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.