Subject Number : S-18-MS-0017
Support Type : Collaborative research
Proposal Title (English) : Mechanistic insight into the fast SCR-NH3 of NO over anatase-TiO2 (001): A DFT-D3 study
Username (English) : Supawadee Namuangruk
Affiliation (English) : National Nanotechnology Center (NANOTEC), National Science and Technology
Development Agency, Thailand

1. Summary
This work investigates the fast SCR and a role of NO2 on anatase-TiO2 (001) catalyst by using Density Functional Theory (DFT) method. Our calculations suggested that the (001) surface is very reactive. We found that NO2 plays the role to the SCR reaction when Brønsted acid sites present. Brønsted sites on (001) lead to different electronic charge nature and different selectivity from bare surface. Those aspects lead to different intermediates and mechanism from the SCR reaction on bare (001) surface.
2. Computational method
DFT calculations were performed by using VASP software. The projector-augmented wave (PAW) with the generalized gradient approximation (GGA) refined by Perdew, Burke and Ernzerhof (PBE) were used in our calculations. Grimme’s DFT-D3 was applied for the dispersion contribution. The energy convergence and the force convergence are 1×10-6 eV/cell 2.5×10-3 eV/Å, respectively. The energy cutoff of 400 eV and Monkhorst-Pack grids of 6×6×1 were applied. The transition states offast SCR-NH3 of NO reaction were attained by using the climbing-image nudged elastic band (CINEB) and the DIMER methods. The criteria of force convergence is less than 0.025 eV/Å.
3. Results ad Discussion
In bare TiO2(001), NO3 can be formed simultaneously from 2NO2. The calculated result demonstrates that NO3 does not facilitate NH3 dissociation. The NH3 dissociation via HNO3 requires Ea ~1.33 eV, while H dissociation from NH3 to the O2c site consumes only 0.63 eV as observed in our previous work.
For the Brønsted acid (001) model in this work, all active O2c sites on the surface are totally formed OH. The adsorption energies (Ead) of NH3, NO and NO2 are -0.54 eV, -2.78 eV and -2.95 eV, respectively. The proposed reaction is shown in Figure 1. NO and NH3 reaction on pre-adsorbed NO2 via HN2O3 and N2O intermediates. The calculation suggested that this reaction is facile. The produced N2O is weakly bound to the surface. When N2O is adsorbed on Brønsted TiO2(001) surface, it is simultaneously dissociated and N2 is released as a product. Then NH2 can interact with NO to produce NH2NO and further reduce to N2 and H2O.

Figure 1. Catalytic reduction NO2 and NO by NH3 over Brønsted acid (001) surface.

4. Others
N/A
5. Publication/Presentation
(1) A. Junkaew, S. Namuangruk, P. Maitarad, M. Ehara, Manuscript in preparation.
(2) A. Junkaew, P. Maitarad, S. Namuangruk, M. Ehara, 1st TTV Workshop, Taiwan, March 22-23, 2018.
6. Patent
N/A