CeO2 Rods Research Articles

Modularization of Regional Electronic Structure over Defect-Rich CeO2 Rods for Enhancing Photogenerated Charge Transfer and CO2 Activation.

Oxygen vacancy (OV) engineering has been widely applied in different types of metal oxide-based photocatalytic reactions. Our study has shown that the redistributed OVs resulting from voids in CeO2 rods lead to significant differences in the band structure in space. The flat energy band within the highly crystallized bulk region hinders the recombination of photogenerated carrier pairs during the transfer process. The downward curved energy band in the surface region enhances the activation of the absorbents. Therefore, the localization of the band structure through crystal structure regionalization renders V-CeO2 capable of achieving efficient utilization of photogenerated carriers. Practically, the V-CeO2 rod shows a remarkable turnover number of 190.58 μmol g-1 h-1 in CO2 photoreduction, which is ∼9.4 times higher than that of D-CeO2 (20.46 μmol g-1 h-1). The designed modularization structure in our work is expected to provide important inspiration and guidance in coordinating the kinetic behavior of carriers in OV defect-rich photocatalysts.

Cu/Ni-loaded oxygen vacancy-rich CeO2 rod derived from metal organic framework for efficient photothermal CO2 hydrogenation

Cu/Ni-loaded oxygen vacancy-rich CeO2 rod derived from metal organic framework for efficient photothermal CO2 hydrogenation

Distinct structure-activity relationship and reaction mechanism over BaCoO3/CeO2 catalysts for NO direct decomposition

The dependency on morphology is crucial for achieving highly efficient direct decomposition of NO. Herein, a BaCoO3/CeO2 catalyst is synthesized using CeO2 small particles (p), spheres (s) and rods (r) as supports. The NO conversion to N2 (NTN2) at 800 °C follows the order BaCoO3/CeO2-r (78.8 %) > BaCoO3/CeO2-s (75.9 %) > BaCoO3/CeO2-p (56.9 %) > BaCoO3 (8.6 %) at a space velocity 1 g s/cm3. BaCoO3/CeO2-r exhibts high tolerance to O2 and stability with conversion decreasing from 78.8 % to 74.6 %, 60.0 % and 50.0 % at 800 °C with 1, 5 and 10 vol% O2, respectively. The high redox activity, higher active oxygen mobility and NO adsorption capability ensures its superior performance, while the high surface area (31.29 m2/g) and uniform distribution of active sites on the surface further promote the activity. The mechanism of NO direct decomposition is elucidated by in situ Diffuse reflectance infrared Fourier transform spectroscopy, 18O2 isotopic transient exchange experiments and density functional theory (DFT) calculation.

A Detailed Insight into the Effects of Morphologies of Cerium Oxide on Fenton-like Reactions for Different Applications.

As an exceptional Fenton-like reagent, cerium oxide (CeO2 ) finds applications in biomedical science and organic pollutants treatment. The Fenton-like reaction catalyzed by CeO2 typically encompasses two distinct processes: one resembling the classical Fenton reaction, wherein cerium (Ce3+ ) triggers the decomposition of hydrogen peroxide (H2 O2 ) to yield reactive oxygen species (ROS), and the other involves the complexation of H2 O2 on the Ce3+ surface, leading to the formation of peroxides. However, the influence of diverse CeO2 morphologies on these two reaction pathways has not been comprehensively explored. In this study, CeO2 exhibiting three typical morphologies, rods, cubes, and spheres, were prepared. The generation of ROS and peroxides was evaluated using the 3,3,5,5-tetramethylbenzidine (TMB) oxidation reaction and the reduction current of H2 O2 , respectively. Moreover, the impacts of pH variations and CeO2 /H2 O2 concentrations on the production and conversion of these two reaction products were investigated. To corroborate the distinctions between the resultant products and their applicability, apoptosis assays and acid orange 7 (AO7) degradation analyses were performed. Notably, CeO2 rods exhibited the highest proportion of Ce3+ , predominantly engaging in complexation with H2 O2 to foster peroxide formation, thereby facilitating the robust degradation of AO7. However, the generated peroxides appeared to occupy Ce3+ sites, thereby impeding the H2 O2 decomposition process. Conversely, Ce3+ species on the surface of CeO2 cubes were primarily involved in H2 O2 decomposition, leading to heightened ROS production, and thus showcasing substantial potential for damaging A549 tumor cells. It is worth noting that the ability of these Ce3+ species to form peroxides through complexation with H2 O2 was comparatively reduced. In summation, this study sheds light on the intricate interplay between distinct CeO2 morphologies and their divergent impacts on Fenton-like reactions. These findings expand our comprehension of the influences on its reactivity of CeO2 morphologies and open new insights for applications in diverse domains, from organic dye degradation to tumor therapy.

Microwave energized preparation and electrochemical performance of Ag added NiO/CeO2ternary nanocomposites for energy storage applications

Noble metal incorporated nanocomposites are extensively useful in supercapacitor applications owing to the nature of higher specific capacity and good rate capability. We have prepared Ag added NiO/CeO2 ternary mixed oxides through green synthesis route. The influence of Ag concentration on the structural, morphological and electrochemical characteristics of NiO/CeO2 has been examined and reported. The microstructure analysis reveals that the ternary mixed oxides to consist of Ag nanoclusters, CeO2 rods and NiO flakes. The formation of ternary mixed oxides has promoted the diffusion rate of electrolyte ions resulting in superior electrochemical performance. A maximum capacity of 639 C g–1 was obtained at a current density of 2 mA cm–2 for the ternary nanocomposites containing 9 mol% of silver. Moreover, the incorporation of substantial amount of Ag has effectively improved the lifespan and reduced charge transfer resistance. The findings of the present study strongly indicate that the Ag incorporated NiO/CeO2 is a suitable candidate for supercapacitor electrode fabrication.

Investigation on morphologies and supporter of cerium dioxide nanostructure on oxime based electrochemical sensors for organophosphorus detection

Pralidoxime (PAM) chloride has been taken as be an effective electrochemical probe to detect organophosphorus pesticides (OPs). In our previous work, CeO2 nanoparticles were proved to be able to significantly improve the sensitivity of the as-fabricated electrochemical sensor. In this paper, PAM-based sensors with different morphologies and supporters of nano-structured CeO2 were investigated. Firstly, CeO2 particles, CeO2 cubes and CeO2 rods were prepared and characterized. The results show that the CeO2 rods exhibits the best electrochemical performance because of its larger specific surface and better electrocatalytic activity. Secondly, multi-walled carbon nanotubes (MWCNTs), carbon powder (CP) and Carbon aerogel (CA) were adopted as supporter to disperse CeO2 rods. The results show that CA with large specific surface area and excellent adsorption property makes the fabricated sensor exhibit the best performance. Under the optimized conditions, the sensor has a chlorpyrifos detecting limit of 3.4 × 10−12 M in the range from 5 × 10−11 M to 1 × 10−7 M. Besides, the sensor also shows good repeatability, stability and reliability in the detection of chlorpyrifos.

Nanoshaped Cerium Oxide with Nickel as a Non-Noble Metal Catalyst for CO2 Thermochemical Reactions

Four different nanoshapes of cerium dioxide have been prepared (polycrystals, rods, cubes, and octahedra) and have been decorated with different metals (Ru, Pd, Au, Pt, Cu, and Ni) by incipient wetness impregnation (IWI) and ball milling (BM) methods. After an initial analysis based on oxygen consumption from CO2 pulse chemisorption, Ni-like metal, and two forms of CeO2 cubes and rods were selected for further research. Catalysts were characterized using the Brunauer-Emmett-Teller formula (BET), X-ray spectroscopy (XRD), Raman spectroscopy, scanning electron microscopy (SEM), UV-visible spectrophotometry (UV-Vis), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (H2-TPR) and CO2 pulse chemisorption, and used to reduce of CO2 into CO (CO2 splitting). Adding metals to cerium dioxide enhanced the ability of CeO2 to release oxygen and concomitant reactivity toward the reduction of CO2. The effect of the metal precursor and concentration were evaluated. The highest CO2 splitting value was achieved for 2% Ni/CeO2-rods prepared by ball milling using Ni nitrate (412 µmol/gcat) and the H2 consumption (453.2 µmol/gcat) confirms the good redox ability of this catalyst.

In Situ Neutron Scattering Studies on the Oxidation and Reduction of CeO2 and Pt–CeO2 Nanorods

The oxygen vacancy structure of ceria plays a key role in its performance as a favored material for catalysis applications. Here, we develop an understanding of the effects of Pt loading on the structural evolution of ceria nanorods under redox gas environments that mimic real automotive catalytic converters. In situ neutron scattering studies under redox flow reveal that both CeO2 and Pt–CeO2 nanorods share a bulk fluorite structure with the presence of surface Frenkel-type oxygen defects. However, Pt–CeO2 nanorods are more easily reducible than CeO2 rods as evidenced by an increased concentration of Ce3+, determined by NAP-XPS. Importantly, this work finds no evidence of oxygen vacancy ordered surface reconstruction which has been reported in earlier ex situ investigations. Thus, this work highlights the discrepancy between ex situ and in situ structural observations and emphasizes the need for robust in situ investigations of catalysts to develop industrially relevant materials.

Integrated CO2 capture and methanation on Ru/CeO2-MgO combined materials: Morphology effect from CeO2 support

Integrated CO2 capture and methanation (ICCM) is attracting more attention to promote the reduction of CO2 emission. This work developed and applied a set of combined materials using Ru/CeO2 as catalyst and physically mixed Li, Na, K-doped MgO as adsorbent for the ICCM process. The influences of morphologies of CeO2 (rod, particle, and cube) in combined materials are investigated explicitly in terms of CO2 conversion and CH4 yield. Compared to the CeO2 with cube morphology, the CeO2 with rod and particle morphologies showed better Ru dispersion and more abundant support-metal interaction (SMI). The combined materials with rod and particle morphologies CeO2 (Ru/rod-CeO2-MgO and Ru/particle-CeO2-MgO) show more superior catalytic performance (0.33 and 0.29 mmol/g for CH4 yield and 55.7% and 59.8% for CO2 conversion, respectively) than that with Ru/cube-CeO2-MgO. Furthermore, the Ru/rod-CeO2-MgO shows excellent catalytic stability and reusability during 9 cyclic ICCM evaluations. In situ DRIFTS of Ru/CeO2-MgO revealed that the formates and dissociated CO2 (Ru-CO) might be the critical methanation intermediates in ICCM.

Ceria morphology-dependent Pd-CeO2 interaction and catalysis in CO2 hydrogenation into formate

Several Pd catalysts supported on CeO2 with different morphologies (i.e. CeO2 rods (r-CeO2), cubes (c-CeO2) and polyhedra (p-CeO2)) were tested for the CO2 hydrogenation into formate. Remarkable morphology - dependent Pd-CeO2 interaction was observed, which was related to the oxygen vacancies in the CeO2. The r-CeO2 with the highest concentration of oxygen vacancy resulted in smaller Pd particles and more positively-charged Pd species in the Pd/r-CeO2 catalyst. The best performance was obtained over the Pd/p-CeO2 catalyst, giving a turnover frequency of 746 h−1 at 40 °C. The enhanced activity was due to the highest content of metallic Pd species in the catalyst, which was responsible for the facile activation of H2. Moreover, in situ spectroscopic results revealed that the hydrogenation of the carbonaceous intermediates was the rate - determining step. This work demonstrates oxide morphology engineering as a powerful strategy in developing efficient Pd - based catalysts for CO2 hydrogenation.

Ni-containing CeO2 rods for dry reforming of methane: Activity tests and a multiscale lattice Boltzmann model analysis in two model geometries

Experimental and theoretical modeling on low-temperature dry methane reforming over Ni-containing CeO2 rods was studied. The catalyst was characterized by means of N2 physisorption, in-situ XRD, TPR and H2 chemisorption techniques. The characterization studies revealed the distortion of CeO2 flourite structure due to the Ni incorporation. Lattice expansion (due to reduction) and contraction (due to oxidation) suggest the reversible redox nature of CeO2. Ni–O–Ce solid solution formation was evidenced by both XRD and TPR studies. H2 chemisorption study revealed that the catalyst reduction temperature plays a significant role in Ni dispersion. The catalyst showed similar activity trends in two model geometries: a between-two-plates microchannel fixed-bed reactor and a conventional fixed-bed reactor. The activity tests were conducted in the kinetic regime, where conversions of CH4 were not influenced with the gas flow rate. A lattice Boltzmann model for mixed gas flow was developed along with a boundary condition for catalytic sites. The lattice Boltzmann model was used in a multiscale simulation of the studied reaction systems and produced data that qualitatively matched the experiments.

Understanding morphology-dependent CuOx-CeO2 interactions from the very beginning

Elucidation of the CuOx-CeO2 interactions is of great interest and importance in understanding complex CuOx-CeO2 interfacial catalysis in various reactions. In the present work, we have investigated structures and catalytic activity in CO oxidation of CuOx species on CeO2 rods, cubes and polyhedra predominantly exposing {110}+{100}, {100} and {111} facets by the incipient wetness impregnation method with the lowest Cu loading of 0.025%. The structural evolution of CuOx species was found to depend on both the Cu loading and the CeO2 morphology. As the Cu loading increases, CuOx species are deposited preferentially on the surface defect of CeO2 and then aggregate and grow, accompanied by the formation of isolated Cu ions, CuOx clusters strongly/weakly interacting with the CeO2, highly dispersed CuO nanoparticles, and large CuO nanoparticles. The isolated Cu+ species and CuOx clusters weakly interacting with the CeO2 were observed mainly on the O-terminated CeO2{100} facets. Meanwhile, more Cu(I) species are stabilized during CO reduction processes in CuOx/c-CeO2 catalysts than in CuOx/r-CeO2 and CuOx/p-CeO2 catalysts. The catalytic activities of various CuOx/CeO2 catalysts in CO oxidation vary with both the CuOx species and the CeO2 morphology. These results comprehensively elucidate the CuOx-CeO2 interactions and exemplify their morphology-dependence.

Boosting the Removal of Diesel Soot Particles by the Optimal Exposed Crystal Facet of CeO2 in Au/CeO2 Catalysts.

Optimized surface facet of the catalysts is an efficient strategy to boost catalytic purification of diesel soot as important components of atmospheric fine particles. Herein, we have elaborately constructed the nanocatalysts of Au nanoparticles supported on the well-defined CeO2 (rod, cube, and polyhedron) with predominantly exposed facets of {110}, {100}, and {111}, respectively. The strong interaction between Au and CeO2 with the optimal crystal facet is crucial to adjust the active site density for activated O2, and the synergy effect of Au and the CeO2{110} facet possesses the largest density of active sites compared with other crystal facets of {100} and {111}. The catalytic activity for soot combustion was tuned by exposed crystal facets of CeO2. The Au/CeO2-rod catalyst exhibits the highest catalytic activity (T50 = 350 °C, TOF = 0.18 h-1) and the lowest apparent activation energy (72 kJ mol-1) during soot combustion. Based on the results of in situ Raman spectra, the formation and stability of oxygen vacancy located at the interface of the Au-O-Ce bond, boosting the key step of NO oxidation to NO2, are dependent on the exposed crystal facets of CeO2. It highlights a new strategy for the fabrication of high-efficient CeO2-based catalysts for the removal of soot particles or other pollution.

Investigations of supported Au-Pd nanoparticles on synthesized CeO2 with different morphologies and application in solvent-free benzyl alcohol oxidation

Au-Pd bimetallic nanoparticles immobilized on series of CeO2 supports with different morphologies, e.g., rod, cube, and polyhedrons were prepared through the deposition-precipitation method with a consequent investigation on their catalytic performances for benzyl alcohol oxidation in the absence of solvent. The experimental results exhibited that the morphology of CeO2 has a markedly impact on the catalytic performance of Au-Pd/CeO2. In which Au-Pd supported on CeO2 rod could achieve higher benzyl alcohol conversion than that supported on CeO2 polyhedrons and CeO2 cube, however, CeO2 cube supported Au-Pd showed the highest selectivity towards the production of benzaldehyde. ICP-AES, XRD, Raman, N2-BET, TEM, HAADF-STEM, and XPS were conducted to characterize the catalysts. The results revealed that the excellent behavior of Au-Pd/CeO2-rod in benzyl alcohol oxidation was closely related with the smaller size of CeO2 particle, the higher concentration of oxygen defects in support and the higher number of Ce3+ and Pd2+ species on the catalyst surface. The present study on the morphologies of CeO2 support in solvent-free benzyl alcohol oxidation would offer a notable approach for the future catalyst design.

Morphology-dependent CeO2 catalysis in acetylene semihydrogenation reaction

We herein investigated the catalytic performances and reaction mechanisms of CeO2 cubes (denoted as c-CeO2), CeO2 rods calcined at 500 °C (denoted as r-CeO2-500), and CeO2 rods calcined at 700 °C (denoted as r-CeO2-700) in the acetylene semihydrogenation reaction. r-CeO2-500 is most catalytically active while r-CeO2-700 is least. The acetylene semihydrogenation reaction catalyzed by various CeO2 nanocrystals was observed to follow the same reaction mechanism. C2H2 adsorbs at both O and Ce sites on CeO2 surfaces to form C2H2(a) species that facilely hydrogenates stepwise to C2H3(a) and C2H4(a). The surface hydrogenation reactions proceed more facilely at the O site than at the Ce site. The desorption of C2H4(a) proceeds slowly and is the rate-limiting step. c-CeO2, r-CeO2-500 and r-CeO2-700 do not exhibit obvious differences among these elementary surface reactions, but show much different abilities to dissociate H2 and chemisorb C2H2. The C2H2(a) coverage follows an order of r-CeO2-500 ≫ c-CeO2 ≈ r-CeO2-700. The ability to dissociate H2 follows an order of c-CeO2 > r-CeO2-500 ≫ r-CeO2-700. The observed morphology-dependent behaviors of various CeO2 nanocrystals were correlated to their defects and exposed facets. These results successfully demonstrate morphology-dependent CeO2 catalysis in acetylene semihydrogenation reaction and elucidate the underlying mechanisms.

Methanol plasma-catalytic oxidation over CeO2 catalysts: Effect of ceria morphology and reaction mechanism

The effect of CeO2 morphology on efficient methanol oxidation and the detailed reaction mechanism were investigated in a plasma-catalytic system at room temperature. CeO2 with different morphologies (i.e. rod, particle, and cube) were prepared by a hydrothermal method and characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), Raman and X-ray photoelectron spectroscopy (XPS). Among the three CeO2 morphologies, CeO2 rod catalyst had the most amount of oxygen vacancy. All the catalysts were tested for methanol oxidation in plasma, and the results showed that CeO2 rod catalyst exhibited the highest methanol conversion (94.1%), CO2 selectivity (90.1%) and ozone suppression. In situ Raman spectroscopy experiments proved that the performance of ozone decomposition was related to the amount of oxygen vacancy in CeO2. Surface oxygen vacancies in CeO2 rod catalyst acted as active sites for ozone decomposition, resulting in more reactive oxygen species that could effectively oxidize methanol and increase CO2 selectivity in the plasma-catalytic system. Finally, the evolution of adsorbed intermediate species and some key steps of methanol oxidation were discussed based on the results of plasma-catalytic in situ Fourier Transform Infrared Spectrometer (FTIR) experiments.

Structure-dependent activity of CeO2 supported Ru catalysts for CO2 methanation

In this study, CeO2 rods (CeO2/r), cubes (CeO2/c) and octahedra (CeO2/o) supported catalysts with identical Ru particle size were prepared. Trend in the activity of these catalysts for CO2 methanation was compared with the trend in their oxygen vacancy concentration measured after calcination. Ru/CeO2/r outperforms the other two catalysts with a reaction rate of 11.0 × 10−8 mols-1mRu-2 and selectivity to methane of 99% at 250 °C. Temperature-programmed reduction (TPR), Raman and X-ray photoemission spectroscopy (XPS) results confirms that Ru addition enhances reduction of CeO2. Also, Ru/CeO2/r is more reducible and contains more oxygen vacancies as compared to Ru/CeO2/o and Ru/CeO2/c, both after calcination as well as under reducing conditions. H2 consumption during TPR shows removal of oxygen equivalent to about 3 monolayers, implying diffusion of vacancies into the subsurface or bulk of CeO2. The catalyst with the highest concentration of oxygen vacancies is also the most active catalyst, suggesting that reactive adsorption CO2 at an oxygen vacancy is the rate determining step.

CO oxidation over ceria supported Au22 nanoclusters: Shape effect of the support

Gold (Au) nanoclusters have recently emerged as ideal models for understanding Au catalysis, because the nanosized Au particles have precise atomic numbers and uniform size. In this work, we studied for the first time the support shape effect on the catalysis of Au nanoclusters by using CO oxidation as a model reaction. Au22(L8)6 (L=1,8-bis(diphenylphosphino) octane) nanoclusters were supported on CeO2 rods or cubes, then pretreated at different temperatures (up to 673K), allowing the gradual removal of the organic phosphine ligands. CO oxidation test over these differently pretreated samples shows that CeO2 rods are much better supports than cubes for Au22 nanoclusters in enhancing the reaction rate. In situ IR spectroscopy coupled with CO adsorption indicates that the shape of CeO2 support can impact the nature and quantity of exposed Au sites, as well as the efficiency of organic ligand removal. Although CeO2 rods are helpful in exposing a greater percentage of total Au sites upon ligands removal, the percentage of active Au sites (denoted by Auδ+, 0<δ<1) is lower than that on CeO2 cubes. The in situ extended X-ray absorption spectroscopy (EXAFS) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) results show that the Au nanoclusters bound more strongly to the CeO2 rods than to the cubes where the Au nanoclusters show more sintering. Considering the typical redox mechanism for CO oxidation over supported Au nanoclusters and nanoparticles, it is concluded that the reactivity of the lattice oxygen of CeO2 is the determining factor for CO oxidation over Au22/CeO2. CeO2 rods offer more reactive lattice oxygen and abundant oxygen vacancies than the cubes and thus make the rods a superior support for Au nanoclusters in catalyzing low temperature CO oxidation.

Crystal plane dependent dopant migration that boosts catalytic oxidation

CeO2 rods with {110} facets and cubes with {100} facets were utilized as catalyst supports to probe the effect of crystallographic facets on the iron species and the structure-dependent catalytic performance.

Well-defined palladium-ceria interfacial electronic effects trigger CO oxidation.

Metal-support electronic interactions were investigated in CO oxidation by using a Pd/CeO2 model catalyst with well-defined interfaces, and electron transfer from Pd cubes to CeO2 nanorods through interfaces triggered CO oxidation at low temperature where standalone Pd and CeO2 are inert.