Hydrogenative Ring-Rearrangement of Biobased Furanic Aldehydes to Cyclopentanone Compounds over Pd/Pyrochlore by Introducing Oxygen Vacancies

Upgrading furanic aldehydes (such as furfural or 5-hydroxymethyl furfural) to cyclopentanone compounds (such as cyclopentanone or 3-hydroxymethyl cyclopentanone) is of great significance for the synthesis of high-value chemicals and biomass utilization. Developing an efficient reduced metal/acidic support with Lewis acidity is the key to facilitating the carbonyl hydrogenation and hydrolysis steps in the hydrogenative ring-rearrangement reaction. Herein, three pure Lewis acidic pyrochlore supports of the form A₂B₂O₇ (La₂Sn₂O₇, Y₂Sn₂O₇, and Y₂(Sn_0.7Ce_0.3)₂O_7‑δ) with the same crystal structures and different metals are synthesized. The Lewis acidity and the surface properties of the pyrochlore can be tuned by inserting different kinds of A and B site metals. After impregnation, Pd nanoparticles with appropriate particle sizes are uniformly loaded on the surface of pyrochlore. For the reaction of the furanic aldehydes, all of these pyrochlore-based catalysts exhibit hydrogenation and hydrolysis rates that are both faster than those of traditional support-based catalysts due to the oxygen vacancy and pure Lewis acidity of the support. Among these pyrochlore-based catalysts, Pd/Y₂Sn₂O₇ exhibits activity and selectivity that are higher than those of Pd/La₂Sn₂O₇. Moreover, the Y₂Sn₂O₇-based catalyst partially substituted by Ce³⁺ ions at the B site is more efficient, with the highest cyclopentanone yield and 3-hydroxymethyl cyclopentanone yield of 95.0% and 92.5%, respectively. Furthermore, the catalyst can still maintain an effective activity and stability after 4 runs. This study not only presents an efficient biobased route for the production of cyclopentanone compounds but also focuses on the acid catalytic performance of pyrochlore based on its pure Lewis acidity.