Kinetic Modeling of Total Oxidation of Propane over Rhodium

The heat release rates of fuel-lean propane/air mixtures over a rhodium wire catalyst were measured with microcalorimetry experiments and simulated with a 2D reactive code. Based on these studies, global reaction parameters of the total oxidation of C3H8 over Rh were extracted and a full catalytic reaction mechanism was developed. Wire microcalorimetry experiments were performed at atmospheric pressure and temperatures up to 900 K, while surface kinetic data was determined within the kinetic-controlled regime below 630 K. The dissociative adsorption of C3H8 on Rh and its subsequent decomposition reaction were fitted based on the global reaction parameters, and a thermodynamically consistent reaction mechanism for the total oxidation of C3H8 on Rh was constructed by incorporating these two fitted steps into a CH4-Rh surface mechanism. The constructed catalytic reaction mechanism well reproduced the measured heat release rates in the wire microcalorimeter and was further validated against 2D Raman measurements of major gas-phase species concentrations in an Rh-coated planar channel. Moreover, when working in conjunction with a recently reported pressure dependence of catalytic reactivity and a detailed gas-phase chemistry, the developed catalytic reaction mechanism excellently captured the catalytic reactivity and the homogeneous ignition during hetero-/homogeneous combustion in the planar channel at pressures up to 6 bar. The hetero-/homogeneous coupling of the intermediate species (such as CO) appreciably affected the onset of homogeneous ignition, while the corresponding coupling via radical (O, H and OH) reactions was very weak. Finally, the key reactions controlling catalytic ignition and homogeneous ignition during hetero-/homogeneous combustion were identified