Design and additive manufacturing of novel ceramic monolithic catalysts for low emission vehicles

Environmental concerns and stringent emission standards have underlined the significance of developing more efficient catalytic converters for exhaust gas aftertreatment. Although the state-of-the-art ceramic honeycomb substrate designs provide a high surface area and low backpressure, further emission reduction advantages can be obtained by introducing advanced designs. The research work presented in this thesis addresses the design and fabrication of advanced ceramic monolithic catalysts using Digital Light Processing (DLP) ceramic additive manufacturing technology. By embracing the advantage of unconstrained conceptual design and overcoming the limitations of traditional manufacturing capabilities, DLP shows a potential use as a catalyst substrate fabrication method to improve catalytic efficiency through advanced catalyst designs. Firstly, monolithic substrates based on diamond-lattice structures were proposed as an attractive replacement for the conventional honeycomb substrate. The comparison of the thermal hydraulic characteristics of the honeycomb design and the diamond lattice substrate was achieved by pairing numerical simulations and experimental studies. The results show an increase in the axial temperature distribution for diamond lattice structures and a significant decrease in the pressure drop (38–45%) in comparison with the benchmark honeycomb with a similar surface area. Secondly, ceramic slurry preparation processes and printing parameters were evaluated to manufacture lattice structures. A Design of Experiments (DoE) technique was used to generate an experimental plan based on all the relevant process parameters, followed by an Analysis of Variance (ANOVA) approach which was then used to determine the optimal processing window and assess the manufacturability along with dimensional accuracy of the lattice structures. The ceramic slurry with the dispersant pre-treated powder showed appropriate rheological and photopolymerisation behaviour for manufacturing lattice structures with feature sizes up to 500 µm. ANOVA revealed the exposure time, the exposure power and the interaction effect of both had significant influence on the dimensional accuracy of lattice strut diameters. Thirdly, to demonstrate the potential of the additively manufactured lattice-based substrates as catalytic converters, they were manufactured and coated with Pt-Pd catalyst supported on γ-Al\(_2\)O\(_3\). Their light-off behaviour was tested in an exhaust gas environment. In addition, the effect of hydrogen presence on their performance was investigated. The light-off experiments showed superior catalytic activity for abatement of carbon monoxide, hydrocarbons, and nitrogen oxides for additively manufactured diamond-lattice catalysts, in comparison with the conventional honeycomb design, with a significant reduction in the light-off temperatures. The intricate lattice structures allowed greater exhaust gas-solid contact and more efficient utilisation of the given surface area. The light-off curves of all studied species in hydrogen-enriched exhaust gas stream shifted to lower temperatures