Theoretical study on borophene as metal-free catalyst for selective conversion of NO

The electrocatalytic reduction of NO (NORR) and selective catalytic reduction of NO by CO (CO-SCR) are the two most attractive approaches for selective conversion of NO. Herein, a bifunctional metal-free catalyst 2-Pmmn borophene is reported that is effective for both NORR and CO-SCR. NO can form NH₃ and N₂ through NORR and CO-SCR respectively. The results show that NO chemically adsorbed on the surface of borophene through the N–O terminal can be electrocatalytically reduced to NH₃. The optimal reaction path for NO to generate NH₃ is through the protonation process of *NHO instead of *NOH. The rate-determining step is the hydrogenation of *NH₂O to *NH₂OH, and the free energy increases by 0.41 eV. At the same time, NO can also react with CO on the surface of borophene to form N₂ and CO₂. First, NO can form chemically adsorbed ONNO intermediate through N–N coupling, then ONNO can be denitrified to form N₂ and residual oxygen, and finally residual oxygen and CO can generate CO₂ through the LH mechanism. The rate-determining step of the reaction is the N–N coupling process of NO, and activation energy barrier is 1.27 eV. The present work provides theoretical insights for the effective conversion of NO.