Investigations about coke burning and oxygen spillover

Abstract

Different carbon blacks and graphite were used as model substances to investigate coke burning on biftmctional catalysts. The bunting rate was markedly increased by Pt on A1203 as compared with pure carbon blacks or graphite as a consequence of lowered activation energies.

FTIR spectroscopic investigation of oxygen spillover especially through the gas-phase. A reaction interesting in coke burning

“…2 too, giving an activation energy of 142.2 • 1.7 kJ mo1-1 for both oxide divisions, a value not much below that for the uncatalyzed reaction. These results obtained by means of indirect catalysis are in agreement with those known from directly catalyzed reactions, showing no significant change in activation energy in presence of the catalyst [9,10].…”

Investigations about gas phase oxygen spillover

“…The reproducibility of the measurements is clearly better than in the investigations with mixtures of Pt/Alz03 with carbon blacks [3]. The reaction rate is doubled in the presence of platinum, or the temperature at which a certain conversion is reached is lowered by about 30 K. Assuming that the two oxidation mechanisms are independent parallel reactions, subtraction of both conversion functions should give the ,,pure" Pt reaction given in Table 1 too.…”

“…After a certain time the soot opposite to [1,3] the rings was widely burnt, while that in the other positions burned more slowly. As a photographical documentation of these experiments was not very convincing, glass plates were used for the following experiments.…”

“…In earlier investigations [1][2][3] we discussed oxygen spillover from platinum on alumina to benzoic acid (adsorbed on alumina) or to carbon in the form of graphite or different carbon blacks. In these cases we could not obtain information about the mechanism by which the activated oxygen particles migrate form the metal to the oxidizable substance.…”

A Theory/Experience Description of Support Effects in Carbon-Supported Catalysts

“…In many studies, spillover is proposed to occur on the surface of an oxide, which can be the support of Pt (Al2O3 or SiO2) or the catalyst itself (transition metal oxides or CeO2). 1160,1161,[1194][1195][1196] However, experimental studies dealing with catalytic soot oxidation have shown that activated oxygen atoms (oxygen spillover) can migrate from the metal (Pt) to the carbon via the gas phase. 1162,[1197][1198][1199] In particular, Zeng et al have stated that activated oxygen is mainly transported via the gas phase and that the generally accepted surface transport is indeed negligible.…”