Hydrogen spillover technique

These hydrogenations are rapid and quantitative. Conversely, the gas-solid hydrogenations of alkenes that were doped by platinum metal compounds on their recrystallization maybe incomplete as, for example, the hydrogenation of trans-cinnamic acid or N-vinylisatin [58,61], which should be milled for completion. Furthermore, the spillover technique by mixing powders of substrate and catalyst followed by application of hydrogen and several hours or days rest [69,70] appears inappropriate for quantitative conversions. Milling is, however, not applicable if volatile liquids have to be constantly pumped off [69] or if the products become liquid or sticky [70]. 

When in situ dosing onto two different samples of Pt/silica (45, 48) and onto Cu/MgO was used (49), no evidence for spillover was found from NMR. Only one detailed study based on fully relaxed spectra led to observation of a non zero spillover (4T). In a Ru/Si02 catalyst, the silanol protons w ere exchanged for deuterons, the sam.ple was evacuated at 623 K, and a reference NMR spectrum w as taken at room, temperature. The sample was then exposed to 20 Torr of H2, an NMR spectrum was taken, and the difference with respect to the reference was calculated (line in Fig. 14). This represents the sum of reversible and irreversible hydrogen on the metal (resonating at -65 ppm) and spilled over on the support (at about 3 ppm). Then the sample was pumped out at room temperature for 10 min, and again a difference spectrum with the reference state was obtained (dashed line in Fig. 14) this represents irreversible hydrogen both on the support and on the metal. Similar in situ NMR techniques were used... 

The reducibility of Ti02 has in recent years been studied with ESR and NMR techniques (21-23). In the course of our studies (21) we noticed that support reduction is a relatively slow process and that, as a consequence, hydrogen chemisorption on a metal on Ti(>2 catalyst has a fast component, due to adsorption on the metal surface, and a slow component, due to spillover of H atoms from metal to support and subsequent support reduction. We have studied the time dependence of H2 chemisorption, as well as that of (>2 chemisorption, in more detail and the results of this study are presented In this paper. 

It would be wrong to suggest that no intercourse at all between the twin disciplines has taken place. The concepts of relating bulk (metallic) properties of a catalyst to the rate of a reaction at its surface, as described in detail by Bond, have been quoted and adopted by the majority of workers in the field of electrocatalysis. Concepts such as the Volcano relationship of Balandin or the Spillover of adsorbed hydrogen as suggested by Boudart have been widely and successfully transferred to electrochemical reactions. The experimental techniques employed to investigate catalytic processes have been... 

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