Gas phase acetone self-condensation over unsupported and supported Mg–Zr mixed-oxides catalysts

Abstract

Acetone gas phase aldol condensation over bulk and carbon-supported Mg–Zr has been studied in this work. The condensation yields C6 (mainly mesityl oxide) and C9 (phorones, isophorones and mesitylene) compounds, depending on reaction temperature and distribution of acid and basic sites. The influence of the temperature (323–723K) was studied, higher C9 selectivities being obtained at higher temperatures (close to 50%). The influence of the concentration and the distribution of basic and acid sites was analyzed by comparing the results obtained with the bulk Mg–Zr and with Mg–Zr supported on non-microporous carbonaceous materials: high surface area graphites (HSAG) and carbon nanofibers (CNF). In addition, two different preparation methods (dry impregnation and co-precipitation) were tested.The performance of the catalysts is related to the distribution of acid and basic sites. Acid–basic pairs are needed for the acetone condensation, weak acidity for dehydration and cyclation reactions, and the strongest basicity for the condensation of mesityl oxide.