Origin of water-induced deactivation of MnO2-based catalyst for room-temperature NO oxidation: a first-principles microkinetic study

MnO₂-based catalysts exhibit remarkable activities in a room-temperature NO oxidation reaction (RT-NOR) but are challenged by water-induced deactivation. To improve the water-resistance driven by molecular-level mechanistic understanding, we herein report a systematic first-principles study and microkinetic simulation on elucidating the water-modulated RT-NOR mechanism on the notable β-MnO₂ catalyst. Results show that RT-NOR preferentially follows the Mars-van Krevelen mechanism on β-MnO₂(110) and that the coupling of lattice O (O_lat) with NO sitting on the surface Mn_cus site is the rate-limiting step. The presence of H₂O results in a competitive effect against NO adsorbing on Mn_cus and inhibits NO₂ formation. More crucially, the H₂O-dissociated H species eventually accumulate on O_lat and are difficult to remove, which seriously poison the catalyst, although the Mn_cus-anchored OH intermediate can oxidize NO to NO₂ via the nitrite/nitrate route. Weakening the H adsorption on O_lat, as well as the H₂O adsorption on Mn_cus, is thus proposed as conductive to alleviating MnO₂ deactivation. More essentially, we find that the vacancy formation energy of O_lat, E_f(O_vac), can serve as a unified descriptor for balancing H₂O-resistance and catalytic activity; the excessively low E_f(O_vac) is the intrinsic origin of MnO₂ susceptible to deactivation by H₂O. By doping engineering guided by such a descriptor, we identify that the Cr-, Nb-, Ru-, or Rh-substituted doping can properly increase the E_f(O_vac) of MnO₂ and weaken the H₂O-induced deactivation in RT-NOR. These results may provide a theoretical basis on optimizing MnO₂-based catalysts with improved H₂O-resistance.