Ethanol Dehydration Reaction Research Articles

A Comparative Study of Different Al-based Solid Acid Catalysts for Catalytic Dehydration of Ethanol

In this present study, the catalytic dehydration of ethanol over three different Al-based solid acid catalysts including H-beta zeolite (HBZ), modified H-beta zeolite with γ-Al 2 O 3 (Al-HBZ) and mixed γ- χ phase of Al 2 O 3 (M-Al) catalysts was investigated. The ethanol dehydration reaction was performed at temperature range of 200 to 400 o C. It revealed that all catalysts exhibited higher ethanol conversion with increased temperatures. At low temperatures (ca. 200 to 250 o C), diethyl ether (DEE) was obtained as a major product for all catalysts. However, with increased temperatures (ca. 300 to 400 o C), ethylene was a major product. Among all catalysts, HBZ exhibited the highest ethanol conversion giving the ethylene yield of 99.4% at 400 o C. This can be attributed to the largest amount of weak acid sites present in HBZ, which is related to the Bronsted acid. It should be mentioned that HBZ also rendered the highest yield of DEE (ca. 35.3%) at 250 o C. As the results, HBZ catalyst is promising to produce ethylene and DEE from ethanol, which is considered as cleaner technology.

Light olefins from renewable resources: Selective catalytic dehydration of bioethanol to propylene over zeolite and transition metal oxide catalysts

Propylene is an important constituent of many products that we rely upon in our daily life. This essential raw material is currently produced from fossil-derived feedstocks such as oil and natural gas. However, conversion of bioethanol to propylene represents an interesting opportunity for the utilization of renewable feedstocks such as bioethanol as one of the main biomass-derived products via dehydration process. The catalytic production of propylene from bioethanol has gained significant attention recently as a renewable alternative to conventional technologies. This review will discuss the state-of-the-art on the use of catalytic materials, such as zeolites and transition metals, in catalytic conversion of bioethanol to propylene and related reactions. The corresponding mechanisms are reviewed with emphasis on the possibilities provided by these materials to develop alternative processes for selective production of propylene and other olefins from bioethanol. Important aspects such as catalyst texture and architecture, the impact of promoters and co-feeding water on ethanol to propylene reaction and fundamental understanding of reaction mechanisms involved in ethanol dehydration reaction are discussed accordingly.

High field 27Al MAS NMR and TPD studies of active sites in ethanol dehydration using thermally treated transitional aluminas as catalysts

High field quantitative 27Al single pulse (SP) MAS NMR combined with temperature programmed desorption (TPD) of ethanol is used to study the surface of γ-Al2O3 during phase transformation processes induced by calcination in the temperature range of 500–1300°C. Following ethanol adsorption, ethylene is generated during TPD with a desorption temperature above 200°C. The amount of ethylene decreases monotonically with increasing calcination temperature prior to TPD. Significantly, 27Al SP MAS NMR reveals that the amount of penta-coordinated Al3+ ions also decreases with increasing calcination temperature. A quantitative (within experimental error) correlation between the amount of penta-coordinated Al3+ ions and the amount of strongly adsorbed ethanol molecules (i.e., the ones that convert to ethylene during TPD) is obtained. These results provide good evidence for a proposal that the penta-coordinated aluminum sites are the catalytic active sites on alumina surfaces during ethanol dehydration reaction across the entire course of γ-to-α Al2O3 phase transformations.

Hydrothermally Synthesized Ceria with a High Specific Surface Area for Catalytic Conversion of Ethanol to Ethylene

Morphological control can be used to improve the catalytic activity of cerium oxide (ceria, CeO2). In this study, ceria with a high specific surface area was synthesized via the hydrothermal reaction of ceric nitrate and was tested for the catalytic conversion of ethanol to ethylene. As a reference, ceria was also synthesized via a precipitation reaction of cerous nitrate using aqueous ammonia. The Japan reference catalyst JRC-CEO-1 also served as a reference. The specific surface area of the hydrothermally synthesized ceria was as high as that of JRC-CEO-1, but was much higher than that of either reference after calcination at 873 K. Thermogravimetric analysis and IR spectroscopy revealed that the cerias made by hydrothermal and precipitation reactions consisted of high-purity CeO2, whereas JRC-CEO-1 contained 1.5% decomposable functional groups (OH-, CO3 2-). For both ethanol conversion and ethylene selectivity in a catalytic dehydration reaction of ethanol, the activity of the hydrothermally developed ceria was higher than that for either reference. The reaction pathway for the dehydration reaction of ethanol over ceria showed that the specific surface area and the basicity of the Lewis basic sites of the ceria were influential properties. The high catalytic activity of the hydrothermally synthesized ceria was derived from its high specific surface area and high-purity CeO2.

Effect of Mo-Doped Mesoporous Al-SSP Catalysts for the Catalytic Dehydration of Ethanol to Ethylene

The catalytic dehydration of ethanol to ethylene over the mesoporous Al-SSP and Mo-doped Al-SSP catalysts was investigated. The Al-SSP catalyst was first synthesized by the modified sol-gel method and then doped with Mo by impregnation to obtain 1% Mo/Al-SSP and 5% Mo/Al-SSP catalysts (1 and 5 wt% of Mo). The final catalysts were characterized using various techniques such as XRD, N2physisorption, SEM/EDX, TEM, and NH3-TPD. The catalytic activity for all catalysts in gas-phase ethanol dehydration reaction was determined at temperature range of 200°C to 400°C. It was found that the most crucial factor influencing the catalytic activities appears to be the acidity. The acid property of catalysts depended on the amount of Mo loading. Increased Mo loading in Al-SSP resulted in increased weak acid sites, which enhanced the catalytic activity. Besides acidity, the high concentration of Al at surface of catalyst is also essential to obtain high activity. Based on the results, the most suitable catalyst in this study is 1% Mo/Al-SSP catalyst, which can produce ethylene yield of ca. 90% at 300°C with slight amounts of diethyl ether (DEE) and acetaldehyde.

Modification of ferrierite through post-synthesis treatments. Acidic and catalytic properties

The main emphasis of this work was placed on a detailed characterization of structural, textural and acidic properties of FER zeolites with different Si/Al ratios in terms of their activity in ethanol dehydration reaction. Subsequent dealumination and desilication procedures were found to be an efficient methods of a secondary system of mesopore generation in the ferrierite crystals with preservation of their microporous characteristics. Through ethanol dehydration both the acidic and the textural features have a significant influence on catalytic performance of hierarchical ferrierites. It was shown that higher catalytic activity and selectivity to ethylene is ensured by zeolites with highly preserved microporous characteristic, i.e. well-developed micropore area and intrinsic acidity.

Computational Study of Ethanol Conversion on Al8O12 as a Model for γ-Al2O3

Correlated molecular orbital theory at the coupled cluster CCSD(T) level with density functional theory geometries is used to study ethanol dehydration, dehydrogenation, and condensation reactions on an the Al8O12 cluster which is a model for γ-Al2O3. The Al in the active site on the cluster is a strong Lewis acid. The reactions begin with formation of a very stable Lewis acid–base ethanol–cluster adduct. Dehydration proceeds by β-H transfer to a bicoordinate oxygen leading to the direct formation of ethylene and two OH groups following an E2 mechanism. Dehydrogenation proceeds directly by α-H transfer to the active metal center and a proton transfer to a bicoordinate bridge O to form acetaldehyde plus a metal hydride and a hydroxyl, again an E2 mechanism. After addition of a second ethanol, diethyl ether is generated by an α-C transfer from the first to the second ethanol, an acid-driven SN2 mechanism. Condensation and dehydration with two alcohols have comparable energy barriers. The addition of a secon...

Synthesis of framework lithium zirconium molybdate phosphates and their catalytic properties in ethanol conversion reactions

We have synthesized NASICON-type mixed phosphates with the general formula Li1 − xZr2P3 − xMoxO12, having different degrees of molybdenum substitution (x = 0, 0.1, 0.5, 1.0) and ranging in particle size from 50 to 300 nm. Their structure and morphology have been investigated using X-ray diffraction, scanning electron microscopy, and X-ray microanalysis. Analysis of the catalytic properties of the synthesized compounds in ethanol conversion reactions demonstrates that all of them exhibit catalytic activity for ethanol dehydration and dehydrogenation reactions and that the relationship between them depends on molybdenum content.

Simple synthesis of Al2O3 sphere composite from hybrid process with improved thermal stability for catalytic applications

Aluminium oxide spheres were synthesized by the hybrid process applying the biopolymer chitosan. After the calcination process the porous spheres were characterized by Chemical elemental analysis (XRF), X-ray diffraction (XRD), Scanning electron microscopy and Energy Dispersive X-ray Spectroscopy (SEM-EDS), N2 adsorption–desorption isotherms, infrared spectroscopy (IR), and CO2 temperature programmed desorption (CO2-TPD). The effect of thermal treatment on surface properties of the oxide spheres was also evaluated by the catalytic ethanol dehydration reaction. The hybrid method produced interesting results related to the thermal stability against sintering process and consequently low decreases of surface area. The hybrid spheres calcination at 900 and 1200 °C produced a metastable phases of alumina with a high surface area, and nanometric crystallites. Additionally, the spheres of mixed silica-alumina synthesized by this method reveal the formation of porous spheres with highly acidic OH groups, which was suggested by the catalytic performance.

Hydrogen by steam reforming of ethanol over Co–Mg incorporated novel mesoporous alumina catalysts in tubular and microwave reactors

Bio-ethanol is an excellent hydrogen carrier with a good potential to be used as a resource for on-board hydrogen production. In this work, a set of new Co incorporated mesoporous alumina (MA) catalysts, which were modified with Mg, were synthesized and tested in steam reforming of ethanol. Results proved that, the synthesis route of these materials had a highly significant effect on their catalytic performances. Co@Mg–MA and Co–Mg–MA catalysts, which were prepared by direct addition of Mg into the mesoporous alumina framework, gave the best performance in steam reforming of ethanol, with very high hydrogen yield values. This was concluded to be due to the presence of Co0 and CoO phases within the structures of these catalysts. However, Co–Mg@MA and Co@MA catalysts, which were prepared by the impregnation of Co/Mg or Co into mesoporous alumina, mainly catalyzed ethanol dehydration reaction to yield ethylene, rather than steam reforming. This was concluded to be due to the high Lewis acidity of these catalysts and the presence of cobalt aluminate phase in their structure. Activity tests of the synthesized catalysts were made both in a tubular reactor which was conductively heated and also in a focused-microwave system. Better energy utilization and more stable performance with much less coke formation were achieved in the focused-microwave reactor than the conventionally heated system.

Surface and catalytic properties of some γ-Al2O3 powders

The physicochemical and catalytic properties of some γ-Al2O3 samples have been investigated by XRD, SBET, porosity measurements, TEM, chemical analysis (ICP-MS) and IR spectroscopy of the surface OH groups and of adsorbed CO and pyridine. Catalytic activities in the ethanol dehydration reaction were also studied in gas phase in a tubular flow reactor from 423K to 723K at atmospheric pressure with 1.44h−1 WHSV in nitrogen as well as by ethanol temperature programmed reaction (Ethanol-TPR) in a TG/DTA/MS thermal analyzer. Even small amounts of alkali (300ppm) modify significantly the spectra in the OH stretching region and kill part of the alumina strongest Lewis acid sites with a clear decrease of catalytic activity, while 1% Na completely modifies the surface behaviour. Differences are also observed for clean samples showing slightly different morphology (lamellar versus bulky). The data showed that the catalytic activity of γ-Al2O3 is determined by a small number of sites, which are likely located on edges, corners and defects of the crystals more than on plain surfaces.

Site-Dependent Lewis Acidity of γ-Al2O3and Its Impact on Ethanol Dehydration and Etherification

We examine the heterogeneity of the Lewis acidity on the (100) and (110) facets of γ-Al2O3 by computing the binding energies of various oxygenates, in addition to the reaction barriers of dehydration and etherification reactions of ethanol. We show that the ethanol dehydration barrier is moderately affected by site heterogeneity (barriers between 1.2 and 1.6 eV); in contrast, a nearly 3-fold change in the ethanol etherification barrier is found among the various Al3+ sites. In order to rationalize these results, the s-conduction band mean of the Al3+ sites is introduced as a descriptor to characterize the ability to transfer electron charge from the adsorbate to the Lewis acid site. It is shown for the first time that this descriptor quantitatively correlates the oxygenate binding energies and the ethanol dehydration reaction barriers. However, for the ethanol etherification reactions the s-conduction band mean of the Al3+ sites describes barriers only qualitatively due to the bimolecular nature of this reaction, which results in a change in the nucleophilicity of the ethoxy species by a nearby adsorbed ethanol. As a result, the strength of the Lewis acid sites is not the only descriptor for etherification chemistry. Hydration of the (110) facet indicates an increase in Lewis acidity strength as described by the s-conduction band mean that results in stronger binding. However, this increase in Lewis acidity results in either a negligible change of the ethanol dehydration reaction barriers on some sites or an increase due to a reduction in the basicity of the adjacent oxygen by the dissociated water. Similarly, ethanol etherification is slowed down by the presence of water due primarily to the change in nucleophilicity of the ethoxy species. Overall, our results clearly indicate that while the binding energy is an excellent descriptor of Lewis acidity strength and dehydration chemistry on the clean alumina surfaces, cooperative phenomena (i.e., modulation of the nucleophilicity of the ethoxy by the nearby oxygen or water and the basicity of oxygen in the presence of water) are key issues that lead to a breakdown in the correlation between Lewis acid strength in terms of the binding energy or the s-conduction band mean and the reaction barriers.

Kinetics and Mechanism of Ethanol Dehydration on γ-Al2O3: The Critical Role of Dimer Inhibition

Steady state, isotopic, and chemical transient studies of ethanol dehydration on γ-alumina show unimolecular and bimolecular dehydration reactions of ethanol are reversibly inhibited by the formation of ethanol–water dimers at 488 K. Measured rates of ethylene synthesis are independent of ethanol pressure (1.9–7.0 kPa) but decrease with increasing water pressure (0.4–2.2 kPa), reflecting the competitive adsorption of ethanol–water dimers with ethanol monomers; while diethyl ether formation rates have a positive, less than first order dependence on ethanol pressure (0.9–4.7 kPa) and also decrease with water pressure (0.6–2.2 kPa), signifying a competition for active sites between ethanol–water dimers and ethanol dimers. Pyridine inhibits the rate of ethylene and diethyl ether formation to different extents verifying the existence of acidic and nonequivalent active sites for the dehydration reactions. A primary kinetic isotope effect does not occur for diethyl ether synthesis from deuterated ethanol and onl...

酸化コバルトの酸性度に対する硫酸塩含浸法による硫酸化の影響

To enhance the acidity of cobalt oxide, sulfation was carried out using aqueous solution of cobalt sulfate impregnated on cobalt oxide and the product calcined at high temperatures. Conventional sulfation of oxides by sulfuric acid could not avoid dissolution of cobalt oxide in the sulfuric acid. The activity of cobalt oxide for acid-catalyzed ethanol dehydration reaction was greatly enhanced by sulfation using cobalt sulfate. The activity of the prepared sulfated cobalt oxide was comparable to that of conventional SiO2–Al2O3 acid catalyst. The sulfated cobalt oxide did not show activity for pentane isomerization, which was catalyzed by sulfated zirconia prepared by the same methodology of sulfate salt impregnation, using zirconium sulfate solution was impregnated onto zirconia. The highest activity was obtained by heat treatment at 1073 K. This treatment temperature is the highest among solid acid catalysts reported so far.

Dimethyl ether, diethyl ether & ethylene from alcohols over tungstophosphoric acid based mesoporous catalysts

Tungstophosphoric acid (TPA) incorporated silicate structured new mesoporous catalysts were synthesized following one-pot hydrothermal and impregnation procedures. Surface area of TPA@MCM-41, which was prepared by impregnating TPA into MCM-41, was two orders of magnitude higher than the surface area of pure TPA and this catalyst showed very high activity in dehydration reactions of both ethanol and methanol. Ethanol fractional conversion values reaching to 1.0 was obtained at 300°C at a space time of 0.27s.g/cm3, over TPA@MCM-41. Diethyl ether selectivity showed a decreasing trend by increasing temperature from 180 to 400°C in ethanol dehydration reaction. Ethylene yield values approaching to 100% were obtained at temperatures over 250°C. DME yield passed through a maximum at about 200°C with this catalyst, over which coke formation caused catalyst deactivation. One-pot hydrothermal synthesis procedure was very successful to synthesize a catalyst (TRC-W40) which did not lose any activity after repeated washing steps. This catalyst gave highly stable catalytic performance in dehydration of both ethanol and methanol. Well dispersed WOx clusters were formed within the mesoporous silicate matrix of this material. This catalyst showed very good activity in dehydration reactions of alcohols, giving 100% conversion in ethanol dehydration at 400°C and 100% DME selectivity in methanol dehydration at temperatures less than 300°C.

Synthesis, characterization and catalytic properties of nanocrystaline Y2O3-coated TiO2 in the ethanol dehydration reaction

In the present study, TiO 2 nanopowder was partially coated with Y 2 O 3 precursors generated by a sol-gel modified route. The system of nanocoated particles formed an ultra thin structure on the TiO 2 surfaces. The modified nanoparticles were characterized by high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD) analysis, Zeta potential and surface area through N 2 fisisorption measurements. Bioethanol dehydration was used as a probe reaction to investigate the modifications on the nanoparticles surface. The process led to the obtainment of nanoparticles with important surface characteristics and catalytic behavior in the bioethanol dehydration reaction, with improved activity and particular selectivity in comparison to their non-coated analogs. The ethylene production was disfavored and selectivity toward acetaldehyde, hydrogen and ethane increased over modified nanoparticles.

Ethanol Steam Reforming over La<sub>2</sub>O<sub>2</sub>CO<sub>3</sub> Supported Ni-Ru Bimetallic Catalysts

A series of Ni-Ru bimetallic catalysts over La2O2CO3 are prepared by an impregnation method. The catalytic properties are evaluated in ethanol steam reforming reaction from 350 to 700 °C under atmospheric pressure. Ni-Ru/La2O2CO3 containing 6 wt% Ni and 3 wt% Ru is found to be more efficient, and Ni-La composite oxide could be formed in the catalyst. Ru is more active in the ethanol dehydration reaction to form ethylene than Ni. The presence of Ru could improve the selectivity for hydrogen of Ni catalyst. TG results reveal that Ni-Ru/La2O2CO3 has excellent resistance to carbon deposition.

(100) facets of γ-Al2O3: The Active Surfaces for Alcohol Dehydration Reactions

Temperature programmed desorption (TPD) of ethanol, as well as ethanol and methanol dehydration reactions were studied on γ-Al2O3 in order to identify the active catalytic sites for alcohol dehydration reactions. Two high temperature (>473 K) desorption features were observed following ethanol adsorption. Samples calcined at T ≤ 473 K displayed a desorption feature in the 523–533 K temperature range, while those calcined at T ≥ 673 K showed a single desorption feature at 498 K. These two high temperature desorption features correspond to the exclusive formation of ethylene on the Lewis (498 K) and Bronsted acidic (~525 K) sites. The amount of ethylene formed under conditions where the competition between water and ethanol for adsorption sites is minimized is identical over the two surfaces. Furthermore, a nearly 1-to-1 correlation between the number of under-coordinated Al3+ ions on the (100) facets of γ-Al2O3 and the number of ethylene molecules formed in the ethanol TPD experiments on samples calcined at T ≥ 673 K was found. Titration of the penta-coordinate Al3+ sites on the (100) facets of γ-Al2O3 by BaO completely eliminated the methanol dehydration reaction activity. These results demonstrate that in alcohol dehydration reactions on γ-Al2O3, the (100) facets are the active catalytic surfaces. The observed activities can be linked to the same Al3+ ions on both hydrated and dehydrated surfaces: penta-coordinate Al3+ ions (Lewis acid sites), and their corresponding –OH groups (Bronsted acid sites), depending on the calcination temperature. Temperature-programmed desorption of ethanol, as well as steady state dehydration reactions of ethanol and methanol, indicate that the (100) facets are the primary active surfaces of γ-Al2O3. The active centers on both the hydroxylated and dehydroxylated (100) facets are related to the coordinatively unsaturated Al3+ ions

Solvent effects in liquid-phase dehydration reaction of ethanol to diethylether catalysed by sulfonic-acid catalyst

The liquid-phase dehydration of ethanol to diethylether over heterogeneous sulfonic-acid catalysts was carried out in a stirred batch reactor. The different Amberlyst catalysts were found to have similar activities for this reaction; even though Amberlyst 70 showed a lower acid capacity compensated by a higher specific activity. By comparing the conversion of ethanol as a function of reaction mixture composition, it was found that reaction rates greatly depended on ethanol concentration but also on reaction mixture polarity. The swelling of the used resins could not explain the observed variations of initial reaction rate since this effect was observed both with resins and with homogeneous catalyst, i.e. p-toluenesulfonic acid. The initial ethanol concentration has a complex effect on initial reaction rates that could not be correlated by usual kinetic models. Taking account of the intrinsic reactivity trends of the SN 2 etherification reaction, a strong dependence was found between solvent properties and initial reaction rate.

Molybdenum oxide modified HZSM-5 catalyst: Surface acidity and catalytic performance for the dehydration of aqueous ethanol

The catalytic dehydration of ethanol into ethylene was studied over 5 wt% Mo/HZSM-5 prepared by impregnation. The effect of calcination temperature on the structure, acidity and catalytic performance of the catalysts was investigated by XRD, N 2 adsorption, NH 3-TPD and TG. A correlation between the catalytic performance of Mo modified catalysts and the amount of weak and medium acidity was observed. It was found that 5 wt% Mo/HZSM-5 catalyst calcined at 500 °C exhibited the highest weak and medium acidity and much better catalytic performance in ethanol dehydration reaction compared with HZSM-5. TPR characterization showed that the Mo species on the external surface of HZSM-5 was easier to be reduced during the reaction. Combining quantitative analyses of NH 3-TPD and H 2-TPR profiles of fresh and used catalysts revealed that the decrease of weak and medium acidity could be correlated with the reduction of Mo species. It is proposed that reduction of Mo species caused the decrease of weak and medium acidity, which contributed to activity drop at the initial reaction stage.