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 H-2 carrier gas, WHSV =1 g(EtOH).g(cat)(-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 H-2; 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.