Fast Li-ion Storage and Dynamics in TiO2 Nanoparticle Clusters Probed by Smart Scanning Electrochemical Cell Microscopy

Anatase TiO₂ is a promising material for Li-ion (Li⁺) batteries with fast charging capability. However, Li⁺ (de)intercalation dynamics in TiO₂ remain elusive and reported diffusivities span many orders of magnitude. Here, we develop a smart protocol for scanning electrochemical cell microscopy (SECCM) with in situ optical microscopy (OM) to enable the high-throughput charge/discharge analysis of single TiO₂ nanoparticle clusters. Directly probing active nanoparticles revealed that TiO₂ with a size of ≈50 nm can store over 30 % of the theoretical capacity at an extremely fast charge/discharge rate of ≈100 C. This finding of fast Li⁺ storage in TiO₂ particles strengthens its potential for fast-charging batteries. More generally, smart SECCM-OM should find wide applications for high-throughput electrochemical screening of nanostructured materials.     

Photocatalytic reduction of CO2 with H2O on TiO2 and Cu/TiO2 catalysts

Photoinduced reduction of CO₂ by H₂O to produce CH₄ and CH₃OH has been investigated on wellcharacterized standard TiO₂ catalysts and on a Cu²⁺ loaded TiO₂ catalyst. The efficiency of this photoreaction depends strongly on the kind of catalyst and the ratio of H₂O to CO₂. Anatase TiO₂, which has a large band gap and numerous surface OH groups, shows high efficiency for photocatalytic CH₄ formation. Photogenerated Ti³⁺ ions, H and CH₃ radicals are observed as reactive intermediates, by ESR at 77 K. Cu-loading of the small, powdered TiO₂ catalyst (Cu/TiO₂) brings about additional formation of CH₃OH. XPS studies suggest that Cu⁺ plays a significant role in CH₃OH formation.     

Physicochemical Characterization and Catalytic Properties of Titania Gel Doped with Lithium and Rubidium

The effect on titania of doping with lithium and rubidium titania gels has been studied in samples prepared with titanium (IV) tetra-n-butoxide co-gelling with the alkaline metal precursors. Titania and doped titania were characterized by X-Ray diffraction, which showed that the catalysts were nanostructured. In samples calcined at 400°C, the crystallite size of the anatase phase was 17 and 14 nm, and 78 and 38 nm for samples calcined at 600°C, for Li/TiO₂ and Rb/TiO₂, respectively. The specific surface areas of doped samples (400°C) are lower in Li/TiO₂ (90 m²/g) than in Rb/TiO₂(125 m²/g). Evaluation of their basic properties has been carried out in the acetone condensation reaction. It was found that the activity strongly depended on the Li and Rb ionic radii.     

Photocatalytic removal of nitrogen oxides from air on TiO<Subscript>2</Subscript> modified with bases and platinum

The efficiency of TiO₂ (Degussa P-25) modified with an alkaline admixture (urea, BaO), sulfuric acid, or platinum in the photocatalytic oxidation of NO (50 ppm) with a flowing 7% O₂ + N₂ mixture under UV irradiation in a flow reactor at room temperature and atmospheric pressure is reported. Because of the progressive blocking of active sites of the photocatalyst by the reaction products (NO₂, NO₃⁻), it is impossible to realize prolonged continuous removal of NO _x (NO + NO₂) from air without catalyst regeneration at elevated temperatures. The efficiency of the photocatalysts is characterized by specific photoadsorption capacity (SPC) calculated from the total amount of NO _x adsorbed during 2-h-long irradiation. Modification of TiO₂ with 5% BaO or 5% urea raises the SPC of the catalyst by a factor of 2–3. Presumably, this promoting effect is due to the basic properties of these dopants, which readily sorb NO₂ and NO₃⁻. A considerable favorable effect on SPC is also attained by adding 0.5% Pt to (5% BaO)/TiO₂. The SPC of the (0.5% Pt)/TiO₂ catalyst depends on the state of the platinum. The samples calcined in air at 500°C, which contain Pt⁺ and Pt²⁺, have an approximately 2 times higher SPC than unpromoted TiO₂ and ensure a much larger NO₂/NO ratio at the reactor outlet. Conversely, the samples reduced in an H₂ atmosphere at 200°C, whose platinum is in the Pt0 state, show a lower SPC than the initial TiO₂ and cause no significant change in the NO₂/NO ratio.     

Widely Controllable Syngas Production by a Dye‐Sensitized TiO2 Hybrid System with ReI and CoIII Catalysts under Visible‐Light Irradiation

Visible‐light irradiation of a ternary hybrid catalyst prepared by grafting a dye, an H₂ evolving Co^III catalyst and a CO‐producing Re^I catalyst on TiO₂ have been found to produce both H₂ and CO (syngas) in CO₂‐saturated N ,N ‐dimethyl formamide (DMF)/water solution containing a 0.1 m sacrificial electron donor. The H₂/CO ratios are effectively controlled by changing either the water content of the solvent or the molar ratio of the Re^I and Co^III catalysts ranging from 1:2 to 15:1. The controlled syngas formation is discussed in terms of competitive electron flow from TiO₂ to each of the CO₂‐reduction and hydrogen‐evolving sites depending on the efficiencies of the two catalytic reaction cycles under given reaction conditions.     

Catalytic olefin hydrogenation with the application of a new water soluble rhodium catalyst

The catalyst precursor preparedin situ from rhodium dimer [Rh(cod)Cl]₂ and a new water-soluble phosphine Ph₂PCH₂CH₂CONHC(CH₃)₂CH₂SO₃H (in Li⁺ salt form) has been found to act as an effective olefin hydrogenation catalyst. Catalytic hydrogenation reactions have been tested in either two phase: aqueous catalyst/insoluble olefin or methanolic catalyst/olefin systems. The observed reaction rates were higher for terminal than for internal olefins. 1-Hexene in methanolic solution has been hydrogenated with a turnover frequency of about 8000 h^–1. This system has also been applied in the form of a supported aqueous phase catalyst.     

Synthesis and properties of a CO oxidation catalyst based on plasma-chemical silicon carbide,titanium dioxide,and palladium

A catalyst based on plasma-chemical β-SiC and TiO₂ with a palladium content of 10 wt % has been synthesized. The dependence of the rate of the CO oxidation reaction at room temperature and low CO concentrations (less than 100 mg/m³) on the β-SiC content has been studied. It has been found that with a β-SiC content of 8 to 10 wt %, the catalyst has a maximum reaction rate, which is three times that on a catalyst based on pure TiO₂ including palladium clusters. The catalysts are promising for use in catalytic and photocatalytic air purification systems.     

Construction of Optically Active Quaternary Propargyl Amines by Highly Enantioselective Zinc/BINOL‐Catalyzed Alkynylation of Ketoimines

A general and efficient method for the highly enantioselective alkynylation of ketoimines through a zinc/1,1′‐bi‐2‐naphthol (BINOL)‐catalyzed process has been developed. A variety of ketoimines, including α‐fluoroalkyl α‐imine esters, α‐aryl α‐imine esters, and trifluoromethyl aryl ketoimines, are applicable and provide their corresponding quaternary propargyl amines in excellent yields with high ee values (up to 99 % ee). Both the steric and electronic effects of substituents at the 3,3′ positions of BINOL are critical for the reaction efficiency and enantioselectivity. To demonstrate the usefulness of the method, (R)‐α‐CF₃ α‐proline has been prepared in a highly efficient manner. The notable features of this protocol are its broad substrate scope, high reaction efficiency (up to 99 %) and enantioselectivity (up to 99 % ee), low catalyst loading (5 mol % of BINOL derivative), and mild reaction conditions.     

TiO2薄膜光催化氧化I-的研究

采用溶胶-凝胶法,在玻璃珠表面涂覆均匀透明的TiO     

组合型Pt/TiO_2催化剂用于低温催化甲苯完全氧化

将均匀分布的纳米Pt粒子直接吸附到TiO2载体上,即制得了组合型Pt/TiO2催化剂(Pt/TiO2-AS).与浸渍法制备的Pt/TiO2催化剂(Pt/TiO2-WI)比较,Pt/TiO2-AS催化剂在催化甲苯完全氧化反应中表现出了很好的催化性能,甲苯转化率为100%时的反应温度低至150°C,而且即使在较高甲苯浓度和较高气体空速下,该催化剂也能保持较好的催化性能.通过X射线衍射(XRD)、N2吸附-脱附(BET)、透射电子显微镜(TEM)、X射线光电子能谱(XPS)、氢气程序升温还原(H2-TPR)及傅里叶变换红外(FTIR)光谱等对两种Pt/TiO2催化剂的结构和表面性能进行了表征.结果表明组合型Pt/TiO2-AS催化剂粒径小(2.5 nm),活性组分主要以Pt0形式存在且分布在载体表面,而且载体表面Ti―O键活化使催化剂具有较强的催化氧化能力.另外,活性中心的价态变化(Pt0→Ptδ+)是导致Pt/TiO2-AS催化剂失活的主要原因.     

Magnesium chloride supported high-mileage catalysts for olefin polymerization. I. Chemical composition and oxidation states of titanium

The chemical composition of a MgCl₂-supported, high-mileage catalyst has been determined at every stage of its preparation. Ball milling of MgCl₂ with ethyl benzoate (EB) resulted in the incorporation of 95% of the EB present to give MgCl₂·EB_0.15. A mild reaction with a half-mole equivalent of p-cresol (PC) at 50°C for 1 h resulted in near quantitative retention of p-cresol by the support. The composition is now approximately MgCl₂·EB_0.15P?_0.5. Addition of an amount of AlEt₃ corresponding to half-mole equivalent of p-cresol liberated one mole of ethane per mole of p-cresol, thus signaling quantitative reaction between the two components. The support contains on the average one ethyl group per Al. Further reaction with TiCl₄ resulted in the incorporation of titanium of approximately 8, 38, and 54% in the oxidation states of +2, +3, and +4, respectively. The ratio of Al to Ti in the catalyst lies in the range of 0.5–1.0. Only 19% of all the Ti⁺³ species in the catalyst can be observed by electron paramagnetic resonance (EPR); these are attributable to isolated Ti⁺³ complexes. The remaining EPR silent Ti⁺³ species are believed to be bridged to another Ti⁺³ by Cl ligands. The total Cl content is equal to the sum of 2 × Mg + 3 × Al + 3.5 × Ti. Most of the p-cresol moiety apparently disappeared from the support, leaving much of ethyl benzoate in the catalyst. Activation with AlEt₃/methyl-p-toluate complex reduces 90% of the Ti⁺⁴ in the catalyst to lower oxidation states. The ester apparently moderates the alkylating power of AlEt₃ to avoid excessive formation of divalent titanium sites. There appears to be a constant fraction of 1/4–1/5 of the titanium which is isolated and the remainder is in bridged clusters independent of the oxidation states of titanium.     

A Useful,Reliable and Safer Protocol for Hydrogenation and the Hydrogenolysis of O‐Benzyl Groups: The In Situ Preparation of an Active Pd0/C Catalyst with Well‐Defined Properties

A simple, highly reproducible protocol for the hydrogenation of alkenes and alkynes and for the hydrogenolysis of O‐benzyl ethers has been developed. The method features the in situ preparation of an active Pd⁰/C catalyst from Pd(OAc)₂ and charcoal, in methanol. The mild reaction conditions (25 °C) and low catalyst loading required (0.025 mol %), as well as the absence of contamination of the product by palladium residues (<4 ppb), make this a sustainable, useful process for organic chemists. Alternatively, the protocol can be carried out under microwave activation, to shorten the reaction times, with cyclohexene as the hydrogen source.     

Synthesis of spiroannulated dihydroisobenzofuranylated monosaccharides

An efficient synthesis of spiroannulated dihydroisobenzofurans is achieved using easily accessible carbohydrate-derived furanyl propargyl ethers via an AuCl₃ promoted intramolecular Diels-Alder (IMDA) reaction. The scope of the spiroannulation protocol was demonstrated using a diverse range of pentofuranosyl, hexofuransoyl and hexopyranosyl derived substrates in order to synthesize spiroannulated dihydroisobenzofurans. The reaction is high yielding, moisture tolerant, fast and uses only a catalytic amount of AuCl₃.     

High Catalytic Efficiency of Nanostructured Molybdenum Trioxide in the Benzylation of Arenes and an Investigation of the Reaction Mechanism

The synthesis and characterization of nanostructured MoO₃ with a thickness of about 30 nm and a width of about 450 nm are reported. The composition formula of the MP (precipitation method) precursor was estimated to be [(NH₄)₂O]_0.169?MoO₃? (H₂O)_0.239. The calcination of the precursor in air afforded nanostructured pellets of the α‐MoO₃ phase. The nanostructured MoO₃ catalyst exhibited high efficiency in catalyzing the benzylation of various arenes with substituted benzyl alcohols, which were strikingly different to common bulk MoO₃. Most reactions offered >99 % conversion and >99 % selectivity to monoalkylated compounds. MoO₃ is a typical acid catalyst. However, the benzylation reaction over nanostructured MoO₃ does not belong to the acid‐catalyzed type or defect site‐catalyzed type, since the catalyst has no acidity and defect site on surface. Characterization with thermal, spectroscopic, and electronic techniques reveal that the catalyst contains fully oxygen‐coordinated MoO₆ octahedrons on the surface but partially reduced species (Mo⁵⁺) within the bulk phase. The terminal oxygen atoms of Mo?O bonds on the (010) basal plane resemble oxygen anion radicals and act as active sites for the adsorption and activation of benzyl alcohols by electrophilic attack. Such sites are indispensable for catalytic reactions since the blocking of these sites by electron acceptors, such as tetracyanoethylene (TCNE), can greatly decrease catalytic activity. This work represents a successful example of combining a heterogeneous catalysis study with nanomaterial synthesis.     

Highly Regio‐ and Stereoselective Hydrosilylation of Internal Thioalkynes under Mild Conditions

A general and mild hydrosilylation of thioalkynes is described. With the cationic catalyst [Cp*Ru(MeCN)₃]⁺ and the bulky silane (TMSO)₃SiH, a range of thioalkynes underwent smooth hydrosilylation at room temperature with excellent α regioselectivity and syn stereoselectivity. DFT calculations provided important insight into the mechanism, particularly the unusual syn selectivity with the [Cp*Ru(MeCN)₃]⁺ catalyst. The sulfenyl group in the substrates was found to provide important chelation stabilization to direct the reaction through a new mechanistic pathway.     

EPR Studies of Photoreduction of Ni/TiO2 Catalysts

Irradiations of Ni/TiO₂ catalyst by UV in hydrogen at 77 K produced not only Ni⁺ ions on the catalyst surface, but also Ni³⁺ and Ti³⁺ species in bulk or near the interface between nickel and titania. These photo-generated species were detected and characterized by low temperature electron paramagnetic resonance (EPR) spectroscopy. Relative spin concentrations of the photogenerated paramagnetic species (Niⁿ⁺ and Ti³⁺) varied with the nickel content in titania. A high nickel content in the sample resulted in a high peak intensity ratio of Niⁿ⁺ to Ti³⁺. It was found that the photoinduced self-redox reaction of Ni²⁺ ions to form Ni⁺ and Ni³⁺ ions has a priority over the photoreduction of Ti⁴⁺ to Ti³⁺ ions. The characteristic EPR spectrum of the Ni³⁺ (3d⁷) ions with g₁ = 2.268, g₂ = 2.237, and g₃ = 2.045 indicates that the Ni³⁺ ions are most likely located in the substitutional sites of TiO₂, possibly near the surface rutile phase. The Ni⁺ species (3d⁹) with g₄ = 2.130 and g₁ = 2.063 are on the surface of TiO₂. Both Ni⁺ and Ni³⁺ ions are quite stable in hydrogen. The Ni³⁺ ions seem to be responsible for anchoring the nickel ions onto titania and stablizing the Ni⁺ species on the surface. The Ni⁺ ions are thus free from oxygen poisoning and still show a high activity toward olefin oligomerization.     

Hydrolysis of Methylphenyldiethoxysilane with Rare Earth Superacid Catalysts SO2− 4/TiO2/Ln3+

Abstract

An environmentally benign hydrolysis of methylphenyldiethoxysilane (MePhSi(OEt)₂) catalyzed by a rare earth superacid catalyst SO ^2? ₄ /TiO₂/Ln³⁺ has been investigated. The hydrolysis rates decrease in the order SO ^2? ₄ /TiO₂/Nd³⁺ > SO ^2? ₄ /TiO₂/Y³⁺ > SO ^2? ₄ /TiO₂/Sm³⁺ > SO ^2? ₄ /TiO₂. The hydrolysis of MePhSi(OEt)₂ is a first-order reaction with respect to the concentration of MePhSi(OEt)₂, and the hydrolysis rate constant increases with increasing temperature. The activation energy E _a and the pre-exponential factor for this hydrolysis catalyzed by SO ^2? ₄ /TiO₂/Nd³⁺ have been determined as 322.50 kJ mol^?1 and 7.12 × 10⁴¹ s^?1, respectively. The products of the hydrolysis are oligomers of polymethylphenylsiloxane. The mechanism of MePhSi(OEt)₂ hydrolysis is also discussed.     

Visible Light-induced Oxygen Generation and Cyclic Water Cleavage Sensitized by Porphyrins

Zinctetramethylpyridylporphyrin (ZnTMPyP⁴⁺) in acidic aqueous solution sensitizes efficiently oxygen generation by visible light in the presence of acceptors such as Fe³⁺ - and Ag⁺-ions and colloidal RuO₂/TiO₂ redox catalyst. Hydrogen and oxygen are cogenerated under visible light illumination of ZnTMPyP⁴⁺ solutions when a bifunctional catalyst (Pt and RuO₂ codeposited onto TiO₂) is employed.     

Preparation and photocatalytic behavior of TiO2-carbon nanotube hybrid catalyst for acridine dye decomposition

A new kind of hybrid catalyst, TiO₂-carbon nanotubes, was prepared via sol-gel method for the first time. Its photocatalytic activity in the photodegradation of acridine dye aqueous solution at low concentration was tested. There was no measurable effect on the formation of crystalline phase of TiO₂ catalyst with the addition of 10 wt.% carbon nanotubes to TiO₂ samples. AFM photograph of TiO₂-carbon nanotubes sintered at 300°C showed that the carbon nanotubes were enwrapped by TiO₂, which greatly increased the adsorbing ability of the catalyst and was in favor of photocatalytic reaction. Compared with naked TiO₂ powder the hybrid catalyst prepared in this way showed high efficiency in the photodecomposition of acridine dye.     

High‐Speed Living Polymerization of Polar Vinyl Monomers by Self‐Healing Silylium Catalysts

This contribution describes the development and demonstration of the ambient‐temperature, high‐speed living polymerization of polar vinyl monomers (M) with a low silylium catalyst loading (≤ 0.05 mol % relative to M). The catalyst is generated in situ by protonation of a trialkylsilyl ketene acetal (^RSKA) initiator (I) with a strong Brønsted acid. The living character of the polymerization system has been demonstrated by several key lines of evidence, including the observed linear growth of the chain length as a function of monomer conversion at a given [M]/[I] ratio, near‐precise polymer number‐average molecular weight (M_n, controlled by the [M]/[I] ratio) with narrow molecular weight distributions (MWD), absence of an induction period and chain‐termination reactions (as revealed by kinetics), readily achievable chain extension, and the successful synthesis of well‐defined block copolymers. Fundamental steps of activation, initiation, propagation, and catalyst “self‐repair” involved in this living polymerization system have been elucidated, chiefly featuring a propagation “catalysis” cycle consisting of a rate‐limiting C? C bond formation step and fast release of the silylium catalyst to the incoming monomer. Effects of acid activator, catalyst and monomer structure, and reaction temperature on polymerization characteristics have also been examined. Among the three strong acids incorporating a weakly coordinating borate or a chiral disulfonimide anion, the oxonium acid [H(Et₂O)₂]⁺[B(C₆F₅)₄]^? is the most effective activator, which spontaneously delivers the most active R₃Si⁺, reaching a high catalyst turn‐over frequency (TOF) of 6.0×10³ h^?1 for methyl methacrylate polymerization by Me₃Si⁺ or an exceptionally high TOF of 2.4×10⁵ h^?1 for n‐butyl acrylate polymerization by iBu₃Si⁺, in addition to its high (>90 %) to quantitative efficiencies and a high degree of control over M_n and MWD (1.07–1.12). An intriguing catalyst “self‐repair” feature has also been demonstrated for the current living polymerization system.