Experimental and numerical study on the transient behavior of partial oxidation of methane in a catalytic monolith

The objective of this investigation is a better understanding of transient processes in catalytic monoliths. As an example, the light-off of the partial oxidation of methane to synthesis gas (H2 and CO) on a rhodium/alumina catalyst is studied experimentally and numerically. Methane/oxygen/argon mixtures are fed at room temperature and atmospheric pressure into a honeycomb monolith, which is preheated until ignition occurs. The exit gas-phase temperature and species concentrations are monitored by a thermocouple and mass spectroscopy, respectively. In the numerical study, the time-dependent temperature distribution of the entire solid monolith structure and the two-dimensional laminar reactive flow fields in the single monolith channels are simulated. A multi-step heterogeneous reaction mechanism is used, and the surface coverage with adsorbed species is calculated as function of the position in the monolith. During light-off, complete oxidation of methane to water and carbon dioxide occurs initially. Then, synthesis gas selectivity slowly increases with rising temperature.