Ethanol Dehydration Reaction Research Articles

An Effective Synthesis of Phosphated Silica (PO<sub>4</sub>/SiO<sub>2</sub>) Catalyst and its Performance for Converting Ethanol into Diethyl Ether (DEE)

Research on phosphated silica (PO4/SiO2) as a heterogeneous acid catalyst in the dehydration reaction of ethanol into diethyl ether has been carried out. The PO4/SiO2 was prepared from TEOS by a wet impregnation method with various concentrations of H3PO4 (1, 2, 3, 4 M) and calcination temperatures (400, 500, and 600 °C) to obtain it with an optimum acidity. Afterward, the catalysts were characterized by FTIR, XRD, SEM-EDX, SAA, and TG-DTA. Ethanol dehydration was run using a fixed-batch reactor with a flow of N2 gas, and GC determined the selectivity of diethyl ether. The PS-4-400 catalyst had the highest activity and selectivity in the ethanol dehydration to diethyl ether at a temperature of 225 °C, with a conversion of 58.00% and a DEE selectivity of 3.71%.

In situ visualisation of zeolite anisotropic framework flexibility during catalysis

Zeolites exhibit framework flexibility driving their chemical and catalytic properties. Since the zeolitic pores are extremely small, a slight strain generated in the crystal induces compelling changes in shape, connectivity, accessibility, and the framework chemical properties. These modifications affected the adsorption and desorption of reactants/products and the diffusion within the channels during reaction. Using in situ 3D Bragg coherent X-ray diffraction imaging, we unveil the dynamics of the zeolite structure during catalysis, contraction and/or expansion of its framework also known as zeolite framework flexibility. We imaged three-dimensionally a single faujasite zeolite crystal during the ethanol dehydration reaction revealing anisotropic lattice dynamics simultaneously to guest molecules formation. Understanding zeolite flexibility could permit to tune zeolites properties towards potentially higher adsorption and selectivity.

Synthesis of alumina/ferric oxide nanofibers and application to catalysts for ethanol dehydration reaction by adding palladium oxide

AbstractAlumina/ferric oxide (Al₂O₃/Fe₂O₃) composite nanofibers were fabricated via electrospinning followed by heat treatment. Structural characterization revealed mesoporous morphology with high porosity and surface area and uniform dispersion of catalytically active Fe₂O₃ nanoparticles. Catalytic evaluation for ethanol dehydration demonstrated superior performance for nanofibers containing 5 wt% Fe₂O₃, attributed to their unique structural features. Further enhancement was achieved by incorporating palladium oxide (PdO), resulting in improved catalytic activity, particularly in ethylene productivity. Surface acid properties were altered with PdO addition, suggesting a role of Lewis acid sites in augmenting catalytic performance. The developed PdO/Al₂O₃/Fe₂O₃ nanofibers exhibit stable performance over multiple cycles, offering promising prospects for efficient ethanol dehydration catalysts.

An integral design and synthesis approach to heterogeneous catalysts: Tailoring the surface characteristics and mass and heat transport properties

A novel integrated approach to designing and synthesizing heterogeneous catalysts with customized surface characteristics and improved heat and mass transport properties is studied. This unique approach utilizes hydrothermal reactions of aluminum (Al) metal substrates with controlled interfacial chemistry, manipulating the kinetics of aluminum hydroxide crystal growth to develop Al@Al2O3 core–shell metal-ceramic composite micro-architectures. The shapes, spatial orientation, and surface-exposed crystal facets of the porous γ-Al2O3 crystallites of the Al@Al2O3 core–shell are effectively tailored via modulation of the specific charge interaction of the boehmite crystallites with heteroatom ions in the solution. The reaction chemistry and formation mechanism of the Al@Al2O3 core–shell micro-composites with morphologically modulated γ-Al2O3 crystallites are studied in detail, along with their physicochemical and catalytic properties. For the acid-catalyzed ethanol dehydration reaction, the Al@Al2O3 catalysts with tailored morphologies and exposed γ-Al2O3 crystal facets demonstrate the high effectiveness of the integrated design and synthesis approach to heterogeneous catalysts, modulating the intrinsic catalytic activities with enhanced mass and heat transport properties at the same time.

Photodehydration of Ethanol Mediated by CuCl2-Ethanol Complex.

Biomass ethanol is regarded as a renewable resource but it is not economically viable to transform it to high-value industrial chemicals at present. Herein, a simple, green, and low-cost CuCl2-ethanol complex is reported for ethanol dehydration to produce ethylene and acetal simultaneously with high selectivity under sunlight irradiation. Under N2 atmosphere, the generation rates of ethylene and acetal were 165 and 3672 μmol g-1 h-1, accounting for 100% in gas products and 97% in liquid products, respectively. An outstanding apparent quantum yield of 13.2% (365 nm) and the maximum conversion rate of 32% were achieved. The dehydration reactions start from the photoexcited CuCl2-ethanol complex, and then go through the energy transfer (EnT) and ligand to metal charge transfer (LMCT) mechanisms to produce ethylene and acetal, respectively. The formation energies of the CuCl2-ethanol complex and the key intermediate radicals (e.g., ·OH, CH3CH2·, and CH3CH2O·) were validated to clarify the mechanisms. Different from previous CuCl2-based oxidation and addition reactions, this work is anticipated to supply new insights into the dehydration reaction of ethanol to produce useful chemical feedstocks.

The behavior of aluminum sites in H-[Al]-RUB-18 catalysts: A theoretical-experimental investigation

Functional acidic sites can be generated in the structure of layered silicates by the isomorphic substitution of silicon by aluminum atoms, leading to suitable heterogeneous catalysts. H-[Al]-RUB-18 samples were synthesized with Si/Al molar ratios of 15, 30, and 60. Experimental characterizations showed that two different aluminum sites were obtained: one tetrahedrally coordinated (framework-Al), very similar to those found in microporous zeolites; and the other octahedrally coordinated, analogous to silanol groups (hydrated aluminol sites). Computational simulations based on Density Functional Theory (DFT) were used to test the atomic positions of these aluminum sites and confirmed, in terms of electronic energies, the tetrahedral and octahedral positions already predicted in the experimental characterizations. In addition, ethanol dehydration reaction was used to probe the acidic sites and evaluate the performance of the different [Al]-RUB-18 samples. Although a widely known reaction for zeolites and other porous solids, the chemical analysis in this work indicated that the Al-substituted layered silicates are promising candidates to be used in heterogeneous catalysis. The experimental catalytic data showed that the presence of aluminum atoms improved the reaction conversion. Moreover, MEP calculations also presented, in each step of ethanol dehydration, Alframework sites with the lowest electronic energy barriers.

Hierarchical leaf-like alumina-carbon nanosheets with ammonia water modification for ethanol dehydration to ethylene

A hierarchical leaf-like alumina-carbon nanosheet catalyst was prepared by a chelate-assisted co-assembly method to improve the catalytic behavior of ethanol dehydration reaction, based on the chemical etching effect of ammonia water. The uniformly dispersed leaf-like nanosheet structure possessed a relatively large specific surface area and exposed more active sites, which could promote the ethanol dehydration reaction. This catalyst was promising to obtain a higher catalytic behavior (conversion of 98.3 % and ethylene selectivity of 97.0 %) than the sample without ammonia water modification (conversion of 63.2 % and ethylene selectivity of 46.7 %) at 450 ℃. The addition of ammonia water played an essential role in influencing the formation of the leaf-like nanosheet structure and the generation of Brönsted acid active sites, which remarkably promoted the proceed of ethanol dehydration. Importantly, a direct relationship was observed between the nanosheet thickness and the alumina content. The best catalytic activity with TOF of 361.8 h−1 was obtained when the Al loading of 13.9 wt%, attributed to the suitably balanced weak/moderate acidic active sites ratio of ∼ 4.37. In-situ FTIR spectra of ethanol dehydration reaction clearly confirmed that ethanol was first converted to the intermediate product diethyl ether and then subsequently decomposed to ethylene at a higher temperature. The catalyst also maintained a good recyclability upon time on stream of 144 h at 450 ℃. This work provides an alternative way of developing non-noble metal catalyzing ethanol dehydration to ethylene.

Preparation of Metal-Acid bifunctional catalyst Ni/ZSM-22 for palmitic acid catalytic deoxygenation

In this work, methods employing ethanol for dispersion as well as precursor combination by rotary evaporation were combined to produce Ni-based ZSM-22 catalysts. The catalytic activity in palmitic acid deoxygenation over Ni/Z22@E was enhanced compared with that of the wet-impregnated method. The conversion of palmitic acid reached 98.9 %, in which C16/C15 alkane was as high as 4.07. The Ni species on the surface of catalysts showed strong stability so that not susceptible to inactivation by coking or leaching. In addition, the mechanism and kinetics of the palmitic acid deoxygenation reaction were analyzed. The results showed that the ethanol dehydration reaction was the most difficult to occur, and the high C16 alkanes selectivity can be attributed to the low activation energy of the hydrodeoxygenation (HDO) pathway. Both experimental and kinetics calculation results suggested that there may be a mechanistic change in the fatty acid deoxygenation reaction at around 240 °C that resulted in a large increase in the hydrodecarboxylation (HDX) pathway. Based on this, selected adjustments of the products were proposed for fatty alcohols below 220 °C, C16 alkanes between 260 and 280 °C, and C15 alkanes above 280 °C.

Thermogravimetry Applied for Investigation of Coke Formation in Ethanol Conversion over Heteropoly Tungstate Catalysts

Thermogravimetric analysis (TGA) was used to evaluate the thermal stability and the amount of coke deposition resulting from the deactivation of catalysts during ethanol dehydration reaction in a fixed bed continuous flow reactor. In this study, a series of catalysts containing 30% of Pd doped and pure 12-tungstophosphoric acid and its insoluble Cs2.5H0.5PW12O40 salt supported on SBA-15 were prepared. The catalytic efficiency of ethanol dehydration reaction was also evaluated. Two types of coke are identified from the TPO (Temperature programmed oxidation) profiles and assigned to the coke precursor and hard coke, respectively. The results indicate that cesium salts reduced the formation of hard coke. The amount of total coke formed was significantly reduced by supporting the catalysts on mesoporous SBA-15 molecular sieves.

Tuning the selectivity of cerium oxide for ethanol dehydration to ethylene

Ethylene is a prized raw material in the chemical industry, as well as a valued monomer to produce important commodities. At present, ethylene is mainly produced via the cracking of hydrocarbons, but there is an increasing interest in exploiting renewable biomass-derived feedstocks. The catalytic dehydration of bioethanol is a sustainable alternative route to produce ethylene. Ceria-based catalysts are active for ethanol dehydration to ethylene at low-temperature, but their selectivity is limited by the undesired formation of acetaldehyde. Partially reduced ceria can promote the dehydration of primary alcohols into alkenes over their dehydrogenation to aldehydes. This work provides computational insight into the role of surface oxygen vacancies in the selectivity of ceria. Based on this, it is proposed that the selectivity of ceria toward ethylene can be tuned by substituting Ce4+ with La3+ cations. This is tested using both density functional theory (DFT) calculations and temperature-programmed desorption (TPD) experiments to quantify the impact of doping ceria with lanthanum on the production of ethylene and acetaldehyde. The La-doped ceria sample is found to be more active and selective. This insight can guide the rational design of new ceria-based catalysts for an ethanol dehydration reaction with high selectivity to ethylene.

Modeling and Optimization of Ethanol to Ethylene Production over γ‐Al2O3 and CeZrO2 Catalysts Using RSM[1] Method

AbstractCatalytic performance of catalysts is influenced by process conditions. In this work the influence of temperature, residence time and C2H5OH feed concentration was investigated in ethanol dehydration reaction using the response surface methodology (RSM) for γ‐Al2O3 and CeZrO2 catalysts. The γ‐Al2O3 was prepared using calcination method and CeZrO2 precipitation method. The process indicators (conversion, yield, selectivity) were modeled through the RSM method, and the equations obtained showed a good fit to the experimental data. The optimization results indicate different optimum conditions for each catalyst. For γ‐Al2O3 at 420 °C, 23.5 % of ethanol concentration and 0.65 gs/L, 0.6 molethylene/molethanol is obtained and total conversion. For CeZrO2 at 495 °C, 59 % ethanol concentration and 300 gs/L, 0.38 molethylene/molethanol is obtained and total ethanol conversion. Catalyst characterization was performed using, XRD (x‐ray diffraction), BET (Brunauer‐Emmett‐Teller surface area analysis), TPR (Temperature‐programmed reduction) and TPD (Temperature‐programmed desorption).

Progress in Development of Magadiite to Produce Multifunctional Lamellar Materials.

The attractive properties of magadiite, a lamellar and crystalline material, could give rise to new industrial processes due to its unique and modulating intrinsic properties. In this context, the high degree of expansion of its lamellae, a key factor for its potential use in several areas of scientific research, has attracted the attention of several researchers. The aim of this review is to provide a historical overview of the hypothetical models developed to explain the magadiite crystalline structure. Furthermore, different synthesis strategies for the preparation of magadiites as sodic, protonic, and hybrid (inorganic-inorganic and inorganic-organic) materials are discussed along with several routes for obtaining modified magadiites. Also, the use of magadiite in catalytic reactions, notably in ethanol dehydration and fructose conversion reactions, is a growing area of research. Other potential applications include the adsorption and absorption of environmental pollutants (e.g., phenol and methylene blue in wastewater), use as a photocatalyst in the oxidation of toluene, and use in medicine (e.g., as a drug delivery or antibacterial/antifungal agent). This highlights the many opportunities for the development of new synthesis methods to obtain multifunctional materials in the search for new applications.

Effectively Synthesizing SO4/TiO2 Catalyst and Its Performance for Converting Ethanol into Diethyl Ether (DEE)

This SO4/TiO2 catalyst as a heterogeneous acidic catalyst was synthesized in various concentrations of H2SO4. The activity and selectivity of the SO4/TiO2 catalyst on the dehydration reaction of ethanol to diethyl ether were studied as well. The SO4/TiO2 was prepared from TiO2 powder by wet impregnation method with a various aqueous solution of H2SO4 (1; 2; 3 M H2SO4) and calcination temperature (400, 500, and 600 °C) to obtain a catalyst with optimum acidity. The catalysts were characterized using FTIR, XRD, SEM-EDX, SAA, TGA/DSC, and acidity test gravimetrically with ammonia. The liquid product of DEE was analyzed by gas chromatography (GC) to analyze the selectivity of the catalyst. The catalyst TS-3-400 had the highest activity and selectivity in the dehydration reaction of ethanol to diethyl ether at a temperature of 225 °C, with a conversion of 51.83% and a DEE selectivity of 1.72%.

Low temperature ethanol dehydration performed by MOR catalysts obtained from 2D–3D transformation

The silanol groups present on the surface of lamellar silicates are excellent reaction sites for a varied number of chemical modifications. The conversion of these solids into zeolitic structures has shown to be an interesting synthetic alternative, once avoiding hard templating methods and producing materials with particular characteristics. In this work, a post-synthesis OSDA-free procedure was employed for the 2D–3D transformation of Na-RUB-18 lamellar silicate into mordenite zeolite. The conversion was performed at 140 °C and produced small zeolitic crystals (300–500 nm) after 12 and 24 h of crystallization. The reaction presented 65% yield (mol/mol SiO2), producing materials with a similar Si/Al molar ratio (around 6). The 27Al MAS NMR spectra showed signals related to tetrahedrally coordinated aluminum. The N2 adsorption/desorption isotherms confirmed the solids microporous nature and volume (0.36 and 0.43 cm3 g−1). The number of acidic sites was determined by NH3-TPD (976 and 848 µmol g−1), which also revealed sites with weak and moderate to strong acidity. Finally, the samples’ catalytic activity was evaluated by the ethanol dehydration reaction performed at low temperature (150 °C). The synthesized materials were compared to a commercial sample and all the catalysts showed ethanol conversion around 70%, producing ethene and diethyl ether; the latter being the major product at the employed temperature. Unlike the commercial sample, the synthesized ones did not present any deactivation during the time on stream. This feature was attributed to their low-defect structure and subtle mesoporosity.

The impact of preparation route on the performance of silver dodecatungstophosphate/β zeolite catalysts in the ethylene production

Heteropolyacids and their salts comprise catalytic centers for the production of ethylene, one of the most important constituents in the chemical industry. The paper emphasizes different synthesis routes of hybrid materials consisting of dodecatungstophosphoric acid silver salt (AgPW) and β zeolite—stepwise wet impregnation, silver-exchange in β zeolite, and dry mixing of precursors. Composite preparation procedures induced minor effects on the weak acid sites, while strong acid sites were increased significantly. β/AgPW composites prepared by two-steps wet impregnation and ion-exchange procedures have strong acid sites content and total acidity higher in comparison to the pure AgPW salt and β zeolite. This is a result of precursors synergetic effect—cumulative strong acidic sites are generated in the presence of well-dispersed Keggin ions on the zeolite network. Composite samples with a higher content of strong acid centers exhibit higher conversion in the ethanol dehydration reaction, i.e., the ion-exchanged βAgPW sample has attained a conversion over 81%, while the wet-impregnated sample has a significant 86%. The distribution and presence of AgPW active phase are found to be crucial for both stable conversion and high selectivity results in ethylene production from ethanol, which is regarded as one of the most significant processes in environmental and sustainable industrial chemistry.Graphic abstract

Characterization of H4SiW12O40 supported on mesoporous silica (SBA-15), non-structured amorphous silica and γ-alumina

H4SiW12O40 (HSiW) was supported on mesoporous silica (SBA-15), non-structured amorphous silica (AEROSIL) and γ-alumina (Al2O3) by impregnation. The supported HSiW samples were characterized by X-ray diffraction (XRD), N2 adsorption-desorption isotherms, infrared (IR) spectroscopy and ethanol dehydration reaction as a model reaction. HSiW was not highly dispersed even at 29 wt% loading, but the hexahydrate (HSiW·6H2O) was stable under evacuation below 150 °C on silica supports, while destruction of Keggin units occurred on Al2O3. IR spectra of HSiW·6H2O loaded SBA-15 and AEROSIL were analyzed in detail in combination with changes in surface area and XRD patterns. The loaded HSiW·6H2O crystals possessed weak secondary interaction with adjacent silanol groups. The crystal size was increased in three dimensions on AEROSIL by increasing loading amount, while the extension of the size to the pore direction was found on SBA-15. The number of protons in supported HSiW·6H2O was quantified by the integrated intensity of the key band of pyridinium cation (C5H5N+H) at 1538 cm−1 in IR spectra. At high loading (>29 wt%) four hydrogen atoms per Keggin unit in HSiW·6H2O were detected as proton on AEROSIL and SBA-15 with negligible amount of Lewis acid sites, while less than a half on Al2O3 with a majority of Lewis acid sites. Thus, IR method using pyridine as a probe can quantify Brønsted and Lewis acid sites in the absence of thermal decomposition of loaded HSiW·6H2O. It was also found that all the protons detected by pyridine adsorption could not catalyze the reaction over HSiW/Al2O3, suggesting the necessity of a caution to relate the acid amount measured by probe molecules to catalysis.

Precisely regulating the Brønsted acidity and catalytic reactivity of novel allylic C–H acidic catalysts

Due to the lack of effective active centers, the catalytic performances of covalent organic frameworks (COFs) materials are rarely reported. In this work, on the basis of the acidic 1,1,3,3-tetratriflylpropene structure proposed by List et al. (Angew. Chem. Int. Ed.2017, 56, 1411–1415), a series of allylic C–H acids with varied acidic strengths were theoretically designed by altering the terminal functional groups. The acidity of allylic C–H acids was found to be closely related to the electron-withdrawing capacity of terminal substituent groups. Furthermore, the probe molecule approaches and ethanol dehydration reactions were theoretically performed to evaluate the diverse acidity of allylic C–H acids as well as establish the structure–reactivity correlations of such catalytic systems. Moreover, benefiting from allylic C–H acids can be perfectly embedded into the framework structures of COFs, the versatile catalytic performances for these promising porous materials may be realized in the foreseeable future. This work may open up an avenue on the directed design and/or modification of these novel organic solid acid catalysts for practical applications.

Niobium on BEA Dealuminated Zeolite for High Selectivity Dehydration Reactions of Ethanol and Xylose into Diethyl Ether and Furfural.

In this work, we investigated the role of solid-state dealumination by (NH4)2SiF6 (25% Al removal and 13% Si insertion), the impregnation of niobium (10, 18, and 25 wt. %) on dealuminated *BEA (DB) zeolite and their catalytic properties in ethanol and xylose transformations. Among all the studied catalysts, 18%Nb-DB showed increased mesoporosity and external areas. A leveling effect in the number and strength of the proposed two sites (Brønsted and Lewis) present in the catalyst (n1 = 0.24 mmol g−1, −ΔH1 = 49 kJ mol−1, and n2 = 0.20 mmol g−1, –ΔH2 = 42 kJ mol−1) in the catalyst 18%Nb-DB, might be responsible for its good activity. This catalyst presented the highest selectivity for diethyl ether, DEE (97%) with 61% conversion after 50 ethanol pulses at 230 °C (turnover number, TON DEE = 1.15). These features allowed catalytically fruitful bonding of the ethanol molecules to the neighboring sites on the channels, facilitating bimolecular ether formation through a possible SN2 mechanism. The same catalyst was active and selective for transformation of xylose at 180 °C, showing 64% conversion and 51% selectivity for furfural (TON Furfural = 24.7) using water as a green solvent.

Catalytic activity of heteropoly tungstate catalysts for ethanol dehydration reaction: Deactivation and regeneration

The pure and palladium doped 12-tungstophosphoric acid - H3PW12O40 (HPW) and its cesium salts CsxH3-xPW12O40 (x = 1, 2, 2.25 and 2.5) were prepared and characterized by thermal analysis, FTIR, XRD, BET and XPS methods. In this paper were determined the optimal reaction temperature and the effect of palladium on the coke content during the dehydration of ethanol in the temperature range of 200−350 °C. Above 300 °C, a strong deactivation of the catalysts was caused by coke formation. The catalytic tests demonstrate that by supporting the HPW and PdyPW (y = 0.15, 0.2 and 0.25) on mesoporous molecular sieve SBA-15 the catalytic activity in ethanol dehydration reaction was improved. Palladium doping of HPW/SBA-15 significantly decreases the formation of coke deposit. The formation of coke during the ethanol dehydration does not affect the Keggin structure which led us to conclude that such catalysts can be regenerated in air and regain their catalytic activity for a short time.

A computational-experimental investigation on high ethylene selectivity in ethanol dehydration reaction found on WOx/ZrO2-activated carbon bi-support systems

The high ethylene selectivity exhibited on the zirconia-activated-carbon bi-support catalyst is investigated by experiment and density functional theory–based (DFT) analysis. This bi-support catalyst systems prepared by the physical mixing method for the tungsten catalyst show a significant increase in ethylene selectivity up to 90% compared to the zirconia single support system (~58%) during the ethanol dehydration reaction. Besides, the optimal percent weight ratio of zirconia to activated carbon, which results in the highest ethanol conversion is 50:50. The DFT–based analysis is used to investigate high ethylene selectivity in the bi-support system. It shows that the WO5/zirconia is the most stable model for the zirconia single-support tungsten catalyst represented by the zirconia (101) facet of the tetrahedral phase. The carbon atoms were added to the WO5/zirconia to model the tungsten catalyst on the bi-support system. The Bader charge analysis is carried out to determine the electron transfer in the catalyst. The bonding between ethylene and the WO5 active site on the catalyst is weakened when the system is bi-support, where the added carbon atoms on the catalyst in the ZrO2 region decrease the ethylene adsorption energy. Thus, the desorption and the selectivity of ethylene are promoted. The decrease in adsorption energy can be explained via the analysis of the projected density of states (PDOS) profiles of atom involving the adsorption. It was found that the added carbon in the ZrO2 region induces the electron transfer from the ethylene molecule to the surface, especially to the ZrO2 region. The depletion of the electron around the ethylene molecule weakens the bonds, thus, promote desorption. Hence, the advantages of using the bi-support system in the tungsten catalyst are that the catalyst exhibit (1) high conversion due to the zirconia support and (2) high ethylene selectivity due to the added carbon promoting the desorption of ethylene via the induction of electron from an ethylene molecule to surface.