YNU-2 is a pure-silica version of MSE-type zeolite obtained by steam-assisted crystallization (SAC) technique, followed via suitable stabilization by postsynthesis modification. Taking advantage of the SAC method, the change of zeolitic phase during the crystallization was tracked. In the presence of organic structure-directing agent (OSDA), the Beta phase first appeared as an intermediate followed by the formation of OSDA-MSE composite, YNU-2P, as the final crystallization product. When the YNU-2P was directly calcined at temperatures higher than 400 °C to remove the occluded OSDA, the MSE framework collapsed due to the existence of a large number of site defects in the framework. The highly crystalline YNU-2 was only obtained when the YNU-2P was steamed or acid-treated under appropriate conditions. The framework stabilization was achieved by various techniques that cause Si-migration. The extent of Si-migration was dependent on the treatment conditions. For the Ti-incorporation to prepare [Ti]-YNU-2, enough but incomplete Si-migration by steaming is necessary rather than thorough acid-treatment to fill all the site defects. [Ti]-YNU-2 exhibits a catalytic performance superior to that of [Ti]-MCM-68, even though the former has a local hydrophilic field in the micropores that gives a type-V water adsorption isotherm, suggesting that the Si-migration occurs during the steaming and generates hydrophilic supermicropores.
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