Comprehensive Experimental and Theoretical Study of the CO + NO Reaction Catalyzed by Au/Ni Nanoparticles

Abstract

The catalytic and structural properties of five different nanoparticle catalysts with varying Au/Ni composition were studied by six different methods, including in situ X-ray absorption spectroscopy and density functional theory (DFT) calculations. The as-prepared materials contained substantial amounts of residual capping agent arising from the commonly used synthetic procedure. Thorough removal of this material by oxidation was essential for the acquisition of valid catalytic data. All catalysts were highly selective toward N 2 formation, with 50–50 Au:Ni material being best of all. In situ X-ray absorption near edge structure spectroscopy showed that although Au acted to moderate the oxidation state of Ni, there was no clear correlation between catalytic activity and nickel oxidation state. However, in situ extended X-ray absorption fine structure spectroscopy showed a good correlation between Au–Ni coordination number (highest for Ni 50 Au 50 ) and catalytic activity. Importantly, these measurements also demonstrated substantial and reversible Au/Ni intermixing as a function of temperature between 550 °C (reaction temperature) and 150 °C, underlining the importance of in situ methods to the correct interpretation of reaction data. DFT calculations on smooth, stepped, monometallic and bimetallic surfaces showed that N + N recombination rather than NO dissociation was always rate-determining and that the activation barrier to recombination reaction decreased with increased Au content, thus accounting for the experimental observations. Across the entire composition range, the oxidation state of Ni did not correlate with activity, in disagreement with earlier work, and theory showed that NiO itself should be catalytically inert. Au–Ni interactions were of paramount importance in promoting N + N recombination, the rate-limiting step.

Single Ir Atoms Anchored on Ordered Mesoporous WO3 Are Highly Efficient for the Selective Catalytic Reduction of NO with CO under Oxygen‐rich Conditions

“…Thus, the control of NO emissions has become a research hotspot in recent years. Among various denitrification technologies, CO selective catalytic reduction (CO‐SCR) has attracted great attention from researchers and stands out as a promising technology [6–12] . Because NO and CO coexist in many industrial exhaust gases, CO‐SCR can simultaneously eliminate these two harmful gases.…”

Tracking the redox reaction-induced reconstruction of NiAu nanoparticles via environmental scanning transmission electron microscopy

“…3,4 In particular, bimetallic nanoparticle (NP) catalysts containing Au (e.g., Ni-Au) show various intriguing catalytic properties, such as excellent CO 2 hydrogenation activity, superior activity and robust durability for hydrogen evolution reaction, great sensitivity on non-enzymatic glucose sensing and high efficiency in automotive exhaust gas purification. [5][6][7][8] Continuous optimization of the bimetallic catalysts is achieved through controlling its morphology and structure, regulating the content of two distinct metals, reducing the coordination number of surface atoms and utilizing suitable supports to enable unique synergies. [9][10][11][12] It is known that the surface structure and state have a large impact on the performance of a catalyst during the reaction; however, less attention has been paid to the influence of a post-synthesis treatment at a specific atmosphere.…”

Synthesis of small Ni-core–Au-shell catalytic nanoparticles on TiO2by galvanic replacement reaction

“…However, these thermal treatments can be detrimental to both the original size distribution and structures of the NPs. 23,35 Galvanic replacement reaction (GRR), also called galvanic displacement or direct redox reaction, is an elegant way to prepare supported bimetallic NPs. 36,37 Galvanic replacement of metal 1 (M1) by metal 2 (M2) leads to the deposition of metal 2 onto metal 1, provided that the redox potential of M2 ions (Ox2) is higher than that of M1 ions (Ox1), so that the following reaction can take place:…”