Selective conversion of lactic acid to acrylic acid over alkali and alkaline-earth metal co-modified NaY zeolites

Abstract

Alkali and alkaline-earth metal cation co-modified NaY zeolites were systematically synthesized and comprehensively investigated as catalysts for gas-phase dehydration of lactic acid (LA) to acrylic acid (AA). The long-term (time-on-stream >55 h) catalytic performance in four repeated reaction–regeneration cycles was studied. The best performing catalyst shows a consistently high AA selectivity of ∼84% at different weight hourly space velocity (WHSV) values ranging from 0.48 to 4.8 h⁻¹. Most importantly, the catalyst can still deliver a high AA selectivity of ∼82% after four long-term reaction–regeneration cycles. The investigation shows that mild etching increases the defect density of the zeolite and thus leads to poor hydrothermal stability in the long-term reaction–regeneration cycles. The strong acidic adsorbate/catalyst surface interaction (base property) and the acidity of the catalyst are responsible for the catalyst deactivation. The role of the alkali and alkaline-earth metal cations and the transformation of these cations during the reaction and regeneration process are presented.