Sn-Beta Zeolite Research Articles

Electro-Assisted Synthesis of Sn-Beta Zeolite Leads to Record Tin Incorporation and Superior Lewis Acid Catalysis

Electro-Assisted Synthesis of Sn-Beta Zeolite Leads to Record Tin Incorporation and Superior Lewis Acid Catalysis

Pt–Sn nanoalloys on Sn-Beta zeolite for efficient propane dehydrogenation

Zeolite-tailored bimetallic Pt-Sn catalysts have been shown to be effective for propane dehydrogenation (PDH). Here, we have successfully prepared and compared two Sn-Beta-supported bimetallic PtSn catalysts (Pt/Sn-Beta (DG) and Pt/Sn-Beta (DA)), in which the Sn-Beta zeolite was prepared by a dry-gel (DG) synthesis method involving in situ Sn incorporation or a post-synthesis method involving dealumination and Sn incorporation (DA), respectively. The as-prepared Pt/Sn-Beta (DG), possessing a less fraction of extra-framework Sn species comparing to Pt/Sn-Beta (DA), shows a superior performance in terms of activity (TOF, 1.8 s-1), selectivity (99.0%) and stability (7360 min) at 550 °C using 40 kPa propane and 60 kPa nitrogen gas, reflecting one of the highest PDH performances for bimetallic Pt-Sn catalysts under similar conditions. By a combination of the state-of-the-art electron microscopy-based techniques and advanced spectroscopy techniques, we found that the proper Pt-Sn nano-alloying in Pt/Sn-Beta (DG), rather than Sn coverage on Pt species in Pt/Sn-Beta (DA) owing to the migration of excess extraframework Sn species, is essential for providing an enhanced PDH performance, as the active Pt species could be well isolated, accessed and stablized in Pt/Sn-Beta (DG) by alloying.

The Al-Containing Silicates Modified with Organic Ligands and SnO2 Nanoparticles for Catalytic Baeyer-Villiger Oxidation and Aerobic Carboxylation of Carbonyl Compounds.

The Baeyer-Villiger Oxidation (BVO) of ketones and aldehydes produce lactones and formates, while aerobic carboxylation of aldehydes manufactures carboxylic acids, both having high added value. This work prepared a series of Al-containing silicates modified with organic ligands and SnO2 nanoparticles, which were then employed as catalyst in BVO and carboxylation. Characterizations revealed the morphology of the synthesized catalyst was changed from micron-sized thin sheets to smaller blocks, and then to uniform nanoparticles (size of 50 nm) having the doped SnO2 nanoparticles with a size of 29 nm. All catalysts showed high BET surface areas featuring silt-like mesopores. In determining the priority of BVO and carboxylation, an influence evaluation of the parameters showed the order to be substrate > oxidant > solvent > catalyst. Cyclic aliphatic ketones were suitable for BVO, but linear aliphatic and aromatic aldehydes for carboxylation. Coordination of (S)-binaphthol or doping of Sn into catalyst showed little influence on BVO under m-CPBA, but the Sn-doped catalyst largely increased BVO under (NH4)2S2O8 and H2O2. Calculations revealed that the catalyst containing both Al and Sn could give BVO intermediates lower energies than the Sn-beta zeolite model. The present system exhibited merits including wider substrate scope, innocuous catalytic metal, greener oxidant, as well as lower catalyst cost.

Post-synthesis of Sn-beta zeolite by aerosol method.

Sn-beta zeolite is a Lewis acid catalyst which can activate the C-O and C[double bond, length as m-dash]O bonds of many organic compounds. In this paper, a simple aerosol method has been firstly applied to the post-synthesis of Sn-beta zeolite. The aqueous solution containing SnCl2 and dealuminated beta zeolite was rapidly dried using an aerosol generator to obtain the Sn-beta zeolites with different Sn contents. The physicochemical properties of the Sn-beta zeolites were further characterized by XRD, nitrogen adsorption-desorption, FT-IR and Py-FT-IR techniques. The catalysts exhibited good catalytic performances in the Baeyer-Villiger oxidation reaction of cyclohexanone.

Hydrothermal synthesis of nanosized Sn-beta zeolites by interzeolite transformation for glucose isomerization

Nanosized Sn-beta zeolite was hydrothermally synthesized from FAU zeolite via a novel interzeolite transformation method, which presented excellent fructose yield in glucose isomerization into fructose in water.

Direct Synthesis of Lactide from Lactic Acid by Sn-beta Zeolite: Crucial Role of the Open Sn Site

Direct Synthesis of Lactide from Lactic Acid by Sn-beta Zeolite: Crucial Role of the Open Sn Site

Au/Sn-Beta catalyst with metal-Lewis acid cooperative sites steers aerobic oxidation of 5-hydroxymethylfurfural

2,5-Furandicarboxylic acid (FDCA) is a potential substitute of petroleum-based terephthalic acid to manufacture polymer. The selective aerobic oxidation of renewable 5-hydroxymethylfurfural (HMF) to FDCA is a promising and appealing route for establishing sustainable and environmentally friendly chemical process. Au catalysts have exhibited exceptional catalytic performances for this highly anticipated chemical transformation, where the used support intensively impacts the catalytic productivity from the standpoint of metal-support and guest organic-support interactions. Herein, Sn-Beta zeolite was straightforward and rapidly synthesized via structural reconstruction without the auxiliary of any solvents, which was adopted as support for Au catalyst to construct bifunctional catalysts. As for Au/Sn-Beta sample, Lewis acid sites were related to Sn4+ ions in the zeolite framework, while electronic properties and particle size of Au species were capable of being modulated by Au dosages. In addition, charge transfer from Au species to framework Sn4+ ions resulted in the formation of Auδ+ species. Au/Sn-Beta catalyst with metal-Lewis acid cooperative active sites showed unique catalytic productivity of FDCA product in the aerobic oxidation of HMF to FDCA, whose catalytic performance was correlated with Lewis acid amounts as well as geometric and electronic effect of Au particle. Reaction mechanism analysis revealed the pathway and concrete step that Lewis acid site functioned. The aim is to provide some guidance for constructing a task-specific multifunctional supported catalyst from the view of support-enhanced effect for the catalytic conversion of biomass resource with multi-functional-groups.

Direct synthesis of lactide from concentrated lactic acid catalyzed by hierarchical Sn-beta zeolite

<p indent="0mm">Direct synthesis of lactide from concentrated lactic acid (LA) is an energy-efficient method, which is of great significance to reduce the cost of polylactic acid production. It is difficult to produce lactide with high yield from commercial concentrated LA due to the great quantity of LA oligomers. Herein, the hierarchical Sn-beta (Sn-beta-M) zeolite was prepared as a catalyst for the conversion of 97 wt% LA to lactide with yield of 86.5% in 3 h. The mesoporosity in Sn-beta-M characterized by N₂ adsorption/desorption test shortened the diffusion path way in the micropores, which facilitated the fast escape of lacide avoiding decyclization and oligomerization. L₃A and L_{<italic>n</italic>}A’s conversion to lactide may be attributed to the Sn sites present in mesopores. The Sn⁴⁺ coordinated in Sn-beta-M framework, exhibited strong Lewis acidity and could act as the active center for the synthesis of lactide. We speculated that the Sn and the surrounding O in Sn-beta-M acted as strong Lewis acid sites and weak base sites respectively in mediating C–O bond formation of lactide from L₂A and L_{<italic>m</italic>}A (<italic>m</italic>≥3).

Accelerated synthesis of Sn-Beta with less silanols by alkaline (earth) salt for efficient transformation of glucose to methyl lactate

Sn-Beta zeolite is an excellent catalyst for the transformation of biomass derived carbohydrates. However, the long synthesis time restricted its application. Here, alkaline (earth) salt was used as promoter to accelerate the crystallization of Sn-Beta. Different alkaline (earth) salts and the amount of MgCl2 were investigated. The properties of the synthesized samples were characterized by various techniques and compared with Sn-Beta, and the catalytic performance was investigated for the conversion of glucose to methyl lactate (MLA). The results indicate that a small amount of alkaline (earth) salt, especially MgCl2, promoted dramatically the crystallization of Sn-Beta. The full crystallization time was shortened from 15 d to 5 d with the aid of MgCl2 (nMg/nSn of 1.0) for Sn-Beta with nSi/nSn of 100. Sn4+ cations were incorporated into the framework sites, while Mg2+ cations replaced the protons of silanol defects. Mg–Sn-Beta with strong Lewis acid sites and less silanols showed high activity and selectivity for glucose conversion to MLA. The yield of MLA is 20% over the fully crystallized Sn-Beta at 120 °C for 15 h and glucose concentration of 3.1 wt%, which increased significantly to 44% over the fully crystallized 1 Mg–Sn-Beta. Furthermore, Mg–Sn-Beta is stable and recyclable.

Sn-Beta Catalyzed Transformations of Sugars—Advances in Catalyst and Applications

Beta zeolite modified with Sn in the framework (Sn-Beta) was synthesized and introduced as a heterogeneous catalyst for Baeyer–Villiger oxidations about twenty years ago. Since then, both syntheses strategies, characterization and understanding as well as applications with the material have developed significantly. Remarkably, Sn-Beta zeolite has been discovered to exhibit unprecedented high catalytic efficiency for the transformation of glucose to fructose (i.e., aldoses to ketoses) and lactic acid derivatives in both aqueous and alcoholic media, which has inspired an extensive interest to develop more facile and scalable syntheses routes and applications for sugars transformations. This review survey the progress made on both syntheses approaches of Sn-Beta and applications of the material within catalyzed transformations of sugar, including bottom-up and top-down syntheses and catalyzed isomerization, dehydration, and fragmentation of sugars.

Controlled Synthesis of l-Lactide Using Sn-Beta Zeolite Catalysts in a One-Step Route

Polylactic acid (PLA), as a biodegradable and renewable polymer, has been widely used in biomedical and commercial applications. The energy-efficient synthesis of lactide from lactic acid (La) via a one-step route is highly desired for megaton-scale PLA production. In this work, stereo-pure l-lactide was synthesized with high yield (88.2–95.8%) via a one-step route catalyzed by Sn-beta zeolites. Sn–O–Si bonds on tin–silica catalysts are indeed important for a high l-lactide yield. The Sn4+ ions with four isolated coordinates in tetrahedral configuration of Sn-beta zeolites are more active for l-lactide synthesis than those with hexacoordinated polymeric Sn–O–Sn-type species. l-La was first converted into a lactic acid dimer (L2a) and then formed l-lactide catalyzed by a Sn-beta zeolite, and the average reaction rate in first 20 min (R20minav) increased linearly with increasing Sn content. Importantly, lactic acid trimers (L3a) formed during the reaction could also be converted to l-lactide in the later stage of the reaction, and the diffusion of L3a to the active site within the Sn-beta zeolite pore is the rate-limiting step. The lactic acid oligomer (Lna, n ≥ 4) was limited to form lactide with an R20minav of only 0.013 mmol min–1 gcat–1.

Effect of silica source on the synthesis, property and catalytic performance of Sn-Beta zeolite

Sn-Beta zeolite is a promising heterogeneous Lewis acid catalyst. Hydrothermal synthesis of Sn-Beta(TEOS) using tetraethyl orthosilicate (TEOS) as silica source is a classical method. However, the hydrolysis of TEOS generates considerable ethanol, which is unfavorable for scalable production of Sn-Beta. Herein, cheap fumed silica and silica sol were used as Si sources to synthesize Sn-Beta and compared with that synthesized from TEOS. The crystalline phase, morphology, physicochemical properties, and the state of Sn were characterized. It was found that Sn-Beta can be successfully prepared with fumed silica and silica sol as well as TEOS as silica source. Sn was introduced into the framework of these samples. Sn-Beta synthesized from fumed silica (Sn-Beta(FS)) and silica sol (Sn-Beta(Sol)) had similar crystallization behavior and full crystallization time as well as morphology, crystal size with that from TEOS. Sn-Beta(Sol) has less silanols and lowest ratio of open/closed tin site among these samples. It exhibited higher catalytic activity for the conversion of glucose to methyl lactate and lower catalytic activity for the isomerization of glucose as compared with the other two samples. Sn-Beta(FS) showed similar catalytic performance in the studied reactions with Sn-Beta(TEOS).

Propane dehydrogenation catalyzed by single Lewis acid site in Sn-Beta zeolite

The gap between supply and demand of propylene has become more and more evident, because of a large consumption of the downstream products derived from propylene. Propane dehydrogenation (PDH) constitutes an important alternative for the production of propylene, and thus considerable attention has been paid to the development of eco-friendly and cost-efficient catalysts for this process. Herein, we discover that the Sn-Beta zeolite with Lewis acid sites can activate the C-H bond, and exhibits high catalytic performance in the PDH. XRD, STEM, and XPS characterizations confirm that Sn species are incorporated into the zeolite framework, and H2-TPR suggests that there is a strong interaction between Sn species and zeolite framework. It is found that the Lewis acid is the active site for dehydrogenation reaction, and the Brønsted acid is responsible for cracking reaction. The dehydrogenation rate/cracking rate is positively proportional to the L/B ratio, and a high L/B ratio is beneficial for the propane dehydrogenation reaction. The Na-Sn-Beta-30 catalyst possessing the highest amount of Lewis acid but the lowest Brønsted/Lewis ratio, exhibits the best performance in the PDH, which delivers propane conversion of 40% and propylene selectivity of 92%. Most importantly, these Sn-Beta zeolites are extremely stable without any detectable deactivation under the harsh reaction condition for 72 h. Density functional theory calculations reveal that both Sn and adjacent O atom or OH group cooperativelyact as the active sites. The PDH occurs through the direct reaction mechanism in which hydrogen molecule is produced by the direct coupling of H atom of primary C3H7 motif with the Brønsted proton in closed sites or the proton of water in open sites. It seems that open sites are more reactive than the closed ones, and the intrinsic enthalpy barriers are calculated to be 242 ~ 301 kJ/mol depending on the hydroxylation extents. These efficient Sn-Beta zeolites could provide a new possibility for the development of a new generation of PDH catalysts with a high stability for the production of propylene.

In Situ Synthesis of Sn-Beta Zeolite Nanocrystals for Glucose to Hydroxymethylfurfural (HMF)

The Sn substituted Beta nanocrystals have been successfully synthesized by in-situ hydrothermal process with the aid of cyclic diquaternary ammonium (CDM) as the structure-directing agent (SDA). This catalyst exhibits a bifunctional catalytic capability for the conversion of glucose to hydroxymethylfurfural (HMF). The incorporated Sn acting as Lewis acid sites can catalyze the isomerization of glucose to fructose. Subsequently, the Brønsted acid function can convert fructose to HMF via dehydration. The effects of Sn amount, zeolite type, reaction time, reaction temperature, and solvent on the catalytic performances of glucose to HMF, were also investigated in the detail. Interestingly, the conversion of glucose and the HMF yield over 0.4 wt% Sn-Beta zeolite nanocrystals using dioxane/water as a solvent at 120 °C for 24 h are 98.4% and 42.0%, respectively. This example illustrates the benefit of the in-situ synthesized Sn-Beta zeolite nanocrystals in the potential application in the field of biomass conversion.

Catalytic Formation of Lactic and Levulinic Acids from Biomass Derived Monosaccarides through Sn-Beta Formed by Impregnation

In the present study, the use of Sn-Beta zeolite to facilitate the conversion of lignocellulosic biomass-derived glucose and xylose into lactic and levulinic acid was explored. The reactions were carried out in a batch reactor using water as the solvent. Water is the preferred solvent over methanol as it reduces downstream product acid recovery and purification complexity. Optimization experiments were performed for reaction temperature and residence time. Under optimized reaction conditions, the Sn-Beta facilitated reaction of a pure sugar solution resulted in lactic acid yields of 13 and 19 wt% of inlet carbon of glucose and xylose, respectively, plus levulinic acid yields of 18 and 0.8 wt%, respectively. When actual biomass-derived sugar solutions were tested, the yields of lactic acid were significantly higher than those from the optimized model solution experiments with lactic acid yields of 34 wt%. These biomass-derived sugar solutions contained residual levels of CaSO4 from the neutralization step of the hydrolysis process. Further experiments were performed to examine the potential effects from CaSO4 contributing to this increase. It was found that the sulfate ions increased the Brønsted basicity and the calcium increased the Lewis acidity of the reaction solution, and that the combination of both effects increased the conversion of the original sugars into lactic acid. These effects were verified by testing other organic bases to isolate the Brønsted acid neutralization effect and the Lewis acid enhancement effect. The addition of CaSO4 resulted in attractive lactic acid yields, 68 wt% and 50 wt% of inlet carbon from pure glucose and xylose solutions, respectively. Increasing the actual corn stover and forage sorghum derived sugars concentration (in water) allowed lactic acids yields of greater than 60 wt% to be achieved. When the optimized Sn-Beta reaction system was applied to corn stover and forage sorghum mixtures, it was found that the ratio of lactic-to-levulinic acid generated was inversely dependent upon the glucose-to-xylose ratio in the recovered sugar mixture.

Synthesis of hierarchical Sn-Beta zeolite and its catalytic performance in glucose conversion

Hierarchical Beta zeolites are successfully synthesized with hydrothermal method in the presence of polydiallyldimethylammonium chloride (PDADMA). Followed a dealumination process, hierarchical Sn-Beta are post-synthesized by the solid-gas reaction of dealuminated Beta zeolite with SnCl4 vapor. All samples are charcterized with XRD, N2 sorption, SEM and TEM. SEM images show that both Beta zeolite and Sn-Beta zeolite exhibit rough spherical-like morphology of about 500−900 nm in diameters, N2 sorptions show the pore size distributions in micropore and mesopore ranges, indicating the formation of mesoporous Beta zeolites. It is proofed that Sn species are doped into the framework in a tetrahedral environment during solid-gas reaction and the introduction of Sn species has negligible impact on the structure of Beta zeolites. Furthermore, the dehydration of glucose into HMF which needs both Brönsted and Lewis acid is selected to evaluate the catalytic performance of hierarchical Sn-Beta. It displays good catalytic activity, the conversion of glucose (99 %) and selectivity to HMF (42 %) are higher than those of the conventional Beta (96 % and 32 %, respectively). This is attributed to the intra-crystalline mesoporous structure and efficient diffusion of reactant/product molecules. Moreover, the catalyst exhibits steady catalytic performance after the fifth repeated run.

Density functional study of the effect of cation exchanged Sn-Beta zeolite for the diels-alder reaction between furan and methyl acrylate

We investigated the Diels-Alder (DA) reaction between furan and methyl acrylate over Lewis acidic Sn-Beta zeolite exchanged with Li, Na, K, Be, Mg and Ca cations by using density functional calculations. Sn-Beta requires lower barrier compared to uncatalyzed system due to its higher charge transfer from the furan to the adsorbed methyl acrylate, at the transition state. The catalytic activity for the CC bond formation in DA reaction can be altered by the exchange of cations in Sn-Beta. The catalytic activity of different tetravalent metal centers (Zr and Hf) substituted into Li-Sn-Beta is finally compared and found to be similar.

Continuous Conversion of Glucose into Methyl Lactate over the Sn-Beta Zeolite: Catalytic Performance and Activity Insight

In this study, we developed an efficient technology for the continuous conversion of glucose into methyl lactate over the Sn-Beta zeolite with a trickle bed reactor. The catalyst exhibited a high yield of 59.7% for lactic acid in water, and the total yield of methyl lactate and xylitol reached 59.8% (37.3% for methyl lactate) in methanol. The continuous evaluation of Sn-Beta demonstrated a maximum yield of 45.0% for methyl lactate along with 99% conversion of glucose in methanol, and the catalyst was continuously operated for over 434 h at 165 °C. The changes in Sn coordination and fouling stand as the dominant reason for the activity loss of Sn-Beta. Compared with the rapid decline of activity in water, reaction in methanol exhibited much less carbon deposition, structural changes, and Sn leaching after a long-term operation. The promising result indicated the potential application of Sn-Beta as an industrial catalyst for biomass utilization.

Fabrication of Hierarchical Sn-Beta Zeolite as Efficient Catalyst for Conversion of Cellulosic Sugar to Methyl Lactate

In this work, BEA-type hierarchically structured stannosilicate zeolite Sn-Beta-H was developed, which involved alkali-induced degradation of all-silica Beta (Si-Beta) and self-assembly of the resu...

Promotion effect of Mg on a post-synthesized Sn-Beta zeolite for the conversion of glucose to methyl lactate

Mg-Sn-Beta zeolites with different Mg/Sn molar ratios were prepared from the parent deAl-Beta by a coimpregnation method. It shows higher selectivity for the conversion of glucose to methyl lactate than post-synthesized Sn-Beta.