LAUSR

Ethanol to n-butanol conversion is a process that can increase the carbon number of alcohols by coupling. There is increasing interest in the mechanisms for n-butanol production in a simple step through the effective use of bifunctional acid–base catalysts. In this context, commercial hydroxyapatite (HAP) and two synthetized model supported catalysts, Ca/Al2O3 and Ca-P/Al2O3, were used in bioethanol condensation. Characterization and acid–base sites were considered, and Fourier-transform infrared (FTIR) spectroscopy and diffuse reflectance infrared Fourier-transform spectroscopy–mass spectrometry (DRIFT-MS) reactivity tests were performed in situ, as a first approximation to design a sustainable catalytic process rationally, and with the aim of understanding the process at the catalytic surface. The results indicated that the reactions occur at a large range of temperatures (200–450 °C). Hydroxyapatite and Ca/Al2O3 have similar basic sites (low and medium) and Ca-P/Al2O3 presented the strongest Brönsted and Lewis combined acid sites. Three major reactions were identified: non-oxidative dehydrogenation, aldol condensation, and intermolecular reduction, associated with the basic-acid sites Ca-O-Ca/Ca-O-P/ Ca-O-Al. Side reactions also occur involving different acid sites related to Lewis alumina centers favoring ethylene or diethyl-ether production. © 2020 Society of Industrial Chemistry and John Wiley & Sons Ltd