Synthesis, Characterization And Catalytic Performance Of Titanium Containing Porous Materials

Since titanium silicalite was synthesized first in 1983,it has attracted much attention for its excellent catalytic performance in the selective oxidation of organic molecules with H₂O₂. Though traditional Ti-containing zeolites possess high activity and stability,the narrow channel make thern inacitive in the reactions of bulky molecules.Ti-containing mesoporous silicas have capacious framework pores(＞2.0nm) and large surface area and exhibit high activity in some large molecular reactions.However,the relative lower oxidation ability and stability of these mesoporous materials,arising from the amorphous nature of their pore walls prevent their wide uses in the industrial process.The purpose of this paper is synthesizing novel materials with multiporous and highly active sites,in order to overcome the shortcoming of existing catalytic materials.The paper has the following main contents.The synthesis,characterization and catalytic performance of Ti-HMS mesoporous molecular sieve are studied.It has been shown that traditional Ti-HMS is synthesized under slightly alkaline condition.When the n(HCl)/n(DDA) is 0.07 and the corresponding pH value is 10.72,the obtained Ti-HMS has high quality.With the increase of the amount of titanium source,the contents of both framework and extra-framework titanium species in the products are increased and the optimal n(SiO₂)/n(TiO₂) is 50.Higher crystallization temperature is adverse to the synthesis of Ti-HMS and the pH value of mother liquid change little during the crystallization process.Traditional Ti-HMS possesses wormlike structure.Ti-HMS exhibits excellent performance in oxidation of bulky sulfides.For the reaction of small molecules, however,the activities of Ti-HMS are not as good as TS-1.Ti-containing mesoporous silicas Ti-HMS can also be synthesized with soluble sodium silicate as silica source.A novel Ti-containing mesoporous material with wormlike structure(Ti-WMS) is assembled from the preformed TS-1 precursors with long-chain alkylamine under ambient temperature.The structural and catalytic performances of obtained Ti-WMS have been researched.The results show that comparing with conventional Ti-HMS,Ti-WMS has a lower order degree and a larger wall thickness.Ti-WMS contains the structural units of TS-1 and the zeolite-like active sites.Besides the uniform mesopores,there are some micropores in the Ti-WMS.Ti-WMS possesses highly oxidation ability and exhibits much higher activity than Ti-HMS in thiophene oxidation.In oxidation of some bulky sulfides,Ti-WMS is also active,with similar activities to Ti-HMS.A novel Ti-containing meso-microporous material Ti-HMS/TS-1 is synthesized by assembly of TS-1 gel with partial crystallization with dodecylamine at ambient temperature. The material is characterized by a series of techniques and its catalytic performance is investigated by means of sulfides oxidation.It has been shown that Ti-HMS/TS-1 possesses simultaneously a mesoporous phase and a crystalline zeolitic phase and two phases are composite rather than the physical mixture.In addition,relative to conventional Ti-HMS,the mesoporous phase in the Ti-HMS/TS-1 has lower order degree and larger pore wall thickness and may contain the zeolitic structural units.Ti-HMS/TS-1 combines the advantage of single Ti-HMS and TS-1 and exhibits high activity in oxidation of both bulky and small molecular sulfides.