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论文类型：期刊论文

发表时间：2011-01-10

发表刊物：CHEMISTRY-A EUROPEAN JOURNAL

收录刊物：SCIE、EI

卷号：17

期号：2

页面范围：598-605

ISSN号：0947-6539

关键字：colloids; heterogeneous catalysis; iron; nanotechnology; X-ray diffraction

摘要：High-temperature, stable core shell catalysts for ammonia decomposition have been synthesized. The highly active catalysts, which were found to be also excellent model systems for fundamental studies, are based on alpha-Fe(2)O(3) nanoparticles coated by porous silica shells. In a bottom-up approach, hematite nanoparticles were firstly obtained from the hydrothermal reaction of ferric chlorides, L-lysine, and water with adjustable average sizes of 35, 47, and 75 nm. Secondly, particles of each size could be coated by a porous silica shell by means of the base-catalyzed hydrolysis of tetraethylorthosilicate (TEOS) with cetyltetramethylammonium bromide (CTABr) as porogen. After calcination, TEM, high-resolution scanning electron microscopy (HR-SEM), energy-dispersive X-ray (EDX), XRD, and nitrogen sorption studies confirmed the successful encapsulation of hematite nanoparticles inside porous silica shells with a thickness of 20 nm, thereby leading to composites with surface areas of approximately 380 m(2)g(-1) and iron contents between 10.5 and 12.2 wt%. The obtained catalysts were tested in ammonia decomposition. The influence of temperature, iron oxide core size, possible diffusion limitations, and dilution effects of the reagent gas stream with noble gases were studied. The catalysts are highly stable at 750 degrees C with a space velocity of 120000 cm(3) g(cal)(-1)h(-1) and maintained conversions of around 80% for the testing period time of 33 h. On the basis of the excellent stability under reaction conditions up to 800 degrees C, the system was investigated by in situ XRD, in which body-centered iron was determined, in addition to FeN(x), as the crystalline phase under reaction conditions above 650 degrees C.