Exploring Hydrothermal Synthesis of SAPO-18 under High Hydrostatic Pressure.

Area of Science:

• Materials Science
• Chemical Engineering
• Crystallography

Background:

• Microporous materials like silicoaluminophosphates (SAPO) are crucial in catalysis and separations.
• Hydrothermal synthesis is a common method for producing these materials.
• Understanding synthesis parameters is key to controlling material properties.

Purpose of the Study:

• To investigate the effect of external hydrostatic pressure on the hydrothermal synthesis of SAPO-18.
• To determine the influence of synthesis mixture concentration on SAPO-18 formation under pressure.
• To elucidate the role of pressure in the interaction between organic templates and the SAPO framework.

Main Methods:

• Hydrothermal synthesis under varying hydrostatic pressures (up to 200 MPa) and temperatures (150 °C).
• Characterization of synthesized materials using X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES), Thermogravimetric Analysis (TG), and solid-state Nuclear Magnetic Resonance (NMR) spectroscopy (27Al and 31P MAS NMR).

Main Results:

• Hydrothermal synthesis of SAPO-18 was inhibited at 150 °C and 200 MPa with diluted synthesis mixtures.
• SAPO-18 was successfully synthesized under all tested conditions when using concentrated synthesis mixtures.
• Characterization confirmed the successful formation and structure of SAPO-18.

Conclusions:

• External hydrostatic pressure significantly influences the hydrothermal synthesis of SAPO-18.
• Synthesis mixture concentration is a critical factor in overcoming pressure-induced inhibition of SAPO-18 crystallization.
• Pressure affects the interaction between the organic structure-directing agent and the silicoaluminophosphate framework during synthesis.