N2O decomposition on CoOx, CuOx, FeOx or MnOx supported on ZrO2: The effect of zirconia doping with sulfates or K+ on catalytic activity

Abstract Zirconia doped with sulfates or K + were prepared by impregnation with (NH 4 ) 2 SO 4 , or KNO 3 aqueous solutions. MeO x /ZrO 2 and MeO x /doped-ZrO 2 catalysts (Me = Co, Cu, Fe or Mn) were prepared by wet impregnation of zirconia and doped-zirconia supports. The effect of doping on MeO x properties was studied by XRD, UV–vis DRS, H 2 -TPR and FTIR and the influence of doping on the catalytic activity for N 2 O decomposition was investigated under ideal conditions (N 2 O in He) and under real reaction conditions (addition of NO, O 2 , and water vapour to the reactant mixture). Characterization results indicated that all samples contained mainly dispersed Me n+ species interacting with the support. In MeO x /sulfated-ZrO 2 the doping with electron-withdrawing sulfates stabilized the Me n+ oxidation state. In CoO x /K-ZrO 2 samples the doping with electron-releasing K + increased the poly-nuclear CoO x reducibility. FTIR characterization suggested that the electron-donor capacity of Co 2+ site had the order CoO x /sulfated-ZrO 2 x /ZrO 2 x /K-ZrO 2 . Catalytic results showed that dispersed Me n+ are the active site for N 2 O decomposition on MeO x /ZrO 2 . The “twin peak pattern” of catalytic activity versus tmi d-electron number suggests that formation and stability of the intermediate Me (n+1)+ O - surface complex, requiring the mobility of Me n+ oxidation state, are key factors for activity. Because the electron-withdrawing sulfates lowered the electron-donor capacity of tmi, hindering the formation of Me (n+1)+ O - , the effect of sulfate-doping was to decrease the de N 2 O activity in MeO x /sulfated-ZrO 2 . Conversely, because the electron-releasing potassium cation increased electron-donor capacity of Co 2+ , yielding an easier formation of the intermediate surface complex, the effect of K-doping was to increase the de N 2 O activity in CoO x /K-ZrO 2 . From an applied viewpoint, cobalt supported on ZrO 2 and K-doped ZrO 2 systems, that were affected by reversible inhibitory effect in real reaction conditions, are interesting catalysts for N 2 O abatement and for simultaneous abatement of N 2 O and NO with hydrocarbons.