CuO CeO2 Research Articles

CO Oxidation over Nanostructured Ceria Supported Bimetallic Cu–Mn Oxides Catalysts: Effect of Cu/Mn Ratio and Calcination Temperature

Nanostructured CeO2 supported CuO–MnO2 (CuMn/Ce) catalysts were synthesized by wet co-impregnation method and compared with CuO/CeO2 and MnO2/CeO2 catalysts on CO oxidation. The former shows significantly higher catalytic activity toward CO oxidation than the bimetallic oxides catalysts with minimum T50. Dual synergistic effects in the interfaces of CuO–MnO2 and CuO–CeO2 shall be responsible for the higher oxidation performance of CuMn/Ce catalyst. As Cu/Mn mass ratio varies from 1/0.2 to 1/9, CO oxidation activities of the catalysts present unimodal distribution, and the catalyst with Cu/Mn = 1/1 shows the highest performance (T50 = 45.8 °C; Ea = 24.11 kJ mol−1). Cu acts as CO dissociative adsorption sites, and Mn–Ce supplies activated O species from gas molecule and lattice oxygen, which are both indispensable for improving utilization efficiency of the reactants in the dual redox processes. The catalytic performance of catalyst is also vitally correlated with calcination temperature (160–320 °C). The optimum calcination temperature of CuMn/Ce catalyst is 320 °C. Catalyst characterization results indicate that the pretreatment at 320 °C is decent to obtain desired metal oxides along with fine texture properties.

Synthesis, characterisation, and evaluation of stable, efficient modified nanocopper‐based glycerol hydrogenolysis catalysts

A series of CuO/SiO2 catalysts containing different modifiers were prepared via co-precipitation and used for glycerol hydrogenolysis. CuO–CeO2/SiO2 gave the best glycerol conversion rate (100%) and highest selectivity for 1,2-propanediol (up to 95%). Reactions were carried out under the following conditions: temperature, 220°C; H2 pressure, 0.5 MPa; glycerol concentration, 100 wt.%; and H2/glycerol molar ratio, 35:1. The catalysts were characterised by X-ray diffraction, NH3 temperature-programmed desorption, N2 adsorption, and scanning electron microscopy. The CuO–CeO2/SiO2 catalyst had smaller particle sizes, better dispersion, and greater specific surface area than the CuO/SiO2, CuO–phosphotungstic acid (PTA)/SiO2, and CuO–CeO2–PTA/SiO2 catalysts.

Facile Solvothermal Synthesis of CeO2–CuO Nanocomposite Photocatalyst Using Novel Precursors with Enhanced Photocatalytic Performance in Dye Degradation

This paper reports a facile solvothermal process for synthesizing dendritic CeO2–CuO nanocomposite using [Ce(salen)2] and [Cu(sal)2] as novel precursors in ethylene glycol as a solvent. The morphology and microstructure of the obtained products were characterized by X-ray diffraction pattern, UV–Vis diffuse reflectance spectroscopy, energy dispersive X-ray microanalysis, Fourier transform infrared spectroscopy, transmission electron microscopy, and scanning electron microscopy. Effect of temperature and reaction time, surfactant, and the ratio of reactants on morphology of prepared nanostructures was well studied. Moreover, the efficiency of dendritic CeO2–CuO nanocomposite as a photocatalyst for the decolorization of methylene violet (MV) under ultraviolet and visible light irradiations was evaluated and more than 93 and 72%, respectively, of MV were decolorized after 90 min. Also, the effect of particle size and morphology on the photocatalytic activity was investigated.

Synthesis, characterization and investigation of the electrochemical hydrogen storage properties of CuO–CeO2 nanocomposites synthesized by green method

Pure CuO–CeO2 nanocomposites were synthesized by simple thermal decomposition method in presence of various Cu salts as a copper source and fructose as a green capping agent. In this study, the effect of various parameters such as the type of copper sources, temperature and time of reaction on the morphology and the particles size were studied. The products were characterized via X-ray diffraction (XRD) pattern, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), transmission electron microscopy (TEM), N2 adsorption (BET), vibrating sample magnetometer (VSM), and infrared spectrum (FT-IR). The optical property of the nanocomposite was examined via UV–vis (DRS) spectroscopy and the band gap was calculated to 3 eV. Also, the hydrogen storage capacity of CuO–CeO2 nanocomposites and CeO2 nanoparticles were investigated via chronopotentiometry method for the first time. The discharge capacity of CeO2 nanoparticles and CuO–CeO2 nanocomposites in 1 mA current and 20 cycles obtained 2150 and 2450 mAh/g, respectively.

Optimization Strategies in a Fixed-Bed Reactor for HCl Oxidation

Heterocatalytic oxidation of HCl into Cl2 (HCl conversion process) over a CeO2–CuO catalyst in a fixed-bed reactor has been optimized using four different objective functions and three different methods. For a given residence time, the HCl conversion could be maximized in various reactor configurations, namely with the application of a graded catalyst bed, with partitioning the reactor shell and using multistage temperature control, or with the combination of both methods. However, as the obtained temperature profiles differed considerably from each other, we considered three objective functions in order to smooth the reactor temperature profile. These implement a nonconventional approach since the proposed objective functions aim to deal directly with the temperature changes and HCl conversion is only taken into consideration as a nonlinear constraint. The different results from each method and objective function were compared using the apparent temperature gradients along the length of the reactor. The ...

Low-temperature carbon monoxide oxidation over zirconia-supported CuO–CeO2 catalysts: Effect of zirconia support properties

A study was conducted to investigate the effect of the preparation route of ZrO2 in CuO–CeO2/ZrO2 catalysts for the oxidation of carbon monoxide at low temperature (COX). Four ZrO2 supports were synthetized via either type sol-gel methodology or precipitation. The final Cu-Ce-Zr oxide catalysts were prepared by incipient wetness co-impregnation with copper and cerium solutions (with a loading of 6wt% of CuO and 20wt% of CeO2). The catalyst crystalline phases, texture and active species reducibility were determined by XRD, N2 physisorption at −196°C and H2-TPR, respectively; meanwhile the surface composition and copper-cerium electronic states were studied by XPS. The catalytic activity was evaluated in the oxidation of CO to CO2, in the 40–215°C temperature range. Catalytic results evidenced that the samples prepared by a sol-gel methodology showed, after the impregnation, a severe decrease of specific surface area and pore volume attributable to a wide degree of pore blockage caused by the presence of metal oxide particles and a collapse of the structure partially burying the active sites. A simple co-impregnation of a zirconia support, obtained through facile and fast precipitation, provided instead a catalyst with very good redox properties and high dispersion of the active phases, which completely oxidizes CO in the range 115–215°C with T50 of 65°C. This higher observed activity was ascribed to the formation of a larger fraction of highly dispersed and easily reducible Cu species and ceria nanocrystallites, mainly present as Ce(IV), with an average size of 5nm.

Preparation and characterization of mesostructured cellular foam silica supported Cu–Ce mixed oxide catalysts for CO oxidation

A series of mesostructured cellular foam (MCF) silica supported CuO–CeO2 catalysts with various total metal loadings (10–40 wt%) and various Cu/Ce ratios (Cu/Ce = 1/9, 2/8, and 3/7 wt/wt) were prepared and tested for CO oxidation.

CO oxidation on mesoporous SBA-15 supported CuO–CeO2catalyst prepared by a surfactant-assisted impregnation method

A series of mesoporous SBA-15 supported CuO–CeO2catalysts were prepared by a surfactant-assisted impregnation method with PEG 200 as the surfactant.

Synergistic Catalysis of Methane Combustion Using Cu–Ce–O Hybrid Nanoparticles with High Activity and Operation Stability

A new CuO–CeO2 hybrid nanoparticle (CuCeOx-NP) with a tunable homogeneous chemical composition was successfully prepared for high-performance catalytic methane combustion. The substantial amounts of Cu–Ce–O interfaces were created for enhanced catalysis using gas-phase evaporation-induced self-assembly. The CuCeOx-NP exhibited an ultralow light-off temperature (320 °C), high activity, selectivity, and operation stability for catalytic methane combustion. The optimal reducibility and the corresponding catalytic activity of CuCeOx-NP were achieved when the molar fraction of Ce was 0.17. The operation stability increased as the concentration ratio of oxygen in the reactant gas and the corresponding oxidation rate of carbon species from the catalyst surface increased. This work demonstrates a facile route for controlled synthesis of CuCeOx-NP. The mechanistic understanding of synergistic catalysis developed in this study can be used to further enhance activity of methane combustion and reduce environmental po...

Recent Advances in the Preferential Thermal-/Photo-Oxidation of Carbon Monoxide: Noble Versus Inexpensive Metals and Their Reaction Mechanisms

Preferential oxidation (PROX) of CO is applicable because of its low cost, ease of implementation, and low loss of H2 during purification. Mo–SiO2 and Cr–SiO2 photocatalysts utilized charge separation at metal=O bonds, and the PROX selectivity of CO was high. The CO PROX rates using semiconductor-based photocatalysts were comparable to those of photocatalysts (380 μmol h−1 g cat −1 ) and were also selective (100 %). These photocatalysts are advantageous because they do not activate H2 in comparison to noble metal catalysts. Below 473 K using noble metals, Ru, Rh, Pt, or Au supported on reducible metal oxides exhibited excellent CO thermal-PROX rates of ~4900 μmol h−1 g cat −1 ; however, the CO PROX selectivity of ~48 % was insufficient because of H2 activation on noble metals in nature. CO adsorbed onto TiO2 and O2 was stabilized at the interface between a Ti site and an Au atom. Weakly adsorbed water increased the effective number of active sites by stabilizing Au–OOH or Au–COOH. The PROX rates of CO using Au/TiO2-based catalysts under dark conditions increased under UV–visible light by the effect of charge separation and surface plasmon resonance and the promoted electron transfer to the adsorbed O2. In the case of CuO–CeO2 catalysts, CO adsorbed onto CuO and reacted with lattice O atoms at the boundary between CuO and CeO2 to form CO2 at an O vacancy, which was subsequently filled with an O2 molecule. The combination of Cu or Co with a reducible metal oxides also provided performance comparable to or higher than that of CuO–CeO2 owing to adequate standard reduction potential for Cu2+, Co3+, Mn3+/4+, and Ce4+. Finally, binary metal–organic framework consisting of oxyhydroxide Ti clusters interlinked by organic ligands and Cu oxyhydroxide ligands showed superior CO PROX performance (76 % conversion and 99 % selectivity) to that achieved using CuO–CeO2 owing to effective dispersion of Cu–O–Ti connection in microporous crystallites. Further progress is needed to alleviate the activity loss in the presence of moisture and/or CO2 based on suggestions that steric hindrance of some types of microporous crystallites would suppress the blocking of moisture or CO2.

Improved Low-Temperature Activity of CuO–CeO2–ZrO2 Catalysts for Preferential Oxidation of CO in H2-Rich Streams

In this work, CuO–CeO2–ZrO2 catalysts for CO preferential oxidation have been prepared by ultrasound assisted reverse coprecipitation and slow coprecipitation, and characterized via BET, XRD, XPS and H2-TPR techniques, respectively. It is found that the catalyst prepared with ultrasound assisted reverse coprecipitation preserves large specific surface area, fine crystalline grain and high dispersion of active copper species. Meanwhile, the reducibility is improved significantly and more active copper species and oxygen vacancies are formed in the copper–ceria boundaries. The ultrasound assisted reverse coprecipitation prepared CuO–CeO2–ZrO2 catalyst exhibits superior low-temperature activity and CO2 selectivity, over which the temperature responding to 50 % CO conversion is as low as 67 °C, and the temperature window of full CO conversion is significantly widen from 100 to 160 °C. The ultrasound assisted reverse coprecipitation prepared CuO–CeO2–ZrO2 catalyst exhibits superior low-temperature activity for CO preferential oxidation and wide temperature window of full CO conversion comparing with the catalyst prepared with slow coprecipitation.

In Situ EPR Study of the Redox Properties of CuO–CeO2 Catalysts for Preferential CO Oxidation (PROX)

Understanding the redox properties of metal oxide based catalysts is a major task in catalysis research. In situ electron paramagnetic resonance (EPR) spectroscopy is capable of monitoring the change of metal ion valences and formation of active sites during redox reactions, allowing for the identification of ongoing redox pathways. Here in situ EPR spectroscopy combined with online gas analysis, supported by ex situ X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), temporal analysis of product (TAP), and mass spectrometry (MS) studies, was utilized to study the redox behavior of CuO–CeO2 catalysts under PROX conditions (preferential oxidation of carbon monoxide in hydrogen). Two redox mechanisms are revealed: (i) a synergetic mechanism that involves the redox pair Ce4+/Ce3+ during oxidation of Cu0/Cu+ species to Cu2+ and (ii) a direct mechanism that bypasses the redox pair Ce4+/Ce3+. In addition, EPR experiments with isotopically enriched 17O2 ...

Hyperbranched polyethyleneimine towards the development of homogeneous and highly porous CuO–CeO2–SiO2 catalytic materials

A novel templating strategy for the development of composite nanoporous CuO/CeO2/SiO2 materials with advanced properties and significant thermal stability is proposed in this work, for potential use in automotive catalysts. The synthetic process is based on the dual role of low cost hyperbranched polyethyleneimine (PEI) acting both as a reactive template to control the formation of a siliceous porous network and as a metal chelating agent to facilitate the incorporation of finely dispersed CuO/CeO2 nanoparticles into the silica matrix. Direct Ce(III)/Cu(II) introduction into the reaction mixture or post-synthetic impregnation of a preformed hybrid organic/inorganic xerogel was employed. Materials properties were assessed by means of XRD, SEM, TEM, N2 adsorption, TPR and XPS techniques. Final Cu loading was determined by a novel UV–Vis spectroscopic method. Activity tests were performed under stoichiometric, O2-deficient and O2-rich conditions simulating realistic exhaust environment. Catalytic performance was found to be strongly depended on the employed synthetic pathway. The CuO/CeO2/SiO2 composites prepared by direct introduction, exhibited enhanced structural characteristics (BET≈680m2/g), high homogeneity, superior oxidation performance and notable thermal stability, with great potential for use in automotive aftertreatment systems.

Study on CuO-CeO2/SiC catalysts in the sulfur-iodine cycle for hydrogen production

The structure and activity of ceria–copper oxides supported on nanometer silicon carbide (nano-SiC) particles for sulfuric acid decomposition were studied. The promoting activities and stabilities of CuO–CeO2 complex oxides loaded on nano-SiC grains were prominently higher than those of CuO–CeO2 without carriers, especially at <800 °C. The results of X-ray diffraction (XRD), transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HRTEM) showed that copper-cerium composite oxides grains were well dispersed and fixed on the surface of SiC particle, and the average sizes of CuO–CeO2 complex oxides carried by SiC particles were considerably smaller than those of CuO–CeO2 without carriers. Based on the analysis of HRTEM images, X-ray photoelectron spectroscopy (XPS) spectra, and infrared radiation (IR) pattern, the majority of SiC surfaces were converted to SiO2 layers, in which CeO2 grains immobilized by coordination bonding Ce–O–Si bridges. From the temperature programmed reduction (TPR) patterns, compared with those of CuO–CeO2 without carrier, the reduction temperature of CuO to Cu2O in CuO–CeO2/SiC catalysts was lowered, especially at (Ce + Cu)/SiC atomic ratio of 5 mol.%. The catalysts also showed relatively high activities at 727 °C for 20 h of continuous operation. A mechanism of SO3 decomposition on CuO–CeO2/SiC was proposed according to the characterization results. Copyright © 2016 John Wiley & Sons, Ltd.

Au/CuO–CeO2 catalyst for preferential oxidation of CO in hydrogen-rich stream: Effect of CuO content

A series of Au/CuO–CeO2 with various amounts of CuO was prepared. CuO–CeO2 was prepared by co-precipitation and Au was loaded by deposition–precipitation. The aim of this study was to develop a catalyst which is highly active and selective in preferential oxidation of CO in hydrogen stream (PROX). These catalysts were characterized by N2-sorption, XRD, TEM, HR-TEM, and XPS. The PROX reaction was carried out in a fixed bed continuous flow reactor with a feed of CO: O2: H2: He = 1.33: 1.33: 65.33: 32.01 in volume ratios. The incorporation of copper ion into ceria lattice increased the oxygen storage capacity of ceria and enhanced the activity of the catalyst. The excess CuO would present on the surface of CeO2. Au particles were well dispersed well on the support and the particle size of gold was in the range of 2 and 4 nm. Au was the active species and CuO played the promoter role. Those CuO presented on the surface of CeO had negative effect for CO oxidation. The selectivity of oxygen reacting with CO increased with increasing CuO content. Adding suitable amount of CuO in Au/CeO2 is beneficial for CO conversion and suppressing hydrogen oxidation in fuel cell operation condition.

Influence of calcination temperature on CuO–CeO2/SiC catalysts for SO3 decomposition in the sulfur–iodine cycle for hydrogen production

The copper-cerium composite oxides supported on silicon carbide (SiC) catalysts (CuO–CeO2/SiC) for sulfuric acid decomposition were studied in sulfur-iodine (SI or IS) cycle. The influence of calcination temperatures (800 °C–1000 °C) of CuO–CeO2/SiC catalysts on their activities and morphology were investigated in this study. The activity of CuO–CeO2/SiC was prominently higher than that of CuO–CeO2 composite oxides catalyst. The SO3 conversion ratio of CuO–CeO2/SiC catalyst increased with calcination temperature from 800 °C to 900 °C, while decreased with calcination temperature at 900 °C–1000 °C. XRD pattern, TEM (HRTEM) images and Energy Dispersive X-ray (EDX) spectra revealed that copper–cerium composite oxides were well dispersed and immobilized on the surface of SiC grains. XRD pattern showed that the accelerated transformation of SiC crystals to amorphous SiO2 and the rapid expansion of CeO2 sub-grains at the calcination temperature of 900 °C–1000 °C, as well as the accelerated amorphization of CuO crystals at 800 °C–900 °C. The agglomeration of catalysts with sintering temperature was also proven by the BET test. At a higher calcination temperature, X-ray photoelectron spectroscopy (XPS) of Cu2p spectra revealed the reduction of more Cu2+ in the process of SiC oxidation. According to TEM (HRTEM), XPS, and infrared radiation, the amorphous SiO2 was produced by the oxidation of superficial SiC particles, and the thickness of the SiO2 layers on SiC grains increased with the calcination temperature. A simple mechanism depicted the oxidation of CuO–CeO2/SiC was created.

Novel CeO2–CuO-decorated enzymatic lactate biosensors operating in low oxygen environments

The detection of the lactate level in blood plays a key role in diagnosis of some pathological conditions including cardiogenic or endotoxic shocks, respiratory failure, liver disease, systemic disorders, renal failure, and tissue hypoxia. Here, we described for the first time the use of a novel mixed metal oxide solution system to address the oxygen dependence challenge of first generation amperometric lactate biosensors. The biosensors were constructed using ceria-copper oxide (CeO2–CuO) mixed metal oxide nanoparticles for lactate oxidase immobilization and as electrode material. The oxygen storage capacity (OSC, 492 μmol-O2/g) of these metal oxides has the potential to reduce the oxygen dependency, and thus eliminate false results originated from the fluctuations in the oxygen concentration. In an effort to compare the performance of our novel sensor design, ceria nanoparticle decorated lactate sensors were also constructed. The enzymatic activity of the sensors were tested in oxygen-rich and oxygen-lean solutions. Our results showed that the OSC of the electrode material has a big influence on the activity of the biosensors in oxygen-lean environments. While the CeO2 containing biosensor showed an almost 21% decrease in the sensitivity in a O2-depleted solution, the CeO2–CuO containing electrode, with a higher OSC value, experienced no drop in sensitivity when moving from oxygen-rich to oxygen-lean conditions. The CeO2–CuO decorated sensor showed a high sensitivity (89.3 ± 4 μA mM−1 cm−2), a wide linear range up to 0.6 mM, and a low limit of detection of 3.3 μM. The analytical response of the CeO2–CuO decorated sensors was studied by detecting lactate in human serum with good selectivity and reliability. The results revealed that CeO2–CuO containing sensors are promising candidates for continuous lactate detection.

Boosting soot combustion efficiencies over CuO–CeO2 catalysts with a 3DOM structure

A CuO–CeO2 catalyst with a well-defined 3DOM structure exhibited superior catalytic activity for soot combustion compared to its 3DOM CeO2 counterpart.

Selective catalytic reduction of NO by NH3 over CuO–CeO2 in the presence of SO2

The reaction between NO2 and NH3/NH4+ induced the formation of NHX&lt;3 species with high oxidability; NHX&lt;3 promoted the surface sulfate decomposition; high de-NOX performance was achieved in the presence of SO2 at low temperature.

Fabrication and formation mechanism of Ce2O3–CeO2–CuO–MnO2/CNTs catalysts and application in low-temperature NO reduction with NH3

Ce2O3–CeO2–CuO–MnO2/CNTs catalysts were synthesized via a redox strategy, and presented 58–85% NO conversion at 80–180 °C.