Framework Ti Research Articles

Comparison of Brønsted Acidic Silanol Nests and Lewis Acidic Metal Sites in Ti-Beta Zeolites for Conversion of Butenes

The Lewis acidic framework Ti sites in Ti-Beta and Si-Beta catalysts were compared by FT-IR and NMR characterization methods before they were applied to the conversion of four butenes. The results showed that Si-Beta has fewer Lewis acid sites and abundant weak Brønsted acidic silanol nests, which play an important role in conversions between n-butene, cis-2-butene, and trans-2-butene. The conversions for these butenes over Si-Beta were always higher than those over a series of Ti-Beta catalysts with gradient-varied Lewis acidic framework Ti sites and silanols. This is because isobutene can only oligomerize, which requires stronger acidity, so its conversion over Si-Beta was lower than those over Ti-Beta zeolites. For a series of Ti-Beta catalysts with different abundances of Lewis acidic Ti sites, the more Lewis acid sites it had, the higher the conversions for the four butenes.

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.

Direct propylene epoxidation with molecular oxygen over titanosilicate zeolites.

The direct epoxidation of propylene with molecular oxygen represents a desired route for propylene oxide (PO) production with 100% theoretical atomic economy. However, this aerobic epoxidation reaction suffers from the apparent trade-off between propylene conversion and PO selectivity, and remains a key challenge in catalysis. We report that Ti-Beta zeolites containing isolated framework Ti species can efficiently catalyze the aerobic epoxidation of propylene. Stable propylene conversion of 25% and PO selectivity of up to 90% are achieved at the same time, matching the levels of industrial ethylene aerobic epoxidation processes. H-terminated pentacoordinated Ti species in Beta zeolite frameworks are identified as the preferred active sites for propylene aerobic epoxidation and the reaction is initiated by the participation of lattice oxygen in Ti-OH. These results are expected to spark new technology for the industrial production of PO toward more sustainable chemistry and chemical engineering.

Ammonia-regulated dynamic evolution of Ti precursor incorporating into dealuminized beta for efficient 1-Hexene epoxidation

Demetalation-metalation method has gained prominence for its higher metal loading, efficiency and shortened synthetic period, particularly in the incorporation of metal atoms with large radii into zeolite framework in recent years. An ammonia-regulated approach has been developed for selectively evolved deep-substituted Ti precursors in dealuminized beta zeolites, which enables a controlled promotion of metalation of Ti atoms. Additionally, this ammonia-regulated approach could also enhance 1-hexene kinetic adsorption by constructing mesopores, which is demonstrated by the lower reaction order of 1-hexene. The synthesized ammonia-regulated N-Ti-beta exhibits rich framework Ti species and a high specific surface area, leading to significantly improved 1-hexene epoxidation performance (conversion of 61%, selectivity of 98%, and a high H2O2 utilization efficiency of 93%). This study not only provides a new strategy to dynamically regulate evolution of Ti precursors by ammonia but also holds promise for advancing related industrial processes in demetalation-metalation methods.

The promoting role of framework Ti(IV) in enhancing the hydrodeoxygenation performance of palmitic acid over a mesoporous TS-1 supported Ni catalyst

Developing a highly efficient Ni-based hydrodeoxygenation catalyst is crucial for the production of renewable biodiesel. Herein, a mesoporous TS-1 zeolite supported Ni catalyst (Ni/TS-1-M) exhibited exceptional hydrodeoxygenation (HDO) activity and achieved 100 % yield of deoxygenated hydrocarbons (97.3 % pentadecane vs 2.7 % hexadecane), outperforming other catalysts such as Ni on mesoporous ZSM-5 (Ni/ZSM-5-M), mesoporous Silicalite-1 (Ni/Silicalite-1-M) and TiO2 (Ni/TiO2). The Ti(IV) atoms in the form of TiO4 and TiO6 can transfer its electron to nearby metal Ni, leading to the increase in electron density of metal Ni, which enhanced the hydrogenation activity and facilitated the C–C bond cleavage of the hexadecanal to produce pentadecane. Furthermore, the framework Ti(IV) species accelerated the esterification process to generate palmityl palmitate, which was easily hydrogenolyzed to the main intermediate of hexadecanol under the synergistic effect of metal Ni and Ti(IV) on Ni/TS-1-M catalyst. The formed hexadecanol mainly underwent successive dehydrogenation/decarbonylation process to transform into pentadecane.

Effect of TiO2 on catalytic performance of gold-titanium-catalyzed gas-phase epoxidation of propylene

The gas-phase epoxidation of propylene with H2/O2 is a promising method to generate propylene oxide (PO). Au/TS-1 is preferred catalyst due to the synergistic effect between Au nanoparticles and framework Ti species. TS-1 with high Ti content are used as support for Au catalysts, which are expected to achieve fantastic catalytic performance. However, their actual catalytic properties are generally unsatisfactory. The reason for this phenomenon is that the role of TiO2 in Ti-containing support is unclear. Here, we found that increasing TiO2 content in Ti-containing supports offered improving isoelectric point (IEP), which could be responsible for the obviously enhanced Au loading. More Au nanoparticles inserted into the TS-1 micropore favors their cooperation with framework Ti sites to realize higher C3H6 conversion. Simultaneously, propanal generated via direct propylene oxidation catalyzed by Au/TiO2 leads to the decrease of PO selectivity. A volcanic-shaped relationship between TiO2 content and PO formation rate is emerged.

Zeolite structure descriptor for guiding the synthesis of efficient titanosilicalites through matching Ti sites and framework topologies for 1-Hexene epoxidation

Rational design of metal-containing zeolites with different framework topologies can boost catalytic performance, but the successful synthesis of metal-containing zeolites typically requires selection of suitable zeolite scaffolds. Herein, a zeolite structure descriptor (i.e., the local framework disturbance index, LFDI) is proposed to guide the design of Ti-containing zeolites by matching Ti sites and different framework topologies to enhance olefin epoxidation performance. Theoretical calculations of the incorporation of Ti metal atoms into different crystallographic T sites indicate that the BEA framework exhibits the more negative average substitution energy (-0.50 eV) than MFI and MEL frameworks due to the lowest average LFDI (3.14). As expected, the BEA framework showed the highest capacity of framework Ti species than MFI and MEL frameworks by atom-planting method. This high framework Ti content demonstrated outstanding 1-hexene epoxidation performances (TON: 1827.5). This work paves the way to rationally design Ti-containing zeolites by atom-planting method for epoxidation reactions.

Production of Oximes Directly from Sustainable Lignocellulose-Derived Aldehydes and Ammonia over HTS-1 Catalyst.

Oxime chemicals are the building blocks of many anticancer drugs and widely used in industry and laboratory. A simple but robust hierarchically porous zeolite (HTS-1) catalyst was prepared by hydrothermal methods and used for the preparation of vanillin oxime from vanillin in NH3 ⋅ H2 O/DIO (v/v 1/10) system. The results of the catalyst characterization showed that the larger pore size and more framework Ti were conducive to promote the transformation of the substrates. The conversion of vanillin and the yield of vanillin oxime were both higher than 99 % under optimized reaction conditions. It was found that the reaction proceeded by oxidation of NH3 to hydroxylamine (NH2 OH), and oximation of hydroxylamine with vanillin to obtain vanillin oxime, where the rate-controlling step was the hydroxylamine formation, and the apparent activation energy was 26.22 kJ/mol. The corresponding oximation products could also be obtained by extending this method to other compounds derived from lignin. Furthermore, the catalytic system was used directly to the conversion of birch biomass to obtain oxime products such as vanillin oxime, syringaldehyde oxime, and furfural oxime etc. This work might give insights into the sustainable production of N-containing high-value products from lignocellulose.

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.

Optimization of MOFs-induced strategy for preparing anatase-free hierarchical TS-1 towards 1-hexene epoxidation: TPAOH dosage regulation, silanization and stabilizing acidic sites

Metal organic frameworks (MOFs)-induced synthetic strategy has been proven a convenient and efficient way for preparing anatase-free hierarchical TS-1 zeolite in our previous study. Here, to further enhance the catalytic performance on 1-hexene, the MOFs-induced hydrothermal synthesis route is optimized by adjusting the amount of tetrapropylammonium hydroxide (TPAOH) and performing different degrees of silanization treatment. A low TPAOH dosage can ensure the synthesized samples have abundant and dense active framework Ti at the expense of partial hierarchical structure. Further deep silanization treatment created mesoporous structure ranging between 20 and 30 nm without affecting the content or distribution of active titanium. The obtained anatase-free hierarchical TS-1 sample Sil-0.150 possesses excellent 1-hexene conversion of >38%. Based on detailed NH3-TPD and Py-IR tests, the presence of high-density Lewis acid sites (LAS) leads to a decreased epoxy product selectivity of 91.5%, and the optimized MOFs-induced synthesis strategy may open up new perspectives for the design and application of high-performance TS-1 catalysts in selective epoxidation reactions of various alkenes.

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.

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.

Aromatic compounds‐mediated synthesis of anatase‐free hierarchical TS‐1 zeolite: Exploring design strategies via machine learning and enhanced catalytic performance

AbstractSimultaneous achievement of constructing mesopores and eliminating anatase is a long‐term pursuit for enhancing the catalytic performance of TS‐1. Here, we developed an aromatic compounds‐mediated synthesis method to prepare anatase‐free and hierarchical TS‐1 for olefin epoxidation. A series of hierarchical TS‐1 zeolites were prepared by introducing aromatic compounds containing different functional groups via the crystallization process. The formation of intercrystalline mesopores and insertion of titanium into framework were facilitated at different extent. The synergistic coordination of carboxyl and hydroxyl in aromatic compounds with Ti(OH)4 realizes the uniform distribution of titanium species and eliminates the generation of anatase. Noteworthily, eight machine learning models were trained to reveal the mechanism of additive functional groups and preparation conditions on anatase formation and microstructure optimization. The prediction accuracy of most models can reach more than 80%. Benefiting from the larger mesopore volumes (0.37 cm3·g−1) and higher content of framework Ti species, TS‐DHBDC‐48h samples exhibit a higher catalytic performance than other zeolites, giving 1‐hexene conversion of 49.3% and 1,2‐epoxyhenane selectivity of 99.9%. The paper provides a facile aromatic compounds‐mediated synthesis strategy and promotes the application of machine learning toward the design and optimization of new 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.

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.

Synthesis of ultra-fine TS-1 catalyst with high titanium content and its performance in phenol hydroxylation

The study of simultaneous control over framework Ti and particle size was achieved using the incorporation of NH4HCO3 and PVA into the synthesis medium of the TS-1 catalyst.

Lived experiences of post-mastectomy women: A qualitative study of Western Rajasthan.

Women's breasts have biological functions to lactate, socially and culturally seen as sensual, and the essence of her femininity. In the world, breast cancer is the most constantly occurring non-cutaneous cancer among women. The qualitative phenomenological study aimed to explore the lived experiences of post-mastectomy women. A total of 14 post-mastectomy women were recruited through non-probability convenience sampling based on data saturation, at the radiation unit of a tertiary care hospital, in Basni, Jodhpur, Rajasthan, from September to November 2020. The data was collected using an in-depth interview schedule. It was firstly audio-recorded and transcribed, and then themes and subthemes were extracted. Experiences of women were recorded and analyzed using Colaizzi"s framework (1978) and ATLAS ti. 9 scientific software. This revealed five main themes and their subthemes: Body image changes, physical impacts, emotional impacts, treatment impacts, and coping and support sources. In India, the lack of exploration regarding this topic is due to the stigmatization of very private parts, i.e., breast involvement and people rarely discuss it. Thus, there is a need for more such studies to be done, and more attention is required on the role of nurses to assist post-mastectomy women psychologically, spiritually, and physically to cope with their conditions. Findings highlight that mastectomy as a surgical treatment may negatively affect a woman's body image. It's highly recommended to address individual women's psychosocial needs and preferences before undergoing mastectomy in educational sessions by physicians involving nurses with them. Also, proper knowledge about reconstructive procedures should be provided to improve their body image. The counseling sessions can be conducted pre and post-mastectomy by a professional counselor.

Effect of hydrolysis of tetraethyl orthosilicate (TEOS) on titanium distribution of TS-1 zeolite

The hydrolysis process of tetraethyl orthosilicate (TEOS) was tracked by FT-IR analysis, and the effect of hydrolysis time on the distribution of titanium species in TS-1 zeolites was discussed through XRF and UV-vis. The catalytic oxidation performance of TS-1 zeolite was tested by 1-hexene epoxidation as a model reaction. The results show that moderate hydrolysis of tetraethyl orthosilicate can effectively inhibit the formation of extra-framework Ti and increase the content of framework Ti. However, shorter or longer hydrolysis time is not conducive to the entry of titanium into the skeleton and reduce the catalytic performance of TS-1 zeolites. TS-1 prepared with 2 h TEOS hydrolysis time has the best catalytic performance for epoxidation of 1-hexene. Under the reaction conditions of atmospheric pressure and 60 °C, the conversion of 1-hexene can reach 37.5% and the selectivity of 1,2-epoxy hexane can maintain at about 85%, and the result has a guiding role for the development of olefin epoxidation catalyst.

Impact of raw materials for TS-1 zeolite on its crystallization process, Ti species and catalytic properties

To obtain a highly active TS-1 zeolite, we focused on the manipulation of the crystallization process of TS-1 zeolite; the incorporation of Ti species into the MFI-framework along with the hydrolysis and/or dissolution processes was investigated with various Si sources including TEOS, amorphous silica and silicalite-1. We also investigated the effect of the TPAOH content in the synthesis gel on the formation of TS-1. Based on the catalytic evaluations for 1-hexene epoxidation reaction, it was found out that the TS-1 zeolite synthesized using amorphous SiO2 was more efficient than that with TEOS and silicalite-1. Finally, we have found that the framework Ti species experiencing the dissolution and re-construction processes are highly active for 1-hexene epoxidation.

Method for introducing heteroatoms into the framework of FER-type zeolite by intercalation of sub-zeolite of Lamellar precusor PLS-3

A method for introducing heteroatoms Al, Ti, and Sn into the framework of FER-type zeolite was provided. The incorporation of heteroatoms was achieved by intercalation of sub-zeolite of lamellar precursor PLS-3 that possessed disordered structure along layered direction using 4-amion-2,2,6,6-tetramentylniperidine together with salts containing a heteroatom. During intercalation, the molar ratio of Si and heteroatoms can be adjusted between 30 to ∞. Heteroatoms entered the material with the help of hydrothermal synthesis conditions used in the intercalation process, resulting in reordered layered metalosilicate structure. After mild acid treatment of these metalosilicates to remove extra-framework heteroatoms and further calcination, we obtained a three-dimensional zeolite of FER topology with framework Al, Ti, and Sn.