Functional Modification Of Mesoporous Materials And Their Catalytic Performance

The chemical modification methods for mesoporous materials, such as framework insertion, ion exchange, surface impregnation, etc., can be used to create new active sites and hence to improve the catalytic performance of the modified materials. The functional modification of mesoporous molecular sieves has attracted considerable attentions of researchers owing to its significant roles played in designing and developing novel catalysts for both homogeneous catalysis and heterogeneous catalysis. By choosing different precursors and preparation methods, active species with different structural characteristics can be incorporated into the mesoporous materials. Combining compositional analysis, structural characterization, and catalytic tests, the correlation between structural characteristics and catalytic performance can be performed and the design and preparation of a highly effective catalyst can be optimized.SBA-15 is a new type of mesoporous silica molecular sieves with uniform hexagonal channels ranging from 5 to 30 nm, thick walls (3.1-6.4 nm), and with higher hydrothermal stability than those of MCM-41. However, the SBA-15 materials have been generally synthesized under strongly acidic hydrothermal condition that easily induce the dissociation of the M-O-Si bonds and therefore relatively little work has been done on the synthesis of the metal-substituted SBA-15 materials. In order to improve the catalytic activity, making use of interaction effect of different atoms and the theory of electric neutral, we combine the defect theory in solid chemistry with preparation of molecular sieve to design and synthesize bimetallic substituted molecular sieves, that is two different metal ions are used to substitute the framework silica atom simultaneously. Based on the acid-base pair theory, considering the interaction of different metal salt, we choose suitable inorganic precursors to synthesize bi-substituted SBA-15 mesoporous materials. Moreover, mesoporous materials possess high surface area and uniform mesoporous channels, the active species can be in a high dispersion state, so the material is an ideal catalyst support. We prepared FePO₄/SBA-15 materials by in-situ coating method using SBA-15 as support, and Heteropoly acid (H₆PMo₉V₃O₄₀ and H₃PW₁₂O₄₀) with Dawson structure was immobilized into the channel of mesoporous TiO₂ by chemical bonding with amine groups, and the catalytic performance of the resultingmaterials was investigated.The main contents are as follows:( 1 ) Using triblock copolymers as template, phosphoric acid as acid medium and aluminum nitrate as mineralizing agent, we synthesized copper substituted SBA-15 (Cu-SBA-15) . The resulting material has high catalytic performance to hydroxylation of phenol.(2) And we supported VOx on the host of Cu-SBA-15 (VOx/Cu-SBA-15) catalyst by impregnation and investigated its catalytic activity to hydroxylation of benzene using molecular oxygen as oxidant. In terms of the detailed investigation of the reaction parameters, including temperature, pressure, reduction agent and solvent, proposed the reaction mechanism of hydroxylation of benzene using molecular oxygen as oxidant.( 3) Iron ion substitute the framework silica atom of SBA-15, which forms a donor defect, phosphorous atom incorporate into the framework forming an acceptor defect simultaneous, which can sustain the zero electric charge neutral. We synthesized Fe-P substituted SBA-15, and the resulting materials have high catalytic activity to hydroxylation of benzene to phenol with H₂O₂ as oxidant.( 4 ) So we choose quinquevalent vanadium as high valent transition metal ions, it can form a proton hole, and trivalent iron as low valent metal ions to form electron hole. Using triblock copolymers as template, we synthesized bimetallic substitution Fe-V SBA-15 molecular sieve under acid condition. The results of XRD and N₂ adsorption-desorption characterization indicate that the materials possesses highly ordered hexagonal mesoporous structure, and have high catalytic activity to the hydroxylation of...