TS-1 Zeolite Research Articles

Preparation and Catalytic Performance in Propylene Epoxidation of Hydrophobic Hierarchical Porous TS-1 Zeolite

Preparation and Catalytic Performance in Propylene Epoxidation of Hydrophobic Hierarchical Porous TS-1 Zeolite

Sn species modified mesoporous zeolite TS-1 with oxygen vacancy for enzyme-free electrochemical H2O2 detecting.

Sn species modified zeolite TS-1 with a unique mesopore structure (Sn-TS-1) and rich oxygen vacancy defects has been designed via a sol-gel method and an ion-exchange process, which can be used as an enzyme-free electrochemical sensor for H2O2 detection. The resultant composite Sn-TS-1 has a high BET surface area of 191 cm2 g-1, fast electron transfer, rich oxygen vacancies, and abundant active sites, showing super performance in H2O2 reduction with a low detection limit (0.27 μM, S/N = 3). The current is linear with H2O2 concentration from 1 to 1000 and 1000 to 11 000 μM, and the corresponding sensitivities are 360.4 and 80.44 μA mM-1 cm-1, respectively. More importantly, this Sn-TS-1 sensor also shows excellent anti-interference ability and stability. This work provides a new idea for an enzyme-free sensor for H2O2 detection in biological environments, which has promising potential in point-of-care (POC) testing for H2O2.

Au supported defect free TS-1 for enhanced performance of gas phase propylene epoxidation with H2 and O2

A facile strategy for the synthesis of a high quality TS-1 zeolite without anatase Ti species via a hydrothermal method using urea as a mineralizer was reported, which exhibits excellent performance in the direct gas phase epoxidation of propylene.

Impact of a polymer modifier on directing the non-classical crystallization pathway of TS-1 zeolite: accelerating nucleation and enriching active sites.

The crystallization process directly affects the physicochemical properties and active centers of zeolites; however, controllable tuning of the zeolite crystallization process remains a challenge. Herein, we utilized a polymer (polyacrylamide, PAM) to control the precursor structure evolution of TS-1 zeolite through a two-step crystallization process, so that the crystallization path was switched from a classical to a non-classical mechanism, which greatly accelerated nucleation and enriched active Ti sites. The TS-1 crystallization process was investigated by means of various advanced characterization techniques. It was found that specific interactions between PAM and Si/Ti species promoted the assembly of colloidal precursors containing ordered structural fragments and stabilized Ti species in the precursors, leading to a 1.5-fold shortened crystallization time and enriched Ti content in TS-1 (Si/Ti = 29). The PAM-regulated TS-1 zeolite exhibited enhanced catalytic performance in oxidative reactions compared to conventional samples.

Switching between classical/nonclassical crystallization pathways of TS-1 zeolite: implication on titanium distribution and catalysis.

In the MFI zeolite crystallization process, the classical crystallization mechanism based upon the addition of silica species is often concomitant with the nonclassical route that is characteristic of the attachment of silica nanoparticle precursors. However, the factors that govern the preferences for each mechanism remain unclear. In this work, we present the impact of switching between these two crystallization pathways on the active sites and the resulting catalytic performance of the titanosilicate TS-1 zeolite. By controlling the self-assembled precursor structures in the early crystallization stage which are mediated by the Ti and H2O in the reaction system, we could achieve the preferred modes of crystal growth of the TS-1 zeolite. We indicate that by directing the predominant crystallization path from the classical to the nonclassical route, it is possible to generate more stable bridging peroxo species upon reaction with hydrogen peroxide, as confirmed by 17O solid-state nuclear magnetic resonance spectroscopy, thus substantially increasing the catalytic performance of the resulting TS-1 for olefin epoxidation.

Synthesis of Hierarchical TS-1 and Its Recycling Catalytic Property for Oxidative Desulfurization

Because of its unique pore structure, good hydrothermal stability and high specific surface area, hierarchical TS-1 zeolite (HTS-1) has become an important catalyst for the deep oxidative desulfurization of fuel oils. In this work, HTS-1 has been successfully synthesized by a hydrothermal crystallization method using the C-SiO2 composite as both silicon source and mesoporous template, tetrapropylammonium hydroxide as microporous template, and tetrabutylorthotitanate as titanium source. The C-SiO2 composite is obtained by mild carbonization of the SiO2/T-40 (Tween 40) xerogel, which is prepared by the two step sol-gel method. The reaction conditions for the oxidative desulfurization (ODS) of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) over HTS-1 are optimized systematically, and the recycling performances of HTS-1 are investigated in detail. After the 15th run, HTS-1 still maintains high DBT conversion (90.6%) and 4,6-DMDBT conversion (86.0%) without deactivation. The samples before and after recycle tests are characterized by XRD, FT-IR, CHN analysis, UV-Vis and SEM techniques. The results indicate that the crystal structure and morphology of regenerated HTS-1 samples are well kept, which accounts for the good structural stability and reusability of HTS-1. In addition, active intermediates for the ODS of bulky organic sulfides over HTS-1, i.e., Ti-peroxo (Ti-OOtBu) species, are captured by the UV-Vis technique. Finally, a possible reaction mechanism for the ODS process over HTS-1 is proposed.

Light-driven carbon dioxide reduction over the Ag-decorated modified TS-1 zeolite

Cu species doped defective Ag/TS-1 owns Ti3+–Vo which could play an vital part in stabilizing Cu2O. It shows high selectivity for CO and C2H5OH under light excitation and photoelectric condition. The possible pathway of CO2RR process is proposed.

Tpaoh Post-Treatment of Dry Gel to Make Hierarchical Ts-1 Zeolites for Catalysis

Tpaoh Post-Treatment of Dry Gel to Make Hierarchical Ts-1 Zeolites for Catalysis

Synthesis of hydrophobic nanosized hierarchical titanosilicate-1 zeolites by an alkali-etching protocol and their enhanced performance in catalytic oxidative desulphurization of fuels

Nanosized hierarchical titanosilicate-1 zeolites (nanoTS-1_D) with variable Ti doping content were synthesized by a simple and sequent two-step procedure consisting of microporous TS-1 nanocrystal synthesis through steam-assisted dry-gel conversion and post alkali-etching treatment for mesopore formation. Comprehensive characterizations, e.g. XRD, N2 sorption isotherms, DLS, UV-Vis, SEM, TEM and water-droplet contact angle, indicated that the resultant nanoTS-1_D materials not only possess abundant intracrystal mesopores and high surface area, but importantly maintain the intrinsic surface hydrophobicity as those of microporous TS-1 zeolites. Consequently, they showed the expected superior catalytic performance in both bulky cyclohexene/cyclooctene epoxidation and phenol hydroxylation probe reactions, contrast to the microporous TS-1 and amorphous Ti-MCM-41 mesoporous counterparts. In the oxidative desulfurization of fuels, they exhibited 100% removal ability for thiophene and its bulky derivatives and excellent recyclability. In addition, a new Ti-dopant directed alkali-etching mechanism has been proposed to illustrate the synthesis of high-specific-surface-area nanoTS-1_D.

TS-1 zeolite with homogeneous distribution of Ti atoms in the framework: synthesis, crystallization mechanism and its catalytic performance

The distribution of titanium (Ti) active sites in the framework of TS-1 zeolite is one of the critical factors affecting its catalytic performance, since it can influence accessibility of the Ti active sites and the catalytic utilization of Ti atoms. Here, TS-1 zeolite with homogeneous distribution of titanium atoms in the framework (named BUS-TS-1) is successfully synthesized via bottom-up strategy at high basicity conditions, and BUS-TS-1 zeolite exhibits better catalytic performance for both olefin and alkane oxidation. The comprehensive explorations on the crystallization behavior of BUS-TS-1 zeolite show that, the gripper-like silicon species, as condensed matter in Q2 and Q3 states (detected by 29Si NMR), can be obtained by the condensation of tetraethyl orthosilicate (TEOS) at high alkalinity conditions. The gripper-like silicon species can condense with Ti-OH to form stable and isolated Si-O-Ti species, so that the phase transfer rates of Si and Ti species match during the entire crystallization process, resulting in the homogeneous distribution of Ti atoms. This work offers a useful strategy for the synthesis of high-performance catalysts by regulating the distribution of Ti active-site within TS-1 framework.

Hydrophobized hollow TS-1 zeolite as pickering interfacial catalyst for selective oxidation reactions

Design of catalyst particles bearing excellent diffusion performance and suitable surface wettability is of great importance to the successful application of Pickering interfacial catalysis. In this study, selective oxidation reactions over hydrophobized hollow TS-1 zeolite were applied as probe reactions to investigate the influence of catalyst diffusion performance closely related to mesopore size on its catalytic activity. Hydrophobized hollow TS-1 zeolite particles were prepared via a post desilication treatment accompanied with precrystallization treatment. The synthesized hydrophobized hollow TS-1 zeolite was characterized by Scanning electron microscopy, Transmission electron microscopy, X-ray diffraction, UV–vis absorption spectrometry, Fourier-transform infrared spectroscopy and Nitrogen adsorption-desorption. Stable Pickering emulsions including 1-hexene-hydrogen peroxide, cyclohexene-hydrogen peroxide and cyclohexanone-water were prepared with hydrophobized hollow TS-1 zeolite particles as emulsifier. HTS-1–393(2)-S zeolite synthesized with precrystallization at 393 K for 2 h presented the maximum values of 43.9 mol/(Ti-mol·h) for 1-hexene epoxidation, 15.7 mol/(Ti-mol·h) for cyclohexene epoxidation and 247.3 mol/(Ti-mol·h) for cyclohexanone ammoximation. In addition, HTS-1–393(2)-S zeolite particles displayed good reusability for more than five cycles.

Synthesis of hierarchically porous zeolite TS-1 with small crystal size and its performance of 1-hexene epoxidation reaction

TS-1 is a typical microporous zeolite, which is hindering the timely diffusion of reaction products and is likely to cause secondary side reactions in heterogeneous catalytic reaction due to the micropore size. However, zeolite TS-1 with hierarchical pores of micropores and mesoporous/macropores can solve this problem to a great extent. In view of this, hierarchical zeolite TS-1 is synthesized by using tetrapropylammonium hydroxide (TPAOH) as structure directing agent and polyacrylamide (PAM) as a hierarchical pore-directing template. The texture property of hierarchical TS-1 can be optimized by changing the amount of PAM in the synthesis gel. With the increase of PAM content, the pore volume and specific surface area of the hierarchical zeolite TS-1 increases. Compared with the conventional TS-1, the hierarchical TS-1 samples have obvious pore size distribution in the range of 20–80 nm. It is interesting that the particle size of TS-1 decreases after adding PAM. When the hierarchical TS-1 is applied to the epoxidation reaction of 1-hexene with H 2 O 2 , the selectivity of the desired product 1,2-epoxyhexane is significantly increased. • Hierarchical zeolite TS-1 with small crystal size has been synthesized by using PAM as template. • The texture property of hierarchical TS-1 can be controlled by changing the amount of PAM. • The selectivity of 1,2-epoxyhexane was greatly improved in 1-hexene epoxidation with H 2 O 2 catalyzed by hierarchical TS-1.

Amino acid-assisted synthesis of TS-1 zeolites containing highly catalytically active TiO6 species

Tailoring the Ti coordination states in titanosilicate zeolites to simultaneously improve feedstock conversion and maximize the target product selectivity remains a challenge in the pursuit of high-performance catalysts for selective oxidation reactions. Herein, we provide a facile strategy to synthesize hierarchical anatase-free TS-1 (MFI-type) zeolites with tetrahedrally coordinated (TiO4) and octahedrally coordinated Ti species (TiO6). The TiO4 species provide high epoxide selectivity, while the TiO6 species afford improved alkene conversion. This strategy is achieved by synergistically using an L-lysine-assisted approach and a two-step crystallization; the two-step crystallization approach prevents the formation of anatase TiO2, while L-lysine stabilizes the TiO6 species and ensures efficient incorporation of TiO6 into the anatase-free TS-1 zeolites. Compared with their conventional counterparts, which only contain TiO4 species, the as-prepared TS-1 zeolites (Si/Ti = 36.9) result in a higher 1-hexene conversion (33%), higher TON value (153), and comparable epoxide selectivity (95%). This synthetic strategy provides avenues to tailor the amount and distribution of Ti species in titanosilicate zeolites to achieve high catalytic performances in various processes.

Tailoring Porosity and Titanium Species of TS-1 Zeolites via Organic Base-assisted Sequential Post-treatment

Tailoring Porosity and Titanium Species of TS-1 Zeolites via Organic Base-assisted Sequential Post-treatment

Liquid-Phase Epoxidation of Propylene with H2O2 over TS-1 Zeolite: Impurity Formation and Inhibition Study

Liquid-Phase Epoxidation of Propylene with H₂O₂ over TS-1 Zeolite: Impurity Formation and Inhibition Study

Synthesis TS-1 nanozelites via L-lysine assisted route for hydroxylation of Benzene

L-lysine is used as a crystallization regulator, and a two-step synthesis method is adopted in a concentrated gel system, which provides a new route to synthesize of nano-sized TS-1 zeolite. The new synthesis strategy was used to successfully synthesize TS-1 zeolite with a particle size less than 100 nm. The rate of crystal nucleation is faster than the crystal growth at the low temperature in the first step. Introduction of L-lysine can prevent crystal growth to form nano-sized TS-1 zeolite at the high temperature in the second step. Meanwhile, L-lysine decrease the pH value of the gel system, which is favorable for Ti atoms to incorporate the TS-1 framework. TS-1 nanozeolite can effectively reduce the diffusion resistance, and nanozeolite has a large specific surface area and high stability. Therefore, TS-1 nanozeolite exhibits the excellent catalytic performance during the hydroxylation of benzene. The conversion of benzene has been greatly improved and the types of by-products are effectively reduced. The conversion of benzene reached 50.2%, and the yield of phenol was 30.8% without by-product benzoquinone. TS-1 nano-zeolite as a catalyst for benzene hydroxylation shows great potential in industrial application.

Effect of ammonium salt on the distribution of titanium species in the synthesis of TS-1 zeolites

Titanium silicalite (TS-1) zeolites with different distribution of Ti species were synthesized through altering different amounts of (NH4)2SO4 as crystallization-mediating agent. The distribution of titanium species of TS-1-X samples (X represents the molar ratio of (NH4)2SO4 to SiO2) was systematically investigated via ICP-AES, FT-IR, UV-vis, UV-Raman and other techniques. The TS-1-X zeolite samples were applied in the epoxidation of 1-hexene reaction. It was found that the appropriate amount of ammonium salt not only facilitated the enrichment of titanium species from liquid phase to solid phase and promoted the incorporation of Ti into the MFI skeleton, but also resulted in the formation of uniformly small TS-1 crystals due to the inhibition of rapid growth of crystals. However, much more amounts of (NH4)2SO4 led to the formation of extra-framework Ti, including anatase TiO2 and amorphous Ti species. Meanwhile it promoted the rapid growth of grain resulting in larger TS-1 crystals. Ti-rich TS-1 sample synthesized with molar ratio of (NH4)2SO4 to SiO2 of 0.2 exhibited higher conversion of 1-hexene (42%) and effective utilization of H2O2 (81.8%). In addition, the effect of ammonium salt's composition on the properties of TS-1 was investigated by experiments and characterizations. It was found that ammonium salt could regulate the process of crystallization through its own anion and changing pH of the synthesis gel.

The Clean Synthesis of Small-Particle TS-1 with High-Content Framework Ti by Using NH4HCO3 and Suspended Seeds as an Assistant.

The synthesis of a TS-1 zeolite with high-content framework Ti and small particles has been developed by adding NH4HCO3 and suspended seeds as an assistant. With the addition of NH4HCO3, the Hofmann decomposition of the tetrapropylammonium cation (TPA+) decreased, and the framework Ti content of the zeolite increased first and then decreased while the particle became larger. With the assistance of suspended seeds, the TS-1 synthesized under a low-alkalinity system possesses small particle size and high-content framework Ti, and it shows the best catalytic activity among the prepared catalysts. Because the decomposition of TPA+ decreased, the mother liquid could be reused in the next run of preparation. Even though the recycled mother liquid was reused five times, all obtained TS-1 samples exhibited similar catalytic performances in propylene epoxidation. This work provides an efficient process for preparing TS-1 with good catalytic performance and reduces the discharge of the waste liquid.

Titanium-rich TS-1 zeolite for highly efficient oxidative desulfurization

The exploration of highly efficient catalysts based on nano-sized Ti-rich titanosilicate zeolites with controllable active titanium species is of great importance in zeolite catalytic reactions. Herein, we reported an efficient and facile synthesis of nano-sized Ti-rich TS-1 (MFI) zeolites by replacing tetrabutyl orthotitanate (TBOT) with tetrabutyl orthotitanate tetramer (TBOT-tetramer) as the titanium source. The introduced TBOT-tetramer slowed down the zeolite crystallization process, and accordingly balanced the rate of incorporating Ti and the crystal growth and inhibited the massive formation of anatase species. Notably, the prepared Ti-rich TS-1 zeolite sample had a Si/Ti as low as 27.6 in contrast to conventional one with a molar ratio of 40. The TBOT-tetramer endowed the titanosilicate zeolites with enriched active titanium species and enlarged external surface area. It also impeded the formation of anatase species, resulting in superior catalytic behavior toward the oxidative desulfurization of dibenzothiophene compared with the conventional TS-1 zeolite counterpart prepared with TBOT.

Gold Stability and Diffusion in the Au/TS-1 Catalyst

The structure and mobility of gold nanoclusters entrained in the titanosilicate zeolite TS-1 were investigated using ab initio molecular dynamics to characterize the stability and diffusion of cata...