Titanium Silicalite Research Articles

Ultrastable emissive perovskite nanocomposite via dual protection of polymer-grafted TS-1 zeolite for backlight display application

Instability of all-inorganic perovskite quantum dots (PQDs) driven by the inherent ionic nature poses a grand challenge towards their long-term stability in optoelectronic devices. Herein, we report the crafting of a highly stable dual-protected CsPbBr3 perovskite nanocomposite by capitalizing on the encapsulation of a hydrophobic Styrene-Divinylbenzene (St-Dvb) copolymer grafted hierarchical titanium silicalite-1 (TS-1) zeolite shell. Firstly, an optimal hot injection method was used to accommodate CsPbBr3 PQDs into hierarchical TS-1 zeolite. After the modification of terminated Si-OH groups on the surface of TS-1 by phenyltriethoxysilane (PTES), a subsequent polymerization of St and Dvb was implemented using azobisisobutyronitrile (AIBN) as initiator to result in the highly emissive CsPbBr3-TS@St-Dvb nanocomposite, exhibiting outstanding luminescent stability against heat, polar solvents, and UV light irradiation. The as-prepared CsPbBr3-TS@St-Dvb nanocomposite also showed strongly suppressed anion exchange and high compatibility in polymer matrix, enabling improved applicability for versatile lighting and optical display applications. Ultimately, a white light-emitting diode (WLED) composed of green-emitting CsPbBr3-TS@St-Dvb and red-emitting K2SiF6:Mn4+ phosphor onto a commercial blue InGaN LED chip with wide color gamut and excellent stability is demonstrated. This work highlights a judiciously-designed and hard-soft dual-protected strategy to produce ultrastable perovskite nanomaterials with high brightness and durability for backlight display application.

Photoassisted synthesis of high-crystallinity TS-1 with triblock copolymer F127 and its application for photodegradation of erythromycin

As a successful industrial catalyst, titanium silicalite-1 zeolite (TS-1) is limited as a photocatalyst in wastewater treatment due to the complexity and high energy consumption of its synthesis. Here, a novel synthesis hierarchical TS-1 was developed using triblock copolymer F127 and a phototreatment synthesis method. This method resulted in a super high crystallinity of the synthesized TS-1. A synthesis mechanism was proposed, and some reactions between Si and Ti species were studied by density functional theory (DFT) calculations. Compared to TS-1 synthesized using the conventional method, the catalyst in this study exhibited superior performance in the interfacial charge transport efficiency. In the removal of the antibiotic erythromycin from water, the synthesized catalyst demonstrated exceptional performance in terms of adsorption, photoactivity, stability and anti-interference ability against pH, anions, and cations. These findings suggested that the synthesis method used in this work is feasible, and the TS-1 products have great potential in pollutant degradation.

Enhanced Oxidation of p-Toluidine Using Supported Zeolite Nanoparticles.

Supported nanomaterials are becoming increasingly important in many industrial processes because of the need to improve both the efficiency and environmental acceptability of industrial processes. The unique properties of supported nanomaterials have attracted researchers to develop efficient catalytic materials in nanoscale. The extremely small size of the particles maximizes the surface area exposed to the reactant, allowing more reactions to occur. The environmental hazards resulting from the conventional manufacturing procedures for organic fine chemicals and intermediates by classical oxidation catalysis using mineral acids have forced chemical industries to seek less polluting processes. The present study aimed to oxidize p-toluidine by hydrogen peroxide in the presence of magnetite supported on nanocrystalline titanium silicalite-1 (M/NTS) zeolite at ambient temperature. The products detected are 4,4'-dimethylazobenzene as major product and 4,4'-dimethylazoxybenzene as minor product. Good selectivity, low cost, low wastage of materials and enhanced environmental friendliness of heterogeneous magnetite nanoparticle supported zeolite catalysts were observed. The effect of various reaction parameters such as mole ratio, catalyst weight and reusability of catalyst were studied. At the optimum reaction conditions, the oxidation activity of M/NTS catalyst was compared with M/NS catalyst, and it was found that titanium in the framework of M/NTS provided higher activity and selectivity.

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

AbstractAbstract. Continuous‐flow epoxidation of aliphatic and aromatic alkenes with hydrogen peroxide (H2O2) was carried out to give epoxides using a fixed‐bed liquid flow reactor equipped with a solid titanium silicalite‐1 (TS‐1) catalyst column. The developed flow reaction enables continuous synthesis of 4‐phenyl‐1,2‐epoxybutane from 4‐phenyl‐1‐butene in 90%–98% yields (22.4 g) for 150 h from a catalyst column of 5 mm inner diameter with 100 mm length. Employment of a mixed solution of MeCN and MeOH with preservation of the Ti active site in TS‐1 crystal structures with few defects permits continuous epoxidation of less‐reactive long‐chain terminal alkene and multifunctional alkene to give epoxides in 12%–98% yields with 78%–99% selectivity.magnified image

Nano-Cavities within Nano-Zeolites: The Influencing Factors of the Fabricating Process on Their Catalytic Activities.

Titanium silicalite-1 (TS-1) is a milestone heterogeneous catalyst with single-atom tetrahedral titanium incorporated into silica framework for green oxidation reactions. Although TS-1 catalysts have been industrialized, the strategy of direct hydrothermal synthesis usually produces catalysts with low catalytic activities, which has still puzzled academic and industrial scientists. Post-treatment processes were widely chosen and were proven to be an essential process for the stable production of the high-activity zeolites with hollow structures. However, the reasons why post-treatment processes could improve catalytic activity are still not clear enough. Here, high-performance hollow TS-1 zeolites with nano-sized crystals and nano-sized cavities were synthesized via post-treatment of direct-synthesis nano-sized TS-1 zeolites. The influencing factors of the fabricating processes on their catalytic activities were investigated in detail, including the content of alkali metal ions, the state of titanium centers, hydrophilic/hydrophobic properties, and accessibility of micropores. The post-treatment processes could effectively solve these adverse effects to improve catalytic activity and to stabilize production. These findings contribute to the stable preparation of high-performance TS-1 catalysts in both factories and laboratories.

Macro-meso-microporous titanium silicalite-1 catalyst featuring self-assembled nanocrystals and multiple active species for propylene epoxidation

Titanium silicalite-1 (TS-1) is an important catalyst for many oxidation reactions. Catalytically active titanium species with favourable particle morphology and pore structure to support diffusion are vital to the performance of this catalyst. Herein, by growing TS-1 nanocrystals on solid silicalite-1 cores followed by hollowing both the cores and TS-1 nanocrystals, a macro-meso-microporous (3 M) structured 3 M−TS−1(ML) catalyst was produced using only a solo template, tetrapropylammonium hydroxide. This catalyst demonstrates superior catalytic performance for propylene epoxidation to propylene oxide, and contains only catalytically active Ti(OH)(OSi)3, Ti(OH)2(OSi)3 and Ti(OH)4(OSi)2 species and is free from inactive Ti species such as anatase-TiO2. Through rationally designed comparative evaluations, this work shows that the high catalytic activity of 3 M−TS−1(ML) is the results of both having excellent diffusion conditions from its unique 3-tiered pore structure and containing high activity Ti species such as Ti(OH)4(OSi)2.

Catalytic Performance of Amorphous Ti/SiO2 in the Gas‐Phase Epoxidation of Propylene with H2O2

AbstractThe epoxidation of propylene with dilute H2O2 aqueous solution over titanium silicalite‐1 (TS‐1) zeolite catalyst is a green chemical reaction for propylene oxide (PO) production. Carrying out the reaction in gas‐phase can get rid of problems caused by using methanol solvent. This paper reports an attempt of using non‐zeolite catalyst for the gas‐phase epoxidation. Amorphous Ti/SiO2, obtained by grafting amorphous SiO2 with TCl4 in ethanol solvent in a chemical liquid‐phase deposition (CLD) process, has been used as the catalyst. Results show that the CLD Ti/SiO2 with appropriate Si/Ti molar ratio is an active catalyst for gas‐phase epoxidation, achieving 9.8 % propylene conversion and 66.9 % PO selectivity with 40.3 % H2O2 utilization, which indicates that this amorphous Ti/SiO2 catalyst deserves extensive studies in the future.

Efficient conversion of propylene to propylene glycol by coupling H2O2 electrosynthesis and TS-1 thermocatalysis

It is highly desirable to develop an efficient and sustainable strategy for converting propylene into high value-added products under mild conditions. In this work, the tandem oxidation of propylene to propylene glycol was achieved by coupling electrosynthesis of H2O2 by 2e- ORR on an oxygen-doped carbon catalyst with thermocatalytic oxidation of propylene by H2O2 on titanium silicalite-1 (TS-1) in a flow cell. For a composite catalyst with the optimal composition which balances electron transfer and H2O2 mass transport, the selectivity towards propylene glycol and the utilization efficiency of H2O2 can reach 79.7 % and 47.6 %, respectively. The yield of propylene glycol is 4.28 mmol gcat-1h−1. This study provides a promising approach to electrochemical propylene conversion in the future.

Beyond TS-1: Background and recent advances in the synthesis of Ti-containing zeolites

The discovery of Titanium-Silicalite-1 (TS-1), reported in the late 1970s, is a milestone in the science and technology of zeolites. As an oxidation catalyst, TS-1 operates under mild conditions with high activity and selectivity, and it is presently applied in several industrial processes. As a medium-pore zeolite, the small size of the 10-ring pore openings imposes diffusion limitations when working with even relatively large molecules. To overcome this drawback, a thriving line of research was soon undertaken aimed at incorporating Ti into the framework of zeolites with different pore architecture and sizes. In this review, we would like to retrace the fundamental steps of the synthesis of crystalline microporous titanosilicates, highlighting not only the early works but, above all, the most recent advances. The analysis of the literature provides an exhaustive picture of the efforts made by the researchers together with useful indications for developing increasingly selective and efficient catalytic materials.

Tannic Acid Assisted Construction of Au-Ti Integrated Catalyst Regulating the Local Environment of Framework Ti toward Propylene Epoxidation under H2/O2

The local environment of framework Ti determines the catalytic properties of titanium silicalites (TS-1) for olefin epoxidation. As for the Au/TS-1 catalyst toward vapor phased propylene epoxidation with H2/O2, regulating the framework Ti site from the Au-Ti integration level remains difficult due to the lack of Au-Ti interfacial interaction. To address this issue, an Au-Ti integrated catalyst with a zeolite encapsulation structure was first proposed herein via in situ solvent-free synthesis, exploiting tannic acid as functional agent to anchor the bifunctional components. The as-prepared [email protected] catalyst features highly dispersed and integrated Au-Ti active sites, as mutually confirmed by HR-TEM, ICP and UV-vis. Thus, the Au-Ti interfacial interaction is enhanced to regulate the Ti-O-Si micro-environment, thus improving the electronic-positivity of framework Ti to stabilize the active species. Such crucial regulation effects were stepwise elucidated by mutually complementary characterizations including X-ray photoelectron spectra (XPS), adsorption infrared spectra (IR), Raman spectroscopy, X-ray near edge structure (XANES) and density functional theory (DFT) simulations. As anticipated, the integrated catalyst [email protected] exhibits a concomitant increment in PO selectivity (90.2%) and H2 efficiency (26.7%). The methodology and insights stated herein could guide the rational optimization of Au-Ti catalysts and help unravel the role of tannic acid assisted strategies for various integrated catalyst preparations.

Boosting Selective Oxidation of Ethylene to Ethylene Glycol Assisted by In-situ Generated H2O2 from O2 Electroreduction.

Ethylene glycol is a useful organic compound and chemical intermediate for manufacturing various commodity chemicals of industrial importance. Nevertheless, the production of ethylene glycol in a green and safe manner is still a long-standing challenge. Here, we established an integrated, efficient pathway for oxidizing ethylene into ethylene glycol. Mesoporous carbon catalyst produces H2O2, and titanium silicalite-1catalyst would subsequently oxidize ethylene into ethylene glycol with the in-situ generated H2O2. This tandem route presents a remarkable activity, i.e., 86% H2O2conversion with 99% ethylene glycol selectivity and 51.48 mmol gecat-1h-1production rate at 0.4 V vs. reversible hydrogen electrode. Apart from generated H2O2as an oxidant, there exists •OOH intermediate which could omit the step of absorbing and dissociating H2O2over titanium silicalite-1, showing faster reaction kinetics compared to the ex-situ one. This work not only provides a new idea for yielding ethylene glycol but also demonstrates the superior of in-situ generated H2O2in tandem route.

Hierarchical Titanium Silicalite-1 Zeolites Featuring an Ordered Macro–Meso–Microporosity for Efficient Epoxidations

The epoxidation reaction over titanium silicalite-1 (TS-1) zeolites is a green way to produce epoxides that are important intermediates for chemicals. Nevertheless, the conventional microporous TS-1 zeolite shows limited diffusion ability for bulky molecules, leading to poor activity and low selectivity. Constructing hierarchical porosity in microporous materials is an effective strategy to enhance the diffusion properties of catalysts. However, there are few reports on the design and synthesis of TS-1 zeolites with hierarchical structure featuring multilevels, interconnectivity, and regularity for efficient diffusion and epoxidations. Herein, hierarchical TS-1 zeolites with ordered macro–meso–microporosity (OMMM-TS-1) are obtained by a method combining a templated effect of ordered macro–mesoporous matrices and a confined in situ crystallization process. The OMMM-TS-1 possesses ordered macropores with tunable size (∼200–600 nm), ordered mesopores (∼8 nm), and intact micropores (∼0.5 nm). The OMMM-TS-1 achieves a cyclooctene conversion as 3.6 times and 1.8 times and a selectivity to epoxy product as 1.6 times and 1.3 times higher than the conventional TS-1 (C-TS-1) and nanosized TS-1 (Nano-TS-1) zeolites, respectively. The OMMM-TS-1 also outperforms the C-TS-1 and Nano-TS-1 zeolites in epoxidations of a series of alkenes. Such a novel hierarchical structure can be applied in the design and synthesis of many other catalysts.

Tetrapropylammonium Hydroxide Treatment of Aged Dry Gel to Make Hierarchical TS-1 Zeolites for Catalysis.

This work presents the development and systematic study of a method to prepare hierarchical titanium silicalite-1 (TS-1) zeolites with high tetra-coordinated framework Ti species content. The new method involves (i) the synthesis of the aged dry gel by treating the zeolite precursor at 90 °C for 24 h; and (ii) the synthesis of hierarchical TS-1 by treating the aged dry gel using tetrapropylammonium hydroxide (TPAOH) solution under hydrothermal conditions. Systematic studies were conducted to understand the effect of the synthesis conditions (including the TPAOH concentration, liquid-to-solid ratio, and treatment time) on the physiochemical properties of the resulting TS-1 zeolites, and the results showed that the condition of a TPAOH concentration of 0.1 M, liquid-to-solid ratio of 1.0, and treatment time of 9 h was ideal to enable the synthesis of hierarchical TS-1 with a Si/Ti ratio of 44. Importantly, the aged dry gel was beneficial to the quick crystallization of zeolite and assembly of nanosized TS-1 crystals with a hierarchical structure (S ext = 315 m2 g-1 and V meso = 0.70 cm3 g-1, respectively) and high framework Ti Species content, making the accessible active sites ready for promoting oxidation catalysis.

Liquid Phase Epoxidation of Propylene to Propylene Oxide with Hydrogen Peroxide on Titanium Silicalite-1: Spatially Resolved Measurements and Numerical Simulations

The spatial profile measurement technique was applied for the first time to a liquid phase reaction to study the selective oxidation of propylene to propylene oxide with hydrogen peroxide on titanium silicalite-1 catalyst, also known as the HPPO process. A spatial profiling reactor based on minimal invasive capillary sampling measurements was used to obtain the experimental data. The reactor is able to measure spatially resolved concentration and temperature profiles at industrially relevant conditions, that is, 40 °C and 20–35 bar pressure, with propylene in the liquid phase. The reaction was carried out at different contact times of LHSV 3.0, 6.0, and 12.0 h–1, respectively, achieving high conversion and selectivity. The experimental data show that the concentration profiles of the main epoxidation reaction follows a pseudo-zeroth-order behavior. In contrast, the side product concentration profiles exhibit a nonlinear trend. The primary side products of the reaction 1-methoxy-2-propanol, 2-methoxy-1-propanol, and propylene glycol were quantified. Furthermore, hydroxacetone and methoxyacetone from the consecutive reaction of 1-methoxy-2-propanol, 2-methoxy-1-propanol, and propylene glycol with hydrogen peroxide were detected as secondary side products. Formic acid, methylformate, dipropylene glycol methyl ether isomers, and dipropylene glycol isomers were detected in trace amounts. Quantitative data for the formation of hydroxyacetone is provided for the first time. The experimental concentration profiles were simulated using an axial 1D-pseudo-homogeneous dispersion model with two kinetic models reported in the literature. Additionally, a kinetic model based on the Eley–Rideal mechanism is proposed. Upon linearization, the derived model shows a correlation of R2 = 0.99 and R2 = 0.98 with the linearized form of the experimental differential rate. Statistical analysis of the models in this work shows that the derived Eley–Rideal mechanism has the highest correlation with the concentration gradients measured within the catalyst bed.

Design of PtM (M = Ru, Au, or Sn) bimetallic particles supported on TS-1 for the direct dehydrogenation of n-butane

In this study, a theoretical model based on the use of PtM (M = Ru, Au, or Sn) bimetallic clusters supported on titanium silicalite (TS-1) was built and used to investigate the dehydrogenation of n-butane. The catalysts that were suitable for the dehydrogenation process were screened using the cluster model, and a relationship between the d-band center and the energy barrier of the first dehydrogenation step was established. To verify the theoretical results, a series of PtM bimetallic particles supported on TS-1 were prepared and tested in the n-butane dehydrogenation reaction. The order of increasing turnover frequencies and the apparent activation energies of the PtM bimetallic catalysts were essentially consistent with the theoretical results. This study can be used to guide the design of catalysts toward the dehydrogenation of n-butane.

Synthesis of hierarchical titanium silicalite-1 by seed silanization for selective oxidation reactions

The sole microporous structure of titanium silicalite-1 (TS-1) zeolite usually leads to diffusion resistances, which would negatively influence its catalytic performance. Herein, a small-crystal TS-1 zeolite with micropore/mesopore structure has been successfully synthesized by silanization of seed in a tetrapropylammonium bromide (TPABr)-ethanolamine hydrothermal system. Dodecyltrichlorosilane (DTS) was used to modify the surface of nanosized S-1 seed, then the synthetic precursor of TS-1 was crystallized around the silanized seed, and the mesopores were generated in the spaces occupied by the organosilanes as a result of the calcination of solid zeolite material. The pore diameter of mesopore could be adjusted from 2.9 nm to 7.3 nm relative to the changing of the molar ratio of DTS to SiO2 in seed from 0.05 to 0.45. The resultant hierarchical TS-1 with micropore/mesopore structure exhibited excellent catalytic performances in the propylene epoxidation and cyclohexanone ammoximation, which were even superior to that of hollow TS-1 obtained from post-synthesis treatment. This approach for the preparation of TS-1 with micro-mesopores could be easily realized in industrial application to provide a feasible strategy for the exploration of other hierarchical zeolites.

New penta- and hexa-coordinated titanium sites in titanium silicalite-1 catalyst for propylene epoxidation

Creating and identifying catalytically active titanium sites is vital to further enhance performance of titanium-containing zeolites, particularly for environmentally friendly titanium silicalite-1 catalyst (TS-1). Herein, we prepared a typical TS-1 with two new Ti-sites including the penta-coordinated Ti(OH)2(OSi)3 and hexa-coordinated Ti(OH)4(OSi)2. They are identified by UV resonance Raman spectroscopy and their coordination structures delineated by density functional theory calculations. Evaluated by propylene epoxidation to propylene oxide, Ti(OH)4(OSi)2 is more active than Ti(OH)2(OSi)3. Furthermore, Ti(OH)4(OSi)2 delivers the catalytic activity about 8.7 times the activity of known tetra-coordinated framework Ti(OSi)4 sites. Thus, Ti(OH)4(OSi)2 is found to be highly active in this reaction.

Epoxidation of light olefin mixtures with hydrogen peroxide on TS-1 in a laboratory-scale trickle bed reactor: Transient experimental study and mathematical modelling

Direct epoxidation of light olefin mixtures with hydrogen peroxide and titanium silicalite (TS-1) catalyst is interesting from a pure scientific viewpoint and it might have a considerable economic and environmental advantages. Direct epoxidation of olefin mixtures implies a significant process intensification as the separation steps of alkenes prior to the epoxidation process is avoided. Binary and ternary mixtures of ethene, propene and 1-butene were selectively epoxidized with hydrogen peroxide in the presence of TS-1 as the heterogeneous catalyst. Methanol was used as the solvent. Transient and stationary kinetic experiments were conducted in a laboratory-scale trickle bed reactor, which was operated under atmospheric pressure and isothermal conditions at 15–55 °C. The experiments were designed to investigate the kinetics of the epoxidation of light olefins at different temperatures, alkene-to-hydrogen peroxide molar ratios as well as gas and liquid residence times in the trickle bed reactor. The recorded transient responses of the reaction products confirmed that the components in the alkene mixtures are epoxidized simultaneously. The epoxide selectivity was 90 % or higher in most experiments; ring-opening products formed from the epoxides and methanol were observed as by-products. The concentration maxima of epoxides during the transient experiments were explained by accumulation of the epoxide products inside the catalyst, which resulted in partial blocking of active sites. After-treatment of the catalyst with methanol and nitrogen completely restored the initial activity. Kinetic modeling was applied, based on presumed elementary steps on the TS-1 surface to describe the behavior of the system at steady state conditions. The trickle bed reactor was described with a dynamic multiphase model, taking into account the kinetic and mass transfer effects. The numerical values of the activation energies, kinetic constants and mass transfer parameters were estimated by nonlinear regression analysis. The model gave a satisfactory description of the experimental data.

Framework Ti-rich titanium silicalite-1 zeolite nanoplates for enhanced photocatalytic H2 production from CH3OH

As a successful industrial catalyst, titanium silicalite-1 zeolite (TS-1) also possesses unique photocatalytic activity, but still challenging due to the unsatisfactory activity and unclear photocatalytic mechanism. Here, we achieved the optimization of TS-1 in both the morphology and content of framework Ti by a facile dual-structure directing agent method. The Ti-rich TS-1 nanoplates exhibit enhanced photocatalytic H2 production performance from methanol. The structure-activity relationship was revealed that the nanoplate-like morphology is beneficial to the photocatalytic activity, owing to the largely retainment of photogenerated electrons. Combined with in-situ DRIFTS and theoretical calculations, it is proposed that Ti−O group would function as a whole to serve as the active site, rather than separated Ti and O sites for reduction and oxidation half reactions respectively. The formation of hydroxylated Ti can also promote the photocatalytic performance. These insights into the mechanisms suggest the great potential of Ti-rich TS-1 nanoplates as commercial photocatalytic materials.

Removal of Gaseous H2S by the Titanium Silicalite-1/H2O2 Wet Oxidation System

A wet oxidation system of titanium silicalite-1 (TS-1)/hydrogen peroxide (H2O2) was proposed for gaseous hydrogen sulfide (H2S) removal in this study, and the effects of the TS-1 dosage, H2O2 concentration, H2S concentration, reaction temperature, gas flow, and reaction time on the removal rate of H2S (η) were investigated. Samples were characterized by transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance, and N2 adsorption–desorption. An experiment using isopropanol, benzoquinone, and butylated hydroxytoluene was carried out as well to verify the active substance in the TS-1/H2O2 system. The results show that η reached 86.3% when bubbling 160 ppm of H2S through a 500 mL solution (pH 4.21) containing TS-1 (0.5 g/L) and H2O2 (0.33 mol/L, 1.12 wt %) at 293 K and atmospheric pressure with a flow rate of 265 mL/min. Subsequently, the mechanism of the reaction was proposed. After the H2S diffuses onto the surface of TS-1, it is first oxidized by adsorbed H2O2 and eventually oxidized to H2SO4; this process is controlled by H2S diffusion. The final product of the process is sulfuric acid, which is pollution-free and can be recycled to achieve resource utilization. The removal of H2S by the TS-1/H2O2 system is a green, simple, low-cost, resource-saving, safe, and efficient method.