Zeolite Beta Research Articles

Tuning of the acid sites in the zeolite-alumina composite Ni catalysts and their impact on the palm oil hydrodeoxygenation reaction

The hydrodeoxygenation (HDO) of bio-oil is one of the potential approaches to produce green diesel. However, HDO catalyst requires the development of bifunctionality which translates to the simultaneous presence of acidic and metal sites for desired catalytic activity and selectivity. Zeolites and their composites are attractive candidates for the conversion of biomass to fuels. In the present work, a series of Ni-incorporated Al2O3-zeolite beta bifunctional composite catalysts with distinct Al2O3 (25–75 wt%) and Ni contents (5–15 wt%) were synthesized via a facile one-pot method directly from nickel acetate, nano-boehmite (γ-AlO(OH)) and the NH4+ form of beta zeolite (NH4+-BZ). The nano-boehmite particles, due to the positive charges on their surface, electrostatically attract negatively charged beta zeolite crystals, which leads to the assembly of a hierarchical pore structure upon calcination. Interestingly, the composite catalysts synthesized were quite homogeneous with uniform dispersion of Ni particles. All composite catalysts were thoroughly characterized using XRD, SEM-EDX, SEM-mapping, HR-TEM, H2-TPR, H2-TPD, NH3-TPD, XPS, 31P MAS NMR, 27Al MAS NMR and N2 sorption analysis. The synthesized composite catalysts with distinct Al2O3 contents showed diverse textural properties, distinct nature of acid sites and improved performance in hydrodeoxygenation of palm oil. Particularly, the Ni/BZ-Al50 (with BZ:Al2O3 = 50:50) composite catalyst significantly enhanced the conversion of palm oil (up to 90%) and yield of n-C15-C18 hydrocarbons (up to 69%) at moderate temperature of 375 °C as compared to 10Ni/BZ catalyst (Conv. = 75%, yield of n-C15-C18 = 52%). The higher catalytic performance realized with composite catalysts can be ascribed to its hierarchical pore structure, moderate acidity (chemisorption studies), tuned acid sites nature (solid state NMR) and homogeneous distribution of active Ni sites (H2 chemisorption) which helps to improve product selectivity by minimizing side reactions. The time-on-stream (TOS) experiments were carried out up to 20 h which clearly showed that composite catalysts are more stable suggesting the lower amount of coke deposition (TPO studies) and suppression of metal sintering.

Investigation of a liquid-mediated defect-healing treatment in zeolite beta

We report the application of a liquid-mediated defect-healing treatment based on tetraethylammonium (TEA+) hydroxide and ammonium fluoride, and variants thereof, to the H+ form of zeolite beta. Through comparison between H-beta of high (730) and lower (28.6) SiO2: Al2O3 ratios, and characterisation of the treated samples before and after calcination, insights into the interaction of TEA+ and F− with H-beta under hydrothermal conditions were gained. In general, the treatments resulted in the loss of crystallinity and the generation of relatively large mesopores in the more siliceous samples, but improvements in long-range order and the development of relatively small mesopores in the less siliceous samples. The healing of silanol defects was observed for most of the treatments. A partial mechanism is proposed to explain the action of defect-healing treatments based on pore-occupying cations and F−; fluorine may be essential in some cases because it balances the charge of the organic cations, preventing the “trapping” of silanol groups as charge-balancing silanolate groups which resist healing.

Esterification of crude tall oil catalyzed by Beta zeolite

In softwood Kraft pulping process, fatty/resin acids (extractives) react with the white liquor and are saponified, producing Tall Oil Soap (TOS). TOS can be converted back to the respective fatty/resin acids, generating Crude Tall Oil (CTO). In this work, TOS was converted into CTO according to standard methods, producing residual lignin and an aqueous phase as co-products. Then, CTO was esterified in the presence of Beta zeolites with different Si/Al ratios and particle sizes in rotary Teflon-lined stainless-steel autoclave. Compared to esterification of oleic and palmitic acids, esterification of CTO is a slow process, with conversions limited to no more than 83 % after 6 h at 393 K. Smaller particles (0.26 μm) and lower Si/Al ratio (15) showed greater conversion. This may be associated with a higher strength of Brønsted acid sites (due to lower Si/Al ratio) but also with an improved diffusion of reactants/products within zeolite micro- and mesopores (due to the relatively smaller particle size). The esterification product was mainly composed of esters of fatty acids, such as dimethyl 4-isopropyloctanedioate, methyl elaidate and methyl palmitate. Esters of resin acids (methyl abietate and dehydroabietate), phthalic acids, as well as paraffins are also present, but probably in lower concentrations.

Enhanced generation of aromatic-enriched bio-oil from sewage sludge pyrolysis using zeolite-based catalysts under H2-rich conditions

Sewage sludge is solid waste resulting from wastewater treatment processes, and its improper management adversely affects the environment and human health. This study aims to convert sewage sludge into valuable aromatics, including benzene, toluene, ethylbenzene, and xylenes, or BTEX, via the catalytic pyrolysis using mono- and bimetal-modified protonated Zeolite Socony Mobil–5, or HZSM-5, catalysts under nitrogen, methane and methane decomposition conditions. In the methane medium, HZSM-5 yielded more BTEX (20.91 wt%) compared to those obtained using protonated Y zeolite (HY) (17.24 wt%) and protonated beta zeolite (Hβ) (11.70 wt%) owing to its proper acidity, higher shape selectivity, and higher methane activation. When HZSM-5 is used, the BTEX yield increased considerably in the methane decomposition environment (27 wt%), 1.29 and 1.46 times higher than those produced under methane and nitrogen, respectively. This increase is attributed to the dual effects of the surplus in situ hydrogen (H2) and direct involvement of methane, which resulted in accelerated hydrocracking, hydrodeoxygenation, and co-aromatization reactions. Under methane decomposition conditions, the use of the Ni/HZSM-5, Mo/HZSM-5, and Ni-Mo/HZSM-5 catalysts led to 1.23-, 1.30-, and 1.66-fold increases in BTEX production, respectively, than that of the parent HZSM-5, owing to the dual effects of acidity enhanced by the newly formed Lewis acid sites, increased oxygen vacancies, and improved physical properties of the catalysts. Hence, the catalytic pyrolysis of sewage sludge using mono- and bimetal-modified HZSM-5 catalysts in a H2-rich environment proposed in this study is expected to be an efficient and sustainable method for converting undesirable materials into valuable biofuels.

Micro- and Mesoporous Structural Effects of Beta Zeolites for Volatile Organic Compound Sorption.

To fully exploit pore engineering in the design of more efficient zeolite adsorbents for volatile organic compound (VOC) treatment, the roles of meso- and micropores need to be clarified to provide the theoretical basis and feasible measures. In this work, the three VOC sorption properties of conventional and hierarchical porous beta zeolites were comparatively investigated to study the roles of meso- and micropores. There is a division of functions between micro- and mesopores, with micropores being the main VOC adsorption sites and mesopores greatly enhancing VOC diffusion and adsorbent reusability. On the one hand, micropores should be preserved as much as possible because obtaining mesopores by sacrificing micropores (i.e., alkali treatment) results in 28-60% decreases in adsorption capacities. On the other hand, mesopore introduction is highly desirable, which results in an enhancement of VOC intraparticle diffusion rates by 1.3-2.3 times (at the VOC concentration of 600 ppm) and chlorobenzene adsorption capacity on the 20th cycle increasing from 78% of the initial value to 89 and 93%. The findings may provide valuable information about zeolite-based adsorbents for adsorption removal or recovery of VOCs.

Catalytic performance of Pd catalyst supported on CeO2 or ZrO2 modified beta zeolite for methane oxidation

Two kinds of oxide-zeolite composite support, Ce-beta and Zr-beta were prepared by a simple wet impregnation method and adopted for the preparation of palladium-based catalysts for catalytic oxidation of methane. The Pd/6.8Zr-beta catalyst showed superior methane oxidation performance, achieving T50 and T90 of 417 °C and 451 °C, respectively, together with robust hydrothermal stability. Kinetic analysis has shown that incorporating Zr into the catalyst significantly enhanced its efficiency, nearly tripling the turnover frequency (TOF) for methane combustion compared to the Pd/beta catalyst. This enhanced performance was attributed to the dispersion of Zr on the zeolite surface, which not only promoted the formation of active PdO sites but also helped maintain the high Pd2+ content via facilitating the oxygen migration during the reaction, thus improving both the catalyst's activity and stability. In the Pd/8.6Ce-beta catalyst, doped CeO2 tended to aggregate in the zeolite's pores, adversely affecting the catalyst's efficiency. This aggregation promoted the formation of inactive Pd4+ species, a result of the enhanced metal-support interaction. This finding is critical for understanding the implications of dopant selection in the design of high-activity methane oxidation catalysts.

Anchoring Pt sites via chemical confining functional ZnOx islands in propane dehydrogenation

The surface properties of heterogeneous catalysts regulated by the modified support are considered to be the key factors in determining catalytic performance. In propane dehydrogenation, PtZn catalysts have poor catalytic life due to the structural instability of Zn species although it owns high intrinsic activity. Herein, the dealuminated Beta zeolite is harnessed for chemically confining the introduced Zn species, the formed functionalZnOx (0 < x < 2) islands are further responsible for anchoring Pt1Zn1 alloys. According to the comprehensive characterization, the modifying surface defects on the Beta support can provide benign metal-support interaction and modulate the electronic structure of supported metal species. Hence, the Pt/ZnOx-SiBeta catalyst embodies 59.5 % propane conversion with a high propylene selectivity of 99.2 % and no obvious deactivation undergoing 100 h of dehydrogenation reaction. The optimal electronic interaction exists between ZnOx and SiBeta, which inhibits the aggregation of Pt sites and the coking formation.

Highly selective production of renewable methyl acrylate via aldol condensation over Cu modified nitrogen-containing Beta zeolites

Highly selective production of renewable methyl acrylate via aldol condensation over Cu modified nitrogen-containing Beta zeolites

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.

Synthesis, characterization, and evaluation of the CO2 adsorption capacities of beta, ZSM-12, ZSM-48, and silicalite-1 zeolites obtained in the presence of tetraethylammonium hydroxide and 1,6-diaminohexane as organic structure-directing agents

Synthesis, characterization, and evaluation of the CO2 adsorption capacities of beta, ZSM-12, ZSM-48, and silicalite-1 zeolites obtained in the presence of tetraethylammonium hydroxide and 1,6-diaminohexane as organic structure-directing agents

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.

Adsorption of 3‐monochloropropane‐1,2‐diol ester and glycidyl ester from refined bleached deodorized palm oil using zeolite‐based adsorbents

AbstractPalm oil processing can result in different food products like cooking oil and margarine. Nevertheless, these food products might contain harmful contaminants, namely 3‐monochloropropane‐1,2‐diol ester (3‐MCPDE) and glycidyl ester (GE), which can negatively affect animal organs and potentially cause human cancer. Therefore, the objective of this study was to lower the concentration of 3‐MCPDE and GE in refined, bleached, and deodorized palm oil (RBDPO) using zeolite as an adsorbent. Adsorption experiments were conducted in a batch reactor, varying the percentage of adsorbents, temperature, type of zeolite, and the use of a mixture of zeolite and activated carbon (AC). The sample was analyzed before and after adsorption using gas chromatography–mass spectroscopy (GC–MS) to confirm the concentration alteration of 3‐MCPDE and GE. The study showed that the most effective temperature for adsorption was 35°C and used a zeolite percentage of 2%. Beta zeolites resulted in the highest removal of 3‐MCPDE (86%) among the evaluated zeolites attributed to their elevated pore volume, Si/Al ratio, and overall acidity strength. Through a synergistic combination of beta zeolite and AC, the removal percentage of 3‐MCPDE was enhanced to 94%, with a corresponding 75% reduction in GE. This study paves the way for addressing 3‐MCPDE and GE concerns in RBDPO by combining zeolite and AC.

Improved performance of polyamide nanofiltration membrane embedded with zeolite beta

In this study, zeolite beta nanoparticles were incorporated into an interfacial polymerization procedure for the fabrication of thin film nanocomposites (TFNs). The successful introduction of zeolite beta into the polyamide (PA) selective layer was confirmed by surface attenuated total reflection infrared spectroscopy (ATR-FTIR), and x-ray photoelectron spectroscopy (XPS). The introduction of porous structured zeolite beta improved the water flux and rejection rate of the TFN membrane compared to the PA thin film composite (TFC) membrane. A quantitative performance coefficient is further proposed in this work, comprehensively considering the flux and rejection rate to evaluate the performance of TFNs. For five salt solutions, we found that the TFN0.3 membrane with 0.3 wt% of zeolite particles had a high coefficient of performance. With the help of zeolite particles, the TFN0.3 membrane achieved a high flux of 92.53 L/(m2·h) under an operating pressure of 5 bar. For ion separation from binary solutions, the TFN0.2 membrane with 0.2 wt% zeolite content was a better choice for a wide range of binary mixtures, which is because the addition of zeolite beta resulted in smaller pore sizes, the strongest zeta potential, and the thickest thickness (scanning electron microscope, SEM determined) of the TFN0.2 membrane. All these factors contribute to the selectivity of the TFN0.2 membrane. Our study provides an efficient and cost-effective method to simultaneously improve the permeability and rejection of nanofiltration membranes, facilitating the development of nanofiltration for water recovery.

Hydrodeoxygenation of lignin bio-oil model compounds and surrogate mixtures over zeolite supported nickel catalysts

Bifunctional catalysts based on nickel supported on ZSM-5 and BETA zeolites were studied in the hydrodeoxygenation of lignin derived model compounds as well as in surrogate mixtures simulating the light fraction of lignin fast pyrolysis bio-oil. A screening of the hydrodeoxygenation reaction conditions (temperature, time, H2 pressure, catalyst amount) was carried out using the simplest phenolic compound, phenol. As in real lignin bio-oils more complex phenolic compounds are present, a series of relevant alkyl- and methoxy-substituted phenol and benzene (o- and m-cresol, catechol, anisole, guaiacol, syringol, creosol and 1,2,3-trimethoxybenzene) were also investigated as feedstocks. Furthermore, the effect of the different porous and acidic properties of the zeolitic supports was investigated in the hydrodeoxygenation of guaiacol. The conversion of the model phenolics and the yield of the respective (alkyl)cyclohexanes at relatively mild conditions (220 °C, 50 bar H2, 1 h) were in the range of 80–100% and 47–83%, respectively, being dependent mainly on the complexity/side-chain group of the phenolic/benzylic ring and on the balanced content of Brønsted acid sites of increased strength. Regarding the hydrodeoxygenation of the surrogate mixture (C7-C10 phenolics), 100% hydrodeoxygenation efficiency was achieved towards >60% yield of (alkyl)cyclohexanes (C6-C9 hydrocarbons). All hydrodeoxygenation tests were conducted in hexadecane as solvent/substrate in order to simulate model co-processing (i.e. bio-based phenolics with petroleum derived feedstocks) conditions. Reusability tests revealed the stability of the catalysts which showed partial (30%) deactivation after the third catalytic cycle.

Insights into the Synthesis of Spiral Beta Zeolite with Enhanced Catalytic Performance in VOC Abatement.

The rational synthesis of zeolites with designed morphology is a highly challenging task. In this study, we propose 1,5-bis(methylpiperidine)pentylammonium hydroxide (BMPPAOH) as an organic structure-directing agent (OSDA) based on theoretical calculations. The morphology of zeolite samples is characterized by XRD, SEM, TEM, N2 sorption isotherms, and UV Raman spectroscopy. This simple bis-quaternary ammonium salt favored the formation of spiral morphology in Beta zeolite spheres (S-Beta). The crystallization of zeolite in the presence of BMMPAOH is a two-stage process, where nanoparticles agglomerate into spheres in the early stages followed by the emergence of S-Beta crystals with spiral morphology. The synthesized Pt-S-Beta catalysts show higher catalytic activity in VOC abatement compared with other Pt-Beta samples.

A surfactant-directed sol-gel evolution in the formation of hierarchical zeolite beta

Even though cetyltrimethylammonium bromide (CTAB) has been successfully used in the surfactant-templating system to create the mesostructured zeolites, the formation mechanism of the pore structure still remains elusive. Here, we investigated the sol-gel and structure evolution in the hierarchical zeolite Beta synthesis focusing on the role of CTAB in a dual templating system. It is found that the induction period was prolonged and the Ostwald ripening was retarded by the presence of CTAB in crystallization. CTAB was involved in the synthesis and incorporated within the solid phase at the first stage when mesopores were formed. However, the incorporated CTAB was released later into the solution when the crystallized microporous structure was developed. The thermogravimetric analysis revealed that CTA+ cation worked both as structure directing agent (SDA) for micropores and mesoporogen for the secondary lager pores in the matrix of hierarchical zeolite Beta. Moreover, CTA+ competed with tetraethylammonium cation (TEA+) to work as the SDA for micropores, with a decrease of the total amount of CTA+ and TEA+ when the concentration of CTAB in the synthesis solution was increased. It is anticipated that the understanding of the role of CTAB in the sol-gel and structure evolution in the hierarchical zeolite Beta synthesis process can provide a basis for designing the synthesis of hierarchical zeolites.

Study on Preparation of Sn–Er–Beta Zeolite and Its Catalysis of Glucose to Lactic Acid

Study on Preparation of Sn–Er–Beta Zeolite and Its Catalysis of Glucose to Lactic Acid

Experimental and simulation investigation on the different iron content beta zeolite for controlling the cold-start hydrocarbon emission from a gasoline vehicle

In this work, cold start experiments results showed that the HC catcher coated with 1% iron content is more effective than that with 3% iron content, the peak HC emission is reduced from 0.0029 g to 0.0018 g. To further reveal the reasons for the effects of BEA zeolite molecular sieves with different iron contents on HC adsorption, the measured HC emission components (butene, propene, ethene, acetaldehyde, and acetylene) were used as HC simulation molecules for molecular simulation experiments, the simulation results showed that, for single-component adsorption, the adsorption effect of beta zeolite molecular sieves with high iron content was better; for multi-component adsorption, acetaldehyde and butene maintained higher adsorption amounts, and the adsorption of acetaldehyde increased with the increase of the iron content in the beta zeolite molecular sieves; in the presence of water and CO2, the effect of water is greater than that of carbon dioxide, and its effect increases with the increase of iron content in beta zeolite molecular sieves. The maximum adsorption capacity of water can reach 4.5mmol/zeolite, which seriously affected the adsorption of HC molecules. Properly reducing the iron content of BEA zeolite molecular sieve is useful for enhancing its adsorption effect on the main HC simulated molecules.

High-electrophilic (SiO)2Nb(OH)(=O) sites confined in silanol defects over Nb-Beta zeolite for efficient cyclic alkene epoxidation reactions

Dealuminated Beta zeolite has a large amount of silanol defects on its interface, which provides an ideal place for embedding metal species and creating metal active sites in a confined microenvironment. The confined metal sites as well as their surroundings are closely related to the reactant activation and transient state achievement. Hence, unraveling the confined metal sites is of great significance for the catalytic reaction process. Herein, niobium species were incorporated into the silanol defects over dealuminated Beta zeolite with a facile dry impregnation method, co-grinding the niobium precursor with dealuminated Beta zeolite support. The successful incorporation of niobium into the silanol defects for 30Nb-Beta zeolite was verified by DRIFT, 1H MAS NMR, UV–Vis and UV-Raman characterizations. XAS characterization and DFT calculations further disclosed that the confined Nb species existed as (SiO)2Nb(OH)(=O), containing two Si−O−Nb bonds, one Nb=O bond as well as one Nb−OH bond. The synthesized 30Nb-Beta zeolite catalyst displayed a superior cyclohexene conversion of 51.1%, cyclohexene oxide selectivity of 83.1% as well as TOF value of 188.2 h−1 ascribed to the inherent electrophilicity of Nb(V) for confined (SiO)2Nb(OH)(=O) species as well as the low oxygen transfer energy barrier for NbV−OOH species. Furthermore, the prepared 30Nb-Beta zeolite can be effectively employed to other cyclic alkene epoxidation reactions.

Mechanochemistry-based liquid-assisted synthesis of hydrophobic Zr-Beta with high metal loading for Meerwein-Ponndorf-Verley reduction

Heteroatom-incorporated zeolite catalysts are critical for biomass utilization and feedstock valorization in green chemistry. Key features are adjustable acidity, high stability, and a tailored range of functionalities. However, an environmentally benign synthesis of zeolites with good crystallinity and especially with high levels of metal substitution into the lattice remains challenging. Here, we propose a mechanochemistry-based liquid-assisted method (MCLA) for Zr-incorporated Beta zeolites that is high yielding, facile and sustainable. Compared with the fluoride-mediated hydrothermal method, crystallization times were considerably shortened so that Si-Beta and Zr-Beta (Si/Zr 100) zeolites can be synthesized within 9 and 15 h, respectively. Using the MCLA route, Beta zeolites with Zr loading up to 10.4 wt% (Si/Zr 12.5) were obtained. The materials have excellent catalytic activity for Meerwein-Ponndorf-Verley reductions with much higher water tolerance compared to Zr-Beta prepared by the post-synthesis method. The hydrophobic nature of the MCLA-synthesized zeolites makes them particularly useful as catalysts for organic reactions.