High efficient styrene mineralization through novel NiO-TiO2-Al2O3 packed pre-treatment/treatment/post-treatment dielectric barrier discharge plasma

A pre-treatment/treatment/post-treatment multiple functional dielectric barrier discharge (DBD) plasma is developed with different gamma-Al2O3 based catalysts packed in this research to deeply mineralize styrene and reduce by-products generation. NiO/gamma-Al2O3 is packed in the first pre-treatment cell to effectively destroy the branched chains in styrene and weaken the benzene rings. TiO2/gamma-Al2O3 is packed in the second treatment cell due to their high catalytic oxidation activity to mineralize the generated aromatic compounds thoroughly. Finally, bare gamma-Al2O3 is packed in the last post-treatment cell to reduce the concentrations of by-products including O-3 and NO generated by air over oxidation. The combinations of these three catalysts are optimized through the treatment of 3000 mg m(-3) styrene at specific input energy of 189 J L-1. In comparison with single TiO2/gamma-Al2O3 packed reactor with the total discharge length of 8 cm, the selectivity of CO2 can be significantly improved from 33% to 62% when the first 2 cm TiO2/gamma-Al2O3 is replaced by NiO/gamma-Al2O3. Furthermore, the concentrations of O-3 and NO in outlet can also be effectively reduced from 8.44 mg L-1 and 81 mg m(-3) to 3.72 mg L-1 and 25 mg m(-3), respectively, when the last 2 cm TiO2/gamma-Al2O3 is replaced by bare gamma-Al2O3. The effects of specific input energy and styrene initial concentration are also investigated.