Ti-containing Zeolites Research Articles

Synergizing tetra-coordinated Ti sites anchored onto micropore-free silica with Au sites to boost propylene hydro-oxidation

Constructing tetra-coordinated Ti sites on the micropore-free oxide surface as a substitute for the Ti-containing zeolites to synergize with Au sites for propylene epoxidation with H2 and O2 to propylene oxide (HOPO) can solve the problems resulting from micropores but remains a great challenge. Here, we report a facile strategy to anchor tetra-coordinated Ti sites onto micropore-free silica by precisely cleaving the surface hydroxyl and siloxane bridges of silica to generate under-coordinated O sites to bind Ti sites. Multiple spectroscopic characterizations, including ultraviolet Raman, UV–vis and Fourier transformation infrared and 29Si solid nuclear magnetic resonance spectroscopy, demonstrate the anchored Ti sites on the surface of silica are mainly the target tetra-coordinated ones. It is further unveiled that the removal of surface hydroxyl also improves the hydrophobicity of synthesized Ti-SiO2, which enhances the desorption of PO. Benefitting from the weak acidic properties, high hydrophobicity and micropore-free structures, the tetra-coordinated Ti sites on silica synergize well with Au sites in propylene epoxidation, demonstrating high activity, selectivity and stability, which are superior to those achieved on the most extensively researched Au/TS-1 catalysts.

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.

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.

Evolution of Morphology, Fractal Dimensions, and Structure of (Titanium) Aluminosilicate Gel during Synthesis of Zeolites Y and Ti-Y

Zeolite Y and Ti-containing zeolite Y (1%, 2% and 5% TiO2) were synthesized by a hydrothermal seed-assisted method. In order to evidence the evolution of morphology, structure, and fractal dimensions during the zeolitization process at certain time intervals, a small volume from the reaction medium was isolated and frozen by lyophilization. The obtained samples were characterized by scanning electron microscopy (SEM), wide-angle X-ray diffraction (XRD), and small-angle X-ray scattering (SAXS). The fractal dimension values of the isolated samples, calculated from SAXS data, evidenced a transition from small particles with a smooth surface (2.021) to compact structures represented by zeolite crystallites with rough surfaces (2.498) and specific organization for zeolite Y. The formation of new structures during hydrothermal treatment, the increase in crystallite size and roughness due to the continuous growth were suggested by variation of fractal dimensions values, SEM microscopy images and X-ray diffractograms. The incorporation of titanium in low concentration into the zeolite Y framework led to the obtaining of low fractal dimensions of 2.034–2.275 (smooth surfaces and compact structures). On the other hand, higher titanium concentration (2%) led to an increase in fractal dimensions indicating structures with rougher surfaces and well-defined self-similarity properties. A mechanism for zeolite synthesis was proposed by correlation of the results obtained through morphological, structural, and fractal analysis.

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.

Construction of Ti-containing zeolite with highly enhanced catalytic activity by active species surface implanting strategy

Herein, highly efficient Ti-containing zeolite catalyst (Ti/Al-HSZ) has been prepared by an active catalysis species surface implanting strategy (ACS-SIS) through the combination of precedent acid treatment and subsequent recrystallization. Compared with commercial titanosilicate zeolite catalysts and Ti-HSZ catalyst synthesized by one-step method, Ti/Al-HSZ-c-3.5d-AT catalyst presents highly enhanced catalytic activity and turnover number values in the epoxidation of linear and cycloalkenes by using 30% H2O2 as oxygen agent under mild reaction conditions. Particularly for the conversion of bulky linear alkene and cycloalkene (1-dodecene and cycloheptene), the catalytic activity of Ti/Al-HSZ-4M‐3.5d‐AT can attained more than three times than that over Ti-HSZ-3.5d-AT. Based on systematical comparison and analysis, on one hand, the excellent catalytic performance of Ti/Al-HSZ is ascribed to its unique hollownest morphology that acts as ideal reaction space by providing with plenty of hierarchical porous structure and high external surface, which is beneficial for the diffusion and mass transfer of bulky substrate. On the other hand, the high content of active open Ti species locating on the surface of catalyst is particularly beneficial for the formation of transition state to accelerate the epoxidation reaction. Not only the Ti source utilization rate but also the Tiopen incorporated rate of Ti/Al-HSZ-4M‐3.5d‐AT prepared by ACS-SIS is much higher than that of Ti-HSZ prepared by one-step hydrothermal synthesis route. The effects of acid treatment and recrystallization on the zeolite framework, morphology, chemical composition, and Ti coordination states have been thoroughly discussed. The ACS-SIS is believed to be an effective route to construct excellent solid heterogeneous catalyst to meet the urgent need of green chemistry for sustainable development.

A novel conversion of Ti-bearing blast furnace slag into Ti-containing zeolites: Comparison study between FAU and MFI type zeolites

In this work, the synthesis of FAU and MFI type Ti-containing zeolites from Ti-bearing blast furnace slag was first achieved via a facile hydrothermal method. The synthesized zeolites were identified to be Ti-NaX and Ti-NaZSM-5 zeolites, with excellent specific surface area of 663.2 and 325.2 m2/g, respectively. Ti species in the Ti-NaX zeolite contained the framework Ti species and amorphous extraframework Ti species, while the Ti species in Ti-NaZSM-5 zeolite were in the form of the two species of above and another anatase TiO2. To investigate the potential application of the synthesized zeolites in photocatalysis field, an exploratory study was carried out by degradation of methyl orange under UV irradiation. As demonstrated, the Ti-NaZSM-5 zeolite showed higher photocatalytic performance and was more suitable to be the support of the TiO2 photocatalyst than the Ti-NaX zeolite. Innovative conversion of TBFS into Ti-containing zeolite materials does provide not only a novel and low-cost approach to waste management, but also a promising material candidate for catalytic oxidation and environmental purification.

Direct Synthesis of Ti-Containing CFI-Type Extra-Large-Pore Zeolites in the Presence of Fluorides

Ti-containing zeolites showed extremely high activity and selectivity in numerous friendly environmental oxidation reactions with hydrogen peroxide as a green oxidant. It will be in high demand to synthesize Ti-containing crystalline extra-large-pore zeolites due to the severe restrictions of medium-pore and/or large-pore zeolites for bulky reactant oxidations. However, the direct synthesis of extra-large-pore Ti-zeolites was still challengeable. Here, we firstly report a strategy to directly synthesize high-performance Ti-containing CFI-type extra-large-pore (Ti-CFI) zeolites assisted with fluorides. The well-crystallized Ti-CFI zeolites with framework titanium species could be synthesized in the hydrofluoric acid system with seed or in the ammonium fluoride system without seed, which showed higher catalytic activity for cyclohexene oxidation than that synthesized from the traditional LiOH system.

Fluoride-mediated synthesis of TON and MFI zeolites using 1-butyl-3-methylimidazolium as structure-directing agent

In this work, 1-butyl-3-methylimidazolium (1B3MI) cation has been employed as a structure-directing agent for the synthesis of pure silica and Ti-containing zeolites in fluoride media. The 1B3MI OSDA exhibited distinct phase selectivity depending on the synthesis conditions, and particularly the concentration of the synthesis gel. Thus, under more diluted conditions (H2O/SiO2 = 14), the 1B3MI cation yielded pure silica TON zeolite with high crystallinity. Attempts to obtain Ti-containing zeolites, however, failed at this diluted condition even after 15 days of synthesis. In contrast, highly crystalline Ti-MFI was the only phase obtained upon reducing the H2O/SiO2 molar ratio from 14 to 7. The presence of Ti in the MFI zeolite framework was confirmed by both infrared and DRS UV-vis spectroscopies. The presence of intact OSDA molecules within the micropores was inferred from elemental analysis and 13C CP-MAS NMR spectroscopy. On the other hand, thermogravimetric analyses showed a different packing of the 1B3MI cation in the pure silica TON and Ti-MFI samples. Moreover, the environments for Si and F species in the as-made materials were investigated by means of 29Si and 19F MAS NMR, respectively. Finally, molecular simulations showed that the most stable arrangement of the 1B3MI cations involves the location of the imidazolium rings on the channel intersections and of the butyl chains on the sinusoidal channels.

Direct Hydroxylation of Benzene to Phenol Using Palladium–Titanium Silicalite Zeolite Bifunctional Membrane Reactors

A series of titanium silicalite zeolite catalysts were successfully incorporated inside a Pd membrane reactor aiming to improve the direct hydroxylation of benzene to phenol. The correlation between the membrane structure and the reaction efficiency was investigated. The influences of reactor configuration, feed mode, and catalysts on benzene conversion, product yield, hydrogen conversion, and water production rate were examined in detail. The reaction was very sensitive to the porosity of Ti-containing zeolite film and the bonding state of the titanium atom in the titanosilicates (i.e., framework and extraframework titanium). The framework titanium could adsorb active oxygen species to form Ti peroxo species which would suppress the decomposition, while the extraframework titanium promoted the decomposition of active oxygen species leading to more water production. Large inter- and intracrystalline pores as well as mesopores provided the reactive species greater opportunity to contact directly with frame...

Design of Layered Silicate by Grafting with Metal Acetylacetonate for High Activity and Chemoselectivity in Photooxidation of Cyclohexane

We succeeded in the immobilization of Ti(IV) acetylacetonate onto interlayer surfaces of a layered silicate HUS-2 (Hiroshima University Silicate-2, Si20O40(OH)4·4[C5H14NO]) and investigated the photocatalytic acitivity of Ti-incorporated HUS-2 toward the partial oxidation of cyclohexane to cyclohexanol and cyclohexanone under solar light irradiation. XRD, SEM/EDX, (13)C CP and (29)Si MAS NMR and UV-vis measurements of Ti-incorporated HUS-2 confirmed that the isolated tetrahedral Ti species were homogeneously immobilized onto silicate sheets via Si-O-Ti covalent bond and acetylacetonate ligands were removed after calcination. Ti-incorporated HUS-2 showed ca. 100% selectivity for partial cyclohexane oxidation and considerably higher yields (cyclohexanol and cyclohexanone) than TS-1, a typical Ti-containing zeolite. Higher yields were obtained when the calcined Ti-incorporated HUS-2 with a larger amount of the grafted Ti were used.

Highly Selective Liquid-Phase Oxidation of Cyclohexane to KA Oil over Ti-MWW Catalyst: Evidence of Formation of Oxyl Radicals

Various types of Ti-containing zeolites, i.e., Ti-MWW, TS-1, Ti-MOR, and Ti-BEA, have been evaluated as candidates for the liquid-phase oxidation of cyclohexane using t-butyl hydroperoxide (TBHP, 7–8 wt %) as model oxidant. Ti-MWW zeolite displayed the highest activity for cyclohexanol and cyclohexanone (KA oil) with an overall selectivity higher than 90% at 80 °C, making this catalyst a candidate of choice for industrial KA oil production by deperoxidation of cyclohexyl hydroperoxide. The effect of the reaction temperature, reaction time, catalyst amount, and catalyst stability on Ti-MWW was surveyed in detail. The Ti-MWW catalyst showed a stable performance and could be recycled at least four times without detectable Ti leaching and loss of structural stability. The active sites for cyclohexane oxidation appeared to be located near external 12-ring cups in the Ti-MWW framework as suggested by a series of position-selective poisoning tests with tripropyl- and triphenylamine, impelling cyclohexane diffusi...

Oxidative Desulfurization of Fuel Oils

Several attractive approaches toward oxidative desulfurization of fuel oils, such as using H 2 O 2 /organic acids, H 2 O 2 /heteropolyacid, H 2 O 2 /Ti-containing zeolites, and other non-hydrogen peroxide systems (e.g., t -butyl hydroperoxide etc.) are reviewed. A new alternative oxidative desulfurization process using emulsion catalysts was developed mainly by our group, is introduced in detail. Limitations because of interphase mass transfer are greatly reduced in the emulsion reaction medium. The amphiphilic emulsion catalysts can selectively oxidize the sulfur-containing molecules present in diesel to their corresponding sulfones when using H 2 O 2 as the oxidant under mild conditions. The sulfones in the oxidized fuel oils can be removed by a polar extractant. The sulfur level of a prehydrotreated diesel can be lowered from a few hundred μg/g to 0.1 μg/g after oxidation and subsequent extraction whereas the sulfur level of a straight-run diesel can be decreased from 6000 to 30 μg/g after oxidation and extraction. 摘要：综述了燃油的氧化脱硫, 包括一些具有吸引力的氧化脱硫方法, 如 H 2 O 2 /有机酸, H 2 O 2 /杂多酸, H 2 O 2 /含钛分子筛和其它非过氧化氢体系 (如叔丁基过氧化物等). 对本课题组开发的新型乳液催化氧化脱硫体系进行了详细的介绍. 在乳液体系中, 界面间的传质限制被大大降低. 在温和条件下, 双亲性乳液催化剂可以将柴油中的含硫化合物选择氧化成其相应的砜类化合物. 氧化得到的砜可以使用极性萃取剂将其从油品中除去. 经过氧化和萃取之后, 加氢柴油中的硫含量可以从几百 μg/g 降低至 0.1 μg/g, 而直馏柴油中的硫含量则可以从 6000 μg/g 降低至 30 μg/g. The sulfur-containing compounds in diesel can be oxidized to their corresponding sulfones by the amphiphilic emulsion catalysts under mild conditions, and the sulfones can be removed by a polar extractant.

Hydrophobic Modification of Ti-Containing Zeolite (TS-1) and Their Applications in Liquid-Phase Selective Catalytic Reactions

Abstract Hydrophobic modification of Ti-containing zeolite (TS-1) was performed by using triethoxyfluorosilane (TEFS). TS-1 after modification with TEFS (w = 1%) showed higher catalytic activity for the ammoximation of cyclohexanone than those on unmodified and modified TS-1 with TEFS (w = 5%) due to effective modification without covering the underlying catalytically active Ti-oxide species.

New Route for the Preparation of Pd and PdAu Nanoparticles Using Photoexcited Ti-Containing Zeolite as an Efficient Support Material and Investigation of Their Catalytic Properties

A simple and unique route to synthesize nanosize Pd particles using a zeolite support including a single-site Ti oxide moiety (TS-1) under UV-light irradiation has been developed. By the photoassisted deposition (PAD) method, a Pd precursor can be deposited directly on the photoexcited tetrahedrally coordinated Ti oxide moiety within the zeolite frameworks from an aqueous solution of Pd. The subsequent reduction with H2 generates the nanosized Pd metal particles with a narrow size distribution (PAD-Pd/TS-1). Characterization by XAFS and TEM analysis revealed that the size of the metal particles depends on the preparation methods and that the smaller sizes of Pd nanoparticles were formed on the photodeposited catalysts compared with the conventionally prepared impregnated catalysts. PAD also provides PdAu bimetallic nanoparticles from an aqueous solution of mixture of PdCl2 and HAuCl4. The catalytic activities in the direct synthesis of hydrogen peroxide (H2O2) using H2 and O2 gases under atmospheric pressure were strongly dependent on the preparation method and the presence of Au atoms. Here, both deposition of PdAu onto the TS-1 moiety under UV-light irradiation was the most efficient for the above reaction. The applicability of the present catalytic system is highlighted by the one-pot reaction of phenol using PAD-Pd/TS-1 in the presence of H2 and O2, in which both Pd nanoparticles and isolated Ti oxide moieties within the frameworks participate in the formation of H2O2 and oxidation of phenol, respectively.

Photocatalytic Oxidation Desulfurization of Diesel Oil Using Ti-containing Zeolite

Photocatalytic oxidation of dibenzothiophene with hydrogen peroxide using Ti-containing zeolite (TS-1) as photocatalyst at ultraviolet lamp irradiation has been studied. The effect of the amount of photocatalyst and hydrogen peroxide concentration were investigated in detail. Optimal photocatalyst amount and hydrogen peroxide concentration were obtained at amounts of near 0.1 g/10 mL and 3 mL/10 mL, respectively. The oxidation proceeds in the oil phase and most of the oxidation products transfer to water phase, resulting in the successive removal of the dibenzothiophene from the n-octane phase without additional extraction by solvent. Kinetics parameters of the photocatalytic oxidation of DBT were measured and calculated. The result shows the kinetics of photocatalytic oxidation of DBT is first-order. The activity of photocatalyst was not obviously decreased after reuse ×5. Using this photocatalytic oxidation system can effectively reduce the sulfur content in diesel oil. The resulting oil contained less than 100 μg/g sulfur, and this corresponds to 90% removal.

Synthesize of nano-sized Pd metal catalyst on Ti-containing zeolite using a photo-assisted deposition (PAD) method

Using a photo-assisted deposition (PAD) method, the nano-sized Pd metal can be highly deposited on Ti-containing silicalite zeolite (TS-1). This nano-sized Pd metal can exhibit the high efficiency for H2O2 production under a flow of H2 and O2 and further applied to the subsequent partial oxidation of phenol on TS-1.

Catalysis of nanosized Pd metal catalyst deposited on Ti-containing zeolite by a photo-assisted deposition (PAD) method

Abstract Using a photo-assisted deposition (PAD) method, nanosized Pd metal can be highly dispersed on Ti-containing silicalite zeolite (TS-1) under UV-light irradiation (PAD-Pd/TS-1). The nanosized Pd metal was deposited directly on the photo-excited tetrahedrally coordinated titanium oxide species (tetra-Ti-oxide) of TS-1 zeolite. Under the flow of H2 and O2 in water solvent, the efficient formation of H2O2 could be observed by the PAD-Pd/TS-1 catalyst under mild reaction conditions (ambient temperature and atmospheric pressure). Furthermore, the presence of phenol in this reaction system led to the formation of the products from the partial oxidation of phenol with the formed H2O2.

Structure and Reactivity of Metal Ion Species in High‐Silica Zeolites.

Publisher Summary One of the recent trends in the development of heterogeneous catalysts is connected with metal-containing zeolites. Metal cations can be introduced into a zeolite at the synthesis stage as well as through various methods of zeolite modification. There are a number of unique catalysts showing high activity and selectivity in the diverse processes. Typical examples of such catalysts and processes are Ti-containing zeolites, Fe zeolites, Zn and Ga zeolite, and Cu, Fe, and Co zeolites. Fine dispersion of the active component seems to be one of the main factors that make molecular sieves very promising for the development of efficient catalysts. Another aspect of the correlation between the stability and reactivity of the cation species relates to possible competition between different structural forms of the cations located in various positions of the zeolite matrix. The main problem of computer modeling of structures relates to accounting the structural relaxation of the lattice in the formation of hydro-peroxide activation intermediate, as the latter process is accompanied by the hydrolysis of the lattice bonds. The formation of cationic positions of monovalent metal ions in zeolites is determined by the distribution of aluminum through zeolite lattice. Stabilization of multivalent metal ions in zeolites can be achieved by the incorporation of ELO into the structure and formation of bi- or multinuclear complexes, wherein each cation interacts efficiently only with the zeolite fragment containing a single Al ion.

Application of an Ion Beam Technique for the Design of Visible Light-Sensitive, Highly Efficient and Highly Selective Photocatalysts: Ion-Implantation and Ionized Cluster Beam Methods

As a new concept for the design of effective photocatalysts, an ion beam technology using accelerated metal ions, a metal ion implantation and an ionized cluster beam (ICB) method, have been applied to design unique photocatalysts. The metal ion implantation of TiO2 and Ti-containing zeolites with highly accelerated metal ions (V+, Cr+, etc.) is useful in designing photocatalysts that can operate efficiently under visible light irradiation. Also, an ICB method with a low acceleration energy is useful in preparing transparent TiO2 thin films on various types of substrates for the efficient photocatalytic degradation of pollutants diluted in water and air. The combination of the ICB method and metal ion implantation can develop the TiO2 thin films that are able to operate not only under UV light but also under visible light irradiation.