Toward Automated Catalyst Preparation of Monolithic Honeycombs for Ammonia Oxidation by Robot-Controlled Washcoating

While the catalyst development for emission control mostly starts at the powder level, structured coated catalysts are crucial for application. Hence, the transfer of manual catalysts preparation methods to robot-controlled processes is a key step toward reproducibility, scalability, and optimization, all needed in academia and industry. In this study, a laboratory-scale robot-controlled dip-coating device was developed and systematically evaluated for washcoating of monolithic honeycomb substrates. Parameters such as dwell time and dipping speed were independently varied. The washcoats were quantified using a photo-analysis method, providing descriptors such as open channel area and channel clogging. Using γ-Al2O3 as a model material, optimized robot-controlled parameters were identified. Next, 2 wt% Pt/Al2O3, 2 wt% Pt/TiO2, and 2 wt% Pt/CeO2 catalysts were automatically washcoated and compared to manually coated counterparts. The monolithic catalysts were evaluated in ammonia oxidation in an oxygen excess, with respect to NH₃ conversion and selectivity toward N2, N2O, and NOX. The results demonstrate that robot-controlled washcoating replicates key characteristics of manually prepared samples. Comparable open channel areas, catalyst loadings, and catalytic performances were achieved, particularly for Pt/Al2O3. While manual washcoating currently offers slightly finer control over coating thickness, the automated process provides significant advantages. The differences in activity and selectivity for Pt/TiO2 and Pt/CeO2 highlight the importance of further optimization for different support materials. Overall, this work establishes small scale robot-controlled washcoating as an alternative to manual methods, offering a platform for systematic catalyst optimization, including several catalyst layers and zone coatings.