Applied reaction dynamics: Efficient synthesis gas production via single collision partial oxidation of methane to CO on Rh(111)

Abstract

Supersonic molecular beams have been used to determine the yield of CO from the partial oxidation of CH4 on a Rh111 catalytic substrate, CH4+12O2-->CO+2H2, as a function of beam kinetic energy. These experiments were done under ultrahigh vacuum conditions with concurrent molecular beams of O2 and CH4, ensuring that there was only a single collision for the CH4 to react with the surface. The fraction of CH4 converted is strongly dependent on the normal component of the incident beam's translational energy, and approaches unity for energies greater than approximately 1.3 eV. Comparison with a simplified model of the methane-Rh111 reactive potential gives insight into the barrier for methane dissociation. These results demonstrate the efficient conversion of methane to synthesis gas, CO+2H2, are of interest in hydrogen generation, and have the optimal stoichiometry for subsequent utilization in synthetic fuel production (Fischer-Tropsch or methanol synthesis). Moreover, under the reaction conditions explored, no CO2 was detected, i.e., the reaction proceeded with the production of very little, if any, unwanted greenhouse gas by-products. These findings demonstrate the efficacy of overcoming the limitations of purely thermal reaction mechanisms by coupling nonthermal mechanistic steps, leading to efficient C-H bond activation with subsequent thermal heterogeneous reactions.

Oxidation and reforming reactions of CH4 on a stepped Pt(557) single crystal

“…Hickman and Schmidt propose that oxygen scavenges the surface of carbon to form CO and the hydrogen liberated during the decomposition of methane desorbs into the gas phase [52]. No carbon dioxide formation was observed during a supersonic molecular beam study of methane partial oxidation on Rh(1 1 1) suggesting that a direct mechanism may be applicable under single collision conditions [64].…”

State-Resolved Reactivity of Methane (ν2 + ν4) on Ni(111)

“…Monitoring the yield of surface-bound reaction products and the energetics of scattered species reveals how E trans affects the incident molecule's reactivity and interaction with the surface. Beam-surface scattering studies have explored the role of translational and internal energy in promoting methane dissociation on a range of transition metal surfaces, including W(110), 3 Pt(111), 4 Pt(110) (1×2), 5 Ni(111), 6 Ni(100), 7 Rh(111), 8 Ir(111), 9 Ir(110) (2×1), 10 Ru(0001), 6e and Pt(553). 11 Because vibrations do not cool well during supersonic expansion, one can vary seeding conditions and the nozzle temperature of the molecular beam source to investigate how the reagent's vibrational energy (E vib ) influences reactivity.…”

“…Monitoring the yield of surface-bound reaction products and the energetics of scattered species reveals how E trans affects the incident molecule’s reactivity and interaction with the surface. Beam-surface scattering studies have explored the role of translational and internal energy in promoting methane dissociation on a range of transition metal surfaces, including W(110), Pt(111), Pt(110) (1×2), Ni(111), Ni(100), Rh(111), Ir(111), Ir(110) (2×1), Ru(0001), and Pt(553) …”