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Abstract:

The direct conversion of trioses (dihydroxyacetone and glyceraldehyde) to lactates represents an important step towards the conversion of biomass derived glycerol to added value products [1]. A set of zeolites Y with various Si/Al ratios and different degree of dealumination were tested as catalysts for this reaction. Ultrastable zeolites Y (USY) with low Si/Al ratio displayed the highest yield and selectivity towards the desired alkyl lactate and could be reused in various successive cycles without loss of activity [2]. The study was further developed by exploring the conversion of trioses with aluminium and gallium oxides and with a series of substituted mesoporous MCM-41 materials, presenting different amount and type of acid sites. Gallium oxide showed good catalytic activity and an improved selectivity towards the lactate product compared to the USY zeolites. This study highlighted the importance of the type and strength of the acid sites of the catalyst in determining the yield and the selectivity of the reaction. A combination of mild Brønsted acidity and of Lewis acidity is proposed to be the most suitable for catalysing the formation of alkyl lactates. On the other hand, strong Brønsted acidity proved to be detrimental for the selectivity of the reaction because it catalyses the formation of the dialkyl acetal of pyruvic aldehyde by product.