High performance iridium loaded on natural halloysite nanotubes for CO-SCR reaction

Iridium nanocatalysts are ideal candidates for the selective catalytic reduction of NO x by CO (CO-SCR) in excess oxygen. Here, a high-performance Ir nanocatalyst supported on natural halloysite nanotubes (HNTs) was applied for the CO-SCR. The HNTs loaded with only 0.5 wt% Ir achieved 78 % NO x conversion at 250 °C in the presence of 5 % O 2 , which was the highest among catalysts with varied Ir loadings or reduction temperatures. It also possessed an excellent SO 2 and H 2 O tolerance during longevity tests. An interesting SO 2 -enhanced CO-SCR long-term stability was observed, which was ascribed to the inhibitory effects of SO 2 on the side reaction between CO and O 2 . The loading amount and the reduction temperature could modulate the size of Ir nanoparticles and the percent of Ir 0 , which were two key factors determining the CO-SCR activity. DRIFTS characterizations and DFT calculations coherently revealed the favorable adsorption sites of CO (top) and NO (hcp) on Ir nanoparticles. The Ir atoms served as a charge transfer bridge from the C atom of CO to the N atom of NO, leading to the enhanced breakage of N-O bonds. This work provides Ir/HNT as a promising CO-SCR material with high performance and robustness to tackle NO x pollution.