Bioinspired Single-Atom Sites Enable Efficient Oxygen Activation for Switching Anodic/Cathodic Electrochemiluminescence

Exploring advanced co-reaction accelerators with superior oxygen reduction activity that generate rich reactive oxygen species (ROS) has attracted great attention in boosting luminol-O₂ electrochemiluminescence (ECL). However, tuning accelerators for efficient and selective catalytic O₂ activation to switch anodic/cathodic ECL is very challenging. Herein, we report that enzyme-inspired Fe-based single-atom catalysts with axial N/C coordination structures (FeN₅, FeN₄© SACs) can generate specific ROS for cathodic/anodic ECL conversion. Mechanistic studies reveal that FeN₅ sites prefer to produce highly active hydroxyl radicals and afford direct cathodic luminescence by promoting the cleavage of O−O bonds through N-induced electron redistribution. In contrast, FeN₄© sites tend to produce superoxide radicals, resulting in inefficient anodic ECL. Benefiting from the enhanced cathodic ECL, FeN₅ SAC-based immunosensor was constructed for the sensitive detection of cancer biomarkers.     

Glycolysis of poly(ethylene terephthalate) (PET) using basic ionic liquids as catalysts

The glycolysis of poly(ethylene terephthalate) (PET) was studied using several ionic liquids and basic ionic liquids as catalysts. The basic ionic liquid, 1-butyl-3-methylimidazolium hydroxyl ([Bmim]OH), exhibits higher catalytic activity for the glycolysis of PET, compared with 1-butyl-3-methylimidazolium bicarbonate ([Bmim]HCO₃), 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) and 1-butyl-3-methylimidazolium bromide ([Bmim]Br). FT-IR, ¹H NMR and DSC were used to confirm the main product of glycolysis was bis(2-hydroxyethyl) terephthalate (BHET) monomer. The influences of experimental parameters, such as the amount of catalyst, glycolysis time, reaction temperature, and dosages of ethylene glycol on the conversion of PET, yield of BHET were investigated. The results showed a strong influence of the mixture evolution of temperature and reaction time on depolymerization of PET. Under the optimum conditions of m(PET):m(EG): 1:10, dosage of [Bmim]OH at 0.1 g (5 wt%), reaction temperature 190 °C and time 2 h, the conversion of PET and the yield of BHET were 100% and 71.2% respectively. Balance between the polymerization of BHET and depolymerization of PET could be changed when the reaction time was more than 2 h and contents of catalyst and EG were changed.     

Effect of Hydrohalogenation of Metal/Zeolite Catalysts for Cyclohexene Hydroconversion ‐Part 3‐ Pd/H‐ZSM‐5 Catalysts

Cyclohexene (CHE) hydroconversion was performed in a flow reactor at atmospheric pressure and temperatures of 50–400 °C using: Pd/H‐ZSM‐5, Pd/H‐ZSM‐5(HCl), and Pd/H‐ZSM‐5(HF) catalysts. These catalysts were characterized for acid site strength distribution via NH₃ TPD, Pd dispersion via H₂ chemisorption, TPR via reduction of the metal oxide in the catalysts and XRD for tracing crystallinity The hydroconversion steps proceeded as follows: CHE → Cyclohexane (CHA); CHE → Methylcyclopentenes (MCPEs) → Methylcyclopentane (MCPA); CHE → Cyclohexadienes (CHDEs) → Benzene → Alkylbenzenes; CHE and others → Hydrocrackedproducts. The overall hydroconversion of CHE was achieved in the catalyst order: Pd/H‐ZSM‐5 > Pd/H‐ZSM‐5(HF) > Pd/H‐ZSM‐5(HCl). CHE hydrogenation step was the major reaction at low temperatures which significantly inhibited via HCl treatment, but slightly enhanced via HF treatment. At medium temperatures, on all catalysts, isomerisation to MCPEs and MCPA increase to a maximum then a decline with a further increase of temperature. The overall isomerisation of CHE was highest on the untreated catalyst. During the higher temperature range, dehydrogenation, alkylation and hydrocracking were increased with temperature. Dehydrogenation of CHE always yielded larger amounts of 1,3‐CHDE than 1,4‐CHDE. These cyclohexadienes were produced in the catalyst order: Pd/H‐ZSM‐5(HF) > Pd/H‐ZSM‐5(HCl) > Pd/H‐ZSM‐5. In general, benzene alkylation to toluene exceeded that of xylenes, indicating that the second methylation is more difficult than the first. However, the catalytic activities for benzene and toluene production were in the order: Pd/H‐ZSM‐5 » Pd/H‐ZSM‐5(HCl) > Pd/H‐ZSM‐5(HF), whereas for xylenes production, Pd/H‐ZSM‐5 » Pd/H‐ZSM‐5(HF) > Pd/H‐ZSM‐5(HCl). Intrapore diffusion plays an important role during the dehydrogenation reactions as well as during the interconversion of individual aromatic hydrocarbons.     

氧化铝负载高分散γ-Mo2N的制备与结构表征

由NH3的程序升温还原反应（TPR）制备了不同Mo担载量的氮化态Mo/γ-Al2O3催化剂，用XRD和EXAFS方法研究了样品在氮化前后的体相结构及Mo原子局域配位结构。氮化前样品的Mo K-边径向结构函数与非负载MoO3类似，样品中Mo以晶粒度较小，分散度较高的MoO3形式存在；氮化所样品的径向结构函数与非负载的γ-Mo2N基本相同，样品中Mo主要以分散度较高的γ-Mo2N形式存在。EXAFS拟合结果表明，样品的第一配位壳层（Mo-N)的配位数较非负载γ-Mo2N有明显降低，热无序和结构无序均较大，并且随担载量降低，无序度有增大的趋势。     

Bidirectional Tandem Electrocatalysis Manipulated Sulfur Speciation Pathway for High-Capacity and Stable Na-S Battery

The sluggish polysulfide redox kinetics and the uncontrollable sulfur speciation pathway, leading to serious shuttling effect and high activation barrier associated with sulfur cathode. We describe here the use of core–shell structured composite matrixes containing abundant catalytic sites for nearly fully reversible cycling of sulfur cathodes for Na-S batteries. The bidirectional tandem electrocatalysis provide successive reversible conversion of both long- and short-chain polysulfides, whereas Fe₂O₃ accelerates Na₂S₈/Na₂S₆ to Na₂S₄ conversion and the redox-active Fe(CN)₆⁴⁻-doped polypyrrole shell catalyzes Na₂S₄ reduction to Na₂S. The electrochemically reactive Na₂S can be readily charged back to sulfur with minimal overpotential. Simultaneously, stable cycling of Na-S pouch cell with a high reversible capacity of 696 mAh g⁻¹ is also demonstrated. The bidirectional confined tandem catalysis renders the manipulation of sulfur redox electrochemistry for practical Na-S cells.     

Unveiling the CO Oxidation Mechanism over a Molecularly Defined Copper Single-Atom Catalyst Supported on a Metal–Organic Framework

Elucidating the reaction mechanism in heterogeneous catalysis is critically important for catalyst development, yet remains challenging because of the often unclear nature of the active sites. Using a molecularly defined copper single-atom catalyst supported by a UiO-66 metal–organic framework (Cu/UiO-66) allows a detailed mechanistic elucidation of the CO oxidation reaction. Based on a combination of in situ/operando spectroscopies, kinetic measurements including kinetic isotope effects, and density-functional-theory-based calculations, we identified the active site, reaction intermediates, and transition states of the dominant reaction cycle as well as the changes in oxidation/spin state during reaction. The reaction involves the continuous reactive dissociation of adsorbed O₂, by reaction of O_2,ad with CO_ad, leading to the formation of an O atom connecting the Cu center with a neighboring Zr⁴⁺ ion as the rate limiting step. This is removed in a second activated step.     

Template-Oriented Polyaniline-Supported Palladium Nanoclusters for Reductive Homocoupling of Furfural Derivatives

Developing well-defined structures and desired properties for porous organic polymer (POP) supported catalysts by controlling their composition, size, and morphology is of great significance. Herein, we report a preparation of polyaniline (PANI) supported Pd nanoparticles (NPs) with controllable structure and morphology. The protocol involves the introduction of MnO₂ with different crystal structures (α, β, γ, δ, ϵ) serving as both the reaction template and the oxidant. The different forms of MnO₂ each convert aniline to a PANI that contains a unique regular distribution of benzene and quinone. This leads to the Pd/PANI catalysts with different charge transfer properties between Pd and PANI, as well as different dispersions of the metal NPs. In this case, the Pd/ϵ-PANI catalyst greatly improves the turnover frequency (TOF; to 88.3 h⁻¹), in the reductive coupling of furfural derivatives to potential bio-based plasticizers. Systematic characterizations reveal the unique oxidation state of the support in the Pd/ϵ-PANI catalyst and coordination mode of Pd that drives the formation of highly dispersed Pd nanoclusters. Density functional theory (DFT) calculations show the more electron rich Pd/PANI catalyst has the lower energy barrier in the oxidative addition step, which favors the C−C coupling reaction.     

Atomically Dispersed FeN2P2 Motif with High Activity and Stability for Oxygen Reduction Reaction Over the Entire pH Range

The past decade has witnessed the great potential of Fe-based single-atom electrocatalysis in catalyzing oxygen reduction reaction (ORR). However, it remains a grand challenge to substantially improve their intrinsic activity and long-term stability in acidic electrolytes. Herein, we report a facile chemical vapor deposition strategy, by which high-density Fe atoms (3.97 wt%) are coordinated with square-planar para-positioned nitrogen and phosphorus atoms in a hierarchical carbon framework. The as-crafted atomically dispersed Fe catalyst (denoted Fe-SA/PNC) manifests an outstanding activity towards ORR over the entire pH range. Specifically, the half-wave potential of 0.92 V, 0.83 V, and 0.86 V vs. reversible hydrogen electrode (RHE) are attained in alkaline, neutral, and acidic electrolytes, respectively, representing the high performance among reported catalysts to date. Furthermore, after 30,000 durability cycles, the Fe-SA/PNC remains to be stable with no visible performance decay when tested in 0.1 M KOH and 0.5 M H₂SO₄, and only a minor negative shift of 40 mV detected in 0.1 M HClO₄, significantly outperforming commercial Pt/C counterpart. The coordination motif of Fe-SA/PNC is validated by density functional theory (DFT) calculations. This work provides atomic-level insight into improving the activity and stability of non-noble metal ORR catalysts, opening up an avenue to craft the desired single-atom electrocatalysts.     

Hollow STW-Type Zeolite Single Crystals with Aluminum Gradient for Highly Selective Production of p-Xylene from Methanol-Toluene Alkylation

Zeolites with uniform micropores are important shape-selective catalysts. However, the external acid sites of zeolites have a negative impact on shape-selective catalysis, and the microporosity may lead to serious diffusion limitation. Herein, we report on the direct synthesis of hierarchical hollow STW-type zeolite single crystals with a siliceous exterior. In an alkalinous fluoride medium, the nucleation of highly siliceous STW zeolites takes place first, and the nanocrystals are preferentially aligned on the outer surface of the gel agglomerates to grow into single crystalline shells upon crystallization. The lagged crystallization of the internal Al-rich amorphous gels onto the inner surface of nanocrystalline zeolite shells leads to the formation of hollow cavities in the core of the zeolite crystals. The hollow zeolite single crystals possess a low-to-high aluminum gradient from the surface to the core, resulting in an intrinsic inert external surface, and exhibit superior catalytic performance in toluene methylation reactions.     

Isolated Tin(IV) Active Sites for Highly Efficient Electroreduction of CO2 to CH4 in Neutral Aqueous Solution

The development of efficient electrocatalysts with non-copper metal sites for electrochemical CO₂ reduction reactions (eCO₂RR) to hydrocarbons and oxygenates is highly desirable, but still a great challenge. Herein, a stable metal–organic framework (DMA)₄[Sn₂(THO)₂] (Sn-THO, THO⁶⁻ = triphenylene-2,3,6,7,10,11-hexakis(olate), DMA = dimethylammonium) with isolated and distorted octahedral SnO₆²⁻ active sites is reported as an electrocatalyst for eCO₂RR, showing an exceptional performance for eCO₂RR to the CH₄ product rather than the common products formate and CO for reported Sn-based catalysts. The partial current density of CH₄ reaches a high value of 34.5 mA cm⁻², surpassing most reported copper-based and all non-Cu metal-based catalysts. Our experimental and theoretical results revealed that the isolated SnO₆²⁻ active site favors the formation of key *OCOH species to produce CH₄ and can greatly inhibit the formation of *OCHO and *COOH species to produce *HCOOH and *CO, respectively.