In situ infrared spectroscopic study of the reaction pathway of the direct synthesis of n-butanol from ethanol over MgAl mixed-oxide catalysts

Ethanol Coupling Reactions over MgO-Al2O3 Mixed Oxide-Based Catalysts for Producing Biofuel Additives

Catalytic conversion of ethanol to 1-butanol was studied over MgO-Al₂O₃ mixed oxide-based catalysts. Relationships between acid-base and catalytic properties and the effect of active metal on the hydrogen transfer reaction steps were investigated. The acid-base properties were studied by temperature-programmed desorption of CO₂ and NH₃ and by the FT-IR spectroscopic examination of adsorbed pyridine. Dispersion of the metal promoter (Pd, Pt, Ru, Ni) was determined by CO pulse chemisorption. The ethanol coupling reaction was studied using a flow-through microreactor system, He or H₂ carrier gas, WHSV = 1 gEtOH·gcat.-1·h-1, at 21 bar, and 200-350 °C. Formation and transformation of surface species under catalytic conditions were studied by DRIFT spectroscopy. The highest butanol selectivity and yield was observed when the MgO-Al₂O₃ catalyst contained a relatively high amount of strong-base and medium-strong Lewis acid sites. The presence of metal improved the activity both in He and H₂; however, the butanol selectivity significantly decreased at temperatures ≥ 300 °C due to acceleration of undesired side reactions. DRIFT spectroscopic results showed that the active metal promoted H-transfer from H₂ over the narrow temperature range of 200-250 °C, where the equilibrium allowed significant concentrations of both dehydrogenated and hydrogenated products.

Optimal Conditions for Butanol Production from Ethanol over MgAlO Catalyst Derived from Mg-Al Layer Double Hydroxides

The MgAlO catalyst was obtained from thermal decomposition of the MgAl-LDH catalyst having Mg/Al molar ratio of 5. The catalytic Guerbet reaction of ethanol was investigated to determine the effect of WHSV and nitrogen flow rate on butanol production and product distribution. It was performed in a fixed-bed microreactor under continuous flow of vaporized ethanol mixed with N₂. The MgAlO catalyst had high total basic sites and high total acid sites that were crucial for ethanol Guerbet reaction. The MgAlO catalyst showed the highest butanol selectivity at 300℃ under WHSV = 3.10 h^-1 and nitrogen flow rate = 3,600 mL/h, and the highest butanol yield at 400℃ under WHSV = 3.10 h^-1 and nitrogen flow rate = 900 mL/h. It can be summarized that in order to enhance the butanol yield, the low WHSV is preferred to increase the contact time of ethanol and catalyst under moderate temperature.

Renewable Butanol Production via Catalytic Routes

Fluctuating crude oil price and global environmental problems such as global warming and climate change lead to growing demand for the production of renewable chemicals as petrochemical substitutes. Butanol is a nonpolar alcohol that is used in a large variety of consumer products and as an important industrial intermediate. Thus, the production of butanol from renewable resources (e.g., biomass and organic waste) has gained a great deal of attention from researchers. Although typical renewable butanol is produced via a fermentative route (i.e., acetone-butanol-ethanol (ABE) fermentation of biomass-derived sugars), the fermentative butanol production has disadvantages such as a low yield of butanol and the formation of byproducts, such as acetone and ethanol. To avoid the drawbacks, the production of renewable butanol via non-fermentative catalytic routes has been recently proposed. This review is aimed at providing an overview on three different emerging and promising catalytic routes from biomass/organic waste-derived chemicals to butanol. The first route involves the conversion of ethanol into butanol over metal and oxide catalysts. Volatile fatty acid can be a raw chemical for the production of butanol using porous materials and metal catalysts. In addition, biomass-derived syngas can be transformed to butanol on non-noble metal catalysts promoted by alkali metals. The prospect of catalytic renewable butanol production is also discussed.

Ethanol condensation at elevated pressure over copper on AlMgO and AlCaO porous mixed-oxide supports

The coupling of ethanol to produce C₄-compounds by Guerbet condensation at 325 °C was studied using porous mixed oxide catalysts of AlMgO and AlCaO prepared by the emulsion mediated method with and without the addition of Cu.

Role of Different Feedstocks on the Butanol Production Through Microbial and Catalytic Routes

Among the renewable fuels, butanol has become an attractive, economic and sustainable choice because of cost elevation in petroleum fuel, diminishing the oil reserves and an increase of green house effect. Butanol can be derived from renewable sources by using the natural bio-resources and agro-wastes such as orchard wastes, peanut wastes, wheat straw, barley straw and grasses via Acetone Butanol Ethanol (ABE) process. On the other hand, butanol can be directly formed from chemical route involving catalysts also such as from ethanol through aldol condensation. This review presents extensive evaluation for the production of butanol deploying microbial and catalytic routes.

Catalytic Upgrading of Ethanol to n-Butanol: Progress in Catalyst Development

Because n-butanol as a fuel additive has more advantageous physicochemical properties than those of ethanol, ethanol valorization to n-butanol through homo- or heterogeneous catalysis has received much attention in recent decades in both scientific and industrial fields. Recent progress in catalyst development for upgrading ethanol to n-butanol, which involves homogeneous catalysts, such as iridium and ruthenium complexes, and heterogeneous catalysts, including metal oxides, hydroxyapatite (HAP), and, in particular, supported metal catalysts, is reviewed herein. The structure-activity relationships of catalysts and underlying reaction mechanisms are critically examined, and future research directions on the design and improvement of catalysts are also proposed.

Chemicals from ethanol: the acetone synthesis from ethanol employing Ce0.75Zr0.25O2, ZrO2 and Cu/ZnO/Al2O3

Acetone is an important solvent and widely used in the synthesis of drugs and polymers. Currently, acetone is mainly generated by the Cumene Process, which employs benzene and propylene as fossil raw materials. Phenol is a co-product of this synthesis. However, this ketone can be generated from ethanol (a renewable feedstock) in one-step. The aim of this work is to describe the influence of physical–chemical properties of three different catalysts on each step of this reaction. Furthermore, contribute to improve the description of the mechanism of this synthesis. The acetone synthesis from ethanol was studied employing Cu/ZnO/Al₂O₃, Ce_0.75Zr_0.25O₂ and ZrO₂. It was verified that the acidity of the catalysts needs fine-tuning in order to promote the oxygenate species adsorption and avoid the dehydration of ethanol. The higher the reducibility and the H₂O dissociation activity of the catalysts are, the higher the selectivity to acetone is. In relation to the oxides, these properties are associated with the presence of O vacancies. The H₂ generation, which occurs during the TPSR, indicates the redox character of this synthesis. The main steps of the acetone synthesis from ethanol are the generation of acetaldehyde, the oxidation of this aldehyde to acetate species (which reduces the catalyst), the H₂O dissociation, the oxidation of the catalyst producing H₂, and, finally, the ketonization reaction. These pieces of information will support the development of active catalysts for not only the acetone synthesis from ethanol, but also the isobutene and propylene syntheses in which this ketone is an intermediate.Graphical abstract