Designing alkali-exchanged ZSM-5 catalysts for the dehydration of lactic acid to acrylic acid

This report shows that complete control of the degree of alkali exchange is possible by controlling the pH strength, and that is possible to distinguish the selectivity of the cations themselves in the lactic acid (LA) dehydration reaction by excluding undesired active sites arising from excess salts. We discovered that strong base conditions induced by alkali hydroxides (e.g., KOH) increase the degree of alkali ion exchange, and that in the absence of additional salts−such as halogen anions, oxides−the KOH-ZSM-5 catalyst exhibited high acrylic acid (AA) selectivity (∼70%) and durability (100 h). Characterization via temperature-programmed desorption (TPD) and pyridine-infrared (Py-IR) analysis revealed a full exchange of the protons bound to the Si–O–Al sites with potassium in commercial ZSM-5. In addition, structural pore expansion due to the desilication by KOH leads to significant enhancement in the selectivity for AA. The mechanistic impact of KOH treatment on lactic acid dehydration is also systematically verified by in situ IR spectroscopy. [Display omitted] •The effect of alkali-cations and anions of alkali-zeolites in LA dehydration to AA are investigated.•The pH according to anions impacts the degree of alkali exchange, contributing to the AA selectivity.•Strong base condition(-OH) allows for the full exchange of the alkali ions with protons in Al sites.•The collaboration of potassium cation and hydroxyl group achieves the high AA selectivity of ∼70 %.