Dehydration Of Alcohols Research Articles

Zwitterionic covalent organic framework membranes for efficient liquid molecular separations

Covalent organic frameworks (COFs) featuring uniform topological structure and devisable functionality have emerged as promising membrane materials. The design and precise manipulation of COF membranes with advanced spatial structure to achieve efficient liquid molecular separations are of great necessity. Herein, zwitterionic COF membranes have been in-situ fabricated on porous polymeric substrates using an interfacial polymerization modification strategy. The continuous defect-free COF membranes with two-dimensional in-plane dominant growth can be achieved by optimizing the fabrication parameters including reaction time, monomer concentration, and catalyst concentration. Subsequent zwitterionic modification thereon not only favors the formation of hydrophilic surface but also improves the sieving capability by sheltering effect. Attributed to the synergistic contribution, the optimized zwitterionic COF membrane possesses a superior separation factor of 2839 with the water content in the permeate up to 99.7 wt%, while maintaining a comparable permeation flux of 3309 g m−2 h−1 during the ethanol dehydration process, outperforming most of other representative membranes. Furthermore, the excellent durability of the zwitterionic COF membrane in the ethanol dehydration process and its efficient separation performance towards other alcohol dehydration systems demonstrate its potential practical applications. The easy scalability of the fabrication and regulation method offers crucial guidance for the engineering of advanced COF membranes in efficient liquid molecular separations.

Innovative sample preparation using alcohol dehydration and high refractive index medium enables acquisition of two-channel super-resolution 3D STED image of an entire oocyte.

Super-resolution (SR) microscopy is a cutting-edge method that can provide detailed structural information with high resolution. However, the thickness of the specimen has been a major limitation for SR methods, and large biological structures have posed a challenge. To overcome this, the key step is to optimise sample preparation to ensure optical homogeneity and clarity, which can enhance the capabilities of SR methods for the acquisition of thicker structures. Oocytes are the largest cells in the mammalian body and are crucial objects in reproductive biology. They are especially useful for studying membrane proteins. However, oocytes are extremely fragile and sensitive to mechanical manipulation and osmotic shocks, making sample preparation a critical and challenging step. We present an innovative, simple and sensitive approach to oocyte sample preparation for 3D STED acquisition. This involves alcohol dehydration and mounting into a high refractive index medium. This extended preparation procedure allowed us to successfully obtain a unique two-channel 3D STED SR image of an entire mouse oocyte. By optimising sample preparation, it is possible to overcome current limitations of SR methods and obtain high-resolution images of large biological structures, such as oocytes, in order to study fundamental biological processes. Lay Abstract: Super-resolution (SR) microscopy is a cutting-edge tool that allows scientists to view incredibly fine details in biological samples. However, it struggles with larger, thicker specimens, as they need to be optically clear and uniform for the best imaging results. In this study, we refined the sample preparation process to make it more suitable for SR microscopy. Our method includes carefully dehydrating biological samples with alcohol and then transferring them into a mounting medium that enhances optical clarity. This improved protocol enables high-resolution imaging of thick biological structures, which was previously challenging. By optimizing this preparation method, we hope to expand the use of SR microscopy for studying large biological samples, helping scientists better understand complex biological structures.

Enhancing Ballistic Transport and C3–C4 Alcohol Dehydration through Machine Learning-Designed Cationic Graphene Oxide Membranes

Enhancing Ballistic Transport and C₃–C₄ Alcohol Dehydration through Machine Learning-Designed Cationic Graphene Oxide Membranes

Selective oxidation of organic pollutants by unactivated and carbonate-activated peroxymonosulfate (PMS): Mechanism, kinetics, and transformation pathway

Although the activation mechanisms of peroxymonosulfate (PMS) by various homogeneous and heterogeneous catalysts have been reported, the chemistry of PMS in catalyst-free systems and its interaction with background oxygenated anions remains poorly understood. In this study, the unactivated PMS and carbonate-activated PMS (CO32–/PMS) systems for removal of various organic pollutant (including oxytetracycline (OTC), metronidazole (MNZ), methylene blue (MB), and acid orange G (OG)) were investigated. The results showed that 74.5 %, 90.21 %, 1.22 %, and 2.25 % of OTC, MB, OG, and MNZ were removed, respectively within 180 min in the unactivated PMS system due to the formation of ·OH and 1O2. 95.88 %, 100 %, 100 %, and 6.09 % of OTC, MB, OG, and MNZ were removed, respectively in the CO32–/PMS system, which is primary due to the generation of 1O2. The removal efficiencies of these four pollutants were significantly improved under alkaline conditions. In addition, the TOC removal rates were 21.88 % for MB and 26.53 % for OTC within 180 min in the CO32–/PMS system. The presence of Cl− and SO42− can greatly enhance the OTC removal efficiency both in the unactivated and CO32–/PMS systems. Through the high performance liquid chromatography-mass spectrometry (HPLC-MS) analysis, OTC degradation products in the unactivated PMS and CO32–/PMS systems were identified, revealing six different reaction mechanisms, including hydroxylation (+16 Da), decarbonylation (−28 Da), demethylation (−14 Da), secondary alcohol oxidation (−2 Da), deamination (−15 Da), and dehydration (−18 Da). This study provides insight into the reaction mechanism of catalyst-free PMS systems and may promote the application of unactivated PMS and CO32–/PMS systems for the remediation of organic contaminated water.

Silicon quantum dot-enhanced thin-film nanocomposite membranes for efficient alcohol dehydration via pervaporation: A sustainable approach

This study explores the effectiveness of silicon quantum dots (SiQDs)—specifically, amine-functionalized (NSiQDs) and amine-hydroxyl-functionalized (NOSiQDs)—in optimizing thin-film nanocomposite (TFN) membranes for pervaporation dehydration of various alcohols. The SiQDs were integrated into the membranes via an innovative interfacial polymerization technique, involving the dispersion of SiQDs in an aqueous amine solution followed by polymerization with trimesoyl chloride. This approach ensured uniform integration of SiQDs, significantly enhancing the nanostructure and surface characteristics of the membranes. Such modifications led to improved water transport capabilities, substantially boosting pervaporation efficiency. Exceptional performance was demonstrated by the TFN-NOSiQDs(400) membranes, which achieved a peak permeation flux of 4195.8 g·m−2·h−1 and maintained over 99 wt% water concentration in the permeate when tested with a 70 wt% isopropanol/water solution at 25°C. Comprehensive long-term stability assessments confirmed the robustness and consistent functionality of the membranes, highlighting their suitability for industrial applications that demand reliable and efficient alcohol separation processes.

Active site requirements for bio-alcohol dehydration: Effect of chemical structure and site proximity

Synthesis-structure-activity relations are reported, describing how interzeolite conversion (IZC) allows synthesis of ZSM-5 (MFI framework) with fixed physicochemical properties, except the variable local acid site (Al) arrangement, by variation of the synthesis time. Local confinement and acidity effects are probed by applying both H-ZSM-5 and Na-ZSM-5 samples in alcohol dehydration. Pyridine and divalent cobalt ion probing are used to quantify the amount of accessible acid sites and of Al in close proximity. Al in close proximity shows a strong influence on n-butanol dehydration turnover rates. The turnover rates are also strongly dependent on local confinement: in Na-form, ZSM-5 synthesized with more Al present as isolated species is a factor of 3–7 times more active than Na-ZSM-5 with fewer isolated Al. However if the zeolites are in proton form, ZSM-5 with more proximate sites show a higher activity compared to ZSM-5 with more isolated sites. Linear butene selectivity increases in Na-ZSM-5 compared to H-ZSM-5, caused by a suppressed dibutyl ether formation. The selectivity towards 1-butene is enhanced to a greater extent on proximate sites, likely due to a local/steric constraint at the active site. Decomposition of DBE over Na-ZSM-5 is more active compared to n-butanol dehydration, independent of acid site proximity. Also for 2-propanol dehydration, Na-ZSM-5 is less active than H-ZSM-5, yet the activity difference is attenuated compared to n-butanol dehydration. Essentially, due to the intrinsic higher reactivity of 2-propanol, the acid site requirement is less stringent. These findings highlight the importance of local confinement and Al proximity in acid-catalyzed conversion of oxygenated compounds.

Engineered digestate-derived biochar mediated peroxymonosulfate activation for oxytetracycline removal in sustainable wastewater remediation

Nowadays, biochar is extensively used in wastewater remediation with the aim of achieving water security and circularity with minimal impacts on ecosystems and the environment. In this study, digestate biochar was prepared and modified using different methods and then employed as a peroxymonosulfate (PMS) activator to oxidize oxytetracycline, a model antibiotic pollutant in wastewater. The optimal biochar catalyst was characterized, spin trapping tests were carried out to confirm the dominant catalytic mechanism, and in silico toxicity prediction was conducted based on structure-activity relationships. Assessment of the catalytic performance of the pristine and engineered biochar showed that nitrogen doping increased oxytetracycline degradation efficiency by 1.92-fold (i.e., 100% oxytetracycline degradation with the engineered biochar compared to 52% with pristine biochar), while pyrrolic nitrogen was identified as a major PMS activation site. It was discovered that several parameters, such as catalyst dose, pH, PMS concentration, and competing ions, affected oxytetracycline degradation efficiencies. Additionally, the toxicity of the degradation intermediate was studied. Scavenger trapping tests showed that 1O2 and SO4•- were the most prevalent species during oxytetracycline degradation in the system, with four possible degradation pathways proposed, including secondary alcohol oxidation, hydroxylation, dehydration, and deamidation. Overall, it is anticipated that this study would contribute to our understanding of metal-free biochar activation of PMS as an attractive treatment scheme for antibiotic-polluted water.

Dehydration of Tetrahydrofurfuryl Alcohol Into Dihydropyran on γ-Al2O3 Catalyst: Reaction Monitoring by In Situ DRIFT Spectroscopy

AbstractIn this study, in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was used to analyze the surface reactivity during the dehydration of tetrahydrofurfuryl alcohol (THFA) to 3,4-dihydro-2H-pyran (DHP). The dehydration reaction of THFA is carried out in the gas phase at 648 K using activated γ-Al2O3 as catalyst. Under these conditions, a yield of 84% DHP is obtained in a fixed-bed reactor and the catalyst shows no signs of deactivation after 70 h. The information obtained with DRIFT in situ spectroscopy depends on the reaction conditions, with the concentration of THFA in the gas phase being a critical variable. The temperature and time on stream have also been studied. This technique has allowed to identify DHP, the product of interest, two products with carbonyl group (C = O) formed in the surface of the catalyst during the reaction, and also the formation of carboxylates from the reaction of surface species with the oxygens of the oxide catalyst. This is of considerable significance, as an understanding of the molecular processes occurring at the surface during the reaction would permit the rational design of catalysts to enhance their catalytic properties. Therefore, in situ DRIFT spectroscopy is a valuable tool for studying active catalysts in the THFA dehydration reaction.

The catalytic performance of γ-Al2O3/red clay as a highly active, selective, and stable catalyst for methanol dehydration to dimethyl ether at competitive low reaction temperature

This study aims to a more environment eco-friendly approach for producing dimethyl ether (DME), as an alternative fuel, through the dehydration of methanol. The method involves utilizing Egyptian natural red clay (ERC) that has been modified with various percentages of γ-Al2O3 (ranging from 3 to 30 wt%) as catalysts. The most active catalyst (10 % γ-Al2O3/ERC) was then modified with varying HCl percentages (3–7 wt%). The synthesized catalysts properties were examined by various techniques, including X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2-sorption analysis, and transmission electron microscopy (TEM). The surface acidity of the catalysts was assessed using two methods: dehydration of isopropyl alcohol and chemisorption of pyridine and 2,6-dimethyl pyridine. The results of the catalytic activity study reflected that the treatment of ERC by HCl and γ-Al2O3 improved its activity toward DME production. Specifically, the 5 % HCl/10 % γ-Al2O3/ERC catalyst displayed outstanding activity, achieving conversion value of 90 % with 100 % selectivity to DME at 200 °C. Furthermore, this catalyst demonstrated long-term stability, as it maintained its performance over one week without deactivation. Acidity, and the textural characteristics were identified as the key factors contributing to the remarkable improvement in catalytic activity.

Dehydration of Alcohols to Olefins Catalyzed by ZrAPSO-34 Molecular Sieve

The lower olefins (Ethylene, propylene, and butylene) are considered the key to the polymeric and petrochemical industries. Dehydration of alcohols to produce light olefins (Methanol-to-olefins reaction) over SAPO-34 molecular sieve has attractedintoigh attention. Modified SAPO-34 zeolite catalyst with Zr metal was successfully prepared under microwave irradiation using morpholine as a structure direct agent. The microwave energy power used was 800 w and the crystallization time was 200 min. The catalyst sample was characterized by XRD, SEM, EDX, BET, FTIR, and TGA analysis. XRD analysis exhibited a typical chabazite structure with high crystallinity. The analysis showed macrocrystalline particles with moderate distribution of silica in the framework structure and a low surface area of 77 m2/g. The vibration peaks of the prepared catalyst showed agreement with the SAPO-34 CHA structure. Catalyst performance towards methanol-to-olefins conversion was performed in a trickle bed reactor with temperatures of 350, 400, 450, and 500 oC at a weight hourly space velocity of 7.7 h-1. The results also reveal at a temperature of 400 oC , that the best olefins selectivity was obtained, reaching 70%, with a longer lifetime of 500 min. methanol conversion was almost 100% at all reaction temperatures. In addition, the effect of methanol concentration was investigated and the results showed that increasing of water content plays a role in increasing catalyst lifetime and preventing coke depositions in pores.

Highly Regio- and Stereoselective Dehydration of Allylic Alcohols to Conjugated Dienes via 1,4-syn-Elimination with H2 Evolution.

Dehydration of alcohols is one of the most fundamental transformations in the organic chemistry class and one of the most widely used methods for producing alkenes in synthetic research. Numerous methods and reagents have been developed to control the regio- and stereoselectivity as well as the dehydration efficiency of normal alcohols. Despite these achievements, regio- and stereoselective and predictable dehydration of allylic alcohol has seldom been reported, except for limited substrates with a native preferred elimination position, as a result of the challenges that many potential dienes could be formed via 1,2- or 1,4-syn- or anti-elimination. Here, we report a tBuOK/potassium 2,2-difluoroacetate-mediated 1,4-syn-dehydration of allylic alcohol for the synthesis of regio- and stereodefined conjugated dienes via an in situ generated directing group strategy. This reaction exhibits a broad substrate scope and good functional group compatibility for primary-tertiary alcohols. The simple and scalable (up to 0.6 mol) procedure with readily available and inexpensive reagents makes it a practical method for conjugated diene synthesis. Mechanistic studies reveal that an acetate with tert-butoxide and allyloxide acetal moiety is formed as an intermediate, in which the acetate and the acetal act as the directing group for the base-promoted elimination. An unusual H2 evolution is also involved in the reaction.

Constructing High-Active Surface of Plasmonic Tungsten Oxide for Photocatalytic Alcohol Dehydration.

Plasmonic semiconductors with broad spectral response hold significant promise for sustainable solar energy utilization. However, the surface inertness limits the photocatalytic activity. Herein, a novel approach is proposed to improve the body crystallinity and increase the surface oxygen vacancies of plasmonic tungsten oxide by the combination of hydrochloric acid (HCl) regulation and light irradiation, which can promote the adsorption of tert-butyl alcohol (TBA) on plasmonic tungsten oxide and overcome the hindrance of the surface depletion layer in photocatalytic alcohol dehydration. Additionally, this process can concentrate electrons for strong plasmonic electron oscillation on the near surface, facilitating rapid electron transfer within the adsorbed TBA molecules for C-O bond cleavage. As a result, the activation barrier for TBA dehydration is significantly reduced by 93% to 6.0kJ mol-1, much lower than that of thermocatalysis (91kJ mol-1). Therefore, an optimal isobutylene generation rate of 1.8mol g-1 h-1 (selectivity of 99.9%) is achieved. A small flow reaction system is further constructed, which shows an isobutylene generation rate of 12mmol h-1 under natural sunlight irradiation. This work highlights the potential of plasmonic semiconductors for efficient photocatalytic alcohol dehydration, thereby promoting the sustainable utilization of solar energy.

TFA-Promoted Cascade Sulfonylation/Rearrangement/Cyclization of 1,5-Diynols and Sodium Sulfinates to Construct Sulfonylated Benzo[b]fluorenes.

A novel conversion of 1,5-diynols into sulfonylated benzo[b]fluorenes is reported by a TFA-promoted cascade cyclization with sodium sulfinates under mild conditions. This strategy provides an efficient and practical approach for accessing various sulfonated benzo[b]fluorenes in moderate to excellent yields under metal-free conditions. On the basis of the control experimental results and density functional theory calculations, a possible cascade transformation mechanism consisting of the dehydration of propargylic alcohols, sulfonylation, allenylation, and Schmittel-type cyclization is proposed. It is worth noting that TFA played an important role in this cascade cyclization, which promoted C-SO2R bond cleavage in a propargylic sulfone intermediate to form allenyl sulfones, followed by Schmittel-type cyclization to give the target product.

Elucidating reaction mechanisms in the oxidative depolymerization of sodium lignosulfonate for enhancing vanillin production: A Density Functional Theory study

Lignin is a vital organic constituent of plant biomass and it can be transformed into value-added chemicals through chemical processes. This study employs the Density Functional Theory (DFT) to investigate the mechanistic effects of various oxidants on the depolymerization of sodium lignosulfonate model compounds into vanillin. Under alkaline conditions, OH- ions participation in the hydrolysis of β-O-4 bonds has been predicted. The dehydration of dihydroconiferyl alcohol to form eugenol, with an energy barrier of 69.0 kcal/mol was identified as the major rate-determining step in the oxidation reaction. In the absence of an oxidant, the energy barrier for the oxidation of eugenol to vanillin was 77.8 kcal/mol. However, when using nitrobenzene or H2O2 as oxidants, the energy barrier has significantly decreased to 12.6 kcal/mol and 21.4 kcal/mol, respectively. The effects of temperature and pressure on the rate-determining step of the reaction were analyzed using Statistical Product and Service Solutions (SPSS) software. These results have demonstrated that the energy barrier for the hydrolysis reaction's rate-determining step is positively correlated with temperature but negatively correlated with pressure. These theoretical findings would potentially help in designing the experiments and aid in enhancing the selectivity and yield of vanillin.

Selective and scalable catalytic dehydration of primary alcohols to linear alpha-olefins over CeO2-doped Al2O3

Catalytic dehydration of primary alcohols has been developed for selective and sustainable linear alpha-olefins (LAOs) production. While Al2O3-based catalysts with tunable Lewis acidity and thermal stability have shown promise in enhancing LAO selectivity, challenges like acidity loss and compromised selectivity persist. This study addresses the need for an efficient catalyst system, synthesizing CeO2-doped Al2O3 catalysts with varying Ce loading and assessing their performance in the dehydration of 1-hexanol. Characterization using various techniques revealed that 10 wt% CeO2–Al2O3 (10CA) catalyst exhibited the highest 1-hexene yield (88.1%) under optimized conditions. CeO2 doping enhanced both acidic and basic strength, with excess Ce (>15%) leading to acidity and basicity loss. The 10CA catalyst demonstrated effectiveness across alcohols of different chain lengths (C5 and C8) at varying temperatures, showcasing the impact of carbon chain length on product selectivity. The scalability of the process was explored, with the 10CA catalyst successfully applied from lab-scale (0.0072 L/day) to bench-scale (4.33 L/day) reactions. The bench-scale reaction yielded 79.9% 1-hexene with 90.5% conversion of 1-hexanol and 88.2% selectivity for 1-hexene. The successful scale-up of the catalytic dehydration process using the 10CA catalyst underscores its potential as a pivotal component in the green economy, promoting sustainability and environmental friendliness in producing LAO.

Zirconia-incorporated yttria with a Lewis pair of acid–base surface sites for chemoselective dehydration of alcohols into alpha olefins

Alpha olefins are currently made by ethylene oligomerization to a broad range of carbon number. An alternative conversion is selective alcohol dehydration in which the conventional catalyst development focused on the addition of any basic components into acidic supports. We herein demonstrated that the Zr4+ addition to Y2O3 (acid-to-base addition) was more effective than the Y3+ addition to ZrO2 in alcohol dehydration to alpha olefins. The zirconia-incorporated yttria with 4 mol% Zr (named 4ZIY) was structurally more stable than the yttria-stabilized zirconia (YSZ) counterpart. Moreover, the 4ZIY showed a high purity of alpha olefins when various C4 and C6 alcohols were used. Catalyst characterization works revealed that the 4ZIY contains a large amount of strong Lewis base sites, which is associated with oxygen vacancy, with a little Lewis acid sites. Consequently, the 4ZIY is suggested to have the favorable acid–base pair for the conversion of alcohols to alpha olefins.

Template-Free Synthesis of High Dehydration Performance CHA Zeolite Membranes with Increased Si/Al Ratio Using SSZ-13 Seeds.

Pervaporation is an energy-efficient alternative to conventional distillation for water/alcohol separations. In this work, a novel CHA zeolite membrane with an increased Si/Al ratio was synthesized in the absence of organic templates for the first time. Nanosized high-silica zeolite (SSZ-13) seeds were used for the secondary growth of the membrane. The separation performance of membranes in different alcohol-aqueous mixtures was measured. The effects of water content in the feed and the temperature on the separation performance using pervaporation and vapor permeation were also studied. The best membrane showed a water/ethanol separation factor above 100,000 and a total flux of 1.2 kg/(m2 h) at 348 K in a 10 wt.% water-ethanol mixed solution. A membrane with high performance and an increased Si/Al ratio is promising for the application of alcohol dehydration.

Pairing Ga/Al-Zeolites with tailored acidity as tandem catalysts for the conversion of alcohols to olefins

Zeolites are versatile catalysts owing to their tunable acidity where the active site(s) can be placed within the crystal framework or as extra-framework species in confined pores. A common approach to tailor Brønsted acidity is heteroatom exchange involving the replacement of framework aluminum with alternative elements. Introduction of heteroatoms often results in less acidic catalysts that can be used in tandem reactions for targeted reactive intermediates. In this study, we prepare a series of three different zeolites with MWW, CHA, and MFI frameworks as aluminosilicates and gallosilicates to demonstrate their performance in alcohol dehydration reactions. The two reactions examined in this study are methanol conversion to dimethyl ether and ethanol conversion to ethylene. Our findings reveal that Ga-zeolites exhibit superior performance with Ga-MCM-22 (MWW) achieving nearly 100 % alcohol conversion and selectivity to desired products at contact times that are significantly less than most dehydration catalysts reported in literature. The unique properties of Ga-zeolites are attributed to their reduced acid site strength via a direct (one-pot) synthesis that avoids conventional time-intensive, multi-step post-synthesis modifications of Al-zeolites. Here we demonstrate the use of Ga-zeolites as tandem catalysts when paired with a downstream Al-zeolite in a dual-bed reactor configuration to convert cheaper reagents (alcohols) upstream to more desired intermediates as feeds for downstream catalysts to produce light olefins. We demonstrate that dual beds using Ga-zeolite – Al-ZSM-5 (upstream–downstream) pairings outperform single bed configurations with Al-ZSM-5 or a physical mixture (Ga-/Al-zeolite) for methanol to hydrocarbons reactions, with notable improvements in catalyst lifetime and increased light olefins selectivity. Similarly, dual beds using Ga-zeolite – Al-SSZ-13 (upstream–downstream) pairings result in improved performance for ethanol to propylene reactions with significant increases in propylene selectivity (>20 %) compared to a conventional single bed configuration of Al-SSZ-13. Overall, this study offers a new perspective on the use of heteroatom-exchanged zeolite catalysts in tandem reactions as a means of capitalizing on their reduced acid site strength and suggests differences in the intrinsic acidity of zeolite crystal structures.

Promoted catalytic performance of sugarcane bagasse ash supported by γ‐alumina as efficient, stable, and ecofriendly catalyst for dehydration of methanol to dimethyl ether

AbstractThe aim of this study was to use different proportions (1% to 20% by weight) of γ‐alumina to modify sugarcane bagasse ash (SCBA) for the production of dimethyl ether (DME) through the dehydration of methyl alcohol. A simple precipitation method was utilized to fabricate (1–20 wt.%) Al2O3/SCBA catalysts. X‐ray fluorescence, X‐ray diffraction, Fourier‐transform infrared spectroscopy, transmission electron microscopy, and N2 sorption were used to explore the structural, spectroscopic, morphological, and textural features. The XRD pattern of Al2O3/SCBA catalysts showed a new peak that corresponded to the formation of γ‐Al2O3. In addition, the average crystallite sizes of pure SCBA and 10% and 20%Al2O3/SCBA catalysts were calculated and found to be 20.1, 21.6, and 22.6 nm, respectively. To evaluate the acidity of these catalysts, the dehydration of isopropyl alcohol and the chemisorption of basic probe molecules were employed. The acidity test results displayed that these catalysts have weak to moderate acidic sites. The 10% Al2O3/SCBA catalyst calcined at 400°C showed high efficiency for the conversion of methyl alcohol to DME, attaining 89% conversion with 100% selectivity. This observation can be attributed to the even distribution of active sites and the acid–base equilibrium on the surface. Moreover, its catalytic activity and selectivity remain unchanged over a continuous 2‐week operation without coke formation, demonstrating its extremely high stability. A strong correlation was observed between the catalytic activity and both the surface area and acidity of the catalysts.

Direct Intramolecular Coupling of Primary/Secondary Alcohols with Secondary Alcohols for Macrocyclic Alkenylation Using Ni‐Zeolite Catalyst Under Continuous‐Flow Conditions

AbstractHerein, we report the direct intramolecular coupling of primary and secondary alcohols for the selective synthesis of macrocyclic olefins in the presence of Ni‐zeolite catalyst under continuous flow. This reaction proceeds via dehydration of secondary alcohols to alkenes, which subsequently undergo intramolecular dehydrative coupling reaction with a primary alcohol to obtain moderate yields of macrocyclic olefins. This reaction is also effective for the coupling of secondary‐secondary alcohols and alkene‐alcohols to produce diverse macrocyclic olefin products. This unique approach has various advantages including step‐economy, no additives and pre‐functionalization required, inexpensive and reusable catalyst, and exemplification with 23 macrocycles in different ring sizes. The continuous flow macrocyclisation afforded higher productivity and space‐time yield than the batch reaction conditions.