NOx conversion involving multi-step reduction processes to produce N2 is recently receiving much attention due to environmental and social issues. According to the substantial use in industry and agriculture, nitrates has become a critical water pollutant and it demands harsh reaction conditions to be reduced. As a main detrimental components of exhaust gas, NO2, NO and N2O also should be converted effectively under the flue gas conditions. In nature, such conversion known as denitrification occurs via a multi-step process to reduce nitrate (NO3−) to N2 as a part of biological nitrogen cycle. Although the efficient enzymatic reactions attractively operate under mild conditions, four different metalloenzymes are needed to convert a series of intermediate NOx species. In other words, their applications to the NOx conversion catalyst are limited due to the complications of reaction path that comes from the inherent biological purpose. To achieve an efficient NOx conversion catalyst, simplification of the system is one of the essential factors. Herein, a stepwise reduction from nitrate to dinitrogen at a single nickel center will be discussed. The PNP nickel scaffold (PNP– = N[2-PiPr2-4-Me-C6H3]2) can nicely accommodate NOx species allowing further deoxygenation to be performed. A sequential conversion of a nickel nitrate species (PNP)Ni(ONO&lt;span style="font-size:10.8333px"&gt;2&lt;/span&gt;) to a nitrosyl species (PNP)Ni(NO) occurs via a stepwise oxygen atom transfer with CO. Additional treatment of 2 equiv. NO to nickel nitrosyl species cleanly produces (PNP)Ni(NO2) with nitrous oxide. Further reaction of (PNP)Ni(NO) with N2O generates N2 with (PNP)Ni(NO2) which is a relatively slow reaction. The entire conversion is the first example of showing a full denitrification with a single metal complex, and it has the potential to be a cornerstone of the future exhaust gas consecration catalyst.

Stepwise reduction of NO3– to N2 at a single nickel center

256th National Meeting (2018)

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