Efficient synthesis of MSE-type zeolite using a highly effective organic structure-directing agent and excellent catalytic performance of its derived titanosilicate

The use of organic structure-directing agents (OSDAs) is effective in constructing zeolite frameworks with high hydrophobicity and thermal stability. Since OSDAs are guest molecules that stabilize cyclic hosts, designing guest molecules and realizing strong host-guest interactions is one of the reasonable strategies for controlling the structure of zeolites. A very powerful OSDA for the synthesis of MSE-type zeolite was designed and successfully prepared. When using conventional OSDA, TEBOP²⁺, more than 10 d of crystallization time was necessary to give the conventional MSE-type zeolite (=MCM-68), whereas the use of the new type of OSDA, CHDMP²⁺, gave another MSE-type zeolite (MSE_CHDMP/STZ-1) within only 32 h of crystallization time. The computed values of stabilization energy showed that CHDMP²⁺-MSE composite was thermodynamically more stable than TEBOP²⁺-MSE composite, indicating the stronger host-guest interaction was realized by the CHDMP²⁺. Since CHDMP²⁺ has a suitable C/N⁺ value for the synthesis of high-silica zeolites, the strong host-guest interaction from the viewpoints of both geometry and hydrophobicity could cause frequent nucleation, giving the MSE-type zeolite with smaller crystals, i.e. STZ-1. The STZ-1 was thoroughly dealuminated and Ti atoms were introduced to the defect sites. Thus-obtained titanosilicate, Ti-STZ-1, was found to be an excellent catalyst for the phenol oxidation reaction. In particular, the total product yield and the para-selectivity were up to 92.2 % and 95.9 % in the presence of ethanol, respectively. Superior activity of Ti-STZ-1 to conventional Ti-MCM-68 was ascribed to smaller particle size caused by the stronger host-guest interaction between CHDMP²⁺ and MSE framework.