Adsorption of ethylene on Ir(111)

Mechanistic Insights into Ethylene Transformations on Ir(111) by Density Functional Calculations and Microkinetic Modeling

“…The remarkable low barrier and large releasing heat suggest that the dehydrogenation of ethylidene to ethylidyne is fast and favorable thermodynamically. The result is consistent with the experimental observation that ethylidene can transform to ethylidyne at as low as 180 K.…”

“…Ethylidyne prefers adsorption at an hcp site over an fcc site on Ir(111). The C−C bond on Ir(111) is perpendicular to the metal surface in good agreement with earlier experimental description, see Figure S2c. The adsorption energy of ethylidyne at the 3‐fold hcp site on Ir(111) is −6.19 (−6.04) eV at 1/9 (1/3) ML, using the doublet state of ethylidyne in the gas phase as reference.…”

“…As discussed above, the formation of ethylidyne is favorable kinetically with a largest barrier of 0.61 eV, and also favorable thermodynamically, where all steps leading to the formation of CCH 3 are exothermic. Thus, ethylidyne formation from ethylene transformations is quite feasible at room temperature and should be easy to be observed, which is consistent with the experiments …”

“…The peak at 2940 cm −1 is assigned to the CH 3 group of ethylidyne in experiments while our calulations show the vibrations of ethylidyne yield some peaks near 3020 cm −1 and the vibrations of ethyl yield the peaks at 2970 and 2962 cm −1 . HREELS experiments show a peak at 1260 cm −1 at 500 K, which was attributed to a CC stretching mode of ethynyl CCH spices . This cannot be confirmed by the present calculations.…”

“…They find that ethylene converts to ethylidyne via ethylidene CHCH 3 first, and in a second moment into C atoms, the building blocks of graphene. The HREELS data suggest ethylidyne dehydrogenates to a CCH species which is the precursor to carbon monomer on Ir(111) . Following adsorption, ethylene also undergoes self‐hydrogenation by starting with a C−H bond breaking step which provides hydrogen atoms to other ethylene molecules .…”