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

Abstract

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 °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 °C to 240 °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 LaCo0.9Ni0.1O3 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. CO2* 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.