Selective conversion of lactic acid to renewable acrylic acid over SDA-free Na-ZSM-5: The critical role of basic sites of sodium oxide

Abstract

Dehydration of biomass-derived lactic acid (LA) is a promising, sustainable alternative to conventional acrylic acid (AA) production through the oxidation of petroleum-derived propylene. Although alkali-exchanged zeolites (e.g., K-ZSM-5) are known to be active for AA production, controlling the selectivity of competitive decarbonylation remains elusive. Herein, we report on a new, highly selective, and durable catalyst—NaxOy/Na-ZSM-5 catalyst for the high-yield production of AA (∼80%) up to 200 h. When Na-ZSM-5 was directly synthesized using Na cations as the structure-directing agent under strongly basic (NaOH) conditions, the inevitable excess sodium residue remained on the surface. Characterization performed by TPD and 23Na NMR analyses revealed the presence of sodium oxide (NaxOy) in addition to Na cations coordinated to Si–O–Al sites in the synthesized ZSM-5, providing the additional basicity and thereby leading to significant enhancement in the AA selectivity through the synergy between two active sites. The catalytic role of NaxOy in LA dehydration was systematically verified by the direct sodium impregnation experiments and in-situ IR spectroscopy.