Synthesis of FER/MFI composite zeolite using isopropylamine as a structure-directing agent

A comprehensive investigation into the synthesis of the FER/MFI composite zeolite based on the isopropylamine-silica sol-NaAlO2-H2O system has been carried out. Parameters such as the Na2O/SiO2 molar ratio, SiO2/Al2O3 molar ratio, water concentration, and structure-directing agent (SDA) concentration were of great importance in the crystal phase transition and the morphology control. FER/MFI composite zeolites could be successfully prepared under the conditions of the SiO2/Al2O3 molar ratio ranging from 20 to 30 in the gel mixture. SEM and TEM images showed that the two different crystals (FER and MFI frameworks) in FER/MFI composite zeolites had a state of co-existence and staggered growth, which was typical of composite zeolites. Among these factors influencing the synthesis process, adjusting the Na2O/SiO2 molar ratio was easy to control the relative contents of each phase in the composite zeolites. The higher Na2O/SiO2 molar ratio was, the more content of the FER phase was. NH3-TPD and FT-IR of adsorbed pyridine results showed the acidity properties of composite zeolites were significantly different from those of corresponding physical mixtures. Interestingly, the distribution of aluminum between the FER and MFI structures in the composite zeolites was unequal, and aluminum atoms tended to enrich in the phase predominating in the FER/MFI composite zeolites. The catalytic performance in the cracking of olefins like butene and pentene of the FER/MFI composite zeolite was superior to that of the pure ZSM-5 zeolite. The FER/MFI composite zeolite after further modification is expected to become an excellent catalyst for the catalytic cracking of low carbon olefins to ethylene and propylene.