Investigating the Crystallization of a Hydroxycarbonate Precursor for a Ni-Mg-Catalyst through In Situ and Ex Situ...

Area of Science:

• Materials Science
• Catalysis
• Green Chemistry

Background:

• Nickel-based catalysts are vital for methanation reactions.
• Developing efficient catalysts for green methanation is crucial for sustainable energy.
• The synthesis of Ni-Mg catalysts involves complex precursor chemistry.

Purpose of the Study:

• To investigate the crystallization process of a coprecipitated precursor for Ni catalysts used in green methanation.
• To explore the previously uncharacterized hydrothermal aging step in the synthesis of Ni-Mg hydroxycarbonate precursors.
• To elucidate the transformation mechanisms of amorphous precipitates into crystalline solid-solutions.

Main Methods:

• Utilized a combination of ex situ and in situ techniques including Powder X-ray Diffraction (PXRD), Infrared Spectroscopy (IR), Energy-Dispersive X-ray Spectroscopy (EDX), Scanning Electron Microscopy (SEM), and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES).
• Monitored in situ IR and pressure changes during the hydrothermal aging process.
• Characterized the initial amorphous precipitate and its subsequent crystalline forms.

Main Results:

• Identified hydrothermal aging as a key step where amorphous precipitates transform into crystalline solid-solutions within 30 minutes.
• Established the sum formula of the initial amorphous precipitate as (Ni1-xMgx)2(CO3)(OH)2·2.5H2O.
• Clarified the evolution of metal ion ratios, crystallization, and carbonate incorporation, highlighting the role of dissolved species.

Conclusions:

• The hydrothermal aging step is critical for the formation of the desired crystalline Ni-Mg hydroxycarbonate solid-solution.
• Understanding the aqueous precursor chemistry and interconversion of hydroxycarbonate phases is essential for optimizing Ni catalyst synthesis.
• Dissolved species in the mother liquor play a significant role in the precursor crystallization and catalyst performance.