Metal-containing TUD-1 mesoporous silicates as versatile solid acid catalysts for the conversion of bio-based compounds into valuable chemicals

Three-dimensional mesoporous silicates of the TUD-1 family were synthesised with different metals (Zr, Hf and Sn) incorporated in the framework of the material. The mesoporosity of the prepared TUD-1s was confirmed by X-ray diffraction (XRD), nitrogen physisorption and TEM. The incorporation of the metals in the silicate structure was investigated by FT-IR and UV–Vis spectroscopy. All three TUD-1 materials present a combination of Lewis and mild Bronsted acid sites, as determined by TPD-FT-IR of pyridine adsorption. The metal-containing TUD-1 materials were tested as solid acid catalysts for the conversion of three bio-based compounds into valuable chemical products. In the conversion of dihydroxyacetone into ethyl lactate, complete selectivity towards the desired lactate product was achieved with Zr-, Hf- and Sn-TUD-1. The three heterogeneous catalysts displayed similar activity, with Hf-TUD-1 reaching the highest conversion and metal-based turnover number. Sn-TUD-1 also displayed high activity and selectivity in two acetalisation reactions, i.e. the synthesis of solketal from acetone and glycerol and the reaction of vanillin with propylene glycol. The catalytic performance of these TUD-1 materials is ascribed to the high accessibility of their active sites and to the suitable combination of acid sites. The catalysts were successfully reused in consecutive runs and did not suffer from leaching.