骨架硅铝比对改性H-ZSM-5沸石孔结构及硅铝脱除行为的影响

摘要

H-ZSM-5 zeolites with different silica-alumina ratio were synthesized from silica sol and sodium aluminate,and then were modified through a combined alkali-acid treatment. The effects of the initial silica-alumina ratio of the H-ZSM-5 zeolites on the pore structure of the modified zeolites and their behavior in desilication and dealuminization were investigated by means of XRD,N2 adsorption,FTIR,SEM and TEM. The results indicated that,the synthesized samples possessed the characteristic diffraction peaks of the H-ZSM-5 zeolites,and the alkali-acid treatment promoted the removal of amorphous aluminium and silicon and improve the additional mesoporosity. With the increase of the initial silica-alumina ratio,the mesoporous area and volume of the modified zeolites increased,and their microporous area and volume firstly decreased and then increased. The increase in the initial silica-alumina ratio led to an increased desilication selectivity but a decreased dealuminization selectivity. In the alkali-acid treatment,the selectivity of the H-ZSM-5 zeolites to the desilication was much larger than that to the dealuminization. Partial amorphous aluminium and silicon on the crystal surface disappeared and textured cracks appeared. And the number of the surface defects increased with the increase of the initial silica-alumina ratio.%以硅溶胶为硅源、铝酸钠为铝源，制备不同硅铝比的H-ZSM-5沸石，采用碱-酸处理方法对制备的沸石进行改性，利用XRD、FTIR、SEM、TEM和N2吸附-脱附手段对处理前后的试样进行表征，考察了起始硅铝比对改性沸石孔结构和硅铝脱除行为的影响。实验结果表明，所制备的试样均具有H-ZSM-5沸石的特征衍射峰，碱-酸处理有利于脱除骨架外无定形硅铝和提高附加介孔率。随起始硅铝比的增大，沸石的介孔面积和介孔体积均增大，微孔面积和微孔体积先减小后增大， H-ZSM-5沸石的脱硅选择性增大，脱铝选择性减小。碱-酸处理过程中，H-ZSM-5沸石的脱硅选择性远高于其脱铝选择性；碱-酸处理后晶体表面部分无定形硅铝消失，出现织构性裂痕，且表面缺陷位数量随起始硅铝比的增大而增加。