Catalytic non-thermal plasma reactor operating at low applied voltage for the removal of toluene in air

Volatile organic compounds (VOC) represent a large group of pollutants characterized by high volatility. They can cause problems both for humans and the environment. This work aimed to examine the non-thermal plasma (NTP) technology combined with a heterogeneous catalyst ("in plasma catalysis", IPC) for the removal of toluene from the air at an applied voltage lower than that commonly reported in the literature. The NTP system was studied in the absence and presence of two commercial catalysts (γ-Al2O3 spheres and TiO2 pellets) investigating the influence of the operating conditions (inlet flow rate, inlet pollutant concentration, water vapor presence and applied voltage). The results demonstrated that NTP without catalyst can remove toluene at voltages not less than 13.20 kV. On the other hand, the use γ-Al2O3 in IPC configuration allowed to achieve better performance than TiO2 with the lowest applied voltage (10.67 kV) for plasma generation. Specifically, with an air flow rate of 15 NL/h at 8.7% of relative humidity and containing 500 ppm of toluene, a pollutant conversion of about 89% and a CO2/CO molar ratio equal to 4.72 was achieved. Moreover, contrary to what was observed in the NTP system without catalyst, the presence of both γ-Al2O3 and TiO2 in the IPC configuration allowed to avoid the presence of O3 and NOx at the reactor outlet. Finally, the calculated energy efficiency was in the order NTP+γ-Al2O3 > NTP+TiO2 > NTP alone.