Novel SCR catalyst derived from Mn@Yeast materials: Insight to covalent Mn C N roles and NH3 activation on coordination sites

The yeast was innovatively used to participate in the catalyst synthesis. Herein, the β-Mn-Y-1 (Mn@Yeast-1) catalyst for NH3-SCR DeNOx was produced by introducing yeast into the solution of Mn ions using one-step method during the process of synthesizing β-MnO2. β-Mn-Y-1 catalyst achieved the NOx conversion more than 90 % at 175 ∼ 225 °C, and still kept at > 80 % at 250 °C, in contrast, β-Mn-Y-2 (Mn@Yeast-2 by two-step method) has no catalytic activity similar to β-MnO2 that all the NOx conversion were below 10 % at 50 ∼ 250 °C. The abundant organic functional groups on yeast surface mostly were complexed with amorphous Mn ions to generate various Mn-organic groups (Mn3+CN, MnCO, Mn-COOH, etc) on β-Mn-Y-1 catalyst, and some could work as acid and coordination sites to adsorb and activate NH3 to participate in low-temperature SCR process, but rather than the traditional Mnm+-O in β-MnO2 crystal structure in both β-MnO2 and β-Mn-Y-2, which indicated that the pre-obtained MnO2 crystalline phase was difficult to cooperate with yeast. More importantly, the covalent Mn3+CN due to the effect of σ-π bond can activate L-NH3 adsorbed on MnCO to react with NO(g) by Eley-Rideal mechanism belonging to the coordination catalysis, while B-NH4+ species from Mn-COOH cannot react with NO at low temperatures.