Two-dimensional modeling of partial oxidation of methane on rhodium in a short contact time reactor

Partial oxidation of methane in monolithic catalysts at very short contact times has recently been shown to offer a promising route to convert natural gas into syngas (CO, H2), which can subsequently be converted to higher alkanes or methanol. Detailed models are needed to understand the complex interaction of transport and kinetics occurring in these reactors. In this work, the partial oxidation of methane on rhodium is studied numerically as an example of short contact time reactor modeling. A tube wall catalytic reactor, which serves to model a single pore or channel of the monolithic catalyst, is simulated. The simulation is carried out using a fully two-dimensional flowfield description, which is coupled with a detailed surface reaction model. The catalyst is characterized by its temperature and coverages of adsorbed species, which vary in the flow direction. The simulation offers a detailed description of the complex interaction between mass and heat transfer as well as chemistry. At the catalyst entrance, an extremely rapid variation of temperature, velocity, and transport coefficients is found. The competition between complete and partial methane oxidation is explained using the calculated surface coverages whereby CO2 and H2O are formed in the entrance region of the catalytic reactor. Methane conversion as well as H2 and CO selectivity are found to increase with increasing temperature. Increasing reactor pressure reduces methane conversion, although the syngas selectivity decreases only slightly.