA leads to controllable generation of a surface network containing branched carbon nanotubes and regional distributed graphitic carbons, in addition to the nanostructures with a well-defined size and porous surface made by cobalt nanoparticles. The surface structures can be tailored through variations in pyrolysis temperatures, therefore enabling a simple and robust route to facilitate a suitable structural surface. The heterostructure of the ZIF nanocomplex allows the existence of dielectric loss and magnetic loss, therefore yielding a significant improvement on EM wave absorption with a minimum reflection coefficient (RC_min) of -50.9 dB at 17.0 GHz at a thickness of 1.9 mm and an effective absorption bandwidth (EAB) covering the full Ku-band (12.0-18.0 GHz).

Zr-Based Metal-Organic Frameworks with Intrinsic Peroxidase-Like Activity for Ultradeep Oxidative Desulfurization: Mechanism of H2O2 Decomposition

The restriction of sulfur content in fuels has become increasingly stringent as a result of the growing environmental concerns. Although several MOF-derived materials like POM@MOF composites have shown the ability to catalyze oxidative desulfurization (ODS), their catalytic activities inevitably obstructed by the encapsulated catalytic sites like POM due to the blockage of cavities. Therefore, MOFs with intrinsic and accessible catalytic sites are highly desirable for their applications in ultradeep ODS. Herein, four representative Zr-based MOFs (Zr-MOFs), namely, UiO-66, UiO-67, NU-1000, and MOF-808, were assessed for catalytic ODS. These MOFs were confirmed that they have peroxidase-like activity and can catalyze ODS with H₂O₂ as oxidant. Among them, MOF-808 showed the highest catalytic activity and it can fully desulfurize dibenzothiophene (DBT) in a model gasoline with a S concentration of 1000 ppm under 40 °C within 5 min. An extremely low apparent Arrhenius activation energy (22.0 KJ·mol^-1) and an extraordinarily high TOF value (42.7 h^-1) were obtained, ranking MOF-808 among the best catalysts for the catalytic DBT oxidation. Further studies confirmed that the excellent catalytic activity is mainly responsible for the high concentration of the accessible Zr-OH(H₂O) catalytic sites decorated in MOF-808. The superoxide radicals (^•O₂^-) and hydroxyl radicals (^•OH) were identified and were proved to involve in the DBT oxidation. Besides, the effects of Brönsted and lewis acidity to the catalytic efficiency were also discussed. Based on the experimental results, a plausible mechanism concerning on Zr-OH(H₂O) groups promoting the H₂O₂ decomposion in to both ^•O₂^- and ^•OH was first proposed. Moreover, MOF-808 can be facilely reused for at least eight runs without significant loss of its catalytic activity. By the integration of facile synthesis, high catalytic efficiency, and good stability, MOF-808 thus represents a new benchmark catalyst for catalytic oxidative desulfurization.

Dual-Purpose 3D Pillared Metal-Organic Framework with Excellent Properties for Catalysis of Oxidative Desulfurization and Energy Storage in Asymmetric Supercapacitor

This study proposes an approach for improving catalysis of oxidative desulfurization (ODS) of diesel fuel under mild reaction conditions and enhancing supercapacitor (SC) properties for storage of a high amount of charge. Our approach takes advantage of a novel dual-purpose cobalt(II)-based metal-organic framework (MOF), [Co(2-ATA)₂(4-bpdb)₄] _n (2-ATA: 2-aminoterephthalic acid and 4-bpdb: N, N-bis-pyridin-4-ylmethylene-hydrazine as the pillar spacer), which is called NH₂-TMU-53. Due to the stability of the used compound, we decided to evaluate the capability of this compound as a novel electrode material for storing energy in supercapacitors, and also to investigate its catalytic capabilities. It is demonstrated that the addition of H₂O₂ as an oxidant enhances the efficiency of sulfur removal, which indicates that NH₂-TMU-53 can efficiently catalyze the ODS reaction. According to the kinetics results, the catalyzed process follows pseudo-first-order kinetics and exhibits 15.57 kJ mol^-1 activation energy. Moreover, with respect to the radical scavenging evaluations, the process is governed by direct catalytic oxidation rather than indirect oxidative attack of radicals. Furthermore, NH₂-TMU-53 was applied as an electrode material for energy storage in SCs. This material is used in the three-electrode system and shows a specific capacitance of 325 F g^-1 at 5 A g^-1 current density. The asymmetric supercapacitor of NH₂-TMU-53//activated carbon evaluates the further electrochemical activity in real applications, delivers the high power density (2.31 kW kg^-1), high energy density (50.30 Wh kg^-1), and long cycle life after 6000 cycles (90.7%). Also, the asymmetric supercapacitor practical application was demonstrated by a glowing red light-emitting diode and driving a mini-rotating motor. These results demonstrate that the fabricated device presents a good capacity for energy storage without pyrolyzing the MOF structures. These findings can guide the development of high-performance SCs toward a new direction to improve their practical applications and motivate application of MOFs without pyrolysis or calcination.

Cyclohexene Oxidation with H2O2 over Metal-Organic Framework MIL-125(Ti): The Effect of Protons on Reactivity

The catalytic performance of the titanium-based metal–organic framework MIL-125 was evaluated in the selective oxidation of cyclohexene (CyH) with environmentally friendly oxidants, H2O2 and tBuOOH. The catalytic activity of MIL-125 as well as the oxidant utilization efficiency and selectivity toward epoxide and epoxide-derived products can be greatly improved by acid additives (HClO4 or CF3SO3H). In the presence of 1 molar equivalent (relative to Ti) of a proton source, the total selectivity toward CyH epoxide and trans-cyclohexane-1,2-diol reached 75–80% at 38–43% alkene conversion after 45 min of reaction with 1 equivalent of 30% H2O2 at 50 °C. With 50% H2O2 as the oxidant, the total selectivity toward heterolytic oxidation products increased up to 92% at the same level of alkene conversion. N2 adsorption, powder X-ray diffraction (PXRD), and infrared (IR) spectroscopy studies before and after the catalytic oxidations confirmed the absence of structural changes in the Metal–organic framework (MOF) structure. MIL-125 was stable toward titanium leaching, behaved as a truly heterogeneous catalyst, and could easily be recovered and reused several times without any loss of the catalytic properties.

Fast and deep oxidative desulfurization of dibenzothiophene with catalysts of MoO3–TiO2@MCM-22 featuring adjustable Lewis and Brønsted acid sites

The synthesis of high-performance and recyclable catalysts for oxidative desulfurization (ODS) from fuels has been a significant challenge.

Preparation of core–shell PW12@TiO2 microspheres and oxidative desulfurization performance

Polyoxometalate-based heterogeneous catalyst with core–shell structure.

Combining the Photocatalysis and Absorption Properties of Core-Shell Cu-BTC@TiO₂ Microspheres: Highly Efficient Desulfurization of Thiophenic Compounds from Fuel

A core-shell Cu-benzene-1,3,5-tricarboxylic acid (Cu-BTC)@TiO₂ was successfully synthesized for photocatalysis-assisted adsorptive desulfurization to improve adsorptive desulfurization (ADS) performance. Under ultraviolet (UV) light irradiation, the TiO₂ shell on the surface of Cu-BTC achieved photocatalytic oxidation of thiophenic S-compounds, and the Cu-BTC core adsorbed the oxidation products (sulfoxides and sulfones). The photocatalyst and adsorbent were combined using a distinct core-shell structure. The morphology and structure of the fabricated Cu-BTC@TiO₂ microspheres were verified by scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive x-ray spectroscopy, X-ray powder diffraction, nitrogen adsorption-desorption and X-ray photoelectron spectroscopy analyses. A potential formation mechanism of Cu-BTC@TiO₂ is proposed based on complementary experiments. The sulfur removal efficiency of the microspheres was evaluated by selective adsorption of benzothiophene (BT) and dibenzothiophene (DBT) from a model fuel with a sulfur concentration of 1000 ppmw. Within a reaction time of 20 min, the BT and DBT conversion reached 86% and 95%, respectively, and achieved ADS capacities of 63.76 and 59.39 mg/g, respectively. The BT conversion and DBT conversion obtained using Cu-BTC@TiO₂ was 6.5 and 4.6 times higher, respectively, than that obtained using Cu-BTC. A desulfurization mechanism was proposed, the interaction between thiophenic sulfur compounds and Cu-BTC@TiO₂ microspheres was discussed, and the kinetic behavior was analyzed.