Development of a Robust Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) Cell for Elucidating Reaction Mechanisms in Nonthermal Plasma Catalysis

Applying diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to nonthermal plasma catalysis is important to gain mechanistic information to advance the electrified technology. However, conventional DRIFTS cells are often suboptimal, exhibiting unstable, non-uniform discharges and failing to replicate the plasma characteristics of practical reactors such as dielectric barrier discharge (DBD) systems. This study devises a dome-type DRIFTS flow cell that enables stable glow discharge, closely emulating the electric field distribution and flow dynamics of DBD reactors. The dome cell exhibits excellent operational stability over extended durations (>1 h) and under various plasma conditions (e.g., different excitation modes and gas switching), while delivering high-fidelity IR signals. Using the dome cell, operando DRIFTS studies of plasma catalytic CO₂ methanation under pulse excitation are conducted. The results reveal that, for a Ni/MgAlO_x catalyst, i) the surface reaction mainly follows the Langmuir-Hinshelwood mechanism with formate hydrogenation as the rate-determining step, and ii) the Eley-Rideal/Langmuir-Rideal mechanism indeed exists under plasma conditions but contributes marginally. This robust DRIFTS platform provides a reliable in situ and/or operando diagnostic tool for plasma catalytic systems, while offering mechanistic insights essential for rational catalyst/system design and optimization.