氟化铵对HZSM-5分子筛改性的研究

STUDIES ON THE MODIFICATION OF ZEOLITE HZSM-5 WITH NH_4F

利用XRD,IR,MAS-NMR,TEM,XPS和SIMs等方法研究了经不同浓度NH_4F浸渍后的HZSM-5分子筛结构和表面性质的变化,并用NH_3-TPD和吡啶吸附的IR光谱研究了分子筛表面酸性的变化。发现NH_4F对HZSM-5分子筛有脱铝和脱硅作用,并有羟基氟化铝微晶生成。经改性后的HZSM-5表面富铝,F以取代O或OH的形式与分子筛中的Si或Al结合。NH_4F使HZSM-5总酸量减少,酸性减弱,B酸比例增加。经改性后,HZSM-5分子筛对甲苯歧化反应的催化性能将得到改善,乙苯-乙醇烷基化反应稳定性和二乙苯收率得到提高。

XRD,IR,MAS-NMR and TEM results showed that there was apprreciable aluminum removal from the framework of zeolite HZSM-5 when it was treated with 0.1, 0,4, 1.0 and 4.0mol/1 ammonium flouride aqueous solutions, and the structure was singnificatly affected by this latter treatment. XPS and SIMS showed that aluminum was enriched on the surface after the treatment and O atoms or OH could be substituted by F during the modification process. Infrared and TPD studies of these samples suggest that impregnated fluoride changes the ratio of different acidic sites. When impregnated with ammonium fluoride of an appropriate concentration, the activity and stability for toiuene disproportionation and the stability for ethanol-ethylbenzene alkylation can be improved. It appears that the medium strong acid sites are more active for the former reaction and the weak acid sites are more suitable for the latter reaction.