29 research outputs found
Dissociation of CH Species on Ni(111):A HREELS Study
The isothermal dissociation rate of CCH and CH on Ni(111) was measured by following, with HREEL spectroscopy, the intensity of the CH stretching peak as a function of time. By repeating the experiment at several different temperatures we obtained an activation energy of 8±3 kcal/mol for the CCH dissociation reaction and of 12±3 kcal/mol for the CH dissociation reaction. Pre-exponential factors were found to be 10^3±1 s-1 in both cases. Independent thermal desorption spectra show a feature at 470 K and a tail extending up to 600 K which can be assigned to the CCH dissociation and the CH dissociation respectively. The two experiments are quantitatively consistent
Surface structure of Pd(111) with less than half a monolayer of Zn
We have characterized the structural properties of submonolayer amounts of Zn on Pd(111) using
scanning tunneling microscopy (STM) and spot-profile analysis low energy electron diffraction (SPA-LEED).
Following room temperature deposition of E0.06 monolayers (ML) Zn onto Pd(111), we observe the
substitution of Zn for Pd in the surface layer. At E0.20 ML of deposited Zn, STM reveals a locally ordered
phase with a 2/sqrt3x2/sqrt3R30deg unit cell located near Zn substitutions; SPA-LEED patterns reveal the
same periodicity. We attribute this phase to the metastable bonding of atoms or clusters predominantly
in hollow sites surrounding Zn substitutions in the surface layer. At Therta=0.4 ML, STM images reveal local 2/sqrt3x2/sqrt3R30deg and (2x1) ordering on surfaces annealed to 350 K. At coverages near 0.5 ML, both STM and SPA-LEED show the onset of the formation of the (2x1) ordering associated with the Zn: Pd 1 : 1
alloy phase. At all coverages, the surface is dominated by island growth; the islands\u2019 size and density is
shown to depend critically on annealing at temperatures as low as 350 K. These results provide insight
into the structural features of a Zn/Pd(111) coverage regime that has been much debated in recent years
Kinetics of the C2H2 Dissociation on Ni(111): A HREELS Study
The C2H2 isothermal dissociation rate on Ni(111) was measured by following, with HREEL spectroscopy, the intensity of the CH stretching peak as a function of time. By repeating the experiment at several different temperatures we have obtained an activation energy of 1.2±0.1 eV/molecule and a pre-exponential factor of 10^14±1 s-1 for the first step of the C2H2 dissociation reaction.
CO dissociation and recombination reactions on Ni(100)
The kinetics of atomic carbon and oxygen buildup on a Ni(1OO) surface exposed to carbon monoxide at high temperatures have been investigated by Auger electron spectroscopy. The experimental data, taken at different sample temperatures (453 ≤ T ≤ 573 K) and at different CO partial pressures (3x10^-7 ≤ PCO ≤ 3x10^-6 mbar) allowed the identification of the CO dissociation mechanism. By fitting the experimental data with a set of rate equations describing CO dissociation, CO reduction of surface oxygen, and C and O recombination, we have been able to determine the pre-exponential factors and the activation energies of these processes
CO dissociation on Ni(100) studied by Auger electron spectroscopy
Auger Electron Spectroscopy (AES) has been used to investigate the kinetics of CO dissociation on a Ni(100) single crystal surface. The coverages of carbidic carbon and oxygen on the surface have been monitored as a function of time for different sample temperatures (453 K ≤ T ≤ 573 K) and CO pressures (3 × 10−7 mbar ≤ PCO ≤ 3 × 10−6 mbar). The experimental data have been compared to the results of rate equations relative to different dissociation models. This procedure led to the identification of the probable reaction mechanism, whose most relevant step in this pressure range resulted to be the rupture of the CO bond. The activation energy of the process has been evaluated
Comparison between optically excited and electron-excited transitions above oxygen and nitrogen K edges in Cu2O, O/Al, O/Ni, SiO2 and Si3N4
We compare transitions observed in photoabsorption spectra above the oxygen and nitrogen K edges in several compounds and chemisorption systems with transitions excited by the process of electron-energy loss detected in the reflection mode. We find few but significant discrepancies between the two, mainly attributable to quadrupole transitions and double inelastic scattering in the electron-energy-loss spectra. The problem of the extraction of structural information from the measurements is considered
Ferromagnetic Stoner excitations detected by electron-energy-loss spectroscopy
Spin-flip Stoner excitations have been detected in Fe80B15Si5 using simple electron-energy-loss spectroscopy via the strong energy dependence of the exchange process involved. The Stoner-excitation contribution, obtained as the difference between energy-loss spectra taken with low-energy and high-energy primary electrons, is in good agreement with the results of spin-polarized electron-energy-loss spectroscopy and with theoretical predictions
Coverage-dependent hydrogen adsorption site determinationon Rh(100) by means of high-resolution core-level Spectroscopy
Patent number WO2015124595: Method for the catalyzed reduction of halogen oxyanions in aqueous solutions
Titolo brevetto italiano: metodo per la riduzione catalizzata di ossoanioni di alogeni in soluzioni acquose.; Domanda di brevetto in Italia n. 102014902234549 del 18/02/2014, pubblicata in data 19/08/201