Dual Templating of Macroporous Silicates with Non-crystalline

J. Am. Chem. Soc. 1999, 121, 4308-4309

Dual Templating of Macroporous Silicates with Zeolitic Microporous Frameworks

Brian T. Holland,^† Lloyd Abrams,^‡ and Andreas Stein^†*

Department of Chemistry, University of Minnesota, Minneapolis, Minnesota, 55455
DuPont Central Research & Development, Contribution No. 7910, Wilmington, Delaware, 19880

Abstract

Macroporous silicalite with a bimodal pore structure containing combinations of micropores and macropores was synthesized by a dual templating method. Latex spheres were utilized for the fabrication of macropores and tetrapropylammonium hydroxide (TPAOH) as a structure-directing agent for the generation of silicalite walls. The porous product was prepared by percolating a mixture of TPAOH and tetraethyl orthosilicate (TEOS) through an array of close-packed latex spheres. Heat treatment at 130 deg. C in a Teflon-lined autoclave, followed by removal of the organic components by calcination produced zeolitic walls around 250 nm void spaces. Hg porosimetry measurements confirmed that the macropores were accessible. Powder X-ray diffraction (PXRD), FT-IR, and ²⁹Si MAS-NMR identified the microporous phase as silicalite (MFI), a zeolite with Å0.55 nm pores. Nitrogen adsorption/desorption isotherms confirmed the presence of microporosity within the sample. SEM micrographs showed no distinct large silicalite crystals external to the macroporous solids. The PXRD pattern remained unchanged after the sample was refluxed in water for 13 h, indicating that the zeolitic walls were more hydrothermally stable than, for example, mesoporous silica with the MCM-41 structure. These bimodal pore systems may find use as chromatographic supports and size-selective solid catalysts that combine the advantages of size-selectivity in the smaller pores and easy access through the macropores.