Heterolytic dissociation of C-H bond of methane over Ag+-exchanged ceolites and conversion of methane into higher hydrocarbons in the presence of ethene or benzene

The heterolytic dissociation of CH4 over silver cationic clusters (Ag-n(+)) in Ag+-exchanged zeolites leads to the formation of silver hydride (Ag-n-H) and methyl cations, which then reacts with C2H4 to form C3H6. This process provides methane conversion of 13.2% at 673 K to afford higher hydrocarbons, such as toluene. Under these reaction conditions, H-ZSM-5 only catalyzes ethene conversion to higher hydrocarbons, such as butenes, and no methane conversion occurs. The reaction of CH4 with benzene also proceeds to form toluene and xylenes over Ag-ZSM-5 at 673 K. Zeolites prepared by exchange with other metal cations, including In and Ga, also activate CH4 in the presence of C2H4. Using C-13-labeled methane ((CH4)-C-13) as a tracer, propene is shown to be a primary product for the ethene reaction based on the observation of a significant proportion of singly C-13-labeled propene ((CC2H6)-C-13). In-ZSM-5 catalyzes the formation of not only propene, but also benzene and toluene. C-13 label atoms are not found in the benzene thus produced, indicating that benzene originates entirely from C2H4. However, the occurrence of singly C-13-labeled toluene ((CC6H8)-C-13) implies that toluene is formed by the reaction of benzene with (CH4)-C-13. The alternative reaction path, involving (CC6H8)-C-13 formation by reaction of propene with n-butenes generated by ethene dimerization, can be refuted by confirmation of the toluene origin through direct reaction of (CH4)-C-13 with benzene.