Manganese-cerium oxide catalysts prepared by non-thermal plasma for NO oxidation: Effect of O₂ in discharge atmosphere

Highlights: • A novel method is proposed to modify the properties of metal oxide catalyst. • High catalytic efficiency is obtained by low O₂ concentration plasma treatment. • Amorphous state Mn-O-Ce structure is formed by plasma preparation method. • The correlation of surface absorbed oxygen and Ce³⁺ species is obtained. • The correlation of catalytic activity and surface absorbed oxygen is obtained. - Abstract: Non-thermal plasma with different O₂ concentration in discharge atmosphere was applied to synthesize manganese and cerium mixed-oxides catalysts, which were compared in NO oxidation activity. Discharge atmosphere displayed a crucial influence on the performance of the catalysts prepared by plasma. Relatively low O₂ concentration in discharge atmosphere allows synthesizing manganese-cerium oxides catalysts in a moderate environment and therefore is favorable for better physicochemical properties which lead to superior catalytic behavior. The best catalyst was obtained by treatment with 10% O₂/N₂ plasma and presented over 80% NO conversion in the temperature range of 275–325 °C, whereas catalyst prepared in pure O₂ discharge atmosphere had the same activity with a catalyst prepared by calcinations. A correlation between the surface properties of the plasma prepared catalysts and its catalytic activity in NO oxidation is proposed. The amount of the surface adsorbed oxygen has an obvious linear correlation with the amount of Ce³⁺, the H₂ consumption at low temperatures and the catalytic performance. The superior catalytic performance is mainly attributed to the stronger interaction between manganese oxides and ceria, and the formation of poorly crystallized Mn-O-Ce phase in the catalyst which resulted from the slow decomposition of nitrates and organics during plasma treatment. Catalysts prepared in relatively low O₂ concentration have large specific surface area and is abundant in Ce³⁺ species and active oxygen species. The study suggests that plasma treatment with proper discharge gas components is a promising method to prepare effective manganese- cerium oxides catalyst for NO oxidation.