Isolated Copper Ions Research Articles

Effects of the preparation method of Cu⁃SAPO⁃34 catalysts in de-NOx SCR by propylene

Cu-SAPO-34 catalysts prepared by incipient wet impregnation (IWI), liquid ion-exchange (LIE) and one-pot (OP) hydrothermal methods were applied in selective catalytic reduction of NO with propylene (C3H6-SCR). Under diesel engine exhaust conditions containing 10% O2 and 5% H2O, Cu-SAPO-34(OP) obtained ~95% NOx conversion and ~95% N2 yield at 250–300 °C. Compared the IWI and LIE samples, the Cu-SAPO-34(OP) sample had abundant Lewis acidic sites, the largest specific surface area, and the most isolated Cu2+ species, thus it exhibited the best de-NOx performance. In contrast, more inactive CuO species formed on the surface of the LIE and IWI samples. The isolated Cu2+ ions in the 8MR rings have high reducibility, and are supposed to be the main active sites of Cu-SAPO-34 catalysts in the C3H6-SCR reaction. In situ DRIFTS suggests that isolated copper ions are favourable for the adsorption and activation of NOx and C3H6, thus enhancing the formation of isocyanate (-NCO) and -CN species, which act as key intermediates and further produce N2. This study can be helpful to provide some references for the design of HC-SCR catalyst and application of diesel NOx abatement.

Isolated copper ions and surface hydroxyl groups as a function of non-redox metals to modulate the reactivity and persulfate activation mechanism of spinel oxides

In advance oxidation processes (AOPs), modulating the activation mechanism from free radical to the non-radical pathway is the most attractive strategy for the treatment of recalcitrant pollutants. Herein, we achieved this goal after modifying the spinel CuFe2O4 catalyst by introducing non-redox metals (M = Mg, Ca, Ba, and Zn) as CuMFe2O4. The modified catalysts were evaluated for the removal of acetaminophen (ACE) using the persulfate (PS) activated system. The results revealed that the non-redox metals not only enhanced the catalytic activity of CuFe2O4 in the order of Mg > Zn > Ca > Ba but also switched the original radical pathway of CuFe2O4/PS system to the non-radical one (i.e., direct electron transfer path) of CuMgFe2O4/PS system. The critical role of non-redox metals to modulate the reaction mechanism was studied in detail using the extensive radical scavengers, EPR analysis, target pollutants selectivity, electrochemical studies, decomposition of oxidants, and identification of degradation products. Additionally, various experiments and characterizations, including XRD, EPR, H2-TPR, XPS, and FTIR, showed that the changes in the activation mechanism and catalytic activity (6–8 folds higher in the case of CuMgFe2O4) were related to the generation of a large amount of surface-bound isolated Cu2+ ions and abundant surface hydroxyl groups. The non-radical pathway of the CuMgFe2O4/PS system showed less susceptibility to the changing solution pH, excessive amount of humic acid (HA) or anions, and complete recyclability, and thus demonstrating good practical utility for wastewater. This study provides deep insight into the intrinsic role of non-redox metals to modulate both the activation mechanism and catalytic properties of the catalyst and to design new catalysts for the persulfate-based advance oxidation process.

Controlled synthesis of Cu-based SAPO-18/34 intergrowth zeolites for selective catalytic reduction of NOx by ammonia

Cu-based SAPO-18, SAPO-18/34 intergrowth and SAPO-34 zeolites were applied for the selective catalytic reduction of NOx by ammonia (NH3-SCR) catalysts. Comprehensive characterization results revealed that the SAPO-18/34 with higher amount and strength of acid sites could facilitate the generation of more isolated copper ions (Cu2+ and Cu+) and suppress the formation of CuOx, which might account for the fact that intergrowth crystal structure of Cu-SAPO-18/34 exhibited higher fresh NH3-SCR activity, more robust hydrothermal durability and better SO2-resistance ability than that Cu-SAPO-18 and Cu-SAPO-34. In situ DRIFTS results provided the formation of reaction intermediates, such as -NH2, NH4+, NO3-, NO2-, etc. Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) reaction mechanisms were both involved in Cu-based SAPO-18 and SAPO-18/34 intergrowth zeolites, but the L-H mechanism dominated the NH3-SCR reaction, in addition, Cu-SAPO-34 only followed “L-H” mechanism.

Fabrication of copper supported on hollow silica–alumina composite spheres for catalytic decomposition of nitrous oxide

In this work, we fabricated copper supported on hollow silica–alumina composite spheres for catalytic decomposition of nitrous oxide. The copper supported on the hollow spheres was obtained by impregnation of the active copper species on the hollow silica–alumina composite sphere support prepared by the template method using spherical polystyrene particles. The supported copper catalysts on the hollow spheres showed higher conversion of nitrous oxide than supported copper catalyst on fine silica–alumina composite particles. The catalyst activity was significantly improved by adjusting impregnation temperature, and the supported copper catalyst impregnated at 353 K exhibits around 75% of nitrous oxide conversion at 573 K. The results of the DR UV–Vis spectra, the EDX analysis, and nitrogen adsorption measurement indicate that the highly active catalyst consisted of high ratio of isolated copper ions inside the shell of the hollow spheres.

In situ regeneration of sulfated Cu/SAPO-34 catalyst for the selective catalytic reduction of NOx with NH3

The regeneration mechanism of sulfated Cu/SAPO-34 catalysts in reducing atmospheres (5% H2/Ar and NH3/Ar at 600 °C) was investigated by using a series of characterization methods. Hydrogen regeneration improved the catalysts’ NH3-SCR activity from 150 to 550 °C remarkably, while ammonia regeneration exhibited relatively less obvious promotion effect. The TPR of hydrogen and EPR spectra data show that the regeneration process affects the amount and the coordination of the active isolated Cu2+ species significantly. The desulfation increases the amount of isolated copper ions and improves the catalytic activity of SCR.

Quantitative control and identification of copper species in Cu–SAPO-34: a combined UV–vis spectroscopic and H2-TPR analysis

A series of Cu–SAPO-34 catalysts with different copper contents were prepared using a modified ion-exchange method, i.e., impregnation–activation. Controlled amounts of well-dispersed active copper species and integrated physical properties were obtained by this method. The Cu–SAPO-34 catalysts retained the CHA structure, high specific surface area, and pore volume of the H–SAPO-34. Based on a combined analysis of UV–vis spectra and H2-TPR, these common laboratory techniques enabled the identification of the different copper species present in the catalysts. Only isolated copper ions balanced by two framework charges were present in the catalysts at copper contents ≤ 0.8 wt%. With increasing the Cu content, isolated Cu2+ ions charge-balanced by one negative charge became dominant. Further higher Cu contents could result in formation of copper oxides after consumption of all ion-exchange sites.

Effect of Cu and Zn ion-exchange locations on mordenite performance in dimethyl ether carbonylation

Cu2+ and Zn2+ ion-exchange locations in mordenite (MOR) were evaluated using infrared spectroscopy, pore-size distribution, and temperature-programmed reduction. Isolated copper ions were the most abundant ion-exchanged species, as detected by UV-vis spectroscopy, in addition to oxide nanoparticles, with no presence of binuclear species, which was assigned to a low copper loading of 0.3 Cu/Al. The characterization revealed that only zinc could exchange in 8-membered rings. Hartree-Fock modeling confirmed copper exchange into 12-membered rings involving at least one T1 atom, and zinc exchange in T4 sites and in 8-membered structures, including T3 sites. Copper ion exchange did not offer improvement in the dimethyl ether carbonylation rate or selectivity over acidic mordenite. Zinc ion exchange led to the selectivity and stability improvement with some loss of activity. This work contributes to the understanding of acid and metal site contribution to DME carbonylation and contributes to the understanding for Cu2+ and Zn2+ ion-exchange locations in MOR with a low metal/Al loading (<0.2).

Facile Synthesis of KFI-type Zeolite and Its Application to Selective Catalytic Reduction of NOx with NH3

The small-pore KFI-type zeolite was synthesized via the hydrothermal conversion of zeolite Y with Na+ and K+ ions without using an organic structure-directing agent (OSDA). The effects of alkali-metal ions and hydroxide ion on the crystallization of KFI were individually investigated by introducing both hydroxide and nitrate salts into synthesis media. The zeolite KFI synthesized under the optimized conditions was copper ion exchanged and then applied for selective catalytic reduction of NOx with an NH3 (NH3-SCR) reaction. Cu-KFI was found to exclusively contain isolated copper ions up to very high loading (Cu/Al2 = 75%) on the basis of the Cu K-edge extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES), ultraviolet visible near-infrared spectroscopy (UV–vis–NIR), and temperature-programmed reduction by H2 (H2-TPR) analyses. Interestingly, Cu-SSZ-13 and Cu-KFI have almost identical activation energies for the NH3-SCR reaction as well as the reduction temperature of...

Novel promotional effect of yttrium on Cu–SAPO-34 monolith catalyst for selective catalytic reduction of NOx by NH3 (NH3-SCR)

Cu–SAPO-34 and CuY–SAPO-34 catalysts for NH3-SCR were prepared by the wet-impregnation method. XRD, UV–vis DRS, ESR and NH3-TPD results showed that the introduction of Y effectively improved the dispersion of copper species, increased the amount of isolated copper ions and enhanced the acid density. In addition, the activity test, NH3-TPD and TGA results reflected that the CuY–SAPO-34 catalyst showed better C3H6 oxidation activity, lower dropping degree of acid sites after C3H6/O2 treatment and less adsorption of C3H6/O2 than Cu–SAPO-34 catalyst. Therefore, the addition of Y promoted the NH3-SCR performance and the hydrocarbon (HC) resistance of Cu–SAPO-34 catalyst.

Novel coloring of geopolymer products using a copper solution immersion method

Geopolymer products were fabricated from a slurry composed of metakaoline, potassium silicate solution, and potassium hydroxide with a mass ratio of 57.1:34.3:8.6, which was cured at 60°C and 100% relative humidity for 1week. The hardened geopolymer products were immersed in a 0.1mol/L copper chloride solution at 25°C for 1–168h. The copper chloride solution to geopolymer product mass ratio was maintained at 2.5. According to visual observations, the spread of color from the surface to the interior of the geopolymer product seemed to stop once the immersion time reached 24h. After immersion for 168h, atacamite (Cu2Cl(OH)3) crystals were partially formed on the geopolymer product surface and at depths of 150–300μm. These precipitated atacamite crystals contributed to a green coloration of the sample. However, the observed green coloration, which reached a depth of approximately 900μm in the geopolymer product after an immersion time of 168h, was mostly caused by the presence of isolated copper ions due to the substitution of potassium ions in the geopolymer product by copper ions from the solution. Thus, two coloring mechanisms were active in this system.

Cu-substituted ZSM-5 catalyst: Controlling of DeNOx reactivity via ion-exchange mode with copper–ammonia solution

The regularities of sorption and stabilization of Cu2+ ions in Cu–ZSM-5 catalysts prepared via the ion-exchange have been studied. The copper sorption by H–, Na–, and NH4–ZSM-5 from aqueous and ammonia solutions of copper salt had a good approximation as the Langmuir mould of a monolayer adsorption. At ideal ion-exchange condition, only the isolated copper ions located in the zeolite ion-exchange position are formed. Observation of other Cu structures with extra-lattice oxygen is a result of the hydrolysis of hexaaquacopper(II) complex and its polycondensation reactions. They exist as (1) dimer and copper-oxide structures with chain-like and square-planar coordination of extra-lattice oxygen ligands, which are located inside zeolite channels, and (2) oxide clusters and CuO nanoparticles dispersed on the zeolite crystallite surface.The RedOx properties and DeNOx reactivity in selective catalytic reduction of nitrogen oxide by propane of copper-substituted ZSM-5 have been compared. The dynamics of DeNOx reactivity correlates with the growth in the number of the isolated Cu2+ ions and the Cu structures with extra-lattice oxygen, which are formed during the ion exchange of H–ZSM-5 with water–ammonia solutions of copper acetate with NH4OH/Cu2+ close to 6 (pH∼10.5). On the other hand, reactivity decreases with an increase in the content of copper-oxide clusters on the external surface of zeolite, which are observed in the ion-exchanged Cu–ZSM-5 at NH4OH/Cu2+ below 6. Besides, the Cu2+ ions stabilized during the ion-exchange mode with strong-alkaline ammonia–copper solution (NH4OH/Cu2+=30) are less reducible in H2-TPR experiment compared with catalysts produced from ammonia-free and weak-ammonia solution of copper acetate, probably due to the low copper loading, stabilization of isolated Cu2+Oh ions with large distance between each other, decoration of copper ions by a thin silica/alumina layer or formation of Cu-silicates.

Temperature-dependent polymorphism and magnetic properties of three-dimensional copper pyromellitate coordination polymers containing 4,4′-dipyridylamine

A pair of three-dimensional divalent copper pyromellitate (1,2,4,5-benzene-tetracarboxylate, pyro) coordination polymers containing 4,4′-dipyridylamine (dpa) was hydrothermally prepared and structurally characterized by single-crystal X-ray diffraction. The higher-temperature phase {[H2dpa][Cu3(pyro)2(H2O)3]·2.5H2O}n (1) displays an acentric 3-D 4,4,6-connected anionic network with (445.6)(5482)(44546374) topology, featuring {Cu2(OCO)4} paddlewheel dimers and isolated copper ions. Charge-balancing H2dpa cations are embedded in incipient voids. Prepared at lower temperature, {[Cu3(pyro)2(dpa)2(dpaH)2]·3H2O}n (2) manifests a 3-D 4,4,4-connected neutral network with uncommon (4264)4(6482) frl topology based on {Cu3(OCO)2} linear trimers. Antiferromagnetic coupling (J=–82(5)cm–1) was observed within the {Cu2(OCO)4} dimeric units in 1, while weak ferromagnetic coupling (J=1.0(4)cm–1) was evident for the {Cu3(OCO)2} linear trimers in 2. Thermal degradation behavior of these new materials is also presented.

A Study of Electron Paramagnetic Resonance on Copper Ions on Alkali-Alkali Earth Zinc Phosphate Glass

42%P2O5- 40%ZnO- 2%CaO- (16-x) %Na2O-xCu2O glass system (x=o, 2, 4, 6, 8, 10%mol) were prepared by conventional melt-quenching technique. It was investigated by means of electron paramagnetic resonance (EPR) to study the structural changes induced by different amount of copper ions. The spin Hamiltonian parameters like g∥, g⊥ and A∥ show that Cu+2ionare in tetrahedral coordination with dxy as the ground state. Modification of EPR band width by increasing copper content suggests that band consists of two overlapping bands; one of them is related to asymmetric band due to isolated copper ions and the other is symmetric due to cluster ions Cu+2-Cu+2. Calculation of the optical basicity indicates to that polarizability decrease by increasing copper content due to increase electron cloud density at the Cu2+ site.

Cogeled copper–silica aerogel as a catalyst in hydrogen production from methanol steam reforming

In this work, the copper–silica aerogel catalyst was prepared by cogelation of copper and silica precursors in a sol–gel process followed by chemical surface modification and ambient pressure drying. The results of characterizations by XRD, BET, FE-SEM, TEM, FTIR and TPR showed the prepared catalysts had high surface area and pore size distribution in the range of 1–10 nm. Also, uniform nanostructural morphology with particle size of 5–20 nm was observed. The copper loading and calcination temperature influenced the morphology and texture of the catalyst and the nature of copper species. So, copper existed within the silica matrix as highly dispersed isolated copper ions or CuO crystallite clusters which have good interaction with the matrix. Catalytic performance for hydrogen production from methanol reforming was evaluated at 300 °C in the methanol feed rate of 12–65 mmol g−1 h−1. The catalyst activity was increased by increasing the copper loading and calcination temperature. In comparison with CuO/ZnO/Al2O3 commercial catalyst which showed 6–11% CO selectivity, no CO formation was detected using the prepared Cu/SiO2 aerogel catalysts.

Dipyridylamide Donor Disposition and Isophthalate Substituent Steric Effect on the Dimensionality and Topology of Divalent Copper Coordination Polymers

AbstractDivalent copper coordination polymers containing an isophthalate ligand and a dipyridylamide ligand show different dimensionalities and topologies depending on pyridyl nitrogen donor disposition and the steric bulk of the substituent on the dicarboxylate aromatic ring. According to single‐crystal X‐ray diffraction, [Cu(ip)(3‐pna)]n (1, ip = isophthalate, 3‐pna = 3‐pyridylnicotinamide) shows a (4, 4) layered grid structure based on {Cu2(OCO)2} dimeric units. {[Cu(ip)(3‐pina)]·H2O}n (2, 3‐pina = 3‐pyridylisonicotinamide) exhibits similar dimeric units, but in contrast to 1 these are connected into a non‐interpenetrated 3D 658 cds network. Both [Cu(mip)(3‐pina)]n (3, mip = 5‐methylisophthalate) and [Cu(meoip)(3‐pina)]n (4, mip = 5‐methoxyisophthalate) display dimer‐based 41263 pcu networks in contrast to 2. Use of 5‐hydroxyisophthalate (H2hip) as a precursor afforded a mixture of {[Cu2(hip)2(3‐pina)4]·9.5H2O}n (5) and [Cu(hip)(3‐pina)]n (6). Compound 5 shows a 2D interdigitated structure with [Cu(hip)]n coordination polymer layers featuring {Cu2(OCO)2} dimeric units and pendant 3‐pina ligands, while 6 also showed a dimer‐based 41263 pcu network. Use of the very sterically bulky 5‐tert‐butylisophthalate (tbip) ligand afforded the 1D chain coordination polymer {[Cu(tbip)(3‐pina)2(H2O)]·H2O}n (7), which contains isolated copper ions in contrast to 1–6, and has a curious “butterfly“ resemblance. Very weak antiferromagnetic coupling is seen within the {Cu2(OCO)2} dimeric units in 1. Thermal decomposition behavior is also discussed.

Effect of the Nature and Location of Copper Species on the Catalytic Nitric Oxide Selective Catalytic Reduction Performance of the Copper/SSZ‐13 Zeolite

AbstractThe nature and location of copper in Cu/SSZ‐13 zeolites synthesized by using a one‐pot hydrothermal approach with Cu–tetraethylenepentamine as a template and by the ion exchange of SSZ‐13 were investigated by applying H2‐temperature‐programmed reduction, FTIR, EPR, and in situ Raman spectroscopic techniques. The one‐pot synthesized Cu/SSZ‐13 zeolite contains predominantly isolated copper ions in the large cages, whereas copper species in the ion‐exchanged Cu/SSZ‐13 zeolite occupy sites in the large cages of the chabazite (CHA) structure and the six‐membered rings of the CHA structure. If the one‐pot synthesized Cu/SSZ‐13 zeolite is exchanged with the NH4NO3 solution in addition to the removal of a part of copper ions, the remaining copper ions in the CHA structure relocated from the large cages to the six‐membered rings. Isolated copper dominated in all Cu/SSZ‐13 zeolites. The in situ Raman spectra demonstrated that CuOCu dimers form at higher copper content. The bis‐μ‐oxo dicopper(III) complex is observed only in the ion‐exchanged sample upon dehydration. The higher NO selective catalytic reduction activity of the one‐pot synthesized sample in a wide temperature range appears to be due to the predominance of isolated Cu2+ sites in the large cages, and their higher reactivity is possibly owing to the lower stability of Cu2+ at these sites.

Different Metal Aggregation in Copper Acetate Chain Coordination Polymers with Dipyridyl Tethers Bearing Hydrogen Bonding Capable Functional Groups

AbstractHydrothermal synthesis has afforded a pair of divalent copper acetate coordination polymers containing either 4, 4′‐dipyridylamine (dpa) or 4‐pyridylisonicotinamide (4‐pina), both of which hydrogen‐bonding capable central functional groups. X‐ray crystallography revealed that both exhibit a 1D chain dimensionality. Use of the kinked tethering ligand dpa produced [Cu(OAc)2(dpa)]n (1), which possesses a simple chain based on dpa linkage of isolated copper ions. On the other hand, employing the straighter amide ligand 4‐pina generated {[Cu(OAc)2(4‐pina)]·0.5H2O}n (2), which exhibits {Cu2O2} rhomboid dimers formed through bridging acetate ligands. Weak antiferromagnetic coupling [g = 1.984(3), J = –3.2(3) cm–1] was observed within the axial‐equatorial bridged {Cu2O2} dimers in 2, with possible ferrimagnetism due to spin canting below 11 K.

Divalent copper trans-1,4-cyclohexanedicarboxylate coordination polymers with isomeric dipyridylamide ligands: new pillared and self-penetrated binodal networks

Hydrothermal synthesis has afforded a pair of divalent copper coordination polymers containing trans-1,4-cyclohexanedicarboxylate (t-14cdc) and one of two isomeric dipyridylamides, 3-pyridylnicotinamide (3-pna) or 3-pyridylisonicotinamide (3-pina). Both of these materials feature unprecedented 3-D topologies. [Cu(t-14cdc)(3-pna)]n (1) manifests [Cu(t-14cdc)]n 4·82 layers featuring embedded anti–syn axial–equatorial bridged [Cu(OCO)]n chain motifs, pillared by anti-conformation 3-pna ligands into a new yet very simple binodal 3,5-connected (4·6·8)(4·66·83) network topology. {[Cu2(t-14cdc)2(3-pina)2(H2O)]·5H2O}n (2) shows two different copper/t14cdc chain motifs with isolated copper ions and {Cu2O2} dimeric units, respectively. These are linked together by 3-pina ligands to afford a new self-penetrated 4,6-connected binodal net with (4·64·8)2(42·612·8) topology. Variable temperature magnetic susceptibility experiments reveal very weak ferromagnetism (g = 2.01(1), J = 0.04(1) cm−1) along the [Cu(OCO)]n chains in 1 and weak antiferromagnetism (g = 1.906(3), J = −3.4(3) cm−1) within the {Cu2O2} dimeric units in 2. Thermal properties are also presented.

Regulation of the copper-oxide cluster structure and DeNOx activity of Cu-ZSM-5 catalysts by variation of OH/Cu2+

The present work studies RedOx properties and reactivity in N2O decomposition and selective catalytic reduction of NO (NO-SCR) by propane of Cu-modified ZSM-5 catalysts prepared by hydrolytic polycondensation (HPC). Their characteristics are compared with properties of Cu-ZSM-5 samples having the same copper content (1wt.%) and produced by ion exchange (IEX) with water–ammonia solutions of copper chloride at NH4OH/Cu2+ equal to 6–30.The HPC method consists in the treatment of the copper-impregnated zeolite by water–ammonia solution for polycondensation of hydrolyzed copper ions in the zeolite pores. It is shown that varying the NH4OH/Cu2+ ratio allows a regulation of the size and structure of copper active complexes. The copper-impregnated zeolite contains copper as CuO-like particles after calcination. At NH4OH/Cu2+ equal to 1–3, active sites in dried samples are disordered polynuclear copper-hydroxo complexes, which are characterized by symmetric ESR signal with g0=2.18. Increase of NH4OH/Cu2+ to 6–30 lead to the orbital ordering of Cu2+ ions in the copper–ammoniate complexes, observed as the rhombic ESR signals (gzex,1=2.18, gyex,1=2.08, gxex,1=2.03 and g∥ex,2=2.24, g⊥ex,2=2.03), and to dispersion of CuO-like particles during following thermal treatment at 500°C. The dried 1%Cu(30)ZSM-5-HPC sample prepared at NH4OH/Cu2+=30 has a higher amount of isolated tetraammine–copper complex and a lower number of weak associates of Cu2+ ions among samples.The addition of ammonia solution to the copper-impregnated zeolite for hydrolytic polycondensation has a favorable impact on the Cu-ZSM-5 activity in DeNOx processes. In N2O decomposition, the ion-exchanged CuZSM-5 catalysts were more reactive in the low-temperature region, while the ex-polycondensation catalysts provided a high N2O conversion at high temperatures. In NO-SCR by propane, the more reactive were the ion-exchanged catalysts, and NO reduction rate increased with NH4OH/Cu2+ grew for 10. It is suggested that the ordered associated Cu2+ ions of ex-polycondensation and ion-exchanged catalysts have higher reactivity and selectivity in both DeNOx processes as compared to the isolated copper ions.

The synergetic mechanism between copper species and ceria in NO abatement over Cu/CeO 2 catalysts

Copper supported on ceria prepared by the impregnation method was used as a model catalyst to investigate the synergetic mechanism between copper species and ceria for NO reduction by CO. To identify the copper species in the catalyst, we treated the as-synthesized Cu/CeO 2 by 30 wt.% nitric acid solution. Fresh and nitric acid treated Cu/CeO 2 catalysts were characterized and compared with AAS, XRD, TPR, EPR, Raman and NO-TPD techniques. It is found that, after nitric acid treatment, there is only 0.27 wt.% Cu left (vs. 5 wt.% Cu in fresh sample); this is present in the following forms: (1) isolated copper ions in octahedral sites of ceria, (2) copper oxide clusters and (3) copper ions in ceria lattice. The residual small amount of Cu has a significant effect on surface structure, redox property and catalytic behavior of ceria, indicating that these copper species are crucial copper species inducing copper–ceria interactions. Moreover, it is suggested that the relative free movement of oxygen from ceria to supported copper, caused by the three copper species, leads to oxygen vacancies in ceria, significantly enhancing the NO conversion of Cu/CeO 2 during NO + CO reaction.