Plasma-chemical promotion of catalysis for CH4 dry reforming: unveiling plasma-enabled reaction mechanisms

Abstract

A kinetic study revealed that a Ni/Al₂O₃ catalyst exhibited a drastic increase in CH₄ and CO₂ conversion under nonthermal plasma when lanthanum was added to the Ni/Al₂O₃ catalyst as a promoter. For a better fundamental understanding of the plasma and catalyst interfacial phenomena, we employed in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) under plasma-on conditions to elucidate the nonthermal plasma-enabled reaction enhancement mechanisms. Compared with thermal catalysis, plasma-activated CO₂ shows a 1.7-fold enhancement for bidentate (1560 and 1290 cm⁻¹) and monodentate carbonate (1425 and 1345 cm⁻¹) formation on La. Moreover, new peaks of bicarbonate (1655 cm⁻¹) and bridge carbonate (1720 cm⁻¹) were formed due to nonthermal plasma interactions. CO₂-TPD study after thermal- and plasma-activated CO₂ treatment further confirmed that plasma-activated CO₂ enhances bidentate and monodentate carbonate generation with a 1.5-fold promotion at high temperature (500 °C). XRD and EDS analyses suggest that atomic-scale interaction between CO₂–La and CH_x–Ni is possible over the complex La–Ni–Al oxide; vibrationally excited CO₂-induced carbonates provide the key to enhancing the overall performance of CH₄ dry reforming at low temperature.