Preparation, Modification And Catalytic Performance Of Nano ¦Â Zeolite

Nanocrystalline particle has a crystal size between 1 and 1 OOnm. As an important part of it, there is a growing interest in nanocrystalline zeolite in recent years. nanocrystalline zeolite possesses the following distinctive characteristics compared with larger zeolite: 1) Larger external surface with more active sites situated on it's surface which can eliminate the diffusion effect, increase catalyst efficiency, and probably modify bulky molecule reaction properties; 2) More pore openings at it's outer surface which are not easy to be blocked by the coke or its precursor formed during the reaction, thus may be helpfi.il to keep the catalytic activity.zeolite is an important zeolite in petroleum refining and petrochemical prodution. To solve the accord complexity problem of synthesis nanocrystalline zeolite a step crystallization method in the presence of an additive has been developed in the thesis. The key of the idea of is to decrease high surface energy of zeolite predecessor during the step crystallization by additive's stereoscopic hinder, which can short the induction period, and increase nucleating rate. Particle size is 50-6Onm. The effect of additive is similar to increasing the content of the template used. The technology has advantages that decrease the cost of production, shorten the crystallization period, and simplify synthesis process. Appropriate additive is polyalkane ester and non-ionic surfactant whose molecular weight is 800-1000, content is 0.1-1 .Owt% of theSi02.Although nanocrystalline zeolite ~ has many advantages, its thermal stability is lower, and framework Al is liable lost. To overcome the limitation, nanocrystalline zeolite ~ with transition metal was synthesized. The method is that the silica-gel particles was depolymerized by impregnating with acidified salt solution, then added into hydrothermal crystallization system. All products formed are white and highly crystalline, with the particle size 70-8Onm.Thermal stability and total acidity, especially L acid site, are enhanced obviously. The key of the technology is to modify the silica-gel particles. Suitable condition is PH=l-4, NaOH l-1.5g/L, 250C, 20-24h, salt content 8.3-50.2g/L. The characterization results show that Ni is in tetrahedral coordination, where three of the ligands are lattice oxygens and the fourth is derived from residual water. This is the reason why the thermal stability of the nanocrystalline zeolite ~ was increased.Based on the above result, the catalytic activity and selectivity of nanocrystalline zeolite ~ and modified zeolite ~ was investigated in aromatics alkylation process. Nanocrystalline zeolite exhibits better activity and stability than larger particle in benzene alkylation with dodecene- 1, and modified zeolite ~ further improves the catalytic activity. While, in the synthesis of cumene, the results show that only selectivity is slightly increased by nanocrystalline zeolite ~. These results indicate that the nanocrystallinezeolite has better catalytic activity in bulky molecule reaction and transition metal- nanocrystalline zeolite ~ can further modifis the catalytic property.Additionally, n-octane hydroisomerization process was studied over catalysts comprising noble metal Pd with zeolite ~ .The results show that nanocrystalline zeolite ~ has higher isomerization selectivity. When nanocrystalline zeolite ~ with transition metal was used as the catalyst support, it has higher activity with more 2,5-MeC60 produced. Therefore, nanocrystalline zeolite 13 and transition metal nanociystalline zeolite 13 have potential as catalyst support for hvdroisomerization.