Synthesis Of Titanium Silicalite-1 Research Articles

Synthesis of TS-1 from supported embryonic to nano-/micro-metersized crystalline particles: The impact of accessibility of Ti species on the catalytic performance

This study reports a seeding-polymer-assisted method using inexpensive tetrapropylammonium bromide (TPABr) to synthesize titanium silicalite-1 (TS-1) ranging from supported embryonic (<8 nm) to crystalline nano-/micrometersized (≈0.1–1.0 μm) particles by kinetic regulation. The in situ grown embryonic TS-1 on the amorphous silica presents defective Ti(OH)(OSi)3, tetrahedral framework Ti (“TiO4”), and extraframework Ti (“TiO6”) species, while crystalline nano-/micro-metersized TS-1 particles exhibit either “TiO4” or both “TiO4” and “TiO6” species and a smaller external surface area, Sext. Turnover frequency (TOF) of TS-1 catalysts in the oxidation of dibenzothiophene (DBT) changes by an order of magnitude with the alteration of active Ti species. For instance, the TOF of supported embryonic TS-1 is 224.3 h−1 while it is 32.6 h−1 for the micro-metersized particles due to differences in the active Ti species. However, the TOF of the different TS-1 samples with similar Ti active sites scales only in proportion to Sext. The supported embryonic TS-1 on amorphous silica presents similar structural and chemical stability in comparison with crystalline nano-/micro-metersized TS-1 catalysts under water-free reaction conditions. Consequently, in situ prepared supported embryonic TS-1 combining improved accessibility (via increased external surface area) of different types of Ti species is a promising alternative for the conversion of bulky substrates.

Selective propylene epoxidation by low cost microporous/mesoporous hierarchical Titanium silicalite-1

TS-1 (Titanium silicalite-1) with micro/mesoporous hierarchical framework with regular pores diameter of 3–5 nm has been produced efficiency in a low molar ratio of tetrapropyl ammonium hydroxide/silica (TPAOH/SiO2) by utilizing tetraethyl silicate-40 (TES) as silica source under hydrothermal conditions. For reducing the cost of TS-1 production, TPAOH/SiO2 molar ratio decreased to 0.08 in the presence of non-ionic surfactant. Furthermore, cheaper TES is used instead of tetraethyl orthosilicate (TEOS), which is normally used for industrial synthesis of TS-1. The resulting samples are characterized by XRD, SEM, TEM, FT-IR, UV–Vis spectroscopy and N2 adsorption–desorption. The preparation condition is greatly influenced on TS-1 textural features, particle size, morphology and coordination of titanium species in the structure. Hierarchical TS-1 samples were utilized as catalysts in the propylene epoxidation with hydrogen peroxide in methanol. The catalytic activity was compared with the conventional TS-1.

Synthesis of titanium silicalite-1 (TS-1) zeolite with high content of Ti by a dry gel conversion method using amorphous TiO2–SiO2 composite with highly dispersed Ti species

In this study, we have developed a new method to synthesize mesoporous titanium silicalite-1 (TS-1) with a higher content of active titanium in the framework (more than 5%) than that obtained from the conventional hydrothermal synthesis. The new method combines two methods as follows: (1) a sol-gel method in tetrahydrofuran for the synthesis of TiO2–SiO2 composite with highly dispersed Ti species and (2) a dry gel conversion method for the crystallization to TS-1. This investigation revealed that the dispersion of Ti in the starting materials was quite important to synthesize mesoporous TS-1 with high content of Ti besides dry conversion method. The obtained mesoporous TS-1 with a high content of titanium showed higher catalytic activity in 1-hexene epoxidation than conventional TS-1. This high activity is likely to originate from the high content of titanium in the framework.

Synthesis of Titanium Silicalite-1 with High Catalytic Performance for 1-Butene Epoxidation by Eliminating the Extraframework Ti.

Titanium silicalite-1 (TS-1) with little extraframework Ti was hydrothermally synthesized in a tetrapropylammonium hydroxide system using starch as the additive. The influences of the amount of starch added on the coordination states of titanium ions and the functional mechanism of starch were studied by various characterization means. The addition of starch slowed the crystallization rate of TS-1 so that the insertion rate of titanium to the framework matched well with that of silicon. Therefore, the generation of extraframework Ti, including the anatase TiO2 and octahedrally coordinated titanium, was eliminated. The catalytic performances of the TS-1 samples were evaluated in the epoxidation of 1-butene to produce butene oxide. The catalytic activity of TS-1 was improved significantly due to the increasing amount of framework Ti.

Synthesis and catalytic ammoxidation performance of hierarchical TS-1 prepared by steam-assisted dry gel conversion method: the effect of TPAOH amount

The hierarchical titanium silicalite-1 (TS-1) was synthesized by the steam-assisted dry gel conversion method in one step and characterized by XRD, SEM, N2 adsorption/desorption, UV–Vis, FT-IR, and Raman spectroscopies. And its catalytic activity was tested for ammoxidation of methyl ethyl ketone with hydrogen peroxide as oxidant. The results show that the amount of tetrapropylammonium hydroxide (TPAOH) as template has a major influence on the physicochemical and catalytic properties of the hierarchical TS-1 prepared. When lower amount of TPAOH (TPAOH/SiO2 = 0.08 mol) was used, hierarchical TS-1 can be successfully synthesized. With an increase in TPAOH amount in synthesis solution, the crystal size of TS-1 is decreased and mesoporous surface area is increased; if the excess template was used in the synthesis of TS-1, more extra-framework Ti would be formed in the TS-1 samples prepared. The hierarchical TS-1 exhibits higher catalytic activity than TS-1 prepared hydrothermally for ammoxidation of methyl ethyl ketone. Using hierarchical TS-1 synthesized under TPAOH/SiO2 = 0.18 as the catalyst, which has more tetrahedrally coordinated Ti species in the TS-1 framework, 94.2 % conversion of reactant and 100 % selectivity to methyl ethyl ketone oxime can be obtained after 2 h of reaction at 70 °C.

Effect of sodium ions in synthesis of titanium silicalite-1 on its catalytic performance for cyclohexanone ammoximation

Titanium silicalite-1 (TS-1) has been hydrothermally synthesized with tetrapropylammonium hydroxide (TPAOH) as the template in the presence of various amounts of Na+, characterized by inductively coupled plasma, X-ray diffraction, scanning electron microscope, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy and ultro-violet-visible spectroscopy and studied in cyclohexanone ammoximation. The characterization results show that with the increase of Na+ concentration in the synthesis, both the crystal sizes of TS-1 and extra framework Ti increase but framework Ti decreases. The addition of Na+ below 3 mol-% of TPAOH in the synthesis does not influence the catalytic properties with above 98% conversion of cyclohexanone and 99.5% selectivity to cyclohexanone oxime. However, at the concentrations of Na+⩾3mol-% of TPAOH in the synthesis, the catalysts are deactivated faster with the increase of Na+ addition, which can be attributed to more high molecular weight byproducts deposited in the large TS-1 particles and the loss of the frame-work titanium. The results of this work are of great importance for the industry.

Mechanochemical Assisted Synthesis of Titanium Silicalite-1

Titanium Silicalite-1 (TS-1) zeolite was successfully synthesized through a mechanochemical assisted processing. In this method, an amorphous silica-titania precursor was firstly prepared through a mechanochemical treatment. TS-1 was then synthesized by the hydrothermal treatment of the silica-titania precursor with tetrapropylammonium bromide (TPABr) as the template. The results of the XRD, UV-vis, and FT-IR spectrum indicated that the titanium atom was incorporated into the amorphous silica-titania precursor during the grinding, and was also retained in the final TS-1 framework after the hydrothermal treatment. SEM image showed that the TS-1 appeared in a shape of elongated prism. The catalytic performance of TS-1 was examined by phenol hydroxylation with hydrogen peroxide as the oxidant. The results indicated that TS-1 synthesized by this method exhibited a good activity.

A New Route to Synthesis of Titanium Silicalite-1 by Ball-Milling

Titanium Silicalite-1 (TS-1) was successfully synthesized from amorphous silica and titania powders by using a ball-milling method. In this method, amorphous fumed silica and anatase titania powders were ground in a planetary ball mill to produce a silica-titania precursor. The obtained precursor was then hydrothermally treated where TPABr was used as a template to obtain titanium silicalite-1 (TS-1). The XRD and UV-vis spectra indicate that the titanium in anatase with octahedral coordination is incorporated into the silica-titania precursor and the final TS-1 framework with a tetrahedral coordination. SEM image shows that TS-1 synthesized in this work appears in a shape of elongated prism with a dimension of about 3μm×1μm×0.2μm. This method gives a simple new approach to the synthesis of TS-1 using inexpensive silicon source, titanium source and template.

Synthesis of titanium silicalite-1 with small crystal size by using mother liquor of titanium silicalite-1 as seeds (II): Influence of synthesis conditions on properties of titanium silicalite-1

Titanium silicalite-1 with small crystal size (small-crystal TS-1) was synthesized in a TPABr–ethylamine hydrothermal system by using the mother liquor of nano-sized TS-1 as seeds. The synthesis conditions were systematically studied, including the purification methods of the small-crystal TS-1, Si/Ti molar ratio in TS-1, amount of the added seed and the crystallization period. The as-synthesized TS-1 was characterized by X-ray powder diffraction (XRD), Fourier-transform infrared (FT-IR), Ultraviolet–visible diffuse reflectance (UV–vis), Ultraviolet Raman spectroscopy (UV-Raman), nitrogen sorption, elemental analysis, atomic force microscope (AFM) and scanning electron microscopy (SEM). The size of the TS-1 crystals formed (about 600nm×400nm×250nm) was not significantly affected by the synthesis conditions except for the amount of added seed. The catalytic performance of the synthesized small-crystal TS-1 for the epoxidation of propylene was evaluated. The conversion of hydrogen peroxide, the selectivity of propylene oxide and the utilization of hydrogen peroxide reached 92.2%, 98.0% and 97.0%, respectively, when the mother liquor of small-crystal TS-1 was purified three times by precipitation, the Si/Ti molar ratio was 50, the seed/SiO2 weight ratio was 0.06 and the crystallization time was 48h.

Synthesis of Titanium Silicalite-1 with Small Crystal Size by Using Mother Liquid of Titanium Silicalite-1 As Seed

Titanium silicalite-1 (TS-1) with small crystal size was synthesized in a TPABr-ethylamine system using the mother liquid of nanosized TS-1 as seed. The as-synthesized small-crystal TS-1, the size of which was about 600 nm × 400 nm × 250 nm was characterized with X-ray diffraction (XRD), Fourier transform-infrared (FT-IR), ultraviolet–visible (UV–vis), UV-Raman, N2 sorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Its catalytic performance was evaluated in the epoxidation of propylene and the hydroxylation of phenol. The conversion of hydrogen peroxide and selectivity of propylene oxide (PO) in the propylene epoxidation reached 92 and 98 mol %, respectively. In the hydroxylation of phenol, small-crystal TS-1 also resulted in a high conversion of phenol.

Novel method for synthesis of titanium silicalite-1 (TS-1)

Titanium silicalite-1 (TS-1) was easily synthesized using inorganic silicon and titanium source, tetrapropylammonium bromide (TPABr) or TPAOH as templating molecule, NH3H2O, HDA or TEAOH etc. as base sources. In this system, TPA+ cations (come from TPABr or TPAOH) served as templating agents to direct the MFI structure. NH3H2O, TEAOH or HDA etc. provides the alkalinity necessary for crystallization. X-ray diffraction, UV-Vis, IR spectroscopies, SEM, 29Si MAS NMR showed that the zeolites obtained possessed all the structural characteristics of TS-1, and titanium atoms were introduced into the framework in TS-1. This material was proved to have high crystallinity and high catalytic activity to allyl chloride epoxidation and propylene epoxidation. All the samples synthesized had similar catalytic properties with a standard TS-1 through compared inorganic reactant system with organic synthesis system using propylene epoxidation. The effects of silicon source and TPABr/SiO2 ratio were discussed.

Single-site catalysts and cleaner production processes, the case of TS-1

The synthesis of Titanium Silicalite-1 (TS-1) made possible the development of new oxidation processes, environmentally clean and economically convenient. First industrial application, in 1986, was the hydroxylation of phenol to hydroquinone and catechol (10,000 t/a). In 2003, the production of cyclohexanone oxime became operative within an integrated process for the manufacture of ∈-caprolactam by an entirely new technology (60,000 t/a). The overall process is salt-free and with minimal gaseous emissions. In 2006, the construction of a 300,000 t/a plant for propylene oxide started in Belgium and others have been planned in the world. All three processes utilize hydrogen peroxide produced by the conventional anthraquinone process. Parallel to this, however, an intense research is in progress on the direct synthesis of the oxidant from the elements, to simplify the process and reduce the H2O2 production costs. Other means to achieve the same objectives are process integration, in the short term, andin situ generation, in the longer one. TS-1, on the other hand, will likely remain unrivalled catalyst for many years to come. The metal substituted zeolites, that in last two decades have been prepared in a large number, are catalytically inferior and inadequate to possible industrial applications.

Nanoarchitectured synthesis of TS-1 depending on microwave power

Uniform crystals of titanium silicalite-1 (TS-1) having 1 μm size of diameter were nanoarchitectured to be fibrous-type stacked morphology during microwave synthesis. Nanoarchitectured stacking of TS-1 with MFI structure was demonstrated with different average numbers of stacking layers depending on microwave powers from 360 to 720 W in order to investigate the effect of microwave power for the formation of stacked morphology. All the obtained samples showed well-stacked morphologies but the average numbers of stacking layers were increased with the increase of microwave power. As the power increases, the microwave induced a higher numbers of stacked crystals through the condensation of hydroxyl groups onto the outer surface of crystals due to the role of Ti as a nanoglue.

Synthesis of TS-1 using amorphous SiO 2 and its catalytic properties for hydroxylation of phenol in fixed-bed reactor

Titanium silicalite-1 (TS-1) has been synthesized using amorphous SiO 2 as silicon source and tetrapropylammonium bromide (TPABr) as template. The effects of preparation parameters, such as silicon sources, crystallization temperature and time, aging time, H 2O/SiO 2, SiO 2/TiO 2, TPABr/SiO 2 and n-butylamine (NBA)/SiO 2, and nonionic surfactants on the physicochemical and catalytic properties of TS-1 were investigated in detail. The TS-1 samples were characterized by XRD, FT-IR, UV–vis, SEM, ICP-AES and N 2 adsorption. In the fixed-bed reactor, the catalytic property of TS-1 for the phenol hydroxylation was tested. The studies show that the catalytic performance of TS-1 synthesized using amorphous SiO 2 is close to that of the samples prepared with tetraethyl orthosilicalite (TEOS) for the phenol hydroxylation with H 2O 2. The crystallinity of the sample increases with an increase of the crystallization temperature, crystallization time, the ratio of SiO 2/TiO 2, SiO 2/H 2O and NBA/SiO 2. TS-1 with smaller crystals can be obtained by increasing aging time, H 2O/SiO 2 and NBA/SiO 2, and using the nonionic surfactants. Moreover, adding the nonionic surfactants in the matrix gel can increase the amount of Ti incorporated in framework of zeolite and reduces the amount of TiO 2 in an extra framework.

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.

Synthesis of TS-1 in fluoride medium. A new way to a cheap and efficient catalyst for phenol hydroxylation

Titanium silicalite-1 (TS-1) was synthesized by two different methods in fluoride medium. The preparation of a sol or a gel containing SiOTi bonds prior to fluoride addition is the key step of the synthesis. Characterization of the samples by X-ray diffraction, infrared and diffuse reflectance ultraviolet–visible spectroscopies, and elemental analysis confirms that the titanium species are essentially located in framework positions. The size of the crystals depends on the synthesis variables. In the presence of seeds, small crystallites (<2 μm) are obtained. The corresponding samples exhibit high activity and selectivity for phenol hydroxylation by H 2O 2, similar to TS-1 prepared in the presence of tetrapropylammonium hydroxide.

Synthesis of titanium silicalite-1 using amorphous SiO 2 as silicon source

Titanium-containing silicalite-1 (TS-1) has been synthesized with amorphous silica as silicon source. Two routes have been followed which differ not only in the recipe itself but also in the nature of the titanium alkoxide. Both routes led to the formation of large TS-1 crystals, contrasting with the very small particles usually obtained with tetraethyl orthosilicate. The maximum titanium incorporation did not depend on the synthesis method and was about 2 Ti/unit cell. When samples were synthesized with high Ti concentrations in the gel, the excess of unreacted titanium remained in the solution, and extralattice oxide species were never observed. For comparison, the same experiments performed with colloidal silica led to very irregular and inhomogeneous batches. The crystal size could be decreased significantly by stirring the gel or preceding the crystallization by an aging period at room temperature. In that case, pure TS-1 crystals of about 0.8 μ in size could be obtained after a 3-h crystallization. Critical parameters like the alkalinity or the water content greatly influenced the crystallization process and thus, the morphology of TS-1 crystals. Relatively small crystals could be obtained with concentrated gels, the dilution leading to a considerable increase in the particle size.