Catalytic upgrading of ethanol to n-butanol over a novel Ca-Fe modified mixed oxide Mg-Al catalyst from hydrotalcite-base precursor

Abstract

n-Butanol is used in a wide range of applications and recently, the use of n-butanol as a fuel, which can be employed pure or blended with gasoline or diesel, has been proposed. So, in an attempt to deepen in the one-step catalytic process to produce n-butanol from ethanol, bifunctional catalysts in different chemical/spatial environment as MgAl- and CaFeMg-multioxide catalysts were developed, prepared and characterized. Both mixed oxides were obtained by thermal decomposition of the synthesized hydrotalcites considering the partial substitution of Mg 2+ and Al 3+ by Ca 2+ and Fe 3+ , namely MgAl-Ox and Ca basic properties of the samples were analyzed employing NH 3 and CO 20 2 Fe 20 MgAl-Ox. The nature of acid and as probe molecules, and TPD analysis were performed to quantify the relative contribution of acidic/basic sites. Ca 20 Fe 20 MgAl-Ox sample presented an improved basicity with minimal acidity reduction. The performances of the activated catalysts were measured in a fixed-bed reactor under transient and continuous operation modes by DRIFT-MS studies and under transient pulse experiments. It was verified that both catalysts, but specially Ca 20 C 4 Fe 20 MgAl-Ox, promote the synthesis of -compounds from ethanol due to the modulated acid and basic sites capable of modify the ethanol adsorption in the form of ethoxy-species and a combined higher basicity with centers to catalyze the hydrogenation using the ethanol as the hydrogen donor. Ca 20 71% at 400 ◦ Fe 20 MgAl-Ox reached ethanol conversion values of 36% at 280 C with a higher selectivity to n-butanol and other C 4 ◦ C and -compounds. Two parallel routes at differentiated temperatures: direct acetaldehyde self-condensation and the intermediary crotyl alcohol transfer hydrogenation, were evidenced and prevailing in n-butanol formation.