Catalytic Relevance of Mg-Al-O Basic Centers in the Upgrade of Ethanol to n-Butanol

Abstract

The catalytic relevance of different surface functionalities present on hydrotalcite-derived Mg−Al mixed metal oxides (MgAlO) are investigated in the context of ethanol upgrade to n-butanol. The catalyst structure and active sites were altered through changes in the Mg/Al ratio and introduction of additional redox metal oxide functionalities. After performing a series of catalytic activity tests, operando FTIR characterization, TGA measurements and in situ active center titration; qualitative and quantitative relationships between catalyst structure and catalytic performance are obtained. We found the Mg−Al mixed metal oxides system can catalyze the ethanol to n-butanol process through a Guerbet reaction pathway, though the process is kinetically limited. By introducing redox active metal oxides to the catalyst formulation, such as MoO3 or V2O5, this problem can be partially solved, but at a cost of losing a significant fraction of high-strength basic centers which are the most catalytically relevant function in the system, as they control enolate formation rates leading to the C−C coupling step required for n-butanol formation.