Proponium ions formation

Figure 11. Different ways for the formation of the isomeric proponium ions.

The formation of C-ethanemethonium can occur by protoiytic attack of C-H or C-C bonds, leading to H-proponium or C-proponium pentacoordinated ions, respectively. Proponium ions can further evolve towards isomeric C-ethanemethonium ion via bond-bond rearrangement. The nature of the initial interaction between proton and propane molecule is of little importance because intramolecular reatrangements of energetically close carbonium ion forms take place easily [26]. 

A bimolecular reaction of C-ethanemethonium or C-proponium ions with propane molecule may result in formation of ethane and buthonium ion. The latter may further evolve to n-butane or i-butane via deprotonation and recovering the Brpnsted acid site. This reaction step may occur either via consecutive mechanism [15, 16] involving formation of CH3 carbenium ion bound to the zeolite framework, followed by its addition to propane molecule, or via concerted mechanism involving CHs transfer from carbonium ion to the propane molecule. This mechanistic pathway explains butanes primary formation. Ethane was also found to be a primary product, however selectivity to ethane formation was much lower comparetively to butanes. It may be due to the fact that ethane... 

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