INFLUENCE OF SURFACE NONIDEALITIES ON CATALYST EFFECTIVENESS

This study addresses the important problem of the effect of adsorbate interactions and surface heterogeneity on a surface reaction in the pr esence of pore diffusional resistance (expressed through the conventio nal effectiveness factor plots). Curves for attractive and repulsive i nteractions straddle the no-interaction (Langmuir) curve, the spread o f the curves being quite significant at low pressures. The effect of s urface heterogeneity can also be significant and is a strong function of the type of site energy distribution. Pressure has a nontrivial eff ect on the value of the effectiveness factor on a heterogeneous surfac e; more importantly, it can alter the direction of the effect: lower t han ideal at low pressures, and higher than ideal at higher pressures. An interesting observation is that the effects of interaction and het erogeneity 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.