Synthesis of phosphorus-modified AFX zeolite using a dual-template method with tetraethylphosphonium hydroxide as phosphorus modification agent

Hydrothermal conversion of FAU zeolite was carried out in the presence of both 1,1'-(1,4-butanediyl)bis(1-azonia-4-azabicyclo[2,2,2]octane) (Dab-4) cation as a structure-directing agent and tetraethylphosphonium (TEP) cation as a phosphorus modification agent. By optimizing the synthesis parameters such as the TEPOH/SiO2, [Dab-4](OH)(2)/SiO2, NaOH/SiO2, and H2O/SiO2 ratios in the starting reaction mixtures, we successfully synthesized highly crystalline phosphorus-modified (P-modified) AFX zeolite with truncated hexagonal bipyramidal morphology. The P-modification of the AFX zeolite needed a TEP/(Dab-4 + TEP) ratio higher than 0.9 because TEP cations have no structure-directing ability for the AFX phase. The obtained P-modified AFX zeolite with a Si/Al ratio of 5-6 and a P/Al ratio of 0.07-0.2 exhibited high thermal stability compared to the P-free one.