CO-IMPREGNATED RH/AL2O3 .2. NITRIC-OXIDE REDUCTION AND SO2 POISONING

In the present study, the catalytic reduction of nitric oxide by HZ with eggshell and egg-white HF co-impregnated Rh on γ-Al203 honeycomb catalysts has been investigated to determine the effects of diffusion resistances on the rate and selectivity of the reduction reaction. Intrinsic kinetic data for NO reduction with HZ over Rh/γ-Al203 was measured at 165°C and fit to a simplified Langmuir-Hinshelwood kinetic expression. The intrinsic kinetic model was used to develop a reactor model for NO reduction with RH/γ-Al203 honeycomb catalysts. Theoretically predicted reaction rates and selectivities for the honeycomb catalysts were found to agree closely with measured reactor performance data. Poisoning the honeycomb-supported catalysts with S02 showed that the eggshell and egg-white Rh catalysts deactivated at similar rates. Electron probe microanalysis (EPMA) of the poisoned catalysts revealed that sulfur was distributed throughout the support, indicating that S02 is not limited by diffusion in this system. Analytical electron microscopy (AEM) confirmed a high degree of S/Rh coordination within the egg-white Rh honeycomb catalyst and much less coordination of sulfur with the alumina support. This was attributed to high concentrations of fluorine (1 to 2 wt%) deposited on the support from co-impregnation with HF. This fluorine is postulated to inhibit S02 adsorption onto the support surface. © 1991.