Abstract
The pore structure of a simulated washcoat layer was evaluated using the Mean Transport Pore Model (MTPM). The MTPM provides the mean diffusive pore radius (rm) of a simulated washcoat layer from the experimentally measured effective diffusion coefficient (De). However, data previously published in the literature indicated that the value of rm depended on the choice of diffusive gas for the measurement of De. Therefore, a new, more efficient method was developed to estimate rm. To obtain base data, De was measured in a binary gas diffusion system using a modified Wicke-Kallenbach diffusion cell at room temperature, 473 K, and 673 K. The diffusive gases tested were H2, He, CH4, Ne, N2, O2, C3H6, CO2, and C3H8, and a simulated washcoat layer was used. The results confirmed that the value of rm depended on the type of diffusive gas used. However, many measurements of De are required to avoid problems. In the catalytic R&D process, the measurement of many De values for every experiment is impractical. To balance validity against efficiency for estimating rm, a combination of experimentally measured De and predicted De was used. This method is effective for predicting De using the mean molecular speed instead of a porous structure, and is more efficient than the conventional method of using MTPM. This method also can contribute to investigations of automotive catalysts.
