Sr doping effect on the structure property and NO oxidation performance of dual-site doped perovskite La(Sr)Co(Fe)O3.

In this work, the physico-chemical properties of the La 1-x Sr x Co 0.8 Fe 0.2 O 3 (x = 0, 0.3，0.4，0.5，0.6) catalysts were systematically studied as well as their catalytic activity for NO oxidation. When Sr2+ substituted at La3+ site, [CoO 6 octahedral distortion is amended and the crystal structure transited from rhombohedral to cubic. Co(III) electronic configuration turned from high/intermediate spin state to low spin sate with empty e g filling. Imbalanced positive charge induced by Sr2+ was compensated by tetravalent Co(IV) ions and oxygen deficiencies together. All these factors resulted in better reducibility of Co, increasing oxygen deficiencies and more mobile oxygen species. Thus, NO conversion of 67–69% was attained over the Sr-doped catalysts at 300 °C, much higher than the undoped catalysts (NO conversion of 24.3%). A significant decrease of the apparent activation energy (E a), from 68 kJ/mol down to ~52 kJ/mol, was observed as well. Based on the kinetics results, NO oxidation over the perovskite catalysts is a typical superficial process determined by adsorbed NO and surface oxygen species. Image 1 • Sr doping amended the [CoO 6 octahedral distortion in the LaCo 0.8 Fe 0.2 O 3 structure. • Sr doping decreased e g filling of Co and prolonged Co–O distance, which was favorable for NO adsorption. • Sr doping produced more oxygen deficiencies, which was favorable for O 2 adsorption. • The La(Sr)Co(Fe)O 3 perovskites exhibited much higher NO oxidation activity and lower Ea than the LaCo(Fe)O 3 perovskites. [ABSTRACT FROM AUTHOR]