Abstract
Sustainable catalysts are essential for critical industrial and environmental processes. 2D materials
have exceptional surface area and unique thermal and electronic properties, making them excellent
candidates for catalytic applications. Moreover, 2D materials can be functionalised to create metalfree
active sites, which provide sustainable alternatives to transition and precious metals. Among the
pollutants emitted by combustion engines, NOₓ stands out as one of the most detrimental gases,
contributing to environmental pollution and posing risks to human health. We demonstrate that
functionalised defects in hexagonal boron nitride (hBN) provide a thermodynamically viable route
to removing NOₓ by reaction with a hydrogenated boron vacancy (3HVB). The decomposition of
NO₂ proceeds by initially overcoming an activation energy barrier of 1.12 eV to transfer a hydrogen
atom from the surface, forming a NO₂H species, followed by the elimination of a water molecule. A
thermodynamically favourable product consisting of a surface-bound hydroxyl adjacent to a nitrogen
antisite defect (where a nitrogen atom occupies a site typically occupied by a boron atom) forms after
overcoming an energy barrier of 1.28 eV. NO can further decompose by overcoming an activation
energy barrier of 2.23 eV to form a surface HNO species. A rearrangement of the HNO species
takes place with an activation energy of 1.96 eV, followed by the elimination of water. The overall
reactions reduce NOₓ into defective hBN and H₂O.