Kinetic and mechanistic study of triose sugar conversion on Lewis and Brønsted acid solids

DI COSIMO, J.I.; DÍEZ;, V.K.; PIGHIN, E.A.

Molecular Catalysis

Elsevier

Lugar: Amsterdam; Año: 2018 vol. 458 p. 189 - 197

2468-8231

The effect ofcatalyst acid site nature on the reaction kinetics of the liquid-phaseconversion of dihydroxyacetone with ethanol was investigated using Brønsted andLewis acid solids. The reaction proceeds through a complex reaction networkinvolving a sequence of consecutive and parallel reaction steps. Main finalproducts were ethyl lactate and pyruvic aldehyde diethyl acetal. Differentcatalysts such as the cesium salt of tungstophosphoric acid (Cs-HPA), Amberlystresin and alumina-supported tin and zinc oxides were used. Catalysts were characterized by ICP, X-raydiffraction, N2 physisorption, TPD of NH3 and FTIR ofadsorbed pyridine. Cs-HPA containsonly Brønsted acid sites and alumina-supported tin and zinc samplesshow exclusively Lewis acidity. During dihydroxyacetone conversion, theselectivities to the final products strongly depend on the nature of thesurface acid sites present on the solids. Brønsted acid solids favor the synthesis of pyruvic aldehydediethyl acetal with final yields of up to 93%, whereas the ethyl lactate is themain product on Lewis acid solids, reaching final yields of about 51%. Akinetic model based on a pseudohomogeneous mechanism was proposed to interpretthe experimental catalytic data. The comparison of thekinetic rate constants obtained on both kinds of acid solids confirms that on Brønsted catalysts the route towardpyruvic aldehyde diethyl acetal is clearly favored. On Lewis solids, thesynthesis of ethyl lactate occurs selectively via isomerization of the pyruvicaldehyde hemiacetal intermediate.