Insight into Room-Temperature Catalytic Oxidation of Nitric oxide by Cr₂O₃: A DFT Study

Abstract

Cr-based catalysts have drawn attention as promising room-temperature NO oxidation catalysts. However, the intrinsic active component and reaction mechanism at the atomic level remain unclear. Here, taking the Cr2O3, one of the most stable chromium oxides, as an object, we systematically investigated NO oxidation processes on Cr2O3(001) and -(012) surfaces by virtue of DFT+U calculations, aiming to uncover the activity-limiting factors and basic structure–activity relationship of the Cr2O3 catalyst. It was revealed that NO oxidation could not proceed via a Mars–van Krevelen mechanism involving the lattice oxygen on both surfaces. For the Cr2O3(001) surface exposing the isolated three-coordinated Cr3c, the reactions are inclined to occur through the Eley–Rideal route, in which the NO couples directly with the molecular O2* or atomic O* adsorbed at the Cr3c site to form two key intermediate species (ONOO* and NO2*) following a barrierless process. Nevertheless, the overall activity is limited by the irreversible adsorption of NO2 species on the highly unsaturated Cr3c. In contrast, on the (012) termination, which exposes the five-coordinated Cr5c, the NO2* can be easily released, but the reactant O2 cannot be efficiently adsorbed and also results in a limited overall activity at room temperature. To achieve a higher activity, a thermodynamically favored interface model of monochain CrO3 supported on Cr2O3(012) was proposed, which shows an improved O2 adsorption energy of −0.99 eV and thus an enhanced activity of Cr2O3(012), possibly accounting for the experimentally high activity of Cr-based catalysts usually involving the Cr3+/Cr6+ redox. This study demonstrated the catalytic ability of Cr2O3 for NO oxidation at room temperature, and the presented systematic picture may facilitate the further design of more active Cr-based catalysts.

Quantitative Studies of the Coverage Effects on Microkinetic Simulations for NO Oxidation on Pt(111)

“…Moreover, NO oxidation is also studied on metal 8,[16][17][18][19][20] , perovskite 21,22 and metal oxides [23][24][25] . Our group carried out a series of works on NO oxidation using density functional theory (DFT) 9,26,27 . The activity trend of NO oxidation on several of metals 9 and metal oxides 26 was studied.…”

“…The activity trend of NO oxidation on several of metals 9 and metal oxides 26 was studied. It was discovered that NO oxidation may occur on Cr2O3 catalysts even at room temperature 27 .…”

Pd single-atom monolithic catalyst: Functional 3D structure and unique chemical selectivity in hydrogenation reaction

“…In addition, for the adsorption/desorption processes, the large entropy contributions of gaseous molecules (TΔS), including the vibrational, rotational and translational entropies, must be considered to estimate the Gibbs free energy change (ΔG) at the temperature of 323 K. The ΔG of adsorption/ desorption process was estimated according to ΔG = ΔH − TΔS. The reaction enthalpy (ΔH) was approximated with the total energy difference (ΔE) neglecting the small zero-point energy correction (ΔZPE), heat capacity correction and Δ(pV) term [46].…”

Tuning oxygen reduction activity on chromia surface via alloying: a DFT study

“…Chromium (Cr) materials have been suggested as one of the most active catalysts for ORR based on non-precious metals, [6] especially Cr 2 O 3 , which is the most stable form of Cr oxide at room temperature. [7] In addition, Cr 2 O 3 is also a promising catalyst for many other chemical reactions such as oxygen evolution reaction, [8,9] nitride oxide oxidation [10] and carbon monoxide oxidation. [11] In fact, the improvement of the catalytic effects of oxide has been demonstrated using doping or alloying with foreign metals, [12][13][14] as well as other effects such as water adsorption.…”

“…Chromium (Cr) materials have been suggested as one of the most active catalysts for ORR based on non‐precious metals, [6] especially Cr 2 O 3 , which is the most stable form of Cr oxide at room temperature [7] . In addition, Cr 2 O 3 is also a promising catalyst for many other chemical reactions such as oxygen evolution reaction, [8,9] nitride oxide oxidation [10] and carbon monoxide oxidation [11] .…”