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

Valeric acid (VA), readily obtainable in the biorefinery from sugary biomass streams, can be upgraded to 5-nonanone, a versatile chemical building block 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. This screening reveals a correlation between the metal oxides lattice energy and their catalytic activity for valeric acid ketonization. ZrO2, TiO2, and La2O3, char-acterized 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 ob-served: Cr2O3 and Al2O3 displayed poor catalytic performance despite their elevated lattice energy. The comprehensive characterization of the catalysts, encompassing XRD, N2-physisorption, NH3-TPD, and CO2-TPD analyses, has unveiled the crucial role of important parameters including acid-base properties in addition to lattice energy. Only oxides showing amphoteric properties can catalyse the reaction effectively. Interestingly, low-lattice energy and amphoteric oxides such as SnO2 (showing poor performance) became 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. This study contributes to a refined understanding of catalyst properties governing ketonization efficiency, paving the way for optimizing the conversion of biomass-derived carboxylic acids into valuable biofuel precursors.