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

• Published in: Molecules (Basel, Switzerland) Vol. 28; no. 9; p. 3788
• Main Authors: Vikár, Anna, Lónyi, Ferenc, Makoye, Amosi, Nagy, Tibor, Novodárszki, Gyula, Barthos, Róbert, Szabó, Blanka, Valyon, József, Mihályi, Magdolna R., Deka, Dhanapati, Solt, Hanna E.
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 28.04.2023; MDPI
• Subjects: Acceleration; Acids; Additives; Alcohol; Aluminum oxide; Ammonia; Biofuels; Butanol; Carbon dioxide; Carrier gases; Catalysts; Catalytic converters; Chemical reactions; Chemisorption; Dehydrogenation; DRIFT spectroscopy; Ethanol; ethanol coupling to butanol; Guerbet reaction; Helium; Hydrogen; Hydrogenation; Infrared spectroscopy; Lewis acid; Magnesium oxide; Metals; MgO–Al2O3 mixed oxide-based catalyst; Microreactors; Mixed oxides; Palladium; Particle size; Pore size; Side reactions
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules28093788

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.