Exhaust system for hydrogen fuelled combustion engines: effect of high-water content on the SCR vanadium catalyst

Sammanfattning: Transportation represents a key secot in the journey towards a greener future, and alternative solutions are needed to meet the decarbonaisation need. Hydrogen internal combustion engines could represent a solution in the short-term, allowing for emission reduction with limited modification to the already existing traditional combustion engines. Their use offers however new challenges for the design of the exhaust aftertreatment system in heavy-duty vehicles, as the H2-ICE's exhaust contains significant amounts of water and hydrogen, together with NOx.  The aim of this project was to investigate the effect of high moisture content on the SCR NOx conversion activity, and the consequences of long-term exposure to highly humid environment for the catalyst. First, a flow reactor was used to test the SCR NOx conversion rate under different water content conditions. Then hydrothermal aging of 40 hours at 10% and 30% water content was performed on two samples. Effects from the aging were evaluated through several characterization analyses, including nitrogen physisorption, Scanning Electron Microscopy and NOx reduction.  The first part of the study showed inhibiting effect on the NOx conversion rate due to water content and lower temperatures, while an improvement was noticed for temperatures above ~400°C. In the second part, a reduction of BET surface area and NOx conversion rate were detected in the same aged with 30% water, together with visible deposits of substrate material on the reactor tube despite the short aging time. Several meaningful observations were obtained from this study, which could represent possible starting points for further analysis on the SCR application in hydrogen combustion engines.