Rod-like CeO2 Research Articles

Crystal facet-modulated CuO/CeO2 catalysts for highly selective catalytic reduction of NO by CO

The selective catalytic reduction of NO by CO (CO-SCR) has a significant impact on the sustainable development of the environment. It is crucial to design efficient low-temperature catalysts to overcome the challenges associated with the industrialization of CO-SCR. Herein, we present CuO/CeO2 catalysts with three different exposed crystal facets of CeO2 ((100), (110), and (111)) synthesized by a hydrothermal method followed by impregnation for CO-SCR. Among the three CuO/CeO2 catalysts, CuO loaded on rod-like CeO2 catalyst (CuO/CeO2-R) with exposed CeO2 (110) crystal facet showed the highest catalytic performance in the CO-SCR reaction, achieving complete conversion of NO and 99 % conversion of CO at 250 °C. A series of characterizations reveal that the interaction between CuO and CeO2 with different crystal facets is crucial to regulating the interface structure and oxygen vacancy (Ov) content. During in situ DRIFTS analysis, it was found that the primary adsorption sites for CO are the Cu+-Ov-Ce3+ interface sites. The CuO/CeO2-R catalyst had the highest number of these sites. Furthermore, CuO/CeO2-R contained many Ov sites, which promote NO dissociation and enhance its catalytic efficiency. This study offers insights into CO-SCR catalysis and the design of efficient catalysts by manipulating the exposed crystal facets of support to enhance CO-SCR activity.

Improved UV stability of perovskite devices based on the synergistic effect of electron layer passivation engineering and component engineering

The electron transport layer is one of the key factors in constructing high-performance perovskite solar cells (PSCs). Pb2+ reduction induced by ultraviolet light can cause the generation of vacancies and defects, leading to the degradation of perovskite films and the reduction of PSCs performances. Ethylenediamine tetraacetic acid disodium salt (EDTA) is a chelating agent that can bind to Sn2+ divalent metal ions and hence change material properties. Herein, EDTA-SnO2/CeO2 composite electron transport layers were constructed to improve the ultraviolet light stability of PSCs. The oxygen defect in electron layers of tin dioxide could be passivated by the surface of EDTA; whilst rod-like CeO2 was used as a mesoporous electron transport layer and UV shielding agent, which can reflect UV light and prevent the absorption layer from being damaged. CeO2 has also a suitable band gap; this accelerates the charge extraction and transfer, suppresses the recombination of interfacial carriers. The experimental results showed that the ultraviolet light stability of PSCs was significantly improved. After continuous irradiation of ultraviolet light with energy of 80 mW/cm2 for 12 h, the unencapsulated device with CeO2 maintained nearly 90% the initial efficiency.

Morphology effect of Pd/In2O3/CeO2 catalysts on methanol steam reforming for hydrogen production

Catalyst support morphology strongly influences its surface and structural properties, therefore, may have a significant impact on their reactivity in heterogeneous catalysis. Herein, the Pd/In2O3/CeO2-x (loaded with 1 wt% Pd and In2O3) catalysts with different morphologies of rods(r), cubes(c) and irregularity(w) shapes were prepared by hydrothermal method and impregnation method. At temperature of 275–425 °C, as-prepared catalysts were evaluated for hydrogen production from methanol steam reforming (MSR). The activity data showed the outstanding performance of the rod-shaped Pd/In2O3/CeO2 catalysts, exhibiting the complete conversion of methanol and particularly low CO (1.3%) at 375 °C. The structural properties and physicochemical of Pd/In2O3/CeO2-x with different morphologies were characterized by means of X-ray diffraction (XRD), high resolution transmission microscopy (HR-TEM), CO pulse chemisorption, X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption of methanol (CH3OH-TPD). Activity data and catalyst characterization results correlated, and indicated that the excellent reactivity for the rod-shaped Pd/In2O3/CeO2 catalysts in MSR is ascribed to the large particle size of palladium nanoparticles and the abundant oxygen vacancies induced by the strong interaction between Pd, In and Ce. HR-TEM results revealed that rod-like CeO2 mainly expose (110) crystalline surface with high mobility of surface oxygen and possess the most abundant surface oxygen vacancies with the low formation energy, facilitating the formation of active species of Pd0 on catalyst surface, and promoting the activation and adsorption of methanol and water molecules. Furthermore, the rod-shaped Pd/In2O3/CeO2 catalysts showed excellent reactivity and stability in MSR for 30 h, demonstrating its potential of being used as catalysts in methanol steam reforming in PEMFC systems.

Collaborative influence of morphology tuning and RE (La, Y, and Sm) doping on photocatalytic performance of nanoceria.

Tuning morphology and doping additional rare earth (RE) cations are potential techniques to promote the photocatalytic performance of ceria (CeO2), evaluating the collaborative effects of morphology and RE dopants is significant for producing high active ceria-based catalysts. So in this work, cubic, polyhedral and rod-like nanoceria doped with 10mol % La (lanthanum), Y (yttrium), or Sm (samarium) were synthesized by a facile template-free hydrothermal method. Phases, morphologies, oxygen vacancies (OVs) concentration, energy band structure, photo-carriers separation/recombination, and photodegradation ratio toward methylene blue (MB) dye of as prepared ceria were studied. Results show that doped CeO2 maintains a similar morphology structure with un-doped sample and the band gap narrows slightly. Y-doped nanoceria, with an improved separation and a reduced recombination of photo-excited electrons (e-) and holes (h+), owns a higher MB photodegradation ratio than that of samples doping with La or Sm, which is measured as 79.04, 84.43, and 85.59% for Y-doped cubic, polyhedral, and rod-like CeO2. The collaborative influence of morphology tuning and RE (La, Y, and Sm) doping on photocatalytic performance of nanoceria includes the effects of doped elements and the formation of OVs. The elevation of OVs concentration as well as the separation efficiency of photo-generated e-/h+ are suggested to further enhance the photocatalytic performance of ceria.

Probing the influence of shape and loading of CeO2 nanoparticles on the separation performance of thin-film nanocomposite membranes with an interlayer

Constructing an interlayer in the thin-film nanocomposite (TFN) membranes has been proved to be an effective strategy to break the trade-off between permeability and selectivity. The interlayer plays an important role in the formation of polyamide (PA) layer. In this study, cerium oxide (CeO2) nanoparticles with three shapes, including sphere, rod and flake were used to fabricate the interlayers of TFN membranes. The effects of nanoparticle shape and loading on the morphologies and properties of the interlayers and resultant TFN membranes were systematically investigated. The results showed the morphologies and physicochemical properties of the PA layers could be regulated well by the shape and loading of CeO2 nanoparticles. The surface morphologies of the TFN membranes exhibited the transformation from nodule structure to ridge-valley structure. At the same time, the introduction of interlayer made PA layer coarser, the pore size smaller and the pore distribution more uniform. Under the same loading conditions, the rodlike CeO2 nanoparticles tended to form a homogeneous network-like interlayer due to the large specific surface area and good dispersion. The interlayer reduced the transport path of water molecules in the PA layer based on the “gutter” effect, thus improving the permeability of TFN membrane. The water permeability of the TFN membrane with rodlike CeO2 interlayer could be 124% higher than that of the control, while the rejection of salts did not significantly change. This study deepens our understanding on the role of nanoparticle in regulating the morphologies and properties of interlayer and TFN membrane, and provides an effective method to enhance separation performance of nanofiltration membrane.

Influences of CeO2 morphology on enhanced performance of electro-Fenton for wastewater treatment

As a kind of rare-earth oxide, CeO2 has been considered as a great potential material for its abundant oxygen vacancies and catalysis activity in wastewater treatment. In this study, three ceria samples with different morphological structure were prepared, and their effect on contaminates degradation in electro-Fenton (E-Fenton) system was investigated. It is found that the morphology of CeO2 has great influence on promoting the performance of E-Fenton process. The rod-like CeO2 (R–CeO2) induced E-Fenton system shows higher azo dye X3B removal and mineralization rates than cubs (C–CeO2) and octahedrons (O–CeO2), and the degradation kinetic rate constants are 0.28, 0.169 and 0.181 min−1 respectively, already surpass that of the blank one (0.120 min−1). The H2O2 generation capacity of R–CeO2 induced E-Fenton system is also superior to the others, and the corresponding Faraday current efficiency even increases to 166.2% at 2.5 min. Characterizations by scanning-transmission electron microscopy (STEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), Raman spectroscopy were conducted to disclose the mystery behind this phenomenon. The results indicate that the difference of surface oxygen vacancy density in different shaped CeO2 acts as a magic driving force for the accelerated oxygen reduction, and then leads to the enhanced degradation efficiency of E-Fenton system. This work provides a new insight into the development and application of rare-earth elements based catalyst in E-Fenton technology.

Synthesis of rod-like CeO2 nanoparticles and their application to catalyze the luminal-O2 chemiluminescence reaction used in the determination of oxcarbazepine and ascorbic acid.

Rod-like CeO2 nanoparticles (NPs) were produced by the quick precipitation approach and employed as a catalyzer to increase the chemiluminescence (CL) intensity of the luminol-O2 reaction. The transmission electron microscopy(TEM)images of the CeO2 NPs showed that rod-like particles with the length and diameter about 15nm and 5nm, respectively, were produced. Furthermore, pharmaceuticals including oxcarbazepine (OXP) and ascorbic acid (AA) showed an inhibitory effect against the CL intensity such that the more concentration of the pharmaceuticals, the less was the CL intensity. Therefore, the new CeO2 NPs-luminol-O2 CL reaction was developed to determine OXP and AA in the pharmaceutical formulations. It is the first CL method established for the quantification of OXP. The linear dynamic range of this method for OXP was from 6.0 × 10-7 to 6.0 × 10-5mol L-1 and for AA from 1.0 × 10-6 to 1.0 × 10-4mol L-1.

The rod-like CeO2 supported by the low-loading Au nanoparticles for the efficient catalytic oxidation of CO at room temperature

Au–CeO2 composite with rod-like structure is successfully prepared by simple and mature one-step hydrothermal method. The results of meteorological chromatographic analysis show that the CO conversion rate of 0.7% Au–CeO2 is 50% at 47 °C, and the CO conversion rate of 1.0%Au–CeO2 is more than 70% at room temperature. Characterization results of test show the Au–CeO2 catalyst excellent catalytic activity due to good dispersibility of Au nanoparticles, specific surface area of the material, the enhanced ability of reducing catalyst and catalyst surface mutual synergy between different valence state of ions, which effectively promoted the generation of the oxygen vacancy and marked the surface of the catalyst increase reactive oxygen content. Finally, the catalytic mechanism of Au–CeO2 composites is summarized through the mutual verification between analysis of characterization analysis and performance test results. The main highlight of the research in this thesis is that the low proportion of gold modified ceria catalyst can be catalyzed at room temperature. It is hoped that this work will provide insights into the development of highly active catalysts.

RGO modified R-CeO2/g-C3N4 multi-interface contact S-scheme photocatalyst for efficient CO2 photoreduction

Construction of multi-interface contact step-scheme (S-scheme) photocatalyst is a promising pathway to achieve high-electron transfer efficiency for photocatalytic CO2 reduction. In this paper, g-C3N4 nanosheets were selected as the main photocatalyst, rod-like CeO2 (R-CeO2) with unique Ce4+→Ce3+ conversion property and rGO were loaded on the g-C3N4 surface to construct 2D-1D-2D sandwich photocatalyst. The yields of CO and CH4 were about 63.18 and 32.67 μmol/g after 4 h when the rGO/R-CeO2/g-C3N4 was used as catalyst, which were about 4 and 6 times higher than that of pure CN, respectively. Cyclic experiments proved that the composite had excellent photocatalytic and material stability. Photoelectrochemical tests showed that the construction of S-scheme electron transfer model and the introduction of rGO can great enhance the electron transmission and separation of photogenerated electron-hole pairs. CO2 adsorption test identified that the loading of R-CeO2 and rGO obviously enhanced the CO2 adsorption ability of pure g-C3N4. Density functional theory (DFT) calculations used to analyze the electron transfer path and the formation of the build-in electric field at the semiconductor interface. In-situ FTIR and 13CO2 element-tracer detection carried out to research the process of CO2 photoreduction. A possible multi-interface contact S-scheme electron transfer mechanism for enhanced CO2 photoreduction activity has been discussed.

High dispersed Pd supported on CeO2 (1 0 0) for CO oxidation at low temperature

Nanostructured CeO2 with morphologies of nanorod, nano-cube, and nano-octahedron were successfully synthesized and the effects of cerium morphology were investigated on the catalytic efficiency of Pd/CeO2 for CO combustion. The light-off curves showed that Pd supported on rod-like CeO2 (1 0 0) plane had excellent performance. Subsequently, different contents of Pd were loaded on nanorod CeO2 to investigate the effect of Pd and CeO2 support interaction on the catalytic activity. Under optimal deployment, CO can be completely converted below 50℃. Through cautious analysis of SEM, HAADF-STEM, XRD, XPS, and EDS patterns, Pd was proved to be highly dispersed on the surface of CeO2 carrier (1 0 0) in the form of PdO and PdxCe1-xO2-σ. As a result of the strong metal-support interaction, Pd2+ ions substituted for Ce4+, -Pd2+-O2−-Ce4+- species were formed for enhancing CO oxidation. Simultaneously, the generation of Ce3+/Ce4+ ion pairs can be regulated by adjusting the proportion of Pd. Further in situ DRIFTS characterization revealed that in this reaction system, highly dispersed Pd on the surface of Pd/R-CeO2 could increase the concentration of Ce3+ on the surface, and lattice oxygen was activated in the oxidation reaction to generate abundant oxygen vacancies, which can promote the generation of active centers synergistically, thereby greatly enhancing the reaction activity.

Enhanced reaction lifetime of a bifunctional catalyst for methanol to olefins by combining formaldehyde decomposition on CeO2

A new bifunctional catalyst comprising of CeO2 and SSZ-13 physical mixture was developed, and its lifetime for the methanol to olefins (MTO) reaction was significantly enhanced. Formaldehyde adsorbed on ceria forms formate species, which decomposes to CO or CO2. The formaldehyde decomposition by CeO2 suppressed deposition of the inactive coke species formed (tetramethylnaphthalene), and improved the lifetime of SSZ-13 for MTO catalysis by 4-fold. The morphology of CeO2 has also an impact on the catalytic properties of the physical mixture catalyst, and the solid mixture of rod-like CeO2 and SSZ-13 showed the most extended stability.

Structure and properties of cerium zirconium mixed oxide prepared under different precipitate aging processes

Oriented attachment and Ostwald ripening are two aging mechanisms of precipitation particles which may result in different crystallization mechanism of precipitates during the aging process. In this work, the effects of different aging process on the structure and properties of cerium zirconium mixed oxides were investigated. The results indicated that the mixed structure of 11.48% CeO2 phase and 88.52% Ce0.26Zr0.62(LaPr)0.12O2 solid solution phase were obtained under oriented attachment aging process. The rod-like CeO2 phase coexisted with spherical Ce0.26Zr0.62(LaPr)0.12O2 solid solution phase, which improved the surface area (64 m2/g) and pore volume (0.32 mL/g) of cerium zirconium mixed oxides after 1000 °C 4 h thermal treatment. However, through controlling the aging process, the Ce0.35Zr0.55(LaPr)0.10O2 solid solution with homogenous phase structure was generated by Ostwald ripening aging process, exhibiting higher oxygen storage capacity (501 µmol O2/g) and H2 consumption per gram (1378.3 µmol H2/g).

Support Shape Effect on the Catalytic Performance of Pt/CeO2 Nanostructures for Methanol Electrooxidation

Polyhedral, cubic, and rod-like CeO2 nanostructures have been selectively synthesized and used as supports for Pt nanoparticles. The structures of Pt/CeO2, specially the exposed crystallographic facets of different CeO2 nanosupports, have been investigated by electron microscopy. A shape change induced variation of the exposed facets on CeO2 surface has been confirmed. In methanol electrooxidation, Pt/CeO2 particles have been found to acquire a generally improved and, more importantly, support-shape-dependent electrocatalytic activity. Pt nanoparticles earn the best activity on CeO2 nanorods while they gain the poorest activity on CeO2 nanopolyhedra. The result, indeed, reveals a fact that the {110} and {100} over {111} planes on ceria surface possess a superiority in improving the electrocatalytic performance of their supported Pt nanoparticles.

CeO2/CuO Catalysts with Na2CO3 as Precipitant for Preferential Oxidation of CO

The CeO2/CuO catalysts were synthesized by the hydrothermal method. The study shows that the particle-like CeO2 can self-assemble into the rod-like CeO2 during the hydrothermal procedure and the rods of CeO2 become shorter with the decrease of Ce/Cu molar ratio. The highly dispersed CuO is favorable for CO oxidation at lower temperature, and the bulk CuO can help CO oxidation at higher temperature due to the limitation of reduction.

Comparative study of CeO2/CuO and CuO/CeO2 catalysts on catalytic performance for preferential CO oxidation

The CeO2/CuO and CuO/CeO2 catalysts were synthesized by the hydrothermal method and characterized via XRD, SEM, H2-TPR, HRTEM, XPS and N2 adsorption–desorption techniques. The study shows that the rod-like structure is self-assembled CeO2, and both hydrothermal time and Ce/Cu molar ratio are important factors when the particle-like CeO2 is being self-assembled into the rod-like CeO2. The CuO is key active component in the CO-PROX reaction, and its reduction has a negative influence on the selective oxidation of CO. The advantage of the inverse CeO2/CuO catalyst is that it still can provide sufficient CuO for CO oxidation before 200 °C in the hydrogen-rich reductive gasses. The traditional CuO/CeO2 catalyst shows better activity at lower temperature and the inverse CeO2/CuO catalysts present higher CO2 selectivity when the CO conversion reaches 100%. The performance of mixed sample verifies that they might be complementary in the CO-PROX system.

Inverse rod-like CeO2 supported on CuO prepared by hydrothermal method for preferential oxidation of carbon monoxide

Abstract The CeO 2 /CuO catalysts were synthesized by the hydrothermal method and characterized via XRD, BET, SEM, H 2 -TPR, XPS and HRTEM techniques. The results showed that CeO 2 with two kinds of morphologies (particle and rod-like CeO 2 ) was highly dispersed on the surface of the catalysts when Ce/Cu molar ratio exceeded 0.25. The rod-like CeO 2 exposed more (1 1 1) planes, and this was helpful for oxygen storage and transportation. Moreover, the contact interface between highly dispersed CuO and bulk ceria supplied the active sites not only for CO oxidation but also for H 2 oxidation, but the contact interface of highly dispersed ceria and bulk CuO was more favorable for CO oxidation than H 2 oxidation.

Morphology Control of Cerium Oxide Particles Synthesized via a Supercritical Solvothermal Method

Rod and sphere-like CeO(2) particles were obtained via a supercritical solvothermal method using CeCl(3).7H(2)O and Ce(NO(3))(3).6H(2)O as cerium sources in ethanol and methanol at 400 degrees C for 15 min followed by calcination in air. The rodlike particles were 200-400 nm in diameter and 1-2 mum in length. The spherical particles were 300-500 nm in diameter. The as-prepared rodlike particles using CeCl(3).7H(2)O consisted of mixtures of Ce(OH)(3) and Ce(CH(3)COO)(3) and were converted to rodlike CeO(2) by calcination in air at 500 degrees C. In contrast, the spherical particles prepared using Ce(NO(3))(3).6H(2)O consisted of fluorite-structured CeO(2). The possible formation mechanism was discussed on the basis of the effect of reaction time on the morphology at 400 degrees C. The rod- and spherelike CeO(2) particles exhibited strong UV absorption below 400 nm, and the absorbance edges extend to nearly 500 nm. The rod- and spherelike CeO(2) particles exhibited near-UV emission at 360 nm and blue emission at 465 nm with higher emission intensity compared to the commercial CeO(2) sample.