Mesoporous Titanosilicate Research Articles

Synthesis and Application of Novel NiMoK/TS-1 for Selective Conversion of Fatty Acid Methyl Esters/Triglycerides to Olefins.

Methyl palmitate (or triglyceride) was converted into C15 olefin with remarkable selectivity using nickel–molybdenum oxides on the mesoporous titanosilicate support. The olefin has one carbon atom less than the acid portion of the ester. A new catalyst NiMoK/TS-1 was synthesized in which the effect of acidity of supports and molybdenum loading on the decarboxylation conversion along with product selectivity was investigated in methyl palmitate conversion into C15 olefin. The prepared catalysts were analyzed using ammonia-temperature-programmed desorption (NH3-TPD), thermogravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET) techniques. The reaction was carried out using a vapor-phase fixed-bed downflow reactor system at atmospheric pressure. The NiMoK/TS-1 catalyst at a weight hourly space velocity (WHSV) of 5.6/h was found to be selective toward C15 olefin. The catalyst was stable up to 15 h, and it can be regenerated with no considerable decrease in the activity even after fourth reuse. Beyond 653 K, the conversion of methyl palmitate increased but the selectivity for C15 products and C15 olefin was decreased.

Synthesis of Nanoporous Titanosilicates and Their Structural Characterization by Physical Nitrogen Adsorption

Mesoporous titanosilicate structures synthesized by the sol–gel method using the cetylpyridinium template at different Ti/Si ratios are characterized by high specific surface areas ABET ≈ 800 m2/g and Aext ≈ 900–1000 m2/g, as well as the shape of the isotherms of physical nitrogen adsorption characteristic of the mesoporous molecular sieve MCM-41 with an adsorption branch rising and a section of reversible capillary condensation at a relative pressure of 0.21 < p/p0 < 0.42. An increase in the Ti/Si ratio and pH values leads to a decrease in the dispersion and surface area of the samples. FTIR spectra confirm the presence of titanium(IV) in the silicate framework. The incorporation of titanium(IV) affects the morphology of titanosilicate samples and reduces the ordering of cylindrical mesopores characteristic of MCM-41.

Hierarchically Mesoporous Titanosilicate Single-Crystalline Nanospheres for Room Temperature Oxidative–Adsorptive Desulfurization

Hierarchically mesoporous titanosilicate single-crystalline nanospheres were synthesized by using a polyelectrolyte–surfactant mesomorphous complex templating method. The titanosilicate nanospheres...

Hollow titanosilicate nanospheres encapsulating PdAu alloy nanoparticles as reusable high-performance catalysts for a H2O2-mediated one-pot oxidation reaction

Hollow mesoporous titanosilicate nanospheres encapsulating PdAu NPs can act as an ideal nanoreactor for H2O2-mediated one-pot oxidation reactions.

Titanium(IV)-induced cristobalite formation in titanosilicates and its potential impact on catalysis

Cristobalite, a crystalline form of silica, is shown to be formed within an amorphous titanosilicate, at previously unknown conditions. Mesoporous titanosilicate microspheres (MTSM) were synthesized as efficient catalysts for the epoxidation of cyclohexene with tert-butyl hydroperoxide. High-resolution transmission electron microscopy revealed the presence of crystals in this predominantly amorphous material, after calcination at 750 °C. When calcined at 800 °C, the crystals were identified via PXRD as predominantly cristobalite, which possibly marks its first observation in titanosilicates at such a low temperature, without adding any alkali metals during synthesis. Catalytic experiments conducted with MTSM materials calcined at temperatures varying from 650 to 950 °C, reveal that the amount of cristobalite formed increases with temperature, and that it has a significant impact on the pore structure, and, remarkably, correlates with the catalytic activity of titanosilicates.

Optimization of mesoporous titanosilicate catalysts for cyclohexene epoxidation via statistically guided synthesis

An efficient approach to improve the catalytic activity of titanosilicates is introduced. The Doehlert matrix (DM) statistical model was utilized to probe the synthetic parameters of mesoporous titanosilicate microspheres (MTSM), in order to increase their catalytic activity with a minimal number of experiments. Synthesis optimization was carried out by varying two parameters simultaneously: homogenizing temperature and surfactant weight. Thirteen different MTSM samples were synthesized in two sequential ‘matrices’ according to Doehlert conditions and were used to catalyse the epoxidation of cyclohexene with tert-butyl hydroperoxide. The samples (and the corresponding synthesis conditions) with superior catalytic activity in terms of product yield and selectivity were identified. In addition, this approach revealed the limiting values of each synthesis parameter, beyond which the material becomes catalytically ineffective. This study demonstrates that the DM approach can be broadly used as a powerful and time-efficient tool for investigating the optimal synthesis conditions of heterogeneous catalysts.

Adsorption and Recovery of Polyphenolic Flavonoids Using TiO2-Functionalized Mesoporous Silica Nanoparticles.

Exploiting specific interactions with titania (TiO2) has been proposed for the separation and recovery of a broad range of biomolecules and natural products, including therapeutic polyphenolic flavonoids which are susceptible to degradation, such as quercetin. Functionalizing mesoporous silica with TiO2 has many potential advantages over bulk and mesoporous TiO2 as an adsorbent for natural products, including robust synthetic approaches leading to high surface area, and stable separation platforms. Here, TiO2-surface-functionalized mesoporous silica nanoparticles (MSNPs) are synthesized and characterized as a function of TiO2 content (up to 636 mg TiO2/g). The adsorption isotherms of two polyphenolic flavonoids, quercetin and rutin, were determined (0.05-10 mg/mL in ethanol), and a 100-fold increase in the adsorption capacity was observed relative to functionalized nonporous particles with similar TiO2 surface coverage. An optimum extent of functionalization (approximately 440 mg TiO2/g particles) is interpreted from characterization techniques including grazing incidence X-ray scattering (GIXS), high-resolution transmission electron microscopy (HRTEM), and nitrogen adsorption, which examined the interplay between the extent of TiO2 functionalization and the accessibility of the porous structures. The recovery of flavonoids is demonstrated using ligand displacement in ethanolic citric acid solution (20% w/v), in which greater than 90% recovery can be achieved in a multistep extraction process. The radical scavenging activity (RSA) of the recovered and particle-bound quercetin as measured by a 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay demonstrates greater than 80% retention of antioxidant activity by both particle-bound and recovered quercetin. These mesoporous titanosilicate materials can serve as a synthetic platform to isolate, recover, and potentially deliver degradation-sensitive natural products to biological systems.

Catalytic conversion of 4-tert-butylphenol in hydrogen peroxide solutions in the presence of titanium oxide compounds and titanosilicates

The catalytic conversion of 4-tert-butylphenol (TBP) in hydrogen peroxide solutions in the presence of titanium oxide samples with different phase compositions and crystalline and amorphous titanosilicate samples has been studied. It has been shown that microporous crystalline titanosilicate TS-1 exhibits low activity in the TBP conversion owing to steric restrictions to the diffusion of the substrate molecules to catalytically active sites. The samples of titanium oxide compounds and mesoporous titanosilicates exhibit similar activity, while the selectivity of the latter for 4-tert-butylcatechol (TBC) is higher. The effect of the mesoporous titanosilicate concentration in the reaction mixture and the test temperature and duration on the TBP conversion and the TBC selectivity has been determined.

Selective oxidation of 4-tert-butylphenol by hydrogen peroxide in the presence of titanosilicates

The catalytic transformations of 4-tert-butylphenol in hydrogen peroxide solutions were investigated in the presence of crystalline and amorphous titanosilicates and titanium oxide. The TS-1 microporous crystalline titanosilicate was shown to exhibit low activity in the 4-tert-butylphenol transformation due to the steric limitations on the diffusion of the substrate molecules towards catalytic active centers. Mesoporous amorphous titanosilicates were more selective in the 4-tert-butylcatechol formation than the titanium oxide. The selectivity to 4-tert-butylcatechol in the presence of the TiO2 did not exceed 20 mol%. The maximum 53 mol% selectivity value to 4-tert-butylcatechol was shown to occur over the amorphous mesoporous titanosilicate containing 1.9 wt% of Ti, the 4-tert-butylphenol conversion value being equal to 42 mol%.

Nontemplate sol–gel synthesis of catalytically active mesoporous titanosilicates

A method for the nontemplate sol–gel synthesis of micro-mesoporous and mesoporous titanosilicates is developed using commercially available raw materials (a mixture of oligomer esters of orthosilicic acid (Ethylsilicate-40) and a water–alcohol solution of titanium(IV) ethoxide). The effect of the pH values of the reaction mixture on sol–gel synthesis is studied using the characteristics of the porous structure of titanosilicates. Samples of amorphous structure with different textural characteristics are obtained by varying the pH in the range of 3–10: specific surface area, 320–740 m2/g; micropore volume, 0.04–0.15 cm3/g; and mesopore volume, 0–0.92 cm3/g. It is shown that a sample of mesoporous titanosilicate obtained with alternating pH values has maximum catalytic activity in the oxidation reaction of 4-tert-butylphenol (TBP) in aqueous solutions of hydrogen peroxide. (Conversion of 4-tert-butylphenol, 45 wt %; selectivity of the formation of 4-tert-butylcatechol, 66 wt %. Conditions: 10 wt % of titanosilicate; TBP/H2O2 = 1/2; 75°C; 1 h).

Effective hierarchization of TS-1 and its catalytic performance in cyclohexene epoxidation

The presented data showed that the chemical treatment of TS-1 with alkaline medium resulted in the formation of highly developed hierarchical structures. The esterification of the hydroxyl groups by methanol allowed modifying the hydrophobicity of TS-1 surface and obtaining truly micro/mesoporous material. The preservation of microporous characteristics was confirmed by XRD and low temperature nitrogen sorption studies. Detailed information on acidic properties of mesoporous titanosilicalites was delivered by IR studies of pyridine sorption and implicitly from 29Si MAS NMR investigations. Well-developed internal mesoporosity together with the retaining of Ti4+ atoms in tetrahedral framework positions offered 7-fold higher catalytic activity for the conversion of cyclohexene molecules than the native microporous TS-1. The selectivity to epoxide reached the value of 96% for the most efficient mesoporous titanosilicate.

Template-Free Sol-Gel Synthesis of Catalytically Active Mesoporous Titanosilicates

A template-free sol-gel technique was developed for synthesis of micro-mesoporous and mesoporous titanosilicates using commercially available raw materials such as mixture of oligomer esters of orthosilicic acid (ethylsilicate-40) and an aqueous-alcoholic solution of tetraethoxysilane. The influence of pH of the reaction mixture on the characteristics of the porous structure of titanosilicates prepared by the sol-gel technique was investigated. pH was varied between 3 and 10 to prepare samples of the amorphous structure with different textural parameters: specific surface area 320–740 m 2 /g, micropore volume 0,04–0,15 cm 3 /g, mesopore volume 0–0,92 cm 3 /g. The mesoporous titanosilicate prepared at variable pH showed the maximal catalytic activity to oxidation of 4-tert-butylphenol (TBF) with aqueous hydrogen peroxide solutions (the conversion of 4-tert-butylphenol was 45 wt.%, selectivity for 4-tert-butylpyrocatechol 66 wt.%; conditions: 10 wt.% titanosilicate, TBF/H 2 O 2 = 1/2, 75 °C, 1 h).

Mesoporous titanosilicate nanoparticles: facile preparation and application in heterogeneous epoxidation of cyclohexene

Mesoporous titanosilicate nanoparticles were hydrothermally synthesized from a titanosilicate solution with cetyltrimethylammonium bromide as the template and with a cationic polymer as the size-controlling agent.

Synthesis of single crystal-like hierarchically mesoporous titanosilicate Ti-SBA-1

Abstract Hierarchically mesoporous titanosilicate Ti-SBA-1 was synthesized with organic mesomorphous complexes of polyelectrolyte (poly(acrylic acid) (PAA)) and cationic surfactant (hexadecyl pyridinium chloride (CPC)) as template, tetraethylsiloxane as silica source and titanium ethoxide as titanium source. By adjusting the amount of titanium ethoxide in the synthesis, a series of Ti-SBA-1 particles with different Si/Ti ratio (79–180) were prepared. After incorporation of Ti into the silica framework the well-ordered cubic P m 3 ¯ n mesostructure remained, as well as the morphology, particle size. UV–vis DR spectra of the Ti-SBA-1 materials indicated that incorporated titanium species existed in a highly dispersed state and exhibited tetrahedral and octahedral coordination in the silica framework.

Mesoporous titanosilicates by templated non-hydrolytic sol–gel reactions

A novel templated non-hydrolytic sol–gel synthesis of titanosilicate xerogels is reported. Acetamide elimination from silicon acetate and titanium diethylamide allows obtaining titanosilicates with a high content of Si–O–Ti bonds but low surface areas. These xerogels lose porosity on calcination. However, with addition of Pluronic P123 as a structure-directing agent, we synthesized mesoporous titanosilicate materials with large surface areas (up to 615 m2 g−1) and well dispersed tetrahedral Ti that are stable at temperatures up to 500 °C. These potential catalysts were characterized by variety of physico-chemical methods (IR, GC–MS, XRD, 29Si and 13C CPMAS NMR, DRUV-Vis, and N2 porosimetry) and tested in cyclohexene epoxidation with cumyl hydroperoxide in toluene. They display catalytic activity with the 100 % selectivity to cyclohexene oxide and high catalytic yields up to 96 % which is comparable to previously reported titanosilicate catalysts.

Preparation of mesoporous titanosilicate with isolated Ti active centers for cyclohexene oxidation

We report the preparation of mesoporous titanosilicate catalysts with isolated active Ti centres using CTAB as the structure directing agent and ethylenediamine as the complexing agent (TSC–ED).

Synthesis of bimodal mesoporous titanosilicate beads and their application as green epoxidation catalyst

Bimodal mesoporous titanosilicate beads with interconnected three-dimensional pore architecture (BMB-TiSil) were synthesized through a one-pot dual-templating method in the presence of a porous anion-exchange resin. Whereas the framework mesopores centered at 3.5nm are generated by the templating effect of the surfactant, the continuous large mesopore system originates from removal of the resin body. In the green epoxidations of alkene with aqueous H2O2, BMB-TiSil showed higher turnover frequency (TOF) based on the alkene conversion and higher epoxide yield than Ti-MCM-41, which is mainly ascribed to the continuous large mesopore system favoring the diffusion of the reactants and products to and from the active titanium sites. Importantly, BMB-TiSil is a stable catalyst immune to titanium leaching, and can be reused in three successive catalytic cycles without significant loss of activity due to its continuous large mesopore system and stable Ti-sites.

Preparation and catalytic properties of mesoporous titanosilicate of cubic Pm3n structure

Mesoporous titanosilicate of cubic Pm3n structure was prepared for the first time using cetyltriethylammonium (CTEA+) bromide as pore-directing agent in alkaline condition (pH around 9) with the aid of NaCl salt. The alkaline synthesis condition facilitated the incorporation of Ti(IV) into the silica framework as well as the assembly of mesoporous silica with zeolite seeds. Two kinds of silica sources were used. The material prepared with sodium silicate was named Ti-SBA-1-alk, and the other named Ti-ZSBA-1 was prepared with the seeds of titanosilicalite-1 (TS-1). The studies by UV–Vis and Ti K-edge XANES spectra indicated that the Ti(IV) in Ti-SBA-1-alk was favorably in tetrahedral (Td) coordination and should be incorporated into the framework of mesoporous silica, whereas a larger amount of Ti(IV) in Ti-ZSBA-1 was in octahedral coordination. In oxidation of 2,3,6-trimethylphenol (TMP) to 2,3,5-trimethylbenzoquinone (TMBQ) using hydrogen peroxide as the oxidant, the mesoporous titanosilicate materials were found to be efficient catalysts, while only trace TMP conversion was observed over TS-1 due to its small zeolitic pores. In comparison of mesoporous titanosilicate materials in similar pore diameters, Ti-SBA-1-alk and Ti-ZSBA-1 both of cubic Pm3n structure gave higher TMBQ selectivities than Ti-MCM-41 of 2D channeling pores, attributing to the better diffusion of the phenoxyl radicals in the three-dimensional pores. Moreover, Ti-SBA-1-alk which contained more Td-coordinated Ti(IV) showed higher catalytic activities than Ti-ZSBA-1.

Controllable synthesis and photocatalytic activities of rod-shaped mesoporous titanosilicate composites with varied aspect ratios

Rod-shaped mesoporous titanosilicate composites (RMTSs) with controllable aspect ratios (ARs) were fabricated using cetyltrimethylammonium bromide (CTAB) and ammonium hydroxide (NH4OH) at a continuous stirring rate, resulting in ARs ranging from 1 to 5. Slowing the stirring rate or increasing the concentration of CTAB mainly impacted the length growth, whereas NH4OH affected the width growth. Photocatalytic activity studies revealed that the length of RMTSs played a more significant role than the width at lower ARs in their photocatalytic activity.

Mesoporous Titanosilicate/Reduced Graphene Oxide Composite Adsorbents for a Mixed-Solute Solution

In this study, mesoporous titanosilicate (MTS)/reduced graphene oxide (RGO) composite materials were prepared as a function of the RGO content and used as novel adsorbents for a mixed-solute solution of methylene blue and rhodamine B (RhB). Adsorption capacities of the composite materials were higher than those of MTS or RGO by themselves, demonstrating that adsorptive performances of the composite materials are better than the inorganic or organic materials alone. Composite material containing 20 wt% RGO (20MTSG) showed the best adsorption capacity for both contaminants where its adsorptive behavior in the mixed-solute solution can be ascribed to the unique morphology of the large layered structure of MTS and RGO, as well as many aggregates of small-sized plates. Compared to the other composite materials, 20MTSG contained an abundant edge structure of RGO, resulting in a relatively higher RhB adsorption capacity. RhB preferred the adsorption sites on RGO to the adsorption sites on MTS due to steric hindrance inside the mesopores of MTS.