Enhanced Catalytic NO Reduction in NO–CO–C₃H₆–O₂ Reaction Using Pseudo-Spinel (NiCu)Al₂O₄ Supported on γ-Al₂O₃

Abstract

This study aims to clarify the effect of Ni addition on the enhancement of the NO reduction activity of Cu/Al2O3, which possesses high thermal durability, and to elucidate the associated structure–catalysis relationship. Thermal aging of Ni and Cu supported on γ-Al2O3 at a high temperature (900 °C) induced the formation of a pseudo-spinel (NiCu)­Al2O4 solid solution on the γ-Al2O3 surface, which was observed using X-ray diffraction and high-angle annular dark-field scanning transmission electron microscopy techniques. Owing to the co-presence of Ni, the preferential occupation of octahedral sites by Ni increased the number of tetrahedrally coordinated Cu2+ ions, which played a key role in the reduction of NO in a stoichiometric NO–CO–C3H6–O2 reaction. XPS analysis revealed that Cu active sites with electron-rich states were formed in pseudo-spinel (NiCu)­Al2O4 owing to electron donation from Ni to Cu, which promoted NO adsorption on Cu+ and accelerated NO reduction. The tetrahedrally coordinated Cu formed on the pseudo-spinel oxide was structurally robust, and its local structure remained unchanged even after the redox cycle occurred at a high temperature; this indicated that the formation of pseudo-spinel (NiCu)­Al2O4 was effective for the enhancement of NO reduction activity and thermal durability.

Activity–Composition Relationships of Fe–Ni–Cu Ternary Nanoparticles Supported on Al2O3 as Three-Way Catalysts for NO Reduction

“…This is a recognized trend for a wide range of non-PGM catalysts. 7,10,20,26,37,38 A typical data for Fe 0.33 Ni 0.33 Cu 0.33 is shown in Figure 1, where the NO conversion reaches almost 100% at 600 °C and changes little during 1 h. When the reaction at 600 °C was extended to 8 h, the NO conversion was stabilized at approximately 95% and showed no sign of catalyst deactivation. The catalyst exhibited the activity for CO/C 3 H 6 oxidation superior to those of reference PGM catalysts (Pt/Al 2 O 3 and Rh/Al 2 O 3 ) but was less active for NO reduction (Supporting Information, Figure S2).…”

Selective Formation of Cu Active Sites with Different Coordination States on Pseudospinel CuAl2O4 and Their NO Reduction Catalysis

“…While oxidation demands a stoichiometric or excess amount of O 2 , its presence severely inhibits the NO x reduction process. Additionally, developing catalysts for practical use in automotive emission control systems faces the challenge of thermal durability. ,− Exposure to gasoline engine exhaust at temperatures exceeding 800 °C for prolonged periods leads to severe thermal aging, causing significant sintering of supported metal nanoparticles or changes in the crystal structure, thus degrading the catalyst. To tackle these issues, investigations into solid solution catalyst effectiveness rather than supported metal structures have been explored. − ,,− …”

Role of Ba in an Al2O3‐Supported Pd‐based Catalyst under Practical Three‐Way Catalysis Conditions

“…[1][2][3][4][5] Air pollutants, such as NO x , CO, and hydrocarbons (HCs), are reduced using three-way catalysts that typically use platinum group metals (PGMs), such as Rh, Pd, and Pt, [6][7][8][9][10][11][12][13][14] which are beneficial for catalytic performance and durability compared to other non-precious metals. Although catalysts that contain nonnoble metal components, such as Cu, Ni, and Fe, have recently been intensively studied, [15][16][17][18][19][20][21] real-world operating systems still need large amounts of PGMs to meet strict regulations that require reductions of more than 99 % in tailpipe emissions relative to engine-generated emissions. [22] Therefore, designing effective catalytic supports is very important for maximizing PGM activity.…”