Oxidation behavior of Ni/Al₂O₃ catalyst in nonthermal plasma-enabled catalysis

The oxidation behavior of Ni/Al₂O₃ catalyst in CO₂ plasma was investigated compared with CO₂ thermal oxidation, aiming for providing new insight into oxidation-reduction cycle of plasma catalysis of dry methane reforming (DMR). Temperature programmed reaction spectrometry was applied to enable a quantitative analysis of gas consumption which is related to the oxidation and reduction of Ni/Al₂O₃ catalysts. The nonthermal plasma oxidation mechanism was further analyzed by Raman spectroscopy, showing the cross-sectional distribution of NiO over the 3 mm spherical catalyst pellets. Nonthermal plasma-excited CO₂ oxidizes Ni only near the external surface of spherical pellets with 20 μm depth: both dielectric barrier discharge generation and plasma-excited species diffusion into the internal pores are inhibited. The partially oxidized Ni catalyst in the external surface would promote plasma-enabled oxidation-reduction cycle, which was further correlated with coke formation behavior in plasma catalysis of DMR. (paper)