Synthesis and Catalytic Performance of ZSM-5/MCM-41 Zeolites With Varying Mesopore Size by Surfactant-Directed Recrystallization

Recently, an interest in the catalytic cracking of hydrocarbon fuels is motivated by the desire to enhance engine performance over the entire spectrum of flight regimes. For hypersonic flight, hydrocarbon fuels can serve as not only source of heat through combustion, but also coolant through the cracking reaction to remove waste heat from aircraft systems [ 1 – 5 ]. Huang et al. [ 1 ], Sobel and Spadaccini [ 6 ] and Sicard et al. [ 7 ] investigated the cracking of several fuels, including conventional kerosene-base jet fuels (JP-7, JP-8 and JP-8+100), n -heptane and Norpar 12 (a blended normal paraffin) in a zeolite-coated reactor under the simulated high-speed flight conditions (650 °C and 2.4 MPa). Fan et al. [ 8 ] studied the catalytic cracking of China No. 3 aviation kerosene over wall-coated HZSM-5 zeolite under conditions similar to the practical scramjet applications (777 °C and 7.0 MPa). Liu et al. [ 9 , 10 ] studied the effects of the Si/Al ratio and crystal size (nano- and microscale) of ZSM-5 zeolites coated on the wall of a flowing tubular reactor on the cracking of n -dodecane at 550 °C and 4.0 MPa. The results indicated that HZSM-5 zeolite is an ideal candidate for the cracking of hydrocarbon fuels because of its relatively low coke deposition. However, the relatively small pore size of ZSM-5 zeolite limits the diffusion of bulky molecules from the surface to active sites located in the pores, which makes its catalytic activity being not fully exhibited. To overcome this limitation, one way is to shorten the diffusion length, and another way is to improve the effective diffusivity of the reactant molecules in the zeolite pores. For the latter strategy, micro-/mesopore composite zeolites with the strong acidity of micropore zeolites and the mesopores in the typical range of 2–15 nm have been intensively developed [ 11 ].