Synthesis of Defect-Rich Titanium Terephthalate with the Assistance of Acetic Acid for Room-Temperature Oxidative Desulfurization of Fuel Oil

In Situ Implanting ZrW2O7(OH)2(H2O)2 Nanorods into Hierarchical Functionalized Metal-Organic Framework via Solvent-Free Approach for Upgrading Catalytic Performance

Host-guest catalyst provides new opportunities for targeted applications and the development of new strategies for preparing host-guest catalysts is highly desired. Herein, an in situ solvent-free approach is developed for implanting ZrW2O7(OH)2(H2O)2 nanorods (ZrW-NR) in nitro-functionalized UiO-66(Zr) (UiO-66(Zr)-NO2) with hierarchical porosity, and the encapsulation of ZrW-NR enables the as-prepared host-guest catalyst remarkably enhanced catalytic performance for both for oxidative desulfurization (ODS) and acetalization reactions. ZrW-NR@UiO-66(Zr)-NO2 can eliminate 500 ppm sulfur within 9 min at 40 °C in ODS, and can transform 5.6 mmol benzaldehyde after 3 min at room temperature in acetalization reaction. Its turnover frequencies reach 72.3 h-1 at 40 °C for ODS which is 33.4 times higher than UiO-66(Zr)-NO2, and 28140 h-1 for acetalization which is the highest among previous reports. Density functional theory calculation result indicates that the W sites in ZrW-NR can decompose H2O2 to WVI-peroxo intermediates that contribute to catalytic activity for the ODS reaction. This work opens a new solvent-free approach for preparing MOFs-based host-guest catalysts to upgrade their redox and acid performance.

Modulator-assisted solvent-free synthesis of amorphous zirconium terephthalate catalyst for efficient oxidative desulfurization

Oxidative desulfurization (ODS) emerges as a critical player in enhancing efficient fuel desulfurization and promoting sustainable clean energy. Metal-organic frameworks (MOFs) show great potential as ODS catalysts because of their exceptional porosity and versatility. This study explores the use of amorphous metal-organic frameworks (aMOFs), which combine MOFs' structural advantages with unique properties of amorphous materials, to enhance catalytic efficiency in ODS. Traditional methods for synthesizing MOFs rely on solvent-thermal or solvent-free methods, each with limitations in environmental impact or scalability. To address this, we introduce a novel strategy utilizing a small quantity of benzoic acid (BA) modifier to facilitate the solvent-free, one-pot, mechanical synthesis of amorphous zirconium terephthalate (GU-2BA-3h). The resulting GU-2BA-3h demonstrates exceptional ODS performance, efficiently removing 1000 ppm of dibenzothiophene (DBT) in just 6 min at 60 °C. Amorphous GU-2BA-3h features an expanded external surface area, increased acidic sites, and exceptional stability, resulting in a high turnover frequency (19.6 h-1) and outstanding catalytic activity (53.2 mmol g-1 h-1), establishing it as a highly efficient ODS catalyst. This remarkable performance arises from the formation of dangling carboxyl groups and active metal sites due to the competitive coordination of benzoic acid with the linker. Experimental evidence confirms that these carboxyl groups and exposed Zr-OH sites interact with oxidants, generating hydroxyl radicals that effectively eliminate sulfur-containing compounds. Furthermore, the methodology exhibits universality in constructing amorphous Zr-based MOFs, and provides an eco-friendly, cost-effective route for efficient ODS catalyst production.

Hierarchically porous amino-functionalized nanoMOF network anchored phosphomolybdic acid for oxidative desulfurization and shaping application

The applications of hierarchically porous metal-organic frameworks (HP-MOFs) against traditional microporous counterparts for oxidative desulfurization (ODS) have triggered wide research interests due to their highly exposed accessible active sites and fast mass transfer of substrate molecules, particularly for the large-sized refractory sulfur compounds. Herein, a series of hierarchically porous amino-functionalized Zr-MOFs (HP-UiO-66-NH2-X) network with controllable mesopore sizes (3.5-9.2 nm) were firstly prepared through a template-free method, which were further utilized as anchoring support to bind the active phosphomolybdic acid (PMA) via the strong host-guest interaction to catalyze the ODS reaction. Benefitting from the hierarchically porous structure, accessible active sites and the strong host-guest interaction, the resultant PMA/HP-UiO-66-NH2-X exhibited excellent ODS performance, of which, the PMA/HP-UiO-66-NH2-9 with an appropriate mesopore size (4.0 nm) showed the highest catalytic activity, achieving a 99.9% removal of dibenzothiophene (DBT) within 60 min at 50 °C, far exceeding the microporous sample and PMA/HP-UiO-66. Furthermore, the scavenger experiments confirmed that •OH radical was the main reactive species and the density functional theory (DFT) calculations revealed that electron transfer (from amino group to PMA) made PMA react more easily with oxidant, thereby generating more •OH radical to promote the ODS reaction. Finally, from the industrial point of view, the powdered MOF nanoparticles (NPs) were in situ grown on the carboxymethyl cellulose (CMC) substrates and shaped into monolithic MOF-based catalysts, which still exhibited satisfying ODS performance in the case of model real fuel with good reusability, indicating its potential industrial application prospect.

Insights into the sacrificial structure-activity relationship of a Ti-based metal-organic framework in an oxidative desulfurization reaction

Insights into the relationship between the crystal structure and activity of metal-organic frameworks (MOFs) are meaningful to investigate the potential properties of pristine MOFs for targeted catalytic reactions. Herein, we develop a high-efficiency method for boosting the oxidative desulfurization (ODS) activity of Ti-MOF in the presence of H+. The ODS activity of pristine Ti-MOF prepared via a solvothermal approach is very poor at a low reaction temperature but can be enhanced in the presence of H+. Ti-MOF in the presence of H+ shows ultrahigh ODS activity that can eliminate 1000 ppm sulfur after 7 min at 30 °C with no catalytic activity loss after recycling 11 times. The turnover frequency value reaches 12.4 h-1 at 30 °C, surpassing all the previously reported Ti-MOFs as ODS catalysts even at high temperatures. Characterization and quenching experimental results indicate that more uncoordinated Ti sites can be formed from slight damage to the structure of Ti-MOF during the catalytic reaction, and such exposed Ti sites can easily react with H+ and H2O2 to form Ti-hydroperoxo active species that determine the upgradation of ODS activity. This work provides a significant way to upgrade the catalytic activity of pristine Ti-MOFs for future application.

Defect-Mediated Synergistic Effect of POM/UiO-66(Zr) Host-Guest Catalysts for Robust Deep Desulfurization at Ambient Temperature

Stable platforms of host-guest catalysts are indispensable in the field of heterogeneous catalysis, however, clarifying the specific effect of host remains challenging. Herein, polyoxometalate (POM) is encapsulated in three types of UiO-66(Zr) with different controlled densities of defects by the aperture opening and closing strategy at ambient-temperature. It is found that catalytic activity of POM for oxidative desulfurization (ODS) at room temperature is turned on when encapsulated in the defective UiO-66(Zr), and the sulfur oxidation efficiency shows an obvious increasing trend (from 0.34 to 10.43 mmol g-1 h-1 ) with the increased concentration of defects in UiO-66(Zr) host. The as-prepared catalyst with the most defective host displays ultrahigh performance which removed 1000 ppm sulfur with exceptionally diluted oxidant at room-temperature within 25 min. The turnover frequency can reach 620.0 h-1 at 30 °C, which surpassed all the reported MOFs based ODS catalysts. A substantial guest/host synergistic effect mediated by the defective sites in UiO-66(Zr) is responsible for the enhancement. Density functional theory calculations reveal that OH/OH2 capped on the open Zr sites of host UiO-66(Zr) can decompose H2 O2 to OOH group and enables the formation of WVI -peroxo intermediates that determine the ODS activity.

Ternary choline chloride/benzene sulfonic acid/ethylene glycol deep eutectic solvents for oxidative desulfurization at room temperature

Deep eutectic solvents (DESs) have been extensively studied as promising green solvents to attain a better removal efficiency of sulfide. A new DES system formed from choline chloride (ChCl), benzene sulfonic acid (BSA), and ethylene glycol (EG) as a class of ternary DESs was prepared and used in the oxidative desulfurization (ODS) of different sulfides. Ternary DESs have distinct advantages such as volatility and high activity compared with organic acid-based binary DESs. Under the optimum conditions with VDES/VOil = 1 : 5, O/S (molar ratio of oxygen to sulfur) = 5, and T = 25 °C, the desulfurization efficiencies of dibenzothiophene (DBT), 4,6-dimethyldibenzothiophene (4,6-DMDBT), and benzothiophene (BT) were all achieved to 100% in 2 h. Through experimental and density functional theory (DFT) calculation methods, this new system as a class of ternary DESs shows good stability and excellent desulfurization performance at room temperature. The investigation of this study could supply a new idea of ternary DESs for oxidative desulfurization.

Boosting Catalytic Performance of MOF-808(Zr) by Direct Generation of Rich Defective Zr Nodes via a Solvent-Free Approach

Creation of rich open metal sites (defect) on the nodes of metal-organic frameworks (MOFs) is an efficient approach to enhance their catalytic performance in heterogeneous reactions; however, direct generation of such defects remains challenging. In this contribution, we developed an in situ green route for rapid fabrication of defective MOF-808(Zr) with rich Zr-OH/OH₂ sites (occupying 25% Zr coordination sites) and hierarchical porosity without the assistance of formic acid and solvent. The optimal MOF-808(Zr) not only displayed superior activity in oxidative desulfurization (ODS) for removing 1000 ppm sulfur at ambient temperature within 20 min but also could convert 3.8 mmol of benzaldehyde to (dimethoxymethyl)benzene within 90 s at 30 °C. The turnover frequencies reached 45.4 h^-1 for ODS and 3451 h^-1 for acetalization, outperforming the most reported MOF-based catalysts. Theoretical calculation and experimental results show that the formed Zr-OH/OH₂ can react with H₂O₂ to generate peroxo-zirconium species, which readily oxidize the sulfur compound. Our work provides a new approach to the synthesis of defect-rich MOF-808(Zr) with the accessibility of active sites for target reactions.

Defect Healing of Micro/Nanocrystals via the Coordination Competition of Rare Earth in Crystal Engineering

Defect engineering has been generally observed and utilized in crystal materials including metal oxides, metal-organic frameworks, and so on; however, how to relate the defect formation and crystallization process is needed to be revealed clearly, and how to heal the defect is a big challenge. Herein, based on the new coordination complex (HNU-53), the crystal defects were created by increasing the reaction time and crystal size. Following the crystal growth process, the crystal color centers were simultaneously generated, resulting in fluorescence quenching. To heal the defect, the crystal growth was controlled by the introduction of rare earth ions. With the coordination competition of rare earth ions, the crystal defects were reduced and recovery of fluorescence emission was achieved.

Anisotropic phenanthroline-based ruthenium polymers grafted on a titanium metal-organic framework for efficient photocatalytic hydrogen evolution

Conjugated polymers and titanium-based metal-organic framework (Ti-MOF) photocatalysts have demonstrated promising features for visible-light-driven hydrogen production. We report herein a strategy of anisotropic phenanthroline-based ruthenium polymers (PPDARs) over Ti-MOF, a tunable platform for efficient visible-light-driven photocatalytic hydrogen evolution reaction (HER). Several analytical methods including X-ray absorption spectroscopy (XAS) revealed the judicious integration of the surface-active polymer over the Ti-MOF reinforcing the catalytic activity over the broad chemical space. PPDAR-4 polyacrylate achitecture led to a substantial increase in the H₂ evolution rate of 2438 µmolg^-1h^-1 (AQY: 5.33%) compared to pristine Ti-MOF (238 µmol g^-1 h^-1). The separation of photogenerated charge carriers at the PPDAR-4/Ti-MOF interface was confirmed by the optical and electrochemical investigations. The experimental, as well as theoretical data, revealed their physical and chemical properties which are positively correlated with the H₂ generation rate. This offers a new avenue in creating polymer-based MOF robust photocatalysts for sustainable energy.

Single-Atom Nanozymes: Fabrication, Characterization, Surface Modification and Applications of ROS Scavenging and Antibacterial

Nanozymes are nanomaterials with intrinsic natural enzyme-like catalytic properties. They have received extensive attention and have the potential to be an alternative to natural enzymes. Increasing the atom utilization rate of active centers in nanozymes has gradually become a concern of scientists. As the limit of designing nanozymes at the atomic level, single-atom nanozymes (SAzymes) have become the research frontier of the biomedical field recently because of their high atom utilization, well-defined active centers, and good natural enzyme mimicry. In this review, we first introduce the preparation of SAzymes through pyrolysis and defect engineering with regulated activity, then the characterization and surface modification methods of SAzymes are introduced. The possible influences of surface modification on the activity of SAzymes are discussed. Furthermore, we summarize the applications of SAzymes in the biomedical fields, especially in those of reactive oxygen species (ROS) scavenging and antibacterial. Finally, the challenges and opportunities of SAzymes are summarized and prospected.

Ultrafast oxidative desulfurization of diesel fuel catalyzed by a polyoxometalate-based catalyst immobilized on functionalized Y-SBA-15

Y-SBA-15 was synthesized by doping yttrium (Y) into SBA-15 using a solvent-free solid-state grinding method, and 1-butyl-3-methylimidazolium phosphomolybdic salt ([Bmim]₃PMo₁₂O₄₀, abbreviated as [Bmim]PMoO) was also synthesized. [Bmim]PMoO/Y-SBA-15 was prepared and used for oxidative desulfurization (ODS). The physicochemical characteristics of the catalyst have been characterized by FT-IR, XRD, N₂ adsorption-desorption, FESEM, TEM, XPS, contact angle testing, EPR, etc. A lipophilic surface is beneficial for making the catalyst well disperse in an oil phase, and a hydrophilic core can help to store aqueous oxidants. Therefore, the amphiphilic catalyst 25[Bmim]PMoO/10Y-SBA-15 exhibited high catalytic activity in dibenzothiophene (DBT) ODS, and sulfur compounds can be removed completely within 40 min under the following conditions: V_Oil = 10 mL, m_catalyst = 0.1 g, m_[Bmim]PMoO : m_{[Bmim]PMoO/10Y-SBA-15} = 25%, and O/S = 4 (molar ratio). In addition, the concentration of aromatics exerted little effect on the DBT ODS. Sulfur compounds in real diesel might be reduced to 8 μg g^-1. The hydroxyl radical ˙OH and superoxide radical ˙O₂^- play crucial roles in the ODS reaction, and the ODS reaction mechanism was also proposed.

Switching on photocatalytic NO oxidation and proton reduction of NH2-MIL-125(Ti) by convenient linker defect engineering

Photocatalysis technology has been widely adopted to abate typical air pollutants. Nevertheless, developing photocatalysts aimed at improving photocatalytic efficiency is a challenge. Herein, the linker-defect NH₂-MIL-125(Ti) photocatalyst was synthesized through a convenient one-step heating-stirring method (just adjusting multiple temperatures) to firstly realize efficient photocatalytic performances of NO removal and hydrogen evolution. The optimal sample (named 65-NMIL) with a linker-defect content of 32.08% exhibited a NO removal ratio of 65.49%, which was 37.57% higher than that of pristine NH₂-MIL-125(Ti), and displayed better H₂-production activity. Through ESR, it was confirmed that 65-NMIL can generate more •O₂^- and •OH under visible light, and the radical trapping experiment further proved that •O₂^- played a more important role in photocatalytic activity. Moreover, the photocatalytic NO oxidation process was also monitored by in situ DRIFTS, it was found that the defective samples could promote the oxidation of NO and intermediates to the final product (NO₃^-). On the basis of the above-mentioned photocatalytic experimental results and characterization, a possible mechanism or pathway was proposed and illustrated. This work can provide a new strategy for the subsequent defect engineering for photocatalytic MOFs materials to further solve environmental and energy crises.

A Short Review of Aerobic Oxidative Desulfurization of Liquid Fuels over Porous Materials

Oxidative desulfurization (ODS) has attracted much attention owing to the mild working conditions and effective removal of the aromatic sulfur-containing compounds which are difficult to desulfurize using the industrial hydrodesulfurization (HDS) technique. Molecular oxygen in ambient air have been recognized as an ideal oxidant in ODS due to its easy availability, non-toxicity and low cost in recent years. However, molecular oxygen activation under mild operating conditions is still a challenge. Porous materials and their composites have drawn increasing attention due to their advantages, such as high surface area and confined pore space, along with their stability. These merits contribute to the fast diffusion of oxygen molecules and the formation of more exposed active sites, which make them ideal catalysts for aerobic oxidation reactions. The confined space pore size offers a means of catalytic activity and durability improvement. This gives rise to copious attention toward the porous catalysts in AODS. In this review, the progress in the characteristics and AODS catalytic activities of porous catalysts is summarized. Then, emphasis on the molecular oxygen activation mechanism is traced. Finally, the breakthroughs and challenges of various categories of porous catalysts are concluded.

Oxidative Desulfurization of Fuel Oil Catalyzed by Carbon Nitride Supported Phosphotungstic Acid Based Dicationic Ionic Liquid

In this study, a novel phosphotungstic acid based dicationic ionic liquid [C2(MIM)2]PW12O40 was successfully prepared and immobilized on graphitic carbon nitride (g-C3N4). The supported catalysts wt% [C2(MIM)2]PW12O40/g-C3N4 (wt=3%, 10%, 30%,...

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.

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.

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.

In Situ Implanting of Single Tungsten Sites into Defective UiO-66(Zr) by Solvent-Free Route for Efficient Oxidative Desulfurization at Room Temperature

Design of single-site catalysts with catalytic sites at atomic-scale and high atom utilization, provides new opportunities to gain superior catalytic performance for targeted reactions. In this contribution, we report a one-pot green approach for in situ implanting of single tungsten sites (up to 12.7 wt.%) onto the nodes of defective UiO-66(Zr) structure via forming Zr-O-W bonds under solvent-free condition. The catalysts displayed extraordinary activity for the oxidative removal of sulfur compounds (1000 ppm S) at room temperature within 30 min. The turnover frequency (TOF) value can reach 44.0 h^-1 at 30 °C, which is 109.0, 12.3 and 1.2 times higher than that of pristine UiO-66(Zr), WO₃ , and WCl₆ (homogeneous catalyst). Theoretical and experimental studies show that the anchored W sites can react with oxidant readily and generate W^VI -peroxo intermediates that determine the reaction activity. Our work not only manifests the application of SSCs in the field of desulfurization of fuel oil but also opens a new solvent-free avenue for fabricating MOFs based SSCs.

Size modulation of MIL-125 nanocrystals to promote the catalytic performance towards oxidative desulfurization

The Ti-based metal-organic framework (Ti-MOF) MIL-125 with tunable crystalline size in the range of ca. 50 nm to 1500 nm was synthesized by the coordination modulation method using trans-cinnamic acid (CA) as a modulator. The coordination modulation also induced hierarchical porosity and structure defects on the nanocrystals. A significant size-dependent catalytic activity towards the oxidative desulfurization (ODS) reaction was observed for these MIL-125 nanocrystals. In particular, the MIL-125 nanocrystals with a mean size of ca. 50 nm exhibit dramatically enhanced catalytic performance for the bulky sulfur compound 4,6-dimethyldibenzothiophene (4,6-DMDBT) compared to the microcrystals. It is demonstrated that the size modulation of MIL-125 is an effective approach to promote its performance for the catalysis of bulky molecules.

Vanadium-substituted heteropolyacids (H3+mPW12−mVmO40) encapsulated in Fe3O4@UiO-66 magnetic core–shell microspheres as excellent catalysts for oxidative desulfurization under oxygen

In this study, the novel magnetic core–shell composites Fe₃O₄@UiO-66-HPA, consisting of magnetic Fe₃O₄@UiO-66 and vanadium-substituted Keggin-type heteropolyacid active species supported by Zr-MOF, were prepared via a one-pot method and fully characterized.

A zwitterionic ligand-based water-stable metal–organic framework showing photochromic and Cr(vi) removal properties

A water-stable In-MOF based on the zwitterionic viologen ligand was synthesized. It exhibits photochromic property and Cr(vi) removal performance.