Kim, Sung-Yup Lee, Hong Woo Pai, Sung Jin Han, Sang Soo 2024-01-19T22:02:53Z 2024-01-19T22:02:53Z 2021-09-03 2018-08-08 1944-8244 https://pubs.kist.re.kr/handle/201004/121042 We report a molecular dynamics (MD) simulation employing the reactive force field (ReaxFF), developed from various first-principles calculations in this study, on ammonia (NH3) synthesis from nitrogen (N-2) and hydrogen (H-2) gases over Ru nanoparticle (NP) catalysts. Using ReaxFF-MD simulations, we predict not only the activities and selectivities but also the durabilities of the nanocatalysts and discuss the size effect and process conditions (temperature and pressure). Among the NPs (diameter = 3, 4, 5, and 10 nm) considered in this study, the 4 nm NPs show the highest activity, in contrast to our intuition that the smallest NP should provide the highest activity, as it has the highest surface area. In addition, the best selectivity is observed with the 10 nm NPs. The activity and selectivity are mainly determined by the hcp, fcc, and top sites on the Ru NP surface, which depend on the NP size. Moreover, the selectivity can be improved more significantly by increasing the H2 pressure than by increasing the N2 pressure. The durability of the NPs can be determined by the mean stress and the stress concentration, and these two factors have a trade-off relationship with the NP size. In other words, as the NP size increases, its mean stress decreases, whereas the stress concentration simultaneously increases. Because of these two effects, the best durability is found with the 5 nm NPs, which is also in contrast to our intuition that larger NPs should show better durability. We expect that ReaxFF-MD simulations, along with first-principles calculations, could be a useful tool in developing novel catalysts and understanding catalytic reactions. English American Chemical Society FORCE-FIELD 1ST-PRINCIPLES CALCULATIONS STRUCTURE SENSITIVITY OXIDE CATALYSTS REAXFF ADSORPTION OXIDATION NITROGEN RU(0001) SURFACES Activity, Selectivity, and Durability of Ruthenium Nanoparticle Catalysts for Ammonia Synthesis by Reactive Molecular Dynamics Simulation: The Size Effect Article 10.1021/acsami.8b05070 1 ACS Applied Materials & Interfaces, v.10, no.31, pp.26188 - 26194 ACS Applied Materials & Interfaces 10 31 26188 26194 scie scopus 000441477800039 2-s2.0-85050335297 Nanoscience & Nanotechnology Materials Science, Multidisciplinary Science & Technology - Other Topics Materials Science Article FORCE-FIELD 1ST-PRINCIPLES CALCULATIONS STRUCTURE SENSITIVITY OXIDE CATALYSTS REAXFF ADSORPTION OXIDATION NITROGEN RU(0001) SURFACES ruthenium nanoparticle catalyst ammonia synthesis activity selectivity durability molecular dynamics