NH₃ as unique non-classical content-former within clathrate hydrates.

Area of Science:

• Chemistry
• Materials Science
• Spectroscopy

Background:

• Clathrate hydrates (CHs) are inclusion compounds formed by water cages trapping guest molecules.
• Ammonia (NH3) is a key molecule in various chemical processes, but its behavior in CHs is not fully understood.
• Vibrational spectroscopy is crucial for identifying molecular structures and interactions within CHs.

Purpose of the Study:

• To identify and characterize the vibrational spectroscopic signatures of ammonia (NH3) within binary clathrate hydrates (CHs).
• To elucidate the role of ammonia in the formation and stabilization of clathrate hydrate structures.
• To investigate the long-term effects of guest molecule replacement on ternary CHs.

Main Methods:

• High-quality Fourier-transform infrared (FTIR) spectroscopy was used to analyze aerosols of NH3-THF and NH3-TMO binary clathrate hydrates.
• An all-vapor, sub-second clathrate hydrate formation approach was employed.
• Computational studies were integrated to aid in the identification of spectroscopic signatures.

Main Results:

• Three distinct types of ammonia (NH3) were identified within the clathrate hydrate structure: classical small-cage, nonclassical small-cage, and network ammonia.
• Network ammonia perturbs water bonding, creating orientational defects stabilized by guest molecules, rather than directly inducing non-classical structures.
• The study observed the impact of CO2 and CH4 as NH3 replacement molecules on ternary CHs over time.

Conclusions:

• Ammonia's behavior in clathrate hydrates is complex, involving perturbation of water networks and potential catalytic activity during CH formation.
• The findings offer new insights into the structure and dynamics of ammonia-containing clathrate hydrates.
• Understanding these interactions is vital for applications involving gas storage and separation using clathrate hydrates.