Hydrogenation of CO on Ni(110) by Energetic Deuterium

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.