Synthesis and characterization of microporous titanosilicate ETS-10 with different titanium precursors

This work was aimed to identify the influence of different titanium sources, namely nano-sized Degussa TiO₂ (commercially known as P25), TiCl₃, TiF₄, and (NH₄)₂F₆Ti, on the crystallization of micropoprous titanosilicate ETS-10. The characterization results of XRD, FESEM, Raman, and FTIR showed that the morphology, particle size, and purity of the final products were strongly dependant on the titanium sources because of the different crystallization mechanisms of ETS-10 in the presence of different titanium precursors. The different coordination states of Ti atoms and anions of the titanium precursors were observed to play a role in the formation of ETS-10.     

Hydrothermal synthesis of aluminum-substituted titanosilicate, ETS-10

One of ETS-10 variants, aluminum-substituted ETAS-10 was successfully synthesized with Al/Ti molar ratio of 0.1–0.4 using different titanium sources, titanium sulfate (Ti(SO₄)₂) and titanium oxysulfate (TiOSO₄). Through the compositional study, like ETS-10, the (Na + K)/Na molar ratio significantly affects the crystallinity and phase purity depending on titanium source. The 2³ factorial designs indicate that the high alkalinity mainly by Na⁺ content is very critical to the crystallization of pure ETAS-10 while the content of K⁺ cation should be carefully controlled. It suggests that the increase in K⁺ content with smaller hydrated radius than of Na⁺ makes the formation of ETAS-10 structure difficult. The optimum composition was chosen and applied to kinetic study. The activation energies for three different stages, nucleation, transition and crystallization were calculated using the modified Avrami–Erofeev equation. This result indicates that the nucleation and transition stage proceed at the similar rate, and then the crystallization stage proceeds with lower activation energy than those of previous two stages. In addition, the temperature dependency on the crystallization was quite significant, favoring high temperature.     

Hydrothermal synthesis of gallium-substituted titanosilicate,ETGS-10

One of ETS-10 (Engelhard titanosilicate materials number 10) variants, ETGS-10 was successfully synthesized within limited Ga/Ti molar ratio of 0.1–0.3 using sodium silicate and titanium oxysulfate (TiOSO₄) as silica and titanium sources. Like ETS-10 and ETAS-10, the (Na + K)/Na molar ratio has significant effect on the crystallinity and especially purity of final product. The 2³ factorial methods suggest that the effect of alkalinity on the crystallinity is the most significant for the crystallization of pure ETGS-10. The activation energies calculated from kinetic study also suggest that once nuclei are formed, the transition and crystallization stages of ETGS-10 tend to proceed at a similar rate. Finally, ²⁹Si- and ⁷¹Ga-MAS NMR studies clearly indicate that Ga has been isomorphously substituted for Si tetrahedral site.     

高结晶度ETS-10分子筛的合成与表征

采用水热合成法成功合成出高结晶度ETS-10分子筛。通过XRD、N2吸附-脱附、FTIR、SEM和NMR等方法对样品进行了表征,并考察了不同合成条件对ETS-10分子筛结晶度的影响。结果表明,碱度、硅钛比、晶化时间对分子筛结晶度影响显著。在分子筛制备过程中,钛溶解分散于凝胶体系,并在晶化过程中完全进入分子筛形成Si-O-Ti骨架结构,是合成高结晶度ETS-10分子筛的关键。制备的ETS-10分子筛晶粒形状规整,比表面积高,无杂晶相,具有高的结晶度。     

Effect of crystallization temperature on the synthesis of ETS-4 and ETS-10 titanosilicates

The effect of temperature on the crystallization and purity of (Na,K)-ETS-4 and (Na,K)-ETS-10 from gels with an optimized composition was examined. Microporous titano silicates (Na,K)-ETS-4 and (Na,K)-ETS-10 were obtained by hydrothermal synthesis from gels of molar composition 5x.Na₂O: 3KF: TiO₂: 6.4x.HCl: 7.45SiO₂: 197.5 H₂O where x = 2.0 for ETS-4 and x = 1.0 for ETS-10 in absence of seeds and organic template agents. The kinetics of crystallization at 160, 180 and 200 °C, respectively, by comparing gel crystallinity (%) at different times, the induction times and the apparent activation energies for nucleation and crystallization were studied. The induction time (linked to the formation of the first nuclei) suggests that the nucleation is more difficult in the case of ETS-10 and the crystal growth rates are similar at higher temperatures (>180 °C). The apparent activation energies are smaller for the (Na,K)-ETS-4 (a stable structure) crystallization than of (Na,K)-ETS-10 (a metastable structure). The characterization of these microporous materials was carried out by XRD, SEM and TGA-DSC techniques.     

Hydrothermal conversion of ETS-10 to TS-1

Titanium silicalite-1 (TS-1) was hydrothermally using ETS-10 as a dual source of silicon and titanium after acid and calcination treatment. The conversion process was monitored by XRD, SEM, UV–Vis and FT-IR spectra. Catalytic performance of the prepared TS-1 catalyst was tested by 1-hexene epoxidation using H₂O₂ as oxidant, which established that the TS-1 converted from ETS-10 has essentially identical physicochemical properties to those of conventional TS-1 prepared using pure alkoxide precursors.     

Kinetic and thermodynamic effects during the adsorption of heavy metals on ETS-4 and ETS-10 microporous materials

ETS-10 and ETS-4 microporous materials were synthesized in presence of tetralkylammonium (TAA) ions from gels of molar composition w Na₂O–0.10 TAABr–1 SiO₂–z TiO₂–0.6 KF–1.28 w HCl–39.5 H₂O with TAA = tetramethyl-, tetraethyl-, tetrapropyl- and tetrabutyl-ammonium in hydrothermal conditions at 190 °C. The TAA ions enter the microporous channel of ETS-10, while they cannot penetrate the void spaces of ETS-4. The ETS-10 microcrystals are all cubic, while the ETS-4 crystals are laminar and irregular. The microporous volume of ETS-10 is equal to 0.11–0.13 cm³ g^?1, the microporous volume of ETS-4 is very small, 0.002–0.008 cm³ g^?1. The ion exchange of Cs⁺, Cd⁺⁺, Pb⁺⁺ and Hg⁺⁺ ions using their corresponding nitrates show kinetic effects, i.e. the efficiency of ion exchange is higher at 1 than 2 h, the thermodynamic equilibrium. For ETS-10, partially dehydrated cations intervene in the ion exchange, while for ETS-4 well dehydrated ions can only penetrate the available pores.     

Some New Features on Synthesis of Titanium Silicalite-1 in a Non-TPAOH Inorganic Reactant Synthetic System

Various effects on the synthesis of titanium silicalite-1 (TS-1) were discussed in the non-TPAOH (tetrapropyl ammonium hydroxide) inorganic reactant synthesis system, in which cheap colloidal silica and TiCl₃ aqueous solution, TiCl₄ were used as the silicon and titanium sources, respectively, TPABr (tetrapropyl ammonium bromide) as the template reagent, and weak organic bases as the base source to provide the alkalinity needed for crystallization. The influence of diverse synthesis parameters such as different base sources, SiO₂/TiO₂ ratio, silicon source, titanium source, amounts of template, N₂ protection, seed crystals, aging period, amount of water, crystallization temperature, and crystallization time have been investigated in detail.     

Silica–Titania mixed Oxides: Si–O–Ti Connectivity, Coordination of Titanium, and Surface Acidic Properties

A series of SiO₂–TiO₂ mixed oxides was prepared by the sol–gel route, and the influence of several important preparation parameters (Ti precursors, content, and calcination temperature) on the Si–O–Ti connectivity, coordination of titanium and surface acidity has been studied using various analytical techniques. The solids obtained were largely amorphous and characterized by Ti enrichment on surfaces with low titanium content; however, the addition of titanium greater than 50 mol% into the SiO₂ matrix led to significant phase separation of crystalline anatase. The Ti atoms are tetrahedrally coordinated with Si/Ti ratios higher than 10 and gradually enter into octahedral positions in the silica matrix with further increase in the titanium content. High-temperature treatment can break Si–O–Ti linkages and eliminate hydroxyl groups, resulting in a decrease in acid site density.     

Microwave assisted synthesis of ETS-10

Engelhard Titanium Silicate-10 (ETS-10) has attracted interest for gas adsorption, catalysis, separations and ion-exchange. The practical application of ETS-10 would benefit from improvements in the synthesis. In this paper we present a 30 h microwave assisted synthesis at 230 °C which can be compared with the 72 h required by conventional heating. The effects of different titanium precursors, pH, heating time, and organic templates on ETS-10 were also investigated.     

Photocatalytic conversion of NO using TiO2–NH3 catalysts in ambient air environment

Photocatalytic conversion of nitric oxide (NO) in ambient air was studied in a continuous-flow photoreactor system at room temperature using different TiO₂ catalysts prepared with different titanium precursors of Ti(SO₄)₂, TiOSO₄, and Ti(O-Bu)₄ by either a moderate-temperature hydrothermal process or a hydrothermal reflux process. The physicochemical properties of the prepared catalysts were characterized by XRD, BET, FTIR, and SEM. Analytical results showed that the crystallinity, morphology, nitrogen adsorption–desorption isotherms, specific surface area, and pore size distribution of catalysts were significantly affected by the precursors and hydrothermal processes, but the crystal structure and crystal size of catalysts were not significantly influenced. The NO conversion experiments demonstrated that the TiO₂ catalysts prepared by the moderate-temperature hydrothermal process without ammonia pretreatment could effectively reduce NO to different low levels, in which the catalysts with longer aging time of more than 12 h performed better than the catalysts with shorter aging time. However, it was found that the NO₂ concentration in outlet gas was gradually increased with extension of an experimental period. Two TiO₂ catalysts (TOSO-NH₃ and TOB-NH₃) prepared by the hydrothermal reflux process with ammonia pretreatment demonstrated a very good performance in NO conversion and also maintained a low level of NO₂ concentration in outlet gas. This study indicated that using the TiO₂ catalysts modified with ammonia pretreatment in photocatalytic reaction could provide a good approach to effectively eliminate the accumulation of NO₂ product from NO oxidation in the system and to achieve a sustainable process, which may be applicable for NO elimination in ambient air environment.     

Origin of ohmic losses at Co3O4/Ti electrodes

Co₃O₄/Ti and NiCo₂O₄/Ti electrodes were prepared in different ways to investigate the origin of the ohmic losses observed experimentally. In particular, titanium was pretreated in various ways including etching with a HF mixture, and reduction by cathodic hydrogen discharge prior to coating. Different types of commercial titanium and different concentrations of the precursors in solution were also tried. Some electrodes were prepared with a RuO₂ interlayer. Nickel and mild steel were also used as supports. Parameters to quantify the ohmic losses were the peak distance in voltammetric curves, and the initial slope and the deviation from linearity of current vs sweep rate plots. The experimental picture corroborates the view that the main component of the ohmic drop comes from the insulating barrier which forms at the support/oxide layer interface. The intrinsic conductivity of spinels does not appear to represent the main problem for thermal layers as usually prepared.Author to whom correspondence should be addressed.     

Study on Ti-MCM-41 zeolites prepared with inorganic Ti sources: Synthesis,characterization and catalysis

A novel method for preparing Ti-MCM-41 has been developed. A series of Ti-MCM-41 have been synthesized with different inorganic titanium salts as Ti sources and characterized by XRD, N₂ adsorption, FT-IR and UV–Vis spectroscopy. The hydrolysis rate of inorganic titanium salts was decreased by adding coordination agent to avoid the formation of TiO₂. The characterization results show that most Ti⁴⁺ are isolated and tetrahedrally incorporated into the framework of MCM-41. The nature of inorganic titanium salts has a considerable influence upon the incorporation of Ti into the silica framework.     

钛硅分子筛ETS-10的合成和表征

以硅酸钠溶胶、硫酸钛为起始原料,在含KF碱性水热体系中制备出ETS-10钛硅酸盐分子筛;考察了原料的配比、晶化时间与温度对ETS-10合成的影响。应用XRD、SEM、EDX、FTIR和N2吸附技术表征了合成的ETS-10的结构和物性。结果表明,用组成为n(SiO2)∶n(TiO2)∶n(Na2O)∶n(KF)∶n(H2O)=7.5∶1.0∶5.0∶3.0∶198的凝胶,在463K(48h)和无模板剂的条件下,合成出结晶度良好的ETS-10。ETS-10晶体具有规则的四方切角锥形晶貌和微孔性质,比表面积和孔容分别为383.75cm2/g和0.16cm3/g;典型样品的化学组成接近已知的ETS-10组成表达式(Na,K)2TiSi5O13.4H2O。     

Separation of a binary mixture of ethylene and ethane by adsorption on Na-ETS-10

Ethylene produced by steam cracking and thermal decomposition of ethane must be purified prior to use in the production of plastics, rubber and films. Ethane–ethylene separation is generally achieved by cryodistillation. The energy and equipment costs associated with ethylene purification could be significantly reduced by the development of alternative separation methods. Both modelling predictions for the binary adsorption of ethylene and ethane, and recent work investigating the adsorption of ethane and ethylene on the surface of Engelhard Titanosilicate-10 (ETS-10), a large-pored, mixed octahedral/tetrahedral titanium silicate molecular sieve, indicate that this molecular sieve might be an adsorbent capable of ethylene/ethane separations. However, the actual separation of a binary mixture of ethylene and ethane on ETS-10 has yet to be demonstrated. In this work, Na-ETS-10 was used to separate a mixture of ethylene and ethane (59% C₂H₄, 41% C₂H₆) from an industrial process stream with a measured binary bed selectivity for ethylene over ethane of approximately 5 at 25 °C and 1 atm. In a laboratory-scale demonstration, both high purity ethane and significantly enriched ethylene were produced, and the Na-ETS-10 adsorbent was regenerated for further separation cycles by both steam and microwave desorption, without degradation of the adsorbent or products.     

Vibrational spectroscopic evidence for the presence of TiO6 structural units in titanosilicate molecular sieve ETS-10

A comparison of infrared and Raman spectra of a titanosilicate molecular sieve ETS-10 with literature data on titanium-containing ZSM-5 (TS-1) and perovskite SrTiO₃, provides conclusive evidence for the presence of intraframework TiO₆, octahedral units in ETS-10. The appearance of a very strong band at 723 cm¹ in the Raman spectrum of ETS-10 suggests that the technique can be useful for the characterization of molecular sieves containing TiO₆ structural units.     

Crystalline phase of TiO2 nanotube arrays on Ti–35Nb–4Zr alloy: Surface roughness,electrochemical behavior and cellular response

An investigation was made into the electrochemical, structural and biological properties of self-organized amorphous and anatase/rutile titanium dioxide (TiO₂) nanotubes deposited on Ti–35Nb–4Zr alloy through anodization-induced surface modification. The surface of as-anodized and heat-treated TiO₂ nanotubes was analyzed by field emission scanning electron microscopy (FE-SEM), revealing morphological parameters such as tube diameter, wall thickness and cross-sectional length. Glancing angle X-ray diffraction (GAXRD) was employed to identify the structural phases of titanium dioxide, while atomic force microscopy (AFM) was used to measure surface roughness associated with cell interaction properties. The electrochemical stability of TiO₂ was examined by electrochemical impedance spectroscopy (EIS) and the results obtained were correlated with the microstructural characterization. The in vitro bioactivity of as-anodized and crystallized TiO₂ nanotubes was also analyzed as a function of the presence of different TiO₂ polymorphic phases. The results indicated that anatase TiO₂ showed higher surface corrosion resistance and greater cell viability than amorphous TiO₂, confirming that TiO₂ nanotube crystallization plays an important role in the material's electrochemical behavior and biocompatibility.     

Influence of internal diffusion barriers on carbon diffusion in pure titanium and Ti–6Al–4V during diamond deposition

Diamond coatings were deposited on pure titanium and Ti–6Al–4V, at a temperature in the range of 600–750 °C, in a microwave plasma from CH₄/H₂ and CO/H₂ mixtures. The influence on carbon diffusion of different intermediate layers, especially tungsten, niobium, titanium nitride and pure titanium previously deposited on titanium alloys by physical vapor deposition (PVD) is reported. These intermediate layers are always composed of at least two sub-layers: (1) an internal diffusion barrier and (2) an external titanium layer that allows some carbon diffusion to be maintained. After diamond deposition, X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) observations coupled with energy-dispersive X-ray (EDX) analysis of the final multilayer systems allow us to determine the diffracting phases, their lattice parameters and the efficiency of the different barriers. The carbon diffusion coefficients in the titanium carbide phase and in the α-titanium solid solution are deduced from an experimental study carried out on pure titanium with or without an underlying diffusion barrier. The results are compared to the carbon diffusion in Ti–6Al–4V alloy. This work permitted us to calculate the carbon concentration profiles in both pure titanium and Ti–6Al–4V substrates.     

Adsorption of carbon dioxide and water vapor on fly-ash based ETS-10

CO₂ capture from humid flue gas is always costly due to the irreplaceable pretreatment of dehydration in current processes, which creates an urgent demand for moisture-insensitive adsorbents with considerable CO₂ uptakes as well as remarkable H₂O tolerances. In the present work, the microporous titanium silicate molecular sieve ETS-10 was synthesized with coal fly ash as the only silica source. The as-synthesized ETS-10 was characterized by X-ray diffraction, scanning electronic microscopy and infrared spectroscopy to verify its crystal morphology, in which neither impurity nor aggregation was observed. The following CO₂ adsorption experiments on the thermal gravimetric analyzer demonstrated its similar CO₂ adsorption capacity yet dramatical adsorption kinetics among some other microporous materials, e.g., potassium chabazite. These specific properties consequently guaranteed its favorable CO₂ adsorption capacity even at high temperatures (1.35 mmol/g at 393 K) and shortened the breakthrough time of single CO₂ flow to less than 20 s. In CO₂/H₂O binary breakthrough experiments, the as-obtained ETS-10 still maintained excellent CO₂ uptake of 0.81 mmol/g at 323 K, regardless of the presence of water vapor, making it a promising substitute for direct CO₂ separation from humid flue gases at practical conditions of post-combustion adsorption.     

Characterization of Ti/Si binary oxides prepared by the sol-gel method and their photocatalytic properties: The hydrogenation and hydrogenolysis of CH3CCH with H2O

Titanium-silicon (Ti/Si) binary oxides having different Ti content were prepared by the sol-gel method and utilized as photocatalysts for the hydrogenation and hydrogenolysis of CH₂CCH with H₂O. The photocatalytic reactivity and selectivity of these catalysts were investigated as a function of the Ti content and it was found that the hydrogenolysis reaction (C₂H₆ formation) was predominant in regions of low Ti content, while the hydrogenation reaction (C₃H₆ formation) proceeded in regions of high Ti content. The in situ photoluminescence, diffuse reflectance absorption, FT-IR, XAFS (XANES and EXAFS), and XPS spectroscopic investigations of these Ti/Si binary oxides indicated that the titanium oxide species are highly dispersed in the SiO₂ matrices and exist in a tetrahedral coordination exhibiting a characteristic photoluminescence spectrum. The charge transfer excited state of the tetrahedrally coordinated titanium oxide species plays a significant role in the efficient photoreaction with a high selectivity for the hydrogenolysis of CH₃CCH to produces mainly C₂H₆ and CH₄, while the catalysts involving the aggregated octahedrally coordinated titanium oxide species show a high selectivity for the hydrogenation of CH₃CCH to produce C₃H₆, being similar to reactions of the powdered TiO₂ catalysts. The good parallel relationship between the yield of the photoluminescence and the specific photocatalytic reactivity of the Ti/Si binary oxides as a function of the Ti content clearly indicates that the high photocatalytic reactivity of the Ti/Si binary oxides having low Ti content is associated with the high reactivity of the charge transfer excited state of the isolated titanium oxide species in tetrahedral coordination, [Ti³⁺-O⁻]*.