Effect of Subsurface Oxygen on Selective Catalytic Reduction of NO by H₂ on Pt(100): A First-Principles Study

The mechanisms of NO reduction by H₂ on the Pt(100) surface and the surface modified with subsurface oxygen atoms (Md-Pt(100)) are studied by first-principles calculations. Similar catalytic activity toward NO dissociation is found on both surfaces with barriers of 0.86 and 0.96 eV, respectively. The pathway of N + N → N₂ rather than NO + N → N₂ + O is the N₂ formation pathway on the Pt(100) surface, while these two pathways are competitive on the Md-Pt(100) surface. The NH₃ formation is almost negligible, and reductant hydrogen can effectively remove the surface oxygen on both surfaces. The microkinetic analysis further confirms that, compared to the high selectivity toward N₂O (almost 100% at 300–500 K) on the clean surface, higher N₂ low-temperature selectivity (larger than 90%) is achieved on the Md-Pt(100) surface under lower pressure. The present study shows that subsurface oxygen has an enhanced effect for improving the N₂ selectivity of NO reduction on Pt catalysts

Honeycomb Boron Allotropes with Dirac Cones: A True Analogue to Graphene

We propose a series of planar boron allotropes with honeycomb topology and demonstrate that their band structures exhibit Dirac cones at the K point, the same as graphene. In particular, the Dirac point of one honeycomb boron sheet locates precisely on the Fermi level, rendering it as a topologically equivalent material to graphene. Its Fermi velocity (<i>v</i>_f) is 6.05 × 10⁵ m/s, close to that of graphene. Although the freestanding honeycomb B allotropes are higher in energy than α-sheet, our calculations show that a metal substrate can greatly stabilize these new allotropes. They are actually more stable than α-sheet sheet on the Ag(111) surface. Furthermore, we find that the honeycomb borons form low-energy nanoribbons that may open gaps or exhibit strong ferromagnetism at the two edges in contrast to the antiferromagnetic coupling of the graphene nanoribbon edges