Simultaneous catalytic oxidation of NO and Hg0 over LaBO3 (B = Co, Mn, Ni, and Cu) perovskites

Perovskite catalysts have emerged as potential candidates for simultaneous catalytic oxidation of NO and Hg0 present within the coal-derived flue gas. LaBO3 (B = Co, Mn, Ni, and Cu) perovskites were synthesized by sol–gel method. LaMnO3 and LaCoO3 exhibited better simultaneous oxidation activities among LaBO3 (B = Co, Mn, Ni, and Cu) perovskites (LaMnO3 > LaCoO3 > LaNiO3 > LaCuO3). The experimental results revealed that the simultaneous oxidation conversions of LaCoO3 and LaMnO3 for NO and Hg0 oxidation were all around 80% at 285 °C. The oxidation conversions of NO and Hg0 by LaNiO3 were less than 70%, and for LaCuO3, the NO conversion rate was up to 50%, while Hg0 was less than 20%. The excellent simultaneous oxidation activities of LaBO3 (B = Co, Mn, Ni, and Cu) perovskites originated from the B-site ion activities in the order of Mn4+ > Co3+ > Ni2+ > Cu2+. And surface area, OL/OA ratio and reducibility showed the following trends: LaMnO3 > LaCoO3 > LaNiO3 > LaCuO3. Furthermore, as typical LaMnO3 and LaCoO3 perovskites, the Hg0 would compete with NO for adsorption on the surface, resulting in a decrease in NO oxidation. However, the NO increased the Hg0 conversion, which was related to NO2 oxidized from NO. The reaction mechanisms of LaMnO3 and LaCoO3 were obtained from the characterizations of XPS, NO-TPD, in situ DRIFTS and Hg-TPD. Hg0 was oxidized to HgO, not Hg(NO3)2. NO was converted into free nitrate species and gradually enriched on the perovskite surface; consequently, it turned into NO2.