Octopus carbon

The rate of carbon formation is far less on noble metals than on nickel and this behaviour appears to be related to the difficulty found by noble metals of dissolving carbon in bulk. ° The carbon formed on the surface of noble metals was found to be almost indistinguishable from the catalyst particles. High-resolution TEM images taken from a ruthenium catalyst employed in the SMR reaction revealed a structure in which a few carbon layers were deposited on the surface of the Ru particles. The mechanism by which whiskers grow on the surface of the nickel particles becomes blocked by sulphur poisoning of the catalyst surface. In this specific case, several octopus carbon filaments or whiskers are formed on a given nickel particle. A similar carbon structure has been reported to develop on Ni-Cu alloy catalysts with low nickel contents (20 wt%).ii... 

Figure 5.8 Octopus carbon. A carbon structure with more fibres from one nickel crystal. Bernardo etal. [49]. Reproduced with the permission ofElsevier.

Equilibrium studies for CRt decomposition [390] in the presence of sulphur showed the formation of carbon at close to the equilibrium point for sulphur-free gas. However, at high coverage (0s about 0.7) the whisker carbon structure was replaced by octopus carbon (refer to... 

Pentaerythritol tetrapalmitate, an octopus-like molecule with four water-attracting groups, each esterified by a long chain and arranged symmetrically round a central carbon atom,... 

By now you have noticed that names of alkanes end in -ane. Also, alkanes with five or more carbons in a chain have names that use a prefix derived from the Greek or Latin word for the number of carbons in each chain. For example, pentane, has five carbons just as a pentagon has five sides, and octane has eight carbons just as an octopus has eight tentacles. Because methane, ethane, propane, and butane were named before alkane structures were known, their names do not have numerical prefixes. Table 22-1 shows the names and structures of the first ten alkanes. Notice the underlined prefix representing the number of carbon atoms in the molecule. 

The analysis by STEM of Ni and Ni-Cr catalysts after the carbon deposition by the methane cracking reaction shows the formation of graphitic filaments in large amounts of whisker and octopus types. 

The whisker growth mechanism is also blocked by sulphur poisoning of the nickel surface. When formed, the carbon has a typical octopus structure with several fibres growing fi-om one nickel crystal [390], As shown in Figure 5.8, a similar stmctuie is formed on Ni/Cu catalysts with high copper contents [49],... 

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