Preface

Cerium oxide (CeO2), which is one of important transition metal oxides, acts as an n-type semiconductor material. It is clear from the title that this book is related to CeO2. CeO2 has a cubic fluorite structure, in which each cerium atom is surrounded by eight equivalent oxy‐ gen atoms and each oxygen atom is surrounded by a tetrahedron of four cerium atoms. CeO2 has shown various applications, particularly adsorption, catalysis, photocatalysis, sensing, fuel cells, hydrogen production, semiconductor devices, as well as biomedical uses. CeO2 is also used in petroleum refining and emission controlling systems in gasoline en‐ gines, as well as a diesel fuel-borne catalyst to reduce particulate matter emissions. In recent years, CeO2 nanoparticles have gained greater consideration in the biomedical research com‐ munity since it can be used as an inhibiting cellular agent along with its antimicrobial and antioxidant activities. Because of the dramatic and widespread industrial uses of CeO2 mate‐ rials, it was thought appropriate to present recent developments in the applications and at‐ tributes of CeO2 in the form of a book to the scientific community. This book contains six chapters, which describe the structure, different uses, applications, and attributes of CeO2.

The first chapter is "Cerium oxides for corrosion protection of AZ91D Mg alloy" by A. P. Loperena et al. The chapter describes CeO2-based coatings as an environmentally friendly option to enhance the corrosion resistance of magnesium alloys. The formation of a coating from a solution containing cerium nitrate was studied for controlling the biodegradation rate of AZ91D magnesium alloy in simulated physiological solution.

The second chapter is "Doped CeO2 for solid oxide fuel cells" by Shobit Omar. It describes the highlights of various activities regarding doped CeO2 materials in fuel cell applications and the mechanisms underlying the oxygen-ion conduction process in doped ceria.

The third chapter is "Prototyping a gas sensor using CeO2 as a matrix or dopant in oxide semiconductor systems" by Lucian Pîslaru-Dănescu et al. In this chapter, two important as‐ pects of using CeO2 in the field of gas sensors are discussed. First, the use of binary semicon‐ ductor oxides CeO2–Y2O3 for CO2 detection in the range of 0–5000 ppm. Second, the use of CeO2 as a dopant in a hydride composite, consisting of reduced graphene oxide/ZnO, to in‐ crease sensibility in NOx detection at low concentration in the range of 0–10 ppm.

The fourth chapter is "Waterborne acrylic/CeO2 nanocomposites for UV blocking clear coats" by Miren Aguirre et al. In this chapter, the authors describe the UV absorbing capaci‐ ty of CeO2 nanoparticles and the film-forming capacity of acrylic polymers. It presents the synthetic route to produce waterborne acrylic/CeO2 hybrid nanocomposites for UV absorb‐ ing coating applications, which leads to encapsulated morphology of CeO2 nanoparticles in‐ to the polymer particles resulting in lack of agglomeration during film formation. The photoactivity behavior of CeO2 nanoparticles is also discussed.

The fifth chapter is "Extraction and recovery of cerium from rare earth ore by solvent extrac‐ tion" by Kai Li et al. The authors describe the solvent extraction and recovery of cerium found in a variety of minerals and present in the highest concentration in light rate earth ores. The main approach used is based on the acid-leaching process of rare earth minerals, which produces the leaching solution as well as high purity CeO2products.

The sixth chapter is "Pd-supported catalysts over mixed oxides based on cerium for envi‐ ronmental catalysis purposes" by Victor Ferrer. This chapter presents studies related to the use of CeO2 as a redox promoter in the oxidation reactions of hydrocarbon and the reduc‐ tion of nitrogen oxides, which are carried out in catalytic converters installed in vehicles. The study also discusses the improvement of CeO2 redox properties by the incorporation of elements such as terbium or zirconium in the cerium network, creating a mixed oxide with better performance. Catalytic activity resulting from the CH4 and CO oxidation reactions and reduction of NO by CO in catalysts using Pd as an active phase are also studied.

**Prof. Dr. Sher Bahadar Khan and Prof. Dr. Kalsoom Akhtar**

Chemistry Department Faculty of Science King Abdulaziz University Jeddah, Saudi Arabia **Chapter 1**

**Provisional chapter**

) which is one of the

has cubic

**Introductory Chapter: Cerium Oxide - Applications and**

**Introductory Chapter: Cerium Oxide - Applications and** 

Cerium belongs to lanthanide series and available most abundantly in the crust of the earth with an average concentration of 50 ppm as a rare earth element. Elemental cerium is a flexible and malleable lustrous metal. Cerium metal is iron-gray in color and is highly reactive. It is also known as a strong oxidizing agent and exists as cerium oxide in association with oxygen atoms. It exists as either cerous (Ce3+, trivalent state) or ceric (Ce4+, tetravalent state) in

important transition metal oxides acting as n-type semiconductor materials. It possesses several features resulted from the combination of high amount of oxygen in its structure and the

fluorite structure, in which each cerium atom is surrounded by eight equivalent oxygen atoms and each oxygen atom is surrounded by a tetrahedron of four cerium atoms. Ideally, CeO<sup>2</sup> should have a formal charge of −2 and distance between oxygen–oxygen atoms should be

The main unique characteristics of cerium oxide involve a band gap of 3–3.6 eV, high value of dielectric constant up to κ = 23–26, high refractive index of n: 2.2–2.8, and high dielectric strength

in various applications, especially when they are in nanosized particles. The cerium oxide is a famous member of nanostructured materials having a wide range of applications. Cerium oxide materials/nanomaterials have been utilized in numerous fields including adsorption, catalysis, photocatalysis, sensing, fuel cells, hydrogen production, semiconductor devices as well as bio-

facile change between the reduced and oxidized states (Ce3+ and Ce4+) [2]. The CeO<sup>2</sup>

It is clear from the title that this book is related to cerium oxide (CeO<sup>2</sup>

2.705 Å, in which the formal charge of cerium ions is +4 [3].

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

[4]. Such properties qualify cerium oxide-based materials to be employed

DOI: 10.5772/intechopen.82757

**Attributes**

**1. Introduction**

the form of compounds [1].

reached to 2.6 MV cm−<sup>1</sup>

medical uses [5–10].

**Attributes**

Sher Bahadar Khan and Kalsoom Akhtar

http://dx.doi.org/10.5772/intechopen.82757

Additional information is available at the end of the chapter

Sher Bahadar Khan and Kalsoom AkhtarAdditional information is available at the end of the chapter

#### **Introductory Chapter: Cerium Oxide - Applications and Attributes Introductory Chapter: Cerium Oxide - Applications and Attributes**

DOI: 10.5772/intechopen.82757

Sher Bahadar Khan and Kalsoom Akhtar

Additional information is available at the end of the chapter Sher Bahadar Khan and Kalsoom AkhtarAdditional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.82757
