Dehydration of ethyl lactate over alkaline earth phosphates: Performances, effect of water on reaction pathways and active sites

• Alkaline earth phosphates were evaluated in gas phase dehydration of ethyl lactate.
• Selectivity values to acrylic acid and ethyl acrylate reaching 87% were obtained.
• Addition of water vapor to the feed slows deactivation of catalysts.
• Acrylic acid was mainly formed by a simultaneous dehydration/hydrolysis reaction.
• The presence of a surface amorphous layer containing POH species was evidenced.

In this work, alkaline earth phosphates have been prepared by co-precipitation and evaluated in gas phase dehydration of ethyl lactate to acrylic acid and ethyl acrylate. These solids, which were previously shown to be active for the dehydration of lactic acid, appeared more efficient. Indeed, it was shown that the decarbonylation/decarboxylation route leading to acetaldehyde was strongly inhibited compared to conversion of lactic acid and molar selectivity values to dehydration products reaching 87% were obtained. Furthermore, it was shown that the deactivation of the catalysts could strongly be slowed by addition of water vapor to the feed. The reaction pathways have been studied in the presence and absence of water and it was shown that acrylic acid was mainly formed by a simultaneous dehydration/hydrolysis reaction. The characterization of the catalysts surface from the results of XPS, cross polarization NMR, DRIFT and TEM showed the presence of a surface amorphous layer containing POH species. In situ DRIFT measurements have revealed that formation of POH groups was favored under water vapor and that these species interacted with reactants or reaction products at the reaction temperature.

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