Thermal Desorption and Reaction of NO Adsorbed on Rhodium Cluster Ions Studied by Thermal Desorption Spectroscopy

Abstract

Cationic rhodium clusters, Rh(n)(+) (n = 4-8), were prepared in the gas phase by the laser ablation of a Rh rod. The Rh(n)(+) clusters were introduced into a reaction gas cell filled with nitric oxide (NO) diluted with He, where they were subjected to collisions with NO and He in a thermal equilibrium at 300 K. The NO molecules were found to adsorb sequentially on the Rh(n)(+) clusters forming Rh(n)(+)(NO)m. To examine the adsorption form and the reaction of NO, we heated Rh(n)(+)(NO)m in an extension tube located after the reaction gas cell and the thermal response of the clusters, desorption of the fragments, was recorded as a function of temperature (300-1000 K). The desorption of NO molecules was predominantly observed below 500 K, giving either Rh(n)(+)(NO)n+1 or Rh(n)(+)(NO)n+2, which indicates that there were NO molecules loosely adsorbed on the Rhn(+) clusters. Further desorption was found to proceed at higher temperatures (500-1000 K), whereby NO was released from the smaller clusters, Rh(n)(+) (n ≤ 5). In contrast, for the larger clusters (n ≥ 6), N2 release was clearly observed at high temperatures (>800 K). Thus, the reduction of NO occurred for larger clusters at higher temperatures.

Adsorption Forms of NO on Rhn+ (n = 6–16) Revealed by Infrared Multiple Photon Dissociation Spectroscopy

“…Indeed, no decomposition of NO was observed under thermalized conditions at 300 K, whereas the release of N2 was clearly observed at higher temperatures (>800 K), indicating that NO was reduced on the clusters for n ≥ 7. 17 According to DFT calculations using the LANL2DZ effective core potential and basis set to describe Rh atoms, the most stable geometry of Rh6 + (NO) comprises a tetragonal bipyramid Rh6 + cluster with NO adsorbed molecularly on an on-top site of the Rh6 + cluster with its N atom pointing inwards, with an adsorption energy of −1.5 eV. 17 In the dissociation reaction pathway, a transition state existed with an energy barrier of +1.1 eV relative to the reactants, Rh6 + and NO.…”

“…17 According to DFT calculations using the LANL2DZ effective core potential and basis set to describe Rh atoms, the most stable geometry of Rh6 + (NO) comprises a tetragonal bipyramid Rh6 + cluster with NO adsorbed molecularly on an on-top site of the Rh6 + cluster with its N atom pointing inwards, with an adsorption energy of −1.5 eV. 17 In the dissociation reaction pathway, a transition state existed with an energy barrier of +1.1 eV relative to the reactants, Rh6 + and NO. After this transition state, the complex falls into another minimum, where the N and O atoms are separately adsorbed on hollow sites on the cluster, which is 1.2 eV lower than the geometry before adsorption.…”

Tuning the Dissociative Action of Cationic Rh Clusters Toward NO by Substituting a Single Ta Atom

“…N-bound on-top adsorption at the Ta atom is calculated to be favoured (binding energy 2.1 eV) over O-bound adsorption (1.6 eV): The orientation is common to the adsorption of small, N-containing molecules on metal surfaces. [23][24][25][26][27] According to the natural charges of atoms, the charge is mainly localized on the Ta atom (Natural charge +0.97 e) while Rh atoms are very slightly negatively charged except for the Rh atom that is located at the For Rh6 + , a similar reaction path had previously been proposed (see Figure 4): 9 N-bound on-top adsorption on Rh6 + is exothermic by 1.55 eV. Subsequently, the NO molecule migrates to a bridge site, leaning toward a Rh atom until the O atom in NO binds to it.…”

Reactions involving some gas molecules through sequestration on Al12Be cluster: An electron density based study

“…To probe this concept, we have considered few representative reactions viz. CO oxidation, dissociative addition of CH 3 F and C 2 H 5 F, NH bond decomposition in NH 3 , dissociation of NO, and hydrogenation of C 2 H 2 . We have considered both the thermodynamic as well as kinetic feasibility aspects of the concerned reactions at 298.15 K temperature and one atmospheric pressure.…”

“…Therefore, decomposition of NH 3 is not favorable in such a situation. Similarly, NO decomposition reaction has been extensively studied and in this regard Rh‐based clusters constitute an important choice. In various organic reactions, ethylene plays a pivotal role.…”