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

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 CH(2) 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 CH(2) have the potential to couple into a CH(3) group (or even a CH(4) molecule) and two CH(2) groups may couple into a C(2)H(4) 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.