Special Issue "Ceria-based Catalysts"

A special issue of Catalysts (ISSN 2073-4344).

Deadline for manuscript submissions: closed (31 December 2016)

Special Issue Editors

Guest Editor
Prof. Dr. Enrique Rodríguez-Castellón

President of the Inorganic Chemistry Division of the Spanish Royal Society of Chemistry, Departamento de Química Inorgánica, Facultad de Ciencias, Universidad de Málaga, Spain
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Interests: synthesis and characterization of nanoporous materials for adsorption and catalysis; environmental catalysis, such as HDS, HDN and HDO processes; SCR-NOx; CO-PROX; selective oxidation of H2S; XPS-Auger; quantum dots and sensing
Guest Editor
Dr. Agustín Bueno-López

Inorganic Chemistry Department, University of Alicante, Ap. 99, E03080, Alicante, Spain
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Phone: 00 34 965 903538
Fax: +34 965903454
Interests: materials science; catalysis; gas pollution control; deNOx; deSoot; deN2O; zeolytes; mixed oxides; monoliths
Guest Editor
Dr. Elisa Moretti

Università Ca’ Foscari Venezia, Dipartimento di Scienze Molecolari e Nanosistemi, Via Torino 155/B, 30172 Mestre Venezia, Italy
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Interests: nanostructured materials for energy, optics and catalysis; multi-component oxide systems with controlled porosity and morphology; ceria-based materials; environmental/energy catalysis

Special Issue Information

Dear Colleagues,

Cerium oxide plays a key role as active support and as catalyst in relevant environmental applications and in energy conversion systems, and the development of advanced ceria-based catalysts is a hot topic of ongoing research. Ceria-containing catalysts are being investigated for applications in advanced gas purification systems and fuel cells, along with other relevant chemical processes. Special attention is being paid to the synthesis of advanced ceria nanostructures, such as nanoparticles, 1D, 2D, 3D and core-shell materials, and also to the nanostructure-activity relationship.

This Special Issue focuses on recent advances in the synthesis, characterization and catalytic applications of ceria-containing catalysts, and researchers are encouraged to submit their most recent advances on this topic.

Dr. Enrique Rodríguez-Castellón
Dr. Agustín Bueno-López
Dr. Elisa Moretti
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Catalysts is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • cerium oxide
  • ceria
  • rare earth
  • solid solution
  • mixed oxide
  • environmental catalysis

Published Papers (10 papers)

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Research

Open AccessArticle Nanostructured Ceria-Based Materials: Effect of the Hydrothermal Synthesis Conditions on the Structural Properties and Catalytic Activity
Catalysts 2017, 7(6), 174; doi:10.3390/catal7060174
Received: 7 April 2017 / Revised: 15 May 2017 / Accepted: 27 May 2017 / Published: 2 June 2017
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Abstract
In this work, several nanostructured ceria catalysts were prepared by means of a hydrothermal procedure, in which the synthesis conditions (i.e., temperature and pH values) were varied. CeO2 samples of different shapes and structural properties were obtained, namely cubes, rods, cube and
[...] Read more.
In this work, several nanostructured ceria catalysts were prepared by means of a hydrothermal procedure, in which the synthesis conditions (i.e., temperature and pH values) were varied. CeO2 samples of different shapes and structural properties were obtained, namely cubes, rods, cube and nanorod mixtures, and other polyhedra. The prepared materials were tested using four probe catalytic reactions: CO oxidation, NO oxidation, NOx-free soot oxidation, and NOx-assisted soot oxidation. The physicochemical properties of the prepared catalysts were studied by means of complementary techniques (i.e., XRD, N2-physisorption at −196 °C, CO-TPR (temperature-programmed reduction), field emission scanning electron microscopy (FESEM), micro-Raman spectroscopy). The abundance of defects of the catalysts, measured through in-situ Raman spectroscopy at the typical temperatures of each catalytic process, was correlated to the CO and NO oxidation activity of the prepared catalysts, while the soot oxidation reaction (performed in loose conditions), which was hindered by a poor soot-catalyst contact, was found to be less sensitive to the observed structural defects. Full article
(This article belongs to the Special Issue Ceria-based Catalysts)
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Open AccessArticle Catalytic Behaviour of CuO-CeO2 Systems Prepared by Different Synthetic Methodologies in the CO-PROX Reaction under CO2-H2O Feed Stream
Catalysts 2017, 7(5), 160; doi:10.3390/catal7050160
Received: 10 April 2017 / Revised: 10 May 2017 / Accepted: 15 May 2017 / Published: 18 May 2017
Cited by 1 | PDF Full-text (3329 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
CuO-CeO2 catalysts, with 6 wt % of Cu, have been synthesised by different preparation methods (calcination of nitrate precursors, thermal urea-nitrate combustion, freeze-drying method, using polymethyl metacrylate PMMA microspheres as template and precipitation using NaOH or the decomposition of urea as precipitating
[...] Read more.
CuO-CeO2 catalysts, with 6 wt % of Cu, have been synthesised by different preparation methods (calcination of nitrate precursors, thermal urea-nitrate combustion, freeze-drying method, using polymethyl metacrylate PMMA microspheres as template and precipitation using NaOH or the decomposition of urea as precipitating agents). The obtained materials have been characterised by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, N2 adsorption-desorption at −196 °C, H2 thermoprogrammed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS). The catalysts displayed high dispersion of copper oxide, obtaining CO conversion values of 90–100% at 115 °C in the CO preferential oxidation in excess of hydrogen (CO-PROX) and maintaining this activity even after 48 h of time on stream. The incorporation of CO2 and H2O in the feed stream (simulating a PROX unit) caused a decrease in the CO conversion, except for the catalyst synthesised using PMMA microspheres as a template which maintained a CO conversion of 95% at 115 °C. This catalyst exhibits an excellent catalytic performance, also under real operating conditions, thanks to many and concomitant factors, such as the very small CeO2 particle size (5.6 nm), the surface being rich in copper (atomic ratio Cu/Ce = 0.35) that is easily reducible, and the peculiar morphology and porosity of the material. Full article
(This article belongs to the Special Issue Ceria-based Catalysts)
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Open AccessArticle Total Oxidation of Propane Using CeO2 and CuO-CeO2 Catalysts Prepared Using Templates of Different Nature
Catalysts 2017, 7(4), 96; doi:10.3390/catal7040096
Received: 16 January 2017 / Revised: 7 March 2017 / Accepted: 17 March 2017 / Published: 23 March 2017
Cited by 2 | PDF Full-text (2710 KB) | HTML Full-text | XML Full-text
Abstract
Several CeO2 and CuO-CeO2 catalysts were prepared using different methods, i.e., a homogeneous precipitation with urea, a nanocasting route using CMK-3 carbon as a hard template and a sol–gel process using Poly(methyl methacrylate) (PMMA) polymer as a soft template, and tested
[...] Read more.
Several CeO2 and CuO-CeO2 catalysts were prepared using different methods, i.e., a homogeneous precipitation with urea, a nanocasting route using CMK-3 carbon as a hard template and a sol–gel process using Poly(methyl methacrylate) (PMMA) polymer as a soft template, and tested in the total oxidation of propane. The catalysts were characterized by a number of physicochemical techniques (XRD, N2 adsorption, TPR, XPS, Raman spectroscopy) showing distinct characteristics. For each series, Cu-Ce-O catalysts with low Cu-loadings (5 wt % CuO) showed the highest activity, higher than those samples either without copper or with high Cu-loading (13 wt % CuO). The incorporation of copper leads to an increase of the concentration of bulk defects but if the Cu-loading is too high the surface area drastically falls. The highest activity in the total oxidation of propane was achieved by Cu-containing ceria catalysts synthesized using a polymer as a template, as this method yields high surface area materials. The surface area and the number of bulk/sub-surface defects of the ceria seem to be the main properties determining the catalytic activity. Full article
(This article belongs to the Special Issue Ceria-based Catalysts)
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Open AccessFeature PaperArticle Improved CO Oxidation Activity of 3DOM Pr-Doped Ceria Catalysts: Something Other Than an Ordered Macroporous Structure
Catalysts 2017, 7(2), 67; doi:10.3390/catal7020067
Received: 10 January 2017 / Revised: 10 February 2017 / Accepted: 11 February 2017 / Published: 17 February 2017
Cited by 2 | PDF Full-text (3554 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
It is demonstrated that the synthesis procedure for preparing three-dimensionally ordered macroporous (3DOM) Pr-doped ceria catalysts using a polymethylmethacrylate (PMMA) template not only affects the porous structure, but also the chemistry of the ceria surface. The PMMA template does not affect the crystalline
[...] Read more.
It is demonstrated that the synthesis procedure for preparing three-dimensionally ordered macroporous (3DOM) Pr-doped ceria catalysts using a polymethylmethacrylate (PMMA) template not only affects the porous structure, but also the chemistry of the ceria surface. The PMMA template does not affect the crystalline features (type of phases, crystallite size, and cell parameter) of Pr-doped ceria, Ce and Pr location into the particles, and the bulk reduction of the Ce-Pr mixed oxide catalysts. On the contrary, the utilization of the PMMA template improves both the porosity and surface redox properties. 3DOM Ce-Pr mixed oxide catalysts combine micro, meso, and macropores, the most area being in the macropore range, while a reference unshaped catalyst presents poor porosity in all ranges. However, the catalyzed CO oxidation rates do not correlate with the surface area of the catalysts (neither micro nor meso/macro). The Ce-Pr-3DOM catalyst also presents improved surface reducibility with regards to the counterpart reference material prepared without the template, and improved redox behavior under reaction conditions; that is, it has a higher area and this area is reduced and reoxidized more easily. X-ray photoelectron spectroscopy analysis evidences that this is mainly attributed to praseodymium cations, which accomplish redox cycles more easily than cerium cations. Full article
(This article belongs to the Special Issue Ceria-based Catalysts)
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Open AccessArticle Electrochemical Removal of NOx on Ceria-Based Catalyst-Electrodes
Catalysts 2017, 7(2), 61; doi:10.3390/catal7020061
Received: 23 December 2016 / Revised: 3 February 2017 / Accepted: 8 February 2017 / Published: 16 February 2017
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Abstract
This study reports the electrochemical properties for NOx reduction of a ceria-based mixed ionic electronic conducting porous electrode promoted by Pt nanoparticles, as efficient catalyst for NO oxidation, and BaO, as sorbent to store NOx. This catalytic layer was deposited
[...] Read more.
This study reports the electrochemical properties for NOx reduction of a ceria-based mixed ionic electronic conducting porous electrode promoted by Pt nanoparticles, as efficient catalyst for NO oxidation, and BaO, as sorbent to store NOx. This catalytic layer was deposited by screen-printing on a dense membrane of gadolinia-doped ceria, an O2− ionic conductor. The targeted Ba and Pt loadings were 150 and 5 μg/cm2, respectively. The NOx selective electrochemical reduction was performed between 400 °C and 500 °C with and without oxygen in the feed. Variations of the open-circuit voltage with time were found to be a good sensor of the NOx storage process on the ceria-based catalyst-electrode. However, no N2 production was observed in the presence of O2 phase in spite of nitrates formation. Full article
(This article belongs to the Special Issue Ceria-based Catalysts)
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Open AccessArticle Morphology-Dependent Properties of Cu/CeO2 Catalysts for the Water-Gas Shift Reaction
Catalysts 2017, 7(2), 48; doi:10.3390/catal7020048
Received: 4 January 2017 / Revised: 20 January 2017 / Accepted: 26 January 2017 / Published: 5 February 2017
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Abstract
CeO2 nanooctahedrons, nanorods, and nanocubes were prepared by the hydrothermal method and were then used as supports of Cu-based catalysts for the water-gas shift (WGS) reaction. The chemical and physical properties of these catalysts were characterized by X-ray diffraction (XRD), transmission electron
[...] Read more.
CeO2 nanooctahedrons, nanorods, and nanocubes were prepared by the hydrothermal method and were then used as supports of Cu-based catalysts for the water-gas shift (WGS) reaction. The chemical and physical properties of these catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 adsorption/desorption, UV-Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H2-TPR) and in situ diffuse reflectance infra-red fourier transform spectroscopy (DRIFTS) techniques. Characterization results indicate that the morphology of the CeO2 supports, originating from the selective exposure of different crystal planes, has a distinct impact on the dispersion of Cu and the catalytic properties. The nanooctahedron CeO2 catalyst (Cu-CeO2-O) showed the best dispersion of Cu, the largest amount of moderate copper oxide, and the strongest Cu-support interaction. Consequently, the Cu-CeO2-O catalyst exhibited the highest CO conversion at the temperature range of 150–250 °C when compared with the nanocube and nanorod Cu-CeO2 catalysts. The optimized Cu content of the Cu-CeO2-O catalysts is 10 wt % and the CO conversion reaches 91.3% at 300 °C. A distinctive profile assigned to the evolution of different types of carbonate species was observed in the 1000–1800 cm−1 region of the in situ DRIFTS spectra and a particular type of carbonate species was identified as a potential key reaction intermediate at low temperature. Full article
(This article belongs to the Special Issue Ceria-based Catalysts)
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Open AccessArticle Aqueous and Surface Chemistries of Photocatalytic Fe-Doped CeO2 Nanoparticles
Catalysts 2017, 7(2), 45; doi:10.3390/catal7020045
Received: 7 November 2016 / Revised: 23 January 2017 / Accepted: 23 January 2017 / Published: 29 January 2017
Cited by 2 | PDF Full-text (4985 KB) | HTML Full-text | XML Full-text
Abstract
The present work describes the effects of water on Fe-doped nanoparticulate CeO2, produced by flame spray pyrolysis, which is a critical environmental issue because CeO2 is not stable in typical atmospheric conditions. It is hygroscopic and absorbs ~29 wt %
[...] Read more.
The present work describes the effects of water on Fe-doped nanoparticulate CeO2, produced by flame spray pyrolysis, which is a critical environmental issue because CeO2 is not stable in typical atmospheric conditions. It is hygroscopic and absorbs ~29 wt % water in the bulk when exposed to water vapor but, more importantly, it forms a hydrated and passivating surface layer when immersed in liquid water. In the latter case, CeO2 initially undergoes direct and/or reductive dissolution, followed by the establishment of a passivating layer calculated to consist of ~69 mol % solid CeO2·2H2O and ~30 mol % gelled Ce(OH)4. Under static flow conditions, a saturated boundary layer also forms but, under turbulent flow conditions, this is removed. While the passivating hydrated surface layer, which is coherent probably owing to the continuous Ce(OH)4 gel, would be expected to eliminate the photoactivity, this does not occur. This apparent anomaly is explained by the calculation of (a) the thermodynamic stability diagrams for Ce and Fe; (b) the speciation diagrams for the Ce4+-H2O, Ce3+-H2O, Fe3+-H2O, and Fe2+-H2O systems; and (c) the Pourbaix diagrams for the Ce-H2O and Fe-H2O systems. Furthermore, consideration of the probable effects of the localized chemical and redox equilibria owing to the establishment of a very low pH (<0) at the liquid-solid interface also is important to the interpretation of the phenomena. These factors highlight the critical importance of the establishment of the passivating surface layer and its role in photocatalysis. A model for the mechanism of photocatalysis by the CeO2 component of the hydrated phase CeO2·2H2O is proposed, explaining the observation of the retention of photocatalysis following the apparent alteration of the surface of CeO2 upon hydration. The model involves the generation of charge carriers at the outer surface of the hydrated surface layer, followed by the formation of radicals, which decompose organic species that have diffused through the boundary layer, if present. Full article
(This article belongs to the Special Issue Ceria-based Catalysts)
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Open AccessFeature PaperArticle The Effect of Sr Addition in Cu- and Fe-Modified CeO2 and ZrO2 Soot Combustion Catalysts
Catalysts 2017, 7(1), 28; doi:10.3390/catal7010028
Received: 27 December 2016 / Revised: 11 January 2017 / Accepted: 11 January 2017 / Published: 17 January 2017
Cited by 1 | PDF Full-text (2482 KB) | HTML Full-text | XML Full-text
Abstract
This study investigates the activity of transition and alkaline-earth metal-doped catalysts supported on ceria or zirconia for the NOx-assisted oxidation of diesel particulate. A series of Cu- and Fe-impregnated catalysts over CeO2 and ZrO2 supports were prepared by incipient
[...] Read more.
This study investigates the activity of transition and alkaline-earth metal-doped catalysts supported on ceria or zirconia for the NOx-assisted oxidation of diesel particulate. A series of Cu- and Fe-impregnated catalysts over CeO2 and ZrO2 supports were prepared by incipient wetness impregnation and characterized by BET, X-ray diffraction (XRD), and temperature-programmed reduction (TPR) experiments while their catalytic activity was investigated in NOx-assisted reaction by means of temperature programmed oxidation experiments (TPO). Higher activity was achieved by copper modified catalysts; the addition of Sr positively affected the performance of the materials, suggesting a synergic effect between transition metals and alkaline-earth metal. The role of copper is correlated to the oxidation of NO to NO2, while strontium seems to be mainly involved in the storage of NOx species. Full article
(This article belongs to the Special Issue Ceria-based Catalysts)
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Open AccessArticle N2O Direct Dissociation over MgxCeyCo1−xyCo2O4 Composite Spinel Metal Oxide
Catalysts 2017, 7(1), 10; doi:10.3390/catal7010010
Received: 25 November 2016 / Revised: 16 December 2016 / Accepted: 23 December 2016 / Published: 1 January 2017
Cited by 2 | PDF Full-text (2414 KB) | HTML Full-text | XML Full-text
Abstract
A series of Mg- and/or Ce-doped Co3O4 (MgxCo1−xCo2O4 CexCo1−xCo2O4, MgxCeyCo1−xyCo2O4)
[...] Read more.
A series of Mg- and/or Ce-doped Co3O4 (MgxCo1−xCo2O4 CexCo1−xCo2O4, MgxCeyCo1−xyCo2O4) composite spinel metal-oxide catalyst was prepared by a coprecipitation method and evaluated for N2O direct decomposition. The activity measurement results suggest that Mg0.025Ce0.05Co0.925Co2O4 with a Mg/Ce mole ratio of 0.5 exhibited the highest N2O conversion activity, achieving 100% N2O conversion at T = 250 °C (35 vol % N2O balanced by He, gas hourly space velocity (GHSV) = 30,000 h−1). Characterizations using X-ray diffraction (XRD), Brunauer–Emmett–Teller method (BET), hydrogen temperature-programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS) reveal that there were three main reasons for the excellent catalytic behavior of Mg0.025Ce0.05Co0.925Co2O4: (a) Mg and Ce co-doping could reduce the grain size of composite spinel metal oxide, which thereby significantly increased the BET specific surface area of Mg0.025Ce0.05Co0.925Co2O4 (111.2 g·m2 with respect to that of 32.5 g·m−2 for Co3O4); (b) Mg and Ce co-doping could improve the redox ability of Mg0.025Ce0.05Co0.925Co2O4, including reductions of Co3+ → Co2+ and Co2+ → Co0; and (c) Mg and Ce co-doping not only could improve the migration ability of surface atomic O, but also could increase the concentrations of surface atomic O. Full article
(This article belongs to the Special Issue Ceria-based Catalysts)
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Open AccessArticle Noble Metal-Free Ceria-Zirconia Solid Solutions Templated by Tobacco Materials for Catalytic Oxidation of CO
Catalysts 2016, 6(9), 135; doi:10.3390/catal6090135
Received: 21 July 2016 / Revised: 7 September 2016 / Accepted: 7 September 2016 / Published: 9 September 2016
Cited by 2 | PDF Full-text (8824 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
A series of ceria-zirconia solid solutions were synthesized using tobacco leaves, stems and stem-silks as biotemplates. A combination of physicochemical techniques such as powder X-ray diffraction (XRD), N2 adsorption/desorption measurement, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to
[...] Read more.
A series of ceria-zirconia solid solutions were synthesized using tobacco leaves, stems and stem-silks as biotemplates. A combination of physicochemical techniques such as powder X-ray diffraction (XRD), N2 adsorption/desorption measurement, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were used to characterize the as-synthesized samples. The results show that the morphologies of the templates were well replicated in the obtained ceria-zirconia solid solutions. Catalytic oxidation activities of CO over the ceria-zirconia solid solutions were then investigated. The catalyst templated by tobacco stem-silk exhibited higher conversion of CO at lower temperature than that of ceria-zirconia solid solutions templated by tobacco leaves and stems or without templates due to its special morphology. The catalyst even showed similar CO conversion when compared to ceria-zirconia solid solutions doped with 1.0 wt % noble metals such as Pt, Ag and Au. The results highlighted the advantages of using tobacco as biotemplate. Full article
(This article belongs to the Special Issue Ceria-based Catalysts)
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