The catalytic conversion of biomass into high-value chemicals is an increasing field of research. This study uniquely investigates the use of various Keggin-type heteropoly salts (HPS) for the chemical conversion of sugars into lactic acid under mild conditions of 160°C and 20 bar N2. In the first phase, Nb- and V-substituted HPSs were employed to synthesize lactic acid from dihydroxyacetone, an intermediate in the conversion of sugars to lactic acid. Results indicated that increasing the Nb content within the Keggin structure enhances the yield of lactic acid while reducing the formation of the byproduct acetaldehyde. A correlation was established between the redox activity of the HPS and the catalytic performance. The most active catalyst, Na5[PNb2Mo10O40], (NaNb2) achieved a lactic acid yield of 20.9% after 1 h of reaction. In the second phase of the study, NaNb2 was applied for the conversion of different sugars including glucose, fructose, mannose, sucrose, xylose, and cellobiose. It was demonstrated that the catalyst remains active for complex hexoses, achieving lactic acid yields of up to 12%. Post-mortem analysis using infrared (IR) and Raman spectroscopy, nuclear magnetic resonance (NMR), and inductively coupled plasma optical emission spectrometry (ICP-OES) confirmed the stability of NaNb2.
Keywords: Lactic Acid; Niobium-substituted heteropoly salts; biomass conversion; polyoxometalates.
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