Titanium Species Research Articles

The effect of acid treatment on the active sites and reaction intermediates of the low-cost TS-1 in propylene epoxidation

The role of titanium species and the effect of acid treatment on low-cost TS-1 zeolites have been investigated using gas chromatography-Raman spectrometry during the propylene epoxidation process.

Electrochemical Behavior of Titanium Ions in Various Molten Alkali Chlorides

Cyclic voltammetry and square wave voltammetry were performed for TiCl3 at 1023 K, in molten LiCl, LiCl-KCl, NaCl-CsCl and CsCl, respectively. The anodic process from Ti(III) to Ti(IV) is a simple reversible process in all the alkali chloride melts. Ti(III) can be reduced directly to Ti in one step, in CsCl, while Ti(II) will appear before Ti in LiCl, LiCl-KCl and NaCl-CsCl. The electrode potentials of redox couples of titanium species decrease with the decrease of the polarization power of solvent alkali ion.

Strategies for introducing titania onto mesostructured silica nanoparticles targeting enhanced photocatalytic activity of visible-light-responsive Ti-MSN catalysts

Titanium-mesostructured silica nanoparticles (Ti-MSN) catalysts which are excellent photocatalytic materials for the environment were prepared by supporting mesostructured silica nanoparticles (MSNs) with titanium species synthesized by three different approaches: microwave and in situ and ex situ electrochemical methods, denoted as Ti-MSN-M, Ti-MSN-I, and Ti-MSN-E, respectively. The physicochemical properties of the catalysts were investigated via XRD, 29Si NMR, N2 adsorption-desorption, FTIR, ESR, and UV-DRS analyses. Characterization results revealed that the introduction of mesoporous titania nanoparticles (MTNs) prepared by the microwave method onto MSNs (Ti-MSN-M) did not significantly affect the silica framework. However, the silica network in the Ti-MSN-I and Ti-MSN-E was rather disrupted, particularly for the former catalyst, due to the desilication accompanied by isomorphous substitution of Ti in the MSN framework to form SiOTi bonds. Ti was also found to be exchanged with the terminal hydroxyl groups of all catalysts to form the SiOTi bonds. The addition of Ti species onto MSNs also increased the number of oxygen vacancies (Vo) and metal defect sites. Photocatalytic testing on the decolorization of Congo red (CR) resulted in the following order: Ti-MSN-I (94%) > Ti-MSN-M (90%) > Ti-MSN-E (34%). The Vo and metal defect sites were responsible in lowering the band gap of catalysts and decreasing the electron–hole recombination, while the great numbers of SiOTi bonds as well as large surface area and pore volume increased the active sites and offered a good surface contact with light to enhance the activity of catalysts. A kinetic study demonstrated that the photodegradation followed the pseudo-first-order Langmuir-Hinshelwood model. Ti-MSN-I and Ti-MSN-M maintained their activities for up to five runs without serious catalyst deactivation, indicating their potential for the degradation of dye in wastewater. Mineralization measurements of CR by TOC and BOD5 analyses after 3 h of contact time were 85.7% and 87.6% using Ti-MSN-M, while 83.7% and 80.3% using Ti-MSN-I, respectively. Optimization by response surface methodology showed that the catalyst dosage, pH, and TiO2 loading were the significant factors in the decolorization of CR. This study demonstrated that these two green technologies; electrochemical and MW have a great potential to be used in synthesis of various advanced materials for greener and more sustainable processes.

Analysis of titanium species in titanium oxynitride films prepared by plasma enhanced atomic layer deposition

A comparative study of thin titanium oxynitride (TiOxNy) films prepared by plasma enhanced atomic layer deposition using tetrakis(dimethylamino)titanium (TDMAT) and N2 plasma as well as titanium(IV)isopropoxide and NH3 plasma is reported. The comparison is based on the combination of Ti2p core level and valence band spectroscopy and current-voltage measurements. The TDMAT/N2 process delivers generally higher fractions of TiN and TiON within the Ti2p spectra of the films and stronger photoemissions within the bandgap as resolved in detail by high energy resolution synchrotron-based spectroscopy. In particular, it is shown that higher TiN contributions and in-gap emission intensities correlate strongly with increased leakage currents within the films and might be modified by the process parameters and precursor selection.

Protonated Oxide, Nitrided, and Reoxidized K2La2Ti3O10 Crystals: Visible-Light-Induced Photocatalytic Water Oxidation and Fabrication of Their Nanosheets

Protonated lanthanum titanium oxide H2La2Ti3O10 and oxynitride H2La2Ti3O10–3/2xNx crystals were synthesized from the oxide, nitrided, and reoxidized layered K2La2Ti3O10 crystals prepared by solid-state reaction through proton exchange. Here, we investigated the holding time of nitridation of oxide K2La2Ti3O10 crystals influencing their crystal structure, shape, and absorption wavelength and band gap energy. The XRD and SEM results confirmed that the crystal structure and plate-like shape of the parent oxide were maintained after nitridation at 800 °C for 10 h, and the color of crystals was changed from white to dark green. However, no clear absorption edges were observed in the UV–vis diffuse reflectance spectra of the nitrided crystals due mainly to the reduced titanium species (Ti3+), which act as the recombination center of the photogenerated charge carriers. To decrease the amount of the reduced titanium species, the nitrided crystals were further reoxidized at 400 °C for 6 h. After partial reoxidatio...

ChemInform Abstract: Efficient O‐Acylation of Alcohols and Phenol Using Cp2TiCl as a Reaction Promoter.

A method has been developed for the conversion of primary, secondary, and tertiary alcohols, and phenol, into the corresponding esters at room temperature. The method uses a titanium(III) species generated from a substoichiometric amount of titanocene dichloride together with manganese(0) as a reductant, as well as methylene diiodide. It involves a transesterification from an ethyl ester, or a reaction with an acyl chloride. A radical mechanism is proposed for these transformations.

Effect of silylation temperature on the physicochemical properties and catalytic performance of Ti-containing hexagonal mesoporous silica

Ti-HMS (hexagonal mesoporous silica, HMS) was vapor silylated at 150–450°C. The samples were characterized by Si29 CP/MAS NMR, FTIR, TG, XRD, and N2-adsorption, respectively, as well as evaluated by the continuous epoxidation of propylene with cumene hydroperoxide (CHP) as oxidant. There showed only a peak at 14 ppm assigned to (CH3)3Si*OSi(OSi)3 species in NMR spectra when silylated at low temperatures. The samples at higher temperatures (>250°C) gave an additional peak at 20 ppm, which was assigned to novel titanium species of (CH3)3Si*OTi(OSi)3. The intensity of peaks relevant to trimethyl groups increased with the silylation temperature at 150–350°C and decreased at 350–450°C due to decomposing of organic groups. The intensity reached the highest point at 350°C. The catalytic results showed that the propylene oxide yield also changed as the same trend and reached the longest life of 100% PO yield at 350°C silylation. In conclusion, 350°C is an optimal silylation temperature.

Reactivities study of titanium sites in titanosilicate frameworks by in situ XANES

This study focused on the study of titanium sites, their local structure and reactivities in nanoporous titanosilicates frameworks by using in situ X-ray absorption spectroscopy. XANES provides the information on the oxidation state of the titanium species as well as their change in coordination geometry during de- and re-hydration. Results from in situ XANES studies shows that TS-1 is much more hydrophobic than TiAl or TiFe systems. Pre-edge features of Ti K-edge XANES spectra of these materials also suggested that TiIV is the dominant Ti coordination in dehydrated system whilst TiVI is the dominant in the re-hydrated one.

Dissolution of NaTi2(PO4)3 in Alkaline Solutions and Its Implications for Use As an Aqueous Anode

There are two primary qualities batteries used for grid-scale storage should have (1) a low levelized cost of energy storage (LCOE) or a low $/kWh delivered over the lifetime of the battery and (2) a high degree of safety which includes low toxicity, low flammability, and low corrosiveness. Aqueous rechargeable alkali-ion batteries offer a promising alternative to Li-ion batteries for grid-scale electrochemical energy storage installations because of their lower cost of and higher safety. However, with the exception of systems that utilize activated carbon based anodes, demonstrated chemistries show significant capacity fade. Although a decent amount of research has been done on failure mechanism of intercalation cathodes in aqueous solution, few studies have been carried out to elucidate the role of the anode material in battery failure. Sodium super ionic conductor (NASICON) type NaTi2(PO4)3 is one of the most promising materials for aqueous anodes. It has good chemical stability, a high theoretical specific capacity of 133 mAh/g, low cost of manufacture, and a favorable redox potential. However, it is often reported to be cycled in neutral aqueous solution, which when given its low redox potential implies there will be some amount of water decomposition occurring. Water decomposition occurs due to both direct electrochemical hydrogen evolution, as well as direct chemical oxidation of the fully sodiated NaTi2(PO4)3. In this work we have set out to quantify the inherent chemical stability of NaTi2(PO4)3 in alkaline solutions using inductively coupled mass spectrometry (ICP-MS), x-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), cyclic voltammeter (CV), and in-situ pH measurements. It was found that at pH > 11 dissolution begins to occur but does not become significant until pH > 12.7. At the highest tested pH an unidentified phase with an elongated morphology becomes thermodynamically favorable and begins to precipitate from solution. This secondary phase acts as a sink for dissolved titanium allowing for the continual dissolution of NaTi2(PO4)3 rather then eventual saturation of solvated titanium species. The in-situ pH measurement indicates that upon cycling in neutral solution the electrode undergoes a pH swing from lower pH to higher pH due to the generation of OH- ions, followed by their diffusion out of the electrode. This increase followed by decrease in pH exacerbates the dissolution of NaTi2(PO4)3 and leads to a continual dissolution precipitation reaction. The combination of FTIR and XRD indicate that these precipitated phases were a mixture of layered titantes of the form NaxH2-xTinO2n+1-yH2O. Although NaTi2(PO4)3 appears to be susceptible to dissolution at higher pH, the measured dissolution does not account for the overall capacity fade seen upon cycling. The authors are currently investigating the effect of gas generation and entrapment on the loss of electrochemical surface area and its effect on the apparent capacity fade.

Efficient O-Acylation of Alcohols and Phenol Using Cp2TiCl as a Reaction Promoter.

A method has been developed for the conversion of primary, secondary, and tertiary alcohols, and phenol, into the corresponding esters at room temperature. The method uses a titanium(III) species generated from a substoichiometric amount of titanocene dichloride together with manganese(0) as a reductant, as well as methylene diiodide. It involves a transesterification from an ethyl ester, or a reaction with an acyl chloride. A radical mechanism is proposed for these transformations.

Polytitanium sulfate (PTS): Coagulation application and Ti species detection

Interest in the development of inorganic polymerized coagulants is growing; however, there are only limited studies on the synthesis of polytitanium coagulants, which are expected to exhibit improved coagulation efficiency with better floc properties. This study presents the synthesis of polytitanium sulfate (PTS) for potential application in water purification, followed by characterization of PTS flocs and titanium species detection. Stable PTS solutions were successfully synthesized and standard jar tests were conducted to evaluate their coagulation efficiency. Electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS) speciation analysis revealed that a variety of mononuclear and polynuclear complexes were formed in PTS solution, indicating the polymeric nature of the synthesized coagulant. Floc characteristics were studied through on-line monitoring of floc size using a laser diffraction particle size analyzer. Results showed that PTS had a comparable or in some cases even higher organic matter and particulate removal efficiency than Ti(SO4)2. The effluent pH after PTS coagulation significantly improved toward desirable values closer to neutral pH. Properties of flocs formed by PTS were significantly improved in terms of floc size, growth rate and structure. This study showed that PTS could be an efficient and promising coagulant for water purification, with the additional benefit that its coagulated sludge can be used to recover valuable TiO2 nanoparticles for various commercial applications.

Structural studies of titanium(IV) picolinamide alkoxide and oxide derivatives

Reactions have been carried out using the titanium(IV) precursors TiCl4 and Ti(OiPr)4, with addition of two equivalents of a functionalized picolinamide ligand. The reactions with TiCl4 led to the formation of either a mononuclear titanium species, [Ti(N,O)Cl2X2] or a dinuclear titanium species [Ti(N,O)X3]2[μ-O] (X=OMe or Cl), with incorporation of one picolinamide ligand. The ligand is bound to the titanium centre as the protonated amide. The reactions with Ti(OiPr)4 resulted in the formation of mononuclear titanium bis-picolinamide species [Ti(N,O)2(OiPr)2], and also dinuclear and trinuclear products, [(N,O)Ti(OiPr)2][μ-OiPr]2 and [(N,O)Ti(OiPr)2]2[μ-OiPr]2[(OiPr)2Ti][μ3-O] respectively. In these cases the picolinamide ligand was found to be deprotonated and bound to the titanium as the iminolate. These molecules have been characterized by X-ray crystallographic analysis and structural characteristics are discussed.

Enhanced visible-light-driven photocatalytic performance of mesoporous W-Ti-SBA-15 prepared through a facile hydrothermal route

A facile and one-step hydrothermal procedure was adopted to fabricate a series of W-Ti-SBA15 composites (WTS). These as-prepared composites were systematically characterized by a collection of analytic and spectroscopic techniques. It was found that dual phases of titanium and tungsten species coexisted in mesoporous structures of p6 mm hexagonal symmetry. In addition, these composites were visible-light responsive and exhibited enhanced photocatalytic capability toward degradation of Rhodamine B (RhB) and 2,4-dichlorophenol (2,4-DCP) upon visible-light irradiation in comparison to samples containing single component of titanium or tungsten species. Specifically, the best candidate, sample 8%WTS0.7, had the largest apparent reaction rate constant that was nearly 1.2, 2.1, 2.2, and 5.7 times as high as those of 8%WS, TS0.7, WO3/TiO2, and N-TiO2, respectively. The enhancement of photocatalytic performance was mainly attributed to the well-matched band structures of both components and strengthened visible light adsorption ability, originating from the combination of titania with highly acidic WO3 in SBA15 matrix with large specific surface areas. Active radical species were detected by trapping experiments and a possible photocatalytic mechanism was thus proposed. (C) 2016 Elsevier B.V. All rights reserved.

Rhodium-Containing Multi-Layered Mixed-Metal Oxides As Active Supports for Dispersed PtRu Nanoparticles during Electrooxidation of Ethanol

Recently, there has been growing interest in development of fuel cells (e.g. utilizing small organic molecules) as alternative technologies to hydrogen based electrochemical energy systems. For example, ethanol (biofuel) can be ideally oxidized to carbon dioxide thus delivering twelve electrons. But realistically the reaction is rather slow at ambient conditions. Obviously, there is a need to develop novel electrocatalytic materials. Platinum has been recognized as the most active catalytic metal towards oxidation of ethanol at low and moderate temperatures. But Pt anodes are readily poisoned by the strongly adsorbed intermediates, namely by CO-type species, requiring fairly high overpotentials for their removal. To enhance activity of Pt catalysts towards methanol and ethanol oxidation, additional metals including ruthenium, tin, molybdenum, tungsten or rhodium are usually introduced as the alloying component. More recently it has been demonstrated that catalytic activity of platinum-based nanoparticles towards electrooxidation of ethanol has been significantly enhanced through interfacial modification with ultra-thin monolayer-type films of metal oxo species of tungsten, titanium or zirconium. Also gold in combination with platinum has been demonstrated to produce novel high performance bimetallic catalysts. We pursue a concept of utilization of mixed metal (e.g. zirconium/tungsten or titanium/tungsten) oxide matrices for supporting and activating noble metal nanoparticles (e.g. PtRu) during electrooxidation of methanol and ethanol. Among important issues is incorporation of Rh nanostructures capable of weakening, or even breaking, the C-C bond in the ethanol molecules. On the other hand, rhodium itself is not directly electrocatalytic toward oxidation of ethanol. The oxides and noble metal nanoparticles have been deposited in a controlled manner using the layer-by-layer method. Remarkable increases of electrocatalytic currents measured under voltammetric and chronoamperometric conditions have been observed. The most likely explanation takes into account possibility of specific interactions of noble metals with transition metal oxide species as well as existence of active hydroxyl groups in the vicinity of catalytic noble metal sites. In addition, formation of “nanoreactors” where ethanol is partitioned (at Rh) to methanolic residues further oxidized at PtRu cannot be excluded.

Effect of titanium species on the precipitation of boehmite under digestion conditions

Heterogeneous precipitation of boehmite in Bayer liquor under digestion conditions can be reduced by the presence of a few ppm soluble titanium.In order for the Ti to be effective, it must be added as a solid phase – anatase or ilmenite – which gradually dissolves to some extent. If a Ti solution is added to the liquor, it forms an insoluble hydroxide which cannot affect boehmite precipitation.It is suggested that the soluble titanium species act by adsorbing on growth sites on the boehmite. A sodium titanate gel which precipitates may also block available nucleation sites on the seed material.

Synthetic Reactions Using Low-valent Titanium Reagents Derived from Ti(OR)4 or CpTiX3 (X = O-i-Pr or Cl) in the Presence of Me3SiCl and Mg.

In the presence of Me3SiCl, Ti(OR)4 or CpTiX3 (X = O-i-Pr or Cl) is reduced by Mg powder in THF to gradually generate a specific low-valent titanium (LVT) species that mediates several synthetic reactions. The LVT-catalyzed C-O bond-cleaving reactions of allyl and propargyl ethers and esters generate parent alcohols and carboxylic acids, respectively. O-allyl and propargyl carbamates are also readily deprotected by the LVT to afford parent amines. In addition, the respective reductive N-S or O-S bond cleavage of sulfonamides or sulfonyl esters mediated by the LVT was developed as a novel facile deprotection method. The reagent catalyzes intra- and intermolecular alkyne or alkyne/nitrile cycloaddition to produce substituted benzenes and pyridines, while epoxides and oxetanes are reduced to alcohols via an LVT-mediated homolytic ring opening. The McMurry coupling of aryl aldehydes and ketones proceeds with the LVT under homogeneous and mild reaction conditions and is effective for the polymerization of aromatic dialdehydes, generating conjugated polymers. Finally, imino-pinacol coupling of imines is mediated by the LVT to provide 1,2-diamines.

Total synthesis of lasofoxifene and nafoxidine

ABSTRACTAn intramolecular reductive coupling process of diketone with low-valent titanium species to form a dihydronapthalene skeleton was an important step in the synthesis of nafoxidine (1) and lasofoxifene (2). Diketone 6 was prepared in a convenient, three-step sequence starting from 3-methoxy benzaldehyde in good yields.

Role of doped titanium species in the enhanced photoelectrochemical properties of iron oxide films: Comparison between water oxidation and iodide ion oxidation

The photoelectrochemical properties of titanium-doped iron(III) oxide (α-Fe2O3, hematite) nanoparticulate thin films are investigated using two photoelectrode reactions, the oxidation of water and iodide ions (I−) to elucidate the role of doped Ti4+ species in the enhanced photocurrent. Increase in the calcination temperature of titanium-doped Fe2O3 thin films from 450°C to 550°C provides significant enhancement in their efficiency for water oxidation to evolve O2, which is four-electron transfer slow reaction. In contrast, such a calcination effect is not remarkable for oxidation of I− to I3−, which is two-electron transfer fast reaction. The electrochemical impedance spectroscopy (EIS) study indicates that the surface reaction rates feature heterogeneity only for water oxidation. This heterogeneity in EIS responses decreased with increasing calcination temperature. This shows that calcination creates photoactive surface sites with doped Ti4+ species especially for kinetically limited water oxidation. Long-lived photoholes might be effectively captured in the vicinity of these sites to suppress surface recombination and induce multi-electron transfer water oxidation.

Influence of silicalite-1 nanoparticle seeds on the synthesis of Ti-containing mesoporous zeolites

Mesostructured titanosilicates (Ti-MS1) possessing zeolitic secondary building units (SBU) can be successfully assembled from Sil-1 nanoparticle seeds. The influence of Sil-1 nanoparticle seeds on the formation of Ti-containing mesoporous zeolites was investigated in detail. The samples were characterized by SEM, XRD, XRF, FT-IR, UV–vis and nitrogen physisorption. The catalytic properties of the materials were examined by phenol and benzene hydroxylation reactions. The results show the amount of Sil-1 seed in the synthesis solution has been found to play a significant role in formation of pure mesostructred materials and catalytic performance. The addition of more Sil-1 nanoparticles could result in a mixture with micro- and mesoporous phases. With the increase of Sil-1 nanoparticles, the mesopore size of Ti-MS1 zeolite becomes smaller, while the wall thickness grows thicker. These mesostructured Ti-MS1 zeolites have TS-1-like titanium species and contain more SBU fragments in the mesoporous walls, which are responsible for the better catalytic activity in hydroxylation reactions and excellent hydrothermal stability in boiling water (over 200h), as compared with conventional mesoporous Ti-MN.

Electron Paramagnetic Resonance Study of the Interaction of Surface Titanium Species with AlR3 Cocatalyst in Supported Ziegler–Natta Catalysts with a Low Titanium Content

The electron paramagnetic resonance (EPR) method was used to investigate the formation of alkylated Ti(III) species in superactive titanium–magnesium catalysts with a low titanium content during their interaction with an organoaluminum activator (AlMe3), as well as the interaction of alkylated Ti(III) surface species with carbon monoxide. EPR data on the content of alkylated Ti(III) species in these catalysts agree well with the number of Ti–R bonds that are determined after the interaction of radioactive carbon monoxide (14CO) with catalyst activated by triethylaluminum in the absence of monomer. Parameters of EPR spectra of the Ti(III) species having different structure and composition on the surface of titanium–magnesium catalysts were calculated by quantum-chemical simulations. The calculated g-values are consistent with the g-values observed in EPR spectra of the catalysts. Analysis of the literature data and results of our study made it possible to propose the parameters of EPR spectra characterizin...