Development of a molecular kinetic scheme for methane partial oxidation over a Rh/alfa-Al2O3 catalyst

A kinetic investigation on catalytic partial oxidation of methane over a Rh/α-Al2O3 catalyst was addressed using a structured annular reactor specifically designed for studying ultra-fast reactions at high temperatures and very short contact times, out of thermodynamic control. Information on the kinetics of O2 consumption, so far not available in the literature, were collected with CH4/O2/inert-gas tests at varying temperatures, contact times, and diluting gases. By also running CO/O2/N2 and H2/O2/N2 tests, the relative activities of CH4-, CO-, and H2-rich combustions were identified. The activation of methane was found to be the rate-determining step of steam reforming based on the results of CH4/H2O/N2 tests, in line with recent literature reports. The bulk of the data confirmed that methane partial oxidation proceeds according to an indirect reaction scheme consisting of CH4 deep oxidation, secondary reactions of CH4 reforming responsible for syngas formation, the water–gas shift reaction, and consecutive oxidations of H2 and CO. Molecular kinetic expressions are proposed to explain the wide-ranging experimental campaign.