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Effect of ammonia on cobalt Fischer-Tropsch synthesis catalysts: a surface science approach

机译：氨对钴的费合成催化剂:表面科学的方法

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摘要

Ammonia adsorption and decomposition on defect-rich hcp-Co(0001) surfaces were investigated under ultra-high vacuum conditions in order to provide a fundamental explanation for industrially observed ammonia poisoning of cobalt based Fischer-Tropsch synthesis (FTS) catalysts. Temperature-programmed desorption, infrared spectroscopy and work function measurements indicate that undercoordinated sites bind ammonia stronger than sites on flat Co(0001), and they also induce its dehydrogenation. Density functional theory calculations were employed to explore the reactivity of defective Co surfaces using the fcc-Co(211) as a model. The results indicate that the decomposition products (NHx) adsorb strongly on or around the step site on fcc-Co(211). We find that NH (+2H(ad)), adsorbed in the threefold site on the upper terrace, is equally stable as NH2 (+H-ad), adsorbed in the bridge position at the step edge, both being significantly more stable than the equivalent species adsorbed on the flat Co(0001). The calculated activation barriers for NH3,ad dehydrogenation steps are in reasonable agreement with the barriers obtained by fitting experimental data. Based on these fundamental insights, poisoning of cobalt nanoparticles during FTS by NH3 contaminants can be linked mainly to the blocking of undercoordinated sites by strongly adsorbed NH2 species.
机译：氨吸附和分解defect-rich hcp-Co(0001)表面在超高真空条件下进行为了提供一个基本的原因工业上观察到的钴氨中毒费托合成催化剂(FTS)。程序升温解吸、红外光谱和功函数测量表明undercoordinated网站绑定氨比网站平面有限公司(0001),和他们也促使其脱氢。泛函理论计算了探索缺陷Co的反应性表面使用fcc-Co(211)作为一个模型。表明,分解产品(NHx)强烈吸附或网站的步骤fcc-Co(211)。三倍的网站上露台,同样稳定的氨基(+经历),吸附桥在步骤边缘位置,都是明显比相当于更稳定物种吸附平面有限公司(0001)。计算激活NH3的障碍,广告脱氢步骤在合理的协议通过拟合与障碍实验数据。见解,中毒的钴纳米颗粒在罚球NH3污染物可以联系主要的阻碍undercoordinated网站由强烈吸附NH2的物种。

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