CeO2 Support Research Articles

Cerium(III) Nitrate Derived CeO2 Support Stabilising PtOx Active Species for Room Temperature CO Oxidation

AbstractA new approach for preparing a PtOx/CeO2 catalyst for low‐temperature CO oxidation has been developed. The approach includes; i) preparation of a CeO2 support through the controllable thermal decomposition of Ce(NO3)3 ⋅ 6H2O, and then ii) deposition of polynuclear platinum nitrato complexes ([H3O⊂18‐crown‐6]2[Pt2(μ2‐OH)2(NO3)8][Pt4(μ3‐OH)2(μ2‐OH)4(NO3)10]) on the CeO2 support. The NO3−‐rich ceria support produced at the onset temperature of Ce(NO3)3 ‐> CeO2 transformation (220 °C) yields the “PtOx/CeO2‐220” catalyst that shows intriguingly high activity in CO oxidation, at room temperature and below. To understand the nature of the low‐temperature catalytic activity, prepared catalysts have been studied using X‐ray photoelectron spectroscopy (XPS), Raman and operando X‐ray absorption fine structure spectroscopy (XAFS) and transmission electron microscopy (TEM).

Enhancement of the Generation and Transfer of Active Oxygen in Ni/CeO2 Catalysts for Soot Combustion by Controlling the Ni-Ceria Contact and the Three-Dimensional Structure.

The effect of the three-dimensionally ordered macroporous (3DOM) structure and the Ni doping of CeO2 on the physicochemical properties and catalytic activity for soot combustion was studied. Moreover, the way in which Ni is introduced to the ceria support was also investigated. For this, CeO2 supports were synthesized with uncontrolled (Ref) and 3DOM-structured morphology, and their respective Ni/CeO2 catalysts were prepared by impregnation of the previously synthesized supports or by successive impregnation of both precursors (Ni and Ce) on the 3DOM template. Conclusions reached in this study are: (1) the 3DOM structure increases the surface area of the catalysts and improves the catalyst-soot contact. (2) The doping of CeO2 with Ni improves the catalytic activity because the NiO participates in the catalytic oxidation of NO to NO2, and also favors the production of active oxygen and the catalyst oxygen storage capacity. (3) Ni incorporation method affects its physicochemical and catalytic properties. By introducing Ni by successive infiltration in the solid template, the CeO2 crystal size is reduced, Ni dispersion is improved, and the catalyst reducibility is increased. All of these characteristics make the catalyst synthesized by successive infiltration to have higher catalytic activity for soot combustion than the Ni-impregnated CeO2 catalyst.

Efficient Optimization of Electron/Oxygen Pathway by Constructing Ceria/Hydroxide Interface for Highly Active Oxygen Evolution Reaction

AbstractOwing to the unique electronic properties, rare‐earth modulations in noble‐metal electrocatalysts emerge as a critical strategy for a broad range of renewable energy solutions such as water‐splitting and metal–air batteries. Beyond the typical doping strategy that suffers from synthesis difficulties and concentration limitations, the innovative introduction of rare‐earth is highly desired. Herein, a novel synthesis strategy is presented by introducing CeO2 support for the nickel–iron–chromium hydroxide (NFC) to boost the oxygen evolution reaction (OER) performance, which achieves an ultralow overpotential at 10 mA cm−2 of 230.8 mV, the Tafel slope of 32.7 mV dec−1, as well as the excellent durability in alkaline solution. Density functional theory calculations prove the established d–f electronic ladders, by the interaction between NFC and CeO2, evidently boosts the high‐speed electron transfer. Meanwhile, the stable valence state in CeO2 preserves the high electronic reactivity for OER. This work demonstrates a promising approach in fabricating a nonprecious OER electrocatalyst with the facilitation of rare‐earth oxides to reach both excellent activity and high stability.

Dry reforming of methane over nickel supported on Nd-ceria: enhancement of the catalytic properties and coke resistance.

Nickel (5 wt%) supported on Nd-doped ceria was studied as catalysts in the DRM reaction at stoichiometric conditions in the range of 600–800 °C. Ce1−xNdxO2−δ supports with different Nd contents (x = 0, 0.05, 0.1 and 0.2) were successfully synthesized. The role of oxygen vacancies by the incorporation of Nd3+ into the ceria lattice was investigated. These species were quantified by XRD and Raman spectroscopy, showing a linear dependence as a function of Nd content. Ni/Nd–ceria catalysts were prepared by wet impregnation. Although formation of oxygen vacancies, as well as microstructural features of the support (smaller crystallite sizes, higher surface area, and developed mesoporous structure) were improved as a function of the Nd content, no significant differences were observed in the catalytic properties of Ni/Nd–ceria in the DRM reaction. Despite this, compared to undoped ceria, all the Nd-doped CeO2 catalysts present an enhanced activity and stability, and the best catalytic performance was observed in the Ni/Ce0.95Nd0.05O2−δ sample. Quantification of carbon residues in spent catalysts showed, as expected, lower amounts in the Ni/Nd–ceria samples; nevertheless, among them, the catalyst with the higher amount of oxygen vacancies, is the one with the higher carbon residues. Incorporation of Nd in ceria changes the acid/base properties, diminishing the gasification capacity of the carbonaceous species. These results emphasize that the activity and stability in the Ni/Nd–ceria catalysts for the DRM reaction depend on two key factors, the redox and the acid/base properties of the CeO2 supports, offering insights about the necessary and adequate balance between these properties.

Catalytic Combustion of Chlorobenzene with VOx/CeO2 Catalysts： Influence of Catalyst Synthesis Method

Abstract VOx/CeO2 catalysts with various nanostructure were synthesized by the hydrothermal method and used in catalytic combustion of chlorobenzene (CB) at a low temperature. XRD, BET, TEM, Raman, XPS, and H2-TPR were employed to reveal that catalysts VOx on CeO2 support had considerable activity for CB combustion. VOx/CeO2 catalysts prepared with ammonium to adjust pH value and added P123 as a surfactant, showed the highest CB conversion ratio of 60 % at 250 °C and 100 % at 400 °C. It showed that preparation method could infect the shape evolution and surface species during the synthesis. The new phase CeVO4 formed in VOx/CeO2 catalysts improved the catalysts efficiency by increasing oxygen vacancies.

Uniformity Is Key in Defining Structure-Function Relationships for Atomically Dispersed Metal Catalysts: The Case of Pt/CeO2.

Catalysts consisting of atomically dispersed Pt (Ptiso) species on CeO2 supports have received recent interest due to their potential for efficient metal utilization in catalytic convertors. However, discrepancies exist between the behavior (reducibility, interaction strength with adsorbates) of high surface area Ptiso/CeO2 systems and of well-defined surface science and computational model systems, suggesting differences in Pt local coordination in the two classes of materials. Here, we reconcile these differences by demonstrating that high surface area Ptiso/CeO2 synthesized at low Pt loadings (<0.1% weight) exhibit resistance to reduction and sintering up to 500 °C in 0.05 bar H2 and minimal interactions with CO-properties previously seen only for model system studies. Alternatively, Pt loadings >0.1 weight % produce a distribution of sub-nanometer Pt structures, which are difficult to distinguish using common characterization techniques, and exhibit strong interactions with CO and weak resistance to sintering, even in 0.05 bar H2 at 50 °C-properties previously seen for high surface area materials. This work demonstrates that low metal loadings can be used to selectively populate the most thermodynamically stable adsorption sites on high surface area supports with atomically dispersed metals. Further, the site uniformity afforded by this synthetic approach is critical for the development of relationships between atomic scale local coordination and functional properties. Comparisons to recent studies of Ptiso/TiO2 suggest a general compromise between the stability of atomically dispersed metal catalysts and their ability to interact with and activate molecular species.

Investigating the dynamic structural changes on Cu/CeO2 catalysts observed during CO2 hydrogenation

CO2 hydrogenation is one route for partial CO2 abatement while producing valuable chemical products. Cu/CeO2 catalysts have attracted great interest as materials that facilitate the efficient hydrogenation of CO2 into methanol and CO. This paper investigates the effect of preparation methods on the structure, function and activity of Cu/CeO2 catalysts. The catalysts have been prepared by deposition–precipitation (DP) and the co-precipitation (CP) methods. The activity tests for the catalysts were conducted in a high-pressure packed bed reactor in the temperature range of 200–300 °C at 50 bar pressure. The DP catalyst showed higher methanol productivity and lower methanol selectivity compared its CP counterpart. The reasons for the higher performance of the DP catalyst and other structural and functional differences have been investigated through in-depth characterization using synchrotron radiated in-situ powder diffraction, DRIFTS, XPS, HR-TEM, TPR and N2O decomposition used to determine copper surface area. The higher methanol productivity in the DP catalyst was attributed to the higher Cu surface area and dispersion. Additionally, the in-situ synchrotron-based powder diffraction measurements provide fundamental insights on the interesting differences in the CeO2 structure i.e. the lattice parameter and the lattice microstrain during the reduction step that could be attributed to the size difference in the CeO2 support nanoparticles.

Evaluation of the Redox Performance and Characterization of Fe2O3/CeO2/ZrO2 Oxygen Carriers under High Temperature in Situ Gasification Chemical-Looping Combustion Conditions

Iron-based oxygen carriers with a CeO2 support have interesting redox applications in chemical-looping combustion (CLC). CeO2 behaves as an active support for many oxygen carrier applications becau...

Design of Ceria Catalysts for Low‐Temperature CO Oxidation

AbstractA catalyst active to carbon monoxide (CO) oxidation at low temperature is essential for environmental conservation, saving fuel and improvement of the quality of human life. Rational design of CO oxidation catalyst on the basis of comprehensive understanding of physicochemical properties of catalytic materials, rather than simply searching for the catalyst based on trial‐and‐error, is a promising approach to meet the increasingly stringent regulations. This review covers metal‐doped and ‐loaded system based on CeO2 catalysts as strategies to significantly improve CO oxidation activity at low temperature. When incorporated into CeO2 lattice, active metals significantly lower the oxygen vacancy formation energy (Evf) of the catalyst surface, resulting in high catalytic activities at low temperature. When the active metals are loaded on the CeO2 surface, many active sites could be acquired by increasing the dispersion, and the catalytic activity can be dramatically improved by newly introducing the interfacial sites between the metals and the CeO2 support. Doping the support could further improve this loaded system in terms of specific surface area, oxygen vacancy formation, and spillover effects. In this review, based on this knowledge, we propose a rational design approach to a robust low‐temperature CO oxidation catalysts. The desirable CO oxidation catalysts identified from the interplay between theoretical and experimental approaches would ultimately improve the quality of human life, and create potential economic benefits by alleviating air pollution.

High-performance of nanostructured Ni/CeO2 catalyst on CO2 methanation

Cost-effective CO2 conversion to highly demanded fuels or chemicals is challenging. Accordingly, a nanostructured Ni/CeO2-SGM catalyst synthesized by a simple sol-gel method was developed to make progress in this area for CO2 methanation. CO2 conversion reached 80.5 % and the achieved CH4 selectivity was as high as 95.8 % even at a temperature as low as 250 ºC under a high gas hourly space velocity of 40,000 mL·g−1·h−1 for 106 h over Ni/CeO2-SGM. The activity of Ni/CeO2-SGM is 2–48 times of the state-of-the-art Ni/CeO2 catalysts. It was found that the high-performance mainly results from a formate pathway via a *CHO intermediate along with the significant synergy of efficient dissociation of H2 by small nickel NPs and the strong adsorption and activation of CO2 by CeO2 support. The findings with the performance of nanostructured Ni/CeO2-SGM and the associated reaction mechanism, will be significantly beneficial to development of new generation of CO2 methanation catalysts.

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.

On-Filter Integration of Soot Oxidation and Selective Catalytic Reduction of NOx with NH3 by Selective Two Component Catalysts

A group of catalysts was developed with the purpose of enhancing the soot oxidation in the selective catalytic reduction on filter system, without negatively effecting the NOx conversion associated to NH3 oxidation. The impregnation with alkali metal of a series of supports, characterized by a lack of strong superficial acid sites, improved soot oxidation simultaneously preventing ammonia adsorption, thus its catalytic oxidation. Strong synergy was observed between a ZrO2–CeO2 support and potassium, decreasing the T50 of the soot conversion of 170 °C in loose contact. This catalyst was added to a Fe-ZSM5 selective catalytic reduction (SCR) catalyst without negative effect for the SCR activity. The complex interaction between the potassium-based soot oxidation catalyst and the SCR one was investigated. The soot–soot oxidation catalyst-SCR catalyst contact mode was found to be a key factor and the increased contact of the soot–soot oxidation catalyst is preferable. Such dual component catalyst system was demonstrated to be promising for simultaneous removal of NOx and soot on a single filter.

Engineering the epitaxial interface of Pt-CeO2 by surface redox reaction guided nucleation for low temperature CO oxidation

The interface between metal nanoparticles (NPs) and support plays a vital role in catalysis because both electron and atom exchanges occur across the metal-support interface. However, the rational design of interfacial structure facilitating the charge transfer between the neighboring parts remains a challenge. Herein, a guided nucleation strategy based on redox reaction between noble metal precursor and support-surface is introduced to construct epitaxial interfaces between Pt NPs and CeO2 support. The Pt/CeO2 catalyst exhibits near room temperature catalytic activity for CO oxidation that is benefited from the well-defined interface structure facilitating charge transfer from CeO2 support to Pt NPs. Meanwhile, this general approach based on support-surface-induced-nucleation was successfully extended to synthesize Pd and Cu nanocatalysts on CeO2, demonstrating its universal and feasible characteristics. This work is an important step towards developing highly active supported metal catalysts by engineering their interfaces.

The controlled preparation and performance of Fe, Co-modified porous ceria nanorods for the total oxidation of propane

Porous ceria nanorods modified with Fe or Co were prepared via a hydrothermal method. The structural properties, catalytic activities for the total oxidation of propane, and catalytic mechanisms of these materials were systematically investigated by X-ray diffraction, Raman spectroscopy, N2 adsorption–desorption, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, catalytic activity measurements and in situ Fourier transform infrared spectroscopy. Co-modified ceria exhibited the best catalytic activity during propane oxidation as well as enhanced reducibility due to the synergistic interactions between the Co and the CeO2 support. Variations in the activating ability and reducibility of the catalysts resulted in the formation of distinctive intermediates during the catalytic process, and this explained the observed differences in catalytic performance.

Transfer hydrogenation from glycerol over a Ni-Co/CeO2 catalyst: A highly efficient and sustainable route to produce lactic acid

Bimetallic Ni-Co catalysts supported on nanosized CeO2 were prepared and investigated as heterogeneous catalysts for the transfer hydrogenation between glycerol and various H2 acceptors (levulinic acid, benzene, nitrobenzene, 1-decene, cyclohexene) to selectively produce lactic acid (salt) and the target hydrogenated compound. The bimetallic NiCo/CeO2 catalyst showed much higher activity than the monometallic Ni or Co counterparts (with equal total metal mass), thus indicating strong synergetic effects. The interaction between the metallic sites and the CeO2 support was thoroughly characterised by means of transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDX) mapping, X-ray photoelectron spectroscopy (XPS), hydrogen-temperature programmed reduction (H2-TPR) and X-ray diffraction (XRD). Combining characterisation and catalytic results proved that the Ni species are intrinsically more active than Co species, but that incorporating Co into the catalyst formulation prevented the formation of large Ni particles and led to highly dispersed metal nanoparticles on CeO2, thus leading to the observed enhanced activity for the bimetallic system. The highest yield of lactic acid (salt) achieved in this work was 93% at 97% glycerol conversion (160 °C, 6.5 h at 20 bar N2, NaOH: glycerol = 1.5). The NiCo/CeO2 catalyst also exhibited high activity and selectivity towards the target hydrogenated products in the transfer hydrogenation reactions between glycerol and various H2 acceptors. Batch recycle experiments showed good reusability, with retention of 80% of the original activity after 5 runs.

The Enhancement of the Catalytic Oxidation of CO on Ir/CeO2 Nanojunctions.

Heterogeneous catalysts facilitate various chemical reactions through the changing of their surface charge density. Herein, we demonstrate an interface engineering strategy to enhance the Ir catalytic performance for oxidation of CO by constructing Ir/CeO2 nanojunctions using a wet chemical reduction process. The as-prepared Ir/CeO2 nanojunctions show a complete CO conversion temperature (T100) of 110 °C under 1 vol % CO and retains long-term durability even after 24 h. The Ir atoms and CeO2 supports were connected by O atoms, which changes the surface electronic structure of Ir atoms. DFT calculations demonstrate that the significant increase in electron density at the interface between Ir and CeO2 plays a pivotal role in the enhancement of CO oxidation.

Chemical and Electronic Changes of the CeO2 Support during CO Oxidation on Au/CeO2 Catalysts: Time-Resolved Operando XAS at the Ce LIII Edge

While being highly active for the CO oxidation reaction already at low temperatures, Au/CeO2 catalysts suffer from continuous deactivation with time on stream, with the activity and deactivation depending on the initial catalyst activation procedure. In previous X-ray absorption measurements at the Au LIII edge, which focused on changes in the electronic and geometric changes of Au, we found a modest increase of the Au particle size during reaction, with the Au nanoparticles (NPs) present in a dominantly metallic state during reaction, regardless of the pretreatment. Here we aim at expanding on these insights by examining the changes in electronic and chemical composition of the CeO2 support induced by different pretreatment procedures and during subsequent CO oxidation at 80 °C, by following changes at the Ce LIII near edge region in time-resolved operando X-ray absorption measurements. The results indicate a strong dependence of the initial concentration of Ce3+ ions on the pretreatment, while during subsequent reaction this rapidly approaches a steady-state value which depends on the oxidative/reductive character of the reaction gas mixture, but is largely independent of the pretreatment. These results are discussed and related to earlier finding on the electronic properties of Au nanoparticles under identical reaction conditions.

Liquid-Phase Oxidation of Ethylene Glycol on Pt and Pt–Fe Catalysts for the Production of Glycolic Acid: Remarkable Bimetallic Effect and Reaction Mechanism

A highly active and selective Pt–Fe alloy catalyst on CeO2 support is reported in this work for aqueous phase oxidation of ethylene glycol (EG) to glycolic acid. The Pt–Fe nanoparticles are highly ...

Ceria supported ruthenium nanoparticles: Remarkable catalyst for H2 evolution from dimethylamine borane

Ceria supported ruthenium nanoparticles (Ru0/CeO2) are synthesized by impregnation of Ru3+ ions on CeO2 powders followed by sodium borohydride reduction of Ru3+/CeO2. Their characterization was achieved using analytical methods including TEM, XRD, BET, SEM, and XPS. All the results reveal the formation of ruthenium(0) nanoparticles in 1.8 ± 0.3 nm size on CeO2 support. Ru0/CeO2 nanoparticles show high activity in catalyzing the H2 evolution from dimethylamine borane (DMAB). Ru0/CeO2 nanoparticles with 0.55% wt Ru provide the highest turnover frequency (812 h−1) for releasing H2 from DMAB at 60 °C and a total of 2500 turnovers before deactivation. High activity of Ru0/CeO2 nanoparticles for catalytic dehydrogenation of DMAB is attributable to the reducible nature of CeO2 support. Ce3+ defects formation in ceria under reducing conditions of dehydrogenation causes accumulation of negative charge on the oxide support, which makes oxide surface attractive for the ruthenium(0) nanoparticles. This, in turn, causes an enhancement in the metal-support interaction and thus in catalytic activity. The XPS analysis of bare ceria and Ru0/CeO2 demonstrates the increase in the concentration of Ce3+ defects after catalysis. Ru0/CeO2 nanoparticles are also reusable catalyst for H2 evolution from DMAB retaining 40% of initial activity after 4th run of reaction. The catalytic activity of Ru0/CeO2 nanoparticles and activation energy of catalytic dehydrogenation are compared with those of the other ruthenium based catalysts known in literature.

Surface engineering of nano-ceria facet dependent coupling effect on Pt nanocrystals for electro-catalysis of methanol oxidation reaction

Surface engineering of metal-support coupling interaction is significant in the catalytic reactions. Herein, we demonstrate a nano-ceria facet dependent coupling effect on Pt nanocrystals for the electro-catalysis of methanol oxidation in acid electrolyte for fuel cell reaction. It is found CeO2 exposed with different facets have different Pt nanocrystals trapping/coupling ability, and this interplay induces the different surface chemical states of Pt and Ce in terms of the content of Pt(0) and Ce3+, Pt-O-Ce bonding, the oxygen vacancy and electronic states. The CeO2-rods enclosed by (1 1 0) and (1 0 0) facets coupled Pt nanocrystals show much higher catalytic activity and durability than that of CeO2-plates and CeO2-cubes exposed by (1 1 1) and (1 0 0) facets respectively. Specifically, Pt-CeO2-rods exhibit a specific activity of 2.04 mA cm−2, nearly 1.5 and 2.6-fold enhancement than that of Pt-CeO2-cubes and Pt-CeO2-plates. Facet-dependence anti-poisoning and stability are also discovered after 8000 cyclic voltammetry cycles on the proposed catalyst. The weakened poisoning intermediates adsorption ability via bi-functional mechanism and the metal-support interaction induced by different CeO2 support can account for the facet-dependent methanol electro-oxidation performance on Pt-CeO2 catalyst system. The current work demonstrates the significance of assistant catalyst facet/morphology tuning in the fuel cells catalyst design and fabrication.