Designed Synthesis of SBA-15 Supported Sulfated Zirconia Solid Acid Ma-terials and Their Catalytic Performance for Transesterification Reaction
Ordered mesoporous Zr-SBA-15 material with a highly homogenous distribution of Zr within mesoporous walls was synthesized by a facile one-step high temperature hydrothermal treatment approach.In the proposed approach,the coop-erative self-assembly between amphiphilic triblock copolymer P123 and silicon hydroxyl(Si-OH)species from the hydroly-sis of tetraethyl orthosilicate(TEOS)was carried out to form an organic-inorganic composite with an ordered mesostructure(as-synthesized SBA-15,silica matrices with an embeddedness of P123 micelles)under a weak acidic medium originated from the hydrolysis of zirconium tetranitrate;during the followed high temperature hydrothermal treatment process,the fur-ther hydrolysis of zirconium precursor promotes more Zr4+transferring to zirconium hydroxyl(Zr-OH)species,and the con-densation between the Zr-OH species and Si-OH species,which exist in the synthesis solution and within the mesoporous walls of as-synthesized SBA-15,respectively,leads to a large amount of Zr atoms being highly homogenously grafted into the mesoporous walls of as-synthesized SBA-15 and the formation of framework Zr—O—Si bonds.After calcination to re-move the organic P123 micelles,the ordered mesoporous Zr-SBA-15 material was obtained and used as a support for the immobilization of sulfuric acid by a traditional impregnation method.The characterization results confirmed that compared to supports SBA-15 and SBA-15-supported zirconia(Zr/SBA-15,prepared by the impregnation of SBA-15 with zirconium tetranitrate aqueous soliton followed drying and calcination treatments),the use of support Zr-SBA-15 can realize a stable immobilization of much more sulfuric acid groups,due to the highly homogenous dispersions of ZrOx species on the meso-porous surface of Zr-SBA-15.In addition,the double attracting electron role from supported sulfuric acid group and Si ele-ment with higher electronegativity than that of Zr element can further induce an decrease in the electron cloud density of Zr4+existing in the surface Zr—O—Si bonds,which plays an important role in promoting the formation of super strong Brönsted and Lewis acidic sites.More importantly,the formation of surface Zr—O—Si bonds can exert a significant influence on re-straining the leaching of active sulfated ZrOx species during the reaction.The resultant solid acid SO42-/Zr-SBA-15 exhibits an ordered two-dimensional hexagonal mesostructure,a uniform mesoporous size,a high specific surface area,a large pore volume,and a prominently improved acidity.For soybean oil transesterification with methanol,the catalyst SO42-/Zr-SBA-15 demonstrated a much higher soybean oil conversion(up to 100％)along with a fatty acid methyl ester yield of 99.8％and a desirable reusability,compared to the traditional supported sulfated zirconia catalysts.The superior catalytic performance of SO42-/Zr-SBA-15 is associated with the outstanding structural and textural properties of support Zr-SBA-15 and the for-mation of surface Zr—O—Si bonds,thus benefiting the fast mass and heat transfer and the generation of a large number of stable active sites with a highly homogenous dispersion.
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