Silicalite-1 Framework Research Articles

Boosting propane dehydrogenation over Sn stabilizing dispersed Ptδ+ confined in Silicalite-1 at low temperature

Utilizing the confinement effect of zeolite pores to stabilize active sites has been developed for the improvement of catalytic stability and performance. Herein, a facile strategy is proposed to synthesize a Sn stabilizing dispersed Ptδ+ sites confined in zeolite pore catalyst via Ar calcination for propane dehydrogenation (PDH). 0.2Pt/0.5Sn-S-1-Ar shows excellent propylene formation rate of 10.0 mol C3H6·gPt−1·h−1 and propylene selectivity higher than 99.5% at 450 °C, and the superior catalyst stability in 200 h on-stream. And it has the lowest apparent activation energy barrier of 18.45 KJ/mol over Pt-based catalyst for PDH to our knowledge. According to systemic characterizations, it is demonstrated that the implantation of Sn into Silicalite-1 framework before introducing Pt is essential to generate the highly dispersed Ptδ+ species confined in zeolite pore, and the Ptδ+ species confined in zeolite pore with stronger propane adsorption and propylene desorption ability is responsible for superior PDH performance.

The investigation into the different Co species over Silicalite-1 via modulating heat-treatment atmosphere for propane dehydrogenation

Co-based catalysts have attracted much attention for propane dehydrogenation (PDH) because of their low price, environmental friendliness, and high activity, while the synthesis of anti-reduction Co species to suppress cracking side reactions to realize high-performance PDH is critical. In this work, different Co species over Silicalite-1 are synthesized via modulating heat-treatment atmosphere and investigated for PDH systematically. In comparison with O2-included calcination catalyst, the TOF of Co-S-1-Ar (41.9 h−1) for PDH is about nine times that of Co/S-1-Air (4.6 h−1). According to the combined characterizations, it is confirmed that the highly dispersed tetrahedral coordinated Co2+ species incorporated into Silicalite-1 framework with Lewis acid sites over Co-S-1-Ar is responsible for the superior PDH performance, while bulk aggregated Co3O4 species in Co/S-1-Air has much lower catalytic performance. Through in-situ FT-IR characterization, it is revealed that Co2+ species over Co-S-1-Ar is incorporated into Silicalite-1 framework via replacing the silanol nests of Silicalite-1, in which the Co precursors are driven by Ar to reach the silanol nests highly dispersed and then further anchored by silanol nests and incorporated Silicalie-1 framework with Co2+ species under high temperature calcination, and the other oxygen-free calcination atmosphere, such as H2 and vacuum, are also intensified to be practicable.

Geometrically embedding dispersive Pt nanoparticles within silicalite-1 framework for highly selective ɑ, β-unsaturated aldehydes hydrogenation via oriented C = O adsorption configuration

The issue for thermodynamically favored C = C hydrogenation needs to be overcome in the hydrogenation of ɑ, β-unsaturated aldehydes to unsaturated alcohols. Herein, we employ confinement effect in the catalyst-designing engineering to orient the C = O adsorption by the zeolitic microchannel, where highly dispersed Pt nanoparticles are homogeneously well-embedded within the silicalite-1 framework (Pt@S-1). Comprehensive characterizations, such as HAADF-STEM, H2-TPR, FT-IR of CO adsorption and XPS are carried out to demonstrate the geometric, confinement and electronic properties of metal species. In the hydrogenation of ɑ, β-unsaturated aldehydes with suitable molecular size, Pt@S-1 displays preferential C = O hydrogenation. For example, Pt@S-1 gives conversion of 99.8% and meanwhile the aiming cinnamal alcohol selectivity of 98.7% in the hydrogenation of cinnamaldehyde, outperforming larger Pt nanoparticles ill-suitedly embedded within silicalite-1 (Pt@S-1-is) and highly dispersed Pt nanoparticles supported on the silicalite-1 surface (Pt/S-1). For the hydrogenation of smaller 3-methyl-2-butenal, though the confinement effect boosts the C = O hydrogenation to some extent, the synergetic electronic effect via introducing Fe species effectively increases the unsaturated alcohol selectivity. Investigations on the adsorption configuration by in-situ FT-IR spectroscopy clearly indicate that the unsaturated aldehyde with suitable molecular size is preferentially adsorbed on Pt sites of Pt@S-1 via the oxygen atom of C = O with on-top η1 mode, thus favoring high unsaturated alcohol selectivities, while the di-σCOη2 and η4 adsorption modes on Pt@S-1-is and Pt/S-1 are relatively adverse for prioritized C = O hydrogenation.

Bimetallic Ni-Zn site anchored in siliceous zeolite framework for synergistically boosting propane dehydrogenation

Propane dehydrogenation (PDH) is a prospective benign process for the production of propylene, but generally depends on high-price Pt and toxic Cr(VI) catalysts that often suffer from the rapid deactivation derived from metal sintering and severe coke deposition. To overcome these problems, the breakthroughs in an alternative catalyst design with efficient, low-cost and eco-friendly play a crucial role in successfully developing this process. Here, we facilely fabricate the bimetallic-site catalyst of Ni-Zn anchored in the zeolitic framework of silicalite-1 (depicted as NiZn-S-1) by employing ligand-protected strategy, which performs high temperature stability. Under comparable conditions, the NiZn-S-1 catalyst with high Ni/Zn molar ratio of 3:1 (named 0.2Ni0.06Zn-S-1) exhibits superior catalytic activity (initial propane conversion of 32.5 % and actual TOFpropane of 28.5 min−1) with low deactivation rate (0.0778 h−1) and great propylene selectivity (>90%) after 30 h on stream. In particular, the catalytic performance on this catalyst almost keeps same as that of fresh catalyst after 4 successive oxidation–reduction cycles. Multiple characterizations further demonstrate that the enhancement of PDH performance ought to be attributed to the synergistic effect between bimetallic Ni-Zn sites, which favors the selective activation of C–H bond and propylene desorption to reduce the formation of coke species with high graphitization degree, boosting the improvement of catalyst stability. The design of novel bimetallic-sites catalyst can give a new idea on the development of alternative PDH catalysts with economical- and environment-friendly in the future.

New Insights into Manganese Local Environment in MnS-1 Nanocrystals

Manganese plays an important role in redox catalysis using zeolites as inorganic support materials, but the formation of the preferred redox manganese species (framework or extraframework) is still not well understood. Herein, the influence of the amount of manganese together with conventional and microwave-assisted hydrothermal synthesis paths on the formation of manganese species within the zeolite silicalite-1 (S-1) with MFI structure was investigated. It was found out that both synthesis procedures led to the formation of framework and extraframework manganese species, but in different molar ratios. However, the conventional synthesis procedure with all Mn/Si molar ratios generates more framework Mn in comparison to the microwave procedure. Additionally, the diminution of the zeolite crystals to nanoscale from 100 to 200 nm was achieved via the conventional procedure for the first time. UV–vis, Raman, and X-ray absorption spectroscopic analyses revealed different local environments of manganese: Mn3+ incorporated into the silicalite-1 framework as “framework manganese” and Mn2+/3+ present as “extraframework manganese” (Mn2O3, Mn3O4). TEM reveals the presence of Mn3O4 nanorods. Both framework manganese and extraframework manganese exhibit good catalytic activity for styrene epoxidation. Catalytic results suggest that, in oxidation reactions of hydrocarbons, framework manganese is more active at lower Mn contents (Mn/Si < 0.015), whereas extraframework manganese is more active at higher loadings (Mn/Si > 0.015).

Confinement of Ultrasmall Cobalt Oxide Clusters within Silicalite-1 Crystals for Efficient Conversion of Fructose into Methyl Lactate

Chemocatalysis of sugars to methyl lactate (MLA) exhibits great advantages over the conventional fermentation approach because of its higher productivity and cost-effective separation process. However, widely used supported metal oxide catalysts suffer from deactivation resulting from sintering during the reaction and removal of coke at high temperatures. Herein, we report ultrasmall cobalt oxide clusters (∼1.7 nm) stabilized within silicalite-1 crystals catalyst (CoO@silicalite-1), exhibiting superior catalytic activity and resistance to sintering for the conversion of fructose into methyl lactate. HAADF-STEM, EDS-mapping, and XRD experiments identify the existence of confined CoO clusters. XANES and Raman spectra demonstrated the covalent interaction between CoO and silicalite-1. Thanks to the ultrasmall CoO particle size (∼1.7 nm), the CoO@silicalite-1 affords nearly 100-fold higher Co-mass-based activity (mg MLA/mg Co) compared with CoO or Co3O4 particles outside the silicalite-1 framework. More impor...

Synthesis and characterization of Mn-Silicalite-1 by the hydrothermal conversion of Mn-magadiite under the neutral condition and its catalytic performance on selective oxidation of styrene

The incorporation of manganese into the framework of Silicalite-1 (denoted as Mn-Silicalite-1) was achieved by the hydrothermal conversion manganese ion exchanged magadiite (Mn-magadiite) under the neutral condition. The influences of the synthetic conditions (the reaction time, the reaction temperatures and the precursors) on the synthesis of Mn-Silicalite-1 were studied in detail to reveal the successful synthesis of Mn-Silicalite-1. The introduction of the manganese into the framework of Silicalite-1 was demonstrated by the means of X-ray powder diffraction (XRD), energy-dispersive X-ray spectrometer (EDS), elemental mapping, X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–Vis), field emission scanning electron microscopy (FE-SEM), N2 adsorption/desorption isotherms and temperature-programmed reduction (TPR). The BET surface area (SBET) and pore volume (Vp) of Mn-Silicalite-1 measured 323 m2/g and 0.052 cm3/g, respectively. All results confirmed that Mn atoms were successfully doped into the framework of Silicalite-1 and homogeneous solid-solutions of Mn-Silicalite-1 were synthesized. Furthermore, the catalytic properties of the as-synthesized Mn-Silicalite-1 were evaluated by the styrene oxidation reaction. Mn-Silicalite-1 significantly increased the active sites of the catalyst and improved the catalytic efficiency. Low temperature was beneficial to the formation of styrene oxide and high temperature was beneficial to the formation of benzaldehyde.

Surface modification of silicalite-1 with alkoxysilanes to improve the performance of PDMS/silicalite-1 pervaporation membranes: Preparation, characterization and modeling

The objective of this work was to study the effect of silane coupling agent on the performance of mixed matrix membranes (MMMs) and to develop a mathematical model to analyze the performance of the MMMs. The silicalite-1 modified by various alkoxysilanes was incorporated into polydimethysiloxane (PDMS) to prepare dense MMMs. The modified silicalite-1 and corresponding MMMs were characterized by FT-IR, CA, TGA, DSC and SEM. These results confirmed that the silicalite-1 was successfully modified by various alkoxysilanes. The effects of alkoxysilane chain length and chemical structure on the pervaporation (PV) performance of MMMs were discussed in detail. All the silane modification did not change the framework of silicalite-1. Better dispersion of silicalite-1 in PDMS was attained after modification and all the modified membranes could eliminate the nonselective voids inside the membranes. Moreover, the silane coupling agent had a contradictory effect on the PV performance of the membranes. On the one hand, the silane coupling agent improved the compatibility between silicalite-1 and PDMS. On the other hand, the silane coupling agent introduced a silane phase around the silicalite-1, which depressed the selectivity of the pristine silicalite-1. Silicalite-1 grafted with vinyl group showed the best compatibility with PDMS, and the resulting MMMs had the highest separation factor to ethanol because strong chemical bonds between vinyl-silicalite-1 and PDMS were formed with the thinnest silane film. For the separation of ethanol from a dilute solution, a separation factor of 34.3 was obtained with the vinyl-MMMs, which was 49% higher than that of unmodified membrane. As the silicalite-1 content increased, the separation factor increased. Furthermore, a mathematical model was proposed to predict the performance of MMMs. And both the permeability and selectivity obtained by the proposed model were in good agreement with the experiment data.

An investigation of the conformational behavior of a chlorinated hydrocarbon, 1,1,2-trichloroethane, adsorbed in zeolites by Raman spectroscopy

The conformational behavior of 1,1,2-trichloroethane (TCE) adsorbed in two representative zeolites (silicalite-1 and zeolite L) was investigated by Fourier transform (FT)-Raman spectroscopy in combination with thermogravimetric analysis (TGA) and powder X-ray diffraction (XRD). The results indicate that the conformational properties of the TCE molecules inside a zeolitic host are strongly influenced by both the framework topology and the existence of charge balancing cations. When TCE is adsorbed inside completely siliceous silicalite-1, the population of the trans conformer increases significantly relative to pure liquid. Adsorption of TCE also induces a phase transition from the monoclinic to orthorhombic crystal system in the framework of silicalite-1 at high loading levels. At low loading, the TCE molecules are adsorbed inside the channels of silicalite-1. When at high loading levels, TCE molecules reside at both the channel intersection as well as the midsection of the channels. For zeolite L, the presence of an extra-framework cation shows a strong influence on TCE conformation. The strong interaction of the cation with the large dipole moment of the gauche isomer leads to a large increase in the gauche population. Raman data provide direct evidence that the cations in the framework interact much more strongly with the gauche isomer than the trans isomer.

Adsorbing/Absorbing Effect of Nanosized Metal Oxide and Zeolite Nanocrystals in Lithium Sulphur Batteries

Due to their low cost and high energy density, rechargeable Li-S batteries are among the most promising energy storage devices. Sulphur has a theoretical gravimetric energy density up to five times higher than that of present lithium-ion battery technologies. Despite significant recent advances, there are still some challenges. Upon sulphur reduction and oxidation, intermediate soluble lithium polysulphides readily diffuse into the electrolyte, causing capacity fading and poor columbic efficiency in the cell. To overcome this problem, strong adsorption and absorption materials have been employed to adsorb/absorb lithium polysulphides. As an additive in the sulphur cathode it has been demonstrated that various nano-sized oxides (such as Mg0,6Ni0,4O, Al2O3, La2O3) and mesoporous silicates (SBA-15) can effectively trap polysulphides [1-4].In this contribution we report use of Silicalite-1 zeolite as an additive in the cathode composite in the Li-S batteries. Silicate-1 is a microporous, silica-based molecular sieve with a MFI topology of the tetrahedral framework. Incorporation of transition metals into their framework generates different types of catalytically active sites. MnS-1 (manganese silicalite-1) nanosized crystals (arround 200 nm) have been synthesized under classical hydrothermal procedure and showed Mn3+ incorporated into the silicalite-1 framework as framework manganese. By contrast, MnS-1 synthesised under microwave hydrothermal procedure resulted in incorporation of Mn3+ into the silicalite-1 framework as extra-framework manganese in forms of manganese oxide nano-particles [5-6].Galvanostatic cycling showed good capacity retention of the Li-S cells through the use of zeolite additives as polysulphide reservoirs. We examined the role of silica surface, pore absorption and manganese oxide adsorption. MnS-1 crystals with a small amount of nano-sized manganese oxide particles in the structure appear effective at retaining the soluble polysulphides at the cathode and are limiting the fraction that takes part in the sulphur shuttle mechanism. We assume that, most likely, additionally to the zeolites, the nano-sized manganese oxide serves as an adsorbent of the polysulphides in the cathode material. By utilizing 9 wt.% MnS-1 in cathode material we achieved a higher specific capacity and cycle efficiency in comparison with cathode material without zeolite additive and with 9 wt.% of mesoporous SBA-15 additive. The possible mechanism(s) will be discussed based on results obtained by in operando analytical techniques developed in our lab [7,8]. Acknowledgement: This research has received founding from the Slovenian Research Agency and the European Union Seventh Framework Programme under grant agreement No. 314515 (EUROLIS).

The synthesis of super-hydrophilic and acid-proof Ge–ZSM-5 membranes by simultaneous incorporation of Ge and Al into a Silicalite-1 framework

A new method for synthesis of super-hydrophilic and acid-proof zeolite membranes was presented. It involved simultaneous incorporation of suitable amounts of Ge and Al into a Silicalite-1 framework. The precursor sol was prepared in an ice-water bath, and the alcohols in the precursor sol were removed at about 80°C. It was shown that using the ice-water bath would prevent the formation of GeO2 and removing the alcohols at a relatively high temperature would lead to suitable amounts of Ge and Al in the membranes. The obtained Ge–ZSM-5 membranes were acid-proof and showed high pervaporation performance for dehydrating acetic acid and ethanol solutions. At 353K, for feed acetic acid solutions in a concentration range of 30–98wt%, the permeation flux of water was almost constant (about 0.57kg/m2h), and very little acetic acid permeated through the membrane, resulting in a very high separation factor. Similarly, for dehydration of ethanol solutions (10–98wt%) at 343K a water flux of approximately 2.4kg/m2h was obtained.

Synthesis of a hierarchically micro–macroporous structured zeolite monolith by ice-templating

The zeolite monolith with a micrometre-sized honeycomb structure was prepared by using the ice-templating method. The synthesized samples were characterized by SEM, powder X-ray diffraction analysis, mercury porosimetry, and nitrogen adsorption–desorption measurements. The precursor silica gels with channel diameters of 10–50 µm were prepared by the ice-templating method. Then the amorphous phase of the precursor silica gels was converted into a crystalline phase by the steam treatment in the presence of structure-directing agents. In this work, tetrapropyl ammonium hydroxide was selected as a structure-directing agent, and the crystalline phase of the synthesized sample was identified as silicalite-1 from XRD analysis. After crystallization, the particulate silicalite crystals were generated on the surface of the honeycomb wall, and the honeycomb structure was retained without cracking. The size of the synthesized silicalite crystals was controlled by the crystallization temperature and time. The nitrogen adsorption–desorption isotherm on the synthesized silicalite monolith showed type I isotherms, and the specific surface area calculated by the Brunauer–Emmett–Teller method was 332.0 m2 g−1. These results indicated the existence of micropores in the framework of silicalite-1.

Non-isothermal kinetic studies of the template decomposition from silicalite-1 framework-high temperature X-ray diffraction and thermogravimetric analysis

Non-isothermal decomposition of the tetrapropylammonium cations (TPA +) intercalated in silicalite-1 framework has been carried out using thermogravimetric (TG) analysis and high temperature powder X-ray diffraction (HTXRD) techniques. Conversion factor for template decomposition is calculated using two methods viz., % weight loss from the thermogravimetric analysis and changes in the intensities of the Bragg reflections 101/011 and 200/020 in the HTXRD patterns scanned at different temperatures (range 298–823 K). The calculated apparent activation energy for template decomposition in air was 129 and 125 kJ mol −1, respectively, for the two techniques TG and HTXRD, calculated using the Kissinger method. By Flynn–Wall–Ozawa approach of isoconversion, apparent activation energy for template decomposition in air was 123 and 124 kJ mol −1, respectively, for TG and HTXRD data. The reaction order was determined using the method of Kennedy and Clark and it is ∼2 by both the techniques. The second order of template decomposition can be attributed to the fact that TPA + is positioned in two different orientations inside the silicalite-1 framework. Template removal occurs with a contraction in unit cell dimensions. There is a decrease in the lattice parameters of the as-synthesized silicalite-1 sample after removal of template from the framework.

Synthesis of borosilicalite-1 with more than four boron per unit cell from fluoride containing media

More than four boron per unit cell has been introduced into the framework of silicalite-1, using fluorine containing media. The initial gels were of composition 9MF–xH3BO3–10SiO2–1.25TPABr–330 H2O with M = NH4, Na, K and Cs and x = 0.1–10. The syntheses were carried out in hydrothermal conditions at 170°C. The amount of incorporated TPA+ ions remains quasi constant (3.5–3.8/u.c.) up to 4 B/u.c., while it decreases with increasing boron content. The amount of tetrahedral B/u.c. can be as high as 8 in presence of K+ or Cs+ ions in the as-synthesized samples. It is observed that the preferential countercations to framework negative charges related to the presence of tetrahedral boron, [SiOB]−, are TPA+, K+ and Cs+ ions. It is interpreted, that the −4.0 ppm versus BF3.OEt2 NMR line stems from tetrahedral framework boron, while the −2.9 ppm NMR line represents both extraframework and/or tetracoordinated deformed framework boron in the structure.

XAS studies on incorporation of Mn and Co into silicalite-1

Mn and Co-containing silicalite-1 (MnS-1 and CoS-1) were synthesized hydrothermally. Template-free samples were obtained by calcination at 550 °C for 6 hours in oxygen flow. X-ray diffraction, elemental, thermogravimetric and cation exchange analyses suggested a possible incorporation of Mn and Co cations into the framework positions of the silicalite-1. The valence state and local environment of both cations in the samples were examined by XANES and EXAFS analyses. Results show that Mn and Co cations isomorphously substitute silicon in the silicalite-1 framework only if they are in trivalent oxidation state. Divalent cations are incorporated on extra-framework positions. In the template-free MnS-1 sample all Mn cations are in trivalent state and substitute Si in the framework, forming a distorted and coordinatively unsaturated 3-fold symmetry, which is characteristic for Lewis acid sites. In the template-free CoS-1 sample only part of Co cations are in trivalent state substituting silicon in the framework.

Manganese‐Containing Silica‐Based Microporous Molecular Sieve MnS‐1: Synthesis and Characterization.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Manganese-Containing Silica-Based Microporous Molecular Sieve MnS-1: Synthesis and Characterization

Manganese-containing silicalite-1 (MnS-1) was synthesized hydrothermally in the presence of the structure-directing agent (template) tetraethylammonium hydroxide (TEAOH) for the first time. The highly crystalline MnS-1 crystallized from a gel with a molar composition of 2:1:1:50:25:935 Na2O:K2O:MnO:SiO2:TEAOH:H2O at 175 °C after 3 days. The product was thermally stable up to 700 °C in air. The template-free MnS-1 was prepared by calcination at 550 °C in an oxygen flow. The incorporation of manganese into the framework sites of silicalite-1 was suggested by elemental, thermogravimetric, and cation exchange analyses. The X-ray absorption spectroscopic methods XANES and EXAFS confirmed the incorporation of Mn3+ into a silicalite-1 framework. FT-IR spectroscopic studies of CO adsorption at 100 K on the MnS-1 revealed the Lewis acidity of the sample and the presence of both Mn3+ and Mn2+ cations in the structure.

VS-1 composite membrane: preparation and characterization

The present paper reports the in situ hydrothermal synthesis of a vanadium-containing silicalite-1 zeolite film on a tubular alumina support. In this process, metal-MFI zeolite forms at the surface and within the pores of a porous ceramic alumina support by nucleation and crystallization from a fluoride mixture containing vanadium and silica species. The structure and texture of the prepared composite were identified by XRD and SEM analysis. The presence of V +4 species in the silicalite-1 framework was confirmed by XRD, DSC and EPR studies.

Synthesis of Co-silicalite-1 from a layered silicate

Co-Silicalite-1 (Co2.3Si93.7O192) was synthesized from Co2+ ion exchanged magadiite. The characteristics of Co-Silicalite-1 were investigated by using X-ray powder diffraction, IR spectroscopy, surface area measurement, NH3 temperature programmed desorption, and electron microprobe analysis. The measurements indicate that Co2+ ions replace Si4+ ions in the Silicalite-1 framework. The orthorhombic framework structure of calcined Co-Silicalite-1 has been determined.

New route for synthesizing Mn-silicalite-1

Mn-silicalite-1 (Mn 5.2Si 90.8O 192) was synthesized from Mn 2+ ion-exchanged magadiite. The characteristics of Mn-silicalite-1 were investigated using electron spin resonance, synchrotron X-ray powder diffraction, IR spectroscopy and chemical analysis. The measurements indicate that Mn 2+ ions replace Si in the silicalite-1 framework. The orthorhombic framework structure of calcined Mn-silicalite-1 has been determined. The space group is Pnma, with a=20.1017(3) Å, b=19.8826(4) Å, c=13.3758(3) Å.