Synthesis of Nanoporous Flower-like Y-SAPO-11 Composite Molecular Sieves for Hydrocracking of n-Hexadecane

Abstract

Middle-distillate hydrocracking nanoporous catalysts with good cracking activity and isomerization activity were prepared to improve the middle distillates such as kerosene and diesel quality and yield. Using a hydrothermal method, we synthesized nanoporous flower-like xY-SAPO-11 composite molecular sieves with different weight percentages. For comparison, Y + SAPO-11 mechanical mixture were also prepared by mechanical mixing. A series of characterization methods were used to characterize the composites and mechanical mixture. Hydrocracking catalysts Cat-xY-S and Cat-Y + S were prepared with composites and mechanical mixture as the support acidic components, respectively, and their catalytic performance in hydrocracking was investigated. It is demonstrated that nanoporous composite molecular sieves perform differently from mechanical mixture regarding physicochemical and catalytic properties. The Y-SAPO-11 composite molecular sieves have larger pore volumes and pore sizes and lower acidity than the mechanically mixed molecular sieves with the same weight percentage. This is caused by the interaction between the SAPO-11 and Y phases. This interaction leads to the SAPO-11 and Y phases being combined by chemical bonding, forming a coordination structure of the framework elements. The composite molecular sieves exhibited higher yields of C₈–C₁₂ products than mechanical mixtures in the hydrocracking reaction. When the Y-phase weight percentage was 61.7 wt %, i.e., the Cat-8Y-S catalyst with suitable cracking activity and isomerization activity, it had the highest isomerized C₈–C₁₂ product yield of 33.1% at 360 °C while maintaining a high C₈–C₁₂ product yield.