Unraveling high-temperature mechanism of NO + CO reaction on BaO-Y2O3: An in situ DRIFTS and microkinetic study

Abstract

Understanding high-temperature mechanism of NO reduction by CO on heat-resistant metal oxides is crucial for exhaust aftertreatment systems. We employed the NO + CO light off experiment, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), density functional theory (DFT), and microkinetic study to elucidate the reaction mechanism on BaO-Y2O3 nanocatalyst. The catalytic cycle consisting of “decomposition-oxidation” mode, Mars-van Krevelen (MvK) mechanism, and Langmuir-Hinshelwood (L-H) mechanism is described by in situ DRIFTS and DFT calculations. Their reaction energies and activation barriers are then employed for the microkinetic analysis, revealing that the activity rate is temperature-dependent and aligns with the experimental result. The high-temperature reaction process is primarily governed by the MvK mechanism with rate-determining steps (RDS) of CO + OL ↔ CO2 + Ov, followed by the “decomposition-oxidation” mode. Critically, local CO32- coverage on the BaO surface can facilitate NO and CO adsorption while withstanding the elementary steps such as N2O dissociation and CO oxidation by lattice oxygen. BaCO3-Y2O3 model can be used to interpret the low-temperature reaction process with the RDS of N2O2 ↔ N2O + O, but it impedes reaction kinetics at high temperatures with the rate contribution also predominantly originating from the MvK mechanism. This work provides fundamental insights into how the reaction proceed, and guide the design and optimization of catalysts that can withstand high temperature while maintaining high activity.