Continuous flow transfer hydrogenation of biomass derived methyl levulinate over Zr containing zeolites: Insights into the role of the catalyst acidity

Several catalysts with a 10 wt% loading of zirconium supported on BEA-75 (Si/Al = 37.5) and ZSM-5 (with two different Si/Al = ratio of 15 and 25, respectively) zeolites have been synthesized via ball-milling (mechanochemistry). Samples were characterized by N2 physisorption, X-ray diffraction (XRD), scanning electron microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDS). The incorporation of ZrO2 nanoparticles on the zeolitic material lead to the formation of catalysts with the ability of transform methyl levulinate into γ-valerolactone (GVL). However, the selectivity towards GVL was negatively affected due to side reactions caused by both Lewis and Bronsted acid sites on the zeolites employed as support. The role of each acid site in the selected reaction could be addressed by selective poisoning with different bases (pyridine and 2.6-dimethylpiridine). In general, the deactivation of the active sites by the different bases significantly increased the selectivity towards GVL, completely quenching competitive side reactions, pointing out GVL formation can be promoted by Zr(IV) species according to the Meerwein-Ponndorf-Verley (MPV) mechanism.