Hierarchical MAPSO-11 molecular sieves synthesized from aluminum isopropoxide: synergistic effect of acidity and mor-phology on the hydroisomerization of n-C16

Bifunctional catalysts based on SAPO-11 molecular sieves exhibit high selectivity in the hydroisomerization of long-chain n-paraffins; however, their widespread application is constrained by moderate acidity and diffusion limitations within the 1D channels. Herein, we propose a strategy to enhance catalyst efficiency through the creation of a hierarchical structure and isomorphous substitution with magnesium (MAPSO-11). It was established that the use of aluminum isopropoxide promotes the formation of a hierarchical porous architecture composed of aggregated nanocrystals. The influence of magnesium on the morphology was elucidated: at an optimal MgO/Al2O3 ratio of 0.1, primary crystals of minimal size (~50 nm) are formed, which ensures a maximized external surface area (SEXT= 93 m2/g) and secondary mesopore volume (Vmeso = 0.19 cm3/g). A further increase in magnesium content leads to crystal growth and a reduction in pore accessibility. TPD-NH3 results confirm that the introduction of Mg significantly enhances the total acidity and the concentration of strong acid sites compared to conventional SAPO-11. Catalytic testing of Pt-containing systems in the hydroisomerization of n-hexadecane demonstrated that the developed mesoporosity and enhanced acidity enable a shift of the temperature window for maximum isomer yield to a lower temperature range (20–30 °C below that of SAPO-11). The obtained results demonstrate an effective approach for tuning the activity of hierarchical molecular sieves through precise control of the magnesium content, opening new avenues for the development of low-temperature catalysts for the production of low-pour-point oils and fuels.