Surfactant-Templated Mesostructuring Of Zeolite Y

Zeolite Y is widely used in petroleum refining processes such as fluid catalytic cracking(FCC)and hydrocracking(HC)because of its large pore size,strong acidity,and excellent hydrothermal stability.It's introduction into petroleum refining brought forth a step-change in terms of both catalyst activity and product selectivity as compared to the older amorphous silica–alumina-based catalyst technology.However,in catalytic cracking,slow mass transport in the micropores not only limits the conversion of the feed but also shifts the product selectivity due to overcracking of the intermediate products such as gasoline to smaller and less valuable liquefied petroleum gases(LPG)or formation of other undesired products such as coke through other reaction pathways.This paper mainly used the surfactant as template through "One-step Method" successfully synthesized mesozeolite Y directly:Method 1: Directing agent method--mesozeolite Y,was synthesized successfully through the process of cystallization for 20 days with the temperature of T while YB was taken as the template and the prepared directing agent was added in the gelation process.It could be learned from a variety of characterization methods that the samples prepared through Method 1 showed higher relative crystallinity and large BET surface area of 910 m2/g,but the extra specific surface area of 94 m2/g.The crystal morphology was observed as aggregates accumulated by particles of around 300 nm.Method 2: One-step method--mesozeolite Y,was synthesized successfully through the process of cystallization for 10 days with the temperature of T while YB was taken as the template and no guiding agent was added in the process.It can be concluded from characterizations that the XRD diffraction patterns of the sample prepared through Method 2 was obviously widen which indicated that the zeolite was nanocrystallizationed severely.When the Si/Al was 9:1,from the N2 adsorption characterization results,the sample shows high BET surface area of 707m2/g but low extra specific surface area of 127m2/g,at the same time the pore size distribution was homogeneous(2-10nm);from SEM micrographs,the sample was nano aggregates constituted from particles with the size of 100 nm,and the crystal morphology was homogeneous which is consistent;in the synthetic process,the mesozeolite Y with the same morphology could be also obtained if the template YB was replaced by BY,but the particle size distribution of mesozeolite Y was 2-6 nm since the size of the molecules of the template decreased.When the Si/Al was 7.1,mesozeolite Y with higher specific surface area(217m2/g)and homogeneous pore size distribution but low BET surface area(677m2/g),from the SEM micrographs,the sample had smaller size of 80 nm;when reducing the basicity of the system to 0.046,the particle size became samller to 50 nm and the anocrystallization phenomenon was even obvious.Under the present conditions,it is found that the disproportionation proceeds largely within the micropores,while the isomerization reaction occurs mainly on the external surface.The catalytic properties of mesozeolite Y were investigated in the conversion of 1,2,4-trimethylbenzene in view of the product selectivity.