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Abstract Carbon-supported, promoted Ru-based catalysts for ammonia synthesis proved to be interesting substitutes for the traditional Fe-based ones. A debate recently arose on the active state of promoters, mainly Cs and Ba, and on the effect of the latter on Ru active sites. In the present work a set of Ba-, Cs- and K-promoted samples has been characterised by various techniques. Higher H2 and O2 uptakes have been observed during reduction and chemisorption, respectively, on Cs- and K-promoted samples supported on graphitised carbon. No evidence of this has been observed with samples supported on active carbon. This is in line with the hypothesis of alkaline promoters partial reduction under the ammonia synthesis conditions, favoured by the formation of graphite intercalation compounds. Furthermore, some suggestions are here introduced on the beneficial role of Ba, especially in increasing the support resistance to methanation. Finally, the efficacy of catalyst activation was found to depend on the nature of Ru precursor. Indeed, a prolonged activation at relatively high temperature is usually needed with chloride precursors, to remove the counterion, a poison for the catalyst, whereas less dramatic conditions are required for different precursors, such as nitrosylnitrate. Keywords: Ammonia synthesis catalyst; Intercalation compounds; Temperature programmed reduction; Alkali metals reduction |
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dd99835
木虫 (正式写手)
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Mally89(金币+2): 感谢应助！~欢迎常来！~ 2011-06-17 20:23:04
sltmac(金币+50): 2011-06-23 12:13:15
sltmac(金币+50): 2011-06-23 12:13:19
sltmac(金币+50, 翻译EPI+1): 感谢应助，欢迎常来~~ 2011-06-23 12:13:31
Mally89(金币+2): 感谢应助！~欢迎常来！~ 2011-06-17 20:23:04
sltmac(金币+50): 2011-06-23 12:13:15
sltmac(金币+50): 2011-06-23 12:13:19
sltmac(金币+50, 翻译EPI+1): 感谢应助，欢迎常来~~ 2011-06-23 12:13:31
| 碳架提高了氨合成中钌基催化剂活性，从而证明钌基催化剂可成为传统铁基催化剂的替代品。关于促进剂的活性状态的争议最近被提出，主要是铯和钡，还有后者对铷的活性位点的影响。目前研究中一组Ba-，Cs-和K-促进的样品由不同技术进行了表征。在还原和化学吸附过程中，石墨碳支撑的Cs-和K-样品上分别可观察到较高的氢气和氧气摄取量，活性碳支撑的样品上未观察到相同现象。这与假设是一致的，即氨合成条件下碱性减弱，由形成石墨层间化合物得以促进。而且，在此提出了Ba的有益作用，尤其是在增强抵抗甲烷化的作用。最终催化剂的活化功效被发现依赖于铷前体的性质。事实上，在相对较高温度时通常需要长时间的激活与氯化物前体来去除反离子（催化剂的中毒试剂），然而，对于不同的前体很少需要奇怪条件，比如亚硝硝酸盐。 |
2楼2011-06-17 18:14:43
