A 3-D activity function has been developed on the basis of the active metallic surface area (Pd MSA) in terms of the Pd loading and mileage of the catalyst, which can be used to predict the performance of Pd-based commercial TWCs over a wide range of the Pd loadings from 20 to 280 g/ft(3) and the catalyst mileages from 4k to 100 k miles. The overall reaction kinetics combined with the activity function and the detailed reaction kinetics reasonably well describes the TWC activity of the powder-type TWC as a function of the catalyst Pd loading and mileage. Moreover, the capability of the activity function incorporated into a 2D non-isothermal monolith reactor model including both the heat and mass balance equations has also been demonstrated with reasonable accuracy of its prediction of the TWC performance of a commercial monolith reactor over its mileage from 4k to 100 k miles, providing that the activity function developed in this work may be universally utilized to predict the catalytic activity of any Pd-based TWC with respect to its Pd loading and mileage. (C) 2014 Elsevier B.V. All rights reserved.