Interplay of acid sites and surface hydrophobicity in tin silicate catalysts

Tin-containing silicates are ubiquitous heterogeneous catalysts for biomass conversion and fine chemicals synthesis, owing to their strong and selective Lewis acidity. Traditionally, these materials are synthesized via multi-step procedures such as dealumination of zeolites followed by tin incorporation, which usually offer only limited control on texture and poor metal dispersion. The non-hydrolytic sol gel (NHSG) method offers a streamlined alternative for synthesizing metal silicates with enhanced control over composition, porosity, and active site dispersion. Here, we employed three NHSG routes – i.e. alkyl halide elimination, acetamide elimination, and their combination – to prepare porous tin silicates. Remarkably, the combined route yielded catalysts with high specific surface areas (up to 900 m2 g–1, without requiring the use of any pore-generating agent), uniform tin dispersion, and high Lewis acidity. This correlated with comparable activity in dihydroxyacetone (DHA) conversion to ethyl lactate and aminolysis of styrene oxide to reported literature. Modification with trimethylsilyl groups was used to further tune the catalytic behavior by modulating surface polarity. While hydrophobization markedly improved apparent turnover frequencies – up to fivefold in styrene oxide aminolysis – excessive silylation was detrimental to DHA conversion, underscoring the dual role of Si–OH and Si–OSiMe₃ groups in catalytic performance.