A series of fluorinated nanosized HZSM-5 catalysts were prepared by impregnating the zeolite with NH4F solution. The samples were characterized by XRD, XRF, FTIR-Py, TPD, 27Al and 29Si MAS-NMR. The effect of calcination temperature on the structure and acidity was studied in the range of 400-500°C. When the calcination temperature increases, more framework aluminum atoms are removed due to the fluorination. As a result, the number of acid sites and the acid strength decrease, but the ratio of the total Brönsted acid sites to the total Lewis acid sites (BT/LT) increases. The fluorinated nanosized HZSM-5 catalysts exhibit better stability in the methylation of biphenyl (BP) with methanol. Moreover, the stability increases with the increase of the calcination temperature. When the fluorinated nanosized HZSM-5 is calcined at 500°C, the conversion of BP can keep at about 10% for 50h. The enhancement of stability may be due to the decrease of the acid strength and the increase of the ratio of BT/LT.
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