A multitechnique approach to chemisorption studies: The N2-Ni(110) system

Response of CPO-27-Ni towards CO, N2 and C2H4

“…Despite the relatively large number of known coordination complexes with transition metals containing N 2 as a ligand, [35][36][37] only a few examples of N 2 complexes formed on metal [38][39][40] and oxide surfaces 41 or on metal exchanged zeolites [42][43][44][45][46][47][48][49] have been reported, most of them formed in low temperature and/or high-pressure conditions. Conversely, there are very few systems where the N 2 adsorption is observed at room temperature and low pressure.…”

“…52 Upon coordination to vacant sites of a metal centers, the stretching frequency of N 2 can undergo downward or upward shifts with respect to the Raman frequency of unperturbed N 2 (2331 cm À1 ), depending on the balance between electrostatic and s-donor/p-acceptor interactions, see Table 1. Dinitrogen, upon interaction with a transition zero-valent metal center, undergoes a synergic s-donor/p-acceptor interaction which causes an important negative frequency shift: 36,40 ñ(NN) E 2200 cm À1 . Conversely, with alkali-metal cations, where electrostatic effects are absolutely predominant, a small increase of the ñ(NN) mode is usually observed.…”

“…65 Relatively high adsorption enthalpies are observed for the formation of cation-dinitrogen complexes isolated in cryogenic matrices. 37 Coming to the adsorption on zero-valent Ni centers, N 2 complexes formed on Ni(001) 66 and Ni(110) 38,40 single crystal surfaces exhibits ÀDH ads values in the 44-38 and 35-27 kJmol À1 ranges, respectively, by moving from low to high coverages (y). Fig.…”

Principles of Chemisorption

“…Some typical values for the (110) 112 (±5) [306] entropy of adsorption of several adsorbate systems are listed in Table 2. The entropy of adsorption -which is the quotient of the reversibly exchanged heat and the temperature -may be calculated from the equilibrium heat of adsorption, if the surface tension is known, or from the isosteric heat of adsorption.…”

High-Resolution Helium Atom Time-of-Flight Spectroscopy of Low-Frequency Vibrations of Adsorbates

“…A particularly welldocumented example for this relationship is the chemisorption system N 2 /Ni (110), where the partial molar entropy of the adsorbed layer has been measured as a function of the coverage. 24 As shown in Figure 2, the partial molar entropy S ˜ad varies between 100 and 200 J K -1 mol -1 at a surface temperature of T S ) 150 K. The contribution from the perpendicular Ni-N 2 mode (pω ) 40 meV) 25 and from the internal N-N mode (pω ) 272 meV) 25 amounts to only S ˜vib ) 1.4 J K -1 mol -1 24 indicating that the dominant contribution comes from the low-energy librational modes and from the lateral adsorbate diffusion.…”