Comparison of Cu-Mg-Al-Ox and Cu/Al2O3 in selective catalytic oxidation of ammonia (NH3-SCO)

Abstract

Copper-based materials are promising catalysts in the selective catalytic oxidation of ammonia into nitrogen and water vapour (NH3-SCO). Investigations under applied reaction conditions over such materials seem to be rare and a comprehensive understanding of the involved active copper oxide species could facilitate a knowledge-based catalyst optimization. In the present work, Cu-Mg-Al-Ox mixed metal oxides and Cu/Al2O3 active catalysts in NH3-SCO were investigated under NH3/O2/CO2/H2O/N2 reaction conditions. Powder XRD, BET, NH3-TPD, H2-TPR and XAFS methods were used to characterize Cu-Mg-Al-Ox (Cu/Mg/Al = 8/63/29, mol%) and 10 wt% Cu/Al2O3. Cu-Mg-Al-Ox hydrotalcite derived mixed metal oxides were obtained by coprecipitation, while Cu/Al2O3 was prepared by incipient wetness impregnation. A highly dispersed copper oxide species formed on Cu-Mg-Al-Ox, while a mixture of highly dispersed (CuOx) and bulk copper oxide species (CuO and CuAl2O4) formed on Cu/Al2O3. The comparison of Cu-Mg-Al-Ox and Cu/Al2O3 in NH3-SCO provided good insight into the nature of the active species present in both copper-based catalysts. It was found that highly dispersed easily reducible copper oxide species and bulk copper oxide species appear as active species under NH3/O2/N2 and NH3/O2/CO2/H2O/N2 reaction conditions, respectively.