308nm photochemical reaction of gaseous HNO3 and benzene on α-Fe2O3 surfaces

Direct Formation of Electronic Excited NO2 Contributes to the High Yield of HONO during Photosensitized Renoxification

Photosensitized renoxification of HNO₃ is found to produce HONO in an unexpectedly high yield, which has been considered an important source for atmospheric HONO. Conventionally, the production of HONO is ascribed to the secondary photolysis of the primarily formed NO₂. In this study, by using humic acid (HA) as a model environmental photosensitizer, we provide evidence of the direct formation of NO₂ in its electronic excited state (NO₂*) as a key intermediate during the photosensitizing renoxification of HNO₃. Moreover, the high HONO yield originates from the heterogeneous reaction of the primarily formed NO₂* with the co-adsorbed water molecules on HA. Such a mechanism is supported by the increase of the product selectivity of HONO with relative humidity. Further luminescence measurements demonstrate clearly the occurrence of an electronic excited state (NO₂*) from photolysis of adsorbed HNO₃ on HA. This work deepens our understanding of the formation of atmospheric HONO and gives insight into the transformation of RNS.

Performance of selective catalytic reduction of NO with NH3 over natural manganese ore catalysts at low temperature

Natural manganese ore catalysts for selective catalytic reduction (SCR) of NO with NH₃ at low temperature in the presence and absence of SO₂ and H₂O were systematically investigated. The physical and chemical properties of catalysts were characterized by X-ray diffraction, Brunauer-Emmett-Teller (BET) specific surface area, NH₃ temperature-programmed desorption (NH₃-TPD) and NO-TPD methods. The results showed that natural manganese ore from Qingyang of Anhui Province had a good low-temperature activity and N₂ selectivity, and it could be a novel catalyst in terms of stability, good efficiency, good reusability and lower cost. The NO conversion exceeded 85% between 150°C and 300°C when the initial NO concentration was 1000 ppm. The activity was suppressed by adding H₂O (10%) or SO₂ (100 or 200 ppm), respectively, and its activity could recover while the SO₂ supply is cut off. The simultaneous addition of H₂O and SO₂ led to the increase of about 100% in SCR activity than bare addition of SO₂. The formation of the amorphous MnO_x, high concentration of lattice oxygen and surface-adsorbed oxygen groups and a lot of reducible species as well as adsorption of the reactants brought about excellent SCR performance and exhibited good SO₂ and H₂O resistance.