Mesoporous Methyl-Functionalized Sn-Silicates Generated by the Aerosol Process for the Sustainable Production of Ethyl Lactate

The aerosol-assisted sol-gel process was used to synthesize in a straightforward one-pot procedure a series of methyl-functionalized tin silicates with different degrees of methylation. The successful incorporation of isolated Sn as single site within the silica framework was confirmed via ¹¹⁹Sn solid-state NMR measurements, while ²⁹Si and ¹³C solid-state magic-angle-spinning NMR experiments revealed a degree of methylation close to the theoretical value, hence proving the efficacy of the adopted cosynthetic approach. These materials were tested as catalysts in the synthesis of ethyl lactate from dihydroxyacetone and ethanol. The methylated solids display enhanced performances in terms of both activity and selectivity compared to the nonmethylated analogues, highlighting a strong beneficial role of surface hydrophobicity. Under proper conditions a total conversion and a selectivity higher than 95% were achieved. Moreover, the efficient separation and reuse of the heterogeneous catalyst as well as the possibility of an easily recover of the reaction solvent result in a very low waste production protocol with an exceptionally low E-factor.