Enhanced catalytic performance of CoOx-CeO2 for synergetic degradation of toluene in multistage sliding plasma system through response surface methodology (RSM)

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Post plasma-assisted catalysis for toluene degradation using nanosecond pulsed multistage sliding dielectric barrier discharge (multi-SLDBD) plasma over a series of CoOx-CeO2 catalysts has been studied at atmospheric pressure and ambient temperature. Several characterization methods including BET, XRD, SEM, HRTEM, XPS, and H2-TPR have been utilized to evaluate the influence of Co/Ce molar ratio on the catalyst physiochemical properties. When the multi-SLDBD plasma was combined with catalyst, an obvious improvement could be obtained in toluene degradation efficiency compared to plasma alone even at low SIE. The incorporation of Ce into Co oxides presented higher catalytic activity for toluene degradation and mineralization than Co oxide, which can be ascribed to higher content of surface-adsorbed oxygen (Oads) derived from oxygen vacancy and better catalyst reducibility. The ozone concentration remarkably decreased after the introduction of catalysts, especially for CoOx-CeO2 catalysts. The key process parameters including pulsed power, gaseous hourly space velocity (GHSV), relative humidity (RH), and oxygen content were optimized by response surface methodology (RSM) integrated central composite design (CCD). The proposed optimization model displayed satisfactory correlation between the predicted and experimental results. GHSV was the most significant parameter affecting the energy yield, whereas the COx selectivity was mainly influenced by the pulsed power. Besides, the possible toluene degradation pathway in plasma-catalysis over CoOx-CeO2 was proposed according to the identification of gaseous intermediates and organic aerosol using FT-IR and GC-MS.