Oxygen Storage Capacity Of CeO2 Research Articles

Ceria-Supported Gold Nanoparticles as a Superior Catalyst for Nitrous Oxide Production via Ammonia Oxidation.

The production of nitrous oxide, N2 O, via NH3 oxidation is not on a practical scale due to the lack of a suitable catalyst. Instead, it is produced via thermal decomposition of NH4 NO3 , rendering N2 O too costly and limiting its prospective uses. Herein, we report CeO2 -supported Au nanoparticles (2-3 nm) as a highly selective catalyst for low-temperature NH3 oxidation to N2 O, exhibiting two orders of magnitude higher space-time yield than the state-of-the-art Mn-Bi/α-Al2 O3 and remarkable stability over 70 h on stream. The reaction proceeds via a Mars-van Krevelen mechanism, with the density of interfacial Auδ+ species and the oxygen storage capacity of CeO2 identified as the key performance descriptors. The latter could be enhanced by cobalt doping, improving the catalytic activity and setting a new benchmark for N2 O productivity. These findings establish NH3 oxidation as an efficient process for N2 O manufacture and facilitate its broader utilization in selective oxidations.

Ceria‐Supported Gold Nanoparticles as a Superior Catalyst for Nitrous Oxide Production via Ammonia Oxidation

AbstractThe production of nitrous oxide, N2O, via NH3 oxidation is not on a practical scale due to the lack of a suitable catalyst. Instead, it is produced via thermal decomposition of NH4NO3, rendering N2O too costly and limiting its prospective uses. Herein, we report CeO2‐supported Au nanoparticles (2–3 nm) as a highly selective catalyst for low‐temperature NH3 oxidation to N2O, exhibiting two orders of magnitude higher space–time yield than the state‐of‐the‐art Mn−Bi/α‐Al2O3 and remarkable stability over 70 h on stream. The reaction proceeds via a Mars–van Krevelen mechanism, with the density of interfacial Auδ+ species and the oxygen storage capacity of CeO2 identified as the key performance descriptors. The latter could be enhanced by cobalt doping, improving the catalytic activity and setting a new benchmark for N2O productivity. These findings establish NH3 oxidation as an efficient process for N2O manufacture and facilitate its broader utilization in selective oxidations.

Tailored Alkali Resistance of DeNOx Catalysts by Improving Redox Properties and Activating Adsorbed Reactive Species

SummaryIt is still challenging to develop strongly alkali-resistant catalysts for selective catalytic reduction of NOx with NH3. It is generally believed that the maintenance of acidity is the most important factor because of neutral effects of alkali. This work discovers that the redox properties rather than acidity play decisive roles in improving alkali resistance of some specific catalyst systems. K-poisoned Fe-decorated SO42−-modified CeZr oxide (Fe/SO42−/CeZr) catalysts show decreased acidity but reserve the high redox properties. The higher reactivity of NHx species induced by K poisoning compensates for the decreased amount of adsorbed NHx, leading to a desired reaction efficiency between adsorbed NHx and nitrate species. This study provides a unique perspective in designing an alkali-resistant deNOx catalyst via improving redox properties and activating the reactivities of NHx species rather than routinely increasing acidic sites for NHx adsorption, which is of significance for academic interests and practical applications.

Enhanced catalytic activity of Au-CeO2/Al2O3 monolith for low-temperature CO oxidation

In this study, hierarchical porous structured CeO2/Al2O3 monolith was prepared through the combination of sol-gel and heating-drying-calcination methods. Subsequently, the Au-CeO2/Al2O3 monoliths of different Au loadings were prepared by the deposition-precipitation method. When the Au3.2%-CeO2/Al2O3 monolith was used for low- temperature CO oxidation, compared with Au3.2%-CeO2/Al2O3 powder particles, excellent activity (temperature of 34 °C for complete conversion) and stability (up to 100 h) for the CO oxidation were achieved. Such an excellent performance was attributed to the unique hierarchical porous structure of monolith, the good oxygen storage capacity of CeO2, as well as the excellent CO adsorption and catalytic properties of the monodisperse Au nanoparticles.

Promoted stability and electrocatalytic activity of PtRu electrocatalyst derived from coating by cerium oxide with high oxygen storage capacity

Platinum-ruthenium (PtRu) electrocatalyst is traditionally used in the direct methanol fuel cells (DMFCs) as anodic electrocatalyst since Ru promotes the CO anti-poisoning of the neighbored Pt; however, Ru is dissolvable in acid media resulting in low stability of PtRu electrocatalyst. Here, we report a facile method to decelerate the Ru dissolution and to enhance the CO anti-poisoning by coating PtRu nanoparticles with cerium oxide (CeO2). C/PtRu@CeO2 exhibits only 30% loss in electrochemical surface area (ECSA) after 4200 potential cycles; in contrast, ECSA loss reaches 55% for the bare PtRu electrocatalyst. Meanwhile, the methanol oxidation reaction (MOR) activity is 2.8 fold higher by comparison with bare electrocatalyst. The enhanced MOR activity is attributed to the high oxygen storage capacity of CeO2 promoting the complete methanol oxidation. And the CO stripping voltammetry result shows that the CO oxidation peaks of C/PtRu@CeO2 negatively shift by 60 mV and 250 mV before and after stability test compared to those of C/PtRu electrocatalyst, respectively, suggesting an enhanced CO anti-positioning for C/PtRu@CeO2. Moreover, the fuel cell performance of C/PtRu@CeO2 reaches 49 mW cm−2; while, power density of C/PtRu is 45 mW cm−2 at 80 °C.

Enhancement of N2O decomposition performance by N2O pretreatment over Ce-Co-O catalyst

A series of Ce-Co-O binary oxides catalysts were synthesized by co-precipitation methods and tested for catalytic decomposition of N2O. The catalyst with 10 mol% of Ce showed superior activity. Significant enhancement of decomposition performance over N2O-pretreated Ce-Co-O catalysts was observed. The fresh, N2O-pretreated Co3O4 and Ce-Co-O catalysts were characterized by XRD, Raman, XPS, H2-TPR, TPD studies. It was found the deposited oxygen species (O∗), which generated from the dissociation of N2O, was responsible for the enhancement by N2O pretreatment. Due to the excellent oxygen storage capacity of CeO2, deposited O∗ could transfer from Co3O4 crystallites to CeO2 crystallites during the regeneration process of active sites. Pretreatment of N2O at high temperature resulted in much abundant deposited O∗ on the surface. After cooling temperature, the accumulation of massive O∗ would arouse another surface-to-N2O electron transfer route (from O∗ to N2O), leading to the cleavage of the NO bond. Meanwhile, the results revealed that the existence of electron transfer from catalysts to N2O was possible.

Enhanced oxygen storage capacity of CeO2 with doping-induced unstable crystal structure

Doping CeO2 with certain metallic ions has been shown to be an effective route to improving its oxygen storage capacity (OSC). We aimed to study the effects of dopants on the OSC of CeO2 from the perspective of crystallography. In the present study, we improved the OSC by construction of an extremely unstable CeO2 crystal structure based on crystallographic principles. By doping CeO2 with smaller Hf4+ and Sn4+ cations, the incorporated cations produced a lower cation to anion radius ratio in the crystal. The relative oxygen vacancy concentrations were 0.452 and 0.514, respectively, for 3 mol.% doping of Hf4+ and Sn4+, respectively. Our results showed that smaller dopant cations (radius of Sn4+ < Hf4+) led to more vacancies. The low temperature OSC of a CeO2 sample doped with a saturated amount of Hf4+ was 2.2 times as high as that of undoped CeO2 with a similar BET specific surface area. The partial least squares method was used to construct two linear functions for the Hf4+- and Sn4+-doping concentration vs. lattice parameters, and the relative oxygen vacancy concentration vs. low temperature OSC per BET surface area. Structure-performance relationships were developed to enable the design of CeO2 three-way catalysts.

Enhanced ethanol electro-oxidation on CeO2-modified Pt/Ni catalysts in alkaline solution

Pt/Ni catalysts modified with CeO2 nanoparticles were prepared by simple composite electrodeposition of Ni and CeO2, and spontaneous Ni partial replacement by Pt processes. The as-prepared CeO2-modified Pt/Ni catalysts showed enhanced catalytic performance for ethanol electro-oxidation compared with pure Pt/Ni, and acetate species were proposed to be the main products of the oxidation when using these catalysts. The content of CeO2 in the as-prepared catalysts influenced their catalytic activity, with Pt/NiCe2 (obtained from an electrolyte containing 100 mg/L CeO2 nanoparticles) exhibiting higher activity and relatively better stability in ethanol electro-oxidation. This was mainly due to the oxygen storage capacity of CeO2, the interaction between Pt and CeO2/Ni, and the relatively small contact and charge transfer resistances. The results of this work thus suggest that electrocatalysts with low price and high activity can be rationally designed and produced by a simple route for use in direct ethanol fuel cells.

Catalytic oxidative steam reforming of bio-ethanol for hydrogen production over Rh promoted Ni/CeO2–ZrO2 catalyst

Catalytic steam reforming of bio-ethanol in presence of oxygen for hydrogen production was studied over Ni/CeO2–ZrO2 and Rh–Ni/CeO2–ZrO2 catalysts. The catalysts were prepared by an impregnation-co-precipitation method and characterized by various characterization techniques. Characterization results revealed that addition of ZrO2 improves the oxygen storage capacity of CeO2 which improves catalytic activity. The effects of temperature, ethanol/water/oxygen molar ratio, and space time on ethanol conversion and product selectivities were investigated using a tubular fixed bed reactor at atmospheric pressure. Complete ethanol conversion was achieved at 600 °C with a maximum hydrogen yield of 4.6 mol/mol on the 1%Rh–30%Ni/CeO2–ZrO2 catalyst. Ethanol conversion and H2 selectivity were increased with increasing contact time, while CO and CH4 selectivity decreased. Investigation revealed Rh promoted catalyst exhibited better catalytic activity than 30%Ni/CeO2–ZrO2 catalyst for oxidative steam reforming of ethanol, indicating that addition of Rh improved the catalytic activity significantly by promoting water gas shift reaction.

Characterization of CeO2 Promoter of a Nanocrystalline Ni/MgO Catalyst in Dry Reforming of Methane

AbstractCeria‐promoted nickel catalysts supported on nanocrystalline MgO were prepared and employed in methane reforming with CO2. Their characterization was accomplished by X‐ray diffraction, BET, temperature‐programmed oxidation, and temperature‐programmed reduction (TPR) techniques. Cerium oxide (CeO2) proved to have a positive effect on catalytic activity, stability, and carbon suppression in methane reforming with CO2. A higher CeO2 content increased the catalyst activity and decreased the amount of deposited carbon over the spent catalysts. The suppression of carbon was related to the high oxygen storage capacity of CeO2. In addition, TPR analysis revealed that the CeO2 promoter reduced the chemical interaction between nickel and support, resulting in an increase in reducibility and higher dispersion of nickel.

Synthesis gas production from CO2 reforming of methane over Ni–Ce/SiO2 catalyst: The effect of calcination ambience

Ni–Ce/SiO2 catalysts were prepared by calcination under Ar, CO2, O2 and H2 ambience, and applied in CO2 reforming of methane for synthesis gas production. BET, XRD, XPS, TPR, SEM, TEM and TPH techniques were employed to characterize the fresh and used catalysts. Highly dispersed nickel oxides bearing stronger interaction with SiO2 prevented the metal sintering. The formation of reactive carbon species on Ni–Ce/SiO2 catalyst calcined under Ar ambience effectively promoted the carbon elimination and kept the catalyst more stable. Nevertheless, the oxygen storage capacity of CeO2 might partly lose on Ni–Ce/SiO2 calcined under H2 ambience. As a result, the inhibition of carbon elimination and the deposition of inert carbon were responsible for its partial deactivation.

Single Stage Water–Gas Shift Reaction Over Supported Pt Catalysts

Single stage water–gas shift reaction has been carried out at a gas hourly space velocity of 45,515 h−1 over supported Pt catalysts prepared by an incipient wetness impregnation method. CeO2, ZrO2, MgO, MgO–Al2O3 (MgO = 30 wt%) and Al2O3 were employed as supports for the target reaction in this study. 1 wt% Pt/CeO2 exhibited the highest CO conversion as well as very high CO2 selectivity due to high oxygen storage capacity of CeO2.

Effect of ceria nanoparticles into the Pt/C catalyst as cathode material on the electrocatalytic activity and durability for low-temperature fuel cell

An effective method is developed for preparing highly dispersed CeO2 nanoparticles on a Pt/C catalyst synthesized by a continuous two-step process as a cathode material in low-temperature fuel cell. The XRD patterns of the 20Pt–10CeO2/C catalyst reveal that both crystalline Pt and CeO2 phases coexist. The HR-TEM images show that Pt and CeO2 nanoparticles have average particle sizes of approximately 3.4nm and 4.2nm, respectively, with quite a narrow distribution between 3nm and 5nm. Based on the analysis of the polarization curves for the ORR, the optimum proportion of CeO2 into the 20Pt/C catalyst is 10wt%. In the ORR and single cell tests, the 20Pt–10CeO2/C catalyst shows higher performance than the commercial 20Pt/C catalyst, owing to the oxygen storage capacity of CeO2 and its ability to exchange oxygen rapidly with oxygen in the buffer. In the accelerated stability tests, the 20Pt–10CeO2/C catalyst has a better durability compared to the commercial 20Pt/C catalyst due to the existence of CeO2, which prevents the agglomeration and dissolution of Pt nanoparticles on the carbon support, extending the life of the catalyst.

CeO2 Promoted Ni/Al2O3 Catalyst in Combined Steam and Carbon Dioxide Reforming of Methane for Gas to Liquid (GTL) Process

The effect of ceria promotion over Ni/Al2O3 catalysts on the catalytic activity and coke formation was investigated in combined steam and carbon dioxide reforming of methane (CSCRM) to produce synthesis gas (H2/CO = 2) for gas to liquid (GTL) process. Ce-promoted Ni/Al2O3 catalysts were prepared by co-impregnation method. It has been found that the Ce promotion over Ni/Al2O3 catalyst is beneficial to catalytic activity and coke resistance. As a result, the catalyst promoted with 6 wt% Ce exhibits the highest activity as well as high coke resistance due to the improvement of Ni dispersion and high oxygen storage capacity of CeO2.

Temporal analysis of products (TAP) study on oxygen storage properties over Pt−Rh/CeO2 catalyst

The oxygen storage capacity of CeO2, Ce0.9Pr0.1O2, Pt−Rh/CeO2 and Pt−Rh/Ce0.9Pr0.1O2 was investigated by conventional GC pulse method and transient pulse techniques. It is shown that incorporation of PrOy into CeO2 matrix strongly promotes oxygen storage capacity (OSC) measured using the transient pulse technique. The improvement of OSC at low temperature is observed in Pt−Rh loaded onto CeO2 and Ce−Pr catalysts.