Ammonia Dissociation on Pt{100}, Pt{111}, and Pt{211}:  A Comparative Density Functional Theory Study

Abstract

Density functional theory (DFT) calculations are performed to compare the dissociation of NH x (x = 1−3) species on the Pt{100}, Pt{111}, and Pt{211} surface. Pt{211} is a stepped surface, and Pt{100} consists of square arranged surface atoms. Both surfaces are less compact than Pt{111}. The question is addressed whether the Pt{100} and the Pt{211} surface promote the dissociation of NH x species by lowering the activation barriers with respect to Pt{111}. The NH dissociation reaction is promoted on Pt{100} but not on Pt{211}. The NH2 dissociation reaction is neither promoted by Pt{100} nor Pt{211}. The dissociation of NH3 is also not promoted and turns out to be a two-step reaction on the platinum surfaces. Atop-bonded NH2 is intermediate and equally stable on the three surfaces. The nature of the transition states, which is late in the formation and early in the rearrangement of this atop-bonded NH2, makes the barriers almost independent of the surface topology. Because the reaction energies of the NH x dissociation reactions do depend on the surface topology the findings are unexpected, but they are consistent with an experimentally found moderate structure sensitivity of the ammonia decomposition on platinum.

Catalytic decomposition of ammonia over silicon-carbide nanotube: a DFT study

“…NH ? H in the path of NH 3 dehydrogenation is consistent with the previous result that NH 2 is the most important nitrogen-containing intermediate in the reaction system under realistic reaction conditions [47].…”

“…The successive dehydrogenation of NH 3 leads to the formation of adsorbed nitrogen atom, which has a higher adsorption energy to the catalyst surface, as compared to the other NH x (x = 1-3) species [47]. All of these NH x species have been experimentally observed on metal surface using surface sensitive techniques such as high resolution electron energy loss spectroscopy (HREELS) [48,49].…”

Theoretical study of adsorption and dissociation of NH3 on the Ir{110}(1×2) surface

“…At the second step, NH 2 moves from atop to the bridge position without an additional barrier. This feature is consistent with the NH 3 dissociation on Pt{100} [11] and Pt{111} [12] . For the transition state, there is an imaginary frequency of 503i cm −1 corresponding to the N-H stretching vibration, the dissociating N-H bond length is 0.175 nm and the N-Ir distance is 0.200 nm, and the distance between the dissociating H atom and the Ir atom is 0.166 nm.…”

Mechanism of ammonia decomposition on clean and oxygen-covered Cu (1 1 1) surface: A DFT study

“…Especially, periodic DFT calculations with the slab model have been a powerful approach to study the adsorption and dissociation of small molecules on the metal surfaces. Much attention has been paid to ascertaining the adsorption and dehydrogenation mechanism of NH 3 on numerous metal surfaces, such as Fe [11,12], Co [12], Ni [13][14][15][16], Ir [5,[17][18][19][20][21][22], Cu [23,24], Pd [25][26][27], Pt [28][29][30][31][32], Au [33]. Most of these works were based on density functional theory (DFT) http calculations.…”