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Ceria-based Catalysts

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A special issue of Catalysts (ISSN 2073-4344). This special issue belongs to the section "Environmental Catalysis".

Deadline for manuscript submissions: closed (31 January 2017) | Viewed by 69894

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Prof. Dr. Enrique Rodríguez-Castellón

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Departamento de Química Inorgánica, Universidad de Málaga, 29016 Málaga, Spain
Interests: nanoporous materials; combustion of VOCs; hydrodesulfurization (HDS); hydrodenitrogenation (HDN); hydrodeoxygenation (HDO)
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Prof. Dr. Agustín Bueno López

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Inorganic Chemistry Department, University of Alicante, Ap. 99, E03080 Alicante, Spain
Interests: materials science; catalysis; gas pollution control; deNOx; deSoot; deN2O; zeolytes; mixed oxides; monoliths
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Dr. Elisa Moretti

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

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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.

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Keywords

cerium oxide
ceria
rare earth
solid solution
mixed oxide
environmental catalysis

Published Papers (11 papers)

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Research

2325 KiB

Open AccessArticle

Intrinsic Activity of MnO_x-CeO₂ Catalysts in Ethanol Oxidation

by Dimitrios Delimaris and Theophilos Ioannides

Catalysts 2017, 7(11), 339; https://doi.org/10.3390/catal7110339 - 10 Nov 2017

Cited by 8 | Viewed by 4753

Abstract

MnO_x-CeO₂ mixed oxides are considered efficient oxidation catalysts superior to the corresponding single oxides. Although these oxides have been the subject of numerous studies, their fundamental performance indicators, such as turnover frequency (TOF) or specific activity, are scarcely reported. The purpose of the present work is to investigate the effect of catalyst composition on the concentration of active sites and intrinsic activity in ethanol oxidation by the employment of temperature-programmed desorption and oxidation of isotopically-labelled ethanol, ¹²CH₃¹³CH₂OH. The transformation pathways of preadsorbed ethanol in the absence of gaseous oxygen refer to dehydrogenation to acetaldehyde followed by its dissociation combined with oxidation by lattice oxygen. In the presence of gaseous oxygen, lattice oxygen is rapidly restored and the main products are acetaldehyde, CO₂, and water. CO₂ forms less easily on mixed oxides than on pure MnO_x. The TOF of ethanol oxidation has been calculated assuming that the amount of adsorbed ethanol and CO₂ produced during temperature-programmed oxidation (TPO) is a reliable indicator of the concentration of the active sites. Full article

(This article belongs to the Special Issue Ceria-based Catalysts)

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8025 KiB

Open AccessArticle

Nanostructured Ceria-Based Materials: Effect of the Hydrothermal Synthesis Conditions on the Structural Properties and Catalytic Activity

by Marco Piumetti, Samir Bensaid, Tahrizi Andana, Melodj Dosa, Chiara Novara, Fabrizio Giorgis, Nunzio Russo and Debora Fino

Catalysts 2017, 7(6), 174; https://doi.org/10.3390/catal7060174 - 02 Jun 2017

Cited by 35 | Viewed by 6487

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 nanorod mixtures, and other polyhedra. The prepared materials were tested using four probe catalytic reactions: CO oxidation, NO oxidation, NO_x-free soot oxidation, and NO_x-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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3329 KiB

Open AccessArticle

Catalytic Behaviour of CuO-CeO₂ Systems Prepared by Different Synthetic Methodologies in the CO-PROX Reaction under CO₂-H₂O Feed Stream

by Juan Antonio Cecilia, Ana Arango-Díaz, Jaasiel Marrero-Jerez, Pedro Núñez, Elisa Moretti, Loretta Storaro and Enrique Rodríguez-Castellón

Catalysts 2017, 7(5), 160; https://doi.org/10.3390/catal7050160 - 18 May 2017

Cited by 29 | Viewed by 5867

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 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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2710 KiB

Open AccessArticle

Total Oxidation of Propane Using CeO₂ and CuO-CeO₂ Catalysts Prepared Using Templates of Different Nature

by Benjamin Solsona, Rut Sanchis, Ana M. Dejoz, Tomas García, Lidia Ruiz-Rodríguez, José Manuel López Nieto, Juan Antonio Cecilia and Enrique Rodríguez-Castellón

Catalysts 2017, 7(4), 96; https://doi.org/10.3390/catal7040096 - 23 Mar 2017

Cited by 44 | Viewed by 6473

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 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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3554 KiB

Open AccessFeature PaperArticle

Improved CO Oxidation Activity of 3DOM Pr-Doped Ceria Catalysts: Something Other Than an Ordered Macroporous Structure

by Arantxa Davó-Quiñonero, Jorge González-Mira, Ion Such-Basañez, Jerónimo Juan-Juan, Dolores Lozano-Castelló and Agustín Bueno-López

Catalysts 2017, 7(2), 67; https://doi.org/10.3390/catal7020067 - 17 Feb 2017

Cited by 8 | Viewed by 4733

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 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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3587 KiB

Open AccessArticle

Electrochemical Removal of NO_x on Ceria-Based Catalyst-Electrodes

by Xi Wang, Alexandre Westermann, Yi Xiang Shi, Ning Sheng Cai, Mathilde Rieu, Jean-Paul Viricelle and Philippe Vernoux

Catalysts 2017, 7(2), 61; https://doi.org/10.3390/catal7020061 - 16 Feb 2017

Cited by 10 | Viewed by 4869

Abstract

This study reports the electrochemical properties for NO_x 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 NO_x. 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 NO_x 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 NO_x 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

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3701 KiB

Open AccessArticle

Morphology-Dependent Properties of Cu/CeO₂ Catalysts for the Water-Gas Shift Reaction

by Zhibo Ren, Fei Peng, Jianwei Li, Xin Liang and Biaohua Chen

Catalysts 2017, 7(2), 48; https://doi.org/10.3390/catal7020048 - 05 Feb 2017

Cited by 43 | Viewed by 9910

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 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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4985 KiB

Open AccessArticle

Aqueous and Surface Chemistries of Photocatalytic Fe-Doped CeO₂ Nanoparticles

by Duangdao Channei, Sukon Phanichphant, Auppatham Nakaruk, Sajjad S. Mofarah, Pramod Koshy and Charles C. Sorrell

Catalysts 2017, 7(2), 45; https://doi.org/10.3390/catal7020045 - 29 Jan 2017

Cited by 53 | Viewed by 8909

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 % 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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2482 KiB

Open AccessFeature PaperArticle

The Effect of Sr Addition in Cu- and Fe-Modified CeO₂ and ZrO₂ Soot Combustion Catalysts

by Verónica Rico-Pérez, Eleonora Aneggi and Alessandro Trovarelli

Catalysts 2017, 7(1), 28; https://doi.org/10.3390/catal7010028 - 17 Jan 2017

Cited by 15 | Viewed by 5806

Abstract

This study investigates the activity of transition and alkaline-earth metal-doped catalysts supported on ceria or zirconia for the NO_x-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 NO_x-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 NO_x species. Full article

(This article belongs to the Special Issue Ceria-based Catalysts)

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2414 KiB

Open AccessArticle

N₂O Direct Dissociation over Mg_xCe_yCo_1−x−yCo₂O₄ Composite Spinel Metal Oxide

by Ning Liu, Ping Chen, Yingxia Li and Runduo Zhang

Catalysts 2017, 7(1), 10; https://doi.org/10.3390/catal7010010 - 01 Jan 2017

Cited by 5 | Viewed by 5386

Abstract

A series of Mg- and/or Ce-doped Co₃O₄ (Mg_xCo_1−xCo₂O₄ Ce_xCo_1−xCo₂O₄, Mg_xCe_yCo_1−x−yCo₂O₄) [...] Read more.

A series of Mg- and/or Ce-doped Co₃O₄ (Mg_xCo_1−xCo₂O₄ Ce_xCo_1−xCo₂O₄, Mg_xCe_yCo_1−x−yCo₂O₄) composite spinel metal-oxide catalyst was prepared by a coprecipitation method and evaluated for N₂O direct decomposition. The activity measurement results suggest that Mg_0.025Ce_0.05Co_0.925Co₂O₄ 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 Mg_0.025Ce_0.05Co_0.925Co₂O₄: (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 Mg_0.025Ce_0.05Co_0.925Co₂O₄ (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 Mg_0.025Ce_0.05Co_0.925Co₂O₄, 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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8824 KiB

Open AccessArticle

Noble Metal-Free Ceria-Zirconia Solid Solutions Templated by Tobacco Materials for Catalytic Oxidation of CO

by Donglai Zhu, Deliang Duan, Yi Han, Jiao He, Yi He, Yongjuan Chen, Wei Zhang, Zhiyin Yan, Jiaqiang Wang and Fagui Yuan

Catalysts 2016, 6(9), 135; https://doi.org/10.3390/catal6090135 - 09 Sep 2016

Cited by 8 | Viewed by 5148

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 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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