Particle size regulation of HZSM-22 and Pt/HZSM-22 for n-dodecane hydroisomerization
ZSM-22 zeolite crystals with different c-axis lengths were synthesized by using supersaturated solution method under static hydrothermal conditions and adjusting the water content in the synthetic solution.The as-synthesized ZSM-22 zeolite crystals were characterized by XRD,SEM,N2 physical adsorption,NH3-TPD and Fourier transformed infra-red spectroscopy of pyridine adsorption(Py-FTIR).By loading Pt on the ZSM-22 zeolite crystals,the Pt/ZSM-22 bifunctional catalysts were prepared,in which ZSM-22 zeolite crystals played the role of acid supports and the 0.5%Pt acts as(de)hydrogenation active sites.The hydroisomerization of n-alkanes was carried out with n-dodecane as the probe molecules.The effect of water content in the zeolite synthesis solution on the hydroisomerization performance of Pt/ZSM-22 catalyst was investigated.The results indicated that the less the water,the smaller the ZSM-22 crystals.However,a few cristobalite and ZSM-5 crystals were formed when the content of water in the synthetic solution was reduced to a certain value.HZSM-22 synthesized in the solution with the molar composition of SiO2∶Al2O3∶K2O∶DEA∶H2O=1∶0.01∶0.08∶0.29∶28 showed the highest medium and strong Brønsted acid amount in the three HZSM-22 samples,and shorter c-axis length.The bifunctional catalyst Pt/HZSM-22 prepared with this kind of HZSM-22 crystals showed the best catalytic performance.The conversion of n-dodecane was 73.24%,the yield of iso-alkanes was 57.92%,and the selectivity of iso-alkanes was 79.09%.Moreover,the selectivity of mono-branched iso-dodecane with methyl branching positioned in the center of the chain,5-methylundecane,was up to 17.66%at 320℃.
万方数据
维普
