Performance evaluation of Pt and Pd mono-and bimetallic H 2 -SCR catalysts for NO emission control applications

Abstract

Hydrogen-based selective catalytic reduction (H2-SCR) offers a promising pathway for mitigating NOx emissions, especially in hydrogen internal combustion engine (H2-ICE) systems. This study investigates the role of noble metal identity and metal-metal interactions in governing catalytic performance during H2-SCR of NO. Monometallic catalysts demonstrate that Pd exhibits catalytic activity comparable to Pt while achieving superior N2 selectivity, indicating a more favorable balance between hydrogen activation and selective NOx reduction. In bimetallic Pt-Pd systems, the presence of both metals modifies catalytic performance. A reduction in hydrogen consumption at temperatures below 250 °C and an increase in N2 selectivity is observed. This highlights the critical role of hydrogen activation and availability under low-temperature conditions. The decreased H2 utilization suggests a suppression of non-selective hydrogen oxidation. The differences in catalytic performance of the bimetallic systems cannot be explained by the sole presence of both noble metals. Instead, catalytic testing and H2-TPR characterization indicate the presence of metal-metal interactions, possibly involving electronic modification, partial alloying, or close structural proximity between Pt and Pd species. The results demonstrate that the promoting effects in the bimetallic catalysts arise from a combination of metal coexistence and intermetallic interactions, which collectively influence hydrogen activation and the reaction pathway in H2-SCR of NO.