Promoting effect of ceria on the physicochemical and catalytic properties of CeO2–ZnO composite oxide catalysts
TL;DR: In this article, the authors investigated the effect of ceria in composite oxides for cyclohexanol de-hydrogenation and hydrogen transfer reactions, and showed that the presence of the ceria enhances the surface area and acid-base properties.
Abstract: CeO2–ZnO composite catalysts prepared by amorphous citrate method have been investigated for cyclohexanol dehydrogenation and hydrogen transfer reactions. The precursors and catalysts have been characterized by TGA, CHN analysis, XRD, UV–vis–NIR diffuse reflectance, SEM and acid–base measurements. The amorphous precursors in citrate process contain one molecule of citric acid per Ce4+ or Zn2+ ions. Structural studies of composite oxides indicate the presence of individual oxide phases along with non-equilibrium solid solutions in a limited composition range. The composite oxides contain low coordination Ce3+ and Ce4+ sites. Cyclohexanone was obtained as main product for cyclohexanol transformation reaction carried out over these mixed oxide catalysts due to dehydrogenation on basic sites. The presence of ceria in the composite oxide enhances the surface area and acid–base properties facilitating the dehydrogenation process. At low ceria content, the CeO2–ZnO composite oxide catalysts show higher catalytic activity for both cyclohexanol dehydrogenation and hydrogen transfer reactions due to higher basicity, surface area and smaller crystallite sizes. Hydrogen transfer activity is found to be higher on CeO2(10%)–ZnO catalyst prepared by citrate method compared to the catalyst prepared by decomposition from acetate precursor. This study demonstrates the promoting effect of ceria in CeO2–ZnO catalysts for reactions involving acid–base sites.
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TL;DR: The optimized and highly efficient ZnO/CeO2 (90:10) nanocomposite exhibited enhanced photocatalytic degradation performance for the degradation of methyl orange, methylene blue, and phenol as well as industrial textile effluent compared to ZNO, CeO2 and the other investigated nanocomPOSites.
Abstract: In this study, pure ZnO, CeO2 and ZnO/CeO2 nanocomposites were synthesized using a thermal decomposition method and subsequently characterized using different standard techniques. High-resolution X-ray photoelectron spectroscopy measurements confirmed the oxidation states and presence of Zn(2+), Ce(4+), Ce(3+) and different bonded oxygen species in the nanocomposites. The prepared pure ZnO and CeO2 as well as the ZnO/CeO2 nanocomposites with various proportions of ZnO and CeO2 were tested for photocatalytic degradation of methyl orange, methylene blue and phenol under visible-light irradiation. The optimized and highly efficient ZnO/CeO2 (90:10) nanocomposite exhibited enhanced photocatalytic degradation performance for the degradation of methyl orange, methylene blue, and phenol as well as industrial textile effluent compared to ZnO, CeO2 and the other investigated nanocomposites. Moreover, the recycling results demonstrate that the ZnO/CeO2 (90:10) nanocomposite exhibited good stability and long-term durability. Furthermore, the prepared ZnO/CeO2 nanocomposites were used for the electrochemical detection of uric acid and ascorbic acid. The ZnO/CeO2 (90:10) nanocomposite also demonstrated the best detection, sensitivity and performance among the investigated materials in this application. These findings suggest that the synthesized ZnO/CeO2 (90:10) nanocomposite could be effectively used in various applications.
502 citations
TL;DR: In this paper, the novel ZnO/γ-Mn2O3 (various weight percentages) nanocomposite catalysts were prepared by thermal decomposition method and their size, shape, and surface area were characterized by various techniques.
Abstract: The novel ZnO/γ-Mn2O3 (various weight percentages) nanocomposite catalysts were prepared by thermal decomposition method and their size, shape, and surface area were characterized by various techniques. Further, the prepared samples were used to degrade methylene blue (MB) and methyl orange (MO) in aqueous medium under visible light irradiation. Finally, the best catalyst was employed to degrade phenol and a textile effluent. The recycling ability and their efficiency of catalyst are discussed in detail.
330 citations
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TL;DR: This Review demonstrates that the exceptional surface (and sometimes bulk) properties of ceria make cerium-based catalysts very effective for a broad range of organic reactions.
Abstract: Ceria has been the subject of thorough investigations, mainly because of its use as an active component of catalytic converters for the treatment of exhaust gases. However, ceria-based catalysts have also been developed for different applications in organic chemistry. The redox and acid-base properties of ceria, either alone or in the presence of transition metals, are important parameters that allow to activate complex organic molecules and to selectively orient their transformation. Pure ceria is used in several organic reactions, such as the dehydration of alcohols, the alkylation of aromatic compounds, ketone formation, and aldolization, and in redox reactions. Ceria-supported metal catalysts allow the hydrogenation of many unsaturated compounds. They can also be used for coupling or ring-opening reactions. Cerium atoms can be added as dopants to catalytic system or impregnated onto zeolites and mesoporous catalyst materials to improve their performances. This Review demonstrates that the exceptional surface (and sometimes bulk) properties of ceria make cerium-based catalysts very effective for a broad range of organic reactions.
324 citations
01 Apr 2017
TL;DR: The highly enhanced activity of the ZnO/Ag/Ag2WO4 (15%) nanocomposite was attributed to the surface plasmon resonance effect of metallic silver and the formation of heterojunctions between the counterparts, which effectively suppresses recombination of the photogenerated charge carriers.
Abstract: In this work, plasmonic ternary ZnO/Ag/Ag2WO4 nanocomposites as efficient visible-light-driven photocatalysts prepared by a facile ultrasonic-irradiation method. The as-prepared samples were characterized by XRD, SEM, TEM, EDX, XPS, UV–vis DRS, FT-IR, and PL techniques. The photocatalytic performance of the prepared ZnO/Ag/Ag2WO4 nanocomposites were evaluated by photodegradations of rhodamine B, methylene blue, methyl orange, and fuchsine under visible-light irradiation. The optimal nanocomposite with 15 wt% of Ag/Ag2WO4 to ZnO showed the highest photocatalytic activity for RhB degradation, which is about 95 and 19 times higher than those of the Ag/Ag2WO4 and ZnO samples, respectively. The highly enhanced activity of the ZnO/Ag/Ag2WO4 (15%) nanocomposite was attributed to the surface plasmon resonance effect of metallic silver and the formation of heterojunctions between the counterparts, which effectively suppresses recombination of the photogenerated charge carriers. Lastly, the plasmon-enhanced photocatalytic mechanism associated with the ZnO/Ag/Ag2WO4 nanocomposites was discussed.
261 citations
TL;DR: In this article, the preliminary results of using alkaline earth metal-doped zinc oxide as a heterogeneous catalyst for transesterification of soybean oil were reported, where the highest catalytic activity was obtained with ZnO loaded with 2.5mmol Sr(NO 3 ) 2 /g, followed by calcination at 873k for 5h.
Abstract: Fatty acid methyl esters, derived from vegetable oils or animal fats and better known as biodiesel, have received considerable attention because of their environmental benefits and the limited resources of fossil fuels. Most biodiesel is usually produced by the transesterification of vegetable oils with methanol in the presence of a catalyst. This study reports on the preliminary results of using alkaline earth metal-doped zinc oxide as a heterogeneous catalyst for transesterification of soybean oil. The highest catalytic activity was obtained with ZnO loaded with 2.5 mmol Sr(NO 3 ) 2 /g, followed by calcination at 873 K for 5 h. When the transesterification reaction was carried out at reflux of methanol (338 K), with a 12:1 molar ratio of methanol to soybean oil and a catalyst amount of 5 wt.%, the conversion of soybean oil was 94.7%. Besides, tetrahydrofuran (THF), when used as a co-solvent, could increase the conversion up to 96.8%. However, the recovered catalyst exhibited the lower catalytic activity with a conversion of soybean oil of 15.4%. Furthermore, DTA-TG, IR and the Hammett indicator method were employed for the catalyst characterizations.
250 citations
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TL;DR: A survey of the use of cerium oxide and CeO2-containing materials as oxidation and reduction catalysts is presented in this paper, with a special focus on catalytic interaction with small molecules such as hydrogen, carbon monoxide, oxygen, and nitric oxide.
Abstract: Over the past several years, cerium oxide and CeO2-containing materials have come under intense scrutiny as catalysts and as structural and electronic promoters of heterogeneous catalytic reactions. Recent developments regarding the characterization of ceria and CeO2-containing catalysts are critically reviewed with a special focus towards catalyst interaction with small molecules such as hydrogen, carbon monoxide, oxygen, and nitric oxide. Relevant catalytic and technological applications such as the use of ceria in automotive exhaust emission control and in the formulation of SO x reduction catalysts is described. A survey of the use of CeO2-containing materials as oxidation and reduction catalysts is also presented.
3,077 citations
TL;DR: In this article, the main applications of cerium dioxide in industrial catalysis are reviewed, with particular attention to the role played by ceria, and the main uses of CeO2 are connected to depollution of noxious compounds from gaseous streams originating from industrial productions and from automobiles.
Abstract: The main applications of cerium dioxide in industrial catalysis are reviewed, with particular attention to the role played by ceria. The main uses of CeO2 are connected to depollution of noxious compounds from gaseous streams originating from industrial productions and from automobiles (de-SOx in FCC processes; treatment of emissions from spark-ignited and diesel engines), although ceria is also a key component of catalyst formulation for the dehydrogenation of ethylbenzene to styrene. Recent advances in the application of ceria for the removal of organic compound from wastewater through oxidation (catalytic wet oxidation CWO) are also reviewed. # 1999 Elsevier Science B.V. All rights reserved.
875 citations
TL;DR: In this paper, it is shown that incorporation of ZrO2 into a solid solution with CeO2 strongly promotes bulk reduction of the Rh-loaded solid solutions in comparison to a Rh/CeO2 sample.
Abstract: Temperature-programmed reduction in a H2/Ar mixture of Rh-loaded CeO2-ZrO2 solid solutions with a ZrO2 content varying between 10 and 90% mol and of monoclinic, tetragonal, and cubic structures is reported. It is shown that incorporation of ZrO2 into a solid solution with CeO2 strongly promotes bulk reduction of the Rh-loaded solid solutions in comparison to a Rh/CeO2 sample. The promotion of the bulk reduction results in high oxygen storage capacity (OSC) as measured by oxygen uptake. A structural dependence of both reduction and oxidation processes is observed which is attributed to a higher oxygen mobility in the cubic structure compared to the tetragonal and monoclinic ones.
854 citations
TL;DR: In this article, a metal oxide composite catalyst for the total oxidation of carbon monoxide and methane was prepared by combining fluorite oxides with active transition metals and showed excellent resistance to water vapor poisoning.
Abstract: A novel metal oxide composite catalyst for the total oxidation of carbon monoxide and methane was prepared by combining fluorite oxides with active transition metals The fluorite oxides, such as ceria and zirconia, are oxygen-ion-conducting materials having catalytic properties usually at high temperatures Active base metal catalysts, such as copper, were used as additives to promote the catalytic properties of these oxides The contact of the two types of materials gave rise to a high active oxidation catalyst At a space velocity of about 42,000 h-1, complete carbon monoxide oxidation in air occurred at room temperature on the Au-005[Ce(La)]095Ox catalyst and at ca 100°C on Cu-Ce-O composite catalysts At the same space velocity, total oxidation of methane on the Cu-Ce-O catalyst doped with La2O3 or SrO took place at ca 550°C The specific carbon monoxide oxidation activity of the Cu-Ce-O catalyst was several orders of magnitude higher than that of conventional copper-based catalysts and comparable or superior to platinum catalysts This type of composite catalyst also showed excellent resistance to water vapor poisoning The enhanced catalyst activity and stability resulted from strong interaction of the transition metal and fluorite oxide materials
598 citations
368 citations