Dispersed CuO Species Research Articles

Catalytic Combustion of Acrylonitrile over CuCeOx-HBETA Catalysts

Purpose: Evaluate the acrylonitrile combustion using copper and cerium catalysts supported on BETA zeolite (CuCeOx-HBETA), aiming to reduce the emission of this pollutant in industrial exhaust gases. Theoretical framework: Acrylonitrile (ACN) is one of the most used monomers in the chemical industry. However, it is a volatile organic compound (VOC) of high toxicity, being present in the exhaust gases of its own production process. In this context, selective catalytic combustion (SCC) stands as a highly promising technology for the removal of ACN in industrial gas effluents. Method: CuCeOx-HBETA catalysts were prepared by wet impregnation. For characterize the catalysts, the techniques of X-ray diffractometry (XRD), Fourier transform infrared spectroscopy (FTIR) and reduction with hydrogen at programmed temperature (TPR-H2) were used. Catalytic tests were carried out on ACN combustion by varying the reaction temperature. Results and conclusion: The characterization results showed that copper and/or cerium oxides are present in the catalysts as nanoparticles. The addition of CeO2 improved the dispersion and facilitated the reducibility of CuO. The CuCeOx-HBETA catalysts achieved high ACN conversions at temperatures (300-350°C) much lower than traditional thermal combustion (T > 900°C). The greater activity of the catalysts can be attributed to the presence of highly dispersed CuO species and isolated Cu2+ ions. The 10Cu10Ce-HBETA catalyst, with a copper/cerium ratio equal to 1, was the most active due to the best synergy between copper and cerium species. Research implications: The research indicates great potential for the use of CuCeOx-HBETA catalysts in the combustion of ACN. Originality/value: This study brings new contributions to the research of catalysts to be applied in the catalytic combustion of nitrile compounds.

Ti species regulated CuO/CeO2 catalyst for efficient simultaneously NH3-SCR denitration and CO oxidation under oxygen-rich conditions

Synergistic control of multiple pollutants has high benefits during the control of emissions from fuel utilization, and catalysis can contribute to efficient removal of multiple pollutants. In this work, Ti species regulated CuO/CeO2 (Cu/Ce) catalyst was constructed to efficient simultaneous NH3-SCR denitration and CO oxidation under oxygen-rich conditions. It is found that the introduction of Ti species into Cu/Ce catalyst induces the formation of three-dimensional pore structure and promotes the phase transition from crystalline to amorphous, which significantly enhances the specific surface area and the dispersion of CuO and CeO2. The well dispersed CuO and CeO2 species provide a larger number of adsorbed sites for CO and NO and enhance the Cu-Ce interaction, which can contribute to reducing the competitive adsorption between CO and NO and the formation of a richer surface oxygen vacancies. Owing to above improvements, the Ti species regulated Cu/Ce catalyst can achieve more than 90% removal efficiency of NOx and CO at 148–218 °C, and the active temperature windows widened by 36 °C in comparison with Cu/Ce catalyst. Through this work, we expect to shed some light on the synergistic control of CO and NOx under oxygen-rich conditions.

Enhanced selective catalytic oxidation of triethylamine by VOx-modified CuO@TiO2 catalyst through increased amount of Lewis acid sites and adsorbed oxygen species on catalyst surface

The selective catalytic oxidation (SCO) of nitrogenous volatile organic compounds (NVOCs) has recently garnered significant attention. However, the SCO processes for tertiary amines (such as triethylamine) have not been reported. The impact of vanadium doping in CuO@TiO2 and Cu loading on SCO of TEA to N2 was investigated in this study. The surface acidity of the catalyst is primarily influenced by the VOx doping, as indicated by the results of NH3-TPD and pyridine-IR. Additionally, XPS and H2-TPR results reveal that the highly dispersed CuO species is the key oxidative component in the catalyst. SEM and TEM results show that VOx is beneficial to enhance the dispersion of CuO in the catalyst. The adsorbed oxygen content of CuO@TiO2 catalyst is increased by VOx-modification, as indicated by EPR result. An appropriate amount of adsorbed oxygen in the catalyst can improve the oxidation activity of the catalyst and assure high selectivity of N2. Finally, through the in-situ DRIFTs the reaction intermediate NHx is captured, and a reliable SCO reaction pathway of TEA is proposed. This study provides a solution for the disposal of tertiary amines from NVOCs.

Effect of Ce-BTC precursor morphology on CuO/CeO2 catalysts for CO preferential oxidation in H2-rich gas

In this paper, the precursors of the coordination polymer Ce(1,3,5-BTC)(H2O)6 with different morphologies have been successfully prepared via a facile and rapid method, and then the CuO/CeO2 catalysts were obtained by impregnation method to support copper species. The catalysts were characterized by scanning electron microscopy, scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, ultraviolet Raman spectrscopy, N2 adsorption-desorption, H2 programmed temperature reduction and X-ray photoelectron spectroscopy, respectively. The results showed that U–CuCeO catalyst has stronger CuO dispersion and higher oxygen vacancy concentration on the surface. The high specific surface area of U–CuCeO catalyst facilitates the highly dispersed CuO species and enhances the interaction between copper and cerium, and improves the catalytic performance compared with the other catalysts. For U–CuCeO catalyst, the CO conversion reached 100% at 120 °C. It also exihibited the broadest complete reaction temperature window.

Role of oxygen species and active phase of CuCeZrOx prepared with bacterial cellulose for toluene catalytic oxidation

The present study investigates the active phases and the role of oxygen species in the toluene oxidation process over CuCeZrOx catalysts prepared with bacterial cellulose (BC), and compares them with nitric acid pickling CuCeZrOx-BC(H) and CeZrOx-BC catalysts. The investigation is carried out using in-situ DRIFT, O2-TPD, H2-TPR, XRD, and TEM techniques. Our findings suggest that dispersed CuO species on the catalyst surface, Cu-Ce-Zr-O, and Ce-Zr-O solid solutions are active for toluene oxidation over CuCeZrOx-BC, with corresponding activities decreasing successively. The in-situ DRIFT results demonstrate that gaseous oxygen facilitates the chemisorption of toluene on active oxygen species, forming benzoyl oxide species and partially oxidizing the absorbed intermediates to benzyl alcohol at room temperature. Furthermore, lattice oxygen is experimentally found to be involved in the deep oxidation of toluene, and the lattice oxygen present in dispersed CuO species dominates the toluene oxidation process over CuCeZrOx-BC.

Effect of surface basicity over the supported Cu-ZnO catalysts on hydrogenation of CO2 to methanol

CO2 hydrogenation to methanol can relieve energy shortage and weaken CO2 emission, and Cu-ZnO catalysts show excellent activity, in which the surface basicity improves conversion and selectivity, but the influence mechanism is often ignored. In this work, Cu-ZnO/Al2O3, Cu-ZnO/Al2O3-MgO and Cu-ZnO/MgO were prepared to study the effect of surface basicity on CO2 hydrogenation to methanol. It was found that MgO increased the dispersed CuO species and strengthened surface basicity, leading to higher SCu and electron density on Cu surface, respectively, which promoted CO2 conversion. Meanwhile, the surface basicity strengthened CO adsorption and weakened methanol adsorption, which greatly increased methanol selectivity. In addition, methanol adsorption on catalyst surface seriously inhibited CO2 adsorption, while the strong surface basicity greatly weakened the inhibition. Besides, the strong surface basicity inhibited the dissociation of methanol into CO species. Finally, the Cu-ZnO catalyst with strong surface basicity showed high activity and selectivity.

The effect of copper oxide on the CuO–NiO/CeO2 structure and its influence on the CO-PROX reaction

The effect of copper oxide species on the CuO–NiO/CeO 2 structure and the influence on the preferential CO oxidation in H 2 excess (CO-PROX) reaction at low and high temperatures were investigated. Temperature-programmed surface reaction (TPSR), In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and X-ray photoelectron spectroscopy (XPS) results allowed determining the surface species. The maximum temperature of CO 2 formation or selectivity decreased about 40 °C for the CuO–NiO/CeO 2 catalyst compared to the NiO/CeO 2 , which suggests that the addition of Cu + species increases the active sites due to interaction with the Ni–Ce structure. Therefore, the activity of the catalyst was closely related to the oxygen in vacancies and the formation of Cu + -carbonyl species of the redox mechanism. Besides, the superior selectivity towards CO 2 below 150 °C depends on the carbonyl stabilization at the surface, inhibiting the adsorption and subsequent oxidation of H 2 . Using TPSR and spectroscopic analyzes by DRIFTS and XPS allowed us to propose the reaction mechanisms for low and high temperatures. • Synergistic interaction between dispersed CuO species and Ni–Ce–O solid solution. • The presence of Ce 3+ in CeO 2 indicate formation of oxygen vacancies on the surface. • The activity was closely related to oxygen vacancies and Cu + -carbonyl species. • The temperature of CuNiCeO catalyst decreased about 40 °C compared to the NiCeO. • The oxygen vacancies and Cu + -carbonyl species suggest a multiple-step process.

Hydrogen Production by Ethanol Reforming on Supported Ni-Cu Catalysts.

Supported bimetallic Ni–Cu catalysts with different Ni–Cu loadings on alumina (Al2O3), alumina–silica (Al2O3–SiO2), alumina–magnesia (Al2O3–MgO), alumina–zinc oxide (Al2O3–ZnO), and alumina–lanthanum oxide (Al2O3–La2O3) were prepared and tested in ethanol steam reforming for the production of hydrogen (H2). These catalysts were characterized by X-ray diffraction, H2-temperature-programmed reduction, ammonia-temperature-programmed desorption, X-ray photoelectron spectroscopy, thermogravimetry, and differential scanning calorimetry. Cu addition improved the reducibility of NiO. Among the as-prepared catalysts, 30Ni5Cu/Al2O3–MgO and 30Ni5Cu/Al2O3–ZnO demonstrated much higher H2 selectivity and excellent coke resistance compared to the other investigated catalysts. Over 30Ni5Cu/Al2O3–MgO and 30Ni5Cu/Al2O3–ZnO, the respective H2 selectivity was 73.3 and 63.6% at 450 °C and increased to 94.0 and 95.2% at 600 °C. The strong interaction of Ni–Cu and Al2O3–ZnO (or Al2O3–MgO) led to the formation of smaller and highly dispersed CuO and NiO species on the carrier, which is conducive to improved catalytic performance. These Al2O3–MgO- and Al2O3–ZnO-supported bimetallic Ni–Cu materials can be promising catalysts for hydrogen production from ethanol steam reforming.

On the CuO-Mn2O3 oxide-pair in CuMnOx multi-oxide complexes: Structural and catalytic studies

The current work provide a new understanding on the active site of CuMnOx catalysts and thus offer a new perspective in the development of highly effective and low cost CuMnOx catalysts for heterogeneous catalytic oxidation reactions. A series of dual-component copper-manganese multi-oxide catalysts (CuMnOx) have been successfully synthesized using a surfactant assisted hydrolysis-hydrothermal method and studied by XRD, N2 adsorption–desorption test, ICP-AES, SEM, Aberration-corrected HADDF-STEM, HRTEM, FT-IR, Raman, XPS, H2-TPR. These CuMnOx catalysts were found to be composed with uniform CuO-Mn2O3 oxide pair structure, in which highly isolated/dispersed CuO species are anchored in the framework of Mn2O3. It was found that the speciation in these CuMnOx catalysts presents a shift from highly isolated or even single Cu2+ oxide species (Cu2+Ox) to CuO nanoclusters and CuO microcrystalline with increasing Cu content. In CO oxidation reaction, which was employed to probe the structure of the CuO-Mn2O3 oxide pairs in these CuMnOx catalysts, the Cu-O-Mn sites in those CuMnOx catalysts with highly isolated or highly dispersed CuO species were found to be highly active. For CuO-Mn2O3 oxide pair catalysts, the highly isolated/dispersed CuO species in Mn2O3 framework is essential to achieve high activity.

Enhanced Activity for CO Preferential Oxidation over CuO Catalysts Supported on Nanosized CeO2 with High Surface Area and Defects

Nanosizedceria (n-CeO2) was synthesized by a facile method in 2-methylimidazolesolution. The characterization results of XRD, N2 adsorption-desorption, Raman and TEM indicate that n-CeO2 shows a regular size of 10 ± 1 nm, a high surface area of 130 m2·g−1 and oxygen vacancies on the surface. A series of CuO/n-CeO2 catalysts (CuCeOX) with different copper loading were prepared for the preferential oxidation of CO in H2-rich gases (CO-PROX). All CuCeOX catalysts exhibit a high catalytic activity due to the excellent structural properties of n-CeO2, over which the 100% conversion of CO is obtained at 120 °C. The catalytic activity of CuCeOX catalysts increases in the order of CuCeO12 < CuCeO3 < CuCeO6 < CuCeO9. It is in good agreement with the order of the amount of active Cu+ species, Ce3+ species and oxygen vacancies on these catalysts, suggesting that the strength of interaction between highly dispersed CuO species and n-CeO2 is the decisive factor for the activity. The stronger interaction results in the formation of more readily reducible copper species on CuCeO9, which shows the highest activity with high stability and the broadest temperature “window” for complete CO conversion (120–180 °C).

Hydrodeoxygenation of Benzofuran over Bimetallic Ni-Cu/γ-Al2O3 Catalysts

Bimetallic NixCu(10−x)/γ-Al2O3 catalysts (where x is the mass fraction of Ni) with different Ni/Cu mass ratios were prepared. The catalysts were characterized by X-ray diffractometry, N2 adsorption–desorption, inductively coupled plasma mass spectrometry, X-ray photoelectron spectroscopy, H2-temperature programmed reduction, and transmission electron microscopy. The effect of Ni/Cu mass ratio on benzofuran hydrodeoxygenation was investigated in a fixed-flow reactor. Cu addition improved the NiO reducibility. The strong interaction of Ni and Cu led to the formation of smaller and highly dispersed CuO and NiO species over γ-Al2O3, which favors an improvement in catalytic activity. Among the as-prepared catalysts, the Ni5Cu5/γ-Al2O3 showed the highest deoxygenated product yield (79.9%) with an acceptable benzofuran conversion of 95.2%, which increased by 18.3% and 16.9% compared with that of the monometallic Ni/γ-Al2O3 catalyst. A possible reaction network was proposed, which would provide insight into benzofuran hydrodeoxygenation over the Ni5Cu5/γ-Al2O3 catalyst.

An investigation of Zr/Ce ratio influencing the catalytic performance of CuO/Ce1-Zr O2 catalyst for CO2 hydrogenation to CH3OH

Abstract A series of CuO/Ce1-xZrxO2 catalysts (x = 0.2, 0.4, 0.6 and 0.8) are applied to elaborate the effect of the Zr/Ce ratio on the catalytic performance of CO2 hydrogenation to CH3OH. The best catalytic performance is achieved with CuO/Ce0.4Zr0.6O2, exhibiting XCO2 = 13.2% and YCH3OH = 9.47% (T = 280 °C, P = 3 MPa). The formation of dispersed surface CuO species and larger number of oxygen vacancies are detected over CuO/Ce0.4Zr0.6O2 due to stronger interaction between CuO and Ce0.4Zr0.6O2, resulting in the superior activation ability for H2 and CO2 respectively. Additionally, the evidence is provided by in situ DRIFTS under the activity test pressure (3 MPa) that bi/m-HCOO* species are preferable for accumulating over ceria-rich (CuO/Ce0.6Zr0.4O2 and CuO/Ce0.8Zr0.2O2) catalysts while zirconia-rich (CuO/Ce0.4Zr0.6O2 and CuO/Ce0.2Zr0.8O2) catalysts are benefit to encourage the transformation of bi/m-HCOO* species to CH3OH. The abundant population and high activity of intermediate species over CuO/Ce0.4Zr0.6O2 give a strong positive effect on the catalytic performance.

Facile Design of Highly Effective CuCexCo1–xOy Catalysts with Diverse Surface/Interface Structures toward NO Reduction by CO at Low Temperatures

A series of highly effective CuCexCo1–xOy catalysts with diverse surface/interface structures were synthesized and applied to NO reduction by CO from 100 to 400 °C. The CuCe0.2Co0.8Oy catalyst exhibited superior catalytic performance, achieving 100% NO reduction at 175 °C. The structural and physicochemical properties and the intermediate species were systematically characterized. The results indicated that the surface dispersity of CuO species, the generation of low-oxidation-state metal species (Cu+ and Co2+) and surface oxygen vacancies (SOVs) were greatly enhanced due to stronger interaction between highly dispersed CuO species and supports, which favors for the enhancement of consequent redox properties and the regeneration of SOVs and low-oxidation-state metal ions during NO reduction by CO. The in situ FT-IR (Fourier transform infrared) results illustrated that the adsorption bands of CO2 and N2O on the CuCe0.2Co0.8Oy surface could emerge at lower temperatures, revealing that the CO adsorption/conversion and NO dissociation were significantly promoted by Ce modification.

CO preferential oxidation reaction aspects in a nanocrystalline CuO/CeO2 catalyst

CuO/CeO2 catalysts were prepared by the Pechini method and applied in the CO preferential oxidation (CO-PROX). The CuO content effects on the catalysts and the presence of H2O and CO2 in the reaction stream on the catalytic performance were investigated. The catalyst with 1.0 wt.% CuO presented the highest conversion and selectivity in the COPROX in the temperature range 100–250 °C. It was observed that the catalytic system is sensitive to the dispersion of the active phase and, independently of the copper content, the high activity of the CuO/CeO2 catalysts is closely related to the finely dispersed CuO species strongly interacting with CeO2 support. In the long-term stability test under the real CO-PROX condition with 10 mol% H2O and 15 mol% CO2 in the reactant stream, about 90% CO conversion can be maintained even at low temperature (150 °C) with 95% selectivity.

Stepwise Methane-to-Methanol Conversion on CuO/SBA-15.

The direct partial oxidation of methane to methanol is a challenging scientific and economical objective to expand the application of this abundant fuel gas as a major resource for one-step production of value-added chemicals. Despite substantial efforts to commercialize this synthetic route, to date no heterogeneous catalyst can selectively oxidize methane to methanol by O2 with an economically acceptable conversion. Cu-exchanged zeolites have been recently highlighted as one of the most promising bioinspired catalysts toward the direct production of methanol from methane under mild conditions. In this work, Cu-based catalysts were prepared using mesoporous silica SBA-15 as an alternative support and their activity for this conversion was investigated. The results demonstrate that highly dispersed CuO species on SBA-15 are able to react with methane and subsequently produce methanol with high selectivity (>84 %) through water-assisted extraction. Furthermore, it was confirmed that the main intermediate formed after interaction of the catalyst with methane is a methoxyl species, which can be further converted to methanol or dimethyl ether on extraction with water or methanol, respectively.

CHARACTERIZATION OF CaO-CuO-CeO2 MIXED OXIDE SYNTHESIZED BY THE IMPREGNATION AND INVESTIGATION OF ITS REUSABILITY

CaO-CuO-CeO2 mixed oxide was prepared by the impregnation method and used as the catalyst for the complete decomposition of phenol in the presence of hydrogen peroxide. The CaO-CuO-CeO2 mixed oxide were characterized by XRD, SEM, BET, H2-TPR and Raman spectroscopy. The results indicated that there were three CuO species in the mixed oxide: the finely dispersed CuO species on the surface of CeO2, the Ce1-x-yCuxCayO2-d solid solution and the bulk CuO. Most of particles have clear morphology with relatively uniform size in the range of 30 - 50 nm and the BET surface area was 37.96 m2/g. After three times of use, the catalytic activity of CaO-CuO-CeO2 mixed oxide was still relatively high and much higher than the mixed oxide CaO-CeO2 and CuO-CeO2.

Highly Active Noble‐Metal‐Free Copper Hydroxyapatite Catalysts for the Total Oxidation of Toluene

AbstractHydroxyapatite (Hap) supported Cu materials prepared by the wet impregnation method were designed as noble‐metal‐free catalysts for the total oxidation of toluene. Cu/Hap materials with different Cu loadings (2.5–20 wt %) calcined at 400 °C were characterized by using inductively coupled plasma optical emission spectroscopy, N2 physisorption, XRD, Raman spectroscopy, IR spectroscopy, X‐ray photoelectron spectroscopy, and time‐of‐flight secondary ion MS. The tenorite CuO phase was detected in all materials, and the libethenite Cu2(PO4)OH phase was observed for the sample with 20 wt % Cu. The presence of libethenite was accompanied by the formation of Ca2CO3H+ ions at the Hap surface. Residual NO3− species that interact with Cu and Ca were also found, and their amount increased with the increase of the Cu content in the sample. Interestingly, the specific activity in the total oxidation of toluene increased with the decrease of the Cu content in the catalyst. The rate per mole of Cu was increased by 10 times if the Cu content was decreased by four times. This noticeable result could be related to the presence of acid sites with a moderate strength as well as finely dispersed CuO species on the Hap, which allow the activation of toluene molecules and their oxidation through a redox mechanism. Moreover, Cu2.5 wt %/Hap showed a remarkably stable catalytic performance for 45 h time‐on‐stream, which evidences that this material has a high potential for applications in the removal of volatile organic compounds.

Micropore-enriched CuO-based silica catalyst directly prepared by anionic template-induced method and its boosting catalytic activity in olefins epoxidation

Micropore can efficiently tailor the diffused rate of reactant molecule in heterogeneous catalysis and enhance collision frequency with catalytic active sites, hence increasing catalytic properties. In this study, boosting catalytic activity for olefins epoxidation was obtained using micropore-enriched CuO-based silica catalyst. This special catalyst incorporated with highly-dispersed copper oxides was directly fabricated with anionic surfactant chelating Cu2+ as the template. Dispersed CuO species were in situ produced and encapsulated in the channels of mesoporous silica, avoiding the repeated calcination in the conventional modification process. Meanwhile, massive micropores (ca. 1.6 nm) were directly formed. In addition, to receive optimal catalytic performance, controllable amounts of Cu2+ were employed for modifying anionic micelles. This obtained catalyst exhibited obviously stronger reducibility and better dispersity of CuO in comparison with the post-impregnated sample, more interestingly, the introduction of Cu2+ in the assemble process improved structural properties of silica. In addition, a proper loading (Cu/Si = 4.34%) of CuO was found to be preferable in the catalytic process. Finally, catalytic results revealed that the micropore-enriched catalyst exhibited obviously higher catalytic activity as compared to the mesoporous catalyst, and its further applications in various olefins epoxidation were preferable.

Effect of Zr addition on catalytic performance of Cu-Zn-Al oxides for CO2 hydrogenation to methanol

A series of 50%CuO-25%ZnO-25%Al(Zr) oxide catalysts was synthesized by a reverse co-precipitation method and characterized by XRD, N2 adsorption-desorption, H2-TPR, H2-TPD and CO2-TPD, and used as catalyst for CO2 hydrogenation to methanol under mild conditions(200―260 °C and 1―3 MPa). Consequently, H2-TPR ex-hibited that the dispersed CuO species increased with the zirconium content, while the H2-TPD showed that small amount of zirconia can increase the H2 desorption amount. As a result, Cat-2 and Cat-3 exhibited an enhanced H2-spillover effect, the most H2 desorption amount, which showed an optimum activity of about 7% methanol yield.

Water gas shift reaction over monometallic and bimetallic catalysts supported by mixed oxide materials

In the present work, the water gas shift activities of Cu on ceria and Gd doped ceria were studied for a further enhancement of hydrogen purity after a steam reforming process. The catalytic properties of commercial catalysts were also studied to compare with our as-prepared catalysts. It was found that copper-containing cerium oxide is suitable for the high temperature reaction. Copper-ceria is a stable high-temperature shift catalyst, unlike iron-chrome catalysts which are deactivated severely in CO2-rich gases. 5%Cu/10%GDC (D) was found to have much higher activity than other copper ceria based catalysts. Finely dispersed CuO species is more favorable due to a higher activity, which explains the activity enhancement of this catalyst. The kinetics of the WGS reaction over Cu catalysts supported by mixed oxide materials were measured in the temperature range 200–400°C. An independence of the CO conversion rate on CO2 and H2 was observed. To improve the catalytic performance of copper catalysts, the behavior of the bimetallic catalysts was compared with that of the monometallic catalysts. It was found that an addition of Re to Cu/GDC significantly improved the activity of copper catalysts. The effect of Re on enhancing the WGS activity of Cu catalysts was due to Re increases the reducibility of the surface ceria, In addition, Re contributes to reduction of Ce4+ to Ce3+. The presence of Ce2O3 at the ceria surface gives rise to oxygen vacancies which facilitate the electron movement at the surface leading to ease of surface reduction.