TS-1 Zeolite Research Articles

Effective incorporation of Ti atom into TS-1 zeolite assisted with oxalic acid additive

Abstract The effect of introducing oxalic acid into the mother gel of TS-1 zeolite on the crystallization behavior and physiochemical properties was investigated. The addition of oxalic acid with a buffering action significantly accelerated the crystallization process of TS-1 while simultaneously inhibiting the formation of anatase. The resultant TS-1 zeolites displayed enhanced performance in catalyzing the epoxidation of 1-hexene with H2O2 as an oxidant.

Lysine-assisted synthesis of plate-like TS-1 zeolite for 1-hexene epoxidation

Plate-like TS-1 zeolites offering a short diffusion pathway along the b-axis are highly desirable catalysts in the reaction of alkene epoxidation. Herein, we successfully developed a simple synthetic strategy toward reducing the thickness along the b-axis of TS-1 zeolite crystals, l-lysine adopted as a zeolite growth modifier was firstly proposed to prepare plate-like TS-1 zeolite. Meanwhile, through tuning the preliminary aging time, plate-like TS-1 zeolites with thickness in the range of 80–1000 nm can be controllable obtained. In this work, the synthesis parameters controlling the formation of plate-like TS-1 zeolites are studied, and the factors controlling the zeolite growth were well elucidated. Compared with the conventional TS-1 zeolite as well as the plate-like TS-1 synthesized in the fluoride-containing medium, the obtained plate-like TS-1 shows improved catalytic performances in catalyzing epoxidation of 1-hexene.

Regulating the microenvironments and the d-band center of hierarchical NiMoS/TS-1 catalyst by ZrO2 to enhance the hydrodesulfurization performance of dibenzothiophene

The microenvironments including the surface hydroxyls, the oxygen vacancies, and the d-band center of hierarchical TS-1 zeolite pickled by hydrochloric acid were regulated by ZrO2, the effect of ZrO2 on the physicochemical properties and the catalytic performances of the corresponding NiMoS supported catalysts were studied. The experimental and theoretical calculation results show that the d-band center, the surface hydroxyl groups, and the oxygen vacancies were regulated after incorporation of ZrO2. Resulting in the modulated acidity of the support and the metal support interaction of the catalysts, further promoting the formation of type-II NiMoS active phases. The catalytic performance evaluations show that catalyst NiMo/1-ZAT exhibits the superior HDS performance, kinetic study further demonstrated that the enhanced catalytic activity was mainly contributed by the improved direct desulfurization activity generated from the moderate support acidity, suitable MSI, highest sulfidation degrees, most type-II NiMoS active phase and highest activity of individual active sites.

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.

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.

Accelerated synthesis of TS-1 zeolite for epoxidation of 1-hexene under ambient environment: Role of sodium persulfate in inhibiting the formation of anatase species

Titanium silicalite-1 zeolite (TS-1) has been widely used as a catalyst for the epoxidation of 1-hexene. However, fast synthesis of TS-1 with high activity and stability remains a great challenge. In this study, a new strategy using sodium persulfate (SPS) as a crystallization modifier was proposed for the accelerated synthesis of anatase-free TS-1. The anatase-free TS-1 (TS-20-SPS) could be obtained after 20 h of hydrothermal crystallization. TS-20-SPS had a low Si/Ti ratio (31) and achieved a high conversion (20%) in the epoxidation of 1-hexene at room temperature (298 K), which was 200% higher than that of TS-1 synthesized without adding SPS. The addition of SPS not only accelerated the crystallization due to the generation of ·OH, but also reduced the pH value of the system to avoid the generation of anatase. This SPS-assisted approach offers an avenue for the accelerated synthesis of high-performance, anatase-free TS-1.

Toluene Degradation by Iron-Doped TS-1 Zeolite Heterogeneous Catalyst Supported in a Bubbling Reactor

Toluene Degradation by Iron-Doped TS-1 Zeolite Heterogeneous Catalyst Supported in a Bubbling Reactor

Kinetic insights into reaction pathways of acrolein formation in propylene epoxidation by H2 and O2 over Au/TS-1 catalyst

Propylene epoxidation by H2 and O2 to propylene oxide (HOPO), as a novel method for PO production, has attracted widespread attention due to its economic and environmental advantages. Acrolein is a notable byproduct arising in HOPO reaction over Au/TS-1 catalyst, and is traditionally thought to be exclusively formed on Au site through propylene oxidation. However, on the intraporous and external surface Au sites of Au-Ti catalysts, the HOPO reaction have been shown to proceed by different mechanisms, yet the effect of active sites distribution on acrolein formation is far from being understood. Herein, we found that the reaction orders in acrolein formation on Au/TS-1 catalyst (H2, 0.19; O2, 0.44; C3H6, 0.44) relative to Au/TS-1 with blocked pores (Au/TS-1-B) catalyst (H2, −0.36; O2, 0.61; C3H6, 0.52) were quite different, suggesting a variation in the reaction pathway on the catalysts with different Au locations. Moreover, it is found that PO can be converted to acrolein by O2 on TS-1 zeolite, which is absent on TS-1-B zeolite without micropores. Consequently, acrolein formation on Au/TS-1 catalyst can proceed through two parallel pathways: propylene hydro-oxidation on Au site, and PO conversion by O2 inside micropores. Furthermore, by designing and preparing the Au/TS-1 catalysts with different structures, the Au locations are closely related to acrolein formation mechanism and kinetic behaviors. This work provides kinetic insights into the acrolein formation pathways in the HOPO reaction on Au/TS-1 catalyst, and is helpful to the rational design and preparation of efficient catalysts with high selectivity.

TS-1@MCM-48 Core-Shell Catalysts for Efficient Oxidation of p-Diethylbenzene to High Value-Added Derivatives.

To expand the market capacity of p-diethylbenzene (PDEB), core-shell zeolite (TS-1@MCM-48) is designed as a catalyst for PDEB oxidation. TS-1@MCM-48 catalyst is synthesized by in-situ crystallization method and characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), N2 adsorption-desorption, in-situ electron paramagnetic resonance (EPR) and 29Si nuclear magnetic resonance (29Si MAS-NMR). Oxidation of PDEB by H2O2 was investigated systematically in liquid phase. The conversion of PDEB over TS-1@MCM-48 was 28.1 % and the total selectivity was 72.6 %, where the selectivity of EAP (p-ethylacetophenone) and EPEA (4-ethyl-α-methylbenzyl alcohol) was 28.6 % and 44.0 %, respectively. Compared with TS-1 and MCM-48 zeolite, the conversion rate of reactants and the selectivity of products have been significantly improved. The catalytic performance of TS-1@MCM-48 is derived from its well-crystallized microporous core and mesoporous shell with regular channels, which make active sites of TS-1 zeolite in the catalyst be fully utilized and mass transfer resistance be largely reduced. Further through theoretical calculation, we propose that the oxidation of PDEB is the result of the combination and mutual transformation of free radical process and carbocation process. Core-shell structure ensures the conversion rate of raw materials and improves the selectivity of products.

Fabrication of gold nanoparticles supported on hollow microsphere of nanosized TS-1 for the epoxidation of propylene with H2 and O2

The TS-1 microsphere was facilely prepared via a direct spray drying of the mixture containing the nanocrystal TS-1 and mother liquor. The calcined TS-1 zeolites possess a hollow structure and numerous intercrystalline mesopores, which may facilitate the diffusion properties. Au nanoparticles were loaded on TS-1 support by utilizing a deposition–precipitation process to prepare the Au/TS-1-M catalysts for propylene epoxidation in the presence of H2 and O2 conditions. The effects of the Ti and Au loadings on the structure, porosity, morphology, and catalytic performances of the Au/TS-1 catalysts have been investigated by various techniques. Under the optimized synthesis conditions (Si/Ti molar ratio = 57, 0.49 wt% Au), a propylene conversion of 6.1 % and a PO selectivity of 91.7 % were obtained on the Au/TS-1 catalyst. A PO formation rate of 186.8 gPO·kgcat.−1·h−1 was achieved at the 20th hour.

Synthesis of a hierarchical TS-1 zeolite with tunable macropore size and its performance in the catalytic oxidation reactions

Hierarchical TS-1 zeolites with tunable macropore size were synthesized based on a steam-assisted crystallization strategy, which exhibited excellent activity in the catalytic oxidation reactions.

Ketonization of propionic acid over TS-1 and Ti-Beta zeolites: Mechanism and effects of topology and hydrophobicity

Ketonization of propionic acid has been investigated on Lewis acidic TS-1 and Ti-Beta zeolites to understand the reaction mechanism and effects of pore topology and hydrophobicity. Characterizations showed that TS-1 and Ti-Beta (Si/Ti = 40) exhibited a similar acidity whereas TS-1 was more hydrophobic than the silanol-rich Ti-Beta. TS-1 showed higher activity, selectivity, stability and was more resistance to H2O than Ti-Beta. A combination of infrared spectroscopic, isotopic and kinetic studies showed that the molecularly adsorbed monodentate propionic acid is the most abundant reactive intermediate, and C-C coupling is the rate-determining step. The mechanism of ketonization of propionic acid at isolated tetrahedral Ti centers can be described by a Langmuir-Hinshelwood model. The turnover rate on TS-1-40 is ∼ 1.3 times higher than that on Ti-Beta-40, which is consistent with the lower fitted free activation energy, i.e., the energy difference between C-C coupling transition state and two co-adsorbed propionic acids at a Ti center. The slightly lower activation enthalpy on Ti-Beta-40 than TS-1-40 is over-compensated by much larger entropy penalty, due to more silanol groups and hydrogen bonded propionic acids in close proximity to the Ti center for Ti-Beta-40, which impose additional steric hindrance to bulkier C-C coupling complex at transition state and outweigh the difference of steric hindrance of pore confinement between MFI and BEA frameworks. This work provides insight into the ketonization mechanism on Lewis acidic zeolites, and indicates that moderate pore size with hydrophobic property promotes ketonization of carboxylic acid at isolated tetrahedral Ti centers confined in zeolites.

Novel titanium-containing precursors for the fabrication of hierarchical TS-1 and the enhanced catalytic performance for olefins

Hierarchical TS-1 zeolites with high catalytic activities toward 1-hexene epoxidation were successfully synthesized by using novel titanium-containing precursors. The precursors were prepared by o/m/p-dihydroxybenzene with tetrabutyl titanate, which not only promote the uniform distribution of titanium sources and reduce the aggregation of Ti species, but also contribute to regulating the coordination state of Ti species and increasing the frameworks Ti contents. TS-m/p-DHB-48h zeolites display excellent catalytic performance in the epoxidation reaction of 1-hexene, and the conversion improved by 41.9 % and 34.7 %, respectively. The hierarchical zeolites also exhibit superior 1,2-epoxyhexane selectivity, which will greatly improve the efficiency of industrial production.

Amide-assisted synthesis of TS-1 zeolites with active Ti(OH2)2(OH)2(OSi)2 sites toward efficient oxidative desulfurization

Aiming to promote the activity of TS-1 zeolite in catalytic oxidative desulfurization (ODS), a general amide-assisted strategy was proposed to synthesize hierarchical TS-1 zeolite with rich and homogeneously distributed Ti(OH2)2(OH)2(OSi)2 species. Strong interactions between acrylamide (AM) and Si/Ti as well as self-polymerization of AM in synthetic gels change the zeolite formation process, thus to effectively construct Ti(OH2)2(OH)2(OSi)2, promote Ti evenly distribution and form micro-mesopore structure. The activity of Ti(OH2)2(OH)2(OSi)2 was evaluated by ODS of refractory sulfur-containing compounds. The advantages of Ti(OH2)2(OH)2(OSi)2 over TiO4 in substrate adsorption and reactive intermediate formation for ODS were further proved by theoretical calculations. By adjusting AM amount to optimize the Ti(OH2)2(OH)2(OSi)2 content and distribution, the obtained catalyst achieves 134.8 h-1 of turnover frequency and 100 % DBT removal at ten minutes, and maintains > 92 % removal after seven cycles at 333 K. This facile active-site construction strategy is promising to be extended to other heteroatom-containing zeolite catalysts.

Enhancing the accessible TiO6 concentration and the hydrophobicity of hierarchical TS-1 zeolites for alkene epoxidation and oxidative desulfurization

The accessible TiO6 concentration and the hydrophobicity of hierarchical TS-1 zeolites are both considered as critical factors for promoting the catalytic performance of selective oxidation. However, simultaneously enhancing these two factors still remains a challenge. Herein, hierarchical TS-1 zeolites with high hydrophobicity and concentration of accessible TiO6 were fabricated via sequential amphiphilic organosilane-assisted pre-treatment, dry-gel conversion and hydroxyl radical post-treatment, using amphiphilic organosilane and surfactant as meso-porogens. The synthesis mechanism was investigated, and it was found that the interaction between the amphiphilic organosilane and Ti species formed during the pre-treatment benefited the formation of accessible TiO6 during the subsequent dry-gel conversion. During the post-treatment of zeolite with H2O2 solution under ultraviolet light irradiation, appropriate H2O2 concentration facilitated the generation of hydroxyl radical and thus enhanced the hydrophobicity of zeolite without significantly influencing the TiO6 concentration. The hierarchical TS-1 displayed excellent catalytic performances in 1-hexene epoxidation and oxidative desulfurization, with conversion improvements of 91.2%±2.8% and 348%±17%, respectively, compared with the conventional counterpart.

Approaching High-Performance TS-1 Zeolites in the Presence of Alkali Metal Ions via Combination of Adjusting pH Value and Modulating Crystal Size.

Lewis acid zeolites play an important role in industrially important green reactions closely related to fine chemical and biomass conversion. Titanium-doped TS-1 zeolite is a milestone Lewis acid zeolite widely used in industrially significant green oxidation processes with hydrogen peroxide as an oxidant under mild conditions. TS-1 zeolites are normally synthesized in basic conditions under hydrothermal treatment. Up to now, there has still been no success in synthesizing active TS-1 Lewis acid zeolites by using inorganic alkali, e.g., NaOH or KOH as base, which is cheaper and more stable compared to the quaternary ammonium hydroxide or organic amines used in traditional synthesis. Here, an inorganic base of NaOH was employed in synthesizing active TS-1 zeolites for the first time. The crucial factor was the control of adverse effects of sodium cations on the incorporation of active titanium cations. Higher catalytic activity was achieved by further reducing the size of the TS-1 crystal by using the seed-added strategy, which uses the catalytic activity of a commercial catalyst, the production cost being much lower than commercial TS-1 catalysts, indicating great commercial potential and the possibility of preparing other cheap Lewis acid catalysts by using inorganic alkali.

Utilization of agricultural waste (rice husk) in synthesis of TS-1 zeolite as a support for NiMo nanocatalyst employed in hydrodesulfurization of heavy oil

Agricultural waste, rice husk (RH) was treated to obtain rice husk ash (RHA) and utilized as silica precursor in hydrothermal synthesis of TS-1 zeolite. Results of characterization analyses, XRD, FTIR, FESEM and N2 adsorption-desorption, confirmed that TS-1 zeolite was properly synthesized from RHA. Synthesis of TS-1 was also carried out with TEOS for comparison of textural properties. Prepared TS-1 zeolite with RHA was used as support for HDS catalyst preparation. Molybdenum active phase and nickel promoter were loaded via three different methods, impregnation, precipitation and solution combustion, to obtain NiMo/TS-1 hydrodesulfurization catalyst. EDX dot-mapping and H2-TPR analyses indicated on better preparation of NiMo/TS-1 catalyst by solution combustion method, in terms of distribution and amount of successfully loaded metal over the support surface. Hydrodesulfurization (HDS) activity of synthesized samples was examined in hydrodesulfurization of heavy oil feed, carried out in a continuous fixed bed reactor apparatus. Performance test revealed that NiMo/TS-1 catalyst synthesized by solution combustion method eliminated 63.5 % of the feed sulfur content (4000 ppm); a superior hydrodesulfurziation activity, compared to the samples prepared via impregnation and precipitation methods with 40.8 % and 50.2 % sulfur removal, respectively. Amount of sulfur present in the feed and treated product was determined with GC-MS analysis.

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.

In-Situ Growth of Embryonic TS-1 on Amorphous Silica via Steam-Assisted Crystallization: Correlation of Structural Properties and Catalytic Performance of Embryonic, Crystalline, and Amorphous Titanosilicate Catalysts

In-situ growth of supported embryonic TS-1 zeolite (<10 nm) on a silica support was achieved by steam-assisted crystallization (SAC). The use of low amounts of TPABr and steam at a moderate temperature of 130 °C was the key factor to control partial transformation of silica into supported embryonic TS-1. Compared with the reference crystalline TS-1, supported embryonic TS-1 exhibits a higher activity in dibenzothiophene (DBT) oxidation (TOF: 8–275 h–1 vs 2.7–160 h–1 at 30–98 °C), a higher resistance to poisoning by nitrogen-containing compounds, and a higher selectivity (>97%) in the productive utilization of the oxidant in DBT oxidation. The activity of the amorphous titanosilicate (TOF: 21.2–210 h–1 at 30–80 °C), the solid precursor of the SAC process, was higher than that of the embryonic and the crystalline TS-1. The analysis of the structural properties–catalytic performance of these catalysts showed an improved accessibility to defective Ti active sites “Ti(OH)(OSi)3” with higher catalytic activity. The results of this study should be encouraging to unearth many other active amorphous catalysts with the potential of industrial application.

Defective zeolite TS-1 confined Pt nanoclusters with superior performance for CO and soot catalytic oxidation

Catalytic oxidation is an important reaction in the treatment of diesel exhaust. Herein, a facile self-assembly strategy has been developed to synthesize defective zeolite confined-catalyst Pt@TS-1 with ultra-low Pt loading, which shows super catalytic activity in the CO conversion (T90 = 175 °C) and soot oxidation (T90 = 490 °C). Owing to the confinement effect of zeolite, the obtained catalyst Pt@TS-1 exhibits a high percentage of Pt2+, smaller Pt nanoparticles and sufficient Ti3+-VÖ defects, which can greatly accelerate the adsorption and conversion of CO, and the deep oxidation of soot. In-situ DRIFTS results demonstrate that rich and smaller Pt nanoparticles confined in zeolite may be responsible for excellent CO conversion. Significantly, the catalyst Pt@TS-1 also shows excellent catalytic stability and good resistance to water and sulfur, showing the potential for industrial applications.