Synthesis And Catalytic Performance Of Silicone-assisted Mesoporous Tin-silicon Materials

Mesoporous molecular sieves are functional materials with large specific surface area,rich pore structure and high stability.The specific functional treatment of molecular sieves can make them become a catalyst for certain reactions,and it has great application prospects in the field of catalysis.Numerous studies have shown that heteroatoms in the framework of mesoporous materials can serve as catalytically active centers for heterogeneous reactions,and their accessibility has an important influence on catalytic reactivity.Due to the limitation of the pore wall structure,some of the heteroatoms in the framework are embedded in the framework,resulting in a decrease in the accessibility in the catalytic reaction,which ultimately leads to a decrease in reactivity.Therefore,how to improve the accessibility of the active center in the framework of mesoporous materials through structural design has become an important topic in the research of mesoporous materials.In this paper,a heteroatom-supported mesoporous silica was synthesized by using a silicone-assisted synthesis method which using a synthetic silicone molecule and tetraethyl orthosilicate as a silicon source.Silicone assist can serve two purposes:to make skeleton pores to increase the accessibility of the heteroatom active center and to introduce an amino group to form an acid-base bifunctional catalyst material.Using a silicone molecule as a silicon source,a molecular size pore was introduced into the framework of the tin-containing mesoporous Sn-SBA-15,and a pore-type mesoporous material containing a molecular size pore in the skeleton was successfully prepared?Sn-SBA-15-MSC?.The characterization results show that Sn-SBA-15-MSC still maintains the two-dimensional hexagonal mesoporous structure of traditional Sn-SBA-15,and the use of silicone does not affect its mesoporous structure.At the same time,the Sn species are present in the framework of the mesoporous material in a four-coordinate manner.In the Baeyer-Villiger oxidation reaction of adamantanone,the Sn-SBA-15-MSC gave 1.5 times the catalytic conversion efficiency?TOF?relative to the comparative sample Sn-SBA-15,indicating that the molecular size pores can be significantly improved the accessibility of the active center within the framework of the pore material.Moreover,the pore-type mesoporous material showed high product selectivity?>99%?and good stability.The catalytic activity of the sample did not decrease after three times of repeated use.The amino-modified pore-type Sn-SBA-15?Sn-NH₂-SBA-15-MSC?was prepared by the organic solvent treatment while introducing the molecular size pores in the framework.The characterization results clearly show that Sn-NH₂-SBA-15-MSC has a good two-dimensional hexagonal mesoporous structure.The molecular size pores in the framework are adjacent to the amino group,and some of the embedded Sn species are exposed to the skeleton.Inside.In the continuous catalytic reaction of benzaldehyde dimethyl acetal and ethyl cyanoacetate in Deacetalization-Knoevenagel acid-base,the pore-type bifunctional mesoporous material gives higher catalytic conversion and product yield,and the reaction yield reached 94%at 8 h.Comparing the activity of the catalyst containing no amino group and no hetero atom tin,the Sn species and the amino group are respectively an acid catalytic center and a base catalytic center for realizing the Deacetalization-Knoevenagel reaction.The Sn-NH₂-SBA-15-MSC sample also had good stability.