Adsorption and Dehydrogenation Behaviors of the NH₃Molecule on the W(111) Surface: A First-Principles Study

Abstract

The adsorption and dehydrogenation behaviors of ammonia on W(111) surface have been studied by employing spin-polarized density function theory calculations. In this work, three adsorption sites of the W(111) surface were considered, such as top (T), 3-fold-shallow (S), and 3-fold-deep (D) sites. The most stable structures of each NH x (x = 0−3) species on the W(111) surface have been predicted, and the corresponding dehydrogenation processes were found to be via two specific paths (A and B). In PATH A, the calculated activation energies for NH x (x = 1−3) dehydrogenations are 27.66 kcal/mol (for H 2 N−H bond activation), 32.66 kcal/mol (for HN−H bond activation) and 27.84 kcal/mol (for N−H bond activation), respectively, and the entire process is exothermic by 41.63 kcal/mol. On the other hand, in PATH B, the corresponding activation barriers are 35.97, 29.99, and 29.80 kcal/mol, respectively, and the entire process is 42.19 kcal/mol exothermic. To gain more insight into catalytic processes of the aforementioned conducts, the interaction nature between the adsorbate and substrate is analyzed via detailed electronic analysis.

Computational investigation of NH3adsorption and dehydrogenation on a W-modified Fe(111) surface

“…All these calculated data were fully compared with experimental properties, showing a good agreement with the experimental values. 22 Therefore, in this work we are confident in the reliability of the following simulated results by rPBE functional for NH 3 /W@Fe(111) system.…”

“…If the thermal energy could overcome the energy barrier of TS2 (E a = 29.17 kcal mol À1 ), then all of the NH x dehydrogenation processes could take place on the surface of W@Fe(111). Even though this activation energy of TS2 on the W@Fe(111) surface is somewhat high, it is still lower than those for the NH 3 dehydrogenations on the Pt, 9 Rh 20 and W 22 surfaces, where the rate determining activation energies of the reactions on the metal surface range from ca. 31.3 to 37.1 kcal mol À1 .…”

“…Any attempt to find a minimum of energy in the other symmetric site results in the top site after complete optimization, which is in agreement with the published theoretical works of NH 2 adsorption on transition metals. 21,22 For the geometry of W@FeNH 2 (T-Z 1 -N) with the highest adsorption energy, it is found that the bond length of N-W would dramatically decrease to 1.967 Å as compared to its original counterpart of NH 3 adsorption (W@FeNH 3 (T-Z 1 -N)-a, 2.248 Å). The bond length of the N-H and H-N-H bond angle are 1.018/1.019 Å and 110.51, respectively, which are close to those of isolated NH 2 in the gas-phase (1.024 and 103.41).…”

“…6.25 kcal/mol. 21,22 Besides, the energy barrier for the first dehydrogenation process in NH 3 /W(111) is slightly lower than NH 3 /Fe(111) by ca. 0.7 kcal/mol, and it will turn to be ca.…”

Hydrogenation of Hydrogen Cyanide to Methane and Ammonia by a Metal Catalyst: Insight from First-Principles Calculations

“…About the specific label of these notations (T, S, and D) throughout the article, one can refer to our previously published studies. 42,43 Conversely, the top site makes its electron density highly localized, showing that there exists a certain extent of electron localization at the top site onto W(111) surface. These results could reflect the fact that the tungsten metal in top site would donate electrons to the gaseous molecule as they adsorbed and make the surface oxidized and potentially electron donors.…”