Redox-performance correlations in Ag-Cu-Mg-Al, Ce-Cu-Mg-Al, and Ga-Cu-Mg-Al hydrotalcite derived mixed metal oxides

- Ag(Ga)yCu5Mg66−yAl29 with y = 0.25 gave best performances for NH3-SCO.
- Redox properties determined performances of catalysts with y = 0.25.
- Bulk and surface segregated phases varied activity of catalysts with y ≥ 0.25.
- Gallium modified Cu-Mg-Al-Ox selectively oxidized ammonia into N2.

Ag-, Ce- and Ga-promoted Cu-Mg-Al hydrotalcite derived mixed metal oxides were obtained by standard coprecipitation, followed by calcination. The obtained Ag(Ce, Ga)-Cu-Mg-Al-Ox mixed metal oxides were characterized with respect to their crystalline structure (XRD, TEM), texture (BET), surface acidity (NH3-TPD), redox properties (H2-TPR), chemical surface composition (XPS), and tested in the selective catalytic oxidation of ammonia into nitrogen and water vapour (NH3-SCO). The loading of Agy-, Cey-, or Gay-Cu5-Mg66−y-Al29 (y = 0-1) had a clear effect on the catalytic performances. For materials with low metal loadings (y ≤ 0.25), the redox properties determined the catalytic performances in NH3-SCO. The formation of easily reducible CuOx played a crucial role for enhanced catalytic activity at lower temperatures, with a drop in the selectivity to N2 at higher temperatures. Higher metal loading (y ≥ 0.5) led to the formation of surface and bulk copper oxide species, and other aggregated metal oxide phases, which enhanced the catalytic activity for Ag-Cu-Mg-Al-Ox, and diminished activity for Ce(Ga)-Cu-Mg-Al-Ox.

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