Development of water-resistant catalysts by surface modification of tin-based solids for the upgrading of biomass derivatives

Abstract

Water-resistant Sn-based solid catalysts supported on Al2O3 were prepared. The methods of incipient wetness impregnation and direct silylation with trimethylchlorosilane (TMCS) were used. The textural, structural, acidic and water-resistance properties were investigated. Different physical and spectroscopic techniques (N2 physisorption, XRD, UV–Vis-DRS, FTIR, TPD of NH3, solid interaction with mixtures of vaseline-water, and measurement of contact angles) were employed. The preparation method allowed modifying the surface of the solids making them more resistant during the interaction with water. The FTIR analysis confirmed the existence of surface species resulting from the interaction with TMCS. A decrease in these species was observed by thermal treatment. The contact angles formed by the interaction with a drop of water were measured. These values confirmed an incipient increase in water-resistance due to silylation. Silylated and non-silylated tin-based solids were investigated during conversion of dihydroxyacetone to lactic acid in aqueous medium. Different reaction conditions, including the silylation process, catalyst thermal treatment, reaction temperature and Sn content were optimized. The solids without silylation exhibited lower activity than solids modified with TMCS, which resulted active and selective to the desired product. Final lactic acid yields up to 87 % were obtained on these solids. A surface reaction mechanism involving Sn active sites protected with nearby O-Si(CH3)3 species was proposed. This mechanism fully interprets results obtained during the conversion of dihydroxyacetone in aqueous media on alumina-supported Sn-based catalysts treated with TMCS.