Direct or indirect conversion

An important challenge in Ci chemistry is to circumvent the syngas step by a direct conversion of methane into useful products. Still, yields are far from being economical [238] [287] [307]. The methane molecule is very stable, with a C-H bond energy of 439 kJ/mol hence methane is resistant to many reactants. Electrophillic attack requires superacidic 

This is feasible when Q is an oxidising agent. However, the product often has much weaker C-H bonds than methane, which implies that it is difiScult to eliminate further reactions leading to complete oxidation. 

The direct oxidation of methane to methanol or formaldehyde has been a dream reaction for a long time [537]. Attempts include gas-phase reaction, catalytic reactions, and use of other oxidants than air. Selectivities may be high, but at a lower conversion per pass resulting in yields being inferior for industrial use. 

Other attempts have aimed at creating a carbon-carbon bond fi om methane, although most natural gas sources contain a fraction of ethane and other lower alkanes. 

Catalytic partial oxidation at high temperature and ultra-short residence time over noble metals gauze has shown formation of olefins and oxygenates [206]. The feasibility of this route is still to be analysed. The indirect route via methanol appears to be a more promising route for olefins (see Section 2.6). 

---