Cobalt catalysts hydrogen reduction, surface

The present study revealed effects of various rutile/anatase ratios in titania on the reduction behaviors of titania-supported cobalt catalysts. It was found that the presence of rutile phase in titania could facilitate the reduction process of the orbalt catalyst. As a matter of fact, the number of reduced cobalt metal surface atoms, which is related to the overall activity during CO hydrogenation increased. 

In the case of cobalt, unstable cubic cobalt was identified as the product of the reduction of standard cobalt catalysts, while hexagonal cobalt was found as a product of the hydrogenation of cobalt carbide. Used cobalt catalysts show no carbide by x-ray examination. Bulk phase carbide decreases the activity of cobalt catalysts. Surface area measurements show no appreciable change when the cobalt of cobalt catalysts was converted to cobalt carbide. Carburization at conditions where free carbon is formed increases the area considerably. 

Alcohols and jlkenes are also primary products and are not shown in the simplified Eq. 15.182. The overall reaction is complicated and, as a result, its mechanism has been the subject of considerable debate.188 The reaction may be viewed as the reductive polymerization of carbon monoxide, with molecular hydrogen as the reducing agent. A variety of heterogeneous catalysts, such as metallic iron and cobalt on alumina, have been used. It is believed that carbon monoxide dissociates on the catalytic surface to give carbides and that these are in turn hydrogenated to give surface carbenes 1 " n ... 

The Neel point of cobalt monoxide is 291 K. For obvious reasons this oxide cannot be heated in hydrogen without reduction to the metal. A sample of surface 5.8 m2 g 1 was pretreated in situ by heating it in purified helium at 823 K. The catalyst was then cooled to near room temperature before the admission of hydrogen. Figure 20 shows A k for CoO as a function of extrinsic field up to 18 kOe at 301 K. At this temperature ka was about 7.2 /u.mol m-2 s l. Figure 21 shows results for the same sample at 275 K. Figure 22 shows k0 and AkH at 17.3 kOe over the temperature range 275-300 K. 

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