Periodic DFT study on mechanism of selective catalytic reduction of NO via NH3 and O2 over the V2O5 (001) surface: Competitive sites and pathways

Assignment of Vibrational Bands of Critical Surface Species Containing Nitrogen in the Selective Catalytic Reduction of NO by NH3

The selective catalytic reduction (SCR) of NO by NH₃ on metal oxides plays a key role in minimizing NO_x emissions. Electronic structure calculations at the density functional theory level have been performed to predict the vibrational modes of NH₃/NH₄⁺ bound to validated cluster models of vanadium oxide bound to a TiO₂ surface. Excellent agreement of the scaled calculated values with the observed bands attributed to surface-bound species is found. The presence of NH₃ bound to Lewis acid sites and NH₄⁺ bound to Brønsted acid sites when VOH groups are present is supported by our predictions. NH₄⁺ is expected to dominate the spectra even at low concentrations, with predicted intensities 5 to 30 times greater than those predicted for surface-bound NH₃. This is particularly evident in the lowest-energy N-H stretches of surface NH₄⁺ due to partial proton transfer interactions with the vanadium oxide surface model. The current work is consistent with experimental vibrational spectroscopy results and does not support the presence of a significant amount of NH₂ on the catalyst surface for the SCR reaction on VO_x/TiO₂. The combined experimental and computational results support the presence of both NH₃- and NH₄⁺-type species bound to the surface.

Efficient electrocatalytic reduction of NO to ammonia on BC3 nanosheets

Searching for an economical and highly efficient electrocatalytic reduction catalyst for ammonia synthesis under controllable conditions is a very attractive and challenging subject in chemistry. In this study, we systematically studied the electrocatalytic performance of BC₃ nanosheets as potential NO reduction reaction (NORR) electrocatalysts using density functional theory (DFT) calculations. It was found that BC₃ two-dimensional (2D) materials exhibit excellent catalytic activity with a very low limiting potential of -0.29/-0.11 V along three reaction paths. The total reaction is NO (g)+5H⁺+5e^-→NH₃(g)+ H₂O. The density of states of adsorbed NO, NH_3, and the corresponding crystal orbital hamiltonian population (COHP) analysis revealed the mechanism of NO being activated and the reasons for NH₃ adsorption/desorption on the surface of BC₃. The reaction path, limiting potential, and Gibbs free energy calculations of BC₃ catalyzed NO to ammonia synthesis revealed that for path 1, the potential-determining step is *NO+H⁺+e^-→*NOH, and for path 2/3 the potential-determining step is *NO+(H⁺+e^-)→*HNO. Calculation of the thermodynamic energy barriers for NO dissociation at the BC₃ surface and NO hydrogenation reveals that NO is more likely to be hydrogenated rather than dissociated. The influences of the proton-electron hydrogenation site on the process of ammonia synthesis in the key reduction step were analyzed by Bader charge analysis and charge density, it is pointed out that the electronic structure and affects the reaction process can be controlled by hydrogenation at different sites of intermediates. These results pave the way for using nitrogen oxides not just nitrogen as raw materials for ammonia synthesis with 2D materials.

High Surface Area VOx/TiO2/SBA-15 Model Catalysts for Ammonia SCR Prepared by Atomic Layer Deposition

The mode of operation of titania-supported vanadia (VOx) catalysts for NOx abatement using ammonia selective catalytic reduction (NH3-SCR) is still vigorously debated. We introduce a new high surface area VOx/TiO2/SBA-15 model catalyst system based on mesoporous silica SBA-15 making use of atomic layer deposition (ALD) for controlled synthesis of titania and vanadia multilayers. The bulk and surface structure is characterized by X-ray diffraction (XRD), UV-vis and Raman spectroscopy, as well as X-ray photoelectron spectroscopy (XPS), revealing the presence of dispersed surface VOx species on amorphous TiO2 domains on SBA-15, forming hybrid Si–O–V and Ti–O–V linkages. Temperature-dependent analysis of the ammonia SCR catalytic activity reveals NOx conversion levels of up to ~60%. In situ and operando diffuse reflection IR Fourier transform (DRIFT) spectroscopy shows N–Hstretching modes, representing adsorbed ammonia and -NH2 and -NH intermediate structures on Bronsted and Lewis acid sites. Partial Lewis acid sites with adjacent redox sites are proposed as the active sites and desorption of product molecules as the rate-determining step at low temperature. The high NOx conversion is attributed to the presence of highly dispersed VOx species and the moderate acidity of VOx supported on TiO2/SBA-15.

Theoretical Study of the Catalytic Activity and Anti-SO2 Poisoning of a MoO3/V2O5 Selective Catalytic Reduction Catalyst

In this paper, density functional theory has been applied to study the mechanism of anti-SO₂ poisoning and selective catalytic reduction (SCR) reaction on a MoO₃/V₂O₅ surface. According to the calculation results, the SO₂ molecule can be converted into SO₃ on V₂O₅(010) and further transformed into NH₄HSO₄, which poisons V₂O₅. If V₂O₅ and MoO₃ are combined with each other, charge separation of V₂O₅ and MoO₃, which are negatively and positively charged, respectively, occurs at the interface. In ammonium bisulfate liquid droplets on the MoO₃/V₂O₅ surface, NH₄ ⁺ tends to adhere to the V₂O₅(010) surface and can be removed through the SCR reaction and HSO₄ ^- tends to adhere to the MoO₃(100) surface and can be resolved into SO₃ and H₂O, which can be released into the gas phase. Thus, MoO₃/V₂O₅ materials are resistant to SO₂ poisoning. In the MoO₃/V₂O₅ material, Brønsted acid sites are easily formed on the negatively charged V₂O₅(010) surface; this reduces the energy barrier of the NH₃ dissociation step in the NH₃-SCR process and further improves the catalytic activity.

Density functional theory (DFT) studies of vanadium-titanium based selective catalytic reduction (SCR) catalysts

Based on density functional theory (DFT) and basic structure models, the chemical reactions on the surface of vanadium-titanium based selective catalytic reduction (SCR) denitrification catalysts were summarized. Reasonable structural models (non-periodic and periodic structural models) are the basis of density functional calculations. A periodic structure model was more appropriate to represent the catalyst surface, and its theoretical calculation results were more comparable with the experimental results than a non-periodic model. It is generally believed that the SCR mechanism where NH₃ and NO react to produce N₂ and H₂O follows an Eley-Rideal type mechanism. NH₂NO was found to be an important intermediate in the SCR reaction, with multiple production routes. Simultaneously, the effects of H₂O, SO₂ and metal on SCR catalysts were also summarized.

Theoretical investigation of selective catalytic reduction of NO on MIL-100-Fe

Understanding reaction mechanisms for NO reduction on MIL-101-Fe.

Oxotitanium-porphyrin for selective catalytic reduction of NO by NH3: a theoretical mechanism study

Nitric oxide reduction catalyzed by oxotitanium-porphyrin.

Deep insight into the structure–activity relationship of Nb modified SnO2–CeO2 catalysts for low-temperature selective catalytic reduction of NO by NH3

The structure–activity relationship of Nb modified SnO₂–CeO₂ catalysts was investigated for selective catalytic reduction of NO by NH₃.