氟硅酸铵同晶置换改性ZSM-22分子筛的催化性能

Catalytic Properties of(NH_4)_2SiF_6-Modified ZSM-22 Zeolite

分别采用不同浓度的(NH4)2SiF6水溶液对ZSM-22分子筛进行同晶置换改性,并采用XRD、N2吸附-脱附、NH3-TPD、Py-IR、29Si MAS NMR对同晶置换改性前后的分子筛进行了表征,考察(NH4)2SiF6改性对分子筛孔道结构及酸性的影响。将改性前后的分子筛用浸渍法制备了0.5%Pd/ZSM-22双功能催化剂,并在连续微型固定床反应装置上考察了其对正癸烷(n-C10)加氢异构化反应的催化性能。结果表明,(NH4)2SiF6改性选择性地脱除了分子筛的部分强酸中心,有效地抑制了正癸烷的裂化反应。用0.3mol/L(NH4)2SiF6溶液改性后的分子筛制备的Pd/ZSM-22催化剂的加氢异构化反应活性和异构化选择性均得到提高。

Crystal replacement modification to ZSM-22 zeolite was made in（NH4）2SiF6 aqueous solution of different concentrations.The parent and（NH4）2SiF6-modified ZSM-22 zeolites were characterized by X-ray diffraction,N2 adsorption-desorption,29Si MAS NMR,NH3 temperature-programmed desorption and FT-IR spectroscopy of adsorbed pyridine,to investigate the effect of（NH4）2SiF6 modification on the structure of pores and acidity of HZSM-22 zeolite.The hydroisomerization of n-decane over Pd supported on the ZSM-22 and modified ZSM-22 was carried out,respectively.The results showed that part of strong acid sites of HZSM-22 were removed selectively by（NH4）2SiF6 modification,and the cracking of n-decane was effectively suppressed.The conversion of n-decane and the isomerization selectivity were increased over the bifunctional catalyst Pd/ZSM-22 modified by 0.3mol/L（NH4）2SiF6 aqueous solution.