The Si/Al ratio of the SiO2 coated sample increased from 94 to 114. TEM images showed that the surface of Z5 particles was smooth, and the crystal edge lattice was consistent with the center (Fig. ). However, the surface of Z5@2SiO2 particles was rough and had obvious adhesion, and there was an amorphous shell on the edge of the particles (Fig. ), which effectively proved that the surface of Z5 was successfully wrapped with SiO2 layer. BET results showed that the specific surface area and pore volume of the coated zeolite decreased slightly but the average pore size was almost unchanged (Table ). NH3-TPD and Py-FTIR spectroscopy were used to characterize acid properties. In the NH3-TPD curves (Fig. ), two main peaks at 164 ℃ and 364 ℃ belonged to weak acid and strong acid sites, respectively. The acid amount of weak acid and strong acid decreased from 71.7 and 80.7 mmol/g of Z5 to 40.8 and 25.2 mmol/g of Z5@2SiO2 (Table ), respectively. In the Py-FTIR spectra shown in Fig. , the peaks at 1543 and 1446 cm -1 were attributed to pyridine adsorbed on Brønsted acid and Lewis acid sites, respectively. Both the L-and B-acid amounts of the passivated Z5@2SiO2 were also significantly reduced. These indicated that the SiO2 shell layer effectively covered the acidic sites on the outer surface of Z5.