Designing hierarchical porosity in tin oxide monoliths and their application as a solid acid catalyst†
Abstract
Hierarchically porous tin oxide monoliths have been prepared for the first time from a low-cost tin(IV) chloride precursor through an epoxide-mediated sol–gel process in an aprotic solvent N,N-dimethylformamide. Phase separation is induced in the presence of poly(propylene glycol) in the course of polymerization triggered by an acid scavenger, propylene oxide, leading to macroporous tin-based oxyhydroxide monoliths. The resultant macropores are confirmed to be controlled in the size range of 0.9–2.9 μm. Both the post-gelation solvothermal treatment in 2-propanol and calcination in air gave rise to crystallinity and mesoporosity (2.4–103 nm in size with BET surface area up to 261 m2 g−1), and hierarchically porous tin oxide monoliths have been obtained for the first time. The monoliths are demonstrated as a catalyst for the esterification of valeric acid and methanol.