High-silica ZSM-12 (MTW topology), synthesized with 6-azonia-spiro- (Rimer, 2018; Rimer, 2018) [5,5]-undecane as structure directing agent (SDA), was carefully characterized by using X-ray synchrotron powder diffraction. The structure refinement led to a monoclinic unit cell (space group Cc, Z = 4, a = 25.0814(13) Å, b = 15.0987(8) Å, c = 24.4419(17) Å, β = 107.844(6), V = 8810.8(8) Å3) with a three times enlargement of the unit cell along the b axis with respect to the calcined starting ZSM-12 (space group C2/c, Z = 1, a = 24.8633(3) Å, b = 5.01238(7) Å, c = 24.3275(7) Å, β = 107.7215(6)°). The SDAs conformation and position in the framework structure did not maintain the twofold axes coinciding with the crystallographic twofold axis thus changing the space group symmetry from C2/c to Cc. The structure refinement gave an extraframework content 6.13 SDA molecules per unit cell (corresponding to ~9.0 wt%) in good agreement with the weight loss given by the thermogravimetric analysis. The refined bond distances revealed the occurrence of non-bonding interactions of both azonia molecules with the MTW pore wall. AZO-1 and AZO-2 molecules are H-bonded between them thus forming clusters aligned along the b axis. This information is crucial to tailor the physicochemical properties of zeolites as well as to address their hydrophobicity, pore dimensions and cavities thus optimizing the selectivity of zeolite catalysts.
Location of 6-azonia-spiro- [5,5]-undecane molecules in ZSM-12 using X-ray synchrotron powder diffraction data
Martucci A.
Primo
Supervision
;
2020
Abstract
High-silica ZSM-12 (MTW topology), synthesized with 6-azonia-spiro- (Rimer, 2018; Rimer, 2018) [5,5]-undecane as structure directing agent (SDA), was carefully characterized by using X-ray synchrotron powder diffraction. The structure refinement led to a monoclinic unit cell (space group Cc, Z = 4, a = 25.0814(13) Å, b = 15.0987(8) Å, c = 24.4419(17) Å, β = 107.844(6), V = 8810.8(8) Å3) with a three times enlargement of the unit cell along the b axis with respect to the calcined starting ZSM-12 (space group C2/c, Z = 1, a = 24.8633(3) Å, b = 5.01238(7) Å, c = 24.3275(7) Å, β = 107.7215(6)°). The SDAs conformation and position in the framework structure did not maintain the twofold axes coinciding with the crystallographic twofold axis thus changing the space group symmetry from C2/c to Cc. The structure refinement gave an extraframework content 6.13 SDA molecules per unit cell (corresponding to ~9.0 wt%) in good agreement with the weight loss given by the thermogravimetric analysis. The refined bond distances revealed the occurrence of non-bonding interactions of both azonia molecules with the MTW pore wall. AZO-1 and AZO-2 molecules are H-bonded between them thus forming clusters aligned along the b axis. This information is crucial to tailor the physicochemical properties of zeolites as well as to address their hydrophobicity, pore dimensions and cavities thus optimizing the selectivity of zeolite catalysts.File | Dimensione | Formato | |
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