Mg and Al mixed oxides and the synthesis of n-butanol from ethanol

n-Butanol is used in a wide range of applications, especially for the production of paint, solvents and plasticizers. Recently, some companies have proposed the use of n-butanol as a fuel, which can be employed pure or blended with gasoline or diesel. At present, there is great interest in developing a one-step process that generates n-butanol from ethanol. Some works showed that Mg–Al mixed oxides are very promising catalysts for this matter. Analyzing the physical–chemical properties of these catalysts, this work aims at further studying this reaction. The Mg–Al mixed oxides were obtained by thermal decomposition of hydrotalcites employing two Mg/Al different ratios. Magnesium oxide (MgO) and alumina (Al2O3) were also prepared following the same synthetic route used for the Mg–Al mixed oxides. The synthesized samples were characterized by the following techniques: XRD, NMR, BET and XRF. The acid and basic properties of the samples were also analyzed employing probe molecules. The catalytic tests were performed using a fixed bed reactor at atmospheric pressure. It was verified that the Mg and Al mixed oxides are able to promote the synthesis of C4 compounds from ethanol. Adjacent acid and medium basic sites are needed in order to generate the intermediate compounds. These pairs of acid and medium basic sites are obtained by the insertion of Al in the MgO lattice or in consequence of the presence of Mg in the γ-Al2O3 lattice. It was observed that the higher the concentration of Mg is, the higher the hydrogenation capacity of the catalyst, since a greater selectivity to n-butanol was observed. Strong basic sites and a specific superficial atomic arrangement seem not to be essential for the synthesis of C4 from ethanol.

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► The n-butanol one-step synthesis requires adjacent acid and medium basic sites.
► These pairs are generated by Al in the MgO lattice and also Mg in the γ-Al2O3.
► The C4 synthesis from ethanol does not require strong basic sites.
► High Mg concentration promotes the hydrogenation of C4 compounds to n-butanol.