低有机模板剂对合成ZSM-5沸石及其性能的影响

Effect of Low Amount of Organic Template Agent on the Zeolite ZSM-5 and Its Performance

为在低有机模板剂的条件下合成形貌规则和结晶良好ZSM-5沸石提供策略.本研究以硅溶胶为硅源,偏铝酸钠为铝源,在四丙基溴化铵(TPABr)/SiO2(即模/硅比)为0.03~0.15范围内,采用水热合成法成功制备结晶良好和形貌规则ZSM-5沸石.利用XRD、SEM、N2吸附-脱附、NH3-TPD和ICP等手段对样品进行表征,并考察其在甲苯-甲醇烷基化和正辛烷裂解反应中的催化性能.结果表明,在不同有机模板剂量条件下合成的ZSM-5具有相近Si/Al比、孔结构和酸性能,但其晶粒尺寸在模/硅比为0.03时制备的HZSM-5最大约为1μm,在模/硅比为0.15时制备的HZSM-5晶粒尺寸最大约为178 nm.晶粒较小的ZSM-5在正辛烷裂解反应中具有较高的催化活性,而晶粒较大的ZSM-5在甲苯-甲醇烷基化反应中具有较高的对二甲苯的选择性.

The aim of this paper is to provides a general strategy for preparing zeolites with high crystallini⁃ties and regular morphologies under the condition of low amount of organic template.ZSM 5 zeolites with high crystallinities and regular morphologies were successfully synthesized by hydrothermal synthesis using silica sol as the silicon source and sodium meta-aluminate as the aluminum source in the range of 0.03~0.15 molar ratios of tetrapropylammonium bromide(TPABr)/SiO_(2).The prepared samples were characterized by XRD,SEM,N_(2) adsorption-desorption,NH_(3)-TPD,ICP,and their catalytic properties were investigated in the n-octane cracking and toluene-methanol alkylation reaction.The results showed that the as-synthesized ZSM 5 with the different TPABr amounts had the similar Si/Al ratios,pore structure and acidity as the molar ratios of(TPABr)/SiO2 were in the range of 0.03~0.15.However,the molar ratio of(TPABr)/SiO2 greatly influ⁃enced the crystal size of the as-synthesized ZSM-5.The crystal size ZSM-5 sample synthesized at 0.03 of(TPABr)/SiO2 is about 1μm,while it is about 200 nm for that synthesized at 0.15 of(TPABr)/SiO2.The ZSM-5 samples with the different crystal size exhibited different catalytic performances.In n-octane cracking reaction,the ZSM-5 with a smaller crystal size gave higher catalytic activity than those with bigger crystal sizes.However,the samples with bigger crystal size exhibited higher selectivity to p-xylene than while for smaller mode/silica ratio(0.03)catalyst,applied to toluene-methanol alkylation reaction,has higher selectivi⁃ty than those with smaller crystal sizes.