Deciphering catalyst failure: Sulphur–palladium interplay in the one-pot conversion of furfural to isopropyl levulinate

Abstract

Understanding why multifunctional catalysts fail is critical to advancing biomass valorisation strategies. In this study, we systematically investigate the dynamic deactivation mechanisms that limit the one-pot cascade conversion of furfural (FF) to alkyl levulinates via sequential hydrogenation and alcoholysis. To this end, we designed a series of bifunctional Pd/SO₄^2--ZrO₂–carbon composites derived from NH₂-UiO-66(Zr) through pyrolysis, followed by mechanochemical functionalization. Rather than focusing on catalytic performance, our goal was to elucidate how variations in synthetic protocol – specifically the sequence of pyrolysis, sulphation, calcination atmosphere, and reduction steps – influence structural evolution, Pd–sulphur interactions, and active site accessibility. Through a broad multi-technique characterization campaign, we reveal that Pd deactivation by sulphur is a gradual and reversible process, closely related to the catalyst’s thermal history. While high-temperature H₂ treatments can restore Pd accessibility, they also strip Brønsted acidity by removing surface SO_4^2— groups, revealing a compromise between hydrogenation and alcoholysis functions. These findings highlight the complexity of designing truly cooperative multifunctional catalysts and the importance of integrated synthetic–reactive strategies that move beyond performance optimization alone.