Catalytic Cracking of Supercritical n‑Dodecane over Wall-Coated Nano-Ag/HZSM‑5 Zeolites

A series of Ag modified zeolites were prepared by incipient impregnation of nano-HZSM-5 with AgNO₃ (0.5–2.0 wt %) aqueous solutions. It was found that the ion-exchange and impregnation effect both existed in this impregnation process, resulting in the formation of various silver species which altered the zeolite acid properties. The wall-coated nano-Ag/HZSM-5 zeolites were prepared on the inner surface of 304 stainless steel tubes though the washcoating method. Catalytic cracking of supercritical n-dodecane (4 MPa, 550 °C) was used to examine the catalytic activities of the prepared catalytic coatings. It is found that the modified samples with 1.0% Ag showed higher conversion (up to 1.50 times) than the parent one because of the dehydrogenation effect of silver species and that the overloaded (for example, 2.0 wt %) samples show lower performances ascribing to the blockage of diffusion pores by the silver species.