Bumajdad Ali, Zaki Mohamed I, Eastoe Julian, Pasupulety Lata
Chemistry Department, Faculty of Science, Kuwait University, P.O. Box 5969, Safat, 13060 Kuwait.
Langmuir. 2004 Dec 7;20(25):11223-33. doi: 10.1021/la040079b.
Pure ceria powders, CeO(2), were synthesized in heptane-microemulsified aqueous solutions of CeCl(3) or Ce(NO(3))(3) stabilized by AOT (sodium bis(2-ethylhexyl) sulfosuccinate), DDAB (di-n-didodecyldimethylammonium bromide), or DDAB + Brij 35 surfactant mixtures. Micellar DTAB (n-dodecyltrimethylammonium bromide) and vesicular DDAB systems were also used as media for generating CeO(2). 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 CeO(2) were produced. In the absence of surfactants 21-nm-sized crystallites were formed, comparing with the 85-nm-sized crystallites when cubic CeO(2) was created via thermal decomposition of cerium oxalate. Surface characterization, by X-ray photoelectron spectroscopy, N(2) 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 degrees C). In contrast, the double-chained DDAB was found to generate cubic CeO(2) 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 degrees C). Hence, the latter cerias could be considered as appropriate components for total oxidation (combustion) catalysts.
通过AOT（双（2-乙基己基）磺基琥珀酸钠）、DDAB（二正十二烷基二甲基溴化铵）或DDAB + Brij 35表面活性剂混合物稳定的CeCl₃或Ce(NO₃)₃的庚烷微乳化水溶液中合成了纯二氧化铈粉末CeO₂。胶束状DTAB（正十二烷基三甲基溴化铵）和囊泡状DDAB体系也用作生成CeO₂的介质。通过X射线粉末衍射、激光拉曼光谱和傅里叶变换红外光谱对粉末进行表征，结果表明，在表面活性剂存在的情况下，生成了几乎无团聚的无阴离子空位的立方CeO₂纳米微晶（6 - 13纳米）。在没有表面活性剂的情况下，形成了21纳米大小的微晶，而通过草酸铈热分解生成立方CeO₂时形成的微晶大小为85纳米。通过X射线光电子能谱、N₂吸附法和高分辨率电子显微镜进行的表面表征表明，AOT或（DDAB + Brij 35）稳定的微乳液有助于形成具有大比表面积（高达约250 m²/g）但对高温煅烧稳定性低（800℃时为28 - 13 m²/g）的微晶。相比之下，发现双链DDAB生成的立方CeO₂微晶初始比表面积较低（微乳液为144，囊泡为125 m²/g），但热稳定性较高（800℃时为55 - 45 m²/g）。因此，后一种二氧化铈可被视为完全氧化（燃烧）催化剂的合适组分。
