Modulating the host nature by coating alumina: A strategy to promote potassium nitrate decomposition and superbasicity generation on mesoporous silica SBA-15

A new strategy was utilized to generate strong basicity on mesoporous silica SBA-15 by precoating alumina before modification with the base precursor, potassium nitrate. The nature of the mesoporous silica host was greatly modulated by the alumina interlayer. Such an alumina interlayer plays a double role by enhancing the guest-host interaction to promote the decomposition of potassium nitrate and by improving the alkali-resistance of the mesoporous silica host. The majority of the potassium nitrate is decomposed at 690 A°C on unmodified SBA-15, while the temperature decreases to 460 A°C after precoating an alumina layer. Moreover, the ordered mesoporous structure of the parent, SBA-15, is well-preserved even if the supported potassium nitrate was decomposed to strongly basic potassium oxide, which is quite different from the complete destruction of the mesostructure in the absence of alumina. As a result, materials possessing both a mesoporous structure and superbasicity with a high strength of 27.0 were successfully fabricated. We also demonstrated that both the amount and the location of aluminum in the samples are of great importance for the generation of strong basicity. The content of alumina should reach as high as 20 wt %, which is necessary for the formation of an intact interlayer; thus, the silica frameworks can be well-protected after introducing strongly basic species. Also, the location of aluminum on the pores rather than in the frameworks is demanded from the point of view of mesostructure protection.