The high-pressure behavior of six synthetic zeolites with the MFI topology, characterized by different chemical composition (framework-Si partially replaced by Al or B and counterbalanced by Na or H as extra-framework cations), has been investigated by in-situ powder synchrotron X-ray diffraction using silicone-oil and methanol as hydrostatic pressure-transmitting fluids. For each sample, the compressibility in silicone-oil has been found to be considerably higher than that in methanol. This difference in terms of bulk elasticity is due to the adsorption of methanol already at P < 0.1 GPa, with different magnitudes as a function of the sample crystal-chemistry. The high number of experimental pressure points allowed an accurate determination of the monoclinic-to-orthorhombic phase transition (MOPT), detected between 0.3 and 0.7 GPa in the samples compressed in silicone-oil, whereas the orthorhombic Pnma polymorph has been found to be stable already at ∼ 0.1 GPa in four samples compressed in methanol. This suggests that the adsorption of methanol may increase the P-stability range of the orthorhombic Pnma phase. A comparative analysis of the effect of pressure on the methanol adsorption by MFI-zeolites with different chemical composition is provided, which offers potentially useful information on their application as catalysts in the methanol-to-olefins conversion processes and in industrial high-pressure processes.

The elastic behavior of zeolitic frameworks: The case of MFI type zeolite under high-pressure methanol intrusion

Catizzone E.;
2020

Abstract

The high-pressure behavior of six synthetic zeolites with the MFI topology, characterized by different chemical composition (framework-Si partially replaced by Al or B and counterbalanced by Na or H as extra-framework cations), has been investigated by in-situ powder synchrotron X-ray diffraction using silicone-oil and methanol as hydrostatic pressure-transmitting fluids. For each sample, the compressibility in silicone-oil has been found to be considerably higher than that in methanol. This difference in terms of bulk elasticity is due to the adsorption of methanol already at P < 0.1 GPa, with different magnitudes as a function of the sample crystal-chemistry. The high number of experimental pressure points allowed an accurate determination of the monoclinic-to-orthorhombic phase transition (MOPT), detected between 0.3 and 0.7 GPa in the samples compressed in silicone-oil, whereas the orthorhombic Pnma polymorph has been found to be stable already at ∼ 0.1 GPa in four samples compressed in methanol. This suggests that the adsorption of methanol may increase the P-stability range of the orthorhombic Pnma phase. A comparative analysis of the effect of pressure on the methanol adsorption by MFI-zeolites with different chemical composition is provided, which offers potentially useful information on their application as catalysts in the methanol-to-olefins conversion processes and in industrial high-pressure processes.
In-situ characterization; Methanol adsorption; MFI-topology; MOPT; Olefins; Pressure; Synchrotron X-ray diffraction
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/20.500.12079/53915
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