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Low-temperature fabrication of mesoporous solid strong bases by using multifunction of a carbon interlayer.

Mesoporous solid strong bases are highly promising for applications as environmentally benign catalysts in various reactions. Their preparation attracts increasing attention for the demand of sustainable chemistry. In the present study, a new strategy was designed to fabricate strong basicity on mesoporous silica by using multifunction of a carbon interlayer. A typical mesoporous silica, SBA-15, was precoated with a layer of carbon prior to the introduction of base precursor LiNO3. The carbon interlayer performs two functions by promoting the conversion of LiNO3 at low temperatures and by improving the alkali-resistant ability of siliceous host. Only a tiny amount of LiNO3 was decomposed on pristine SBA-15 at 400 °C; for the samples containing >8 wt % of carbon, however, LiNO3 can be entirely converted to strongly basic sites Li2O under the same conditions. The guest-host redox reaction was proven to be the answer for the conversion of LiNO3, which breaks the tradition of thermally induced decomposition. More importantly, the residual carbon layer can prevent the siliceous frameworks from corroding by the newly formed strongly basic species, which is different from the complete destruction of mesostructure in the absence of carbon. Therefore, materials possessing both ordered mesostructure and strong basicity were successfully fabricated, which is extremely desirable for catalysis and impossible to realize by conventional methods. We also demonstrated that the resultant mesoporous basic materials are active in heterogeneous synthesis of dimethyl carbonate (DMC) and the yield of DMC can reach 32.4%, which is apparently higher than that over the catalysts without a carbon interlayer (<12.9%) despite the same lithium content. The strong basicity, in combination with the uniform mesopores, is believed to be responsible for such a high activity.