MECHANISM AND ENERGETICS FOR DEHYDROGENATION OF METHANE BY GASEOUS IRIDIUM IONS

Ir+ has been observed as the most efficient transition-metal ion for dehydrogenation of CH4 in the gas phase. We carried out theoretical studies of the complete reaction profile for this process and find three salient factors responsible for the high reactivity: (i) the ability of Ir+ to change spin easily, (ii) the strength of the Ir-C and Ir-H bonds, and (iii) the ability of Ir+ to form up to four covalent bonds. We show that among transition-metal ions Ir+ is unique in best possessing all three characteristics. The combination of these factors leads to a global minimum for the singlet Ir(H)2(CH2)+ structure, which plays an important role in the activation. On the basis of these results, we suggest solution-phase analogues that may also activate CH4.