Mid-Infrared Scattering in γ-Al₂O₃ Catalytic Powders

Area of Science:

• Physical Chemistry
• Materials Science
• Chemical Engineering

Background:

• Mid-infrared (MIR) light can enhance heterogeneous catalytic processes by vibrationally exciting gas-phase reactants.
• Efficient light-molecule coupling within catalytic reactors is crucial for light-enabled catalysis.
• Characterizing light scattering by complex catalyst powders is challenging due to their nanoscale features and porous structures.

Purpose of the Study:

• To develop and implement a method for directly measuring light scattering properties of heterogeneous catalyst powders in the MIR.
• To investigate the effect of grain size and metal nanoparticle loading on the MIR scattering behavior of gamma-alumina supports.
• To determine the optimal support material properties for efficient light distribution in MIR light-enabled catalytic reactors.

Main Methods:

• Combined directional hemispherical measurements with in-line transmission measurements to quantify scattered light.
• Studied gamma-alumina (γ-Al2O3) powders with mean grain sizes of 2, 40, and 900 µm.
• Investigated the impact of ruthenium (Ru) and copper (Cu) nanoparticle loading on the scattering properties of the γ-Al2O3 support.

Main Results:

• The 40 µm γ-Al2O3 grains exhibited the highest scattering efficiency (up to 97% at 1220 cm⁻¹).
• Metal nanoparticle addition narrowed the scattering angle but did not significantly reduce scattering efficiency.
• Less than 100 mW of laser power is estimated to be sufficient for significant reactant excitation in a DRIFTS reactor.

Conclusions:

• 40 µm γ-Al2O3 grains are ideal support materials for MIR light-enabled catalysis due to their superior light-scattering capabilities.
• The developed measurement technique provides a foundation for studying light-matter interactions in catalytic systems.
• Findings are applicable to optimizing reactor design and catalyst selection for various light-enabled chemical processes.