Structural evolution of CO2 filled pure silica LTA zeolite under high-pressure high-temperature conditions

TL;DR

This study investigates the structural stability and properties of CO2-filled pure silica LTA zeolite under high-pressure and high-temperature conditions, revealing its stability, compressibility, and thermal behavior with potential for silicon carbonate synthesis.

Contribution

It provides detailed insights into the structural evolution, stability, and thermal properties of CO2-filled silica zeolite under extreme conditions, highlighting the role of guest molecules in preventing amorphization.

Findings

Zeolite remains stable up to 20 GPa with slight distortion.

Insertion of CO2 reverses negative thermal expansion.

No chemical reactions observed up to 750 K and high pressures.

Abstract

The crystal structure of CO2 filled pure SiO2 LTA zeolite has been studied at high pressures and temperatures using synchrotron based x ray powder diffraction. Its structure consists of 13 CO2 guest molecules, 12 of them accommodated in the large alpha cages and 1 in the beta cages, giving a SiO2:CO2 stoichiometric ratio smaller than 2. The structure remains stable under pressure up to 20 GPa with a slight pressure dependent rhombohedral distortion, indicating that pressure induced amorphization is prevented by the insertion of guest species in this open framework. The ambient-temperature lattice compressibility has been determined. In situ high pressure resistive heating experiments up to 750 K allow us to estimate the thermal expansivity at 5 GPa. Our data confirm that the insertion of CO2 reverses the negative thermal expansion of the empty zeolite structure. No evidence of any chemical reaction was observed. The possibility of synthesizing a silicon carbonate at high temperatures and higher pressures is discussed in terms of the evolution of C-O and Si-O distances between molecular and framework atoms.