Sn-Beta Zeolite Research Articles

Fluoride-free hydrothermal synthesis of nanosized Sn-Beta zeolite via interzeolite transformation for Baeyer-Villiger oxidation

Sn-containing Beta (Sn-Beta) zeolite is extensively applied in industrially-relevant reactions as a highly active and robust Lewis acid heterogeneous catalyst. Nonetheless, environmentally-unfriendly fluoride is generally required to the directly hydrothermal synthesis of Sn-Beta. In this work, an innovative strategy of interzeolite transformation with steam-assisted conversion is provided to directly synthesize Sn-Beta zeolite in the absence of fluoride. Silica source of FAU and steam-assisted conversion were two necessary factors for the successful synthesis of Sn-Beta zeolite. It was found that highly crystallized Sn-Beta zeolite with isolated framework Sn ions was hydrothermally synthesized via degradation of siliceous FAU zeolite and recrystallization of degraded silicate species. As far as we know, the crystal of Sn-Beta in this work was minimum in size among all present directly hydrothermal synthesized ones. More importantly, the Sn contents in Sn-Beta could achieve to 2.39 wt % (Si/Sn = 81), breaking through the Sn content restriction of conventional fluoride-mediated method. In addition, the hydrophobicity of this resultant Sn-Beta zeolite was slightly inferior to Sn-Beta-F obtained via traditional fluoride-assisted route. Whereas the smaller crystal size of this Sn-Beta gave rise to relatively good diffusion performance for organics, which made it reveal high activities in the Baeyer-Villiger oxidant of ketones in particular employing bulky tert-butyl hydroperoxide as the oxidant. The current strategy provides an alternative and environmentally-friendly method for the hydrothermal synthesis of Sn-Beta without the assistance of fluoride and alkali metal ions, which can guide further development in metallosilicates crystal engineering in terms of greenization.

Fast hydrothermal synthesis of hierarchical Sn-Beta zeolite with high Sn content in fluoride media

Abstract The incorporation of tetravalent Sn species into the framework of BEA zeolite possesses Lewis acidic property and thus exhibits prominent catalytic performances in several reactions. Unfortunately, the Sn-Beta zeolite obtained by hydrothermal synthesis method suffered from several drawbacks including long crystallization time, limited framework Sn content and large crystal size. To solve the problems, a hierarchical Sn-Beta zeolite was synthesized by an innovative hydrothermal method. A hollow mesoporous Sn–Si oxide produced by a simple aerosol process was used as the precursor. The crystallization was preformed in an extremely dense system for only 2–4 days. More Sn species from the precursor can be incorporated into the Beta zeolite as the framework Sn species, which benefits from the unique structure of the precursor. Moreover, the diffusion property is improved due to the formation of the mesopores. The obtained hierarchical Sn-Beta zeolite catalyst exhibits enhanced catalytic performance in the Baeyer–Villiger oxidation of bulky ketone.

Efficient conversion of cellulose to methyl levulinate over heteropoly acid promoted by Sn-Beta zeolite

One-pot conversion of cellulose to valued-added platform chemicals such as alkyl levulinate is a promising and challenging process of biomass utilization due to the insolubility of cellulose in alcohol. In this work, commercial heteropoly acid combined with postsynthesized Sn-Beta zeolite was employed to transform cellulose to methyl levulinate (MLE) in one pot. The synergistic catalysis of the homogeneous strong Bronsted (B) acid and the solid strong Lewis (L) acid can effectively realize the depolymerization of solid cellulose and the subsequent isomerization, dehydration and hydration steps to MLE. 55% and 62% of MLE yields were obtained from α-cellulose and microcrystalline cellulose, respectively, at 160 °C for 10 h. Various carbohydrates besides cellulose can also be efficiently converted to MLE in high yields over the bifunctional catalyst system. The effects of the amount of B acid and L acid, the reaction temperature and time and the amount of cellulose on the production of MLE were investigated in detail. Finally, the reaction pathway of cellulose to MLE was revealed. Recyclability tests indicated that the binary catalyst can be reused without decrease of catalytic activity.

The synthesis of hierarchical Sn-Beta zeolite via aerosol-assisted hydrothermal method combined with a mild base treatment

Abstract The Sn-Beta zeolite is an efficient Lewis acid catalyst for a wide range of chemical reactions. Here a seed-free aerosol-assisted hydrothermal strategy is used to synthesize plate-like Sn-Beta zeolite with higher tin content. A majority of Sn species were transformed into the framework of Beta zeolite as the desired tetrahedral coordination state, which creates strong Lewis acid sites. Moreover, the diffusion property of the Sn-Beta zeolite can be further improved by a mild base-surfactant (NH3˙H2O-CTAB) treatment. The addition of CTAB can not only narrow the mesopore distribution but also prevent the excessive loss of Sn species. The obtained hierarchical Sn-Beta zeolite exhibits an enhanced catalytic performance in the Baeyer–Villiger oxidation of bulky ketone.

Production of lactic acid derivatives from sugars over post-synthesized Sn-Beta zeolite promoted by WO3

Various metal oxides were used as co-catalysts to improve the production of alkyl lactate over Sn-Beta-P. WO3 exhibited the best promotion effect. The yield of MLA increased from 25% (6.5 g L−1) over Sn-Beta-P (0.2 g) to 52% (13.4 g L−1) over WO3 (0.1 g) and Sn-Beta-P (0.1 g) at 160 °C for 5 h and 3.1 wt% of glucose concentration. MLA yield of 38% was attained even at glucose concentration of 10 wt% and the space-time yield reached 7.1 g L−1 h−1. The action mechanism of WO3 was investigated. Fine WO3 particles adsorbed on surface of Sn-Beta-P in reaction media and decreased the silanol defects of Sn-Beta-P. This promotes retro-aldol of fructose, the rate-determining step of whole reaction, thus facilitated the formation of MLA. Kinetic studies indicate that the presence of WO3 decreased the activation energy of the retro-aldol of fructose. The binary solid WO3 and Sn-Beta-P is recyclable.

Efficient production of lactic acid from sugars over Sn-Beta zeolite in water: catalytic performance and mechanistic insights

Hydrothermal conversion of sugars exceeded 98.0% with lactic acid yield reaching 67.1% over a Sn-Beta zeolite catalyst prepared via a green synthesis.

Surface amino-functionalization of Sn-Beta zeolite catalyst for lactic acid production from glucose.

The catalytic conversion of glucose into lactic acid (LA) provides an alternative approach for LA production to bio-fermentation. Nevertheless, during the process, the dehydration of glucose and fructose into 5-hydroxymethylfurfural catalyzed by Brønsted acid exists as the main side reaction that leads to the decrease in LA yield. In order to promote the yield and selectivity of LA, a series of acid–base bifunctional Sn-Beta-NH2 catalysts were prepared by post-grafting aminopropyl groups with the surface silanol groups of Sn-Beta zeolite. The catalysts were systematically characterized by X-ray diffraction, N2 adsorption–desorption, elemental analysis, X-ray photoelectron spectroscopy, Fourier transform infrared spectra analysis following pyridine adsorption, and CO2 temperature-programmed desorption. The as-prepared Sn-Beta-NH2 catalysts exhibiting both Lewis acid and moderate base sites facilitated the conversion of glucose to LA in competition with undesirable side reactions. In addition, effects of reaction parameters including reaction temperature and time, catalyst dosage, and glucose concentration were investigated. A high LA yield up to 56% was achieved under optimized hydrothermal conditions (190 °C, 2 h), along with a complete conversion of glucose and a 5-hydroxymethylfurfural yield of 7%. The result indicated an alternative modification method of Sn-Beta zeolite for a more favorable LA yield.

Conversion of Sucrose into Lactic Acid over Functionalized Sn-Beta Zeolite Catalyst by 3-Aminopropyltrimethoxysilane.

The utilization of sucrose, an easily accessible disaccharide, in the production of a versatile platform chemical lactic acid (LA), is more attractive than a monosaccharide. In this work, we report a modification approach by 3-aminopropyltrimethoxysilane to introduce an amino group onto the surface of the Sn-Beta Lewis acid catalyst. Using the modified catalyst, a maximum LA yield of 58% was achieved under optimal hydrothermal conditions (190 °C, 4 h) from sucrose, along with a complete conversion and a reduced 5-hydroxymethylfurfural (HMF) yield of 8% compared to Sn-Beta. To evaluate the role of the amino group, different substrates were used as the reactants to produce LA. The experimental results suggested that both fructose and glucose were crucial intermediates in the initial 2 h, whereas glucose is the sole reactant after 2 h. Upon modification, not only the hydrolysis of sucrose was promoted, but the side reaction of HMF formation was also suppressed.

Deactivation of Sn-Beta during carbohydrate conversion

The deactivation of Sn-Beta zeolite catalyst during retro-aldolization and isomerization of glucose is investigated. Confocal fluorescence microscopy reveals that retro-aldolization of glucose in CH3OH at 160 °C is accompanied with the build-up of insoluble oligomeric deposits in the micropores, resulting in a rapid catalyst deactivation. These deposits accumulate predominantly in the outer regions of the zeolite crystals, which points to mass transport limitations. Glucose isomerization in water is not only accompanied by the formation of insoluble deposits in the micropores, but also by the structural degradation of the zeolite due to desilication and destannation. Enhanced and sustained catalytic performance can be achieved by using ethanol/water mixtures as the reaction solvent instead of water.

One-pot synthesis of high value-added chemicals from furfural over bimetal-doped beta zeolite and carbon solid acid catalysts

A series of bimetal-doped beta zeolites were prepared via a simple post-synthesis strategy including dealumination and metal ion incorporation. The incorporation of ferromagnetic metals into lattice sites of Sn-beta was evidenced by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV-Vis spectroscopy and X-ray photoelectron spectroscopy (XPS). The high reduction temperature (1094 K) of cobalt in Co-Sn-beta zeolite, as determined by temperature programmed reduction (TPR), confirms that Co interacts strongly with the zeolite support, consistent with lattice tetrahedral (Td) coordination. Co-doped Sn-beta zeolite was found to be a promising Lewis acid catalyst together with a carbon solid acid for the conversion of furfural to isopropyl 4-oxovalerate (i-PL) and γ-valerolactone (GVL). The highest total yield of 92.02% was obtained after reaction for 16 h at 160 °C, including 48.3% i-PL, 37.7% GVL, and 6.0% levulinic acid (LA). The catalysts could also be applied as robust catalysts in glucose conversion to 5-hydromethylfurfural. Zeolite catalysts designed and prepared by this strategy contain multiple metals, enhancing their flexibility and adjustability of function via changing the species and ratio of metals to derive optimized catalysts for specific reactions.

Aerosol-seed-assisted hydrothermal synthesis of Sn-Beta zeolite and its catalytic performance in Baeyer–Villiger oxidation

It is still a big challenge to hydrothermally synthesize Sn-Beta zeolite by using lower amount of template and mineralizing agent in a relatively short crystallization time. To solve the problems an aerosol-seed-assisted method was used to synthesize Sn-beta zeolites. The optimum synthesis conditions were explored by varying the different synthesis parameters. It was found that the dense synthesis system help to lower the required amount of the template and hazardous mineralizing agent, and shorten the crystallization time. The crystallization of the Sn-Beta zeolite follows the liquid-phase mechanism. The incorporation of the tin species into the framework created strong Lewis acid sites, which was confirmed by UV–Vis, pyridine-FT-IR and CD3CN-FT-IR techniques. The good catalytic performances of the Sn-Beta zeolite catalysts were observed in the Baeyer–Villiger oxidation of cyclohexanone with H2O2.

Sn-Beta zeolite derived from a precursor synthesized via an organotemplate-free route as efficient Lewis acid catalyst

Sn-containing Beta zeolite (Sn-Beta) is an effective solid Lewis acid catalyst useful for a large number of redox reactions. However, it is still a challenging task to prepare Sn-Beta without the usage of organic structure directing agents (OSDAs) and/or fluoride. Considering synthesis cost and the consumption of energy as well as environmental problems, in this study, hierarchical Sn-Beta is successfully prepared via post-synthesis method by incorporating Sn ions into silanol nests of dealuminated Beta zeolite which is synthesized through an OSDA- and fluoride-free route. Prior to deep dealumination, the OSDA-free aluminosilicate Beta is steamed at a mild temperature for a short time (823 K, 30 min), which allows for the effectively stabilizing the Beta framework structure. Then Sn ions are tetrahedrally incorporated into the Beta framework at 773 K under vapor condition via the reaction between the Sn ions and silanol defects derived from the steaming and subsequent acid treatment. The Sn-Beta zeolite thus obtained exhibits better catalytic performances than conventional Sn-Beta-F in the conversion of dihydroxyacetone to ethyl lactate (yield, 89.1% vs. 74.3%) and Baeyer-Villiger oxidation of 2-adamantanone (conversion, 72.3% vs. 58.6%, using H2O2 as the oxidant). The enhanced catalytic performance is predominantly contributed by hierarchical pore channels and the smaller particle size, which greatly enhance mass transfer and lower the apparent reaction activation energy.

Sn-Beta zeolite hydrothermally synthesized via interzeolite transformation as efficient Lewis acid catalyst

An innovative hydrothermal synthesis strategy of heteroatom-containing zeolite, in this case Sn-Beta, via interzeolite transformation is reported in present study. To the best of our knowledge, this prepared Sn-Beta zeolite possesses the highest isolated Sn contents (3.03wt% or Si/Sn molar ratio of 63) in comparison to other hydrothermally synthesized ones. The success of this synthesis strategy to Sn-Beta synthesized from MWW silica is mainly due to its nucleating and growing readily compared with those prepared from amorphous silica source. The introduction of Beta seeds and the structural similarity between the parent zeolite (MWW) and the targeted zeolite (*BEA) are found to be indispensable factors in the crystallization of Sn-Beta zeolite. The obtained Sn-Beta zeolites possess isolated tetrahedral Sn4+ in the framework and high hydrophobicity. Additionally, lowering the molar ratio of H2O2 to cyclohexanone and moderately reducing reaction time are proved to be effective methods to improve the selectivity of ε-caprolactone in the Baeyer–Villiger oxidation of cyclohexanone with H2O2 using Sn-Beta as Lewis catalyst. Thus, the prepared Sn-Beta zeolite demonstrated promising catalytic properties, especially for the desired products selectivity, in the Baeyer–Villiger oxidation of ketones as well as the isomerization–esterification reaction of dihydroxyacetone in ethanol, far outperforming the conventional Sn-Beta-F catalyst, which were attributed mainly to its high Sn content in the framework and excellent diffusion properties resulting from the relatively small crystal size.

Hierarchical Sn-Beta Zeolite Catalyst for the Conversion of Sugars to Alkyl Lactates

Enhancing the yield of alkyl lactate from sugars is in great demand but challengeable to accomplish. Here we report a facile but efficient route to make this by employing a hierarchical and Sn-cont...

Distribution of open sites in Sn-Beta zeolite

A survey of the open site geometries in Sn-Beta has been completed. Comparing the relative energies of 144 distinct open site structures identifies both T9 and T1 sites as the most stable open sites. However, a key feature of these sites is that the Sn-O-Si bridge which is hydrolyzed is opposite the SnOH, rather than adjacent. This results in geometries in which the SiOH in the open site is significantly more acidic than a surface SiOH or a SiOH defect in the zeolite, as found in adsorption calculations of NH3, pyridine, and acetonitrile. Frequency shifts calculated for acetonitrile are consistent with experimental frequency shifts, and the proposed open site geometry suggests a new assignment for a peak observed experimentally by Harris et al. [1] and Otomo et al. [2] The stabilization of the open site silanol by the nearby Sn generates this unusual Brønsted acidity in the Sn-Beta open site, which highlights the need to consider new reaction mechanisms in the Sn-Beta literature.

Synthesis of Methyl Lactate from Glycerol Using Sn-Beta Zeolite

Lactic acid can not only be used to produce multiple chemicals, but can also be the building block for biodegradable and biocompatible polylactic acid identified as a renewable resource. As a by-product in biodiesel production, the glycerol yield increases with a rapid expansion of biodiesel. However, in the chemical and environmental fields it is still a great challenge to produce lactic acid or methyl lactate from glycerol. Herein, Sn-Beta zeolite was prepared through solid-state ion exchange (Sn-Beta SSIE) and was tested for base-free one-pot catalytic selective oxidation of glycerol into methyl lactate in methanol. The results showed that a maximum selectivity of up to 56.7% was achieved with a 36.8% conversion rate at 433 K within 4 h under an initial oxygen pressure of 0.1 MPa. In addition, the methyl lactate yield is not high because of its decomposition in the presence of oxygen. This study aims to contribute to the development of the polylactic acid industry.

Selective Chemical Conversion of Sugars in Aqueous Solutions without Alkali to Lactic Acid Over a Zn-Sn-Beta Lewis Acid-Base Catalyst.

Lactic acid is an important platform molecule in the synthesis of a wide range of chemicals. However, in aqueous solutions without alkali, its efficient preparation via the direct catalysis of sugars is hindered by a side dehydration reaction to 5-hydroxymethylfurfural due to Brønsted acid, which originates from organic acids. Herein, we report that a previously unappreciated combination of common two metal mixed catalyst (Zn-Sn-Beta) prepared via solid-state ion exchange synergistically promoted this reaction. In water without a base, a conversion exceeding 99% for sucrose with a lactic acid yield of 54% was achieved within 2 hours at 190 °C under ambient air pressure. Studies of the acid and base properties of the Zn-Sn-Beta zeolite suggest that the introduction of Zn into the Sn-Beta zeolite sequentially enhanced both the Lewis acid and base sites, and the base sites inhibited a series of side reactions related to fructose dehydration to 5-hydroxymethylfurfural and its subsequent decomposition.

Modification of Sn-Beta zeolite: characterization of acidic/basic properties and catalytic performance in Baeyer–Villiger oxidation

Sn-Beta modified with cations such as Li and Na showed better catalytic performance than non-modified Sn-Beta with “open” sites in Baeyer–Villiger oxidation.

Diels–Alder and Dehydration Reactions of Biomass-Derived Furan and Acrylic Acid for the Synthesis of Benzoic Acid

Routes to benzoic acid starting from furan—obtained from hemicellulose in high yield—and methyl acrylate are reported. These routes involve Diels–Alder and dehydration reactions of furan and acrylic acid (or methyl acrylate) in a two-step reaction protocol that minimizes side reactions. The Diels–Alder reaction of furan and methyl acrylate (or acrylic acid) was run at 298 K and was catalyzed by Lewis acidic (Hf-, Zr-, and Sn-Beta) zeolite catalysts, and achieving a high turnover frequency (∼2 h–1) and no side reactions were observed. The oxanorbornene product was dehydrated at low temperatures (298 to 353 K) in mixtures of methanesulfonic acid and acetic anhydride in 96% yield. This is compared to an only 1.7% yield of methyl benzoate obtained for the dehydration of the oxanorbornene in neat methanesulfonic acid. The effect of oxanorbornene concentration and stereochemistry was found not to decrease the yield of aromatics, while dehydration of the carboxylic acid form of the oxanorbornene led to a decreas...

Catalysis of Glucose to 5-Hydroxymethylfurfural using Sn-Beta Zeolites and a Brønsted Acid in Biphasic Systems

Selective and efficient dehydration of glucose to 5-hydroxymethylfurfural (HMF) has been a widely explored concept recently, especially from the perspective of employing environmentally benign heterogeneous catalysts. However, there has been a relative paucity of data regarding the application of Sn-Beta zeolites, a category of catalysts that are very innocuous, inexpensive, and effective, toward evaluating bio-based conversions. Sn-Beta was shown to possess good Lewis acidity for catalyzing glucose isomerization to fructose in aqueous media at low pH and accelerating dehydration of glucose to HMF in a biphasic system with high yields. Sn-Beta zeolite with NH4F as the mineralizing agent (Sn-Beta-F) was a more effective catalyst for the selective dehydration of glucose to HMF. An optimal HMF yield of 53.0% was obtained over Sn-Beta-F zeolite in an acidic environment (pH 1) after 70 min at 190 °C. The reaction system was also effective for conversion of cellulose to HMF with a yield of 32.2% preliminarily.