Synthesis of SAPO-44/11 composite molecular sieves for n-hexane hydroisomerization

Integrating different molecular sieves facilitates to intensify the advantages of each single species but weaken their deficiencies in applications. The main goal of the present work is to align SAPO-44 and SAPO-11 as a potential composite catalyst for hydroisomerization of normal alkanes. In the present work, microparticles of SAPO-44 were used as seed into the SAPO-11 synthesis gel to synthesize SAPO-44/11 composite molecular sieves. The ratio of SAPO-44 to SAPO-11 in the prepared composites was modulated by changing the dose of SAPO-44 seed. The obtained composites have been characterized by XRD, SEM, N₂ adsorption/desorption and NH₃-TPD. The characterizations demonstrated that the crystalline grains of SAPO-44 and SAPO-11 were tightly integrated. Their amount of acid site, as well as specific surface area, exhibits a compromise of that of SAPO-11 and SAPO-44. More strong acid sites and larger surface areas were observed with the increasing content of SAPO-44. Based on the composite molecular sieves, correspondent Pt/SAPO-44/11 bifunctional catalysts were prepared and applied in hydroisomerization of n-hexane. Expectedly, they exhibited superior conversions and yields, attributed to the optimal pore structure and surface acidity of the composites.