Synthesizing active and durable cubic ceria catalysts(<6 nm)for fast dehydrogenation of bio-polyols to carboxylic acids coproducing green H_(2)

Dehydrogenation is considered as one of the most important industrial applications for renewable energy.Cubic ceria-based catalysts are known to display promising dehydrogenation performances in this area.Large particle size(>20 nm)and less surface defects,however,hinder further application of ceria materials.Herein,an alternative strategy involving lactic acid(LA)assisted hydrothermal method was developed to synthesize active,selective and durable cubic ceria of<6 nm for dehydrogenation reactions.Detailed studies of growth mechanism revealed that,the carboxyl and hydroxyl groups in LA molecule synergistically manipulate the morphological evolution of ceria precursors.Carboxyl groups determine the cubic shape and particle size,while hydroxyl groups promote compositional transformation of ceria precursors into CeO_(2) phases.Moreover,enhanced oxygen vacancies(Vo)on the surface of CeO_(2) were obtained owing to continuous removal of O species under reductive atmosphere.Cubic CeO_(2) catalysts synthesized by the LA-assisted method,immobilized with bimetallic PtCo clusters,exhibit a record high activity(TOF:29,241 h^(-1))and Vo-dependent synergism for dehydrogenation of bio-derived polyols at 200℃.We also found that quenching Vo defects at air atmosphere causes activity loss of PtCo/CeO_(2) catalysts.To regenerate Vo defects,a simple strategy was developed by irradiating deactivated catalysts using hernia lamp.The outcome of this work will provide new insights into manufacturing durable catalyst materials for aqueous phase dehydrogenation applications.

Superionic Conductivity in Ceria‑Based Heterostructure Composites for Low‑Temperature Solid Oxide Fuel Cells

Ceria-based heterostructure composite(CHC)has become a new stream to develop advanced low-temperature(300–600°C)solid oxide fuel cells(LTSOFCs)with excellent power outputs at 1000 mW cm−2 level.The state-ofthe-art ceria–carbonate or ceria–semiconductor heterostructure composites have made the CHC systems significantly contribute to both fundamental and applied science researches of LTSOFCs;however,a deep scientific understanding to achieve excellent fuel cell performance and high superionic conduction is still missing,which may hinder its wide application and commercialization.This review aims to establish a new fundamental strategy for superionic conduction of the CHC materials and relevant LTSOFCs.This involves energy band and built-in-field assisting superionic conduction,highlighting coupling effect among the ionic transfer,band structure and alignment impact.Furthermore,theories of ceria–carbonate,e.g.,space charge and multi-ion conduction,as well as new scientific understanding are discussed and presented for functional CHC materials.

Ceria modified three-dimensionally ordered macro-porous Pt/TiO_2 catalysts for water-gas shift reaction

Three-dimensionally ordered macro-porous （3DOM） TiO2 and ceria-modified 3DOM TiO2 supported platinum catalysts were prepared with template and impregnation methods, and the resultant samples were characterized by scanning electron microscopy（SEM）, X-ray diffractometer（XRD）, high-resolution transmission electron microscopy（HRTEM） and temperature programmed reducfion（TPR） techniques. The catalytic performances over the platinum-based catalysts were investigated for water-gas shift （WGS） reaction in a wide temperature range （180-360 ℃）. The results showed that 3DOM Pt/TiO2 catalyst exhibited obviously better catalytic performance than the corresponding non macro-porous catalyst, owing to the macro-porous structure favoring mass transfer. Addition of celia into 3DOM Pt/TiO2 led to improvement of catalytic activity. TPR and HRTEM results showed that the interaction existed between ceria and titanium oxide and addition of ceria promoted the reducibility of platinum oxide and TiO2 on the interface of platinum and TiO2 particles, which contributed to high activity of the celia modified catalysts. The results indicated that ceria-modified 3DOM Pt/TiO2 was a promising candidate of fuel cell oriented WGS catalyst.

Preparation and CO conversion activity of ceria nanotubes by carbon nanotubes templating method

Ceria nanotubes with high CO conversion activity by means of carbon nanotubes as removable templates in the simple liquid phase process were fabricated under moderate conditions. The pristine CNTs were first pretreated by refluxing in a 30% nitric acid solution at 140 ℃ for 24 h, then dispersed in an ethanolic Ce（NO3）3.6H2O solution with ultrasonic radiation at room temperature for 1 h. Under vigorous stirring, NaOH solution was added drop by drop into the above ethanolic solution until the pH value was 10. The product was collected and repeatedly washed with ethanol and on drying at 60 ℃, the CeO2/CNT composites were obtained. Then, the as-prepared composites were heated at 450 ℃ in an air atmosphere for 30 min to remove CNTs. The ceria nanotubes were characterized by X-Ray Diffraction （XRD）, Transmission Electron Microscopy （TEM）, and X-Ray Photoelectron Spectrum （XPS）. The results showed that the ceria nanotubes were polycrystalline face-centered cubic phase and were composed of lots of dense cefia nanoparficles. The diameter of cefia nanotubes was about 40-50 nm. Catalytic activity of the product for CO oxidation was carded out at the region of 30-300 ℃ in a U-shaped quartz reactor with feeding about 0.15 g of the catalyst, which was loaded on Al2O3 carder. The inlet gas composition was 1.0% CO and 28% O2 with N2 as balance, and the rate of flow was kept at 40 ml/min. The catalytic products were analyzed by gas chromatography. The as-repared CeO2 nanotubes showed higher CO oxidation activity, which indicated that the morphology of ceria products affected the catalytic performance. The ceria nanotubes supported on Al2O3 demonstrated that conversion temperature for CO oxidation to CO2 was lower than that for bulk catalysts.

Effect of samarium doped ceria nanoparticles impregnation on the performance of anode supported SOFC with(Pr_(0.7)Ca_(0.3))_(0.9)MnO_(3-δ) cathode

Solid oxide fuel cell(SOFC) electrodes,after a high temperature sintering,may be impregnated to deposit nanoparticles within their pores to enhance the catalytic function.Samarium doped CeO2(SDC) nanoparticles were infiltrated into(Pr0.7Ca0.3)0.9MnO3-δ(PCM) cathode of anode supported SOFC cells.The cell with 2.6 mg/cm2 SDC impregnated in cathode showed the maximum power density of 580 mW/cm2 compared with 310 mW/cm2 of the cell without impregnation at 850 °C.The cells were also characterized with the impeda...

Combination Therapy with LXW7 and Ceria Nanoparticles Protects against Acute Cerebral Ischemia/Reperfusion Injury in Rats

Ischemia/reperfusion is known to greatly increase oxidative stress in the penumbra,which results in brain damage.Integrin αvβ3 is selectively up-regulated with ischemic injury to the brain and remains elevated throughout reperfusion.We determined whether or not a new compound biotinylated-LXW7-ceria nanoparticle（Ce NP）（b LXW7-Ce NP） plays a role in brain protection in the rat model of middle cerebral artery occlusion/reperfusion and shows better effects than Ce NPs alone in improving the outcomes of focal oxidative stress and apoptosis more effectively.Male Sprague-Dawley rats were subjected to focal cerebral ischemia for 2 h followed by a 24-h reperfusion.Drug treatment was intravenously administered via the caudal vein 1 h after occlusion.Rats were randomly divided into the following 4 groups：b LXW7-Ce NP treatment group（0.5 mg/kg）;Ce NP treatment group（0.5 mg/kg）;control saline group;and sham group.Brains were harvested 24 h after reperfusion,and the neurologic deficit scores,infarction volume,blood-brain barrier（BBB） disruption,and the level of oxidative stress and apoptosis were determined.Results showed that the b LXW7-Ce NP and Ce NP treatments could improve neurologic deficit scores,infarction volume,BBB disruption,and the level of oxidative stress and apoptosis.Compound b LXW7-Ce NP treatment exhibited better effects than Ce Np treatment and showed remarkable statistical differences in the infarction volume,the degree of BBB breakdown,the apoptosis and oxidative stress,apart from neurologic deficit scores.Thus,we concluded that b LXW7-Ce NP protects against acute cerebral ischemia/reperfusion injury.BLXW7,as a ligand of integrin αvβ3,may be able to effectively localize the anti-oxidant Ce NPs to the ischemic penumbra region,which may provide more adequate opportunities for Ce NPs to exert anti-oxidative stress effects and subsequently reduce apoptosis in acute cerebral ischemia/reperfusion.

Redox behavior of gold supported on ceria and ceria-zirconia based catalysts

A series of gold-based catalysts were prepared by deposition precipitation or incipient wetness impregnation on CexZ1-xO2 solid solutions （0.28≤x≤1.00）. The morphological and structural characterization of these catalysts were carried out with X-ray diffraction, trans- mission electron microscopy （TEM） analysis and physical adsorption technique, and their redox properties were studied by temperature programmed reduction using both H2 and CO as probe molecules. Two cycles of oxidation/reduction were carried out in order to evaluate the effects of redox aging and gold sintering on the oxygen exchange capability. As observed with other noble metals, gold enhanced and promoted the ceria reduction at lower temperatures. Reduction by CO was shown to be dependent on the fine dispersion of gold and to be nega- tively affected by the ageing process more than reduction with hydrogen. This might have implications in reactions like water gas shift and CO-PROX which involve CO as a main reactant.

Preparation of Fine Spherical Particle Sized Ceria by Precipitation Method with Ammonium Bicarbonate

Fine spherical particle sized ceria (CeO_2) was prepared by homogeneous precipitation method with ammonium bicarbonate as precipitant. The prepared CeO_2 has the primary particle size of 10～50 nm when calcined between 400～700 ℃ analyzed by XRD and the aggregated particle size is about 300 nm measured by LASER particle sizer. SEM, TG-DTA and Zeta-potential analyzer were employed individually to study the morphology and the formation of CeO_2 product. It was found that excess NH_4NO_3 can serve as an sphericallization agent to prepare spherical CeO_2 powder by precipitation method.

Influence of Nanometric Ceria Coating on Oxidation Behavior of Chromium at 900 ℃

Isothermal and cyclic oxidation behaviors of chromium samples with and without nanometric CeO2 coating were studied at 900℃ in air. Scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, and high-resolution electron microscopy （HREM） were used to examine the morphology and microstructure of the oxide film. It was found that ceria coating greatly improved the oxidation resistance of Cr both in isothermal and cyclic oxidizing experiments. Acoustic emission （AE） technique was used in situ to monitor the cracking and spalling of oxide film, and AE signals were analyzed in time-domain and number-domain according to related oxide fracture model. Laser Raman spectrometer was also used to study the stress of oxide film formed on Cr with and without ceria. The improvement in oxidation resistance of chromium is believed mainly due to that ceria greatly reduced the growth speed and grain size of Cr2O3. This fine grained Cr2O3 oxide film might have better high temperature plasticity and could relieve parts of the compressive stress by means of creeping and maintained ridge character and relatively lower level of internal stress. Meanwhile, ceria application reduced the size and number of interfacial defects, remarkably enhanced the adhesive property of Cr2O3 oxide scale formed on Cr substrate.

Solar chemical looping reforming of methane combined with isothermal H2O/CO2 splitting using ceria oxygen carrier for syngas production

The chemical looping reforming of methane through the nonstoichiometric ceria redox cycle(CeO2/CeO2-δ) has been experimentally investigated in a directly irradiated solar reactor to convert both solar energy and methane to syngas in the temperature range 900–1050 °C. Experiments were carried out with different ceria shapes via two-step redox cycling composed of endothermic partial reduction of ceria with methane and complete exothermic re-oxidation of reduced ceria with H2 O/CO2 at the same operating temperature, thereby demonstrating the capability to operate the cycle isothermally. A parametric study considering different ceria macrostructure variants(ceria packed powder, ceria packed powder mixed with inert Al2 O3 particles, and ceria reticulated porous foam) and operating parameters(methane flow-rate, reduction temperature, or sintering temperature) was conducted in order to unravel their impact on the bed-averaged oxygen non-stoichiometry(δ), syngas yield, methane conversion, and solar reactor performance. The ceria cycling stability was also experimentally investigated to demonstrate repeatable syngas production by alternating the flow between CH4 and H2 O(or CO2). A decrease in sintering temperature of the ceria foam was beneficial for increasing syngas selectivity, methane conversion,and reactor performance. Increasing both CH4 concentration and reduction temperature enhanced δ with the maximum value up to 0.41 but concomitantly favored CH4 cracking reaction. The ceria reticulated porous foam showed better performance in terms of effective heat transfer, due to volumetric absorption of concentrated solar radiation and uniform heating with lower solar power consumption, thereby promoting the solar-to-fuel energy conversion efficiency that reached up to 5.60%. The energy upgrade factor achieved during cycle was up to 1.19. Stable patterns in the δ and syngas yield for consecutive cycles with the ceria foam validated material performance stability.

Research on Calcium Doped Ceria Used in Intermediate-Temperature SOFCs Anodes

As a mixed ion-electronic conductor, doped ceria, especially rare earth doped ceria, were used as anodes or components of anodes in SOFCs. In this work, calcium doped ceria （CCO） was synthesized to be used in intermediate-temperature SOFCs （IT-SOFCs） anodes in order to reduce the cost of anode-supported SOFCs. Electrical conductivity of 20% calcium doped ceria （20CCO） reached 0.209 S·cm^-1 in hydrogen at 850 ℃, and 0.041 S·cm^-1 in air at 800℃, which is about 0.04 S·cm^-1 lower than that of conventional samaria-doped ceria （0.079 S·cm^-1）. Electrochemical performance of Ni-20CCO cermet as anode was investigated using a fuel cell with 35μm-thick SDC electrolyte and Sm0.5Sr0.5 Co-SDC cathode. Maximum power density was 623 mW·cm^-2 under humidified （3% H2O） hydrogen at 650 ℃, inferring high catalytic activity of the Ni-20CCO anode.

Renewable hydrogen production from steam reforming of glycerol(SRG)over ceria-modified Y-alumina supported Ni catalyst

Excess crude glycerol derived as a by-product from biodiesel industry prompts the need to valorise glycerol to value-added chemicals.In this context,catalytic steam reforming of glycerol(SRG) was proposed as a promising and sustainable alternative for producing renewable hydrogen(H2).Herein,the development of nickel(Ni) supported on ceria-modified mesoporous γ-alumina(γ-Al2 O3) catalysts and their applications in catalytic SRG(at550-750℃ atmospheric pressure and weight hourly space velocity,WHSV,of 44,122 ml·g^-1·h^-1(STP)) is presented.Properties of the developed catalysts were characterised using many technique s.The findings show that ceria modification improved Ni dispersion on γ-Al2 O3 catalyst support with highly active small Ni particles,which led to a remarkable catalytic performance with the total glycerol conversion(ca.99%),glycerol conversion into gaseous products(ca.77%) and H2 yield(ca.62%).The formation rate for H2 production(14.4 ×10^(-5)mol·s^-1·g^-1, TOF(H2)=3412 s^-1) was significantly improved with the Ni@12 Ce-Al2 O3 catalyst,representing nearly a 2-fold increase compared with that of the conventional Ni@AI2 O3 catalyst.In addition,the developed catalyst also exhibited comparatively high stability(for 12 h) and coke resistance ability.

Synthesis and characterization of ceria nanoparticles by complex-precipitation route

Ceria(CeO_(2))nanoparticles were successfully synthesized via a simple complex-precipitation route that employs cerium chloride as cerium source and citric acid as precipitant.The elemental analysis results of carbon,hydrogen,oxygen,and cerium in the precursors were calculated,and the results revealed that the precursors were composed of Ce(OH)_(3),Ce(H_(2)Cit)_(3),or CeCit.X-ray diffraction analysis showed that all ceria nanoparticles had a face-centered cubic structure.With the molar ratio of citric acid to Ce^(3)+(n)of 0.25 and pH of 5.5,the specific surface area of the sample reached the maximum value of 83.17 m^(2)/g.Ceria nanoparticles were observed by scanning electron microscopy.Selected area electron diffraction patterns of several samples were obtained by transmission electron microscopy,and the crystal plane spacing of each low-exponent crystal plane was calculated.The ultraviolet(UV)–visible transmittance curve showed that ceria can absorb UV light and pass through visible light.Among all samples,the minimum average transmittance of ultraviolet radiation a(UVA)was 4.42%,and that of ultraviolet radiation b(UVB)was 1.56%.

Study on Agglomeration and Densification Behaviors of Gadolinium-Doped Ceria Ceramics

By synthesizing reactive powders via a self-sustaining combustion synthesis, the glycine-nitrate process, the gadolinium-doped celia （GDC） with the chemical formula Ce0.8Gd0.2O1.9 was prepared. The resultant powders were dispersed with the terpineol as the dispersant through different methods such as ball milling and high-shear dispersing. Coagulation factor （CF） was used to mark the degree of agglomeration on the nano-scale GDC in this work. The effect of agglomeration on the densification behavior at different sintering temperatures was investigated. The studies indicated that agglomeration retarded the densification at the sintering stage. The powders with better dispersion exhibited a higher sintered density at the same temperature. After effective dispersion treatment, GDC could be fully densified at the sintering temperature of 1300 ℃. The densification temperature was significantly lower than those reported previously. The high sintering kinetics of the ceramics was obtained based on the agglomeration control.

Novel Salt-Assisted Combustion Synthesis of High Surface Area Ceria Nanopowders by An Ethylene Glycol-Nitrate Combustion Process

A novel salt-assisted combustion process with ethylene glycol as a fuel and nitrate as an oxidant to synthesize high surface area celia nanopowders was reported. The effects of various tunable conditions, such as fuel-to-oxidant ratio, type of salts, and amount of added salts, on the characteristics of the as-prepared powders were investigated by X-ray diffraction, transmission electron microscopy and BET surface area measurement. A mechanism scheme was proposed to illustrate the possible formation processes of well-dispersed ceria nanoparticles in the salt-assisted combustion synthesis. It was verified that the simple introduction of leachable inert inorganic salts as an excellent agglomeration inhibitor into the redox mixture precursor leads to the formation of well-dispersed ceria particles with particle size in the range of 4 ～6 nm and a drastic increase in the surface area. The presence of KCl results in an over ten-fold increment in specific surface area from 14.10 m^2·g^-1 for the produced ceria powders via the conventional combustion synthesis process to 156.74 m^2·g^-1 for the product by the salt-assisted combustion synthesis process at the same molar ratio of ethylene glycol-nitrate.

Synthesis and characterization of mesostructured ceria-zirconia solid solution

Mesostructured Ce0.6Zr0.4O2 solid solutions were synthesized by coprecipitation combined with evaporation-induced self-assembly process. The obtained materials were characterized by X-ray diffractometer （XRD）, Raman, transmission electron microscopy （TEM）, N2 sorption, and hydrogen temperature programmed reduction （H2-TPR）. The results showed that the solid solutions consisted of uniform nanocrystals, which piled homogeneous mesopores of about 4 nm. Furthermore, different surfactants had little influence on the mesoporous structures. All these samples exhibited high thermal stability.

Effect of ceria on copper／γ－alumina catalysts for carbon monoxide and n－hexane oxidation

In this paper, oxidation activity of CuO/γ-A12O3 catalysts and the addition of CeO2 on CuO/γ-A12O3 catalysts for oxidation reaction of n-hexane (n-C6H14 ) and carbon monoxide (CO ) were studied by means of the flow method techniques, XRD and TPD-MS. Experimental results indicated that (1) the addition of CeO2 improving disperse degree of CuO on CuO/γ-Al2O3 catalysts which caused a large increase in activity; (2) the addition of CeO2 may increase oxygen supplying ability and oxygen recovery ability of catalyst surface.

Effect of different mixing ways in palladium/ceria-zirconia/alumina preparation on partial oxidation of methane

The effect of the mixing ways of Ce0.7Zr0.3O2-Al2O3 mixed oxides on the partial oxidations of methane （POM） was investigated over Pd/Ce0.7Zr0.3O2-Al2O3 catalysts, the mixing ways including salt precursor mixing （ATOM）, precipitator mixing （MOL）, and powder mechanically mixing （MECH）, respectively. The test results indicated that among the three samples, Pd/ATOM had the best catalytic activity while Pd/MOL had the best stability in the stability test. Both the activity sequences of the fresh and used samples were consistent with the order of Pd dispersion. According to the X-ray diffraction （XRD） and BET characterization, the interaction of Ce^4＋, Zr^4＋, and Al^3＋ in the ATOM mixed oxide was in favor of performing higher catalytic activity and thermal stability. The stability test indicated that Pd/MOL had the highest Pd dispersion and least coke formation on the active sites calculated by the Hz-chemisorption and TG results, which was considered to relate to its superior activity of POM to other catalysts.

Recent Developments in Doping and Structural Modification of Ceria-Based Catalysts

Recent development in the modification of ceria-based catalysts for exhaust gas treatment was reviewed with the dependence of redox properties on structural characters of materials. The doping of ceria with different cations such as rare earth or transition metal oxides results in improvement of structural stability, catalytic function and resistance to sintering at high temperatures. Aging and reduction treatment at high temperatures promote ceria reduction and is beneficial for oxygen storage capacity of the three-way catalysts. Chemical filing technique is very effective in modifying the redox property in the low temperature regions.

Effect of Addition of Base on Ceria and Reactivity of CuO/CeO_2 Catalysts for Low-Temperature CO Oxidation

In this work, we have reported the influence of the addition of base （KOH） on the physicochemical property of ceria synthesized by alcohothermal process, and the alcohothermal mechanism was also put forward. Furthermore, the prepared CeO2 was used as the support to prepare CuO/CeO2 catalysts via the wet impregnation method. The samples were characterized by N2 adsorption-desorption, X-ray powder diffraction （XRD）, high resolution transmission electron microscopy （HRTEM）, and temperatureprogrammed reduction by H2 （H2-TPR）. The catalytic properties of the CuO/CeO2 catalysts for lowtemperature CO oxidation were studied using a microreactor-GC system. The crystal size of CeO2-A was much smaller than that of CeO2-B, and the corresponding copper oxide catalysts exhibited higher catalytic activity than that of the CeO2-B-supported catalysts under the same reaction conditions. The alcohothermal mechanism indicated that KOH plays a key role in determining the physicochemical and catalytic properties of ceria-based materials.