Hierarchical Beta Research Articles

Nanosized “rice ball” like hierarchical beta zeolites with inter-crystalline mesopores for efficient catalytic synthesis of lactide

A series of nanosized “rice ball” like hierarchical beta zeolite aggregates (RBZxAy, x = 6, 9, 12 or 15; y = 2, 4 or 6) with hierarchical structures are successfully synthesized via gel aging and hydrothermal method without mesoporous template. The as-prepared RBZxAy zeolites possess two ranges of inter-crystalline mesoporous that formed by zeolite nanoparticles aggregation compared to the non-aged samples (B12Z4). The effects of Si/Al ratio and crystallization time on the morphology, structure and surface acidic properties of RBZxAy were systematically investigated. Meanwhile, RBZxAy as catalysts were applied in the conversion of lactic acid (LA) to lactide (LT) to investigate their catalytic performance. Benefitting from smaller crystal size, hierarchical structures and higher acid content, the representative catalyst (RBZ12A4) exhibited outstanding catalytic activity that the LA conversion was high to 98 % and the LT yield up to 94 %. In addition, RBZ12A4 presented perfect regeneration ability after 10 times recycles. This work provides an effective and facile route to directly synthesis nanocrystals aluminosilicate zeolite with hierarchal structure, and constructs an approach for efficiently converting LA to LT, it has greatly significance for the development of polylactic acid industry.

Vegetation index and livestock practices as predictors of malaria transmission in Nigeria

Nigeria is the most malaria-endemic country in the world. Vegetation and livestock practices have been linked to malaria transmission but little is known about these in Nigeria. The study aimed to evaluate the influence of vegetation and livestock as predictors of malaria transmission in Nigeria. Secondary data obtained from the Nigerian Demographic and Health Survey’s Geospatial Covariate Datasets Manual were used for the analysis. The survey was carried out successfully in 1389 clusters of thirty (30) households each using a two-stage stratified random sampling design. Hierarchical beta regression models were used to model the associations between malaria incidence, enhanced vegetation index (EVI), and livestock practices. The correlation coefficients for vegetation index and livestock-related variables ranged from − 0.063 to 0.074 and varied significantly with the incidence of malaria in Nigeria (P < 0.001). The model showed vegetation index, livestock goats, and sheep as positive predictors of malaria transmission. Conversely, livestock chicken and pigs were observed to reduce the risk of malaria. The study recommends the need to take into account local differences in transmission when developing malaria early warning systems that utilize environmental and livestock predictors.

Furfural Acetalization with Ethanol over Hierarchical vs. Conventional Beta Zeolites

AbstractA set of hierarchical Beta zeolites was synthesized using concentrated reaction mixtures and compared to conventional materials with a similar composition. The obtained zeolite catalysts were investigated in acetalization of furfural with ethanol at room temperature yielding a commercially valuable fuel additive (furfural diethyl acetal). The highest yield of the desired product (91 %) was achieved over a zeolite catalyst possessing developed mesoporosity (Vmeso 0.75 cm3/g) and a high external surface area (280 m2/g). The concentration of accessible acid sites was found to be responsible for high catalytic performance of the tested zeolitic catalysts.

Pt-promoted mesoporous Beta zeolite catalysts for n-Hexane isomerization with enhanced selectivity to dibranched isomers

We report a facile yet effective strategy to prepare hierarchical Beta zeolite with high molecular transport effectivity in catalysis. Alkaline etching involves preferential desilication from Beta framework and collapse of microporosity. The preferential desilication from outer rim of Beta stacking faults enlarged intercrystallite mesopores, while the collapse of microporosity created cylindroid-like intracrystalline mesopore. Part of Altet with lower stability was removed during alkaline etching, leading to a decrease in acid sites density. Alkaline etching of Beta zeolite with 0.2 mol/L NaOH solution greatly improved n-hexane isomerization activity over Pt-based catalysts. The maximum yield of isohexane and dibranched isomers increased by 6.2 % and 38.6 %, respectively. The enlargement of intercrystallite mesopores and the generation of intracrystalline mesopores of Beta zeolite lowered apparent activation energy of reaction. The apparent diffusivities measurements further revealed that Pt/Beta-0.2 M showed much lower transport limitation than Pt/Beta-parent. Our findings provide a promising catalyst for industrial alkane isomerization.

Hierarchical beta zeolites assisted aromatics production from lignin via catalytic fast pyrolysis

Converting lignin waste into aromatics is a challenging but crucial aspect of lignin valorization. Although ZSM-5 zeolite is extensively used in lignin deoxygenation, its 10-membered ring (MR) channels limit the diffusion of bulky phenols and tend to produce coke. Herein, a series of 12-MR beta zeolites with varying acidity and hierarchical porosity were synthesized for lignin catalytic fast pyrolysis (CFP). An optimal lignin pyrolysis temperature of 600 °C was initially selected. Subsequently, lignin CFP demonstrated that beta zeolite with medium acidity facilitated aromatics production, with Beta(36) even outperforming ZSM-5(36). The introduction of mesopores further enhanced lignin deoxygenation and the hierarchical B36-0.3-24 increased aromatics selectivity to 56.0 area%, which was 1.5 times that of Beta(36). Combined with the CFP of model compounds (vanillin and catechol), it was inferred that the mesopores and weak acidity played a key role in heavy phenols conversion and aromatics production. In addition, B36-0.3-24 exhibited outstanding reusability in pyrolysis regeneration cycles, underscoring its potential for practical application in lignin valorization.

Eco-friendly synthesis and environmental impact assessment of hierarchical Beta zeolite from kaolinite and recycled mother liquor

The development of sustainable techniques to produce high-performance zeolite is essential to achieve green production in industry. Herein, we report an eco-friendly route to synthesizing hierarchical Beta zeolite from kaolinite and recycled mother liquor. The results reveal that the unutilized species (such as silicon species and Na+) in mother liquor stayed in a stable concentration during eleven recycled experiments. Moreover, the synthesized Beta zeolites still have comparable physicochemical properties and catalytic performance in the esterification of levulinic acid with ethanol over the initial zeolite although eleven recycled experiments. Life cycle assessment exhibits that the synthesis of Beta zeolite with recycled mother liquor can reduce global warming potential by 23% and resource depletion-water use by 36% compared to that without recycled mother liquor. This quantitatively demonstrates that the approach proposed in this work is really a sustainable one, extremely increasing the utilization efficiency of raw materials and decreasing the environmental burden.

Fine Tuning of Hierarchical Zeolite Beta Acid Sites Strength

Two different synthesis methods to obtain hierarchical Beta zeolite are investigated: direct synthesis using cetyltrimethylammonium bromide (CTAB) as a mesoporous template and post-synthesis desilication by etching with NaOH and TPAOH. The main focus of this study is to show the possibility of fine tuning of the acid site (OH) strength (Brønsted and Lewis acid sites) through wet impregnation of these hierarchical Beta zeolites with divalent metal cations (Mg2+, Co2+, Ni2+, Cu2+, and Zn2+), which are important for various applications. Fourier transform infrared spectroscopy (FTIR) and deuterated acetonitrile as the probe molecule were used as a powerful technique to analyze the quantity and number of Brønsted/Lewis acid sites in the modified zeolite Beta structure. Investigating the influence of different divalent metal cations with a comparable ionic radius on the acidity of the hierarchical Beta zeolites, the present research aims to shed light on the structure–activity relationship that determines their catalytic behavior, for the development of efficient and environmentally friendly catalysts for various industrial applications.

Micro‐Mesoporous Hierarchical Beta Zeolite and its Catalytic Application in Acetic Acid Benzylation

AbstractHierarchical Beta zeolite with tailor‐made pore structure is prepared by post‐synthetic alkali (NaOH) treatment. XRD, FE‐SEM, ICP‐OES, 27Al &amp; 29Si MAS NMR, and N2 sorption isotherms were used to explore the structural transformation of these materials. ICP‐OES analysis showed post‐synthetic base treatment resulting into tuning of the Si/Al ratio, thereby increasing the acidity of the sample. The acidic properties of materials were measured using acid‐base titration, Pyridine FTIR spectroscopy, and NH3‐TPD. Conversion of acetic acid to benzyl acetate by reacting with benzyl alcohol was studied using hierarchical and parent sample. The reaction was evaluated with theoretical and experimental approaches. Under optimum reaction conditions, desilicated Beta zeolite showed 93 % acetic acid conversion and 90 % benzyl acetate selectivity, as confirmed by GC and GC‐MS analyses. Theoretical analysis indicated direct relationship between rate constant and rising reaction temperature, in accordance with the principles of first‐order reaction kinetics (R2&gt;0.95). The activation energy for acetic acid benzylation over Beta‐0.1 M NaOH was found to be 10.21 kJ mol−1, considerably lower value compared to previous reports.

Micron-Sized Hierarchical Beta Zeolites Templated by Mesoscale Cationic Polymers as Robust Catalysts for Acylation of Anisole with Acetic Anhydride

Hierarchical Beta zeolites with interconnected intracrystalline mesopores and high structural stability are highly attractive for catalytic applications involving bulky reactants. Here, by introducing a suitable amount of polydiallyldimethylammonium chloride into the initial synthesis system, micron-sized Beta zeolite crystals with abundant hierarchical porosity (Beta-H) were hydrothermally synthesized. The sample named Beta-H_1 exhibited very high catalytic activity and durability for the Friedel–Crafts acylation of anisole with acetic anhydride. A 92% conversion rate of acetic anhydride could be achieved after 1 h of reaction in a fixed bed reactor, and 71% conversion still remained after 10 h, much better than the rate for conventional Beta zeolite (which decreased rapidly from 85% to 37% within 10 h). The enhanced catalytic performance of Beta-H zeolites could be mainly attributed to the relatively lower strong acid density and the faster transport rate of the hierarchical zeolites. In addition, Beta-H showed high structural stability and could be easily regenerated via high-temperature calcination without obvious loss in catalytic activity, demonstrating its great potential for catalytic applications in the industrially important Friedel–Crafts acylation process.

Catalytic upgrading of a model polyethylene pyrolysis oil by hydroconversion over Ni-containing hierarchical Beta zeolites with tailored acidity

Valorization of waste polyolefins by a sequential combination of thermal pyrolysis and catalytic hydroconversion over a bifunctional metal/acid catalyst (e.g. zeolite) is an efficient route to produce transportation fuels. However, the zeolite strong acidity typically causes extensive cracking and loss of liquid fuels. In this work, mild dealumination with oxalic acid of a hierarchical Beta zeolite was used to achieve Ni 7%/h-Beta catalysts with Si/Al ratios within the 25 – 130 range. These catalysts were tested in the hydroconversion of a model mixture of LDPE thermal pyrolysis product (1-dodecene/n-dodecane, 50/50 w/w). The highest share of liquid fuels (∼ 90%) was achieved over 7% Ni/h-Beta (SiAl = 130). Besides, due to its high accessibility and tailored acidity, the product contained a meaningful amount of isoparaffins (12%) and a negligible content of olefins (< 3.5%). Thus, this catalyst holds promise for plastic waste hydroconversion towards transportation fuels.

Research Progress on the Synthesis of Nanosized and Hierarchical Beta Zeolites

Beta zeolite, a crystal material with a three-dimensional twelve-ring cross-channel structure, has many advantages, such as high Brønsted acid concentration, high Si/Al ratio, thermal/hydrothermal stability, and large surface area. Due to these advantages, beta zeolite shows excellent catalytic performance in petroleum refining and petrochemical processes. However, traditionally microporous beta zeolite has strong steric hindrance and diffusion restrictions, which hinder large molecules from passing through its internal channels. In addition, carbon deposition occurs, resulting in catalyst deactivation. The main strategy to solve this problem is to prepare nanosized or hierarchical beta zeolites, which allow for large molecule conversion and shortening diffusion pathways. Therefore, researchers have explored different synthesis strategies to prepare beta zeolite with different particle sizes and porosities to obtain better zeolite catalysts. This paper briefly describes the recent research progress in the preparation of nanosized and hierarchical beta zeolite. Additionally, the mechanisms of various preparation methods, structural characteristics, and applications of the materials are introduced in detail. Furthermore, the main problems existing in its industrial application are describing by comparing the advantages and disadvantages of the different methods to prepare optimally nanosized and hierarchical zeolite to meet the requirements of industrial development.

Production of Trioxane from Formaldehyde via Hierarchical Beta Zeolite Synthesized Using a Cationic Polymer

Production of Trioxane from Formaldehyde via Hierarchical Beta Zeolite Synthesized Using a Cationic Polymer

A surface modification strategy to prepare hierarchical Beta molecular sieves for glucose dehydration.

In order to balance the contradiction between mesopore introduction and loss of microporosity, a surface modification strategy is proposed by selectively adsorbing organic alkaline molecules on Beta molecular sieves before NaOH etching. Organic alkaline molecules adsorb on framework aluminum sites and the protective function of organic bases is affected by the adsorption configuration and physical barrier effect of organic bases. Organic alkaline molecules serve as a protective agent to increase the bond length of Al-O bonds. Therefore, the as-synthesized hierarchical Beta molecular sieves have more acid sites due to the preservation of aluminum atoms. When employed as catalysts in the dehydration reaction of glucose, 5-hydroxymethylfurfural (5-HMF) is obtained under the synergistic effect of Brønsted and Lewis acid sites. The unique contribution is to realize the porosity regulation and alleviate the acidity loss of Beta molecular sieves. These results are important to broaden the application fields of aluminum-silicon molecular sieves especially for large molecule-engaged acid catalyzed reactions.

A selective alkaline etching strategy to prepare hierarchical Beta molecular sieves for the hydrodeoxygenation of phenol

A selective alkaline etching strategy is reported to prepare hierarchical Beta molecular sieves with cetyltrimethyl ammonium bromide (CTAB). The homogeneityof mesopores is tuned by surface modification of Beta molecular sieves. CTAB selectively interacts with crystal defects and protects primary etched small mesopores from continuous destruction to form large mesopores. Under the synergistic effect of NaOH solution and CTAB, the acidity retention of Beta molecular sieves is higher due to the removal of Si(OSi)4 rather than Si(OSi)3 (OAl) species. When employed as the support of Pt/Beta catalysts, hydroxyl adsorption of phenol on Beta molecular sieves and Pt particles are observed. Dispersion of Pt on the surface of Beta molecular sieves is improved due to the uniform distribution of mesopores. A higher dispersion of Pt attributes to a higher deoxygenation conversion of phenol. The unique contribution of the current research is to propose the role of CTAB in alkaline etching process, realizes the controllable porosity regulation, and alleviates the acidity loss of Beta molecular sieves. These results are important to broaden the application fields of aluminum–silicon molecular sieves especially for large molecules engaged reactions and preparation of supported catalysts with a high metal dispersion.

An efficient like dual-function template used to synthesize hierarchical beta zeolites with abundant intracrystalline mesopores

Using [C12H25(CH3)2N+(CH2)2N+(CH3)2C2H5][Br−]2 as a dual-function template, a hierarchical beta zeolite material was synthesized in the current work. This Beta zeolite material is characterized by a mesopore diameter distribution of about 5.20 nm and a high specific surface area (SBET(Beta)/SBET(MBeta) = 475.9/550.4). This hierarchical beta zeolite material is therefore a suitable catalyst carrier for medium and high-temperature catalytic reaction systems. This is particularly true for processes involving several intermediates and macromolecules.

Florol synthesis via Prins cyclization over hierarchical beta zeolites

A set of hierarchical beta zeolites with variable Si/Al ratios, nanoparticle sizes, textural and acidic properties was prepared using a hydrothermal treatment of a concentrated alkali metal-free protic acid-containing zeolite gel-precursor. The obtained catalysts were investigated in the Prins cyclization of isovaleraldehyde with isoprenol yielding a commercially valuable tetrahydropyranol (Florol). The highest yield of the desired product (55.4%) was achieved over a zeolite catalyst possessing moderate acidity, developed mesoporosity (Vmeso 0.60 cm3/g) and a high external surface area (290 m2/g). Preferable formation of substituted tetrahydropyranol over weak- and medium-strength Brønsted acid sites, on the one hand, and generation of the undesired dehydration products mainly over strong Brønsted acid sites, on the other hand, occurring in parallel routes were supported by the kinetic analysis of the reaction network.

Promoting effect of alkali metal on the catalytic performance of hierarchical Pt/Beta in the aromatization of n-heptane

Previous research showed that hierarchical Beta zeolite supported Pt was an effective catalyst for the aromatization of alkanes and the modification with K could further enhance its catalytic performance; however, the intrinsic effect of alkali metal on the alkanes aromatization over Pt/Beta was still rather obscure. In this work, a series of hierarchical Pt/Beta-Me catalysts were prepared by modifying the Beta zeolite with different alkali metal nitrates (MeNO3, Me = Li, Na, K and Rb) through ion-exchange and used in the aromatization of n-heptane; the effect of alkali metal on the catalytic performance of Pt/Beta-Me was then systematically investigated. The results indicate that the alkali metals used to modify the Pt/Beta-Me catalysts can not only passivate the strong Brønsted acid sites of Beta zeolite, but also enhance the Pt dispersion and induce an electron-rich chemical environment for the supported Pt species. Accordingly, the modification with alkali metal can effectively suppress the cracking reactions and carbonaceous deposition and meanwhile promote the dehydroaromatization of alkanes, in favor of enhancing the catalytic stability and aromatization selectivity of Pt/Beta-Me. The extent of promoting effect of various alkali metals follows the order of Rb > K > Na > Li. In particular, the Pt/Beta-Rb catalyst exhibits excellent performance in the aromatization of n-heptane, with a much higher selectivity to aromatics (78.2%) and larger turnover number of aromatic products (Pt-based TON, 19.4 × 103) than the unmodified Pt/Beta-H one (27.7% and 4.8 × 103, respectively). These results help to clarify the role of alkali metal played in the catalysis of Pt/Beta-Me for n-heptane aromatization and pave the way for designing more efficient catalysts in the aromatization of alkanes.

Selective Synthesis of Levulinic Ester from Furfural Catalyzed by Hierarchical Zeolites

Furfural is a platform molecule that can be catalytically converted using a cascade series of reactions into levulinic esters, essential compounds used as fuel additives. Bifunctional catalysts containing Lewis and Brønsted acid sites such as zeolites are commonly used for these conversions. However, microporous zeolites often present diffusional restriction due to the size similarity of furfural and other molecules to the zeolites’ micropores. Thus, incorporating mesopores in these materials through post-synthetic protocols is a promising pathway to circumventing these limitations. This study presents the creation of hierarchical beta and mordenite using Si or Al removal and their employment in the furfural conversion to isopropyl levulinate (PL). Mordenite zeolite did not produce satisfactory mesopores, while the beta was more efficient in generating them by both acid and alkaline treatments. Beta zeolite treated in an alkaline solution presented larger mesopores (14.9 and 34.0 nm), maintaining a total acidity value close to its parent zeolite and a higher Lewis/Brønsted ratio. The combination of these features led to an improved diffusion of bulkier products and the highest furfural conversion (94%) and PL selectivity (90%), suggesting that a post-modification of beta zeolites produced efficient catalysts for upgrading abundantly available furfural.

Hierarchical Beta Zeolites As Catalysts in α-Pinene Oxide Isomerization

Hierarchical Beta Zeolites As Catalysts in α-Pinene Oxide Isomerization

“Burr Puzzle”-Like Hierarchical Beta zeolite composed of crisscrossed nanorods

Hierarchical Beta zeolite (named ECNU-41) was directly synthesized with commercially available ionic liquid 1-butyl-1-methylpyrrolidinium hydroxide as organic structure-directing agent (OSDA) in the absence of any surfactants or polymers. The ECNU-41 crystals were composed of nanorods through a unique stacking manner, exhibiting a morphology resembling the Chinese traditional toy “burr puzzle”. The orderly crisscrossed stacking ECNU-41 possesses high hydrothermal stability, abundant intercrystal mesoporosity, and enriched phase of polymorph B. In comparison to conventional nanosized Beta zeolites, ECNU-41 aluminosilicate and titanosilicate exhibited more remarkable and competitive catalytic performances in a variety of reactions, including benzene alkylation, methanol to propylene, and alkenes epoxidation. With improved diffusion rate and mass transfer due to the hierarchical structure, ECNU-41 is expected to serve as promising catalysts for those reactions involving bulky molecules. The hierarchical Beta zeolite (named ECNU-41) was synthesized using a small ionic liquid molecule, 1-butyl-1-methylpyrrolidinium hydroxide as the organic structure-directing agent in the absence of any surfactants or polymers. ECNU-41 shows an unusual “interlaced” morphology, and the individual crystal is orderly knitted by nanorods, forming an intersected model like the “burr puzzle”. In comparison to conventional nanosized Beta zeolites, ECNU-41 aluminosilicate and titanosilicate exhibited more remarkable and competitive catalytic performances in a variety of reactions than the commerical nanosized counterparts. With stable and abundant hierarchical pores as well enhanced diffusion rate and mass transfer, ECNU-41 is expected to serve as a promising catalyst for processing the reactions especially involving bulky molecules. • A hierarchical Beta zeolite (ECNU-41) was synthesized in the absence of any mesoporogen additives. • ECNU-41 showed an unusual crisscrossed morphology resembling burr puzzle, which resulted in abundant intercrystal mesopores. • ECNU-41 aluminosilicate and titanosilicate exhibited remarkable and competitive catalytic performances in reactions.