Aqueous‐phase conversion of glyceraldehyde to lactic acid was investigated over Nb2O5, TiO2, ZrO2 and SnO2 in a fixed‐bed up‐flow reactor. Special attention was given to the catalysts acidity regarding the type, amount, strength and tolerance to water of surface acid sites. These sites were assessed by infrared spectroscopy of pyridine adsorbed on dehydrated and hydrated catalysts as well as by isopropanol decomposition. It was found that Nb2O5 and TiO2 have the highest fraction of water‐tolerant Lewis acid sites (40 and 47 %), while only 6 % was estimated for ZrO2. No relevant Lewis acidity was observed on SnO2, but it was noticed the presence of strong base sites. The transformation of glyceraldehyde into lactic acid proceeded via a cascade reaction in which glyceraldehyde is firstly dehydrated to pyruvaldehyde, followed by its rearrangement to lactic acid with the addition of a water molecule. The dehydration step occurs on Brønsted acid sites and/or on water‐tolerant Lewis acid sites. These latter sites also determine the selectivity to lactic acid. Strong base sites promote glyceraldehyde fragmentation leading to formaldehyde with high selectivity.

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Levulinic acid and angelica lactones are important building blocks obtained from hemicellulose. This process comprises multiple chemical reactions at which furfuryl alcohol is an intermediate, but only few studies have investigated its hydrolysis. This work studied the role played by the nature of acid sites and the impact of their strength and amount on furfuryl alcohol hydrolysis over Nb2O5 and NbOPO4. It was disclosed that production of levulinic acid is a two‐step cascade reaction at which angelica lactones are intermediates. These two hydrolysis steps were catalyzed by Brønsted acid sites with no contribution from Lewis centers. Brønsted acidity of Nb2O5 presented no activity while phosphate moieties on NbOPO4 were effective. Mixtures of organic solvent and water hindered side reactions, improving selectivity to valued bioproducts. 1,4‐dioxane was the most suitable organic solvent. This study shows that selectivity of 96 % of levulinic acid and angelica lactones can be accomplished over NbOPO4.

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