Achieving Nearly 100% Targeted Conversion of NO to NO2 through Cooperative Activation of Lattice Oxygen and Molecular Oxygen on Dual-Defect LaMnO3.

Abstract

Inhibiting the deposition of N species on the catalyst surface for the targeted oxidation of NO to NO2 is still a great challenge. Herein, a La and O dual-defective LaMnO3 (2U-L0.8MO) perovskite was fabricated using a urea-nonstoichiometric comodulation strategy, which achieved 97.6% NO oxidation efficiency at 210 °C and 300,000 h-1, and was also capable of nearly 100% targeted oxidation of NO to NO2, as well as exhibited excellent stability and recyclability. Characterizations and theoretical calculations unveiled that the urea-nonstoichiometric modulation method optimized the specific surface area and geometrical structure of perovskite, promoted the formation of La defects and oxygen vacancies (OVs), enhanced lattice oxygen activation and migration, and also facilitated the coadsorption of NO and O2 and increased the d-band center of the perovskite. The synergistic activation of lattice oxygen and molecular oxygen along with the low-temperature oxidation mechanisms of NO was finally revealed: the comodulation strategy caused stretching and distortion of the 2U-L0.8MO lattice, making its lattice oxygen susceptible to activation, thereby oxidizing adsorbed NO to NO2 and simultaneously generating OVs. Afterward, O2 would be captured by the abundant OVs on the 2U-L0.8MO surface and converted to superoxide O2-, which could not only directly oxidize NO but also transform into single 1O2 on the adjacent Mn4+ site for the targeted oxidation of NO. This work realizes the coactivation of O2 and lattice oxygen and also extends the understanding of the low-temperature-targeted oxidation of NO.