Reactive Oxygen Species on Platinum Gauzes during Partial Oxidation of Methane into Synthesis Gas

Abstract

Platinum gauzes have been studied for the partial oxidation of methane in a high-temperature TAP-2 reactor between 800 and 1100 • C. Two different oxidation procedures were used and the oxygen uptake has been measured. Alternating pulse experiments with oxygen and methane with various pulse intervals have revealed mechanistic information about the platinum catalyzed partial oxidation. It has been shown that carbon monoxide and hydrogen can be produced directly from methane and solid oxidized platinum. In the absence of gas phase oxygen, the maximum selectivities to carbon monoxide and hydrogen were 97 and 96%, respectively, at a methane conversion of 25%. At low surface oxygen concentrations, oxygen that is incorporated in the platinum bulk diffuses back to the surface to react with surface carbon to carbon monoxide. In that case the surface lifetimes of carbon monoxide and hydrogen are much shorter than the oxygen diffusion time and no consecutive oxidation reactions occur. The results of this study show that production of synthesis gas with high yields is possible by a direct route.

Catalytic partial ?oxidation of methane to syngas? at elevated pressures

“…A large peak in the H 2 O profile is consistent with the indirect pathway for the CPOX process, in which complete oxidation of methane on the front of the reactor is followed by reforming reactions [20]. On the other hand, low and near constant concentration of CO 2 along the reactor, is consistent with direct partial oxidation pathway in which partial oxidation products directly form on the front of the reactor [10,21,22]. Linear extrapolation of product selectivity vs. conversion plots to zero methane conversion (figure 4) suggests initial partial oxidation reaction as represented by equation (4).…”

Spatial Concentration Profiles for the Catalytic Partial Oxidation of Jet Fuel Surrogates in a Rh/Al2O3 Coated Monolith

“…In studies with Pt and Pt/Rh, hydrogen and CO are shown as primary products at short contact times, whereas an influence on mass transport limitation by the variation of the catalyst geometry has been reported [7,39]. Additionally, a direct formation towards syngas has been suggested in a TAP (temporal analysis of products) reactor, different to this study, albeit on platinum catalysts [40]. There, it was also reported that the definition of the reaction products is driven by oxygen adsorbates, showing different regimes depending on the availability of gas phase oxygen.…”

Effect of different oxygen species originating from the dissociation of O2, N2O and NO on the selectivity of the Pt-catalysed NH3 oxidation

“…Oxygen species dissolved in the bulk of Pt were assumed to be responsible for direct oxidation of methane to carbon dioxide. In general, the ideas about the participation of various oxygen species in different elementary steps of this Pt-catalysed reaction were later confirmed by Fathi et al [11]. In contrast to Mallens et al [10], the latter authors ascribed CO formation to chemisorbed oxygen species formed either via O 2 dissociation or to oxygen atoms diffusing from the bulk of Pt to the surface.…”