Synthesis of a hierarchically micro–macroporous structured zeolite monolith by ice-templating

Abstract

The zeolite monolith with a micrometre-sized honeycomb structure was prepared by using the ice-templating method. The synthesized samples were characterized by SEM, powder X-ray diffraction analysis, mercury porosimetry, and nitrogen adsorption–desorption measurements. The precursor silica gels with channel diameters of 10–50 µm were prepared by the ice-templating method. Then the amorphous phase of the precursor silica gels was converted into a crystalline phase by the steam treatment in the presence of structure-directing agents. In this work, tetrapropyl ammonium hydroxide was selected as a structure-directing agent, and the crystalline phase of the synthesized sample was identified as silicalite-1 from XRD analysis. After crystallization, the particulate silicalite crystals were generated on the surface of the honeycomb wall, and the honeycomb structure was retained without cracking. The size of the synthesized silicalite crystals was controlled by the crystallization temperature and time. The nitrogen adsorption–desorption isotherm on the synthesized silicalite monolith showed type I isotherms, and the specific surface area calculated by the Brunauer–Emmett–Teller method was 332.0 m² g⁻¹. These results indicated the existence of micropores in the framework of silicalite-1.