Engineering the Reactivity of Metal Catalysts:  A Model Study of Methane Dehydrogenation on Rh(111)

Abstract

The first two steps of methane dissociation on Rh(111) have been investigated using density-functional theory, focusing on the dependence of the catalyst's reactivity on the atomic coordination of the active metal site. We find that, although the barrier for the dehydrogenation of methane (CH4 --> CH3 + H) decreases as expected with the coordination of the binding site, the dehydrogenation of methyl (CH3 --> CH2 + H) is hindered at an ad-atom defect, where the first reaction is instead most favored. Our findings indicate that, if it were possible to let the dissociation occur selectively at ad-atom defects, the reaction could be blocked after the first dehydrogenation step, a result of high potential interest for many dream reactions such as, for example, the direct conversion of methane to methanol.

A chromium oxide coated nickel/yttria stabilized zirconia electrode with a heterojunction interface for use in electrochemical methane reforming

“…9,10 The CH 4 or CO 2 activation was reported to be by chemical adsorption on surface defect sites or the thermal spitting of CH 4 on the surface of the metal catalysts. Theoretical investigations of CH x species adsorbed on platinum (111) and rhodium (111) indicate that CH x fragments are preferentially located at a site on the metal surface 11,12 and the stepwise decomposition of CH 4 into CH x fragments on a metal surface can benet the catalysis conversion. However, the chemisorption and dissociation of CO 2 on the metal surface may be benecial for dry CO 2 reforming of CH 4 .…”

DFT study on H2O activation by stepped and planar Rh surfaces

“…These elementary reaction steps have been studied for a wide range of transition metals [1,[8][9][10][11][12][13][14][16][17][18][19][20][21][22][23][24]. Recent works indicate a strong dependence of the rate of the methane dissociation on the coordinative saturation of the surface metal atoms [16][17][18]23,24].…”

Functionalities of Non-Bonding Electrons: Size Emergence

“…An adatom concentration of a few percent is sufficient to dominate the overall reaction rate in a catalytic process because of the higher reaction rate or the lower activation energies of the undercoordinated atoms. For instance, the first methane dehydrogenation process is highly favored at the Rh-adatom site on Rh(111) surface with respect to step or terrace sites [33,34]; adatoms deposited on oxides can activate the C-H bond scission [35], the acetylene ciclomerization [36], and the CO oxidation [37]. Preferential ON uptake occurs at Rh(311) and (533) edges [38].…”