John L. Persson

The influence of a catalytic surface on the gas-phase combustion of H2 + O2

Abstract The OH concentration outside a Pt catalyst at 1300 K, in a stagnation flow of 90% O 2 and 10% H 2 , has been studied by planar laser-induced fluorescence (PLIF), and compared to measurements outside a heated glass surface. The total pressure in the system was varied from 0.2 to 120 torr. At low pressure, surface reactions were observed for the Pt surface, but not for the glass. At higher pressure, gas-phase ignition occurred for both systems, but not at the same pressure: ignition occurred at a lower pressure outside the inert glass surface. Computer modeling using CHEMKIN confirmed these results. The difference in gas-phase ignition is also seen in the modeling results, and it is due to the removal of atomic O and H from the gas by adsorption and reaction on the catalytic surface. The catalytic reaction mechanism on the surface plays an important role as it enhances the removal of radicals, compared to a surface where only radical recombination back to reactants is allowed.

Compensation method for attenuated planar laser images of optically dense sprays

We present a method for compensating laser attenuation in optically dense sprays, in particular for use in combustion engine research. Images of the fuel sprays are produced by planar laser imaging, where Mie scattered light from a cross section of the spray is imaged onto a CCD camera. The compensation scheme is based on the Beer-Lambert law, which is used here to sum up the loss of light along the path of the laser in the image, and to compensate iteratively, pixel by pixel, for this loss.

Reactivity of small transition metal clusters

A new experiment for measuring the reactivity of neutral metal clusters is presented. A low pressure reaction cell is used to measure the sticking ofO2 andD2 gas on small transition metal clusters ofCu, Fe, Co andNi. The experiment yields absolute values for the sticking, at a controlled number of cluster/gas collisions, facilitating comparison with theoretical calculations and other experiments. The most striking result of these preliminary measurements is the difference between oxygen sticking onCoN and onCuN, with the sticking onCuN showing a clear correlation to the electronic shell model, while the sticking onCoN only exhibits a sharp increase with size, reaching sticking probability=1.0 forN>25.

Ionization potentials of oxidized copper clusters

Abstract The ionization potential (IP) of Cu n O 2 clusters ( n = 15−46) has been measured and the shift in IP induced by the adsoprtion of the O 2 molecule evaluated. There are no large discontinuities in the IP of Cu n O 2 , in contrast with the electronic shell closings observed for pure Cu n , but the even-odd alternation in the IP persists upon oxidation. On average, the IP increases after oxidation, with larger shifts for clusters where the pure Cu n have low IP ( n = 21, 41) and small or negative shifts for clusters originally having high IP ( n = 30, 34, 40).

Oxidation of small transition metal clusters

The initial oxidation of gas phase metal clusters is studied in a new experimental configuration. A beam of neutral metal clusters is produced in a laser vaporization source, and after skimming the beam passes a reaction cell where the clusters undergo one or a few collisions with oxygen molecules. The reaction products are detected with laser ionization and mass spectrometry. We have determined the sticking probability, S, of O2 on FeN, CoN and CuN clusters, with Nκ 10–60. FeN and CoN show a similar size dependence with low sticking probability, S < 0.2, for the smallest sizes, then increasing almost monotonically to Nκ 25, where S levels out at a constant value of 0.7 (FeN) or 1.0 (CoN). CuN shows a different size behavior with reactivity minima for clusters with closed electronic shells.

Analysis of the kinetics for the H2 + \( - \frac{1}{2}\)O2 ⇌ H2O reaction on a hot Pt surface in the pressure range 0.10–10 Torr

AbstractThe H2 +

Metal Cluster Oxidation: Sticking Probabilities and Ionization Potential Shiffs

- \frac{1}{2}

OH Gas Phase Chemistry outside a Pt Catalyst

O2 ⇌ H2O reaction on platinum at 700 and 1300 K has been studied. A stagnation flow geometry was used with a gas mixture of H2 and O2 at pressures between 0.10 and 10 Torr. Comparing SHG results with simulations using different reaction parameters, it was concluded that