Additive Manufactured open cell polyhedral structures as substrates for automotive catalysts

• Published in: International journal of heat and mass transfer 2018-11, Vol.126, p.1035-1047
• Main Authors: Papetti, V., Dimopoulos Eggenschwiler, P., Della Torre, A., Lucci, F., Ortona, A., Montenegro, G.
• Format: Article
• Language: English
• Subjects: Additive Manufacturing; Automotive catalysts open cell polyhedral lattices; Catalyst numerical simulations; Heat and mass transfer in catalysts; Honeycombs; Model gas reactor
• ISSN: 0017-9310; 1879-2189
• DOI: 10.1016/j.ijheatmasstransfer.2018.06.061

[Display omitted] •An integral design approach for new generation catalysts’ is proposed.•Numerical study of mass transfer in different polyhedral lattices is performed.•Open cell polyhedral lattices have higher mass transfer than honeycombs.•The optimal cell is Cubic45 with low strut diameter and high porosity.•Tests in a gas flow reactor confirm numerical simulations results. Polyhedral open cell lattice catalyst substrates are proposed based on results of numerical simulations and recent advances in Additive Manufacturing (AM) techniques. Detailed simulations have compared different polyhedral structures in terms of mass transfer (aiming at optimal reactivity in the mass transfer limited domain) and flow through resistance. The simulations have taken into account dimensional limits given by the possibilities of AM techniques. Comparisons with state of art honeycombs have also been used in order to identify the optimal shape. Substrates with these optimal characteristics have been manufactured out of Al2O3 with Stereolithography. Subsequently, these substrates have been coated and used for measurements of C3H6 oxidation in a model gas reactor. Measurements have focused in determining oxidation efficiency at different gas hourly space velocities as well as light-off behaviour. Simulation results show that the optimal open cell structures are comprised by a cubic elementary cell rotated by 45° so that one spatial diagonal of the cube is aligned to the main gas flow. Higher porosities and smaller strut diameters improve the reactivity to pressure drop trade off. However, given the current manufacturing limitations, it is not possible to produce structures with strut diameter lower than 0.5 mm. This results in high porosity but low specific surface area (i.e. ε = 0.95 and Sv = 400 m2/m3). Thus, reaching a target conversion requires higher overall catalyst volume. The simulations show that for a series of geometrical parameters the open cell structures can reach identical conversion in respect to the honeycombs with only a fraction of the overall surface area and thus a fraction of the noble metals, while the overall dimensions are in the same order of magnitude and the pressure drop can reach lower levels. Measurements in the model gas reactor confirm the mass transfer advantages of the polyhedral structures as predicted by the simulations. Measurements also show that the polyhedral lattices have very similar light-off behaviour in spite the four times lower