Search Results (96)

The aim of our work is to theoretically model the conversion of C6 and C5 carbohydrates derived from lignocellulosic biomass waste into C1–C5 carboxylic acids such as levulinic, oxalic, lactic, and formic acids. Understanding the mechanism of these processes will provide the necessary knowledge to better plan the structure of zeolite. In this article, we focus on the theoretical modeling of two carbohydrates, representing C5 and C6, namely xylose and fructose, into levulinic acid (LE) and formic acid (FA). The modeling was carried out with the participation of Na-BEA zeolite in a hierarchical form, due to the large size of the carbohydrates. The density functional theory (DFT) method (StoBe program) was used, employing non-local generalized gradient-corrected functions according to Perdew, Burke, and Ernzerhof (RPBE) to account for electron exchange and correlation and using the nudged elastic band (NEB) method to determine the structure and energy of the transition state. The modeling was performed using cluster representations of hierarchical Na-Al₂Si₁₂O₃₉H₂₃ and ideal Al₂Si₂₂O₆₄H₃₄ beta zeolite. However, to accommodate the size of the carbohydrate molecules in reaction paths, only hierarchical Na-Al₂Si₁₂O₃₉H₂₃ was used. Sodium ions were positioned above the aluminum centers within the zeolite framework. Full article

In our previous work, we fabricated Ni single-atoms within Beta zeolite (Ni₁@Beta-NO₃⁻) using NiNO₃·6H₂O as a metal precursor without any chelating agents, which exhibited exceptional performance in the selective hydrogenation of furfural. Owing to the confinement effect, the as-encapsulated nickel species appears in the form of Ni⁰ and Ni^δ+, which implies its feasibility in metal catalysis and coordination catalysis. In the study reported herein, we further explored the hydrogen production and olefin oligomerization performance of Ni₁@Beta-NO₃⁻. It was found that Ni₁@Beta-NO₃⁻ demonstrated a high H₂ generation turnover frequency (TOF) and low activation energy (E_a) in a sodium borohydride (NaBH₄) hydrolysis reaction, with values of 331 min⁻¹ and 30.1 kJ/mol, respectively. In ethylene dimerization, it exhibited a high butylene selectivity of 99.4% and a TOF as high as 5804 h⁻¹. In propylene oligomerization, Ni₁@Beta-NO₃⁻ demonstrated high selectivity (75.21%) of long-chain olefins (≥C₆⁺), overcoming the problem of cracking reactions that occur during oligomerization using H-Beta. Additionally, as a comparison, the influence of the metal precursor (NiCl₂) on the performance of the encapsulated Ni catalyst was also examined. This research expands the application scenarios of non-noble metal single-atom catalysts and provides significant assistance and potential for the production of H₂ from hydrogen storage materials and the production of valuable chemicals. Full article

Zeolite Battery Research Africa (ZEBRA) batteries (Na-NiCl₂ solid electrolyte batteries, SEBs) have commercial applications in energy storage due to their low costs and recyclability, long lifetime, and high safety. In commercial ZEBRA batteries, Ni electrode and beta’’-alumina solid electrolyte (BASE) have a more than 70% share of the overall cell material costs. Na-ZnCl₂ all-liquid batteries (ALBs), which replace Ni with abundant and low-cost Zn and BASE electrolyte with molten salt electrolyte, could reduce costs and provide a longer lifetime and higher safety, making their application in grid storage promising. However, compared to SEBs, ALBs are in an early development stage, particularly for their molten salt electrolytes, which have a significant effect on the battery performance. Physical and chemical properties of the salt electrolyte like melting temperatures and solubilities of electrode materials (i.e., Na and Zn metal) are vital for the molten salt electrolyte selection and battery cell design and optimization. In this work, the binary and ternary phase diagrams of salt mixtures containing NaCl, CaCl₂, BaCl₂, SrCl₂, and KCl, obtained via FactSage simulation and DSC measurements, as well as the solubilities of electrode materials (Na and Zn metals), are presented and used for the selection of the molten salt electrolyte. Moreover, various criteria, considered for the selection of the molten salt electrolyte, include high electromotive force (EMF) for suitable electrochemical properties, low melting temperature for large charge/discharge range, low solubilities of electrode materials for low self-discharge, low material costs, and high material abundance for easy scale-up. Based on these criteria, the NaCl-CaCl₂-BaCl₂ and NaCl-SrCl₂-KCl salt mixtures are selected as the two most promising ALB molten salt electrolytes and suggested to be tested in the ALB demonstrators currently under development. Full article

The catalytic production of lactic acid from carbohydrates was considered a green way to efficiently utilize renewable biomass resources. In this study, an easy post-synthesis method was used to prepare a Sn-Beta catalyst for the production of lactic acid from glucose at 180 °C, 2 MPa, and 30 min. With optimized reaction time, temperature, pressure, and the ratio of raw material to catalyst, the yield of lactic acid reached an astonishingly high level of 76.0%. In addition, the catalyst characterizations were performed in-depth, revealing the intrinsic relationship between catalyst performance and structure, proving that the 2 wt% Sn was uniformly dispersed in the skeleton of Beta zeolite, which significantly increased the density of Lewis acid. Thus, the enhanced isomerization and retro-aldol condensation processes over the Lewis acid sites led to the high yield of lactic acid. This catalytic system kept stable after five cycles at mild conditions, showing high potential for industrial biomass utilization. Full article

Hierarchical zeolites with micro- and mesoporous frameworks can overcome diffusional limitations of microporous systems. This study investigates the post-synthetic modification of Beta zeolite using different porogeneous agents (NaOH, NH₄OH, NH₄F) under identical conditions to compare their efficiency in generating mesopores. The effect of treatment time was also examined for NH₄OH and NH₄F. The modified materials were characterized using physicochemical techniques and evaluated for catalytic performance in acetic acid esterification with alcohols of different sizes and adsorption of methylene blue. All the modifications increased mesoporosity but reduced acidity. NaOH produced the highest mesoporosity but significantly reduced acidity, while NH₄F retained the most acidity. Catalytic activity in esterification with methanol depended on acidity, but for larger alcohols (n-butanol, benzyl alcohol), activity was influenced by both acidity and mesoporosity. The NH₄OH- and NH₄F-modified materials, with lower mesoporosity but higher acidity, exhibited better performance with larger alcohols. In MB adsorption, the adsorption equilibrium rates increased with mesoporosity. The NaOH-modified sample reached equilibrium the fastest due to its superior mesoporosity, while the NH₄F-modified sample demonstrated the highest adsorption efficiency owing to its abundant Brønsted acid sites. These findings demonstrate that the choice of modifier affects mesoporosity, acidity, and functional performance, offering insights into tailoring hierarchical zeolites for specific applications. Full article

This study presents a groundbreaking method for extracting lithium from beta-spodumene while simultaneously achieving the sustainable synthesis of LTA-type zeolite, designated as LPM-15, without relying on organic solvents or calcination. Lithium extraction was efficiently performed using sodium salts, accompanied by the recycling of the mother liquor, with lithium content in the supernatant precisely quantified via atomic absorption spectroscopy (AAS). The optimized synthesis route enables the concurrent production of Li₂CO₃ and LPM-15, distinguished by a powdered appearance without a well-defined geometric framework and a unique cubic morphology with spherical facets, respectively. To gain deeper insights into the process, density functional theory (DFT) simulations were conducted to analyze how different cation exchanges (Na⁺ replacing Al³⁺, NH₄⁺ replacing Al³⁺, and Ca²⁺ replacing Al³⁺) influence the structural stability and diffusion dynamics within the zeolitic pores of LPM-15. Additionally, cation-exchange capacity (CEC) measurements further assessed ion mobility within the LPM-15 framework. This integrative approach not only sheds light on the fundamental mechanisms underpinning LTA-type zeolite synthesis but also demonstrates their versatile applications, with particular emphasis on water purification technologies. Full article

Ruthenium-based catalysts were prepared through a deposition–precipitation approach, taking beta zeolites with Si/Al ratios of 12.5, 18.5, and 150, respectively, as supports, and 1–3 wt% loadings of metal. Their activation was performed in the presence of either H₂ or NaBH₄. The dispersion of the Ru species and the acid–base properties were influenced by both the preparation method and the activation protocol. The catalysts reduced under H₂ flow presented well-dispersed Ru(0) and RuO_x nanoparticles, while the reduction with NaBH₄ led to larger RuO_x crystallites and highly dispersed Ru(0). These characteristics exerted an important role in the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL). The H₂ dissociation occurred via a heterolytic mechanism involving Lewis acid–base pairs associated with RuO_x and the framework oxygen (Si-O-Al) located near the zeolite pore edge. The Ru(0) nanoparticles activated the –C=O bond of the LA substrate, while the presence of the carrier zeolite Brønsted acid sites promoted the ring-closure esterification of the 4-hydroxyvaleric acid (4-HVA) intermediate to GVL. An optimal combination of these features was achieved for the catalyst with 3 wt% Ru and a Si/Al ratio of 150, which selectively converted LA (X_LA = 96.5%) to GVL (S_GVL = 97.8%) at 130 °C and 10 bars of H₂. Full article

As an important biomass resource, γ-valerolactone (GVL) shows considerable potential for applications in biofuel production, organic synthesis, polymer, and food industries. Herein, an effective method was presented for synthesizing GVL through the catalytic transfer hydrogenation (CTH) of ethyl levulinate (EL) under mild conditions. Using isopropanol as a hydrogen donor, a 100% conversion of ethyl levulinate and an 88.7% yield of GVL were achieved over 2%Zr-Beta-7d catalyst at 110 °C for 8 h. The acidic sites of synthesized Zr-Beta via hydrothermal methods easily adjusted and offered high catalytic activity and selectivity. The Lewis (L) acid sites on the zeolite serve as the active centers for the conversion of EL. Characterization results indicate that the amounts of L acid sites on Zr-Beta increased with the Zr content and crystallization time rose, thus enhancing the selectivity for GVL. Additionally, the influences of catalyst dosage, reaction temperature, and time on catalytic performance are studied, as well as calculations of kinetic parameters such as reaction rate constants and activation energies. The 2%Zr-Beta-7d catalyst retains its high performance after five cycles. The current research may present an efficient approach for the conversion of EL to GVL under mild conditions. Full article

The thermal decomposition of a heat-not-burn (HNB) tobacco at four temperatures (250–400 °C) was studied via thermogravimetric analysis (TGA) and Multi-shot pyrolizer experiments (Py-GC/MS), and the effect of four potential additives, USY Beta and beta zeolites and Silica Lovel 6000 and SBA-15 silicates at three concentrations (5, 15 and 25% w/w) under an inert and oxidative atmosphere was analyzed. Different techniques were applied showing that the presence of the additives modifies the decomposition processes (TGA). Py-GC/MS showed that these tobaccos generate large amounts of Nicotine and Glycerine. Acid compounds are the most abundant compounds under an inert atmosphere, while Oxygenated compounds predominate under an oxidative atmosphere. In both atmospheres, Furans and Aromatics present in a significant abundance at high temperatures. The additives used reduce both the number and the concentration of most of the compounds generated, especially at high temperatures and concentrations. Moreover, SBA-15 shows good aptitudes to reduce the formation of some individual compounds included in the FDA’s HPHC list, such as Acetone and Acetaldehyde. Finally, smoking experiments corroborated that all additives produce marked reductions in TPM, i.e., the majority fraction obtained, and in practically all the compounds generated. Phenol, a toxicant compound that was detected in a significant amount, is also markedly reduced. SBA-15 is the material that presents a major reduction in the TPM and the principal compounds generated. These results may be of great interest for further reducing the toxicity of smoking this type of heat-not-burn tobacco product. Full article

This article presents the conditions for the transformation of pulp containing mixtures that occur in the hemicellulose fraction derived from lignocellulosic biomass. Selected materials with strong acid centers were used as catalytic materials: ion exchange resins, including AMBERLYST 15(H) and DOWEX DR-G8(H), and selected zeolite in the hydrogen form of the Beta type (H-BEA). The group was marked with the abbreviations M1, M2 and M3, where it differs in the content of xylose, mannose, galactose, glucose, rhamnose and uronic acids. The catalytic process was carried out in the reactor as a one-pot technique at temperatures of 180–250 °C for 1–5 h. Based on the collected results, the transformation products of hemicellulose pulp were determined and the catalytic abilities of selected materials were determined. The proposed conditions led to the production of organic acids. Levulinic acid was obtained with a selectivity of 25.95% after 1 h of the process at a temperature of 250 °C with the participation of H-BEA, and lactic acid was obtained with a selectivity of 73.28% after 5 h of the process at a temperature of 250 °C using DOWEX DRG8(H). The presence of oxalic, propionic and acetic acids was also observed. Full article

The alkylation reaction of aromatic compounds gains considerable attention because of its wide application in bulk and fine chemical production. Aromatics alkylated with olefins is a well-known process, particularly for linear alkylbenzene, phenyloctanes, and heptyltoluene production. As octane boosters and precursors for various petrochemical and bulk chemical products, a wide range of alkylated compounds are in high demand. Numerous unique structures have been proposed in addition to the usual zeolites (Y and beta) utilized in alkylation procedures. The inevitable deactivation of industrial catalysts over time on stream, which is followed by a decrease in catalytic activity and product selectivity, is one of their disadvantages. Therefore, careful consideration of catalyst deactivation regarding the setup and functioning of the process of catalysis is necessary. Although a lot of work has been carried out to date to prevent coke and increase catalyst lifespan, deactivation of the catalyst is still unavoidable. Coke deposition can lead to catalyst deactivation in industrial catalytic processes by obstructing pores and/or covering acid sites. It is very desirable to regenerate inactive catalysts in order to remove the coke and restore catalytic activity at the same time. Depending on the kind of catalyst, the deactivation processes, and the regeneration settings, each regeneration approach has pros and cons. In this comprehensive study, the focus was on discussing the reaction mechanism of 1-octene isomerization and toluene alkylation as an example of isomerization and alkylation reactions that occur simultaneously, shedding light in detail on the catalysts used for this type of complex reaction, taking into account the challenges facing the catalyst deactivation and reactivation procedures. Full article

The Lewis acidic framework Ti sites in Ti-Beta and Si-Beta catalysts were compared by FT-IR and NMR characterization methods before they were applied to the conversion of four butenes. The results showed that Si-Beta has fewer Lewis acid sites and abundant weak Brønsted acidic silanol nests, which play an important role in conversions between n-butene, cis-2-butene, and trans-2-butene. The conversions for these butenes over Si-Beta were always higher than those over a series of Ti-Beta catalysts with gradient-varied Lewis acidic framework Ti sites and silanols. This is because isobutene can only oligomerize, which requires stronger acidity, so its conversion over Si-Beta was lower than those over Ti-Beta zeolites. For a series of Ti-Beta catalysts with different abundances of Lewis acidic Ti sites, the more Lewis acid sites it had, the higher the conversions for the four butenes. Full article

Commercial NH₄-Beta and Na-ZSM-5 zeolites were fluorinated with different amounts of NH₄F and using different procedures (room temperature, conventional refluxing, microwave refluxing). Samples were characterized by XRD, N₂ physisorption, FTIR, ¹H NMR, SEM-EDS, and TGA of adsorbed cyclohexylamine. An increase in the concentration of NH₄F led to fluorinated zeolites with higher surface areas and slightly lower amounts of Brønsted acid sites due to some dealumination. Fluorination by conventional or microwave refluxing at shorter times did not dealuminate ZSM-5, resulting in the formation of higher particle sizes. Ni/fluorinated beta catalysts were more active than Ni/fluorinated ZSM-5 catalysts for the hydrodeoxygenation of guaiacol at 180 °C and 15 bar of H₂ for 1 h due to their higher amount of acid sites. The appropriate proportion of metallic and Brønsted acid centers allowed for the selective obtention of cyclohexane (58%) for the Ni supported on beta fluorinated with NH₄F 0.1 M catalyst. The combination of this fluorinated beta to a Ni/ordered mesoporous carbon catalyst significantly boosted its selectivity to cyclohexane from 0 to 65%. Fluorinated ZSM-5 samples, although having stronger Brønsted acid sites, as observed by ¹H NMR, they had lower amounts, leading to higher selectivity to cyclohexanol when used as catalytic supports. Full article

H-Beta zeolite is a solid acid catalyst commonly utilized in the catalytic conversion of biomass resources. In this study, H-Beta zeolite was calcined at different temperatures (350, 550, 750, and 1000 °C) to explore the effects of high temperature-induced dealumination on its physicochemical properties and its catalytic ability to convert glucose into 5-hydroxymethylfurfural (HMF). It was shown that as the calcination temperature increased, the Si-O-Al bond of H-Beta zeolite was broken and its dealumination effect was enhanced. Dealumination led to the collapse of the framework of H-Beta zeolite and a reduction in the number of acid sites, which in turn reduced its catalytic performance and the efficiency of HMF formation from glucose. Furthermore, H-Beta zeolite exhibited an extraordinary catalytic ability for the production of HMF from carbohydrates. Using glucose and cellulose as substrates, superior HMF yields of 91% and 46%, respectively, were achieved under optimal reaction conditions. Further, calcination removes carbon deposits in the recovered H-Beta zeolite, but it affects the cycling stability of the catalyst. Meanwhile, the by-products formed during the synthesis of HMF from glucose catalyzed by H-Beta zeolite catalyst were also clearly detected. Full article

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. Full article