Catalytic dehydration of methyl lactate: Reaction mechanism and selectivity control

• Published in: Journal of catalysis Vol. 339; pp. 21 - 30
• Main Authors: Murphy, Brian M., Letterio, Michael P., Xu, Bingjun
• Format: Journal Article
• Language: English
• Published: San Diego Elsevier Inc 01.07.2016; Elsevier BV
• Subjects: Acrylic acid; Catalysis; Catalysts; Chemical compounds; Chemical reactions; Dehydration; Mechanism; Methyl lactate; NaY; Methyl lactate; Dehydration; Acrylic acid; Mechanism; NaY
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2016.03.026

[Display omitted] •A molecular reaction mechanism for catalytic dehydration of lactates is proposed.•Brønsted acid sites generated in-situ catalyze dehydration and decarbonylation.•The branching point for selectivity control is dissociation of methyl lactate on NaY. Catalytic dehydration of lactic acid and its esters is a promising approach to renewably produce acrylic acid and its esters. Molecular level understanding of the dehydration reaction mechanism on NaY has been achieved via a combination of reactivity and in-situ transmission Fourier transform infrared (FTIR) spectroscopic investigations. Brønsted acid sites generated in-situ with the assistance of water have been identified as the primary active sites for the dehydration pathway. The key branching point between the desired dehydration and undesired decarbonylation pathways is the dissociation of methyl lactate on NaY to form adsorbed sodium lactate and methyl groups. Brønsted and Lewis acid sites mainly catalyze the dehydration of adsorbed sodium lactate, whereas the decarbonylation pathway to acetaldehyde dominates when methyl lactate is not dissociated. Similar mechanistic steps are likely followed in the catalytic dehydration of lactic acid to acrylic acid. The mechanistic understanding gained will enable rational design of catalysts for selective dehydration of methyl lactate.