Nickel methane covered

Figure 6 shows the TPR spectra of adsorbed CO on nickel. The CO was desorbed mostly as the molecular form, whereas the amounts of desorbed carbon dioxide and methane were quite small. Thus, most of the CO adsorbed on nickel is in an undissociated state, and the extent of its adsorption is fairly weak, as the desorption is completed below 200 C. In contrast, the adsorption of methyl acetate on nickel is stronger than those of other reactants or products, as evaluated from the retention time in the nickel-activated carbon column shown in Table III. This fact suggests that most of the nickel is covered by methyl acetate and reaction products, and the coverage of adsorbed CO is quite low under the reaction conditions when the partial pressure of CO is close to that of methyl acetate. The carbonylation is therefore accelerated by increasing the CO/AcOMe ratio which increases the coverage of CO adsorbed competitively with methyl acetate. 

Higher Hydrocarbons. - A number of papers describing the steam reforming of higher hydrocarbons are particularly concerned with the subject of carbon deposition on the catalysts. The subject of carbon deposition on nickel catalysts is considered to be somewhat outside the subject of this review, especially as the subject is covered by two excellent recent discussions of papers on carbon deposition and coking during steam reforming, methanation, and other reactions.202 203... 

Chemisorption of hydrocarbons on various metals, such as nickel, platinum, copper, etc., was investigated in great detail (9, 90, 91, 92). Information on chemisorption of ethylene, acetylene and methane on various metals may be found in Trapnell s review (93). However, direct application of the relations obtained to metal oxide catalysts would scarcely be justifiable. As a rule, oxygen covers the whole surface of the metal, and chemisorption of hydrocarbons occurs either on a thin layer of the given metal oxide formed as an individual phase, or on oxygen that was sorbed on the surface and has filled the adjacent-to-surface layers. Thus data on chemisorption of hydrocarbons on oxides of these metals may be of use in the above cases. 

Water is more strongly adsorbed and hinders the adsorption of methane since adsorption of CH4 and H2O occurs at the same sites. The adsorption of methane on a water-covered nickel surface is rate determining. (This conclusion was tested by studying carbon and... 

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