Catalytic Partial Oxidation of Methane On Platinum Investigated by Spatial Reactor Profiles, Spatially Resolved Spectroscopy, and Microkinetic Modeling

Catalytic partial oxidation (CPO) of methane is an alternative to steam reforming for industrial production of synthesis gas or hydrogen. Since Hickman and Schmidt showed in their pioneering work [1] that equilibrium yields of synthesis gas can be obtained in millisecond contact times by methane CPO on autothermally operated noble metal coated foam catalysts, this reaction has received a lot of attention in academia and industry.

In the present paper spatially resolved profile measurements, Raman spectroscopy, electron microscopy, and microkinetic modeling have been used to study the catalytic partial oxidation of methane on platinum. The measured species profiles exhibit a two-zone structure, with an abrupt change in reaction rates that separates the fast exothermic oxidation chemistry at the entrance of the reactor from the slow endothermic reforming chemistry. Spatially resolved Raman spectroscopy and electron microscopy confirm that the position of the mechanistic change could be correlated with platinum transportation and formation of carbonaceous deposits blocking the majority of active platinum sites in the reforming zone. The species profiles were simulated using a pseudo-2D heterogeneous model, which includes heat and mass transport limitations, and two state-of-the-art chemical kinetic mechanisms. Although both mechanisms are in quantitative agreement with the oxygen profiles, the two mechanisms differ substantially in their predictions of the branching ratio between partial and complete oxidation, as well as surface site coverages. The experimentally observed change in reaction rates is attributed to carbon formation, which the mechanisms are unable to reproduce, since they do not include carbon-carbon coupling reactions.

References

[1]   D. A. Hickman, L. D. Schmidt, Science 1993, 259, 343-346.