Investigation of Si Atom Migration in the Framework of MSE-Type Zeolite YNU-2

Abstract

The change in distribution of Si atom defects in the framework of zeolite YNU-2 by steam treatment was investigated using powder X-ray diffraction and solid-state NMR spectroscopy. The precursor of zeolite YNU-2 (abbreviated to YNU-2P) with a three-dimensional pore system has a large number of Si atom defects (more than 10% of all T sites in a unit cell) around the supercage. These defect sites were confirmed by observation of a Q 3 ((-SiO) 3 Si-OH) resonance peak by 29 Si magic angle spinning NMR spectroscopy. We have shown that steam treatment of YNU-2P at 523 K for 24 h significantly decreases the relative intensity ratio of the observed Q 3 resonance peak for the Q 4 ((-SiO) 4 Si) peak. The Rietveld analysis of steam-treated YNU-2P (YNU-2P ST ) shows a marked increase in the site occupancies of the defective Si sites. Furthermore, the Si atom defects in YNU-2P ST almost disappeared after calcination, yielding siliceous zeolite YNU-2. These results indicate that the defective framework structure was almost restored by steam treatment. Experimental results suggest that Si atom migration in the framework of YNU-2P takes place during steam treatment. The migrated Si atom fragment fills defect sites and is connected with adjacent silanol groups. In addition, the quantity of the half amount of structure-directing agent molecules was removed from the micropores in YNU-2P ST by steam treatment.

Synthesis of hierarchical ZSM-12 nanolayers for levulinic acid esterification with ethanol to ethyl levulinate

“…41,42 For instance, the Q 4 -type Si atoms are related to Si(OSi) 4 . 43,44 The Q 3 -type Si atoms can be referred to Si(OAl)(OSi) 3 or terminal silanol groups in Si(OH)(OSi) 3 , 41,44 whereas the Q 2 -type Si atoms are referred to Si(OAl) 2 (OSi) 2 and geminal silanol groups in Si(OH) 2 (OSi) 2 . [44][45][46] From the results, it is clearly observed that at the initial stage of crystallization (2 h), the Q 4 peak (À111 ppm) is very broad and present as a shoulder peak of the Q 3 peak (À99 ppm), suggesting that the coordination environment of the corresponding framework Si atoms is distorted.…”

The ADOR mechanism for the synthesis of new zeolites

“…Such migration of tetrahedral silicon species has recently been seen by Hong and co-workers in the zeolite natrolite 98 and for the healing of defects in zeolite YNU-2. 99 As a result, this process removes the vast majority of Ge atoms producing high Si/Ge ratios (greater than 200). Calcination of the material leads to IPC-2 zeolite that possesses the same connectivity as zeolite OKO.…”

Selective Production of Light Olefins over MSE-type Zeolite Catalyst

“…Changes to the chemical composition of the product through the direct crystallization of a pure MSE phase is difficult to achieve, and tends to instead generate other phases such as BEA, MTW or MOR. We have previously succeeded in overcoming this limitation by utilizing the steam-assisted crystallization (SAC) method 19), 20) with some post-synthetic modification to obtain a pure-silica version of MSE (YNU-2) 4), 21) . This process requires a crystallization period of ca.…”