Ceria Nanocubes Research Articles

Morphology dependence of catalytic properties of Ni/CeO2 for CO2 methanation: A kinetic and mechanism study

• Ceria nanorods (NR) and nanocubes (NC) are prepared with hydrothermal method. • Ni/CeO 2 -NR holds a higher number of Ce 3+ proportion compared with Ni/CeO 2 -NC. • Ni/CeO 2 -NR shows a higher activity than Ni/CeO 2 –NC. • CO 2 methanation on Ni/CeO 2 goes through a formate route. • The oxygen vacancy are active sites for the formate formation. Ceria has been used for catalyst support for long time due to its unique structural properties resulting from oxygen vacancies and reversible valence change (Ce 4+ and Ce 3+ ). In this report, ceria nanorods (NR) and nanocubs (NC) were prepared with hydrothermal method and 5 wt% nickel was loaded on it. The effect of morphology of ceria supports for CO 2 methanation reaction was studied. Characterization including TPR, TEM, XRD and XPS shows that Ni/CeO 2 -NR had a higher number of Ce 3+ proportion compared with Ni/CeO 2 -NC. Both catalysts showed high conversion and selectivity for methane at low temperature range at200–250 °C and interestingly Ni/CeO 2 -NR exhibited a higher activity than Ni/CeO 2 –NC. A kinetic study and DRIFTs investigation were carried out to formulate the mechanism. It turned out that CO 2 methanation on Ni/CeO 2 goes through a formate route instead of CO 2 dissociation and the oxygen vacant sites are supposed to be the active sites for the formate formation in this mechanism.

Chitosan-coated cerium oxide nanocubes accelerate cutaneous wound healing by curtailing persistent inflammation

Chitosan-coated ceria nanocubes accelerate cutaneous wound healing by curtailing persistent inflammation with powerful anti-inflammation and anti-oxidation properties.

The effect of Eu doping on the growth, structure and red-ox activity of ceria nanocubes

The ordering of oxygen vacancies (in high Eu-doped (x ≥ 0.1) ceria nanoparticles) facilitates the process of Ce4+ to Ce3+ reduction.

Nano-architectured CeO2 supported Rh with remarkably enhanced catalytic activity for propylene glycol reforming reaction in microreactors

The influence of morphology and crystalline facets of nanoshaped ceria oxide support in Rh/CeO2 and Rh/CeO2/Al2O3 catalysts have been investigated by oxidative steam reforming of propylene glycol in microreactors at 630 °C at S/C = 3.5 and O/C = 0.15. First, well−defined ceria nanorods (NRs) and nanocubes (NCs) have been successfully synthesized by a facile hydrothermal method and then they are deposited on to α−Al2O3. The result of transmission electron microscopy indicates that the ceria nanorods exposed (110) and (100) planes but nanocubes possess only (100) planes. The developed shape controlled ceria nanocrystals and they are mixed with alumina have been used as supports for the preparation of highly dispersed and size controlled Rh nanoparticles of Rh/CeO2 and Rh/CeO2/Al2O3 catalysts. Their performance was tested for the propylene glycol reforming reaction in microreactors, which provide high surface of the catalyst coatings, heat and mass transfer rate and controllability. The XPS and TEM results indicate that the CeO2 morphology shows the selective exposure of different crystal planes which has a significant impact on the dispersion of Rh nanoparticles that influenced in the reforming reaction. The steam reforming reaction experiments show that the ceria nanorods supported Rh catalyst was achieved significantly better activity and stability for 100 h of time on stream than for the all other catalysts. This could be related to the better dispersion of Rh species and the higher surface oxygen vacancies associated with the exposed (100) and (110) crystal planes favor the stabilization of Rh nanoparticles against sintering and elimination of carbon deposition on active Rh nanoparticles during reforming reaction.

Controllable Synthesis and Growth Mechanism of Ceria Nanocubes by Template‐Free Hydrothermal Method

AbstractDifferent crystal planes of CeO2 have a different number of broken bonds, surface energy and catalytic activities, so preparing the CeO2 with different exposed planes has attracted extensive attention. In recent years, the preparation of CeO2 nanocubes with {100} exposed plane has been a real hotspot of research because of its good catalytic performance. Based on the research about the alkali concentration, reaction temperature and reaction time, the formation mechanism of CeO2 nanocubes was explored. It is believed that the dissolution‐recrystallization process is accelerated in the condition of strong base, high temperature and high pressure. In other word, the Ostwald ripening process is strengthened, which is the decisive factor for the formation of CeO2 nanocubes.

Optimization and detailed stability study on Pb doped ceria nanocubes for enhanced photodegradation of several anionic and cationic organic pollutants

A series of Pb doped CeO2 nanocubes with seven different Pb loadings (2–12 mol%) were synthesized via modified hydrothermal technique. The prepared samples were characterized by XRD, XPS, FT-IR, TGA, SEM, HR-TEM, EDS and UV–Vis DRS analysis. According to XRD analysis, the crystalline structure of synthesized pure CeO2 and Pb-doped CeO2 samples are cubic structure. The ceria nanocubes showed an increase in amount of oxygen vacancies with increasing the dopant concentrations. When the doping level of Pb is 6 mol%, the optical band gap of Pb-CeO2 is smaller than that of pure CeO2 nanocubes. The HR-TEM results confirms the cubic structure of 6% Pb-CeO2 with average crystallite size of about 15 nm. The photocatalytic ability of Pb-CeO2 catalysts were studied by degrading several anionic and cationic organic pollutants like methylene blue (MB), methylene orange (MO), methylene red (MR), rhodamine B (RhB), reactive blue 160 (RB160), salicylic acid (SA), coumarin and phenol. The 6% Pb-CeO2 nanocubes shows better photocatalytic performance against anionic dyes especially for MB. To find the optimum condition for better photocatalytic performance of 6% Pb-CeO2 nanocubes, the photocatalytic process was conducted in different initial reaction conditions like reaction temperature, catalytic dosage, dye concentration and pH of the reaction solution. The stability and recyclability of 6% Pb-CeO2 photocatalyst was studied by XRD, FT-IR and EDS analysis after 5 cycles of MB degradation. The hydroxyl radical estimation and trapping experiments were conducted to observe the photocatalytic mechanism process in 6% Pb-CeO2 nanocubes. The perfect doping concentration for better organic pollutant degradation by Pb-CeO2 is found to be 6 mol% of Pb.

Oxygen vacancy clusters essential for the catalytic activity of CeO2 nanocubes for o-xylene oxidation

Catalytic oxidation of o-xylene was investigated on CeO2 nanocubes calcined at 350, 450, 550, and 650 °C, among which the samples calcined at 550 °C exhibited the highest activity and long durability. Positron annihilation spectroscopy measurements revealed that the size and distribution of oxygen vacancies for CeO2 nanocubes could be tuned by carefully controlling the calcination temperature. An excellent linear correlation between a factor related to size and density of oxygen vacancy clusters and reaction rate of o-xylene oxidation was revealed on ceria nanocubes. This means that oxygen vacancy clusters with suitable size and distribution are responsible for catalytic reaction via simultaneous adsorption and activation of oxygen and o-xylene. Electron spin resonance spectra revealed that over the CeO2 cubes, water vapor significantly promoted the formation of ∙OH radicals with a sharp decrease in the signals relating to oxygen vacancies, accelerating the transformation of o-xylene to the intermediate benzoate species, resulting in an enhancement of catalytic activity. Water thus serves as a “smart” molecule; its introduction into the feed mixture further confirmed the key role of oxygen vacancies in the catalytic performance of CeO2 nanocubes. A possible mechanism of oxygen vacancy formation during the calcination process was also proposed.

Control synthesis of CeO2 nanomaterials supported gold for catalytic oxidation of carbon monoxide

CeO2 show excellent performance in catalysis due to its oxygen vacancies, high oxygen storage capacity and easy conversation between Ce3+ and Ce4+ oxidation states. The ceria nano-materials with different morphologies were prepared with hydrothermal methods in the present work. It is found that the gold particles on ceria prepared via incipient wetness impregnation method are smaller and more uniform than those prepared via deposition-precipitation method (Applied Surface Science 2017, 416, 183–190). The incipient wetness impregnation method prepared samples also show better catalytic performance for CO oxidation than the samples prepared via deposition-precipitation method. Characterization results reveal that the small sizes as well as the oxidation states of the gold nanoparticles contribute to the higher activity than the deposition-precipitation samples. For the incipient wetness impregnation samples, the 0.5%Au/CeO2NT could reach 100% CO conversion at 70°C, which shows much better activity and stability than the 0.5%Au/CeO2rod and 0.5%Au/CeO2NC. XPS results indicates that this is because the higher Ce3+/Ce4+ and Auδ+/Au0 of 0.5%Au/CeO2NT than 0.5%Au/CeO2rod and 0.5%Au/CeO2NC, since the presence of a specific Auδ+-Ce3+ structure promotes the adsorption of molecular oxygen and further favors the oxidation of CO. In addition, the gold nanoparticle could grow into larger particles on the ceria nanocubes and leads to the deactivition of the catalysts. In contrast the ceria nanorod and nanotube supported catalysts show excellent stability.

Mesoporous Ceria‐Supported Gold Catalysts Self‐Assembled from Monodispersed Ceria Nanoparticles and Nanocubes: A Study of the Crystal Plane Effect for the Low‐Temperature Water Gas Shift Reaction

AbstractMesoporous CeO2 colloidal spheres were obtained by the assembly of CeO2 nanocrystals in two shapes: nanoparticles (NPs) and nanocubes (NCs). CeO2 colloidal spheres assembled by nanoparticles (NPCS) have predominantly exposed {1 1 1} surfaces and that assembled by nanocubes (NCCS) are terminated by {1 0 0} planes. The size and surface area of NPCS and NCCS are comparable. We compared the water gas shift reaction activity over Au/NPCS and Au/NCCS to clarify the nanoscale crystal plane effect of the CeO2 {1 0 0} and {1 1 1} crystal planes. Au/NCCS and NCCS show a better catalytic activity than Au/NPCS and NPCS towards the water gas shift reaction. We used in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to confirm that the water gas shift reaction over Au/NPCS and Au/NCCS follows a formate mechanism and to prove that the formation/decomposition rate of bidentate formates (intermediates) are faster on Au/NCCS and that less monodentate carbonates (inactive species) are accumulated over Au/NCCS. We used X‐ray photoelectron spectroscopy and DRIFTS combined with DFT calculations to demonstrate that more active Auδ+ species could be formed on NCCS than NPCS because of the crystal plane effect. The crystal plane effect is also embodied in the experimental phenomenon that H2O adsorption is more significant on Au/NCCS than Au/NPCS, which is in agreement with the calculation results that H2O adsorption is more facile on CeO2 {1 0 0} than {1 1 1} surfaces.

Predicting NOx Catalysis by Quantifying Ce3+ from Surface and Lattice Oxygen

Our work introduces a novel technique based on the magnetic response of Ce3+ and molecular oxygen adsorbed on the surface of nanoceria and ceria-based catalysts that quantifies the number and type of defects and demonstrates that this information is the missing link that finally enables predictive design of NOx catalysis in ceria-based systems. The new insights into ceria catalysis are enabled by quantifying the above for different ceria nanoparticle shapes (i.e., surface terminations) and O2 partial pressure. We used ceria nanorods, cubes, and spheres and evaluated them for catalytic reduction of NO by CO. We then demonstrated the quantitative prediction of the reactivity of nanomaterials via their magnetism in different atmospheric environments. We find that the observed enhancement of reactivity for ceria nanocubes and nanorods is not directly due to improved reactivity on those surface terminations but rather due to the increased ease of generating lattice defects in these materials. Finally, we demonstrate that the method is equally applicable to highly topical and industrially relevant ceria mixed oxides, using nanoscale alumina-supported ceria as a representative case-a most ill-defined catalyst. Because the total oxide surface is a mixture of active ceria and inactive support and ceria is not likely present as crystallographically well-defined phases, reactivity does not easily scale with surface area or a surface termination. The key parameter to design efficient NO reduction in ceria-based catalysts is knowing and controlling the surface localized excess Ce3+ ion areal density.

Atomic scale environmental transmission electron microscopy study of the surface mobility of ceria nanocubes

Journal Article Atomic scale environmental transmission electron microscopy study of the surface mobility of ceria nanocubes Get access M Bugnet, M Bugnet University of Lyon, INSA-Lyon, UCBL Lyon 1, MATEIS, UMR 5510 CNRS, 69621 Villeurbanne Cedex, France Search for other works by this author on: Oxford Academic Google Scholar S H Overbury, S H Overbury Chemical Science Division, Center for Nanophase Materials Science, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA Search for other works by this author on: Oxford Academic Google Scholar Z Wu, Z Wu Chemical Science Division, Center for Nanophase Materials Science, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA Search for other works by this author on: Oxford Academic Google Scholar F J C S Aires, F J C S Aires University of Lyon, UCBL Lyon 1, IRCELYON, UMR 5256 CNRS, 69100 Villeurbanne, France Search for other works by this author on: Oxford Academic Google Scholar T Epicier T Epicier University of Lyon, INSA-Lyon, UCBL Lyon 1, MATEIS, UMR 5510 CNRS, 69621 Villeurbanne Cedex, France Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 23, Issue S1, 1 July 2017, Pages 898–899, https://doi.org/10.1017/S1431927617005153 Published: 04 August 2017

Improved Oxidase Mimetic Activity by Praseodymium Incorporation into Ceria Nanocubes.

Ceria nanocubes (NC) modified with increasing concentrations of praseodymium (5, 10, 15, and 20 mol %) have been successfully synthesized by a hydrothermal method. The as-synthesized Pr-modified ceria nanocubes exhibit an enhanced oxidase-like activity on the organic dye TMB within a wide range of concentrations and durations. The oxidase activity increases with increasing Pr amounts in Pr-modified ceria nanocubes within the investigated concentration range. Meanwhile, these Pr-modified ceria nanocubes also show higher reducibility than pure ceria nanocubes. The kinetics of their oxidase mimetic activity is fitted with the Michaelis-Menten equation. A mechanism has been proposed on how the Pr incorporation could affect the energy level of the bands in ceria and hence facilitate the TMB oxidation reaction. The presence of Pr3+ species on the surface also contributes to the increasing activity of the Pr-modified ceria nanocubes present higher oxidase activity than pure ceria nanocubes.

CuO nanoparticles supported by ceria for NOx-assisted soot oxidation: insight into catalytic activity and sintering

The current work introduces Cu nanoparticles (Cu-NPs) stabilized by organosilane and deposited as CuO-NPs onto ceria with two different morphologies: spongy, microstructured ceria synthesized by Solution Combustion (CeO2-SCS) and nanostructured ceria nanocubes (CeO2-NC). Catalytic activity tests have demonstrated that combination of CuO-NPs and CeO2-SCS bring significance to CO and NO oxidations as it results in easier reducibility and better metal dispersion on the surface. However, CuO-NPs with CeO2-NC give the opposite effect on CO and NO oxidations: the increase of Cu loading lowers the catalytic activity. However, Cu/CeO2-NC combination, especially the one with low Cu loading, gives the best synergy for normal soot oxidation with oxygen, thanks to the structure-sensitivity of the reaction. In the presence of NOx, Cu/CeO2-SCS catalysts are active for soot oxidation at low temperature as the catalysts favor early NO2 formation. Lastly, a series of repeated tests with NOx-assisted soot oxidation was carried out to confirm that CuO-NPs suffer easily from particle sintering, possibly via migration and coalescence.

Gold supported on ceria nanotubes for CO oxidation

CeO2 is a typical of fluorite structure, semiconductor material, has high oxygen storage capability as well as unique redox property, which is widely used as catalysts supports in catalysis. Ceria nanotubes and nanocubes are prepared via hydrothermal method in the present work, and Au/CeO2 catalysts are prepared using deposition-precipitation technique with HAuCl4 as gold precursor. The prepared samples were used as catalysts for the CO oxidation reaction using a fix-bed reactor at 50–130°C and characterized by XRD, BET, SEM, TEM, XPS, TPR and ICP. It is found that CeO2-NT and CeO2-NC expose different surface planes. The XPS and H2-TPR results illustrates that the {110} surface exposed by CeO2-NT has stronger interaction with gold particles, which benefits the electron and oxygen transfer between Au and ceria. All these characters of the Au/CeO2-NT(3%) result in the better activity and stability than the Au/CeO2-NC(3%).

Fast MAS 1H NMR Study of Water Adsorption and Dissociation on the (100) Surface of Ceria Nanocubes: A Fully Hydroxylated, Hydrophobic Ceria Surface

1H nuclear magnetic resonance (NMR) spectroscopy was used to study hydroxylic surface species on ceria nanocubes, a crystalline, high-surface-area CeO2 that presents mostly (100) facets. Water adsorption and desorption experiments in combination with fast magic angle spinning (MAS, 20–40 kHz) 1H NMR provide high-resolution 1H spectra that allow the observation of ten resonance bands (water or hydroxyl) on or under the (100) surface. Assignments were made using a combination of adsorption and temperature-programmed desorption, quantitative spin counting, deuterium exchange, spin–lattice (T1) and spin–spin (T2) relaxation, and DFT calculations. In air, the (100) surface exists as a fully hydroxylated surface. Water adsorption and dissociation on dry ceria surfaces occur first at oxygen vacancies, but Ce3+ centers are not required since water dissociation is barrier-less on the fully oxidized surface. Surface −OH functionality occurs in two resolved bands representing isolated −OH (1 ppm) and hydrogen-bonded...

Ceria-supported small Pt and Pt3Sn nanoparticles for NOx-assisted soot oxidation

Introduced herein are small Pt and Pt3Sn nanoparticles, stabilized with organosilane or organostannane and impregnated on ceria support, as active sites for NOx-assisted soot oxidation reaction. The catalysts have been tested with four reactions: CO oxidation, NO oxidation, NOx-free soot oxidation and finally NOx-assisted soot oxidation. Our Pt nanoparticles reportedly possess remarkable catalytic activities in CO oxidation, as they actively convert CO at 50°C, while the alloy Pt3Sn nanoparticles are active at higher temperature. The Pt nanoparticles also mediate more actively NO oxidation than their alloy counterpart, leading to more NO2 production beneficial for soot oxidation. The influence of Pt and Pt3Sn active sites on the catalytic activity during NOx-free soot oxidation becomes less prominent than the morphology, due to the high dependency of the reaction on catalyst structure. The presence of Sn, nevertheless, induces lower oxidation reaction temperature. Finally, in the presence of NOx, the metal active sites undoubtedly boost the catalytic activity of soot oxidation. Pt/CeO2-NC (NC stands for “nanocubes”), reported herein as our most achieving catalyst, demonstrates a remarkable activity, lowering the oxidation temperature at about 80°C, thanks to the synergy of the active metal nanoparticles and reactive ceria nanocubes. Surprisingly, the catalytic activity of the alloy counterpart (Pt3Sn/CeO2-NC) is close to Pt/CeO2-NC, indicating the potential of the catalyst as an alternative to reducing the employment of precious metal in automotive catalysis. The thermally aged Pt catalysts have demonstrated good resistance to sintering, thanks to the outer protection by silica patches. However, the catalytic activities of the aged Pt3Sn catalysts rely heavily on support morphology.

Study on the thermal stability of Ce0.8Gd0.2O1.9 nanocubes on Al2O3 and SiO2 supports

The structural evolution of the Ce0.8Gd0.2O1.9 nanocubes supported on Al2O3 and SiO2 was investigated in oxidizing and reducing atmosphere over a temperature range up to 1100°C by XRD, TEM and SEM–EDS methods. The supported Ce0.8Gd0.2O1.9 particles preserved perfect cubic shape to 900°C in oxidizing atmosphere and to 750°C in a hydrogen atmosphere. No evidence of crystalline aluminate or silicate formation was observed for both supports during heating in oxidizing atmosphere up to 1100°C. However, for Ce0.8Gd0.2O1.9/SiO2 segregation of Gd3+ from the mixed oxide and its spreading over the silica surface was noticed at 1000°C–1100°C. Crystalline aluminate/silicate occurred in a hydrogen atmosphere already at 900°C. Apatite type (Ce,Gd)4.67(SiO4)3O mixed silicate was formed after reaction with SiO2 substrate, while monoclinic (Gd,Ce)4Al2O9 and tetragonal (Ce,Gd)AlO3 were formed on Al2O3. The (Gd,Ce)4Al2O9 phase became unstable at 950°C and transformed into (Ce,Gd)AlO3 aluminate, which was stable up to 1100°C. Various mechanisms of the solid-state reaction of mixed ceria with Al2O3 and SiO2 supports operate depending on the size of ceria nanocubes. Small particles (10–30nm) reacted as a whole with the support forming single crystal silicate or aluminate; at the same time, for bigger particles (30–80nm) reactions happen only near the boundary between the particle and the support.

New insights into the support morphology-dependent ammonia synthesis activity of Ru/CeO2catalysts

Different morphologies ceria (nanocubes, nanorods and nanoparticles) were synthesized and exhibited significant support-morphology-dependent catalytic activity towards ammonia synthesis.

新機能創製に向けた無機ナノクリスタルの高次構造制御

To fine-tune the properties of ceramics, they can now be processed into uniform-size nanocrystals with spherical, cube, sheet, rod, wire shapes. Another trend in research aims at arranging individual nanocrystals into superlattices and investigating their unique properties. Despite these recent advances, controlling the shape, crystal structure, and surface characteristics of ceramic nanocrystals is still a difficult task. Here, we report an approach to tailor-made ceramic nanocrystals by means of organic ligand-assisted hydrothermal method. We succeeded in the synthesis of the ceramic nanocrystals such as ceria (CeO2) nanocubes and titania (TiO2) nanosheets. Also importantly, the use of water, instead of an organic solvent, provides an environmentally benign “green” chemistry route to nano building blocks for advanced materials and devices.

Relationship between morphology and structure of shape‐controlled CeO2 nanocrystals synthesized by microwave‐assisted hydrothermal method

The influence of synthesis conditions on morphology and structure of CeO2 nanocrystals prepared by microwave‐assisted hydrothermal method were studied by XRD, TEM, Raman spectroscopy and photoluminescence measurements. Decisive effect of the OH‐/Ce3+ molar ratio in the reaction mixture on the size and shape of CeO2 nanocrystals was established and explained. Rise of the concentration of OH‐ groups at the surface of growing CeO2 nanocrystals promotes shape transformation from irregular (spheroidal) to cube and enables oriented attachment mode of particle growth. I was found that the unit cell parameter and intensity of Ce3+ defect related band in the luminescence and Raman spectra in ceria nanoparticles increase as follows: irregular shape nanocrystals < large cube < small primary cube shape particles. The reason is growing contribution of total subsurface volume under {100} faces, exposed by ceria nanocubes, where enhanced concentration of Ce3+ and oxygen vacancies occur.