Microemulsion-Based Synthesis of CeO 2 Powders with High Surface Area and High-Temperature Stabilities Ali Bumajdad, Mohamed I. Zaki,* Julian Eastoe, † and Lata Pasupulety Chemistry Department, Faculty of Science, Kuwait University, P.O. Box 5969, Safat, 13060 Kuwait Received June 1, 2004. In Final Form: September 10, 2004 Pure ceria powders, CeO2, were synthesized in heptane-microemulsified aqueous solutions of CeCl3 or Ce(NO3)3 stabilized by AOT (sodium bis(2-ethylhexyl) sulfosuccinate), DDAB (di-n-didodecyldimethyl- ammonium bromide), or DDAB + Brij 35 surfactant mixtures. Micellar DTAB (n-dodecyltrimethylammonium bromide) and vesicular DDAB systems were also used as media for generating CeO2. Characterization of the powders by X-ray powder diffractometry, laser-Raman spectroscopy, and Fourier transform infrared spectroscopy revealed that in the presence of surfactants almost-agglomerate-free nanosized crystallites (6-13 nm) of anionic vacancy-free cubic CeO2 were produced. In the absence of surfactants 21-nm-sized crystallites were formed, comparing with the 85-nm-sized crystallites when cubic CeO2 was created via thermal decomposition of cerium oxalate. Surface characterization, by X-ray photoelectron spectroscopy, N2 sorptiometry, and high-resolution electron microscopy showed AOT- or (DDAB + Brij 35)-stabilized microemulsions to assist in formation of crystallites exposing surfaces of large specific areas (up to ca. 250 m 2 /g) but of low stability to high-temperature calcination (28-13 m 2 /g at 800 °C). In contrast, the double- chained DDAB was found to generate cubic CeO2 crystallites of lower initial surface areas (144 (microemulsion) to 125 (vesicles) m 2 /g)) but of higher thermal stability (55-45 m 2 /g at 800 °C). Hence, the latter cerias could be considered as appropriate components for total oxidation (combustion) catalysts. 1. Introduction Ceria (CeO 2 ) and related oxides, namely, Ce-Zr-O and Ce-Pr-O, enjoy a breadth of surface-driven applications in heterogeneous catalysis and in the fabrication of fuel cells, microelectronics, gas sensors, and polishing materi- als. Relevant details of these, and other applications, have recently been reviewed by Trovarelli. 1 Though they have only lately been found to be independent, 2,3 the surface specific area (m 2 /g) and oxygen storage capacity (OSC) are crucial properties for most of these applications. For instance, the potential of ceria in the catalysts developed for the treatment of automotive exhaust gases stems from its ability to store oxygen under lean fuel conditions and to release it when the oxygen concentration becomes virtually nil (rich fuel conditions). 4 This perfectly reversible redox behavior, 5 which facilitates economic production of H 2 when water vapor is used as an oxidant for CeO 2-x , 5 as well as acido-basic surface properties, 6 means that ceria is an important ingredient in the chemical composi- tion of catalysts employed in fluid catalytic cracking, SO x removal, ethylbenzene dehydrogenation, and the water- gas shift reaction. 1,7 Accordingly, synthesis of ceria with large surface specific areas and oxygen storage capacities has been at the focus of numerous researchers. 1 Whereas remarkable advances have been scored toward synthesis of cerias of thermally stable, large OSCs, using zirconia 1-3,8 and praseodia 9 additives, obtaining pure ceria of thermally stable, high- area surfaces has not hitherto been accomplished with- out stabilizing additives of zirconia. 10-15 This latter un- accomplished objective has hindered the promising ap- plications of ceria in combustion catalysts for natural gas turbines. 16 In natural gas combustion processes catalysts must withstand high temperatures (800-900 °C). 16 Al- though endeavors to synthesize high-area ceria powders have profited from recent developments of methods to prepare nanosized solid particles, 17 such as the sol-gel, 1,18 complexation, 1,13,19,20 and hydrothermal 1,10,15,21,22 and mi- croemulsion 1,11,12,14,23,24 methods, the accomplishments hitherto achieved are confined to yielding pure cerias of * Corresponding author. 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