CeO2 Nanocatalysts Research Articles

Characterization of alkaline earth metal-doped CeO2 nanocatalysts and their catalytic activities in the synthesis of dimethyl carbonate through a reaction between methanol and CO2

Alkaline earth metal (Mg2+, Ca2+, Sr2+, and Ba2+)-doped CeO2 nanocatalysts have been prepared by the successive co-precipitation and calcination method.

Effect of morphology and their oxygen vacancies of nanostructured CeO2 catalyst for carboxymethylation of biomass-derived alcohols

An effective and highly selective protocol has been realized for the synthesis of asymmetric organic carbonates using dimethyl carbonate (DMC) as a reactant and solvent. Herein, the performance of CeO2 nanostructures with different morphology was explored in the carbonate interchange reaction (CIR) of alcohols to synthesize asymmetric organic carbonates. The CeO2 nano-catalyst with rod morphology having the highest oxygen vacancy enabled remarkable enhancement in the conversion, to our knowledge this is superior to most of the reported heterogeneous catalytic materials. The CeO2-r (r-rods) is used as low as <0.8 mol% with respect to the limiting reagent (alcohol). The CeO2 characterization data revealed the intriguing properties such as exposed active sites, defect density, coordination state of surface atoms, and reducibility of the catalytic materials are the contributing factors in realizing the highest catalytic activity. The CeO2 was recovered by a simple centrifugation and used in more than four recycles with consistent catalytic activity. The work conducted herein intensifies the utilization of bio-alcohols and CO2 derived DMC for the sustainable synthesis of organic carbonates that have immense applications in various sectors.

Plasma-assisted CO2 decomposition catalyzed by CeO2 of various morphologies

Plasma-assisted catalytic decomposition of CO2 over CeO2 nanocatalysts was investigated in this study. CeO2 nanocatalysts with different morphologies (i.e., cube, rod, and hexagon were prepared by hydrothermal method) were evaluated in a dielectric barrier discharge reaction at room temperature and atmospheric pressure. Among the above catalysts, commercial CeO2 and quartz sands, CeO2 nanorods (CeO2-R) exhibited the highest CO2 conversion under an applied voltage of 8 kV. When the discharge voltage was increased to 9 and 11 kV, all CeO2 catalysts showed increased CO2 conversion with little difference, but when the applied voltage was larger than 11 kV, the difference in catalytic performance became negligible. The better performance of CO2 activation over CeO2-R was attributed to the abundant oxygen vacancies on its exposed (110) crystal plane, which was further confirmed by XPS characterization. Oxygen vacancies on CeO2-R led to twice CO2 adsorption amount compared with the other CeO2 catalysts, and presented a more significant synergistic effect of oxygen vacancies and plasma on CO2 decomposition. The CO2 molecules adsorbed on oxygen vacancies over CeO2-R were partly activated and more easily decomposed in the plasma, resulting in higher CO2 conversion. Meanwhile, the minimum discharge voltage for CO2 decomposition over CeO2-R was 5.0 kV, which was 8.3 kV for commercial CeO2 due to its lowest oxygen vacancy density. However, due to the higher electron density and increased probability for free CO2 splitting under high discharge voltage, most CO2 molecules were activated by the plasma alone, thus less catalyst effect was observed.

Fast Degradation of Tetracycline and Ciprofloxacin in Municipal Water under Hydrodynamic Cavitation/Plasma with CeO2 Nanocatalyst

Although water contamination with drug residues is a threat to public health, there are currently barely any effective methods of purifying water from pharmaceutical substances. In this study, continuous-flow sonoplasma treatment was used for the complete degradation of tetracycline and ciprofloxacin in polluted municipal water. The addition of CeO2 nanoparticles as catalysts significantly increased the degradation rate of the antibiotics, and a degradation degree of 70% was achieved. The presence of reactive oxygen species in the CeO2-nanoparticle-containing sonoplasma-treated system was experimentally proven for the first time using the chemiluminescence technique.

Interface modification of Ru-CeO2 co-infiltrated SFM electrode and construction of SDC/YSZ bilayer electrolyte for direct CO2 electrolysis

A novel electrolysis cell with SDC/YSZ bilayer electrolyte structure and Ru-CeO2 co-infiltrated SFM-SDC electrode has been fabricated by facile drop-coating method and vacuum infiltration process. The drop-coated YSZ thin film facilitates SDC electrolyte to be employed in direct CO2 electrolysis. The results of TPD analysis and AC impedance spectroscopy measurement indicate that the infiltration of Ru and CeO2 nanocatalysts of SFM-SDC electrode significantly enhance the chemical adsorption of CO2 and electrochemical performance of the electrode. With LSM-SDC as the anode, LSM-SDC/YSZ-SDC/Ru-CeO2-SFM-SDC single cell exhibits good coking-resistant and stability for CO2 reduction electrolysis, reaching a peak current density of 1.82 A·cm−2 under an applied voltage of 1.5 V. The combined strategy offers a promising approach to cell structure construction and interface modification for solid oxide electrolysis cells.

Decoy Nanozymes Enable Multitarget Blockade of Proinflammatory Cascades for the Treatment of Multi-Drug-Resistant Bacterial Sepsis.

Sepsis is a life-threatening organ dysfunction characterized by severe systemic inflammatory response to infection. Effective treatment of bacterial sepsis remains a paramount clinical challenge, due to its astonishingly rapid progression and the prevalence of bacterial drug resistance. Here, we present a decoy nanozyme-enabled intervention strategy for multitarget blockade of proinflammatory cascades to treat multi-drug-resistant (MDR) bacterial sepsis. The decoy nanozymes (named MCeC@MΦ) consist mesoporous silica nanoparticle cores loaded with CeO2 nanocatalyst and Ce6 photosensitizer and biomimetic shells of macrophage membrane. By acting as macrophage decoys, MCeC@MΦ allow targeted photodynamic eradication of MDR bacteria and realize simultaneous endotoxin/proinflammatory cytokine neutralization. Meanwhile, MCeC@MΦ possess intriguing superoxide dismutase and catalase-like activities as well as hydroxyl radical antioxidant capacity and enable catalytic scavenging of multiple reactive oxygen species (ROS). These unique capabilities make MCeC@MΦ to collaboratively address the issues of bacterial infection, endotoxin/proinflammatory cytokine secretion, and ROS burst, fully cutting off the path of proinflammatory cascades to reverse the progression of bacterial sepsis. In vivo experiments demonstrate that MCeC@MΦ considerably attenuate systemic hyperinflammation and rapidly rescue organ damage within 1 day to confer higher survival rates (>75%) to mice with progressive MDR Escherichia coli bacteremia. The proposed decoy nanozyme-enabled multitarget collaborative intervention strategy offers a powerful modality for bacterial sepsis management and opens up possibilities for the treatment of cytokine storm in the COVID-19 pandemic and immune-mediated inflammation diseases.

Comparison of different infiltration amounts of CeO2 inside Ni-YSZ anodes to improve stability and efficiency of Single-Chamber SOFCs operating in methane

Electrochemically active oxide-based anodes capable of working in Single-Chamber Solid Oxide Fuel Cells (SC-SOFCs) were developed. Their performance is related to the selectivity of the electrodes. Tests are carried out on lab-scale devices with YSZ pellets as solid electrolytes in electrolyte supported cells. Selecting methane as a fuel, a gas mixture in the ratio CH4/O2 = 2 was chosen. The Ni-YSZ (NiO:YSZ=60:40) anode was optimized through CeO2 nanocatalysts infiltration to enhance the anode catalytic activity and make its reduction easier. Several infiltration amounts were compared, from null to 15% of the electrode weight. Both symmetric and complete cells (with LSCF-based cathodes) were tested in H2 and CH4/O2. For increasing amounts of infiltrated CeO2, symmetric cells tests describe an area specific resistance (ASR) reduction from 40 Ω cm2 to 1.7 Ω cm2 in hydrogen and from 11 Ω cm2 to 3.9 Ω cm2 in the methane/oxygen mixture. While complete cells tests displayed an ASR drop from 30 Ω cm2 to 2.9 Ω cm2 in H2, and from 8.7 Ω cm2 to 4.3 Ω cm2 in the methane/oxygen mixture, while OCP and power grew from 478 mV and 3.7 mW cm-2 to 766 mV and 13 mW cm-2.

Probing the role of surface activated oxygen species of CeO2 nanocatalyst during the redox cycle in CO oxidation.

The oxygen species of CeO2 nanocatalysts plays a key role in the CO oxidation. In this work, nanocrystalline CeO2 with infrared spectroscopy detectable surface superoxide (O2−) species at room temperature is fabricated and CO oxidation is used as a probe reaction for the exploration of the characteristics of surface O2− species on the CeO2 surface. We discover that the surface O2− species have ignorable influences on the overall reaction rate of CO oxidation on pure ceria by comparing P-CeO2 (CeO2 prepared by precipitation method) with HT-CeO2 (CeO2 prepared by hydrothermal method). It is concluded that the reaction between CO molecules and surface O2− species is the first and the fast step in the whole redox cycle, while the release of surface lattice oxygen is the second and the rate determining step of the catalysts. This work gives an intuitionistic exploration on the redox properties of pure nanocrystalline CeO2 with surface O2− species and reveals the influences of these species in the whole redox circle of CO oxidation.

Synergetic effects of green synthesized CeO2 nanorod-like catalyst for degradation of organic pollutants to reduce water pollution

In the last few decades,CeO2 nanoparticles have proven burning candidates in the advanced oxidation process for call-in green and sustainable contrivance for wastewater treatment. Here in we study the consequence of numbers of agents in the advanced oxidation process assisted by H2O2 and CeO2 nano-catalyst for the degradation of model dye methylene blue (MB) and check the kinetics and thermodynamics in detail. CeO2 nano-catalyst, synthesized by a green method using β-cyclodextrin as an excellent stabilizer, exhibited interesting Fenton-like catalytic properties for the degradation of Methylene Blue (MB), Rhodamine B (RhB), and Eriochrome Black T (EBT) in an aqueous solution. XRD and EDAX analysis data suggested that the catalyst consisted of cerium particles covered by CeO2 having band gap 2.34 eV from Tauc plot. SEM and DLS data confirm that the catalyst is a rod-like shape with a 23 nm average hydrodynamic size. The influence of catalyst concentration, H2O2 concentration, pH value, reaction temperature, the effect of acids, and the effect of inorganic salts on the catalyst wasinvestigated. Under optimum conditions Pseudo- first-order fitted well with the experimental data. The formation of.OH radicals via Fenton-like reactions between H2O2 and CeO2 catalyst were responsible for different dye degradation under acidic conditions. The lower activation energy (Ea = 19.38 kJ/mol) for this reaction indicated a very high degradation rate. SEM images of catalyst before and after degradation and same size after four catalytic cycles suggested catalyst's high stability.

Highly efficient and selective heterogeneous catalytic reduction of 2-nitroaniline by cerium oxide nanocatalyst under microwave irradiation

ABSTRACT Efficient nanocatalyst with incredible performance is highly demanding in a heterogeneous catalysis system. Herein, we report the facile fabrication of uniform and highly stable Cerium Oxide nanoparticles (CeO2 NPs), through chemical precipitation method using sodium hydroxide as reducing agent. The synthesized material is characterized through highly sophisticated techniques including UV-Visible, FT-IR, SEM, AFM, XRD, and Zeta Sizer- Potential to check the particle formation, surface morphology, topography, crystalline nature, size, and surface potential. The heterogeneous catalytic performance of CeO2 NPs has been accomplished for the reduction of 2-nitroaniline from the aqueous media. The CeO2 nanocatalyst displayed excellent reusability, while the reduction in several repetitive catalytic cycles against 2-nitroaniline under optimized conditions. The CeO2 nanocatalyst shows 99.12% efficiency within 60s reaction time under a greener source of microwave radiation.

A simple and environmentally benign method for the synthesis of bis(4-hydroxycoumarin) methane derivatives using Nano-CeO2

Coumarins are oxygenated heterocycles that play a structural role in many natural products and have numerous biological activities and therapeutic applications, including anticoagulant activity, antiviral activity, use as an antibiotic, spasmolytic activity, antimicrobial activity, anticancer activity, and antioxidant activity. They also have antifungal, anti-insect, and anti-inflammatory properties and are employed to prevent disease and regulate growth. In addition, they are utilized as food additives and cosmetics. Due to the critical applications of coumarin derivatives, the synthesis of these compounds is of great importance. In this research study, the CeO2 nanocatalyst was exploited as an available catalyst that is also thermally stable in the synthesis of these compounds.

Design, synthesis, and characterization of a porous ceramic-supported CeO2 nanocatalyst for COx-free H2 evolution

The use of fossil fuels threatens environmental systems and causes an increase in greenhouse gas emissions, thereby leading to global warming. Such a scenario has spurred research into renewable hydrogen energy production as a strategy to replace fossil fuels. In this regard, thermochemical water splitting using redox reactions with metal oxides, which generates neither CO nor CO2 gas, is a promising approach with advantages over general hydrocarbon steam reforming. However, preventing catalytic deactivation due to nanocatalyst agglomeration or sintering during thermocycling at high temperatures (>800 °C) is a significant challenge. In this work, the design, synthesis, and characterization of a new CeO2-based catalytic model were carried out through a combination of theoretical and experimental approaches. From thermodynamic simulations, an optimal support material was first selected. A CeO2 nanoparticle-dispersed porous support structure was subsequently synthesized. The recyclable CeO2–support structure showed good capability and repeatability for hydrogen generation during consecutive thermocycles with no undesirable side reactions or particle sintering. It is anticipated that the results of this study will facilitate greater efficiency in the development of catalytic materials and allow for more effective materials to be designed so as to accelerate the realization of economical green energy production based on thermochemical cycles.

CeO2–nanocubes as efficient and selective catalysts for the hydroboration of carbonyl groups

An efficient and reusable CeO2 nanocatalyst has been developed for the selective hydroboration of carbonyl compounds, including aromatic, heteroaromatic, aliphatic, and (hetero)aliphatic aldehydes and ketones.

Improvement the catalytic activity of activated Au/GO–CeO2 nanocatalysts by facile ball milling–hydrothermal methods for PROX operation

Gold-based nanocatalysts have proved to be an appropriate candidate for the selective preferential CO oxidation (PROX) in H2-containing atmosphere. Effectiveness of small gold nanoparticles in the presence of immobilized on GO–CeO2 nanocomposites was investigated by a range of ball milling conditions for the PROX reaction. First, GO–CeO2 nanocomposites were fabricated using the combination of ball milling and hydrothermal methods, and then, the gold nanocomposites were activated at 400 ± 2 °C for 4 h in Ar atmosphere. Next, Au/GO–CeO2 catalysts were synthesized, and after that, the gold nanocontents calcined at 400 ± 2 °C in Ar gas during 4 h. The catalytic activity and selectivity of activated gold catalysts (Au/GO–CeO2) were studied for the preferential CO oxidation at optimized conditions from the ambient temperature to 175 ± 2 °C. The gas and vapor phase components were analyzed by a Fourier Transform Infrared Spectroscopy. The effects of ball mill’s parameters, such as milling time, bead amounts, loading percentage, and milling temperatures, on the catalytic activity and selectivity of gold catalysts were investigated. Under relatively optimized conditions, the results showed the high conversion (C%: 97) and selectivity (S%: 92) for the gold nanocatalysts at 150 °C reaction time towards CO2 as the main product when the Au/GO–CeO2 nanocatalysts were synthesized by the use of 12% of GO solution with 90 zirconia oxide balls at 70 °C for 8 h of the ball milling condition.

Performance and exergy analysis of a diesel engine run on petrodiesel and biodiesel blends containing mixed CeO2 and MoO3 nanocatalyst

In this research, the second law of thermodynamics was employed to analyze the exergy of a diesel engine fueled with diesel–biodiesel blends (B5 and B10) and hybrid nanocatalyst additives at three concentrations (30, 60 and 90 ppm), containing cerium oxide and molybdenum oxide on amide-functionalized multiwall carbon nano tubes (MWCNTs). The research engine was a single-cylinder, four-stroke, direct-injection, air-cooled diesel engine. The exergy analysis was performed under full load conditions, at four engine speeds (1700, 2100, 2500 and 2900 rpm). The results revealed that by increasing the amount of nanocatalysts (CeO2-MWCNTs and MoO3-MWCNTs) in the fuel blends, the net exergy work rate of the diesel engine increased for both fuel blends (B5 and B10). The maximum net exergy work rate of the diesel engine was 7.71 (25.33% of total fuel exergy rate) for the B10 + 90ppm fuel blends at 2500 rpm. The exergy efficiency of the diesel engine ranged from 17.97% to 31% for B5 and 18.3% to 31.7% for B10 fuel blends, respectively. B10 containing 90 ppm nanocatalyst showed the highest exergy efficiency, at an engine speed of 1700 rpm. All fuel blends containing nanocatalyst emitted less carbon monoxide, hydrocarbon and NOx compared with nanocatalyst-free fuel blends.

What are the preferred CeO2 exposed planes for the synthesis of dimethyl carbonate? Answers from theory and experiments

The synthesis of dimethyl carbonate (DMC) from CO2 and methanol was studied on CeO2 nanocatalysts with different exposed planes. The nanocatalysts were prepared by the hydrothermal method from different cerium nitrate precursor salts. XRD and HRTEM were used to characterize the different exposed planes, whereas EPR identified the presence of oxygen vacancies. The CeO2 nanocatalysts were more selective to DMC than the conventional CeO2 material and the results were correlated with the concentration of oxygen vacancies and strength of the basic sites of the materials. The nanocatalyst presenting the (110) plane was the most active and presented the highest concentration of oxygen vacancies. Periodic theoretical calculations, at DFT level, corroborated the experimental results, indicating the preference of CO2 adsorption on the oxygen vacancies of the (110) exposed CeO2 surface, which also led to formation of bidentate carbonate species, a key intermediate on the reaction pathway. The overall results indicated the importance of the (110) exposed plane on the CeO2 surface to increase the catalytic activity to DMC.

Heterostructured CeO2-M (M = Co, Cu, Mn, Fe, Ni) Oxide Nanocatalysts for the Visible-Light Photooxidation of Pinene to Aroma Oxygenates.

Herein, we report the enhanced photocatalytic activity of heterostructured CeO2 nanocatalysts interfaced with Cu, Co, Ni, Mn, and Fe metal oxides. The CeO2 catalysts exhibited an enhanced red shift in the visible-light response compared to CeO2. This improved absorption range effectively suppressed electron (e–)/hole (+h) recombination by forming localized energy bands associated with defect oxygen vacancies (Vo) induced by the Mn+ ions incorporated in CeO2. Under visible-light irradiation, CeO2 catalysts are active for α-pinene oxidation to the aroma oxygenates, pinene oxide, verbenol, and verbenone. Both Fe2O3–CeO2 and NiO–CeO2 gave the highest pinene conversions of 71.3 and 53.1%, respectively, with corresponding pinene oxide selectivities of 57.3 and 58.2%. The enhanced photocatalytic performance of the heterostructured CeO2 catalysts compared to CeO2 is attributed to their enhanced visible-light absorption range and efficient suppression of e–/+h recombination. The Fe2O3–CeO2 catalyst was highly recyclable and did not show any significant loss of its photoactivity.

Insight into the effect of facet-dependent surface and oxygen vacancies of CeO2 for Hg removal: From theoretical and experimental studies

The reaction mechanisms of Hg oxidation on CeO2(111) and (110) surface are clarified by a group of designed experiments and density functional theory (DFT) calculations. CeO2 nanorods and nanoparticles with exposure (110) and (111) faces were prepared by hydrothermal methods, and their morphological properties were investigated using XRD, XPS and HRTEM. Combined experimental and DFT results, the nanorods show better activity than nanoparticles. The total oxidation of Hg can be partially prohibited by the high barriers for the incorporated chlorine activation at reduced surfaces, due to the strong electronic repulsion of heavily accumulated charges. The energy barrier profiles suggest Hg oxidation is much more favorable on CeO2(110) surface than that on CeO2(111) surface. In the Hg oxidation via HCl and O2, the role of O2 is not only replenishment of lattice oxygen, but also could generate surface oxygen as active center for HCl active. The complete catalytic cycle can be identified as four parts: (i) HCl activated by lattice oxygen, (ii) Hg oxidation on defect surface, (iii) HCl activated by adsorbed oxygen and (iv) Hg oxidation on stoichiometric surface. The results of this study provide deep insights into the effects of CeO2 nanocatalyst morphology on the Hg oxidation.

Promotion effect and mechanism of MnOx doped CeO2 nano-catalyst for NH3-SCR

MnOx-CeO2 (denoted as Mn–Ce) nanorod and MnOx-CeO2 nanooctahedra catalysts were synthesized by the hydrothermal method and were used for selective catalytic reduction of NO with NH3. The catalytic performance tests showed that the NO removal efficiency of CeO2 catalysts was obviously improved after loading MnOx. The structure and properties of catalysts had been characterized by SEM、TEM、XRD、BET、XPS、H2-TPR、NH3-TPD and in situ DRIFTS. It was found that Mn–Ce catalyst were of uniform core-shell structure, higher concentrations of Mn4+ and Ce3+, better reducibility, the increase of weak acid sites. The results of in situ DRIFTS indicated that the NH3-SCR reaction should obey the E–R mechanism. Moreover, the promotion effect and mechanism of MnOx doped CeO2 was demonstrated, which improved the catalytic activity of Mn–Ce catalysts.

In-situ fabrication of Ce-rich CeO2 nanocatalyst for efficient CO oxidation

Ceria is widely utilized in the field of CO catalysis due to its outstanding oxygen storage/release capacity (OSC/ORC). In this study, Ce precursor is successfully injected into the plasma electrolytic oxidation (PEO) film in silicate electrolyte through the addition of EDTA-2Na during PEO process. The atomic percentage (at. %) of Ce in PEO film can reach up to 14.80, which is the highest among all the related works. Annealing treatment in air ambient leads to the crystallization and oxidation reaction of Ce species, which mainly exist in the PEO film in amorphous phase and Ce4.667(SiO4)3O. During the annealing process, CeO2 nanocrystals (∼100 nm) are generated under the confinement of amorphous SiO2 layer in PEO film. Subsequent etching treatment removes the amorphous SiO2 capping layer and triggers the catalytic activity of CeO2 nanocrystals. CO oxidation test reveals that these CeO2 nanocatalysts own remarkable catalytic activity in CO oxidation and show strong synergistic effect with noble metal (Au). This study establishes an efficient in-situ fabrication route for the preparation of highly active metal-supported ceria nanocatalysts with strong substrate adherence, showing overwhelming advantage compared with traditional catalyst preparation methods, which is promising for the direct integration of various oxide catalysts towards CO oxidation, TWCs, SCR, etc.