Influence of tailoring acidic sites and silicon distribution of SAPO-11 zeolite via in-situ Zn modification for superior hydroisomerization of Fischer-Tropsch wax

Improving the performance of hydroisomerization catalysts for jet fuel production remains a considerable challenge, due to the difficulty in precisely controlling the balance between metal and acid functions. Although zinc modification offers a promising strategy to enhance the synergy, the underlying mechanistic understanding of Zn-induced framework repair and reconstruction remains unclear, blocking the rational design of bifunctional catalysts. In this work, A series of Zn-modified SAPO-11 zeolites with tunable ZnO/Al 2 O 3 ratios were synthesized via in-situ doping technique. Characterization results revealed that Zn substitution for Al altered the silicon incorporation environment. The formation of Si-O-Zn bonds (NH 3 adsorption energy = -0.99 eV) indicated weaker acidity than Si-O-Al bonds (−1.44 eV). At ZnO/Al 2 O 3  = 0.5% doping, isolated P-O-Zn bonds promoted the dispersion and dissolution of large silicon islands (Si(4Si)), increasing weak Brønsted acid sites. At higher Zn doping, the mechanism shifted inducing Si redistribution and forming medium-strong Brønsted acid sites. Namely, a dual role of Zn was identified as framework repair at low loading and framework reconstruction at high loading. The weakened and dispersed acidity enhanced Pt dispersion and reducibility, enabling Pt/(0.75ZnSAPO-11 + ASA) catalyst to deliver the highest iso-C 22 yield (30.9%) and selectivity (58.7%), with double-branched isomer yield (10.8%) and selectivity (20.6%). This work highlights the underlying mechanism of Zn modification in catalyst framework, and demonstrates its implications for enhancing the industrial application of Zn-modified catalysts in Fischer-Tropsch wax upgrading and jet fuel cold-flow performance.