TiO[sub.2] Catalyzed Dihydroxyacetone Conversion in Water: Evidence That This Model Reaction Probes Basicity in Addition to Acidity

• Published in: Molecules (Basel, Switzerland) Switzerland), 2022-11, Vol.27 (23)
• Main Authors: Abdouli, Insaf, Dappozze, Frederic, Eternot, Marion, Guillard, Chantal, Essayem, Nadine
• Format: Article
• Language: English
• Subjects: Catalysts; Hydrolysis; Investigations; Monosaccharides; Sugars
• ISSN: 1420-3049; 1420-3049
• DOI: 10.3390/molecules27238172

In this paper, evidence is provided that the model reaction of aqueous dihydroxyacetone (DHA) conversion is as sensitive to the TiO[sub.2] catalysts' basicity as to their acidity. Two parallel pathways transformed DHA: while the pathway catalyzed by Lewis acid sites gave pyruvaldehyde (PA) and lactic acid (LA), the base-catalyzed route afforded fructose. This is demonstrated on a series of six commercial TiO[sub.2] samples and further confirmed by using two reference catalysts: niobic acid (NbOH), an acid catalyst, and a hydrotalcite (MgAlO), a basic catalyst. The original acid-base properties of the six commercial TiO[sub.2] with variable structure and texture were investigated first by conventional methods in gas phase (FTIR or microcalorimetry of pyridine, NH[sub.3] and CO[sub.2] adsorption). A linear relationship between the initial rates of DHA condensation into hexoses and the total basic sites densities is highlighted accounting for the water tolerance of the TiO[sub.2] basic sites whatever their strength. Rutile TiO[sub.2] samples were the most basic ones. Besides, only the strongest TiO[sub.2] Lewis acid sites were shown to be water tolerant and efficient for PA and LA formation.