Ketonization of Valeric Acid to 5‐Nonanone over Metal Oxides catalysts

Valeric acid (VA), readily obtainable in the biorefinery from sugary biomass, can be upgraded to 5‐nonanone, a versatile chemical with numerous applications. This study investigates the performance of nine metal oxide catalysts (SnO2, SiO2, Y2O3, CeO2, ZrO2, TiO2, La2O3, Cr2O3, and Al2O3) in the gas‐phase ketonization of VA to 5‐nonanone in the 350‐450°C range. The screening reveals a correlation between the metal oxides lattice energy and their catalytic activity for valeric acid ketonization.ZrO2, TiO2, and La2O3, characterized by high lattice energy, demonstrate the highest catalytic activity. Y2O3, SnO2, SiO2, showing low lattice energy, are barely active. However, exceptions to this trend were observed: Cr2O3 and Al2O3 displayed poor catalytic performance despite their elevated lattice energy. A comprehensive characterization of the catalysts, encompassing XRD, N2‐physisorption, NH3‐TPD, and CO2‐TPD analyses, unveiled the role of important parameters including acid‐base properties in addition to lattice energy. Only oxides showing amphoteric properties can catalyse the reaction effectively. Low‐lattice energy and amphoteric oxides such as SnO2 (showing poor performance) become significantly active at higher temperature (500°C). Analysis of by‐products by online GC‐MS and spent catalyst characterization indicated that in this case the ketonization mechanism changed from the so‐called surface mechanism to the so‐called bulk mechanism.