晶种辅助预晶化法合成纳米ZSM-5分子筛及其在丙烷芳构化反应中的应用OACSTPCD

In the aromatization reaction of propane,the conventional molecular sieve catalyst is prone to carbon deposition and deactivation,resulting in unsatisfactory catalytic performance and service life.Nanometer ZSM-5 molecular sieve(ZSM-5-Nano)was synthesized with pure silica molecular sieve Silicalite-1(S-1)as seed by combination with seed method and pre-crystallization method.The structure of ZSM-5-Nano was characterized by scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray diffraction(XRD)and N2 physical adsorption/desorption.The results show that ZSM-5-Nano is composed of small particles with a particle size of about 50 nm,its specific surface area is up to 395 m2/g,and it is rich in intergranular mesopores.The catalyst Zn-ZSM-5-Nano was prepared by loading Zn with ZSM-5-Nano,and then the catalytic performance of the catalyst for the aromatization reaction(n(N2):n(C3H8)= 7:3,space velocity of 3000 h-1 and reaction temperature of 550 ℃)of propane was evaluated in a fixed bed reactor.The results show that Zn/ZSM-5-Nano has relatively mild acid properties,and shows good catalytic performance in the aromatization reaction of propane.The conversion rate of propane and the selectivity of light aromatics(benzene,toluene and xylene)within 5 h are as high as 88.4％and 86.7％,respectively,and the activity is stable within 5 h.The catalytic performance is better than that of the micrometer ZSM-5 molecular sieve(hydrothermal method)supported Zn catalyst and the nanometer ZSM-5 molecular sieve(pre-crystallization method)supported Zn catalyst.The results of structure activity analysis show that the better catalytic performance of Zn/ZSM-5-Nano is the result of the combination of morphology and acidity,and the shorter diffusion distance and milder acidity effectively delay the formation of carbon deposition.