Abstract
The development of Pd-based alloy catalysts for highly active and selective reduction of NO by CO was investigated. A survey of Pd-based bimetallic catalysts (PdM/Al2O3: M = Cu, In, Pb, Sn, and Zn) revealed that the PdIn/Al2O3 catalyst displayed excellent N2 selectivity even at low temperatures (100% at 200 °C). The catalytic activity of PdIn was further improved by substituting a part of In with Cu, where a Pd(In1-x Cu x ) pseudo-binary alloy structure was formed. The optimized catalyst, namely, Pd(In0.33Cu0.67)/Al2O3, facilitated the complete conversion of NO to N2 (100% yield) even at 200 °C and higher, which has never been achieved using metallic catalysts. The formation of the pseudo-binary alloy structure was confirmed by the combination of HAADF-STEM-EDS, EXAFS, and CO-FT-IR analyses. A detailed mechanistic study based on kinetic analysis, operando XAFS, and DFT calculations revealed the roles of In and Cu in the significant enhancement of catalytic performance: (1) N2O adsorption and decomposition (N2O → N2 + O) were drastically enhanced by In, thus resulting in high N2 selectivity; (2) CO oxidation was promoted by In, thus leading to enhanced low-temperature activity; and (3) Cu substitution improved NO adsorption and dissociation (NO → N + O), thus resulting in the promotion of high-temperature activity.
Highlights
Reactions of nitric oxide (NO) have received an increasing amount of interest among researchers for human health,[1] bioinorganic,[2] industrial,[3] and environmental chemistry applications.[4]
We prepared a series of Pd-based intermetallic compounds supported on alumina (PdM/Al2O3, M 1⁄4 Cu, in the 5p orbital (In), Pb, Sn, and Zn) and tested them in NO reduction by CO
PdIn exhibited a remarkably high N2 selectivity in a wide range of temperatures (>200 C) and high NO conversion compared to pure Pd in a low-temperature region (200 C)
Summary
Reactions of nitric oxide (NO) have received an increasing amount of interest among researchers for human health,[1] bioinorganic,[2] industrial,[3] and environmental chemistry applications.[4]. Attention has been increasingly focused on the use of Pd because of its prominent oxidation activity for hydrocarbons and CO,[11] and its excellent thermal stability.[12] controlling the selectivity of NO reduction to N2 remains a signi cant challenge because signi cant amounts of undesired by-products, such as N2O, which is a powerful greenhouse gas, are evolved when CO is used as a reductant.[6] To the best of our knowledge, no metallic catalyst that shows high NO reduction ability without N2O emission even at low temperatures (
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