Shell Technology Centre Amsterdam, Grasweg 31, 1031 HW Amsterdam, The Netherlands.
J Am Chem Soc. 2010 Jun 30;132(25):8540-1. doi: 10.1021/ja103002k.
Cobalt on carbon nanofiber model catalysts with very small dispersed cobalt particles of 5 nm were subjected to H(2)O/H(2) treatments at 20 bar and 220 degrees C. Using in situ Mossbauer spectroscopy we could unambiguously prove that oxidation of the nanoparticles by water will not occur when hydrogen is present. Only in a water/argon atmosphere did oxidation take place. This rules out oxidation as the deactivation mechanism in Fischer-Tropsch synthesis. Even more important, we define the relative humidity (RH) as a key parameter to understanding deactivation by water. At a RH below 25% sintering was absent even when measuring for 4 weeks, whereas at a high RH of 62% as much as half of the small super paramagnetic cobalt particles (<5 nm) sintered into larger particles in 1 week. Activity loss as measured at Fischer-Tropsch conditions amounted to 73%, which could be directly related to the metal dispersion loss 77% due to sintering as evidenced by detailed TEM analysis of the spent sample.
钴负载在碳纤维纳米纤维模型催化剂上，其中钴纳米颗粒的分散度非常小，仅有 5nm。这些催化剂在 20 巴和 220°C 的条件下进行了 H(2)O/H(2)处理。通过原位穆斯堡尔谱学，我们可以明确证明，当氢气存在时，纳米颗粒不会被水氧化。只有在水/氩气氛中才会发生氧化。这排除了氧化作为费托合成失活的机制。更重要的是，我们将相对湿度 (RH) 定义为理解水失活的关键参数。在 RH 低于 25%的情况下，即使测量 4 周，也没有出现烧结现象，而在 RH 高达 62%的情况下，多达一半的小超顺磁钴颗粒(<5nm)在 1 周内烧结成较大的颗粒。在费托条件下测量的活性损失高达 73%，这可以直接与由于烧结导致的金属分散度损失 77%相关联，这一点可以通过对失活样品的详细 TEM 分析得到证明。
