Tailoring Silicoaluminophosphate SAPO-11 Nanocrystal Morphology: Silicon Content as a Switch for Two-Dimensional Growth and Enhanced Catalytic Performance in Isodewaxing of Gas-to-Liquid Waxes

Traditional silicoaluminophosphate SAPO-11 catalysts for the isodewaxing of gas-to-Liquid (GTL) waxes suffer from severe diffusion constraints within their one-dimensional (1D) channels, reducing their activity and selectivity. While two-dimensional (2D) nanostructures mitigate this issue, their synthesis typically requires expensive and environmentally unfriendly organic structure-directing agents. This work reports a hydrothermal synthesis of 2D SAPO-11 nanosheets without organic additives, utilizing control over the SiO 2 source dispersion and the SiO 2 /Al 2 O 3 molar ratio. The materials were comprehensively characterized (X-ray fluorescence analysis, powder X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscope, 29 Si magic-angle spinning nuclear magnetic resonance spectroscopy, nitrogen adsorption–desorption, X-ray photoelectron spectroscopy, ammonia temperature-programmed desorption), and the 0.5% Pt/SAPO-11 bifunctional catalysts were evaluated in the hydroisomerization of n-hexadecane and real GTL wax derived from CO 2 . It was established that an ultradispersed SiO 2 sol (∼1 nm) at an SiO 2 /Al 2 O 3 ratio of 0.3 acts as a morphological ″switch″, directing the crystallization toward 2D nanosheets (10–20 nm thick) instead of conventional 3D prisms (∼80 nm). TEM-SAED analysis confirmed that the 1D channels are aligned perpendicular to the nanosheet basal plane, resulting in an ultrashort diffusion path length (∼15 nm). Kinetic studies indicated that this morphology control is achieved through the high dissolution rate of the SiO 2 (1 nm) particles, which suppresses three-dimensional crystal growth. The optimized 2D catalyst, Pt/SAPO-11-(1 nm)-0.3, exhibited a high yield of iso-C 16 hydrocarbons (>89%). In the isodewaxing of GTL wax, this catalyst afforded a high lubricant base oil yield (69%) with excellent low-temperature fluidity (pour point = −32 °C) at a process temperature 20 °C lower than that required for a microcrystalline counterpart. This study demonstrates an efficient nanoengineering strategy for designing highly selective SAPO-11 catalysts for the sustainable upgrading of GTL feedstocks.