Reaction mechanism and microkinetics of CO catalytic combustion over Ni-doped LaCoO3 perovskite

Experiments, density functional theory (DFT) calculations and microkinetic modeling were conducted to understand the reaction mechanism and microkinetics of CO catalytic combustion over Ni-doped LaCoO3 perovskite. The results indicate that LaCoO3 shows 94.61% CO conversion at 260 degrees C. The better catalytic activity of LaCoO3 is closely related to its larger oxygen storage capacity. Ni doping can further enhance the low-temperature activity of LaCoO3 towards CO catalytic combustion. The reaction temperature of CO complete conversion decreases from 300 degrees C to 240 degrees C when 10% Ni is doped into LaCoO3. The Co-O-Co and Co-O-Ni bridge sites serve as the main active centers of CO adsorption and oxidation. Compared with the Langmuir-Hinshelwood (L-H) mechanism, the Mars-van Krevelen (MvK) mechanism is mainly responsible for CO catalytic combustion over LaCoO3 and LaCo0.9 Ni-0.1 O-3 due to the lower energy barrier. Ni doping can further decrease the energy barrier of elementary reaction between CO* and lattice oxygen, and thus enhance the reactivity of lattice oxygen. The MvK mechanism includes four elementary reaction steps: CO adsorption, CO* oxidation, CO2* desorption, and oxygen vacancy recovery. CO 2 * desorption has the highest energy barrier of 41.18 kJ/mol, and is identified as the rate-determining step of CO catalytic combustion over LaCo0.9Ni0.1O3. Microkinetic analysis indicates that the reaction between CO* and lattice oxygen is preferred by CO catalytic combustion due to the higher turnover frequency. CO* serves as the important surface species during CO catalytic combustion. (c) 2022 The Combustion Institute. Published by Elsevier Inc. All rights reserved.