Materials Chemistry and Physics 133 (2012) 163–169 Contents lists available at SciVerse ScienceDirect Materials Chemistry and Physics j ourna l ho me pag e: www.elsevier.com/locate/matchemphys Characterization and surface reactivity analyses of ceria nanorod catalyst for methanol interaction Sujan Chowdhury, Kuen-Song Lin ∗ Department of Chemical Engineering and Materials Science/Fuel Cell Center, Yuan Ze University, Chung-Li 320, Taiwan, ROC a r t i c l e i n f o Article history: Received 9 January 2011 Received in revised form 7 November 2011 Accepted 1 January 2012 Keywords: Methanol oxidation Ceria nanorod Ceria Nanomaterial XANES/EXAFS a b s t r a c t The reactivity of commercial ceria powder and as-synthesized one dimensional (1-D) ceria-nanorod (CeNR) for methanol oxidation has been studied at an atmospheric pressure in the present study. Exper- imentally, ceria nanomaterials are consisted with fluorite structure and confirmed using XRD patterns. The surface areas of BET N 2 adsorption isotherms for commercial ceria powder and 1-D CeNR samples are 6 and 78 m 2 g -1 , respectively. The EXAFS spectra reveal that the 1-D CeNR species has a Ce O bonding with a bond distance of 2.4 ˚ A and a coordination number is 6.87. Higher oxygen vacancies and Ce 3+ are formed for CeNR as compared with the ceria powder and confirmed with both XPS and Raman spec- troscopies. Moreover, two major species as named formate and methoxy are contributing on ceria for methanol dissociation, whereas, formation of carbon dioxide is evident effectively for 1-D CeNR. The reactivity for methanol oxidation of the commercial ceria powder and 1-D CeNR has been also compared. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved. 1. Introduction Fuel cell system is promising candidates for the portable power source system. Applications for mobile energy based on methanol and hydrogen in the portable devices are spreading enormously with the exponential demand of electrical energy consumption. Lower energy density belongs with the conventional batteries are not capable of fulfill for this huge energy requirement [1–3]. It is difficult and expensive for the delivery of hydrogen to automotive sector and consumer electric devices. Therefore, these difficulties can be eliminated by reforming of liquid fuels on-board of their applications. Methanol is one of the most promising sources of hydrogen for fuel cell applications included with the advantages of high energy density, easy availability, and safe handling/storage materials [1–4]. High catalytic activity has an important criterion for the application of methanol decomposition in an integrated fuel cell system. In the recent years, oxidation catalysts such as ceria, ceria based materials are receiving considerable attention because of their potential role in the environmentally important fuel cell technolo- gies. Formation of 1-D ceria nanostructure has been effects with the types of precursor, concentration, temperature, and pH. Tang et al. observed that tetravalent Ce salts (CeO 2 , Ce(SO 4 ) 2 ·4H 2 O and Ce(NH 4 ) 2 (NO 3 ) 6 ); and some trivalent hydrate salts (CeCl 3 ·7H 2 O ∗ Corresponding author. Tel.: +886 3 4638800x2574; fax: +886 3 4559373. E-mail address: kslin@saturn.yzu.edu.tw (K.-S. Lin). and Ce(NO 3 ) 3 ·6H 2 O) were used to produce Ce(OH) 4 and/or CeO 2 [5]. Upon the thermal treatment of CeCl 3 , they obtained Ce(OH) 3 crystal as of the major constituents. In addition, alkaline concentra- tion and temperature are significantly dominant to the formation of 1-D CeNR structure [6–10]. Furthermore, morphological differ- ences (such as size and shape) would apply substantial approaches for catalytic applications [7]. As an important component in cat- alysts, ceria promotes high oxygen storage capacity (OSC) and high oxygen ion conductivity. Several morphological structures of CeO 2 such as nanorod, nano-sponge single or multiwall, hollow structure, mesoporous, spindle has been investigated widely for the selective oxidation of mainly carbon monoxide (CO), nitrogen oxides, sulfur oxide, and so on, due to OSC of ceria [8–13]. As well, surface area, structural defects, and oxygen vacancy have a positive effect on CO oxidation [8,9]. The formation of oxygen vacancy can be expressed by the following Eq. (1): 4Ce 4+ + O 2- → 4Ce 4+ + 2e - (V (o) ) + 1 2 O2 → 2Ce 4+ , 2Ce 3+ + V (o) + 1 2 O2 (1) where V (o) represents an empty position (anion-vacant site) originating from the removal of O 2- from the lattice. Charge bal- ance is maintained by the reduction of two cerium cations from +4 to +3. The radius of the Ce 3+ ion is larger than that of Ce 4+ and hence the lattice expansion is a consequence of the reduction of Ce 4+ ions to Ce 3+ . There is a gradual decrease in the concentration of oxygen vacancies extended from the surface to the bulk. Such gradi- ent enables the outward diffusion of lattice oxygen to the surface. Therefore, the reduction of Ce 4+ –Ce 3+ by oxygen ion leads to the generation of surface oxygen vacancy. These oxygen vacancies can 0254-0584/$ – see front matter. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2012.01.002