Ammonia adsorption on Bronsted acid sites of WO3 cluster supported on metal oxide supports: SnO2, ZrO2, and TiO2, is analyzed by PIO analysis. We employed (HO)(WO3)(4)(H) and (HO)(WO3)(9)(H) oil (SnO2)(12), (ZrO2)(12), and (TiO2)(12), respectively, as supported Bronsted acid models and examined two types of Bronsted acid sites, an edge type and a face type. We estimated ammonia adsorption strength by total overlap population (Sigma OP) of all PIOs between the Bronsted acid site and NH3. The order of acidity (EOP) of each model is as follows: edge type: SnO2, 0.0096 > ZrO2, 0.0048 > TiO2, -0.0001 >> face type: ZrO2, -0.0759 > TiO2, -0.0761 > SnO2, -0.0867. The edge type adsorption is far stronger than the face type one. This order in the edge type coincides with the experimental results. The reason of these results is explained by the difference of the influence of oxygen atoms sitting near the N atom of NH3. (c) 2005 Elsevier B.V. All rights reserved.