The presence of energetic hydrogen species in a plasma-enhanced catalysis reactor for CO2 or CH4 reforming could potentially lead to different hydrogenation rates and mechanisms for surface adsorbates, such as carbon monoxide (CO). Hydrogenation of CO on the Ni(110) surface at 100 K under ultrahigh vacuum (UHV) conditions has been studied using coadsorbed surface deuterium (D), subsurface D, and incident D atoms and D2 + ions. Surface-bound D adatoms did not react with coadsorbed CO to form formaldehyde (CD2O) and methanol (CD3OD) in temperature-programmed desorption (TPD) measurements. In contrast, subsurface D formed by incident D atoms can hydrogenate postadsorbed CO in subsequent TPD measurements to form CD2O and CD3OD in characteristic reaction limited thermal desorption peaks at 170 K. Subsurface D formed by 400 eV D2 + ions also produces these products but in peaks at 240 K. D atoms from the gas phase incident on a CO saturated Ni(110) surface at 100 K only formed CD2O in TPD, whereas using 100 eV D2 + ions in a similar experiment formed both CD2O and CD3OD in TPD. Incident D2 + ions were less reactive than subsurface D for the hydrogenation of CO on the Ni(110) surface. Our previous Born-Oppenheimer molecular dynamics (BOMD) simulations have shown that the direct impact of H atoms on a partially CO-covered Ni(110) surface do not hydrogenate CO via an Eley-Rideal or hot-atom mechanism and in this work the BOMD simulations show that the direct impact of H atoms on a clean Ni(110) surface do form the subsurface and bulk hydrogen, which supports the role of subsurface D in this reaction. This information will be useful for a more comprehensive understanding of the reactivity of energetic hydrogen and its role in hydrogenation for plasma-enhanced catalysis over Ni-based catalysts.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films