¹⁴C has become the largest contributor of annual effective dose to the surrounding public in radioactive effluent during normal operation of nuclear power plants whilst ¹⁴CH₄ is the largest and most chemically stable of the ¹⁴C hydrocarbons. However, an effective treatment method for ¹⁴C in the form of hydrocarbons has not yet been established.

This study aims to investigate the treatment performance of a non-thermal plasma/catalytic coupling system for low concentrations of ¹⁴CH₄.

Considering the optimization of radiation protection, ¹²CH₄, which possesses the same physicochemical properties as ¹⁴CH₄, was selected as the experimental subject. The Pd/γ-Al₂O₃ catalyst were prepared by segmental heat treatment and wet impregnation. The discharge behaviors of the plasma were analyzed by the Lissajous figure. The CH₄ treatment performance of the non-thermal plasma before and after the introduction of the catalyst under different discharge voltages, gas flow rates and temperatures were analyzed by the constructed experimental system. The microstructural changes of the catalyst were analyzed by N₂ adsorption-desorption isotherm, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).

The introduction of Pd/Al₂O₃ catalyst can significantly improve CH₄ treatment performance in non-thermal plasma, and the CH₄ treatment efficiency and CO₂ selectivity can reach 100% and 83.7% by increasing the discharge voltage, lowering the reaction temperature and reasonably adjusting the gas flow.

The non-thermal plasma and the Pd/Al?O? catalyst exhibit a synergistic effect. The Pd/Al?O? catalyst can reduce the reaction barriers, optimise the reaction paths and significantly improve the CH₄ treatment performance of the plasma. Furthermore, the plasma-excited reactive species are conducive to the formation of PdO, which is the key reactive phase in the catalyst.