Unravel the Active Sites and Intermediates for Selective Production of Acrylic Acid from Biomass

Producing chemicals from alternative feedstocks such as biomass is promising route for sustainable manufacturing. In this study, we unravel the reaction mechanism and the nature of the active site for the dehydration of biobased lactic acid to acrylic acid through systematic in-situ diffuse reflectance infrared Fourier transform spectroscopic analysis. We demonstrated that the formation and the stability of lactate as the reaction intermediate on the catalyst surface is crucial to obtain high acrylic acid selectivity. The simultaneous presence of Lewis acid sites and stable lactate intermediates appear to be key in pushing the reaction equilibrium toward dehydration of lactic acid to acrylic acid. We suggest that lactate cannot be formed or is not stable in the presence of BrØnsted acid sites, resulting in low acrylic acid selectivity over HY catalysts. In addition, we have shown that alkali and alkaline-metal modification reduces the number of in-situ generated BrØnsted acid sites, promoting stable lactate intermediate formation and thus inhibiting side reactions catalyzed by BrØnsted acidic sites.