Formation of MFI-type zeolite nanoparticles and zeolite-based suspensions

Resumo

Based on a commercial zeolite of the MFI type, nanoparticles have been produced using mechanical methods (grinding in a ball or planetary mill, classification by “stirring-up”) and ultrasonic treatment (UST) of zeolite in water. It has been found by spectral methods (XRD, DRIRS, ²⁷Al and ²⁹Si solid-state NMR) and adsorption analysis that the grinding of the zeolite leads to partial degradation of its structure and appearance of defects in the crystalline framework, whereas the zeolite crystal lattice remains completely intact after sonication in the aqueous medium. The sonication destroys MFI agglomerates to form nanoparticles down to 40–50 nm in size. The dispersion of the zeolite nanoparticles in silicone or hydrocarbon oil–(Syltherm 800 or Dowtherm RP, respectively) as a high-boiling-point liquid leads to the formation of ultrafine suspensions, the stability of which depends on the type of the dispersion medium. The nanosized zeolite suspensions are more stable in Dowtherm RP than in Syltherm 800: without agitation, they are persistent for at least 3 weeks (settling at room temperature).