Framework Titanium Research Articles

Synthesis of titanium silicalite-1 supported zinc catalysts for efficient and clean epoxidation of 1-hexene and methyl oleate

To improve the catalytic epoxidation activity of conventional TS-1 zeolite under acid-free conditions, a series of TS-1-supported zinc (xZn/TS-1) catalysts were prepared and evaluated in the epoxidation of 1-hexene and methyl oleate (MO) with H2O2 oxidant. The microstructure of xZn/TS-1 was investigated using various characterization techniques, and the results showed that the introduction of Zn species was not only well dispersed on the surface of TS-1 but also did not disrupt the crystal structure of TS-1 and tetrahedral framework titanium. Furthermore, the Ti-O-Zn structure can be formed between Zn and Ti species through O-atomic coordination, which improves the vulnerability of the Ti-O bond to attack the H2O2 molecule, and ultimately facilitates the epoxidation reaction between 1-hexene and MO. In addition, the 2% Zn/TS-1 catalysts showed optimal conversions of 45.7 % and 75.41 % for 1-hexene and MO, respectively, and exhibited good catalytic stability and regeneration during the epoxidation process.

Variation in Metal-Support Interaction with TiO2 Loading and Synthesis Conditions for Pt-Ti/SBA-15 Active Catalysts in Methane Combustion.

The control of catalytic performance using synthesis conditions is one of the main goals of catalytic research. Two series of Pt-Ti/SBA-15 catalysts with different TiO2 percentages (n = 1, 5, 10, 30 wt.%) were obtained from tetrabutylorthotitanate (TBOT) and peroxotitanate (PT), as titania precursors and Pt impregnation. The obtained catalysts were characterized using X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), N2 sorption, Raman, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), hydrogen temperature-programmed reduction (H2-TPR) and H2-chemisorption measurements. Raman spectroscopy showed framework titanium species in low TiO2 loading samples. The anatase phase was evidenced for samples with higher titania loading, obtained from TBOT, and a mixture of rutile and anatase for those synthesized by PT. The rutile phase prevails in rich TiO2 catalysts obtained from PT. Variable concentrations of Pt0 as a result of the stronger interaction of PtO with anatase and the weaker interaction with rutile were depicted using XPS. TiO2 loading and precursors influenced the concentration of Pt species, while the effect on Pt nanoparticles' size and uniform distribution on support was insignificant. The Pt/PtO ratio and their concentration on the surface were the result of strong metal-support interaction, and this influenced catalytic performance in the complete oxidation of methane at a low temperature. The highest conversion was obtained for sample prepared from PT with 30% TiO2.

Two-step synthesis of Ti-rich surface TS-1 with controllable microenvironment of titanium species

It is significant to improve the catalytic activity of TS-1 by increasing the content of framework titanium and enhancing the accessibility of active titanium sites. However, developing a simple and economical strategy for modulating the coordination environments and the spatial distribution of titanium species is still a challenge. Here, we constructed anatase-free TS-1 with abundant framework titanium species and Ti-rich surface by a simple two-step crystallization strategy. The effects of the crystallization temperature and time of the first stage on the properties of zeolite have been investigated in detail. The TS-1 with a Ti-rich surface showed a higher conversion of phenol and selectivity to dihydroxylbenzene in phenol hydroxylation reaction compared with traditional TS-1, and it still remained the superior catalytic performance after five cycles. The novel strategy will provide a new perspective for the construction of TS-1 with controllable active Ti species.

Charge transformation of framework titanium (Ⅳ) into titanium (Ⅲ) in vanadium-titanium doped MFI zeolite for enhanced alkene epoxidation

Simultaneous insertion of double heteroatom in the MFI framework generally gives rise to synergistic catalysis effect, however the specific origins for synergistic catalysis is still nebulous. In this study, vanadium-titanium doped MFI zeolite was synthesized via one-pot hydrothermal synthesis with the addition of (NH4)2CO3 and applied as heterogeneous catalyst for the synergistic catalysis of 1-hexene and cyclohexene epoxidation. Simultaneous incorporation of vanadium and titanium induced the partial charge transformation of titanium (Ⅳ) into titanium (Ⅲ), which was verified by EPR and XPS characterizations. UV-Raman and UV–Vis spectra disclosed that partial charge transformation mainly occurred for framework titanium (Ⅳ). In addition, simultaneous insertion of vanadium and titanium gave rise to more Lewis acid sites as well as larger external surface area for VTS(0.15) zeolite in comparison to VS(0.15) and TS(0.15) zeolite. The prepared VTS(0.15) zeolite presented a TOF value of 118.8 h−1 for 1-hexene epoxidation, which is 7.8 folds and 1.3 folds of VS(0.15) and TS(0.15) respectively. Partial charge transformation of framework titanium (Ⅳ) into titanium (Ⅲ), robust Lewis acid sites as large external surface area may induce the synergistic catalysis effect for VTS(0.15) zeolite in the epoxidation reactions. Moreover, the obtained VTS(0.15) zeolite particles showed good reusability for more than five cycles.

Efficient and clean epoxidation of methyl oleate to epoxidized methyl oleate catalyzed by external surface of TS-1 supported molybdenum catalysts

Methyl oleate (MO) macromolecules are unable to access the microporous channel of conventional titanium silicalite-1 (TS-1) zeolite, which leads to the low catalytic activity of epoxidation of MO. Herein, the small-size TS-1 (TS-1-s) zeolite with a large surface area was synthesized successfully through steam-assisted crystallization, and then a novel blocked TS-1-s supported molybdenum (Mo/TS-1-bs) catalysts were prepared for efficient epoxidation of MO with clean H 2 O 2 to produce epoxidized methyl oleate (EMO). Various characterization results show the introduced Mo species are highly dispersed on the outer surface of TS-1-s without destroying the structure of the MFI type zeolite and the tetrahedral framework titanium (Ti 4+ ). Interestingly, a large number of Mo 6+ species exhibit certain epoxidation activity attributing to the generating of electrophilic molybdenum hydroperoxide (Mo–OOH) species via Mo species combined with H 2 O 2 , which could adsorb and react easily with MO molecules. Furthermore, the Mo species are also coordinated with Ti 4+ species through the O atom resulting in the facile attack of the Ti–O bonds by H 2 O 2 and easy to form an active intermediate. Therefore, compared with the conventional TS-1, the Mo/TS-1-bs shows higher catalytic activity in the epoxidation reaction. However, the acidity of Mo/TS-1-bs catalysts increases with increasing the Mo-loading owing to the formation of Lewis acid, which leads to the side reactions and the decrease of EMO selectivity. As a consequence, the efficient, non-corrosive and green catalytic system for epoxidation of MO was developed, and the activity improvement of Mo species and the influence of acid were also demonstrated. • The clean small-size TS-1 and Mo/TS-1-bs catalysts were prepared successfully for epoxidation of methyl oleate (MO). • Mo species can promote the MO epoxidation through generating of molybdenum hydroperoxide and coordination with Ti 4+ . • The acidity of Mo/TS-1-bs catalysts can decrease the selectivity of epoxidized methyl oleate.

Insight into the effect of mass transfer channels and intrinsic reactivity in titanium silicalite catalyst for one-step epoxidation of propylene

One-step epoxidation of propylene to propylene oxide (PO) in TS-1/H2O2 system is a promising green and sustainable formation route. However, the TS-1 catalyst is limited by the small pore channels and inadequate intrinsic reactivity. Herein, tetrapropylammonium hydroxide (TPAOH) is used to modify the TS-1 skeleton structures to improve the mass transfer and intrinsic reactivity. Comparative catalytic performance tests indicate that the optimized temperature for TPAOH treatment to modify TS-1 was 90 °C, and the achieved H2O2 utilization efficiency and the PO selectivity can be over 80%. Different TPAOH treatment temperatures significantly influenced the dissolution and recrystallization behavior of TS-1, which altered the composition and microstructure in terms of the pore volume and size, surface properties, and active sites. Our findings indicated that the enlarged pore channels for favorable mass transfer, improved hydrophobic surfaces, enriched framework titanium, and reduced acid strength of titanium silicalite zeolite should be the primary reasons for the enhanced conversion and yields.

Charge Transformation of Framework Titanium (IV) into Titanium (Iii) in Vanadium-Titanium Doped Mfi Zeolite for Synergistic Catalysis of Alkene Epoxidation

Charge Transformation of Framework Titanium (IV) into Titanium (Iii) in Vanadium-Titanium Doped Mfi Zeolite for Synergistic Catalysis of Alkene Epoxidation

The silanization process for the hydrothermal synthesis of hierarchical titanium silicalite-1

The silanization is an important approach for hierarchical zeolite preparation. Although the influences of the silanization conditions have been detailed studied, the differences in the reactivity of the zeolite precursor should further be analyzed. In this paper, hierarchical titanium silicalite-1 (HTS) was prepared with trimethoxy[3-(phenylamino)propyl]silane (TMPAPS) under the nTMPAPS:nSi = 0.04–0.20 and nTi:nSi = 0.005–0.04 conditions, the changes of the corresponding physicochemical properties were analyzed, and the influences of the condensation activities between silicon/titanium to the organosialne were deduced and verified by density functional theory (DFT) calculations. Generally, more supermicropores and mesopores can be created in the metastable sponge-like HTS crystals with higher TMPAPS and titanium contents. In comparison, the free energy barrier in the condensation reaction with titanium (1.31 eV) is lower than silicon (1.55 eV), it's preferential to prepare HTS with more intracrystalline secondary porosity by increasing the nTi:nSi. More importantly, the titanium can be isolated by the organosilane, and HTS with more framework titanium can be synthesized by silanization.

Synthesis of Low Cost Titanium Silicalite-1 Zeolite for Highly Efficient Propylene Epoxidation.

Developing an effective and low-cost system to synthesize titanium silicalite-1 (TS-1) zeolite is desirable for a range of industrial applications. To date, the poor catalytic activity of the synthesized zeolite due to the low amount of framework titanium and large crystal size is the main obstacle limiting the widespread application of this material. Moreover, a large amount of wastewater is often produced by the existing synthesis process. Herein, a green and sustainable route for synthesizing small-crystal TS-1 with a high fraction of framework Ti was demonstrated via a seed-assisted method using a tetrapropylammonium bromide (TPABr)-ethanolamine hydrothermal system. The influence of the synthesis conditions on the physicochemical properties and catalytic activities of TS-1 was investigated. With the assistance of nanosized S-1 seeds, the incorporation of Ti into the framework of TS-1 was promoted, and the crystallization rate was effectively accelerated. After alkaline etching, the obtained hierarchical TS-1 had higher catalytic activity towards propylene epoxidation with an extremely high turnover frequency of 1,650 h−1. Furthermore, the mother liquid during the hydrothermal reaction could be reused for the next synthesis procedure. Consequently, utilization ratios of both ethanolamine and TPABr exceeding 95% were achieved by recycling the mother liquid. This low-cost approach for reducing wastewater could be easily scaled up to provide a promising synthesis method for the industrial production of TS-1 and other topological zeolites.

Covalent Organic Framework-Titanium Oxide Nanocomposite for Enhanced Sonodynamic Therapy.

Sonodynamic therapy (SDT) has attracted wide attention for its high tissue-penetration depth capacity. However, developing new kinds of sonosensitizers that are capable of generating large amounts of reactive oxygen species (ROS) still remains a challenge. Herein, covalent organic framework-titanium oxide nanoparticles (COF-TiO2 NPs) were successfully synthesized by using COF as a template. Under ultrasound (US) irradiation, large quantities of ROS can be generated, and compared with pure TiO2 NPs, the SDT performance of COF-TiO2 nanoparticles was significantly improved due to the narrower band gap. Both in vitro and in vivo experiments demonstrated the great tumor inhibitory effect via COF-TiO2-mediated SDT. This work broadens the biomedical applications of COF-based composites.

Insight into the formation of framework titanium species during acid treatment of MWW-type titanosilicate and the effect of framework titanium state on olefin epoxidation

Acid treatment before calcination is indispensable for MWW-type titanosilicate to achieve excellent catalytic performance. Our previous study indicated that not only about half of the absolutely dominant low active non-framework TiO 6 species in as-synthesized B–Ti-MWW zeolite was removed but also the other part was transformed into high active framework TiO 4 species by acid treatment. However, it is still not very clear about the transformation mechanism of titanium species and the state of formed framework TiO 4 species during acid treatment, which significantly affects the catalytic performance. Herein, based on the elaborate experimental design/implementation and structural characterizations including UV Raman spectroscopy excited at 244 nm, 11 B MAS NMR, 29 Si MAS NMR and FT-IR spectroscopy, etc., the underlying transformation mechanism of low active non-framework TiO 6 species into high active framework TiO 4 species during acid treatment of as-synthesized B–Ti-MWW zeolite has been studied in depth and revealed as deboration-based titanium incorporation into MWW framework. Specifically, titanium incorporation was almost simultaneous with deboronation, which was unexpectedly nearly accomplished at the very early stage of acid treatment. Moreover, the newly formed framework TiO 4 species was almost inactive in epoxidation of 1-hexene. Encouragingly, with the gradual increase of acid-treated time, the state of framework TiO 4 species gradually became favorable and the catalytic performance in 1-hexene epoxidation was improved significantly. This study further deepens the understanding of B–Ti-MWW zeolite and would be beneficial for developing titanosilicate zeolites with high catalytic performance. • The evolution of titanium species during acid treatment of as-synthesized B–Ti-MWW zeolite has been studied in detail. • The underlying transformation mechanism of titanium species has been revealed as deboration-based titanium incorporation. • Low active framework TiO 4 species was formed at the very early stage of acid treatment. • The state of formed framework TiO 4 species gradually became favorable, resulting in attractive catalytic performance.

Single-crystalline hierarchically-porous TS-1 zeolite catalysts via a solid-phase transformation mechanism

Abstract Hierarchically porous zeolites are a type of very hot catalyst with improved catalytic performances as compared with conventional microporous-only zeolites due to the improved mass transportation among the hierarchical meso/macropores, which are expected to be the next-generation catalysts for conversion of bulky molecules and/or polymers. Moreover, hierarchical zeolites with the single crystalline structure that is an identical registry of micropores within the entire particle identified the less pore blockage and less diffusion limitation compared to an aggregated structure of nano-zeolites. The developed synthetic methods were mostly conducted in a liquid-phase system and usually required expensive additives, such as silanes or mesoporogons, etc. Finding facile and cost-effective synthetic methods have been still challenging. Here, a facile and cost-effective strategy by controlling the growth/crystallization in a solidified hydrogel system was reported for the synthesis of Ti-containing MFI-type zeolites (TS-1) to simultaneously achieve hierarchical porosity, single-crystalline structure, and high catalytic performance in alkene oxidations. The synthesized zeolites were characterized by XRD, SEM, TEM, Nitrogen adsorption analysis, DRUV spectroscopy, IR spectroscopy, etc. The growth processes were also tracked and well-characterized. It was found that the solid-phase transformation mechanism was dominated for forming the hierarchical structure. This strategy could directly produce TS-1 with abundant intracrystalline continuous mesopores and large amounts of active framework titanium species, contributing to higher activity for epoxidation of alkenes compared to the traditional microporous-only TS-1 zeolites.

Efficient elimination behavior and mechanism of heavy metal by eco-friendly potassium titanium trisilicate

Frame structural material holds great potential for adsorption but challenging for stable in harsh aqueous medium. Herein, a framework potassium titanium silicate K2TiSi3O9•H2O with wide acid durability is used for heavy metal purification and shows excellent performance. The adsorption capacity of K2TiSi3O9•H2O reaches maximum 221 and 123 mg/g towards Pb2+ and Cd2+ at room temperature. The residual Pb2+ concentration holds at 0.0006 mg/L that is far below the limits in drinking water, and the removal efficiency of Pb2+ (10–200 mg/L) still remains 60–73% even at strong acid solution. The readily exchanging K sites in K2TiSi3O9•H2O framework and abundant deprotonated hydroxyl groups afford the rapid adsorption rate and large uptake capacity. A large separation factor (102–103) between competitive Na/Ca and heavy metal ions demonstrates this good selectivity. The removal rate of K2TiSi3O9•H2O maintains 85% even after five cycles, indicating its good reproducibility. K2TiSi3O9•H2O is also extendable to cationic dye removal with a capacity of 45.6 mg/g. This work provides this kind of framework titanium silicates with great structural and crystal stability for the high-efficient and massive elimination of heavy metals.

Facile photoinduced pH-adjusting synthesis of high amount framework Ti-containing meso-silica catalyst for cyclohexane oxidation

Here, we report a facile photoinduced pH-adjusting method to prepare highly-active Ti-containing mesoporous silica catalysts (PIMTS) for cyclohexane oxidation, featuring high amounts of framework titanium species (Ti ca. 2.92 mol%) with uniform tetrahedral coordination state. Ordered meso-structure and framework substitutions of titanium are evidenced by a set of mutually complementary characterizations, catalytic tests and item-by-item comparisons with the hydrothermal crystallized counterparts (Ti-SBA-15). PIMTS acts as an efficient catalyst for cyclohexane oxidation, leading to the maximum KA oil TOF up to 393 min−1 when cyclohexane conversion is 49.9%.

Regulation of framework titanium siting in MWW-type titanosilicates by boron and aluminum incorporation and its effect on the catalytic performance

Abstract The exploration of efficient catalysts with more accessible active titanium species based on the titanosilicate zeolites is in incremental demands for the construction of the high utilization active centers to the various reactions. Here, we report an active oxidation catalyst MWW-type titanosilicate (Al-Ti-MWW) with more “Ti” active species distributed on the zeolite surface obtained through the implantation of the heteroatom aluminum to the conventional Ti-MWW synthesis. Combined with the overall measurements, it was deduced that more “Ti” species were regulated to evenly distributed in the zeolite crystal, which was due to the competitive occupancy of the heteroatom Al, B and Ti over T locations. Consequently, the bulky-substrate reaction results such as the cyclohexene epoxidation reaction and cyclohexanone ammoximation reaction showed that the Al-Ti-MWW catalyst had a superior catalytic oxidation activity than that of conventional Ti-MWW. It is believed that the application of the convenient treatment method could provide an effective strategy for designing high-performance titanosilicate catalysts.

Direct Synthesis of Ti-Containing CFI-Type Extra-Large-Pore Zeolites in the Presence of Fluorides

Ti-containing zeolites showed extremely high activity and selectivity in numerous friendly environmental oxidation reactions with hydrogen peroxide as a green oxidant. It will be in high demand to synthesize Ti-containing crystalline extra-large-pore zeolites due to the severe restrictions of medium-pore and/or large-pore zeolites for bulky reactant oxidations. However, the direct synthesis of extra-large-pore Ti-zeolites was still challengeable. Here, we firstly report a strategy to directly synthesize high-performance Ti-containing CFI-type extra-large-pore (Ti-CFI) zeolites assisted with fluorides. The well-crystallized Ti-CFI zeolites with framework titanium species could be synthesized in the hydrofluoric acid system with seed or in the ammonium fluoride system without seed, which showed higher catalytic activity for cyclohexene oxidation than that synthesized from the traditional LiOH system.

Synthesis of Hierarchical Titanium‐Rich Titanium Silicalite‐1 Zeolites and the Highly Efficient Catalytic Performance for Hydroxylation of Phenol

AbstractImproving the framework titanium (Ti) of titanium silicalite‐1 (TS‐1) zeolites and creating inter‐crystalline mesoporosity are two ways to enhance the catalytic properties of TS‐1 for hydroxylation of phenol. Most researches only used one of the ways. In this study, we successfully synthesized of hierarchical Titanium‐Rich (Ti‐rich) TS‐1. Ti‐rich TS‐1 was synthesized in the presence of ammonium carbonate ((NH4)2CO3). The framework Ti content of TS‐1 zeolites synthesized by different content of (NH4)2CO3 was studied by X‐ray fluorescence (XRF), Fourier transform infrared spectra (FTIR) and ultraviolet visible spectra, the framework Ti content was significantly increased by using (NH4)2CO3 as crystallization‐mediating agent. The synthesized samples were evaluated in hydroxylation of phenol. When the molar ratio of ammonium carbonate and tetraethyl orthosilicate in the synthesis gel was 0.2, the molar ratio of Si/Ti reached 34.43 and the Ti‐rich TS‐1 shows the optimum catalytic activity in hydroxylation of phenol. The post‐modification with aqueous solution of tetrapropylammonium hydroxide (TPAOH) was used to further improve the diffusion property. Compared with the parent TS‐1, the secondary pore volume was all increased. The developed hierarchical Ti‐rich TS‐1 zeolites were also assessed in hydroxylation of phenol. It was confirmed that hierarchical Ti‐rich titanium silicalite‐1 zeolites can improve the catalytic activity in phenol conversion considerably.

Direct ring C[sbnd]H bond activation to produce cresols from toluene and hydrogen peroxide catalyzed by framework titanium in TS-1

A series of TS-1 samples with varying Ti content was prepared and applied in the partial oxidation of toluene with H2O2 as oxidant. The TS-1 samples and relevant systems were characterized by XRD, FT-IR, in situ FT-IR, nitrogen adsorption/desorption, DR UV–vis, XPS, ICP-AES, EPR, SEM, TEM and TG. The results showed that the framework Ti species was responsible for the selective ring CH bond activation, resulting in toluene hydroxylation; while the extra-framework Ti species was advantageous to the formation of side chain oxidation products and to the deep oxidation of both kinds of the products formed. Under the optimized reaction conditions, the toluene conversion reached 38.9% with 84.3% selectivity to cresols (TOF, 2.66 h−1), while, the selectivity of para-cresol was 66.8%, which might be caused by the pore structure and steric hindrance of methyl group. The catalyst regenerated by calcination exhibited stable activity and selectivity after the second run.

Post-treatment of TS-1 with Mixtures of TPAOH and Ammonium Salts and the Catalytic Properties in Propylene Epoxidation

TS-1/SiO2 extrudate was post-treated with mixed solution of tetrapropyl ammonium hydroxide (TPAOH) and various ammonium salts solution (NH4F, (NH4)3PO4, (NH4)2CO3, (NH4)2SO4, NH4CH3CO2, NH4NO3, NH4Cl and (NH4)2TiF6). The obtained hierarchical TS-1 catalysts were characterized by many techniques and tested for propylene epoxidation using hydrogen peroxide as an oxidant in a fixed-bed reactor. It was shown that the physicochemical and catalytic properties of the treated TS-1/SiO2 extrudate depended on the types of ammonium salts added. Compared to the treatment with TPAOH alone, the treatment with a mixed solution of TPAOH and some ammonium salts can greatly improve the catalytic properties of the treated TS-1/SiO2 extrudate. Some of these ammonium salts were favorable for the incorporation of titanium in the framework, and the beneficial effect depended on the types of ammonium salt. TS-1/SiO2 extrudate treated with a mixed solution of TPAOH and (NH4)3PO4 exhibited the highest catalyst stability in propylene epoxidation. Such catalytic property can be correlated to high crystallinity, more framework titanium, large specific surface area and large external surface area.

Inter-connected and open pore hierarchical TS-1 with controlled framework titanium for catalytic cyclohexene epoxidation

A post-synthesis method was developed to reduce the extra-framework titanium in TS-1 zeolites in which TPAOH was used to convert amorphous Ti to zeolitic phases.