CuO CeO2 Catalysts Research Articles

Investigating the effect of CuO[sbnd]CeO2 catalyst concentration on methane-air catalytic combustion in the presence of different atomic ratios of oxygen by molecular dynamics simulation

Fossil fuels cause global warming and create greenhouse gases that cause irreparable environmental damage. On the other hand, because the combustion reactions are not completely done, dangerous compounds, such as nitrogen or carbon monoxide are produced which are very toxic and dangerous. As a result, innovative methods were implemented in combustion processes. One such method is to use a catalyst during the combustion process. This study used a molecular dynamics method to examine how the concentration of CuOCeO2 catalyst affected air-methane combustion in a helical microchannel. The results show that the maximum (Max) values of density (Dens), velocity (Velo), and temperature (Temp) in the excess oxygen (EO) state were 0.142 atoms per second, 0.35 Å/ps, and 1089 K, respectively, when the atomic ratio of CuOCeO2 increased from 1 % to 4 %. Subsequently, these values exhibited a declining trend. Also, the values of heat flux (HF), thermal conductivity, and combustion efficiency in 4 % catalyst reached the max values of 2038 W/m2, 1.15 W/m·K and 88 %. The results related to the max values of Dens, Velo, and Temp for the oxygen deficiency state had a similar trend and increased to the max values of 0.103 atom/Å3, 0.41 Å/ps, and 1024 K in 4 % catalyst, and then decreased by increasing the catalyst ratio of CuOCeO2 and reaching 10 %. The thermal behavior of nanostructure was more optimal in the deficient oxygen medium.

Selective synthesis of meta-phenols from bio-benzoic acids via regulating the adsorption state

Phenols are important building blocks widely applied in many fields. The pronounced orientational effect of the phenolic hydroxyl group makes achieving selective synthesis of meta-phenols challenging. Accessing meta-phenols needs lengthy synthetic sequences. Herein, we first developed a heterogeneous CO2-mediated CeO2-5CuO catalyst for decarboxylative oxidation of benzoic acids with a more than 80% selectivity to meta-phenols. This technology is based on a traceless directing group relay method. The CeO2-CuO catalysts with different Ce/Cu ratios exhibited controllable reaction selectivity between decarboxylation and decarboxylative oxidation. Spectroscopy experiments and computational studies showed the adsorption state of benzoic acid was found to be crucial for subsequent reaction pathways. The moderate adsorption on CO2-mediated CeO2-5CuO catalyst contributes to the distinct selectivity of phenol. Furthermore, the paddlewheel intermediate facilitates the synthesis of meta-phenols from benzoic acids. This traceless directing group method would promote the development of useful one-pot meta-substituted phenols from bio-based benzoic acids.

New insights into the relationship between Cu–Ce interaction and reactive Cu species in CuOx-CeO2 catalysts for preferential oxidation of carbon monoxide in excess hydrogen

A group of CuOx-CeO2 catalysts for preferential oxidation of carbon monoxide (CO-PROX) is designed by constructing different distribution status of Cu species on similar CeO2 support to adjust the Cu–Ce interaction strength. Cycled temperature programmed reduction by hydrogen (H2-TPR) indicates the strength of Cu–Ce interaction can impact the amount and redox properties of surface highly dispersed CuOx and strongly bonded Cu-[Ox]-Ce species, which respectively determines the catalytic performance at low and high temperature. Temperature programed desorption of H2 (H2-TPD) reveals the presence of large amounts of Cu-[Ox]-Ce species can inhibit H2 adsorption and dissociation, which increases the O2 selectivity toward CO oxidation. Moreover, temperature programmed desorption of CO2 (CO2-TPD) and in situ diffuse reflectance infrared Fourier transform spectra (DRIFTs) illustrates that H2O and CO2 influences the low-temperature catalytic performance mainly by competitive adsorption with CO on surface highly dispersed reactive Cu+ sites. This work aims to shed light on the underlying Cu–Ce interaction regime, and guide the design of high-performance CuO–CeO2 catalysts in realistic reaction conditions.

Low temperature CO oxidation from sintering flue gas on CuO-CeO2/AC-Fe catalyst

The effects of carbon-iron composite (AC-Fe) on the performance of CO oxidation for CuO-CeO2 catalyst in sintering flue gas are investigated by XRD, H2-TPR, Raman, XPS, FTIR, CO-TPD and SEM. The results show that the AC-Fe can effectively increase the catalytic activity of CuO-CeO2. CuO-CeO2/AC-Fe catalyst with Fe/AC mass ratio of 0.03 achieves the highest activity, corresponding to complete CO conversion at 160 ºC. The defects and oxygen-containing functional groups on AC-Fe can anchor the active particles to inhibit grain growth and facilitate the dispersity of active components. In addition, the Fe species incorporate into CeO2 lattice, resulting in the increase of Ce3+ species and the generation of more oxygen vacancy on catalyst, which can enhance the mobility of reactive oxygen species and the redox property. Moreover, the increase of Cu+ on the catalyst provides more active sites for CO adsorption.

Effect of copper precursors on CO oxidation catalyzed by CuO-CeO2 prepared by solvothermal method

In this paper, the CuO–CeO2 catalyst was prepared by a direct solvothermal method. The effects of different copper salt precursors (copper nitrate, copper acetate, copper sulfate) on the catalytic performance of the prepared catalyst for CO oxidation were investigated. The physical and chemical properties of the prepared catalysts were characterized by X-ray diffraction (XRD), Raman spectroscopy, N2 physical adsorption, inductively coupled plasma-atomic emission spectrometry (ICP-AES), X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption analysis of CO (CO-TPD), in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs), and temperature-programmed reduction with H2 (H2-TPR). The results show that the CuO–CeO2 catalyst prepared with copper acetate as precursor (CC-A) exhibits the best catalytic activity for CO oxidation at low temperatures, with T50 and T90 values of 62 and 78 °C respectively, which is mainly attributed to its large specific surface area, pore volume, CO adsorption capacity, and large amount and strong reactivity of surface oxygen. However, the CuO–CeO2 catalyst prepared with copper nitrate as precursor (CC–N) displays better stability and resistance to water or CO2 poisoning than CC-A.

Low-temperature CO oxidation on CuO-CeO2 catalyst prepared by facile one-step solvothermal synthesis: Improved activity and moisture resistance via optimizing the activation temperature

Development of a highly efficient Cu-based catalyst for low-temperature CO oxidation under moisture condition remains a grand challenge. In this paper, effect of activation temperature (350–800 °C) on catalytic performance of CuO-CeO2, prepared by facile one-step solvothermal synthesis, in CO oxidation was investigated, and the catalysts’ physicochemical properties were studied by TG-DSC, ICP-AES, N2 sorption, XRD, TEM, Raman spectroscopy, XPS, in-situ DRIFTS, H2-TPR, CO-TPD, and O2-TPD. It was found that activation at 550 °C is beneficial for the interaction between CuO and CeO2, leading to the formation of more Cu+ species and oxygen vacancies advantageous for improving the catalytic activity. Activation at 800 °C, nevertheless, would weaken the interaction between CuO and CeO2 due to the sintering of CuO and CeO2, thus decreasing the catalytic activity and moisture resistance. Interestingly, no deactivation was observed over the optimal catalyst (activated at 550 °C) after 50 h testing at a low temperature of 87 °C (at which 90% CO conversion was obtained), even when 4.2% water vapor was added into the feed gas.

Rational Design of Mesoporous CuO-CeO2 Catalysts for NH3-SCR Applications Guided by Multiple In Situ Spectroscopies.

Efficient nontoxic catalysts for low-temperature NH3 selective catalytic reduction (NH3-SCR) applications are of great interest. Owing to their promising redox and low-temperature activity, we prepared CuO-CeO2 catalysts on a mesoporous SBA-15 support using targeted solid-state impregnation (SSI), guided by multiple in situ spectroscopy. The use of template P123 allowed dedicated modification of the surface properties of the SBA-15 matrix, resulting in a changed reactivity behavior of the metal precursors during the calcination process. To unravel the details of the transformation of the precursors to the final catalyst material, we applied in situ diffuse reflectance infrared Fourier transform (DRIFT), UV-visible (UV-vis), and Raman spectroscopies as well as online Fourier transform infrared (FTIR) monitoring of the gas-phase composition, in addition to ex situ surface, porosity, and structural analysis. The in situ analysis reveals two types of nitrate decomposition mechanisms: a nitrate-bridging route leading to the formation of a CuO-CeO2 solid solution with increased low-temperature NH3-SCR activity, and a hydrolysis route, which facilitates the formation of binary oxides CuO + CeO2 showing activity over a broader temperature window peaking at higher temperatures. Our findings demonstrate that a detailed understanding of catalytic performance requires a profound knowledge of the calcination step and that the use of in situ analysis facilitates the rational design of catalytic properties.

Reversible interconversion and functional division of highly dispersed Cu species during CO + NO reaction

CuOCeO2 system has been widely studied in recent decades. Electronic-scale understanding the function and evolution of Cu species in catalytic reaction is benefit for exploring the catalytic potential of Cu-based catalysts. In this work, Cu+-rich CuOCeO2 catalysts was prepared by template method. The studies show that the synergistic effect of CuO/CeO2 is benefit the reversible interconversion between Cu+ and Cu0, and the rapid conversion between Cu+ and Cu0 contribute the high catalytic performance. Cu+ is responsible for the oxidation of CO, and Cu0 is dedicated to the selective reduction of NO. The isolated energy levels of the Cu species near the Fermi levels coordinate with Ce 4f orbitals for the electron transfer between the two phases. This electronic-level description of Cu evolution should have important guiding significance for the exploration of the potential of Cu-based catalysts.

Effects of the Crystalline Properties of Hollow Ceria Nanostructures on a CuO-CeO2 Catalyst in CO Oxidation

The development of an efficient and economic catalyst with high catalytic performance is always challenging. In this study, we report the synthesis of hollow CeO2 nanostructures and the crystallinity control of a CeO2 layer used as a support material for a CuO-CeO2 catalyst in CO oxidation. The hollow CeO2 nanostructures were synthesized using a simple hydrothermal method. The crystallinity of the hollow CeO2 shell layer was controlled through thermal treatment at various temperatures. The crystallinity of hollow CeO2 was enhanced by increasing the calcination temperature, but both porosity and surface area decreased, showing an opposite trend to that of crystallinity. The crystallinity of hollow CeO2 significantly influenced both the characteristics and the catalytic performance of the corresponding hollow CuO-CeO2 (H-Cu-CeO2) catalysts. The degree of oxygen vacancy significantly decreased with the calcination temperature. H-Cu-CeO2 (HT), which presented the lowest CeO2 crystallinity, not only had a high degree of oxygen vacancy but also showed well-dispersed CuO species, while H-Cu-CeO2 (800), with well-developed crystallinity, showed low CuO dispersion. The H-Cu-CeO2 (HT) catalyst exhibited significantly enhanced catalytic activity and stability. In this study, we systemically analyzed the characteristics and catalyst performance of hollow CeO2 samples and the corresponding hollow CuO-CeO2 catalysts.

Role of Benzene-1,3,5-Tricarboxylate Ligand in CuO–CeO2 Catalysts Derived from Metal–Organic Frameworks for Carbon Monoxide Oxidation

Role of Benzene-1,3,5-Tricarboxylate Ligand in CuO–CeO2 Catalysts Derived from Metal–Organic Frameworks for Carbon Monoxide Oxidation

Trace CO elimination in H2-rich streams with a wide operation temperature window: Co deposited CuO-CeO2 catalysts.

This work provides a new strategy to eliminate trace CO in H2-rich gas in a wide operation temperature window for the application of hydrogen fuel cells. We engineered Co deposited CuO-CeO2 catalysts with a Co/(Cu + Ce) molar ratio of 1/1 that manages to maintain the CO level at below 100 ppm from 85 to 240 °C in the H2-rich reformate stream. CO-PROX and CO methanation reaction respectively occurred in the low and high temperature ranges. Multiple characterization techniques demonstrate that the molar ratio of Co/(Cu + Ce) significantly affects the synergistic interactions between the Cu, Co and Ce species, and ultimately the CO oxidation and CO methanation reactions. At low reaction temperatures, the Cu-Ce interaction mainly dominates the CO-PROX process, while at high reaction temperatures, CO methanation reaction takes place due to the reduction of Co3O4 to Co0 and the Co-Ce interaction takes charge of the CO methanation. Moreover, the increment of Co/(Cu + Ce) from 1/2 to 1 gives rise to the reprecipitation of the partially dissolved Cu species on Co3O4, which strengthens the Cu-Co interaction and stabilizes surface Cu+ and Co3+, thus promoting the low temperature CO-PROX catalytic performance.

Low-Temperature Co Oxidation on Cuo-Ceo2 Catalyst Prepared by Facile One-Step Solvothermal Synthesis: Improved Activity and Moisture Resistance Via Optimizing the Activation Temperature

Low-Temperature Co Oxidation on Cuo-Ceo2 Catalyst Prepared by Facile One-Step Solvothermal Synthesis: Improved Activity and Moisture Resistance Via Optimizing the Activation Temperature

Effect of the Configuration of Copper Oxide-Ceria Catalysts in NO Reduction with CO: Superior Performance of a Copper-Ceria Solid Solution.

Various copper-ceria-based composites have attracted attention as efficient catalysts for the reduction of NO with CO. In this comparative study, we have examined the catalytic potential of different configurations of copper oxide-ceria catalysts, including catalysts based on a copper-ceria solid solution, copper oxide particles supported on ceria, and ball-milled copper oxide-ceria. The structurally different interfaces between the constituents of these catalysts afforded very different catalytic performances. The solid solution catalyst outperformed the corresponding ceria-supported and ball-milled CuO-CeO2 catalysts. The copper cations incorporated into the ceria lattice strongly improved the activity, N2 selectivity, and water vapor tolerance compared to the other catalyst configurations. The experimental observations are supported by first-principles density functional theory (DFT) studies of the reaction pathway, which indicate that the incorporation of Cu cations into the ceria matrix lowers the energy required for activating the lattice oxygen, thereby enhancing the formation and healing of oxygen vacancies, and thus promoting NO reduction with CO.

Insight into the role of WO3 on catalytic performance over CuO-CeO2 catalyst for NH3 selective catalytic oxidation reaction

CuO-CeO2 catalysts modified with WO3 were prepared by a sol-gel method and applied in selective catalytic oxidation (SCO) of NH3 to N2. It can be found that the NH3 conversion showed a gradually decreased trend but the N2 selectivity monotonically increased with the WO3 introduced. As evidence from H2-TPR and Raman measurements, the doping of WO3 resulted in a decrease in the concentration of oxygen vacancy and thereby reduced the redox ability of Cu-Ce, which was not helpful for the conversion of NH3. However, NH3-TPD and in situ DRIFTS results showed that WO3 introduction can significantly enhance the density of Brønsted acid sites on the catalyst and thereby promote the adsorption of NH3 molecules. Typically, CuO-CeO2 doping with 15 wt% WO3 (Cu-Ce-15W) presented the highest NH3 storage capacity. This could suppress the over-oxidation of NH3 and thus make contribution to the enhancement of N2 selectivity. This work could help to engineer highly efficient catalysts for NH3-SCO reaction.

CuO-CeO2 catalysts based on SBA-15 and SBA-16 for COPrOx. Influence of oxides concentration, incorporation method and support structure

In this work different variables that can affect the catalytic behavior of CuO-CeO2 supported on mesoporous silica (SBA-15 and SBA-16) were studied. The influence on the COPrOx activity of the relative concentration of the CuO and CeO2 active phase and different impregnation methods in mesoporous support was analyzed. The physicochemical characterization was performed EDS-SEM and TEM-STEM, N2 isotherms, X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). The incipient wetness impregnation method (IWI) was the better alternative to introduce the active phases compared to solid state impregnation (SSI). In addition, the catalysts based on 2-D structure of SBA-15 were more active and selective than those based in 3-D SBA-16. In general, the high surface area of the supports benefited the dispersion of CuO and CeO2 oxides nanoparticles. All catalysts displayed the preservation of the mesostructure and the formation of nanoparticles of active phases (less than 10 nm) detected by TEM. The best COPrOx catalyst, obtained from the SBA-15 fibers by IWI method, with a relative CuO concentration of 0.2, exhibited XCO ≥ 99% at 175 °C and above 90% in a wide window of temperatures. This catalyst showed an adequate performance in presence of CO2 and H2O and good recovery of CO conversion and selectivity. The analysis by XPS revealed that the majority species were Ce4+, however in some catalysts Ce3+ species are also present, which are associated with vacancies oxygen and favor the redox process. In addition, Cu2+ and Cu+ species are present, the latter recognized as a key site of CO adsorption in the reaction mechanism.

Effects of Preparation Method on the Characterization and CO Oxidation Activities of the Carbon-Supported CuO–CeO2 Catalysts

Effects of Preparation Method on the Characterization and CO Oxidation Activities of the Carbon-Supported CuO–CeO2 Catalysts

High-sensitivity CO electrochemical gas sensor based on a superconductive C-loaded CuO-CeO2 nanocomposite sensing material

The surperconductive C-loaded CuO-CeO2 catalyst was fabricated by a high temperature solid phase reaction. The catalyst was annealed at 500 °C for 4 h then was characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM), respectively. The results showed that the as-prepared catalyst was consisted of the particles with the size of 20–50 nm. The gas sensing properties of the superconductive C-loaded CuO-CeO2 to CO were investigated at room temperature. In addition, the as-prepared catalyst exhibited superior activity toward CO. The sensor shows characteristics of a practical-use level: range, 0.1–1000 ppm; sensitivity, 192 mV/ppm; response time, 9 s.

Construction of Cu-Ce interface for boosting toluene oxidation: Study of Cu-Ce interaction and intermediates identified by in situ DRIFTS

A facile hydrothermal method was applied to gain stably and highly efficient CuO-CeO2 (denoted as Cu1Ce2) catalyst for toluene oxidation. The changes of surface and inter properties on Cu1Ce2 were investigated comparing with pure CeO2 and pure CuO. The formation of Cu-Ce interface promotes the electron transfer between Cu and Ce through Cu2+ + Ce3+ ↔ Cu+ + Ce4+ and leads to high redox properties and mobility of oxygen species. Thus, the Cu1Ce2 catalyst makes up the shortcoming of CeO2 and CuO and achieved high catalytic performance with T50 = 234 °C and T99 = 250 °C (the temperature at which 50% and 90% C7H8 conversion is obtained, respectively) for toluene oxidation. Different reaction steps and intermediates for toluene oxidation over Cu1Ce2, CeO2 and CuO were detected by in situ DRIFTS, the fast benzyl species conversion and preferential transformation of benzoates into carbonates through C=C breaking over Cu1Ce2 should accelerate the reaction.

Sn-induced CuO–CeO2 catalysts with improved performance for CO preferential oxidation in H2-rich streams

Sn modified CuO–CeO2 catalysts with different Sn loadings were prepared by a facile, green and solvent-free method. The effect of Sn/Ce ratio over Sn–Cu–Ce-x (x = 0, 1, 2.5, 5, 7.5) samples on CO activity and O2 selectivity was investigated. The samples were characterized by various techniques using N2-adsorption/desorption, XRD, H2-TPR, XPS, Raman and in-situ DRIFTS. It was revealed that stronger interaction between acitve sites and support, higher amounts of Sn2+ and Ce3+, associated with increased amount of oxygen vacancies, were observed on the catalyst of Sn–Cu–Ce-5. As a result, the optimized catalyst displayed an excellent catalytic performance even in the presence of CO2 and H2O. In this sense, probing the Sn modified CuO–CeO2 catalyst can elucidate some useful keys for the development of high CO2 and H2O-resistance catalyst during CO-preferential oxidation in H2-rich streams.

Study of CuO–CeO2 catalysts supported on ordered porous silica with different mesostructure and morphology. Influence on CO preferential oxidation

In the present work, SBA-15 and SBA-16 ordered mesoporous silicas were synthesized with different morphologies such as fibers, spheres, rods and irregular shapes. Copper and cerium oxides active phase was introduced by two methods, incipient wetness impregnation and solid-state impregnation by using a ball mill. The obtained catalysts were evaluated in the CO preferential oxidation reaction (COPrOx). By means of SAXS, XRD, SEM and TEM microscopies, the mesostructures and morphologies were characterized, as well as the preservation of the porous structure and the presence of oxides nanoparticles. In addition, XPS spectroscopy was used to analyze the chemical state and relative surface abundance of the elements present in the catalysts. From the catalytic results, it could be seen that the incipient wetness impregnation method was the most favorable. The unidirectional porous structure SBA-15 with fiber shape and incipient wetness impregnation achieved the highest conversion of CO and selectivity to CO2 (CO conversion 98% at 175 °C). SBA-16 based catalysts were found less active. However, it is noteworthy that the best material was prepared by using an irregular shaped SBA-16 impregnated by incipient wetness procedure. This catalyst exhibited a maximum CO conversion of 80% at 175 °C. Finally, the SBA-15 mesoporous structure and the incipient wetness impregnation method had a greater influence on the better catalytic performance.