Synthesis of isomorphous MFI nanosheet zeolites for supercritical catalytic cracking of n-dodecane

The isomorphous MFI nanosheet zeolites (MFI (M), M = Al, Ga, and Fe) were synthesized hydrothermally and characterized by XRD, SEM, TEM, N₂adsorption-desorption, NH₃-TPD, FTIR and pyridine-absorbed FTIR. The MFI nanosheet zeolites with higher surface area, large mesoporous, ultrathin lamella structure and different acidity strength were applied in the catalytic cracking of n-dodecane and their catalytic activity on the gas generation rate, product selectivity, carbon deposition and heat sink were determined. The gas generation rates of the MFI nanosheet zeolites were higher than that of ZSM-5 zeolite and bare tube. More light alkenes generated over the MFI nanosheet zeolites, and their deactivation rates were lower than that of ZSM-5 zeolite due to the special mesoporous and lamella structure which could prevent the deactivation resulting from pore blocking by carbon deposition. The heat sinks of the n-dodecane cracking at 550 °C under 4 MPa were 2865 kJ/kg for MFI-Al, 3040 kJ/kg for MFI-Ga and 2735 kJ/kg for MFI-Fe which were all higher than that of ZSM-5 zeolite (2542 kJ/kg) and bare tube (2175 kJ/kg). At 600 °C, the heat sinks for MFI-Al, MFI-Ga and MFI-Fe reached to 3124, 3384 and 3221 kJ/kg, respectively. Besides, from the cracking results of the MFI nanosheet zeolites, it can be concluded that the decrease of acidity strength by Ga substitution showed positive effect on the catalytic cracking of n-dodecane.