Seeding on the Synthesis of MCM-22 (MWW) Zeolite by Dry-Gel Conversion Method and its Catalytic Properties on the Skeleton Isomerization and the Cracking of Hexane

Abstract

The effects of seeding on synthesis of MCM-22 (MWW) have been studied by the dry gel conversion (DGC) method. Highly reproducible crystalline MWW zeolite could be obtained by DGC method, using seeds of calcined sodium MWW with SiO 2 /Al 2 O 3 ¼ 31. Crystallization of MWW phase was completed in the presence of seeds (2 mass% against SiO 2 ) at 150 C within two days. The small amount of seed (0.25 mass% against SiO 2 ) was sufficient for the required phase formation of MWW. The MWW with SiO 2 /Al 2 O 3 ratio from 35 to 66 was obtained as pure phase; however, the crystallinity of MWW decreased with further increase in the ratio: products were contaminated with impurities.The catalytic properties of MWW were examined in the skeleton isomerization and the cracking of hexane, and compared to zeolites such as BEA, MFI, and MOR. The catalytic activities were in the order: MFI>BEA>MWW)MOR; however, the selectivity for the isomerization were in the order: BEA>MWW>MFI. These catalytic properties were due to the differences of structures and acid strength of zeolites.

Potassium-Ion-Exchanged Zeolites for Sustainable Production of Acrylic Acid by Gas-Phase Dehydration of Lactic Acid

“…Besides the zeolite type, the number y was also known as an important affecting factor to the acid–base property of zeolite catalysts. − Figures and show the effect of y on the NH 3 - and CO 2 -TPD profiles normalized to a unit surface area for the K 0.90+ m Na 0.10‑ m β_ y (22 ≤ y ≤ 111) and K 0.90+ m Na 0.10‑ m ZSM-5_ y (27 ≤ y ≤ 75) samples with very similar nominal K + -exchange degree ( m ≤ 0.08), respectively. The peak temperature (strength) and surface acidity (amount or peak intensity) registered from the NH 3 -TPD profiles for K 0.90+ m Na 0.10‑ m β_ y increased from 186 °C and 46 × 10 –3 μmol NH 3 ·m –2 to 233 °C and 608 × 10 –3 μmol NH 3 ·m –2 , respectively, when the number y was lowered from 111 to 22 (Figure A).…”

Structural Evolution of Amorphous Precursors toward Crystalline Zeolites Visualized by an in Situ X-ray Pair Distribution Function Approach

“…PDFs can usually be calculated from the total scattering data with synchrotron hard X-ray or neutron sources because it requires a significantly higher signal-to-noise ratio in the high- Q -value range (typically at or above 10 Å –1 ) than that which conventional diffraction experiments achieve . The PDF technique can be applied even if the target material is in a noncrystalline state; thus, many ex situ PDF analyses have been conducted on amorphous precursors for zeolites. − Moreover, in situ PDF analyses have been performed for other materials and have already shown their usefulness. , Nonetheless, this type of analysis has never been conducted for the crystallization of zeolites.…”

Isomerization and Cracking of Hexane over Beta Zeolites Synthesized by Dry Gel Conversion Method

“…1. All XRD patterns are assigned to BEA 24), 26) . We chose BEA(33) and BEA(103) synthesized by the DGC methods for the characterization of properties of BEA.…”

“…In this paper, we investigated the effects of SiO2/Al2O3 ratio of BEA synthesized by DGC methods on the isomerization and cracking of hexane, and compared with MFI, MWW, and MOR for the understanding of catalytic properties of BEA. 26) . MFI(39) was supplied from Tosoh as the ammonium form (HSZ-840NHA), and converted to the H-form by calcination.…”