The reactions of n-hexane have been studied on 6.3% Pt/SiO, (EUROPT-1) at different hydrogen and n-hexane pressures, and at 543-633 K, over fresh catalyst and over catalysts deactivated by long runs. Turnover numbers are compared with literature data: the differences are attributed to hydrogen pressure effects. Deactivation influences first of all, selectivity. In addition, the 'depth' and ' pattern' of hydrogenolysis have been determined.At low temperature multiple splitting s e e m s to be favoured. lsomerization gives predominantly 3-methylpentane.At medium temperatures, isomerization, C,cyclization and internal splitting prevail ; their ratio is controlled by the hydrogen pressure. The ratio of 2-methylpentane to 3-methylpentane is related to the ratio of internal to terminal rupture. Terminal splitting prevails at highest temperature. Aromatization increases with temperature but s e e m s to be independent of the other reactions. The results are interpreted in terms of three different surface states. These correspond to Pt-H, Pt-C-H and Pt-C under increasing severity of conditions.

Pt-black catalysts sintered at 473 and 633 K ("Pt-473" and "Pt-633"), respectively, have been characterized by X-ray diffraction and analyzed by XPS, UPS, and AES after carrying out n-hexane reactions. The analysis has been repeated after O2-H2 regeneration in the preparation chamber of the UHV apparatus. The surface of the blacks contains some carbon and oxygen impurities even after regeneration. Both Pt-473 and Pt-633 show high Pt 4f line intensity. Decomposition of the C 1s line reveals a higher amount of oxidized carbon polymers on Pt-633. This sample is free from lattice strain. The likely higher abundance of exposed hexagonal symmetry faces, namely the (111) plane and analogous stepped and kinked structures, may be one of the reasons why fragmentation and aromatization are favored on Pt-633, as opposed to the higher selectivity of isomerization and C5-cyclization on Pt-473. The higher amount of oxidized carbonaceous polymer overlayer (serving as "hydrogen catcher") on Pt-633 as well as the less-retained hydrogen by its crystallites without lattice strain may also contribute to the different selectivity and hydrogen pressure response of the n-hexane reaction over the two samples. Product ratios are suggested as an additional diagnostic tool for characterizing the hydrogen availability on the catalysts

Alkoxy Radicals / Kinetics / Photochemistry / Radicals / Reactivity of Radicals The hydrogen abstraction from ethylbenzene by 1 -phenylethoxy radicals generated by the photodecomposition of 1 -phenylethyl terf-butyl-peroxide was investigated in acetonitrile as solvent. The rate constant ratios of Habstraction to p-scission were 14 in the case of ethylbenzene, 26 for the peroxide and 0.02 for acetonitrile at 293 K. The activation energy difference of the above two steps was 16.93~0.2 kJ mol-' for ethylbenzene. The quantum yield of the photodecomposition of the peroxide obtained is 0.8. Product accumulation curves received by gas chromatography were simulated using the suggested mechanism with the rate constants compiled both from our experiments and literature data. (HROOBu) was synthesized according to Kornblum and de la Mare (141. Its refraction index was n g = 1.4802 in agreement with literature data (nkb = 1.4806). The purity according to GC analysis was 99.5%. I-Phenylethyl-tert-Bu-peroxideAcefonitrile (AN) HPLC grade quality was used having very low absorbance in the range 2300 -3200 8,.Ethylbenzene: (RH,) has been purified as described previously [19].Nitrogen was freed of oxygen contamination by a column of 40 mm diameter and 300mm length filled with R3-11 (BASF) catalyst and followed by a gas purifier containing pyrogallol solution (50 g KOH in 100 ml water + 5 g pyrogallol) and dried over CaCI,.Reaction vessel: Thermostated quartz vessel was used (15 ml, 30mm diameter) with solutions of 14.7 ml. In each experiment 0.25 ml "zero" sample was taken after freeing the solution from oxygen by N, bubbled for 20 min. Illumination has been commenced afterwards. During illumination 0.1 ml samples were taken with syringe for analysis.Illumination: A 125 W high pressure Mercury lamp (HgLiIH125) served as light source with filter solution (lengths 20 mm, diameter 25 mm, filled with 240 g/1 NiS04.6H,0 +45 g/l CoSO,.7 H,O) as described by Kasha [20]. Transmission was in the range 2300-3200 8,.

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