Synthesis of ZSM-5/SAPO-5 composite by two-step hydrothermal crystallization process

The composite ZSM-5/SAPO-5 molecular sieves were synthesized by two-step hydrothermal crystallization process. The effects of the mixing manner of the ZSM-5 gel and SAPO-5 gel, the acid type used to adjust the pH value of ZSM-5 mother solution, the composition of SAPO-5 gel, and the crystallization time on the synthesis of the composite were investigated. The results showed that the composite could not be obtained by simple mixing of two synthesized gels. The composite was successfully synthesized when the pH value was adjusted by sulfuric acid solution, the mass ratio of ZSM-5/SAPO-5 was 3.5 and the P₂O₅/Al₂O₃ molar ratio in the SAPO-5 gels was 1.2. The composite material contained small amount of amorphous substance, which could not be eliminated completely by extending the crystallization time.