Analysis of the mass transfer controlled regime in automotive catalytic converters

This article concentrates on the analysis of the mass transfer controlled regime in automotive catalytic converters operating under real conditions. The main objective of the work reported is to evaluate the performance of the existing correlations for the mass transfer rate, expressed as the Sherwood (Sh) number, against new experimental data and, if necessary, to establish new correlations that can be used in 1D two-phase models. The experiments have included measurements of conversion efficiencies for hydrocarbons, CO and NOx from ceramic and metallic three way catalytic converters. The present data show that the calculated Sh are always below the asymptotic Sh. This indicates that, in addition to the external mass transfer limitation, both kinetics and internal pore diffusion limitations in the washcoat also contribute to reduce the catalytic converter performance even at high temperatures. In addition, the experimental data reveals that Sh  ’s are chemical species dependent, which, to the best of our knowledge, has not been reported previously. The following correlations for the mass transfer rate were obtained from the experiments: ShHC=0.6272(ReScHCdL)0.934, ShCO=0.9260(ReScCOdL)1.078 and ShNOx=1.2824(ReScNOxdL)1.079.