Titanium Silicalite Research Articles

Quantitative localisation of titanium in the framework of titanium silicalite-1 using anomalous X-ray powder diffraction

One of the biggest obstacles to developing better zeolite-based catalysts is the lack of methods for quantitatively locating light heteroatoms on the T-sites in zeolites. Titanium silicalite-1 (TS-1) is a Ti-bearing zeolite-type catalyst commonly used in partial oxidation reactions with H2O2, such as aromatic hydroxylation and olefin epoxidation. The reaction mechanism is controlled by the configuration of titanium sites replacing silicon in the zeolite framework, but these sites remain unknown, hindering a fundamental understanding of the reaction. This study quantitatively determines heteroatoms within the zeolite-type framework using anomalous X-ray powder diffraction (AXRD) and the changes in the titanium X-ray scattering factor near the Ti K-edge (4.96 keV). Two TS-1 samples, each with approximately 2 Ti atoms per unit cell, were examined. Half of the titanium atoms are primarily split between sites T3 and T9, with the remainder dispersed among various T-sites within both MFI-type frameworks. One structure showed significant non-framework titanium in the micropores of a more distorted lattice. In both samples, isolated titanium atoms were more prevalent than dinuclear species, which could only potentially arise at site T9, but with a significant energy penalty and were not detected.

Investigation of the Ti active site in TS-1 for phenol hydroxylation via seed and dissolution-recrystallization methods

TS-1 (titanium silicalite-1) zeolite has been one of the most popular catalysts for phenol hydroxylation in the industry to produce hydroquinone and catechol for its high catalytic activity. However, ideal Ti active site in TS-1 for phenol hydroxylation is controversial in academia and still remains urgent to be determined for more convincing guidance to prepare TS-1 with higher catalytic activity. Thus, controlled experiments for detailed research were conducted via seed and dissolution-recrystallization methods to explore the Ti active site for phenol hydroxylation. Through comparison of micron TS-1 and hierarchical TS-1, several factors including crystal size, specific surface area, pore volumes and anatase TiO2 were proved to have an influence on catalytic performance for phenol hydroxylation. Furthermore, hierarchical TS-1 using seeds with different molar ratios of Si/Ti were synthesized to regulate the ratio of framework Ti and hexa-coordinated Ti and exclude above variables. With binding analysis of UV–vis, UV-Raman, and XPS, it was found that TS-1 with the most framework Ti showed the best performance with TON of 1461 and dihydroxybenzenes selectivity of 97.3 %, and TS-1 with less framework Ti and more hexa-coordinated Ti showed worse performance. Hence, it was demonstrated that framework Ti was the active site for phenol hydroxylation rather than hexa-coordinated Ti, while hexa-coordinated Ti would cause excessive oxidation of phenol to benzoquinone.

Efficient synthesis of multifunctional α-Fe2O3 QDs/TS-1 as an artificial nanozyme for simultaneous colorimetric detection and photodegradation of tetracyclines

In this study, a multifunctional catalyst was developed innovatively by loading α-Fe2O3 quantum dots (QDs) onto Titanium Silicalite-1 (TS-1), creating an artificial nanozyme capable of simultaneously detecting, adsorbing, and photodegrading tetracyclines (TCs) in water. The catalyst demonstrated a limit of detection (LOD) as low as 19.7 μg/L for oxytetracycline (OTC), 23.1 μg/L for doxycycline (DOX), and 35.9 μg/L for tetracycline (TC). The peroxidase-mimic activity of the nanozyme, which was enhanced by TCs and caused a visible color change in 3,3′,5,5′-tetramethylbenzidine (TMB), was thoroughly investigated using DFT calculations. Additionally, the artificial nanozyme exhibited exceptional adsorption capabilities and photocatalytic activity under solar light irradiation, achieving a total removal rate of about 70 %. The underlying mechanism was also studied. This research provided valuable insights for the scalable production of multifunctional catalysts, thereby advancing the practical application of “integration of diagnosis and treatment” strategies for managing and controlling TCs in the environment.

Spectroscopic Characterization of Ti Sites in MWW Zeolite in Presence of Hydrogen Peroxide

AbstractTi‐MWW zeolite is a promising catalyst for partial oxidation reactions. In the present work, a Ti‐MWW sample with high TiO2 loading was synthesized. It was revealed that the Ti insertion in the purely siliceous MWW framework mainly occurs during the post treatment washing with HNO3, when the double structure directing agent synthetic method is used. By exploiting carbon monoxide, acetonitrile, pyridine and ammonia as probe molecules in infrared spectroscopy and diffuse reflectance ultraviolet spectroscopy, the acidic behavior of the Ti sites and the interaction of the Ti sites with hydrogen peroxide (H2O2) were revealed. The Ti Lewis acid sites showed stronger acidity than the one observed in Titanium Silicalite‐1 (TS‐1), with MFI framework. This is coherent with previously reported results, suggesting that a significative fraction of the Ti sites in Ti‐MWW are TiOH(SiO)3 instead of Ti(OSi)4. The Ti‐peroxo and ‐hydroperoxo complexes formed upon H2O2 were shown to be more labile than in TS‐1 and they were shown to be completely reversible upon calcination.

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.

TS-1 zeolite encapsulated Pt clusters with enhanced electronic metal-support interaction of Pt−O(H)−Ti for nearly-zero-carbon-emitting photocatalytic hydrogen production from methanol

Photocatalytic H2 production from methanol is sustainable, yet challenges remain in avoiding carbon-containing gaseous by-products. Titanium silicalite-1 (TS-1) zeolite possesses attractive photocatalytic performance, but lack of modification strategies due to its microporous framework. Herein, we developed a pre-anchoring strategy to confine ultra-small Pt clusters inside TS-1 with ultra-low loading (0.2 mol%), in which Pt were anchored in Ti−OH nests by electronic metal-support interaction (EMSI). The optimal catalyst achieved a remarkable H2 generation rate of 63.2 mmol g–1 h–1 in CH3OH solutions, along with the production of high-value chemical HCHO as the oxidation product with 96.9% selectivity. Investigations reveal that the EMSI between Pt and Ti facilitated the selective decomposition of CH3OH to H2 and HCHO, leading to a nearly zero-carbon-emission process. Accordingly, we propose a light-driven carbon-negative "CO2→CH3OH→H2" route, coupling CO2 utilization and green H2 production with CH3OH as the intermediate, therefore offering a new perspective for "liquid sunshine".

Inductive effect in amino functionalized ionic liquids modified TS-1 nanosheets for efficiently sunlight-driven CO2 reduction

Photocatalytic technology for converting CO2 into useful chemicals or clean energy is an effective strategy to solve today's energy and environmental problems. In this study, we present a direct photocatalytic pathway for the conversion of CO2-to-CO involving the formation and activation of carboxyl intermediates over amino-functionalized ionic liquid (3-aminopiperidine hydrochloride, [3APip]Cl)-modified titanium silicalite-1 (TS-1) molecular sieve nanosheets. Various in-situ characterizations reveal that the key to activating this pathway lies in the CO2 adsorption capacity and the efficiency of photoexcited charge migration induced by [3APip]Cl in the hybrid catalyst. In the above catalytic pathway, CO2 molecules are first adsorbed on the surface of the [3APip]Cl/TS-1 hybrid catalyst under the induction of amino groups in the ionic liquid. Then, these adsorbed CO2 are activated and transformed into carboxyl intermediate, which can be further converted into CO and CH4 through photoexcited electrons captured by [3APip]Cl. Based on the results of CO2 reduction performance, the optimized [3APip]Cl/TS-1 hybrid catalyst achieves a 6-fold increase, and the CO selectivity is 83.0%. This research provides new insights into the CO2 reduction pathway in mild conditions and emphasizes the importance of the adsorption–activation tandem process for enhancing photoactivity and selectivity.

CeOx‐induced oxygen vacancy‐enhanced Pt‐based titanium silicalite‐1 catalysts for selective conversion of levulinic acid

The selective conversion of levulinic acid (LA) obtained from lignocellulosic biomass represents a crucial pathway for producing the key value‐added chemical compound γ‐valerolactone (GVL). Herein, we constructed a series of Pt‐based titanium‐silicalite‐1 (TS‐1) bifunctional catalysts modified with rare earth metal Ce through a simple spin‐coating impregnation method, and the catalytic performance was significantly improved compared to the unmodified Pt1.2/TS‐1. Pt0.7‐Ce0.5/TS‐1 exhibited the best aqueous‐phase catalytic activity (with a GVL yield of 99.4%). The introduction of CeOx can reduce the particle size of Pt nanoparticles and promote the formation of electron‐rich Pt species while delivering abundant oxygen vacancies (OV) for the catalysts. The characterization and testing results highlight the synergistic effect of OV and electron‐rich Pt sites on the oriented adsorption and selective hydrogenation of LA, providing new insights into constructing more efficient noble metal‐based zeolite catalysts for biomass conversion.

Preparation of hierarchical TS-1 zeolites from ordered macroporous-mesoporous carbon templates for efficient chloropropene epoxidation

The combination of titanium silicalite-1 (TS-1) zeolite and H2O2 oxidant provides an excellent alternative to many highly toxic and polluting olefin oxidation processes due to the by-product being water-only and without deep oxidation. However, the diffusion of bulky reactants and products suffers from the inherent micropores of conventional TS-1 zeolites. Herein, we designed a reticulated ordered macroporous carbon material with uniform and coherent mesopores, and successfully synthesized ordered hierarchical TS-1 zeolites containing intracrystalline macroporous-mesoporous-microporous by dry gel method. The fully interconnected intracrystalline macroporous-mesoporous-microporous hierarchical TS-1 improves the accessibility of the active site and the diffusion efficiency of bulky compounds. It showed excellent catalytic performance during the epoxidation reaction of chloropropene, and its epichlorohydrin yield and H2O2 effective utilization were 70.11% and 77.05%, which were 2.2 and 1.9 times of the catalytic performance of commercial TS-1 zeolites, respectively, and significantly better than the ultrafine TS-1 synthesized by conventional methods. The high catalytic performance was maintained after three cycles of use. This offers a good opportunity for the design and synthesis of efficient zeolite catalysts in the future.

Investigation on Titanium Silicalite-1 Zeolite Synthesis Employing ATPAOH as an Organic Structure Directing Agent

Investigation on Titanium Silicalite-1 Zeolite Synthesis Employing ATPAOH as an Organic Structure Directing Agent

A “three in one” strategy realized using a fluorinated gold-doped titanium silicalite layer on a copper current collector for stable lithium metal batteries

Long cycle life was realized on a fluorinated, Au doped titanium silicalite modified Cu (ATSF-5/Cu) current collector by Li affinity of Au nanoparticles, microporous properties of titanium silicalite and the formation of the LiF-rich SEI layer.

Uncalcined TS-1 supported Au catalyst via NaBH4 reduction method for propylene epoxidation: Insights into the H2 pretreatment effect on catalytic performance

Stable and efficient Au-supported titanium silicalite-1 (TS-1) catalysts are essential for the direct epoxidation of propylene (DEP) using O2 and H2. But the deposition-precipitation method for Au/TS-1 contains low Au capture efficiency and rapid deactivation rate. Herein, Au/TS-1-B (uncalcined TS-1) catalysts were synthesized through a NaBH4 reduction method. The impact of H2-thermal-pretreatment on DEP activities was studied. H2-pretreatment can enhance propylene oxide selectivity, shorten activation time and reduce deactivation rate of catalyst. Organic-templates on the surface of TS-1-B and stabilizers coated on Au-nanoparticles can be partially removed under H2-treatment, thus exposing more active sites for Au and Ti and facilitating their interactions. Furthermore, more porous structures with reduced acid sites and enhanced surface hydrophobicity of pretreated catalyst can promote DEP reaction. Solid stability in TS-1-B, high Au utilization resulting from the reduction method, and favorable modifications through H2-thermal treatment contribute to the exploration of more robust DEP catalyst performance.

Design of Novel Photoactive Modified Titanium Silicalites and Their Application for Venlafaxine Degradation under Simulated Solar Irradiation

Titanium silicalites (TS) are well‐known materials for their use in industrial oxidation reactions, and although they are used as photocatalysts, their activity is limited. Therefore, numerous synthetic strategies are investigated to improve their photocatalytic activity. Herein, three series of modified titanium silicalites are synthesized using three different organotriethoxysilanes at different molar percentages with the aim of modifying the structure of the zeolite, both at a porous and chemical level, to obtain materials with high photocatalytic activity. The study of their morphological, textural, chemical, and UV–vis light absorption properties through various characterization techniques has allowed the selection of the best candidates to test their photoactivity in the degradation of venlafaxine, an antidepressant drug that persists as a contaminant in wastewater and has serious neurotoxic effects. Materials synthesized using a 5% molar percentage of RTEOS and 10% of PhTEOS (Ph = phenyl) are able to degrade venlafaxine, whereas the reference material does not show any photocatalytic activity. These results lead the way to use this synthetic strategy to develop titanium silicates and optimize their photocatalytic activity in degradation reactions of different pollutants.

The electron-rich [ZnH]+ species stabilized by titanium silicalite-1 zeolite for propane dehydrogenation

Propane dehydrogenation to propylene has broad application prospects, so it is of great significance to explore low-cost and environmentally friendly catalysts. Metal hydrides, as active sites, exhibit excellent dehydrogenation property. Herein, we report titanium modified [ZnH]+ ([ZnH]+···TiO6) site with high activity (14.49 mmolC3H6·gcat−1·h−1) and regeneration performance, which is derived from the in-situ conversion of [ZnOH]+ in the dehydrogenation reaction. Combined with in-situ spectroscopic characterizations and ab initio molecular dynamics (AIMD) simulations, the unique [ZnH]+···TiO6 moiety was confirmed, and the evolution process from [ZnOH]+ to [ZnH]+ was clarified. XPS and AIMD calculations show that Zn in the [ZnH]+···TiO6 structure is in an electron-rich state with high H-affinity, which can effectively reduce the propyl C-H cleavage barriers based on slow-growth simulations. In general, titanium modification can effectively stabilize the [ZnH]+ species and enrich the electrons density of zinc, which contribute to the enhanced PDH performance.

Hydrophobicity Manipulation of Titanium Silicalite-1 with Enhanced Catalytic Performance via Liquid-Mediated Defect Healing Treatment

Hydrophobicity Manipulation of Titanium Silicalite-1 with Enhanced Catalytic Performance via Liquid-Mediated Defect Healing Treatment

Preparation and catalytic performance of the supported Ti-MWW zeolites

Nano-size titanium silicalites is difficult to be separate from the reaction solution, lamellar and homogeneous Ti-MWW zeolites are successfully formed a dense zeolite layers on α-Al2O3 pellets by secondary hydrothermal synthesis in this study. Seeded crystals concentration and titanium source have significantly influences on the morphology, thickness and titanium active sites of Ti-MWW zeolites. Doping NH4F in the precursor synthesis solution could conducive to prepare macroscopically and anatase-free Ti-MWW zeolites layer on the outside of α-Al2O3 pellets, and the thickness of the Ti-MWW zeolites layer is ca. 1 mm. Besides, catalytic performance of the supported Ti-MWW zeolites are significantly improved by NH4F. A fixed-bed reactor with the supported Ti-MWW zeolites are applied to catalyze phenol hydroxylation with hydrogen peroxide efficiently, and reaction time and temperature, amount of the supported Ti-MWW zeolites have obvious effects on the phenol conversion and dihydroxybenzene selectivity. When the actual mass of Ti-MWW zeolites to volume of reaction solution is only 10 g/L, the relative phenol conversion and dihydroxybenzene selectivity are 46.45% and 92.72% at 65 °C after 3 h, respectively.

Tandem photocatalytic production of H2O2 and propylene oxide on 5-Bromoisatin modified carbon nitride

Propylene oxide (PO) is an important raw material and synthetic intermediate for organic chemical synthesis. The direct in-situ synthesis of hydrogen peroxide (H2O2) using molecular oxygen to produce PO is considered as one of the most promising methods. Herein, we propose a photocatalytic multiphase system for the production of PO with oxygen. The ligand 5-bromoindoline-2,3-dione doped graphitic carbon nitride (CN/Bd) was employed as a photocatalyst for the in-situ production of H2O2, in tandem with epoxidation catalyst titanium silicalite-1 (TS-1) to achieve the epoxidation of propylene. This system achieved H2-free and efficient production of PO at room temperature with a high yield of 1.33 mmol·g−1·h−1, the selectivity of PO over 99% and H2O2 utilization efficiency over 95%. The combination of in-situ H2O2 generation and selective oxidation reaction realizes the efficient utilization of H2O2 and provides guidance for safer industrial production of PO.

Epoxidation of Light Olefin Mixtures with Hydrogen Peroxide on TS-1 Catalyst

The direct epoxidation of mixed ethene and propene feedstocks using hydrogen peroxide over a titanium silicalite (TS-1) catalyst was investigated within a continuous trickle bed reactor operating in laboratory scale. Methanol was employed as the reaction solvent. This study aimed to streamline the epoxidation process by obviating the need for prior separation of alkenes, thereby enhancing process efficiency. An extensive array of operational parameters was explored in a trickle bed reactor, encompassing experimental parameters such as temperature, total pressure, hydrogen peroxide concentration, liquid flow rate, and gas composition. In contrast to prior investigations involving separate ethene and propene epoxidation, this study revealed a reduction in epoxide selectivity. The principal by-products observed were methoxy species, formed through the interaction between the epoxide and methanol, resulting in a ring-opening reaction. The influence of water on this ring-opening process was negligible. Notably, the tunability of the system was demonstrated, highlighting low temperature and elevated partial ethene pressure as pivotal factors for augmentingthe epoxide selectivity. The findings suggest that binary olefin mixtures exhibit diminished selectivity but improved stability. This behavior is potentially linked to the olefin solubility in methanol, or alterations in the surface species concentrations, typically associated with catalyst activity variations. These insights offer a valuable foundation for understanding and optimizing the direct epoxidation of mixed ethene and propene feedstock.Graphical

Continuous Synthesis of Epoxides from Alkenes by Hydrogen Peroxide with Titanium Silicalite‐1 Catalyst Using Flow Reactors.

The inside cover picture of a waterfall stream illustrates the continuous synthesis of various epoxides from olefins, with hydrogen peroxide as an oxidant, catalyzed by titanium silicalite‐1 (TS‐1). This reaction is applicable to the epoxidation of more than 20 olefins and the only co‐product is water. As a typical example, 4‐phenyl‐1,2‐epoxybutane was continuously synthesized in over 90% yield for more than 150 hours, and ICP‐MS/MS observations showed that little or no Ti loss from TS‐1 was observed. Details can be found in the Communication by Yoshihiro Kon and co‐workers (Y. Kon, T. Nakashima, Y. Makino, H. Nagashima, S. Onozawa, S. Kobayashi, K. Sato, Adv. Synth. Catal. 2023, 365, XXXX–XXXX; DOI: 10.1002/adsc.202300181).

Catalytically active species in bifunctional Aluminum-Containing titanium Silicalite-1 zeolite for ethylene epoxidation

Aluminum-containing titanium silicalite-1 zeolite (Al-TS-1) is an important bifunctional catalyst for green production of ethylene glycol (EG) via a hydrogen peroxide/ethylene process (HPEG). In this work, hydrothermal post-treatments are carried out to a parent Al-TS-1 in (NH4)2CO3 aqueous solutions under varied conditions to produce post-treated Al-TS-1 catalysts. In addition to the framework Ti(OSi)4 species found in both the parent and post-treated Al-TS-1 catalysts, the post-treated catalysts also contain Ti(OH)4(OSi)2 species. For HPEG process, the post-treated Al-TS-1 delivers a significantly higher H2O2 conversion than the parent Al-TS-1. This is attributed to the outstanding catalytic activity of Ti(OH)4(OSi)2 which is ∼ 16.8 times the activity of Ti(OSi)4. Furthermore, although the parent and post-treated Al-TS-1 contain both the framework and extra-framework Al species, the post-treatment is also found to alter the detailed location and amount of framework Al species in the catalyst. Such changes, however, have only minor effect on the EG selectivity.