A theoretical study of formaldehyde adsorption and decomposition on a WC (0001) surface

Abstract

A lot of research attention has been paid to designing and exploring efficient adsorbents for HCHO adsorption and decomposition. Herein, we have demonstrated a highly active material, WC, for HCHO adsorption through first-principles calculations. Due to the exposed three-coordinated W atoms (W_3c) of the WC (0001) surface, HCHO molecules can be settled on the WC (0001) surface through newly formed O_F–W_3c and/or C_F–W_3c bonds, forming different adsorption configurations. When settled on the WC (0001) surface, the molecular configuration of the HCHO molecule and the corresponding C_F–H_F and C_F–O_F bond lengths would be greatly changed. Due to the enlarged C_F–H_F and C_F–O_F bond lengths, the adsorbed HCHO molecules tend to dissociate through two possible pathways; these are the two-step C_F–H_F bond scission or the one-step C_F–O_F bond scission. The former results in two H adatoms and a CO molecule chemisorbed to the surface and the latter produces an O adatom and a CH₂ group on the surface. Further Cl-NEB calculations demonstrate that the pre-adsorbed O atom has little influence on the first C_F–H_F bond scission and the C_F–O_F bond scission, while promoting the second C_F–H_F bond scission. Considering the dissociative products, H and CH₂ have the potential to couple into a CH₃ group (or even a CH₄ molecule) and two CH₂ groups may couple into a C₂H₄ molecule. In the end, we propose that OH ions may couple with the dissociative products of HCHO, so an alkali solution could be used to post-process the WC (0001) surface to restore its surface active sites. These results demonstrated the potential of WC in HCHO sensing and abatement.