Study On The Acidities Of The Modified HZSM-5 Zeolites

The HZSM-5 zeolite catalysts with four different materials Zr,W,B,P were prepared by crystallized calcination and coprecipitation method.The catalysts were characterized by the method of IR, XRD,BET, FT-IR, DSC-TG, SEM and so on. The improved indicator method was established to test the zeolite acidity. The results show that:1.The frame works and shape-selecting catalysis performance of the ZSM-5 zeolites are retained in the modified catalysts prepared by different modifiers and different processes;Total acids and surface of zeolites reduced greatly because of the more loadings and the smaller radius of atoms which easier enter into the inside of ZSM-5 zeolites.2.In the zeolites modified by ZrO2,The surface of zeolite is not change too much,because the Volume of Zr is large and it stays on the outside of zeolite.The amount of strong acids and mid-strong acids on the surface of zeolite increase gradually and the amount of weak acids decrease gradually with increasing the loading of ZrO2.The Bronsted sites increase not obviously and Lewis sites increase obviously.3.In the zeolites modified by WO3,The surface of zeolite is not change, because the volume of W is large and it stays on the outside of zeolite. Compared with the raw zeolite, the ZSM-5 zeolite modified by 0.5%WO3 has less total acids and more mid-strong acids.The ratio of Bronsted and Lewis is 20.2, which is 4.7 times of the raw zeolite. It has a good application prospect.4.In the zeolites modified by B2O3 and P2O5,The surface of zeolite is change too much,because the volume of B,P is small and it enters in the inside of zeolite.The amount of acids on the surface of zeolite decrease obviously with increasing the loading of modifier. The Bronsted sites decrease correspondingly and Lewis sites increase gradually with increasing the loading of B2O3.The strong acids decrease from 0.378mmol/g to 0.054mmol/g and the total acids decrease from 0.756mmol/g to 0.324mmol/g.The Bronsted sites on the surface of zeolite increase because of modified by P2O5.5.The total acids of compound modification for zeolite not change obviously but the part of mid-strong acids increase.Compared with the zeolite modified by B2O3 and P2O5,compound modified zeolite has more total acids and it is more flexible to control the acidic of zeolite for satisfying catalytic demand.