Fe-MgO catalyst

Fe/MgO catalysts with 5 to 30 mol % Fe have been prepared by impregnation and coprecipitation. Their reducibility has been measured and a comparison made of their Fe° surface areas. Catalysts prepared via coprecipitation yielded larger iron areas than those via impregnation. The activity and selectivity of the reduced catalysts for the hydrogenation of propanenitrile at 20-30 bar and 473 K and of ethanenitrile at 1 bar and 508 K have been determined. The most active catalysts are those prepared by coprecipitation and they show high selectivity for primary amines. The activity for ethanenitrile hydrogenation correlates with the iron surface area. 

Supported iron catalysts are notoriously difficult to reduce [6-8] and thus a substantial fraction of the iron can be expected to remain inactive for the catalysis of hydrogenation. Particular attention has therefore been paid to the preparation of Fe/MgO catalysts by several different methods and examination of their effectiveness in producing metallic iron of adequate specific surface area after reduction in hydrogen. The activity and selectivity for primary amine formation have been determined for the hydrogenation of ethanenitrile (acetonitrile) and propanenitrile. 

Fe/MgO catalysts with loadings in the range 5-30 mol % Fe were prepared by four methods (a-d) as follows ... 

Effect of loading and method of preparation on the reducibility of iron in Fe/MgO catalysts... 

STUDY OF Fe-MgO CATALYST STRUCTURAL TRANSFORMATIONS IN THE PROCESS OF PYROLYTIC SYNTHESIS OF CARBON NANOMATERIALS... 

Keywords carbon nanomaterials, Fe-MgO catalyst, Mossbauer spectroscopy, pyrolytic... 

Figure 1. TEM microphoto of pyrolysis synthesis products obtained with Fe-MgO catalyst.

Topspe and co-workers (231) studied calorimetrically the adsorption of CO at 303 K on MgO-supported Fe and on two unsupported Fe ammonia synthesis catalysts. These catalysts displayed quite heterogeneous site energy distributions. For example, the differential heat of adsorption on the Fe/MgO catalyst decreased from about 110 kJ moP to a large plateau at 80 kJ moP before decreasing abruptly to near 40 kJ moP. It was found that the amount of weakly held CO increased with decreasing Fe particle size. The authors used IR spectroscopy to demonstrate that the differences in the site energy... 

Since butenes were also produced from CO + H2 or C2H4 on the same Fe/MgO catalyst it was logical to study the behaviour of propylene on such catalyst. In a third experiment Feo(CO)12 (40 mg 0.08 m.mole) was chemisorbed on a magnesia o (1.1. g) and thermally decomposed under vacuum as previously described. C3H6 (140 Torr) was introduced into this supported catalyst which was heated stepwise from 25 up to 200°C. At 140°C propylene was converted to propane (0.3 Z) (self-ydrogenation) and to a mixture of Cj, C2, C4, C5, mainly olefinic, hydrocarbons (0.1 Z). In the Cj, C2> C4, C5 fraction the selectivity for butenes was 65 Z (CH4 ... 

Lee et al. (17) prepared model Fe/MgO catalysts by deposition of Fe onto MgO(lOO). These surfaces were then characterized in detail following H2 + CO treatments at —0.1 torr by application of a powerful array of surface analytical methods. For Fe layers less than four atoms thick, the Fe was oxidized after reaction with CO + H2. For higher coverages, the Fe was carburized. Carbon deposition was seen at all Fe thicknesses. They saw at least two carbon species, with C-Fe distances of 1.78 and... 

The idea of C7 sites being the most active site in ammonia synthesis on iron has been suggested in the past. Dumesic et al. [42] found that the turnover number for ammonia synthesis was lower on small iron particles than on larger ones. Pretreatment of an Fe/MgO catalyst with ammonia enhanced the turnover number over small iron particles, but did not affect the larger particles. This result was explained by noting that the concentration of C7 sites would be expected to be higher on the smaller iron particles and that restructuring induced by ammonia enhanced the number of these sites on the catalyst. 

---