Catalytic Cracking of Endothermic Fuels over Meso-HZSM-5/MCM-41 Coatings

Novel structured catalysts of meso-HZSM-5/MCM-41 composite coatings were synthesized via a two-step process: washcoating HZSM-5 powder on the internal surface of a stainless steel tube and subsequently converting SiO₂ binder into MCM-41 by sequential desilication and recrystallization. Additional Fe and Al species were incorporated into the MCM-41 framework for increasing the active sites. It was found that the adherence strength of composite coating was remarkably improved, as a result of encapsulation of HZSM-5 crystals into the successive MCM-41 network. Catalytic cracking of supercritical n-dodecane (500 °C and 4 MPa) was employed to test the catalytic performance of the coatings. The ZC-Al/Fe coating with both Fe and Al species incorporated into the MCM-41 framework showed an excellent catalytic performance, with the initial conversion of n-dodecane enhancement by 50.6%, the deactivation rate reduction by 64.5%, and the heat sink improvement by 14.5%, compared to the parent HZSM-5 coating. The performance enhancement for ZC-Al/Fe coating may result from the sequential precracking–cracking–dehydrogenation reaction process catalyzed by acid sites in MCM-41, acid sites in meso-HZSM-5, and redox sites in MCM-41, respectively.