Reaction mechanism of platinum dimer cation with ammonia based on the relativistic density functional study

Abstract

AbstractThe gas‐phase reactions between Pt and NH3 have been investigated using the relativistic density functional approach (ZORA‐PW91/TZ2P). The quartet and doublet potential energy surfaces of Pt + NH3 have been explored. The minimum energy reaction path proceeds through the following steps: Pt(4Σu) + NH3 → q‐1 → d‐2 → d‐3 → d‐4 → d‐Pt2NH+ + H2. In the whole reaction pathway, the step of d‐2 → d‐3 is the rate‐determining step with a energy barrier of 36.1 kcal/mol, and exoergicity of the whole reaction is 12.0 kcal/mol. When Pt2NH+ reacts with NH3 again, there are two rival reaction paths in the doublet state. One is degradation of NH and another is loss of H2. In the case of degradation of NH, the activation energy is only 3.4 kcal/mol, and the overall reaction is exothermic by 8.9 kcal/mol. Thus, this reaction is favored both thermodynamically and kinetically. However, in the case of loss of H2, the rate‐determining step's energy barrier is 64.3 kcal/mol and the overall reaction is endothermic by 8.5 kcal/mol, so it is difficult to take place. Predicted relative energies and barriers along the suggested reaction paths are in reasonable agreement with experimental observations. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007