Catalytic partial oxidation of methane on platinum investigated by spatial reactor profiles, spatially resolved spectroscopy, and microkinetic modeling

[Display omitted] ► Catalytic partial oxidation of methane was studied on Pt foam catalysts. ► Species and temperature profiles were measured through the foam and correlated with spatially resolved Raman spectroscopy and electron microscopy. ► Carbon deposits form and block Pt sites at low O2mol fraction leading to decreased reaction rates (cp. Graphical Abstract). ► Pt is lost from the hot oxidation zone and deposited in the colder reforming zone. ► Species profiles were modeled with two microkinetic mechanisms and a pseudo-2D heterogeneous reactor model. Spatially resolved profile measurements, Raman spectroscopy, electron microscopy, and microkinetic modeling have been used to study the catalytic partial oxidation of methane on Pt. The measured species profiles through Pt coated foam catalysts exhibit a two-zone structure: an abrupt change in reaction rates 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 Pt transportation and formation of carbonaceous deposits blocking the majority of active Pt 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.