What are the methods to increase the silicon-aluminum ratio of molecular sieves?

1. Synthesis regulation

① Adjust the raw material ratio: increase the ratio of silicon source to aluminum source, such as reducing the amount of sodium aluminate or increasing the amount of water glass.

② Select a suitable silicon-aluminum source: select a highly active silicon source and a suitable aluminum source according to demand, such as silica sol, pseudo-boehmite, etc.

③ Add mineralizer template: add mineralizers such as fluoride and different organic amine templates to promote reaction and guide crystal growth.

2. Post-treatment

① Dealumination treatment: acid treatment such as nitric acid, hydrothermal treatment at 400-600℃ or chemical vapor dealumination such as hydrogen chloride gas can be used.

② Secondary synthesis: Based on low silicon-aluminum ratio molecular sieves, add more silicon source during secondary synthesis, and control conditions to reduce aluminum introduction.