Alkanes, higher, hydrogenolysis

Additionally, grafting molecular entities on surfaces has already allowed to discover several reactions the low temperature hydrogenolysis of alkanes including the depolymerization of polyolefins, the alkane metathesis and the cross-metathesis of methane and alkanes. These two latter reactions can allow higher molecular weight alkanes to be built. 

In the hydrogenolysis of the higher alkanes on the nonnoble group VIII metals (i.e., iron, cobalt, and nickel), the mode of cracking is very different from that observed on the noble metals of group VIII (49, 50). On nickel,... 

On the one hand, a comparison of initial rates for various alkane hydrogenolysis shows a marked difference between zirconium and tantalum hydrides (Table 3.2). Indeed, the reaction rates for [(=SiO)(4.,<)Zr(H)J, x = 1, 2) are weakly dependent on the nature of the alkanes. They are higher than those obtained... 

Ruthenium catalysts prepared from Ru3(CO)i2 and other related carbonyl-derived complexes have been widely used in reactions of hydrogenolysis, homologation and dimerization of alkanes [114—116]. Catalysts derived from carbonyl precursors usually show higher catalytic activities than conventionally prepared supported mthenium catalysts. This correlates well with the smaller crystallite size achieved by using carbonyl precursors. 

Silica-supported Ta hydride (=SiO)2Ta-H (93a) presents unusual properties in the activation of alkanes. It catalyzes the metathesis reaction of alkanes to give higher and lower molecular weight alkanes, and the hydrogenolysis of alkanes such as ethane to methane. This hydride also activates the C H bonds of cycloalkanes to form the corresponding surface metal-cycloaUcyl complexes, and catalyses the H/D exchange reaction between CH4 and CD4, prodncing the statistical distribution of methane isotopomers. ... 

Third, besides hydrogenolysis properties, the silica-supported tantalum hydride catalyzes the metathesis of alkanes, which transforms a given alkane into its higher and lower homolog (Scheme 36(c)). This reaction... 

A higher carbon number olefin, 1-hexadecene, was also used as a labeled tracer molecule with the cobalt catalyst. As the carbon number increased from 2 to 16, the fraction of the alkene converted to the corresponding alkane increased, the extent of incorporation into higher products decreased (about 30 percent for ethene versus 6.3 percent for 1-hexadecene) and the fraction undergoing hydrogenolysis (or another type of splitting reaction) increased (4.3 percent for ethene versus 14.1 percent for 1-hexadecene). 

---