Probing the chemical reactivity of the B₂O₃ -I (1 0 1) Surface: Interaction with H₂O and H₂S

Diboron trioxide is of interest because of its unique unreactive functionality properties. In this work we have studied – via computational first-principle techniques - the adsorption and dissociation mechanisms of two hydrogen chalcogenides, namely water (H₂O) and hydrogen sulfide (H₂S) molecules, over the B₂O₃ -I (1 0 1) surface. We show that the water molecules undergo dissociative adsorption over diboron via an activation energy of 39 kJ/mol. Furthermore, desorption of both molecularly adsorbed and dissociated structures of water molecules from the B₂O₃ -I (1 0 1) surface requires activation energies of 124–127 kJ/mol. Our investigation on the other hydrogen-chalcogenide compound, i.e. H₂S, reveals that diboron trioxide attracts H₂S molecules and forms molecular adsorption via sp³ hybridisation between the lone pair electron of the H₂S and the empty p orbital of the B_surf atom without encountering an activation barrier. However, the energy barrier required to dissociate H₂S over the B₂O₃ -I (1 0 1) surface appears exceedingly high at 310 kJ/mol. The present insight resolves the two different behaviours of B₂O₃ concerning hydrogen chalcogenides reported in the literature. While acting as a water scavenger to generate dissociated radicals, it exhibits an inhibitor characteristic towards the dissociation of H₂S molecules, representing an ideal reactor wall coating for desired pure gas phase reactions.