Cerium Tungsten Research Articles

Novel cerium–tungsten–titanium-based catalyst for an efficient oxidative desulfurization material in fuel oil under a laboratory-scale setup

Novel cerium–tungsten–titanium-based catalyst for an efficient oxidative desulfurization material in fuel oil under a laboratory-scale setup

Influence of g-C3N4 doping on the NH3-SCR activity of Cerium–tungsten–titanium mixed oxide catalyst

Influence of g-C3N4 doping on the NH3-SCR activity of Cerium–tungsten–titanium mixed oxide catalyst

Unveiling the Remarkable Arsenic Resistance Origin of Alumina Promoted Cerium-Tungsten Catalysts for NH3-SCR.

The deactivation of selective catalytic reduction (SCR) catalysts by arsenic is a serious problem for NH3-SCR. However, it is tough to design catalysts with good resistance to arsenic compared to other poisons such as alkali metal, SO2, etc., because As not only deteriorates surface acidity but also redox property, causing excessive N2O generation. A novel CeO2-WO3-Al2O3 catalyst is developed with excellent arsenic resistance in this study, which presents only less than 10% activity loss compared to nearly 40% loss for CeO2-WO3 with same arsenic loading (As: 2.1 wt %). Moreover, a significant negative impact on the N2O generation for poisoning catalysts from 26.7 to 7.5 ppm has also been found. The characterization results demonstrated that the interaction between cerium and arsenic lead to Lewis acid sites and oxygen vacancies loss as well as unexpected oxidation sites formation. However, the introduction of Al weakens the deactivation effect by replacing cerium to interact with arsenic. Three aspects are proposed for obtaining excellent arsenic-resistant performance: (1) the protection of Lewis acid sites, (2) release of oxygen vacancies from As restriction, and (3) confinement of As5+ oxidizing capacity. This study may provide an effective strategy to design and develop novel virtuous antipoisoning catalysts.

Selective catalytic reduction of NOx with NH3 over cerium–tungsten–titanium mixed oxide catalyst: Synergistic promotional effect of H2O2 and Ce4+

Abstract

The Role of Nitrate on the Sol-Gel Spread Self-Combustion Process and Its Effect on the NH3-SCR Activity of Magnetic Iron-Based Catalyst

Sol-gel spread self-combustion is the burning of the complexing agent in dried gel and the oxidant. Meanwhile, high temperature takes place during the combustion process, which is harmful to the pore structure of the catalyst. The nitrate from metal nitrate precursors as an oxidant could participate in the spread of the self-combustion process. Therefore, the influence of nitrate from metal nitrate on the spread self-combustion of an iron–cerium–tungsten citric acid gel and its catalytic performance of NOx reduction were investigated by removing nitrate via the dissolution of washing co-precipitation with citric acid and re-introducing nitric acid into the former solution. It was found that the removal of nitrate contributes to enhancing the NH3–SCR activity of the magnetic mixed oxide catalyst. The NOx reduction efficiency was close to 100% for Fe85Ce10W5–CP–CA at 250 °C while the highest was only 80% for the others. The results of thermal analysis demonstrate that the spread self-combustion process of citric acid dried gel is enhanced by re-introducing nitric acid into the citric acid dissolved solution when compared with the removal of nitrate. In addition, the removal of nitrate helps in the formation of γ-Fe2O3 crystallite in the catalyst, refining the particle size of the catalyst and increasing its pore volume. The removal of nitrate also contributes to the formation of Lewis acid sites and Brønsted acid sites on the surface of the catalyst compared with the re-introduction of nitric acid. The in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) demonstrates that both Eley–Rideal (E–R) and Langmuir–Hinshelwood (L–H) mechanisms exist over Fe85Ce10W5–CP–CA at 250 °C with E–R as its main mechanism.

Amorphous saturated cerium–tungsten–titanium oxide nanofiber catalysts for NOx selective catalytic reaction

A nano-fibrous, amorphous supersaturated CeO2/W–TiO2 SCR catalyst endowed with well-connected and open porosity, high reactivity, and tunable chemistry is herein proposed.

Environment-friendly magnetic Fe-Ce-W catalyst for the selective catalytic reduction of NO x with NH3: influence of citric acid content on its activity-structure relationship.

The influence of the citric acid content on the structural and redox properties of a magnetic iron–cerium–tungsten mixed oxide catalyst prepared through a microwave-assisted citric acid sol–gel method is investigated via TG–DTG–DSC, XRD, N2 adsorption–desorption, XPS, H2-TPR and NH3-TPD. Additionally, the NH3-SCR activity of the magnetic FeCeW-m (m = 0.25, 0.5 and 1.0) catalysts are also studied. The results indicate that an increase in citric acid content strengthens the sol–gel reaction between citric acid and metal ions and promotes the formation of the γ-Fe2O3 crystallite not α-Fe2O3. Meanwhile, it decreases the BET surface area and pore volume of the catalyst. Furthermore, the surface concentration of iron species on the catalyst is enhanced when the molar ratio of citric acid/(Fe + Ce + W) increases from 0.25 to 1.0, but its surface absorbed oxygen and total oxygen concentration decrease. The magnetic FeCeW-0.5 catalyst shows the best reducibility at temperatures below 790 °C. The increase in the citric acid content inhibits the formation of acid sites in the catalyst, thus the magnetic FeCeW-0.25 catalyst possesses the most Lewis acid sites and Brønsted acid sites among the catalysts. The enhancement in citric acid content is beneficial to improve the SCR reaction rates normalized by the surface area of the catalyst. This catalyst exhibits high anti-SO2 and H2O poisoning, and the molar ratio of citric acid/(Fe + Ce + W) affects the adsorption of NOx species on its surface.

Methane reforming and water splitting by zirconia-supported cerium-tungsten composite oxides for cyclic production of syngas and hydrogen

Redox cycles of methane reforming (MR) and water splitting (WS) of cerium-tungsten composite oxides were investigated at 1223 K for the cyclic production of syngas and hydrogen. Among various composite oxides tested having different Ce/W ratios, the sample with the Ce/W molar ratio of 1, CeW1/Zr, showed the best performance. When the sample was stabilized after several cycles, most of the Ce was present as Ce3+ and thus only W participated in the redox process. Production of CO2 during MR by the cerium–tungsten composite sample was much less than that by the WO3-only sample, yielding a H2/(CO + CO2) ratio much closer to the desired value of 2. The extent of reduction of W by MR remained nearly constant during repeated cycles, but re-oxidation by WS was not complete during the first several cycles. However, the re-oxidation extent increased to full re-oxidation during repeated cycles; the redox system became very stable after the sixth cycle. These are both beneficial effects owing to the presence of Ce.

Effects of an Electrode Material on a Novel Compound Machining of Inconel718

Compound machining (CM) compounded by arc machining and electrical discharge machining (EDM) milling is a new and fast processing method used to machine so-called “difficult-to-machine” materials. This method has an exciting maximum material removal rate that reaches 11,218 mm3/min with the relative electrode wear rate (REWR) of 1.54% when machining Inconel718. The electrode material is an important factor that affects the processing cost and quality of CM. Traditionally used electrode materials in arc machining and EDM, including pure tungsten (W), cerium tungsten (WCe20), copper (Cu), tungsten copper alloy (W80), and graphite (C), were used as electrode materials to process Inconel718. Experimental results show that tubular C is the best electrode material for CM. When tubular C is unavailable, WCe20 is the suitable electrode material for rough machining and W is a better choice in finish machining. Cu electrode is unsuitable for CM because of its low melting point. Results of this work provide guidance for selecting electrode materials for the industry application of efficient CM.

Flame-Made WO3/CeOx-TiO2 Catalysts for Selective Catalytic Reduction of NOx by NH3

Materials based on a combination of cerium–tungsten−titanium are potentially durable catalysts for selective catalytic NOx reduction using NH3 (NH3–SCR). Flame-spray synthesis is used here to produce WO3/CeOx-TiO2 nanoparticles, which are characterized with respect to their phase composition, morphology, and acidic properties and are evaluated by NH3–SCR. HR-TEM and XRD revealed that flame-made WO3/CeOx-TiO2 consists of mainly rutile TiO2, brannerite CeTi2O6, cubic CeO2, and a minor fraction of anatase TiO2. These phases coexist with a large portion of amorphous mixed Ce–Ti phase. The lack of crystallinity and the presence of brannerite together with the evident high fraction of Ce3+ are taken as evidence that cerium is also present as a dopant in TiO2 and is well dispersed on the surface of the nanoparticles. Clusters of amorphous WO3 homogeneously cover all particles as observed by STEM. Such morphology and phase composition guarantee short-range Ce–O–Ti and Ce–O–W interactions and thus the high surface...

Welding Performance of Tungsten Electrodes with Different Contents of Rare Earth Oxides

In this paper, the influence of different contents of rare earth oxides of tungsten electrodes on the welding performance has been studied. Tungsten inert gas weld was carried out on 1060 aluminum plate, using different contents of rare earth oxides of tungsten electrodes. The content of CeO2 are 2% and 4%, the content of composite rare earth oxides (La2O3: CeO2: Y2O3 = 1:1:3) is 4%. The mechanical properties of these welded joints were investigated. The results indicated that the loss of the CeO2 content of 4% electrode weight was the maximum. The arc stability of the three kinds of tungsten electrodes was good. The arc static characteristic curve of the composite rare earth—tungsten electrode was lower than that of the cerium—tungsten electrode. The loss of rare earth oxides of electrode had little effect on the mechanical properties of welded joints.

Loss mechanism and lifetime estimation of Ce–W cathode in high temperature thermionic emission electrostatic precipitation

Abstract Rare earth tungsten, 2.2% cerium–tungsten (Ce–W), was used as emission cathode material in thermionic emission electrostatic precipitation. The microstructures and emission properties were investigated. A model was established to estimate cathode lifetime in high temperature and oxygen-bearing atmosphere. Results show that there were not great changes in the inner microstructure of emission materials. But on the surface, tungsten was oxidized to tungsten trioxide and then tungsten trioxide and rare earth oxides evaporated and lost. Decrease of oxygen concentration was effective to prolong operation time of cathode. The increase of temperature reduced cathode lifetime remarkably.

Characterization of CeO2–WO3 catalysts prepared by different methods for selective catalytic reduction of NO with NH3

In this work, cerium–tungsten oxide catalysts were prepared by three methods: single step sol–gel (SG), impregnation (IM), and solid processing (SP). The catalysts were used for selective catalytic reduction (SCR) of NOx with ammonia over a wide temperature range. The results indicated that the catalysts prepared by the SP and IM methods exhibited better SCR activity than that prepared via the SG method in 175–500 °C. The excellent activity can be attributed to larger surface area, higher surface concentrations of Ce and Ce3 +, enhanced NO oxidization ability, and greater number of surface acid sites.

Properties of RE–W cathode and its application in electrostatic precipitation for high temperature gas clean-up

In this paper, three rare earth tungsten (RE–W) electrostatic precipitation cathodes (cerium–tungsten (Ce–W), lanthanum–tungsten (La–W) and yttrium–tungsten (Y–W)) were prepared by powder metallurgy. The microstructure and the electron emission properties of the three cathodes were examined. The application of the Y–W cathode in high temperature electrostatic precipitation was investigated. Results show that the addition of the rare earth reduces the tungsten crystal size, with yttrium (Y) affecting the crystal size more significantly than lanthanum (La) and cerium (Ce). The rare earth (cerium, lanthanum or yttrium) exists, in the form of crystalline tungstates, at the tungsten (W) crystal boundary. The effective work function of the La–W cathode has the lowest value of 2.88eV at vacuum condition, but the Y–W cathode shows the best emission properties at atmosphere pressure. The collection performance of an electrostatic precipitator (ESP) using the Y–W cathode was investigated by ash particles with various resistivity and size distribution at various temperatures. The particles with higher resistivity tend to be collected effectively at high ambient temperature, and the collection efficiency rise with the increase in temperature. If the resistivity of dusts is not high enough, corresponding to the highest collection efficiency, there exists an optimum temperature value. As in a conventional corona ESP, the larger particles are collected more effectively in an ESP with Y–W cathode.

ChemInform Abstract: Novel Cerium—Tungsten Mixed Oxide Catalyst for the Selective Catalytic Reduction of NOx with NH3.

AbstractMixed Ce—W oxide catalysts (Ce2WOx, CeWOx, CeW2Ox) are prepared by homogeneous precipitation from aqueous solutions of Ce(NO3)3, (NH4)10W12O41, and (COOH)2 using urea (90 °C, 12 h) followed by calcination in air (500 °C, 5 h).

Novel cerium–tungsten mixed oxide catalyst for the selective catalytic reduction of NOx with NH3

A novel Ce-W mixed oxide catalyst prepared by homogeneous precipitation method presented nearly 100% NO(x) conversion in a wide temperature range from 250 to 425 °C for the selective catalytic reduction of NO(x) with NH(3) under an extremely high GHSV of 500,000 h(-1).

Carbon monoxide gas-sensing properties of CeO2–WO3 thin films

Mixed films of cerium oxide (CeO2) and tungsten oxide (WO3) were deposited on unheated substrates by co-evaporation. The films were annealed in air at 500°C for 2 h. The surface morphology of the films was characterised using atomic force microscopy. The chemical composition was determined using X-ray photoelectron spectroscopy. The optical properties were derived from normal incidence reflectance and transmittance measurements. The films were investigated for the detection of carbon monoxide. The effects of the operating temperature and gas concentration on the performance of the sensor were investigated. The sensor response and recovery times were also measured.

Solvent-free synthesis of rechargeable solid oxygen reservoirs for clean hydrogen oxidation.

Cutting out the coke: The concept of catalytic oxidative dehydrogenation by using solid oxygen exchangers and a solvent-free parallel synthesis of a set of ten bimetallic catalysts is described. The compounds were tested in the selective oxidation of hydrogen in the presence of ethane and ethylene (HCs) at 600 °C. Cerium tungsten oxide was found to be a superb rechargeable “oxygen reservoir” (see picture), with 97 % chemoselectivity and negligible coking levels.

Preparation, luminescence studies, and solution behaviour of a cerium–tungsten heterobimetallic compound

The crystal structure determination of cerium–tungsten compound (2)[Cp″2Ce-(µ-OC)W(CO)(Cp)(µ-CO)]2[Cp″= C5H3(SiMe3)2, Cp = C5H5] shows it to consist of a 12-membered ring in which Ce and W centres are linked by Σ-carbonyls; intact (2) is virtually non-emissive (presumably due to cerium–tungsten excited state energy transfer), but in acetonitrile solvent it serves as a source of the luminescent cerium cation [Cp″2Ce(NCMe)x]+.

Rare Earth Tungsten Bronzes

Abstract : Rare earth tungsten bronzes such as cerium tungsten bronze (CexWO3) europium tungsten bronze (EuxWO3) and gadolinium tungsten bronze (GdxWO3) have been prepared for the first time. All compounds were cooled rapidly from 1000 C to room temperature and exhibit a cubic perovskite type structure. The rare earth bronzes have a wide homogeneity range. For the euronium tungsten bronze, the range of x-values was 0.08 < x < 0.15. The lattice parameter a sub o depends on the rare earth concentration. The electrical conductivity was measured as a function of temperature. The data give evidence that the conductivity of the rare earth tungsten bronzes is nearly metallic. Magnetic susceptibility measurements were carried out by using a Faraday balance. The measurements prove that the rare earth ions are trivalent in the rare earth tungsten bronzes. The results of the magnetic data are discussed on the basis of the electron gas model. (Author)