Effective Removal of CF₄ by Combining Nonthermal Plasma with γ-Al₂O₃

Conversion of CF₄ was experimentally evaluated with three systems including catalytic hydrolysis, NTP-alone and plasma catalysis. Firstly, activity of γ-Al₂O₃ for CF₄ conversion was tested via catalytic hydrolysis. Experimental results indicate that the highest CF₄ conversion (72%) could be achieved with γ-Al₂O₃ in the presence of 45% H₂O_(g) with the operating temperature of 900 °C and the apparent activation energy is calculated as 85 kJ/mol using power rate law model. For plasma-based systems, results indicate that CF₄ conversions achieved with plasma catalysis remain 100% with the applied voltage ranging from 12 to 23 kV, while the highest CF₄ conversion achieved with NTP-alone is 86%. For the effects of various parameters on plasma-based systems, the results indicate that plasma catalysis also has better resistivity for higher total flow rate, CF₄ concentration and O₂ contents. Especially, CF₄ conversion could maintain at 100% with the operating applied of 23 kV as CF₄ concentration is increased to 10,000 ppm. On the other hand, CF₄ conversion achieved with NTP-alone is 18% at the same conditions. In addition, negative effect of O₂ on plasma catalysis could be reduced by the addition of Ar due to its good discharge properties and high excitation threshold energy (13 eV). The kinetics of plasma catalysis is investigated for CF₄ conversion by a simplified model, and the results indicate that overall energy constant achieved with plasma catalysis reaches 0.015 mg J⁻¹. Overall, plasma catalysis is demonstrated with good potential for the reduction of CF₄ emission.