Influence of surface nonidealities on catalyst effectiveness

Abstract

This study addresses the important problem of the effect of adsorbate interactions and surface heterogeneity on a surface reaction in the presence of pore diffusional resistance (expressed through the conventional effectiveness factor plots). Curves for attractive and repulsive interactions straddle the no-interaction (Langmuir) curve, the spread of the curves being quite significant at low pressures. The effect of surface heterogeneity can also be significant and is a strong function of the type of site energy distribution. Pressure has a nontrivial effect on the value of the effectiveness factor on a heterogeneous surface; more importantly, it can alter the direction of the effect: lower than ideal at low pressures, and higher than ideal at higher pressures. An interesting observation is that the effects of interaction and heterogeneity tend to cancel each other out for attractive interactions, thus extending the superficial validity of the ideal Langmuir isotherm even to reactions in the presence of diffusion.