Quasi-operando quantification of Cu(II) ions in Cu-SSZ-13 catalyst by an NH₃ temperature-programmed reduction method

Area of Science:

• Materials Science
• Catalysis
• Chemical Engineering

Background:

• Copper-zeolite catalysts, particularly Cu-SSZ-13, are crucial for selective catalytic reduction (SCR) of NOx.
• Understanding the state and reducibility of copper species is vital for optimizing SCR performance.
• Existing methods may not accurately quantify different copper species under reaction conditions.

Purpose of the Study:

• To develop and validate a quasi-operando NH3 temperature-programmed reduction (NH3-TPR) method.
• To accurately quantify total Cu(II) ions in Cu-SSZ-13 catalysts after SCR-relevant reactions.
• To differentiate between specific copper species, namely [Cu(OH)]+-Z and Cu2+-2Z, and assess their reducibility.

Main Methods:

• A quasi-operando NH3 temperature-programmed reduction (NH3-TPR) method was employed.
• The method utilized a specific gas mixture ratio (N2:Cu = 1:1).
• The accuracy of the NH3-TPR method was validated using in situ Electron Paramagnetic Resonance (EPR) spectroscopy.

Main Results:

• The developed NH3-TPR method accurately quantifies total Cu(II) ions in Cu-SSZ-13.
• Different reduction temperatures allowed for the distinction between [Cu(OH)]+-Z and Cu2+-2Z species.
• The study revealed distinct reducibility characteristics for these copper species under SCR conditions.

Conclusions:

• The quasi-operando NH3-TPR method provides a reliable way to quantify copper species in Cu-SSZ-13.
• The method enables differentiation of key copper species relevant to SCR catalysis.
• Insights into the varying reducibility of copper species can guide catalyst design and performance optimization for SCR.