Porous CeO2 Research Articles

Photochemical Deposition of Highly Dispersed Pt Nanoparticles on Porous CeO2 Nanofibers for the Water‐Gas Shift Reaction

Ceria (CeO2) nanofibers with high porosity are fabricated using an approach involving sol–gel, electrospinning, and calcination. Specifically, cerium(III) acetylacetonate and polyacrylonitrile (PAN) are dissolved in N,N‐dimethylformamide (DMF) and then electrospun into nanofibers. The PAN matrix plays a critical role in stabilizing the porous structure from collapse during calcination in air up to 800 °C. CeO2 porous nanofibers comprising an interconnected network of single crystalline and fully oxidized CeO2 nanoparticles about 40 nm in size are obtained. The hierarchically porous structure of the CeO2 nanofibers enables the facile deposition of Pt nanoparticles via heterogeneous nucleation in a photochemical method. When conducted in the presence of poly(vinyl pyrrolidone) (PVP) and 4‐benzyolbenzoic acid, uniform Pt nanoparticles with an average diameter of 1.7 nm are obtained, which are evenly dispersed across the entire surface of each CeO2 nanofiber. The high porosity of CeO2 nanofibers and the uniform distribution of Pt nanoparticles greatly improve the activity and stability of this catalytic system toward the water‐gas shift reaction. It is believed that this method could be extended to produce a variety of catalysts and systems sought for various industrial applications.

Chemically controlled growth of porous CeO2 nanotubes for Cr(VI) photoreduction

A nanowire-directed templating solution-based synthesis strategy was developed to selectively prepare uniform CeO2 nanotubes and heterostructured nanowires by fine-tuning surface chemistry of K1.33Mn8O16 nanowires. The morphology of CeO2 nanotubes and the decorative growth of solid CeO2 particles on K1.33Mn8O16 nanowires changed as the concentration of sodium dodecyl benzene sulfonate (SDBS) was altered. The resultant porous CeO2 nanotubes showed excellent water purification performance for oxalic acid-induced photocatalytic reduction of Cr(VI) under UV light irradiation at room temperature. The enhanced ability for Cr(VI) photoreduction on the obtained CeO2 nanotubes were investigated. Our findings provide a new means to chemically controlled growth of CeO2 nanostructures and demonstrate a highly robust and potential material for the purification of Cr(VI) polluted water.

Yolk–shell Au@CeO2 microspheres: Synthesis and application in the photocatalytic degradation of methylene blue dye

Porous micro- and nanostructured materials with the desired morphologies are of great interest because of their potential applications in environmental remediation. In this study, novel yolk–shell Au@CeO2 microspheres were prepared from glucose and metal salt precursors via a one-pot hydrothermal synthesis followed by precipitation and calcination. These core/shell structure were characterized by scanning electron microscope, transmission electron microscope, X-ray diffraction, Fourier transform Infrared Spectrometer, X-ray photoelectron spectroscopy and N2 adsorption–desorption techniques. These rattle-type spheres were found to compose of a porous CeO2 shell (thickness≈45nm) and a solid gold core (diameter≈50±20nm) with variable space between the core and the shell. The photocatalytic degradation of methylene blue dye was used as a catalytic test reaction revealing that the activity of the yolk–shell spherical products was substantially higher than that of their hollow counterparts. These new core/shell structures with encapsulated gold nanoparticles may exhibit potential applications in catalysis and adsorption.

A facile synthesis for hierarchical porous CeO2 nanobundles and their superior catalytic performance for CO oxidation

Porous CeO2 nanobundles with hierarchical nanoarchitecture show much better catalytic activities for CO oxidation compared to CeO2 nanorods, nanowires and nanoparticles.

High catalytic performances of CeO2–CrOx catalysts for chlorinated VOCs elimination

A series of porous CeO2–CrOx mixed oxides are synthesized using different precipitants (NaOH, NH4OH, (NH4)2CO3 and urea) and evaluated for deep oxidation of various chlorinated VOCs (CH2Cl2, C2HCl3, C2H4Cl2 and C6H5Cl). The results show that all these materials represent porous structures and small particle sizes (2–8nm). Part of Cr element can go into the lattice of CeO2, resulting in the formation of Ce–Cr–O mixed oxide. Compared with pure CeO2 and Cr2O3, the amount of Cr6+ species and oxygen vacancies in CeO2–CrOx mixed oxides are significantly increased, due to the strong interaction between CeO2 and CrOx. Thus, all the CeO2–CrOx mixed oxides exhibit high catalytic activity and good durability for deep oxidation of chlorinated VOCs, especially the CeO2–CrOx prepared using (NH4)2CO3 as precipitant. Moreover, only slight chlorinated byproducts are detected in the process of chlorinated VOCs oxidation, and the surface accumulation of coke and Cl species as well as the loss of Cr element is slight during the long-term reaction at 265°C, indicating that these CeO2–CrOx materials possess interesting fundamental result, deserving more research before conclusion on practical value.

Facile synthesis of porous metal oxide nanotubes and modified nafion composite membranes for polymer electrolyte fuel cells operated under low relative humidity.

We describe a facile route to fabricate mesoporous metal oxide (TiO2, CeO2 and ZrO1.95) nanotubes for efficient water retention and migration in a Nafion membrane operated in polymer electrolyte fuel cell under low relative humidity (RH). Porous TiO2 nanotubes (TNT), CeO2 nanotubes (CeNT), and ZrO1.95 (ZrNT) were synthesized by calcining electrospun polyacrylonitrile nanofibers embedded with metal precursors. The nanofibers were prepared using a conventional single spinneret electrospinning technique under an ambient atmosphere. Their porous tubular morphology was observed by SEM and TEM analyses. HR-TEM results revealed a porous metal oxide wall composed of small particles joined together. The mesoporous structure of the samples was analyzed using BET. The tubular morphology and outstanding water absorption ability of the TNT, CeNT, and ZrNT fillers resulted in the effective enhancement of proton conductivity of Nafion composite membranes under both fully humid and dry conditions. Compared to a commercial membrane (Nafion, NRE-212) operated under 100% RH at 80 °C, the Nafion-TNT composite membrane delivered approximately 1.29 times higher current density at 0.6 V. Compared to the Nafion-TiO2 nanoparticles membrane, the Nafion-TNT membrane also generated higher current density at 0.6 V. Additionally, compared to a NRE-212 membrane operated under 50% RH at 80 °C, the Nafion-TNT composite membrane exhibited 3.48 times higher current density at 0.6 V. Under dry conditions (18% RH at 80 °C), the Nafion-TNT, Nafion-CeNT, and Nafion-ZrNT composite membranes exhibited 3.4, 2.4, and 2.9 times higher maximum power density, respectively, than the NRE-212 membrane. The remarkably high performance of the Nafion composite membrane was mainly attributed to the reduction of ohmic resistance by the mesoporous hygroscopic metal oxide nanotubes, which can retain water and effectively enhance water diffusion through the membrane.

Morphology control and characterization of broom-like porous CeO2

Abstract In this study, CeO2 with a broom-like porous hierarchical structure was successfully prepared by a simple template-free hydrothermal method. In the whole hydrothermal process, reaction time and temperature play important roles in morphology control. The morphology of the as-prepared samples was characterized by field emission scanning electron microscopy, transmission electron microscopy and high-resolution transmission electron microscopy. Structure information was obtained by using an X-ray diffractometer and Raman analysis. Analyses of elements and chemical valence analysis were carried on X-ray photoelectron spectroscopy. Absorption edge and band gap energy were investigated by UV–vis diffuse reflectance. In addition, the optimum experimental conditions for target products were determined. Compared with various morphology samples’ BET data, relative intensity of Raman peaks, catalytic evaluation, we can draw a conclusion that CeO2 with a broom-like porous hierarchical structure has a higher concentration of oxygen vacancies that results in enhancement of catalytic activity. An Ostwald ripening process with orientative self-assembly was proposed for formation of the broom-like porous hierarchical structure.

Sponge phase producing porous CeO2 for catalytic oxidation of CO.

The aggregation behavior of mixtures of the alkaline amino acid L-Arginine (L-Arg) and bis(2-ethylhexyl)phosphoric acid (DEHPA) in water was studied in detail. At a fixed L-Arg concentration, a phase sequence of micellar phase (L1 phase), vesicle phase (Lαv phase), planar lamellar phase (Lαl phase), and sponge phase (L3 phase) was obtained with increasing DEHPA concentration due to changes in the packing parameter. The phase transition of the lamellar structures was determined by freeze-fracture TEM and (2)H NMR spectroscopy. Rheological measurements reflected the phase transition through significant variations of both the elastic modulus and the viscous modulus. Porous CeO2 materials were produced by utilizing the L3 phase as template, and the porous CeO2 exhibited excellent catalytic oxidation activity toward CO due to its high surface area, which provides more active sites for CO conversion.

Surface status and reduction behavior of porous ceria (CeO2) via amended EISA method

Ceria (CeO2) powder with multi-scale porosity was synthesized by evaporation induced self-assembly (EISA) strategy using tri-block copolymer (P123) as the template. The product was characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), transmission electronic microscopy (TEM), and N2 adsorption–desorption isotherms. Reducing property and repeatability were tested by temperature programmed H2 reduction (TPR). Oxygen storage capacity (OSC) was calculated according to the Gaussian–Lorentz deconvolving to the TPR curves. The results showed that the product possessed multi-scale porosity, sizes of the pores were in the ranges of ∼40μm, ∼2μm and <0.3μm, respectively. Specific surface area of the porous CeO2 was 32.5m2/g. Mechanism in the reduction of surface, near surface and inner parts of porous CeO2 were discussed. Carbonate groups remained on the surface when CeO2 were calcined below 600°C. The initial H2-TPR yielded an OSC of 383mol O2/g, which was attributed to oxygen release from the surface nanocrystals, (near) surface sites as well as the inner parts. While the repeated tests showed an OSC of 418mol O2/g, which was associated with the diminished reaction before 620°C and the enhanced reduction around 782°C. A schematic was proposed for the preparation of CeO2 with multi-scale porosity in the amended EISA strategy, based on the characterization results, and the strategy may provide a candidate to obtain catalyst with excellent properties.

Bottom-up synthesis of cerium–citric acid coordination polymers hollow microspheres with tunable shell thickness and their corresponding porous CeO2 hollow spheres for Pt-based electrocatalysts

Cerium–citric acid CPs hollow spheres and the electrocatalytic properties of Pt/CeO2 hollow spheres.

Improved visible-light-driven photocatalytic activity of CeO2 microspheres obtained by using lotus flower pollen as biotemplate

Porous CeO2 spheres were fabricated through mineralizing lotus flower pollen template via a cerium nitrate infiltration. The resulting products were characterized by FESEM, HRTEM, XRD, nitrogen adsorption, and UV–vis diffuse reflectance spectroscopy. The as-prepared photocatalyst exhibited a large surface area and multiple pore size distribution, which could effectively increase the reaction area and allow better catalytic capability. Surface oxygen activity was enhanced for the biomorphic ceria spheres, as was revealed by XPS measurements. The formation mechanism of hierarchical cerium dioxide microspheres was proposed. Moreover, the synthesized ceria shows high photocatalytic activity and exhibits remarkable ability to remove methylene blue under solar irradiation, suggesting they are promising photocatalyst for wastewater treatment.

Synthesis and Stability of Pd@CeO2 Core–Shell Catalyst Films in Solid Oxide Fuel Cell Anodes

Submonolayer films of highly catalytically active Pd@CeO2 nanocomposites, consisting of a Pd nanoparticle core coated with a porous CeO2 shell, were deposited onto porous solid oxide fuel cell (SOFC) anodes that were functionalized with triethoxy(octyl)silane (TEOOS). SEM results show that in contrast to bare Pd particles, Pd@CeO2 particles grafted onto the surface of the ceramic anode remained highly dispersed, even after calcination in air at 1373 K. SOFC with anodes that were modified with very low loadings (0.01 wt %) of the Pd@CeO2 nanocomposites were shown to exhibit good electrochemical performance when operating with either H2 or CH4 fuels at 973 K. This performance was also maintained after annealing the anode in air at 1173 K. These results demonstrate a strategy for using very low loadings of highly active metal catalysts to enhance the activity of ceramic anodes while maintaining long-term stability.

Graphite oxide-mediated synthesis of porous CeO2 quadrangular prisms and their high-efficiency adsorptive performance

We report a graphite oxide-mediated approach for synthesizing porous CeO2 through a facile hydrothermal process followed by thermal annealing in air. The phase structure, morphology, microstructure and porosity of the products have been revealed by a combination of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and N2 adsorption. The as-prepared CeO2 products show well-defined quadrangular prism morphology, and they are composed of interconnected nanoparticles with diameters around 30–100nm. In particular, the dual-pore hierarchical systems are created in the CeO2 quadrangular prisms with the pore distributions around 4nm and 30nm. The dye sorption capacity of the porous CeO2 is investigated, which exhibits a rapid adsorption to rhodamine B with a high removal efficiency of ∼99%. Moreover, the CeO2 absorbent retains the same performances in different pH solutions.

Enhanced arsenic removal from water by hierarchically porous CeO2–ZrO2 nanospheres: Role of surface- and structure-dependent properties

Arsenic contaminated natural water is commonly used as drinking water source in some districts of Asia. To meet the increasingly strict drinking water standards, exploration of efficient arsenic removal methods is highly desired. In this study, hierarchically porous CeO2–ZrO2 nanospheres were synthesized, and their suitability as arsenic sorbents was examined. The CeO2–ZrO2 hollow nanospheres showed an adsorption capacity of 27.1 and 9.2mgg−1 for As(V) and As(III), respectively, at an equilibrium arsenic concentration of 0.01mgL−1 (the standard for drinking water) under neutral conditions, indicating a high arsenic removal performance of the adsorbent at low arsenic concentrations. Such a great arsenic adsorption capacity was attributed to the high surface hydroxyl density and presence of hierarchically porous network in the hollow nanospheres. The analysis of Fourier transformed infrared spectra and X-ray photoelectron spectroscopy demonstrated that the adsorption of arsenic on the CeO2–ZrO2 nanospheres was completed through the formation of a surface complex by substituting hydroxyl with arsenic species. In addition, the CeO2–ZrO2 nanospheres were able to remove over 97% arsenic in real underground water with initial arsenic concentration of 0.376mgL−1 to meet the guideline limit of arsenic in drinking water regulated by the World Health Organization without any pre-treatment and/or pH adjustment.

Synthesis of multiple-shell porous CeO2 hollow spheres by a hydrogel template method

CeO2 hollow spheres with porous multiple-shell were synthesized via a simple electric-current assisted template method. Dense polyacrylamide network, as the template, plays an important role in the formation of the porous and hollow CeO2 spheres, such as providing favorable nucleation sites for the formation of Ce(OH)3 nanocrystals, controlling the size of the aqueous domains, and limiting crystal arrangement in the domains. Furthermore, the interaction between Ce3+ ions and amide groups of the polyacrylamide was the driving force for the self-assembly of the crystals, resulting in the porous Ce(OH)3 hollow spheres. The effects of the reaction parameters on the morphology, size and number of the shells of the porous hollow structures were investigated, and the formation mechanism of the hierarchical porous CeO2 hollow spheres was proposed.

Facile one-step synthesis of porous ceria hollow nanospheres for low temperature CO oxidation

Herein, porous ceria (CeO2) hollow nanospheres composed of small nanoparticles have been controllably prepared through a simple one-step solvothermal reaction without using any hard-template. The products were characterized by X-ray powder diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), thermogravimetric analysis (TGA), fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM) and N2 adsorption/desorption analysis. It was found that the porous CeO2 hollow nanospheres composed of small nanoparticles with an average diameter of 3nm have a uniform size of 135nm and a high specific surface area of 145m2/g. A self-assembly process coupled with an Ostwald ripening mechanism for the hollow structures formation was proposed based on a series of time-dependent HRTEM observations. The catalytic performance of porous CeO2 hollow nanospheres and the Au/CeO2 composite catalyst for CO oxidation were also tested. The results indicate that these porous CeO2 hollow nanospheres are excellent supports for Au nanoparticles, the CO conversion by catalysis of Au/CeO2-A composite catalyst is 92% at ambient temperature. More importantly, the CO conversion could still be reached to 91% after the catalyst had been continuously used for 20h in CO oxidation at room temperature, indicating that the Au/CeO2-A catalyst had a high catalytic activity and high durability.

An enzymatic biosensor for hydrogen peroxide based on CeO2 nanostructure electrodeposited on ITO surface

In this study, an enzymatic biosensor for amperometric detection of hydrogen peroxide was developed based on the direct electrochemistry of myoglobin (Mb) on a porous cerium dioxide (CeO2) nanostructured film. The developed film accomplished with large surface area was electrodeposited on an indium tin oxide (ITO) substrate. Surface morphological studies revealed that the formed CeO2 film has a large specific surface area with a unique nanostructure on the ITO surface. Cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were employed to demonstrate the electrochemical behavior of Mb immobilized on the fabricated film, which exhibited facile, direct electrochemistry and good electrocatalytic performance without any electron mediator. The electrode displayed a pair of quasi-reversible reduction–oxidation peaks at −0.3 and −0.2V, respectively, due to the Mb [Fe3+/Fe2+] redox couple, which is a surface-controlled electrochemical process with one electron transfer. This reagent-less biosensor showed good stability and high sensitivity for detecting H2O2 without any influence of intermediate compounds. This protein-based biosensor was capable of detecting H2O2 as low as 0.6μM with linearity up to 3mM and a response time of ~8s, compared to those of other modified electrodes. Hence, porous CeO2 is a possible candidate material for fabricating enzymatic sensors or devices.

Performance studies of copper–iron/ceria–yttria stabilized zirconia anode for electro-oxidation of butane in solid oxide fuel cells

Addition of second metal to Cu is useful for electro-oxidation of hydrocarbons in solid oxide fuel cells (SOFC). In this work, electro-catalysts based on Cu–Fe bimetallic anode for use of both H2 and n-C4H10 in SOFC is prepared by wet impregnation method into a porous CeO2–YSZ matrix. The prepared Cu–Fe/CeO2–YSZ anodes are then characterized by thermo-gravimetric analysis (TGA), X-ray diffraction (XRD), elemental dispersive X-ray (EDX) and scanning electron microscopy (SEM). Carbonaceous deposits formed on Cu–Fe/CeO2–YSZ anodes after exposure to n-C4H10 are studied using a combination of i–V characteristics and TGA measurements. It is observed that the addition of Fe to Cu in CeO2–YSZ cermet anode enhance the performance in H2 and n-C4H10 fuels. The performance of cell having molar ratio of Cu–Fe of 1:1 in Cu–Fe/CeO2–YSZ anode shows power density of 240 mW cm−2 and 260 mW cm−2 in n-C4H10 and in H2 after n-C4H10 flow at 800 °C. The i–V curve shows that the conductivity of the anode improves after exposure to n-C4H10. No apparent degradation in performance is observed after n-C4H10 flow except for carbon fibre formation indicating Cu–Fe bimetallic is worth considering as an anode for direct butane SOFC.

Biotemplate Synthesis of Porous Ceria Fiber and Study on its Catalytic Performance

Hierarchical porous ceria with nanocrystalline was successfully synthesized using filter paper as biotemplate. Unique biomorphic microstructures were characterized by Field Emission Scanning Electron Microscope (FESEM), transmission electron microscopy (TEM) and nitrogen absorption-desorption technique. The obtained ceria material showed the repetitious biomimetic structure consisting of fibre with diameter of ca. 1-3 μm and nanopores which had 2-4 nm apertures. The small crystallite diameter (6-8 nm) and the high specific surface area (71.3 m2·g-1) of porous CeO2 were measured by wide-angle X-ray Diffraction (XRD), high resolution TEM (HRTEM) and the BET method. While the concentration of acid fuchsine was 20 mg/L, the porous sample had a higher decoloring rate in a shorter time than others. The decoloring rate can reach 100% after 200 min.

Solvothermal synthesis of hierarchically porous CeO2 nanopalm leaves and their photocatalytic properties

Hierarchically porous CeCO3OH palm leaves were synthesized by using a facile solvothermal method at 180 °C utilizing cerium nitrate and ethylene glycol. Polycrystalline CeO2 palm leaves were obtained from the thermal decomposition-oxidation process of the CeCO3OH nanostructures. CeCO3OH and CeO2 palm leaves were characterized by X-ray diffraction pattern, scanning electron microscopy image, energy dispersive X-ray analyses, and ultraviolet (UV)–visible spectroscopy images. The CeO2 palm leaves exhibited a significant photocatalytic performance in degrading azo dye acid orange II in an aqueous solution under an UV radiation. The formation mechanisms of the CeCO3OH/CeO2 nanostructures were described on the basis of the experimental results.