Carbon-templated hexaaluminates with enhanced surface area and catalytic performance
Carbon-templated hexaaluminates with enhanced surface area and catalytic performance
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DOI：
10.1016/j.jcat.2008.04.017
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发表时间：
2008-07
影响因子：
7.3
通讯作者：
M. Santiago;J. Groen;J. Pérez–Ramírez
中科院分区：
文献类型：
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作者：
M. Santiago;J. Groen;J. Pérez–Ramírez
采用碳模板法制备了高比表面积六铝酸盐LaFeAl11O19六铝酸盐，提高了催化剂的催化性能。通过浸渍、柠檬酸络合、共沉淀法制备了不同乙炔黑掺杂量的氧化物前驱体-模板复合材料。在1473K静态空气中焙烧得到了单相的六铝酸盐。用电感耦合等离子体发射光谱、原位和非原位X射线衍射仪、透射电子显微镜、氮气吸附、氦气比浊法、热重分析、氢-热重分析和X射线光电子能谱等手段对样品进行了表征。碳的模板效应来源于细小的氧化物颗粒。因此，在合成中加入碳后，非模板化六铝酸盐(1-11 m2g−1，取决于制备方法)的比表面积增加到25倍。尽管除碳(973K)和达到137K以上的六铝酸盐相之间存在温差，但小颗粒的稳定仍然存在。除碳后得到的氧化物的形态决定了六铝酸盐颗粒的织构特性。我们的结果表明，受限空间合成并不完全是小颗粒氧化物的作用。当炭为大孔道时，碳表面小晶体的稳定和模板燃烧引起的氧化层的破坏是获得细小分散粒子的关键。模板化六铝酸盐在N2O直接分解反应中的催化活性和流态稳定性均得到了提高。在此应用中，得到了反应速度与样品比表面积之间的准线性关系。H2-Trp和XPS表征表明，合成过程中碳的掺入没有改变LaFeAl11O19中铁的性质。
Carbon templating was used to synthesize high-surface area LaFeAl11O19hexaaluminates leading to improved catalytic performance. The oxide precursor–template composites were prepared by impregnation, complexation with citric acid, and coprecipitation routes varying the amounts of acetylene black incorporated. Calcination in static air at 1473 K led to single-phased hexaaluminates. The samples were characterized at different stages of the synthetic protocol by ICP–OES, in situ and ex situ XRD, TEM, N2adsorption, He pycnometry, TGA, H2-TPR, and XPS. The templating effect of carbon originates fine oxide particles. Consequently, the specific surface area of the non-templated hexaaluminates (1–11 m2g−1depending on the preparation method) increased up to a factor of 25 upon incorporation of carbon in the synthesis. The stabilization of small particles occurs despite the temperature difference between the elimination of carbon (973 K) and the attainment of the hexaaluminate phase above 1373 K. The morphology of the oxide obtained upon carbon removal determines the textural properties of the hexaaluminate particles. Our results demonstrate that the confined space synthesis is not exclusively responsible for small oxide particles. The stabilization of small crystallites on the carbon surface in the composite and breakage of the oxide layer caused by template combustion are key aspects for attaining finely dispersed particles when the carbon is macroporous. The enhanced catalytic activity and time-on-stream stability of the templated hexaaluminates was demonstrated in the direct N2O decomposition using model and simulated feed mixtures. In this application, a quasi-linear relation between the reaction rate and the specific surface area of the samples was obtained. Characterization by H2-TRP and XPS indicated that the nature of iron in LaFeAl11O19was not altered by carbon incorporation in the synthesis.