Quantitatively study acid strength distribution on nanoscale ZSM-5

The acid strength distribution of different samples such as HZSM-5, modified HZSM-5, TS-1 and SiO2 was investigated by modified Hammett indicator and ammonia temperature programmed desorption (NH3-TPD). It has been shown that only acid sites with H0 ⩽ +2.27 contribute to the conversion of toluene in toluene disproportionation, which is only small percent in the total acid amount. The acid sites with strength +4.8 ⩽ H0 ⩽ +6.8 may be ascribed to the acid sites that were produced by silanol group in HZSM-5. In study of HZSM-5 and modified HZSM-5 by NH3-TPD, the lower temperature peak (LT) and higher temperature peak (HT) are ascribed to the acid sites with strength −3.0 < H0 ⩽ +2.27 and H0 ⩽ −3.0, respectively. The two kinds of acid sites origin from framework Al in certain circumstances and one (H0 ⩽ −3.0) is easy to block and the other one (−3.0 < H0 ⩽ +2.27) is the body of acid sites, which is significant to fully understand the acid sites of nanoscale HZSM-5.