Alcohol Dehydration Reactions Research Articles

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.

Researches on heterogeneous acid-base catalysis in Institute for sorption and problems of endoecology of the National Academy of Sciences of Ukraine

In chronological order, the reaseach results of Department of heterogeneous acid-base catalysis at Institute for sorption and endoecology problems in 2003-2023 are described. It relates to the synthesis, study and application of solid superacids WO3/ZrO2, WO3/ZrO2-SiO2, ZrO2-SiO2-Al2O3, ZrO2-SiO2-SnO2, as catalysts, in vacuum gas oil cracking, alkylation of isobutane with isobutanol, acylation toluene, oligomerization of tetrohydrofuran, acylation of methyl tert-butyl ether and other. Some study deals with a search of the correlations between of acid site strength of a catalyst and its activity, in particular, in dehydration reaction of C2-C4 alcohols, and the correlations between ability of primary and secondary alcohols to dehydrogenation and oxidation and their chemical shifts δ (R17OH) and δ (R13СОH ). For the first time, the values of Hammett's acidity function have been measured at elevated (up to 200 °C) temperatures for solid acids. In particular, for H-Y faujasite, H0 reaches superacidic value H0 at 160 °С. Since 2010, the main focus has been on the catalytic conversion of renewable raw materials, mainly bioalcohols (ethanol, glycerol) and C6 carbohydrates, into important products of organic synthesis (ethyl acetate, 1,1 diethoxyethane, n-butanol, propylene glycol, alkyl lactates, lactide, glycolide). In cooperation with “Techinservice Manufacturing Group”, new processes for obtaining ethyl acetate, 1,1 diethoxyethane, n-butanol from bioethanol and racemic lactide from glycerol were developed. Also, new technologies for obtaining propylene oxide from propylene and hydrogen peroxide (НРPОа-process), vapor phase hydrogenation of the pyrolysis C4-5 fraction, and direct high-temperature chlorination of ethylene to vinyl chloride have been developed for Kalush “Karpatnaftochim” plant. The HHPOa installation (2000 t/y) has been started at “Karpatnaftochim” in 2020.

Catalysts for dehydration of isopropyl alcohol based on chlorinated carbon fiber

Gas-phase chlorination of carbon fiber based on polyacrylonitrile was performed and active chlorine-containing precursors were obtained, in which chlorine can be replaced by sulfur-containing functional groups. It is shown that chlorination of carbon fiber samples with carbon tetrachloride at temperatures of 300, 450 and 6000C in an argon stream leads to the introduction of 0.2–1.7 mmol g–1 of chlorine into the surface layer of the fiber. The thermodesorption properties of the modified carbon fiber samples were investigated by thermogravimetry and thermoprogrammed desorption with mass spectrometric registration of products. It was established that the obtained samples exhibit a relatively high thermal stability. The study conducted by means of thermoprogrammed desorption method showed that chlorine is desorbed from the surface in a wide temperature range (up to 8000C). It was found that the treatment of chlorinated samples with sulfur-containing reagents with subsequent oxidation produce the samples of carbon fiber with a concentration of sulfo-groups up to 0.3 mmol g–1, which are catalytically active in the dehydration reaction of isopropyl alcohol in the gas phase. The temperature of 50% conversion of isopropyl alcohol to propylene was used as a measure of catalytic activity. It was found that pre-chlorination leads to an increase in the catalytic activity of the fiber modified with sulfur-containing reagents: the temperature of 50% conversion of isopropyl alcohol to propylene is 215–2900C, depending on the concentration of sulfo-groups.

The structure of lignosulfonates for production of carbon catalyst support

Wood pulp industry generates tons of lignosulfonate by-product waste every year. Rational utilization of lignosulfonates is limited due to non-uniform structure and complex chemical composition. However, presence of different functional groups allows for a broad range of industrial applications, including catalysis in polymer chemistry. Therefore, the aim of this study was to analyze structural composition of sodium lignosulfonate and its modified forms using Fourier transform infrared spectroscopy (FTIR). Sulfuric acid treatment of sodium lignosulfonate was hypothesized to enhance catalytic capacity of the original lignosulfonate by increasing the amount of sulfonic acid catalytic active sites inside the structure of the macromolecule. FTIR analysis identified structural features of the lignosulfonate-based catalysts and their catalytic potential was assessed via alcohol dehydration reaction. As a result, polymeric forms of lignosulfonate were successfully used as a carbon-based catalyst matrix.

Acidity of Al–O(H)–Al Sites in Molecular Aluminosilicate Models Enables Alcohol Dehydration Reactions

Acidity of Al–O(H)–Al Sites in Molecular Aluminosilicate Models Enables Alcohol Dehydration Reactions

Dehydration of isopropyl alcohol with activated carbon functionalized with Br- and S-containing reagents

Bromination of activated carbon GSGD was performed and active bromine-containing precursors were obtained, in which bromine is capable of being replaced by sulfur-containing functional groups. Bromination with liquid bromine and a solution of bromine in potassium bromide at room temperature leads to the introduction of 0.44–0.45 mmol g–1 of bromine into the surface layer of activated carbon. The treatment of brominated samples with sulfur-containing reagents with subsequent oxidation allows obtaining carbon samples that are catalytically active in the dehydration reaction of isopropyl alcohol in a gas phase. The temperature of complete conversion of isopropyl alcohol to propylene is a measure of catalytic activity. The concentration of sulfogroups in the prepared samples is up to 0.3 mol g–1. Thermogravimetry and thermoprogrammed desorption with mass spectrometric registration of products were used to study the thermal stability of modified activated carbon samples. The influence of the nature of brominating reagents, hydrolysis conditions and oxidation conditions on the structure, surface concentration of grafted S-containing groups and catalytic properties of the obtained materials was studied. Pre-bromination leads to an increase in the catalytic activity of activated carbon modified with sulfur-containing groups and the temperature of complete conversion of isopropyl alcohol to propylene decreases up to 400C depending on the concentration of sulfogroups.

Carbon dioxide-promoted palladium-catalyzed dehydration of primary allylic alcohols: access to substituted 1,3-dienes

A carbon dioxide promoted dehydration reaction of primary allylic alcohols gives synthetically important substituted 1,3-dienes in good yields under milder conditions compared with the reaction using a heterogeneous catalyst or carbon monoxide.

Pentacoordinated Aluminum Species: New Frontier for Tailoring Acidity-Enhanced Silica-Alumina Catalysts.

Silica-alumina catalysts, including zeolites and amorphous silica-aluminas (ASAs), are among the most widely used solid acid catalysts and supports to produce petrochemicals, fine chemicals, and renewable energy. The coordination, distribution, and interactions of aluminum in ASAs have an enormous impact on their acidic properties and catalytic performance. Unsaturated tetracoordinated aluminum (AlIV) species are commonly accepted as the key sites in generating catalytically active Brønsted acid sites (BASs) in silica-alumina catalysts. Extensive efforts focus on increasing the concentration of AlIV as the main route to enhance their Brønsted acidity for efficient catalysis. However, increasing the AlIV concentration either weakens the acid strength in zeolites or lowers Brønsted acidity in ASAs at high Al/Si ratios, impeding acidity enhancement of these popular catalysts."Pentacoordinated aluminum (AlV) species" are potential unsaturated Al species like AlIV but rarely observed in silica-aluminas, and thus, are widely considered unavailable for BAS formation or surface reactions. In this Account, we will describe novel strategies for the controlled synthesis of AlV-enriched ASAs using flame-spray pyrolysis (FSP) techniques and highlight the contribution of AlV species in acidity enhancement, together with their structure-activity relationship in the conversion of biomass-derived compounds into valuable chemicals. Using various in situ and advanced 2D solid-state NMR (SSNMR) experiments, the studies of the acidic properties and local structure of AlV-enriched ASAs reveal that AlV species can highly populate on ASA surfaces, promote BASs formation, and facilitate adaptable tuning of BASs from moderate to zeolitic strength by synergy with neighboring Al sites. Moreover, the BASs with enhanced acidity can work jointly with surface Lewis acid sites or metal active species for bifunctional catalysis on AlV-enriched ASAs. Compared to zeolites, these AlV-enriched ASAs are highly active in acid-catalyzed biomass conversion, including alcohol dehydration and sugar conversion reactions, as well as in promoting the performance of supported metal catalysts in chemoselective hydrogenation of aromatic ketones. These new insights provide a state-of-the-art strategy for strongly enhancing the acidity of these popular silica-alumina catalysts, which offers an interesting potential for a wide range of acid and multifunctional catalysis.

Phosphorus containing carbon (submicron)fibers as efficient acid catalysts

Porous carbon fibers catalysts have been prepared by electrospinning of Alcell lignin, a green carbon precursor, which could be obtained as by-product in wood-to-ethanol biorefineries. The addition of H3PO4, a well-known chemical activation agent, to the electrospinning lignin solutions, at different mass ratios and the use of different carbonization temperatures, between 500 and 1600 °C, were analyzed in order to obtain carbon fibers with a large variety of porosity and chemical surface properties. Isopropanol decomposition was used as a catalytic test. Phosphorus-containing carbon fibers showed acid character and high catalytic activity, achieving propylene selectivity of 100 % under inert atmosphere. However, the use of air atmosphere increases the isopropanol conversion but produces the formation of acetone, via oxidative dehydrogenation, at low temperatures (∼20 %). Ethanol and methanol decomposition were also evaluated in air stream for the most active phosphorus-containing carbon catalyst, showing improved alcohol conversions with minimal gasification of the carbon fibers. These results confirmed that phosphorus-containing carbon fibers prepared by electrospinning of lignin solutions were excellent catalysts for alcohol dehydration reactions.

The Surface Chemistry of Metal Oxide Clusters: From Metal-Organic Frameworks to Minerals.

Many metal–organic frameworks (MOFs) incorporate nodes that are small metal oxide clusters. Some of these MOFs are stable at high temperatures, offering good prospects as catalysts—prospects that focus attention on their defect sites and reactivities—all part of a broader subject: the surface chemistry of metal oxide clusters, illustrated here for MOF nodes and for polyoxocations and polyoxoanions. Ligands on MOF defect sites form during synthesis and are central to the understanding and control of MOF reactivity. Reactions of alcohols are illustrative probes of Zr6O8 node defects in UiO-66, characterized by the interconversions of formate, methoxy, hydroxy, and linker carboxylate ligands and by catalysis of alcohol dehydration reactions. We posit that new reactivities of MOF nodes will emerge from incorporation of a wide range of groups on their surfaces and from targeted substitutions of metals within them.

Sustainable short-chain olefin production through simultaneous dehydration of mixtures of 1-butanol and ethanol over HZSM-5 and γ-Al2O3

Dehydration reactions of alcohols are of prime importance in biomass conversions. Although bio-alcohols are generally obtained as mixtures, the dehydration of alcohol mixtures is barely reported. In this work the ability of HZSM-5 and γ-Al2O3 to dehydrate a 1-butanol/ethanol mixture in a 6/1 mass-ratio was studied, corresponding to the butanol/ethanol ratio in typical ABE mixtures, at temperatures from 513 to 613 K. For HZSM-5 the difference in reactivity of the alcohols is too high to fully convert both alcohols to their respective alkenes without catalyzing secondary reactions. For dehydration over γ-Al2O3, the reactivity of ethanol and 1-butanol is more similar, which can be attributed to the lower acid strength and larger pore size, causing lower fractional coverages and diminished competition for adsorption sites, allowing both alcohols to react more simultaneously. Above conversions of 0.6, the difference in reactivity of both alcohols increases due to a shift in dominant reaction pathways towards ether decomposition and the intramolecular dehydration on γ-Al2O3. Approaching full conversion, the selectivity towards olefins is high (>0.95) for both HZSM-5 and γ-Al2O3. Since no secondary reactions occur when using γ-Al2O3, it is deemed the best of both catalysts to dehydrate mixtures of alcohols simultaneously to their corresponding alkenes.

Highly porous hybrid metallosilicate materials prepared by non-hydrolytic sol-gel: Hydrothermal stability and catalytic properties in ethanol dehydration

Herein, we present novel phenylene- and xylylene-bridged silica and metallosilicate materials prepared by non-hydrolytic sol-gel. The hybrid silica are highly porous, chemically similar to periodic mesoporous organosilica (PMO), but amorphous without any pore ordering. Analogous hybrid metallosilicates are obtained by directly incorporating Al, Nb, or Sn in the hybrid silica framework. Exhibiting open texture, surface acidity and tunable hydrophobicity, these materials are excellent candidates for catalytic alcohol dehydration reactions. The gas-phase hydrothermal and thermal stability of these materials is examined. While the hybrid silica is expectedly stable, a stark decrease in stability is observed for phenylene bridged silsesquioxanes upon metal introduction. The extent of the hydrolytic Si–C(sp2) bond cleavage is quantitatively followed by 29Si MAS NMR, TG analysis, and GC-FID analysis of effluent coming from samples exposed to water vapor. Two important features affecting the hydrothermal and thermal stability are identified: (i) the homogeneity of metal dispersion within the silica matrix, and (ii) the electronegativity of the incorporated metal. The stability of hybrid metallosilicates is significantly improved by replacing the phenylene bridges with xylylene bridges, due to the presence of more stable Si–C(sp3) bonds. Interestingly, the latter hybrid metallosilicate proves to be an active catalyst for the dehydration of ethanol to ethylene. Unlike the other hybrid materials presented here, it reaches high ethylene yields without undergoing degradation and deactivation.

Catalytic Oligomerization of Isobutyl Alcohol to Hydrocarbon Liquid Fuels over Acidic Zeolite Catalysts

AbstractCatalytic isobutyl alcohol oligomerization to generate hydrocarbon liquid fuels over zeolite has been investigated over H−Y, SAPO‐34, H‐MOR zeolite and Al‐MCM‐41 catalysts, as a new way to direct conversion of isobutyl alcohol to hydrocarbon liquid fuels, considering the fact that isobutyl alcohol can be obtained from biomass by microbes. In this study, all of the zeolite samples showed good reactivity, especially H‐MOR, achieving 94 % conversion of isobutyl alcohol and 63 % selectivity of C5+ liquid fuels in all products. The effects of reaction conditions including reaction temperature and reaction time were also discussed. The physicochemical properties of the catalysts were characterized by XRD, Nitrogen adsorption‐desorption, NH3‐TPD, TG/DTA, and GS/MS. The reaction system discussed here involves two reactions, i) isobutyl alcohol dehydration reaction via a typical acid catalysis, ii) a polymerization reaction of small molecules into large ones, according to the experimental and characterization results, the pore size and acid property of the zeolite are the two main factors controlling this catalytic dehydration and oligomerization reaction.

Effects of Phosphonic Acid Monolayers on the Dehydration Mechanism of Aliphatic Alcohols on TiO2

The kinetics for surface-catalyzed alcohol dehydration reactions often depend on the structure of the alcohol. Studies of structure–activity relations across primary, secondary, and tertiary alcoho...

Fundamental study of furfuryl alcohol dehydration reaction over molybdenum oxide catalyst

The conversion of furfuryl alcohol (FA) and selectivity towards dimers (C9-C10) and trimers (C14-C15) were investigated over molybdenum oxide (MoO3) catalyst. It was observed that FA conversion increased as an increase of reaction time. However, longer reaction time tended to limit the selectivity to dimers and trimers. Characterization data obtained from XRD, Raman, and XPS showed that after the reaction the terminal MoO bond was elongated and the oxidation state was changed from Mo6+ to Mo5+. This was likely caused by the delocalization of extra electron to the Mo center during the activation of FA on MoO3 surface, instead of the formation of oxygen vacancy. After a proper regeneration process, the structure distortion caused by the elongation of MoO bond was fully restored, however, the oxidation state were only restored to Mo5+/6+. Recyclability test using regenerated MoO3 indicates Mo5+/6+ can be as active as Mo6+.

Methanol, ethanol, propanol, and butanol adsorption on H-ZSM-5 zeolite: an ONIOM study.

The search for renewable raw materials less harmful to the environment, such as methanol, ethanol, 1-propanol, and 1-butanol has become attractive. These products are obtained more rapidly and efficiently by specific solid catalysts, mainly the zeolites. The Brønsted acid sites distributed over the sinusoidal and the straight channels are important for the alcohol dehydration reaction that produces widely used chemicals. Therefore, the ONIOM method was used to study methanol, ethanol, propanol, and butanol adsorption in H-ZSM-5 zeolite. PM6 and DFT levels were used for the high layer ONIOM, while the low layer was calculated using the UFF force field. DFT was calculated using the B3LYP global hybrid GGA, M06-2X hybrid meta-GGA, and the hybrid range separated ωB97X-D functionals at 6-31+G(d) basis set. The high layer ONIOM was completely relaxed. The binding energy shows dependence on the relaxed tetrahedra and position of acid site. The Si/Al ratio was also studied. Graphical Abstract HOMO orbital of adsorbed alcohols showing the main contribution of zeolite for small alcohols.

Influence of network structure on the degradation of poly(ether)amine-cured epoxy resins by inorganic acid

In this paper, we investigate the case of bisphenol-type epoxy crosslinked with poly(ether)amine, immersed in sulfuric acid at elevated temperature. The results show that very high equilibrium mass-change (up to 40%) is observed, and that amine protonation is largely responsible for this behavior. When the acid solution concentration is 5mass% or higher, alcohol dehydration and aromatic ether cleavage reactions occur by excess acid (after amine protonation). A mechanistic degradation model is proposed, which requires no empirical parameters and accounts for polymer network structure differences. The model is supported by calculating the theoretical crosslink density using gravimetric data of penetrated acid at equilibrium.

Synthesis of Symmetric Ethers Using Monocationic and Dicationic Acidic Ionic Liquids

A series of monocationic and dicationic -SO3H functionalized Brønsted acidic ionic liquids (BAILs) are synthesized using different amines int.al., N,N,N′,N′-tetramethylethylenediamine, 1-methylimidazole, pyridine and alkylating agents 1,3-propane- and 1,4-butanesultones. The Hammett acidity (H0) and thermal properties by TG-DSC techniques are investigated. These ionic liquids have been applied to catalyze the dehydration reaction of aliphatic long chain alcohols (1-heptanol, 1-octanol, 1-decanol) at 195 °C. The optimization of reaction conditions and use of dicationic ionic liquids allow to reach rather high yields of symmetric diheptyl ether and dioctyl ether. The reusability of ionic liquids is evaluated using monocationic [PyPS][HSO4], dicationic [TMEDAPS][HSO4] ionic liquids and 1-heptanol.

A computational insight into cyclopropenone activated dehydration reaction of alcohols

The cyclopropenone activated dehydration reaction of alcohols is a promising alternative to alcohol substitution reactions to avoid hazardous byproducts and harsh reaction conditions. Density functional theory calculations at M062X/6–31+G(d,p) level were performed for two proposed reaction mechanisms of the cyclopropenone activated chlorodehydration reaction where alkyl chloride product can be obtained from both of the proposed reaction mechanisms but chloroxalate has only one alternative. The calculations enabled us to explain the rection mechanisms in detail. Additionally, the effects of the various substituents on the cyclopropenone ring for the product distribution ratio was clarified.The substitution with electron donating group on para position of the phenyl ring of cyclopropenone has no effect on the relative free energy of the rate-determining step where the electron-withdrawing group increase the energy values independent from the position. The product ratio values that were calculated from energy barriers are in harmony with the experimentally obtained ones pointing out the reaction mechanism preference.

The effect of Brønsted acidity of WO3/ZrO2 catalysts in dehydration reactions of C3 and C4 alcohols

WO3/ZrO2 catalysts were synthesized by an excess solution impregnation method, and its applications for the dehydration of iso-propanol (IPA) and n-butanol (nBA) and iso-butanol (IBA) as C3–C4 alcohols were investigated. The catalytic activity was maximized at 20wt% WO3 content in the range of 0–30wt% WO3/ZrO2 catalysts. In IPA dehydration, conversion and selectivity to propene were well correlated with Brønsted acidity. In the dehydration of nBA and IBA, conversion was also influenced by Brønsted acidity. However, product selectivity to iso-butene, 1-butene, cis-2-butene (c-butene), and trans-2-butene (t-butene) was not affected by Brønsted acidity. Below 85% conversion in IBA dehydration, the ratio of cis/trans isomer in 2-butenes was almost constant. However, above this range of conversion the catalytic isomerization of iso-butene to t-butene is accompanied with slight deactivation of catalysts with time on stream. In the nBA dehydration the catalytic isomerization of t-butene to 1-butene changes the cis/trans ratio in the formation of 2-butenes resulting that below unity in initial period, and gradually increased as the reaction proceeds.