Effects of Fe doping on oxygen vacancy formation and CO adsorption and oxidation at the ceria(111) surface

To get insight into the catalysis effect of Fe doping in the CeO₂, the structures and electronic properties of Fe-doped CeO₂(111), and CO adsorption on the Ce_0.92 Fe_0.08O₂(111) surface are investigated by using the DFT + U method. The oxygen vacancy formation energy of the Fe-doped ceria(111) is reduced and the Fe dopant tends to be the center of oxygen vacancy clusters. On the Ce_0.92 Fe_0.08O₂(111) surface two types of adsorption of CO are found: physisorbed CO and formed CO₂. For the former, the molecule remains intact and for the latter, a CO₂ molecule releases and an oxygen vacancy forms on the surface.     

Influence of Fe3+-doping on optical properties of CeO2−y nanopowders

Ce_1?xFe_xO_2?y (0≤x≤0.05) nanopowders were synthesized using hydrothermal method at low calcination temperature and low doping regime. Structural and morphological characterization has been carried out by the X-ray diffraction method and non-contact atomic force microscopy. Vibrational properties were investigated by Raman spectroscopy. It was observed that the content of oxygen vacancies increased significantly with Fe doping up to 3 mol%. For higher dopant concentration, phase separation was detected. The optical properties of pure and Fe³⁺-doped CeO_2?y samples were investigated by spectroscopic ellipsometry. Several analytical models were applied to analyze the optical absorption onset of ceria defective structure. It was found that, Cody–Lorentz model most suitably described the sub-band gap region of CeO_2?y nanopowders and consequently gave more accurate band gap values, which are closer to the direct band gap transitions than to the indirect ones. The increased content of localized defect states in the ceria gap and corresponding shift of the optical absorption edge towards visible range in Fe-doped samples can significantly improve the optical activity of nanocrystalline ceria.     

Structure-activity Relation of Fe2O3–CeO2 Composite Catalysts in CO Oxidation

A series of Fe₂O₃–CeO₂ composite catalysts were synthesized by coprecipitation and characterized by X-ray diffraction (XRD), BET surface area measurement, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Their catalytic activities in CO oxidation were also tested. The Fe₂O₃–CeO₂ composites with an Fe molar percentage below 0.3 form solid solutions with the CeO₂ cubic fluorite structure, in which the doped Fe³⁺ initially substitutes Ce⁴⁺ in fluorite cubic CeO₂, but then mostly locate in the interstitial sites after a critical concentration of doped Fe³⁺. With an Fe molar percentage between 0.3 and 0.95, the Fe₂O₃–CeO₂ composites are mixed oxides of the cubic fluorite CeO₂ solid solution and the hematite Fe₂O₃. XPS results indicate that CeO₂ is enriched in the surface region of Fe₂O₃–CeO₂ composites. The Fe₂O₃–CeO₂ composites have much higher catalytic activities in CO oxidation than the individual pure CeO₂ and Fe₂O₃, and the Fe_0.1Ce_0.9 composite shows the best catalytic performance. The structure-activity relation of the Fe₂O₃–CeO₂ composites in CO oxidation is discussed in terms of the formation of solid solution and surface oxygen vacancies. Our results demonstrate a proportional relation between the catalytic activity of cubic CeO₂-like solid solutions and their density of oxygen vacancies, which directly proves the formation of oxygen vacancies as the key step in CO oxidation over oxide catalysts.     

Low Temperature Synthesis of Needle‐like α‐FeOOH and Their Conversion into α‐Fe2O3 Nanorods for Humidity Sensing Application

In this study, we report template and surfactant‐free, low temperature (70°C) synthesis of needle‐like α‐FeOOH and its conversion at 400°C into α‐Fe₂O₃ nanorods using Fe(+2) and Fe(+3) chlorides and urea as a hydrolysis‐controlling agent. The isolated needle‐like α‐FeOOH indicates asparagus‐type growth pattern having length ca. 600 nm with 80 nm diameter at base and apex diameter of around 10 nm. The sample on heating (α‐Fe₂O₃) shows nanorod‐like morphology. The samples were characterized using various physicochemical characterization techniques such as XRD, Raman spectroscopy, UV‐Vis spectroscopy, particle size distribution analysis, Field Emission Scanning Electron Microscopy (FE‐SEM), and humidity sensing performance. The humidity sensing behavior of both α‐FeOOH and α‐Fe₂O₃ was studied. The α‐FeOOH shows quicker (10 s) and higher response toward change in humidity from 20%RH to 90%RH as compared with α‐Fe₂O₃ (60 s). Their typical morphology and crystalline structure plays an important role in humidity sensing behavior.     

Defect induced magnetic transition in Co doped CeO2 sputtered thin films

Cobalt-doped cerium dioxide thin films exhibit room temperature ferromagnetism due to high oxygen mobility in doped CeO₂ lattice. CeO₂ is an excellent doping matrix as there is a possibility of it losing oxygen while retaining its structure. This leads to increased oxygen mobility within the fluorite CeO₂ lattice, leading to formation of Ce³⁺ and Ce⁴⁺ species. Magnetic ceria materials are important in several applications from magnetic data storage devices to magnetically recoverable catalysts. In this paper, the room temperature ferromagnetism of rf sputtered Co doped CeO₂ thin films is reported whereas undoped CeO₂ thin films exhibit paramagnetic behavior. The ferromagnetic properties of the Co doped films were explained based on oxygen vacancies created by Co ions in Ce sites. This is further supported by X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and Raman. Change in surface morphology due to Co doping of the samples were analyzed using atomic force microscopy (AFM).     

ZnO-capped nanorod gas sensors

This paper reports on the synthesis of pristine α-Fe₂O₃ nanorods and Fe₂O₃–ZnO core–shell nanorods using a combination of thermal oxidation and atomic layer deposition (ALD) techniques; the completed nanorods were then used for ethanol sensing studies. The crystal structure and morphology of the synthesized nanostructures were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The sensing properties of the pristine and core–shell nanorods for gas-phase ethanol were examined using different concentrations of ethanol (5–200 ppm) at different temperatures (150–250 °C). The XRD and SEM revealed the excellent crystallinity of the Fe₂O₃–ZnO core–shell nanorods, as well as their uniformity in terms of shape and size. The Fe₂O₃–ZnO core–shell nanorod sensor showed a stronger response to ethanol than the pristine Fe₂O₃ nanorod sensor. The response (i.e., the relative change in electrical resistance R_a/R_g) of the core–shell nanorod sensor was 22.75 for 100 ppm ethanol at 200 °C whereas that of the pristine nanorod sensor was only 3.85 under the same conditions. Furthermore, under these conditions, the response time of the Fe₂O₃–ZnO core–shell nanorods was 15.96 s, which was shorter than that of the pristine nanorod sensor (22.73 s). The core–shell nanorod sensor showed excellent selectivity to ethanol over other VOC gases. The improved sensing response characteristics of the Fe₂O₃–ZnO core–shell nanorod sensor were attributed to modulation of the conduction channel width and the potential barrier height at the Fe₂O₃–ZnO interface accompanying the adsorption and desorption of ethanol gas as well as to preferential adsorption and diffusion of oxygen and ethanol molecules at the Fe₂O₃–ZnO interface.     

Enhanced H2S sensing performance of TiO2-decorated α-Fe2O3 nanorod sensors

Pristine and TiO₂ nanoparticle-decorated Fe₂O₃ nanorods were synthesized via thermal oxidation of Fe thin foils, followed by the solvothermal treatment with titanium tetra isopropoxide (TTIP) and NaOH for TiO₂ nanoparticle-decoration. Subsequently, gas sensors were fabricated by connecting the nanorods with metal conductors. The structure and morphology of the pristine and TiO₂ nanoparticle-decorated Fe₂O₃ nanorods were examined via X-ray diffraction and scanning electron microscopy, respectively. The gas sensing properties of the pristine and TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensors with regard to H₂S gas were examined. The TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensor showed a stronger response to H₂S than the pristine Fe₂O₃ nanorod sensor. The responses of the pristine and TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensors were 2.6 and 7.4, respectively, when tested with 200 ppm of H₂S at 300 °C. The TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensor also showed a faster response and recovery than the sensor made from pristine Fe₂O₃ nanorods. Both sensors showed selectivity for H₂S over NO₂, SO₂, NH₃, and CO. The enhanced sensing performance of the TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensor compared to that of the pristine Fe₂O₃ nanorod sensor might be due to enhanced modulation of the conduction channel width, the decorated nanorods’ increased surface-to-volume ratios and the creation of preferential adsorption sites via TiO₂ nanoparticle decoration. The dominant sensing mechanism in the TiO₂ nanoparticle-decorated Fe₂O₃ nanorod sensor is discussed in detail.     

Promoting effect of Fe in oxidative dehydrogenation of ethylbenzene to styrene with CO2 (I) preparation and performance of Ce1 − xFexO2 catalyst

To improve the lattice structure of CeO₂ and the transmission capacity of oxygen, Ce_1 − xFe_xO₂(x ≤ 0.2)solid solutions were prepared by a hydrothermal method and used in oxidative dehydrogenation of ethylbenzene to styrene with CO₂. Ce_1 − xFe_xO₂ solid solutions were characterized by powder X-ray diffraction, Raman spectroscopy, N₂-adsorption, H₂ temperature-programmed reduction and H₂–O₂ titration. Results showed that approximately 20% of Fe^3 + could dissolve into the CeO₂ lattice while portions of Fe₂O₃ were highly dispersed on the surface of the Ce_1 − xFe_xO₂ solid solution. The formation of Ce–Fe solid solutions could create more oxygen vacancies to promote the absorption and activation of CO₂, which improves the activity of the catalyst and increased ethylbenzene conversion by as much as 13%.     

Mesoporous Fe-doped In2O3 nanorods derived from metal organic frameworks for enhanced nitrogen dioxide detection at low temperature

Mesoporous Fe-doped In₂O₃ nanorods derived from metal-organic frameworks (In/Fe-MIL-68s) were synthesized for NO₂ detection. The morphologies, structures and NO₂ gas-sensing performances of the Fe–In₂O₃ nanorods were systematically investigated. Texture characterizations demonstrate that the as-prepared Fe–In₂O₃ nanorods show rich porous structures, high specific surface areas and reduced grain sizes. Gas-sensing measurements display that the Fe–In₂O₃ nanorods derived from In/Fe-MIL-68s with the Fe(Ⅲ) content of 5 mol.% (Fe(5)-In₂O₃) exhibit high response (82) and short response/recovery time (70/65 s) towards 2 ppm NO₂ at 80 °C compared with their counterparts. Besides, superior selectivity and good stability are observed. The sensing mechanism studies reveal that the improved gas-sensing performances are attributed to the decrease in the gran size, the formation of rich oxygen vacancies and band gaps narrowing caused by Fe(Ⅲ) doping. Therefore, this work indicates that the Fe–In₂O₃ nanorods derived from metal-organic frameworks precursors can be a promising candidate for NO₂ detection.     

Transformation of CeO2 into a mixed phase CeO2/Ce2O3 nanohybrid by liquid phase pulsed laser ablation for enhanced photocatalytic activity through Z-scheme pattern

Cerium-based nanohybrids have attracted considerable attention in photocatalytic research owing to their remarkable potential in the photodegradation of environmental pollutants. However, the process of nanohybrid formation suffers from complex operations with specialized equipment, extreme conditions, long durations, and low yields, making it infeasible for efficient utilization. Considering the above obstacles, we herein describe the first pulsed laser ablation (PLA) for the synthesis of oxygen vacancy affluent CeO₂/Ce₂O₃ nanohybrids, as an alternative to hydrothermal and calcination methods. The microstructures and optical properties of the nanocomposites are characterized by TEM, XRD, XPS, and DRS analysis. The photocatalytic activity of the CeO₂/Ce₂O₃ nanohybrid showed an MB dye degradation rate superior to that of bare CeO₂ nanostructures. The enhanced performance of CeO₂/Ce₂O₃ was attributed to an oxygen-vacancy-driven Z-scheme mechanism, where efficient separation of the photogenerated charge carriers significantly contributed to photocatalytic enhancement. This was further evidenced by both PL and scavenger experiment results. Moreover, the synthesized CeO₂/Ce₂O₃ nanocomposites exhibit a strong blue emission, which could have potential applications in LED manufacturing.     

Hierarchical assembly of SnO2 nanorod on spindle-like α-Fe2O3 for enhanced acetone gas-sensing performance

Preparing a heterojunction structure in different metal oxides is an efficacious method to improve the gas-sensing properties. In this article, a novelty SnO₂ nanorod/spindle-like Fe₂O₃ heterostructure was successfully fabricated through a simple two-step hydrothermal route. The morphological characterization revealed that the spindle-shaped Fe₂O₃ with length and diameter of 400 and 100 nm were firstly fabricated by a hydrothermal process, and then a large number of SnO₂ nanorods (lengths of 30 nm and diameterd of 8 nm) covered the spindle-shaped Fe₂O₃ uniformly. In order to facilitate better practical applications, the gas sensing performance of sensors based on SnO₂/Fe₂O₃ nanostructures and pure Fe₂O₃ nanospindles on volatile organic compounds were systematically studied. Gas sensing tests indicated that such hierarchical SnO₂/Fe₂O₃ heterostructures revealed improved acetone sensing performance compared to pure spindle-like Fe₂O₃, and the enhanced gas-sensitivity performance possibly be attributed to the synergistic effect and heterojunction of the interface between spindle-like Fe₂O₃ and SnO₂ nanorod. Additionally, this research on as-obtained SnO₂/Fe₂O₃ hierarchical assembly may provide a new insight and a rational strategy to upgrade the sensing performance of certain semiconductor metal oxide materials by rationally designing various novel layered nanostructures in the future.     

Defect generation and morphology transformation mechanism of CeO2 particles prepared by molten salt method

Ceria is widely used in industrial fields due to its unique chemical properties. In this work, a series of CeO₂ particles with controllable morphology, size, and defect concentration were obtained by a simple molten salt method. The adjustment of temperature and molten salt concentration has a considerable effect on the morphology and particle size of the final CeO₂ particles while prolonging the holding time has little effect. Ion doping and reducing atmosphere calcination were used to regulate the defect concentration to improve the chemical activity of CeO₂ particles. SEM results show that the morphology of CeO₂ particles transforms from sphere to octahedron under the two treatments. The Rietveld refinement results and the XPS spectra indicate that increasing calcination temperature, reducing atmosphere calcination and ion doping are beneficial to improving the oxygen vacancies and Ce³⁺ concentration of CeO₂ samples, which are the reason for enhancing the photocatalytic activity of the samples. Moreover, the oriented attachment, agglomeration and merging of crystals formed by the decomposition of cerium precursors are the key to the growth of CeO₂ particles. Aggregates with exposed low-energy planes merge directly to form particles of various morphologies to maintain their own low energy.     

Tuning Ba0.5Sr0.5Co0.8Fe0.2O3-δ cathode to high stability and activity via Ce-doping for ceramic fuel cells

Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF) fuel-cell cathode stands out because of its ultrahigh ionic conductivity and excellent electrocatalytic activity, but it is still very subject to instability. Here, a new strategy of Ce doping is proposed to boost the stability and activity of the BSCF cathode. A one-pot combustion method is employed to synthesize (Ba_0.5Sr_0.5)_1–xCe_xCo_0.8Fe_0.2O_3-δ (x=0–0.2) cathodes. Both BSCF and (Ba_0.5Sr_0.5)_0.9Ce_0.1Co_0.8Fe_0.2O_3-δ have a cubic perovskite structure. (Ba_0.5Sr_0.5)_0.8Ce_0.2Co_0.8Fe_0.2O_3-δ shows two phases of cubic perovskite and fluorite ceria. Proper Ce doping can boost the electrical conductivity of BSCF, and can dramatically reduce the polarization resistance of BSCF cathode. Ce doping significantly improved BSCF cathode long-term stability by 160 h. Moreover, ten-percent Ce doping in BSCF highly improves single-cell output performance from 516.33 mW cm^?2 to 629.75 mW cm^?2 at 750 °C. The results reveal that Ce doping as a potential strategy for enhancing the stability and activity of BSCF cathode is promising.     

Catalytic Efficiency of Ceria–Zirconia and Ceria–Hafnia Nanocomposite Oxides for Soot Oxidation

The catalytic oxidation of soot particulates has been investigated over CeO₂, CeO₂–ZrO₂ and CeO₂–HfO₂ nanocomposite oxides. These oxides were synthesized by a modified precipitation method employing dilute aqueous ammonia solution. The prepared catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy, UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) and BET surface area methods. The soot oxidation has been evaluated by a thermogravimetric method under ‘tight contact’ conditions. The XRD results revealed formation of cubic CeO₂, Ce_0.75Zr_0.25O₂ and Ce_0.8Hf_0.2O₂ phases in case of CeO₂, CeO₂–ZrO₂ and CeO₂–HfO₂ samples, respectively. TEM studies confirm the nanosized nature of the catalysts. Raman measurements suggest the presence of oxygen vacancies, lattice defects and oxide ion displacement from normal ceria lattice positions. UV-Vis DRS studies show presence of charge transfer transitions Ce³⁺←O^2? and Ce⁴⁺←O^2? respectively. The catalytic activity studies suggest that the oxidation of soot could be enhanced by incorporation of Zr⁴⁺ and Hf⁴⁺ into the CeO₂ lattice. The CeO₂–HfO₂ combination catalyst exhibited better activity than the CeO₂–ZrO₂. The observed high activity has been related to the nanosized nature of the composite oxides and the oxygen vacancy created in the crystal lattice.     

Oxygen vacancy luminescence and band gap narrowing driven by Ce ion doping with variable valence in SnO2 nanocrystals

Although considerable research works have witnessed the important modulations of oxygen vacancies on the optical, electrical, and magnetic properties of SnO₂ nanostructures, it is not easy to control oxygen vacancy defects in such systems.The difficulty stems from that oxygen vacancy is a kind of atomic defect, and its distribution is sensitive to process conditions and external factors, which makes direct characterization and purposeful control difficult. The purpose of this work on Ce-doped SnO₂ nanocrystals is to investigate the tolerance of the host lattice to Ce ions, the population and evolution of Ce³⁺/Ce⁴⁺ ions, and the possibility to adjust oxygen vacancies by Ce³⁺ ions, and then focus on the influence of oxygen vacancy defects on the band gap and luminescence performance. As Ce doping concentration increases from 0 to 12 at.%, the doped system changes from Ce³⁺ dominated at low doping amount (≤3 at.%) to Ce³⁺/Ce⁴⁺ coexistence at medium doping concentration (3 at.% ∼ 9 at.%), to occurrence of CeO₂ impurity phase at over doping (∼12 at.%). The optimum doping occurs at 6 at.%, which corresponds to the saturated critical point of Ce³⁺ content and the maximum oxygen vacancy concentration. Importantly, the oxygen vacancies in the current Ce-doped SnO₂ nanocrystals is directly regulated by the Ce³⁺ ion concentration on the Sn sites, which plays an important role in the band gap tuning and visible light emission. With Ce concentration increasing from 0 to 12 at.%, the band gap monotonicity decreases from 3.36 eV to 3.12 eV, while the intensity of the oxygen vacancy luminescence band first increases and then decreases, with the turning point at 6 at.%. Both band gap narrowing effect and enhanced emission indicate that Ce-doped SnO₂ should be a promising method to design and manufacture visible light responsive SnO₂ based optoelectronic materials by manipulating oxygen vacancy defects.     

One-step synthesis of ternary MnO2–Fe2O3–CeO2–Ce2O3/CNT catalysts for use in low-temperature NO reduction with NH3

In this article, a facile one-step strategy for the synthesis of ternary MnO₂–Fe₂O₃–CeO₂–Ce₂O₃/carbon nanotubes (CNT) catalysts was discussed. The as-prepared catalysts exhibited 73.6–99.4% NO conversion at 120–180 °C at a weight hourly space velocity (WHSV) of 210 000 ml·g_cat^− 1·h^− 1, which benefited from the formation of amorphous MnO₂, Fe₂O₃, CeO₂, and Ce₂O₃, as well as high Ce^3 + and surface oxygen (O_ε) contents. The mechanism of formation of MnO₂–Fe₂O₃–CeO₂–Ce₂O₃/CNT catalysts was also proposed.     

Direct conversion of methane to synthesis gas using lattice oxygen of CeO2–Fe2O3 complex oxides

Three kinds of complex oxides oxygen carriers (CeO₂–Fe₂O₃, CeO₂–ZrO₂ and ZrO₂–Fe₂O₃) were prepared and tested for the gas–solid reaction with methane in the absence of gaseous oxidant. These oxides were prepared by co-precipitation method and characterized by means of XRD, H₂-TPR and Raman. The XRD measurement shows that Fe₂O₃ particles well disperse on ZrO₂ surface and Ce–Zr solid solution forms in CeO₂–ZrO₂ sample. For CeO₂–Fe₂O₃ sample, only a small part of Fe³⁺ has been incorporated into the ceria lattice to form solid solutions and the rest left on the surface of the oxides. Low reduction temperature and low lattice oxygen content are observed over ZrO₂–Fe₂O₃ and CeO₂–ZrO₂ samples, respectively by H₂-TPR experiments. On the other hand, CeO₂–Fe₂O₃ shows a rather high reduction peak ascribed to the consuming of H₂ by bulk CeO₂, indicating high lattice oxygen content in CeO₂–Fe₂O₃ complex oxides. The gas–solid reaction between methane and oxygen carriers are strongly affected by the reaction temperature and higher temperature is benefit to the methane oxidation. ZrO₂–Fe₂O₃ sample shows evident methane combustion during the reducing of Fe₂O₃, and then the methane conversion is strongly enhanced by the reduced Fe species through catalytic cracking of methane. CeO₂–ZrO₂ complex oxides present a high activity for methane oxidation due to the formation of Ce–Zr solid solution, however, the low synthesis gas selectivity due to the high density of surface defects on Ce–Zr–O surface could also be observed. The highly selective synthesis gas (with H₂/CO ratio of 2) can be obtained over CeO₂–Fe₂O₃ oxygen carrier through gas–solid reaction at 800 °C. It is proposed that the dispersed Fe₂O₃ and Ce–Fe solid solution interact to contribute to the generation of synthesis gas. The reduced oxygen carrier could be re-oxidized by air and restored its initial state. The CeO₂–Fe₂O₃ complex oxides maintained very high catalytic activity and structural stability in successive redox cycles. After a long period of successive redox cycles, there could be more solid solutions in the CeO₂–Fe₂O₃ oxygen carrier, and that may be responsible for its favorable successive redox cycles performance.     

The influence of chelating agents on cerium oxide decorated on graphite synthesized by the hydrothermal route

Morphology features of cerium oxide nanoparticles, such as size and agglomeration, are important as a coating that improves corrosion resistance and as reinforcement in mechanical applications. In this work, the influence of two heat treatments (160° and 190 °C) in combination with three different chelating agents in the preparation of CeO₂ and CeO₂ decorated on graphite (CeO₂_Gr) nanoparticles is studied. The novelty of this work is that CeO₂_Gr was successfully prepared using the hydrothermal method. All the samples evaluated by X-ray diffraction exhibit a single fluorite-type structure in the cubic phase and Fm3m space group. The spherical harmonics method using the Fullprof Suite program was used to determine the average crystallite sizes, which were 9 nm for CeO₂ and 7 nm for CeO₂_Gr. Transmission electron micrographs for the prepared samples with citric acid showed non-agglomerate particles with homogeneous particle sizes and a quasi-spherical shape distribution. Raman spectra show a band centre at 600 cm^-1 associated with the presence of Frenkel-type oxygen vacancies that induced the reduction of Ce⁴⁺ to Ce³⁺. The analysis of X-ray photoelectron spectra corroborates the coexistence of Ce³⁺ and Ce⁴⁺ species for CeO₂ and CeO₂_Gr nanoparticles. This work forms new perspectives in the development of CeO₂ decorated on graphite prepared by the hydrothermal method to obtain composites not only for sensing applications and wastewater treatment but also for corrosion resistance and reinforcement materials.     

Bulk oxygen promoted water–gas shift reaction activity over Pt/Ce0.6Zr0.4O2 catalyst

The water–gas shift (WGS) reaction of Pt/Ce_0.6Zr_0.4O₂ catalyst was studied, as well as the reference catalysts Pt/CeO₂ and Pt/ZrO₂. In situ electronic conductivity measurements under reactive atmosphere show that surface oxygen vacancies of Pt/Ce_0.6Zr_0.4O₂ diffuse into the bulk materials at the temperature typical for the operation of WGS reaction, i.e., bellow 623 K. Compared with Pt/CeO₂, it was found that the oxygen storage capacity (OSC) was higher for Pt/Ce_0.6Zr_0.4O₂ catalyst. Pt/Ce_0.6Zr_0.4O₂ shows a markedly higher CO conversion rate than Pt/CeO₂ and Pt/ZrO₂ catalysts, which was interpreted by more active oxygen species available and higher coke resistance.     

The Mechanism of N2O Decomposition on Fe-ZSM-5: An Isotope Labeling Study

The role of Fe promoters has been investigated on Pd/ceria, Pt/ceria and Rh/ceria catalysts for the water–gas shift (WGS) reaction in 25 torr of CO and H₂O under differential reaction conditions. While no enhancement was observed with Pt and Rh, the activity of Pd/ceria increased by as much as an order of magnitude upon the addition of an optimal amount of Fe. Similarly, the addition of 1 wt% Pd to an Fe₂O₃ catalyst increased the WGS rate at 453 K by a factor of 10 over that measured on Fe₂O₃ alone, while the addition of Pt or Rh to Fe₂O₃ had no effect on rates. The amount of Fe that was necessary to optimize the rates increased with Pd loading but was independent of the order in which Fe and Pd were added to the ceria. Increased WGS activity was also observed upon the addition of Fe to Pd supported on Ce_0.5Zr_0.5O₂. XRD measurements, performed after running the catalyst under WGS conditions, show the formation of a Fe–Pd alloy, even though similar measurements on an Fe/ceria catalyst showed that Fe₃O₄ was the stable phase for Fe in the absence of Pd. Possible implications of these results on the development of new WGS catalysts are discussed.