H2-SCR at high water concentrations with in-situ generated NH3 -SCR for efficient removal of NOx from H2 engines

Abstract

The two main challenges of application of Pd-based catalysts in H2-SCR are catalytic performance and water resistance. In this study, oxide supports (TiO2 and ZrO2) were employed and experimentally demonstrated to exhibit higher catalytic activity than the SSZ-13 zeolite-supported catalyst. Furthermore, doping Mn into Pd/TiO2 further increased the maximum NO conversion to 61% compared to 44% for undoped Pd/TiO2. Comprehensive characterization techniques, including XRD, STEM, XPS, CO-DRIFTS, and H2-reduction experiments, were used to investigate the catalysts' physicochemical properties and hydrogen spillover behavior. Pd/MnTiO2 not only maintained the strong metal-support interaction observed in Pd/TiO2 but also significantly optimized the surface electronic structure. A higher proportion of metallic Pd facilitated H2 dissociation and enhanced hydrogen spillover, leading to improved catalytic activity. Water resistance tests, at 5%, and up to 12% water vapor, revealed that the zeolite-supported catalyst exhibited superior tolerance to water. Although the oxide-supported catalysts were more sensitive to water, they still maintained significantly higher catalytic activity overall. Notably, Pd/MnTiO2 preserved its active temperature window even as the water content increased to 12%. Finally, since NH3 was identified as a major byproduct during H2-SCR over Pd/MnTiO2, a new NOx removal strategy was developed by adding a downstream Cu-SSZ-13 monolith to establish an integrated H2-SCR and NH3-SCR reaction system. This configuration successfully increased the maximum NO conversion to 78%, with N2 and N2O as the only detected products, achieving a nitrogen selectivity of 74%.