Improving oxidation removal of toluene in plasma coupling perovskite catalysts system by constructing Au sites on a La0.5Ce0.5CoO3-δ

Abstract

Plasma-catalysis technique is a promising approach to control air pollution caused by volatile organic compounds (VOCs). Perovskite-type oxides have excited much interest in constructing plasma-catalytic system for the oxidation removal of VOCs owing to their flexible electronic structure, alterable geometry, unique catalytic properties and high stability. However, the perovskites commonly suffer from low surface area and small amounts of active surface sites because of their high synthesis temperature, which limits the synergism between the perovskites and plasma and thus decreases the performance of plasma-catalytic oxidation of VOCs. Here we show that the oxidation removal of toluene (typical refractory VOCs) in the plasma-catalytic system is improved by constructing Au sites on a perovskite of La0.5Ce0.5CoO3-δ (Au/La0.5Ce0.5CoO3-δ). Compared with plasma-catalytic systems integrated by LaCoO3 or La0.5Ce0.5CoO3-δ, coupling the Au/La0.5Ce0.5CoO3-δ with plasma enables the boost of toluene conversion and CO2 selectivity, but suppresses the generation of secondary pollutants (O3 and NOx). The calculation of apparent activation energy (Ea) demonstrates that the plasma-catalytic system integrated by Au/La0.5Ce0.5CoO3-δ obtains lower Ea of 6.9 kJ/mol than those integrated by LaCoO3 (9.5 kJ/mol) and La0.5Ce0.5CoO3-δ (8.1 kJ/mol) as well as plasma alone (15.0 kJ/mol), confirming a favorable toluene oxidation process in the plasma coupling Au/La0.5Ce0.5CoO3-δ system. Catalyst characterizations, discharge diagnosis and density functional theory calculations suggest that depositing Au on the La0.5Ce0.5CoO3-δ render the favorable gas and surface reactions for toluene oxidation in the plasma-catalytic system and thus a strong synergism between the perovskites and plasma, by modulating the discharge mode and creating large numbers of highly active Auδ+-Oδ--Ce interfacial sites on the surface of La0.5Ce0.5CoO3-δ.