Synthesis of alumina supported nickel nanoparticle catalysts and evaluation of nickel metal dispersions by temperature programmed desorption

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• 作者：Subramani Velu and Santosh K. Gangwal
• 关键词：Nanomaterial ; Nanoparticle ; Ni catalyst ; Supported catalysts ; Chemisorption ; Temperature programmed desorption ; Metal surface area ; Metal dispersion
• 刊名：Solid State Ionics
• 出版年：2006
• 出版时间：15 March 2006
• 年：2006
• 卷：177
• 期：7-8
• 页码：803-811
• 全文大小：480 K

文摘

The purpose of this study was to synthesize highly dispersed Ni/Al₂O₃ catalysts and to develop a suitable hydrogen-temperature programmed desorption (H₂-TPD) method for the determination of nickel metal surface area, dispersion, and crystallite sizes. Several highly dispersed Ni/Al₂O₃ catalysts with a Ni loading between 15 and 25 wt. % were synthesized. The reducibility of catalysts was determined by temperature programmed reduction (TPR) experiments. All catalysts exhibited a single reduction peak with a maximum rate of H₂ consumption (T_max in TPR) occurring below 450 °C. Three different H₂-TPD methods were employed to determine the amount of H₂ chemisorbed. In TPD-1, a 10 % H₂/Ar mixture was used for catalyst pre-reduction and surface saturation by cooling down from T_max in TPR to room temperature. In TPD-2, the catalyst surface after pre-reduction was flushed with Ar at T_max in TPR + 10 °C. The TPD-3 was similar to the TPD-2, but used 100 % H₂ instead of 10 % H₂/Ar mixture. In all three TPD methods, the profiles exhibited 2 domains of H₂ desorption peaks, one below 450 °C, referred to as type-1 peaks, and attributed to H₂ desorbed from exposed fraction of Ni atoms, and the other above 450 °C, denoted as type-2 peaks, and assigned to the desorption of H₂ located in the subsurface layers and/or to spillover H₂. Flushing the reduced catalyst surface in Ar at T_max in TPR + 10 °C in TPD-2 and TPD-3 removed most of the H₂ located in the subsurface layers/ spillover H₂. The amount of H₂ chemisorbed to form a monolayer on the reduced Ni/Al₂O₃ catalysts was determined quantitatively from the TPD peak areas of type-1 peaks in TPD-1, and from both type-1 and type-2 peaks in TPD-2 and TPD-3. The Ni metal surface area, dispersions and crystallite sizes were calculated from the chemisorption data and the values were compared with those obtained using the static chemisorption method. Both TPD-2 and TPD-3 gave chemisorption results similar to that obtained from the static method.