Promotion effect of rare earth elements (Ce, Nd, Pr) on physicochemical properties of M-Al mixed oxides (M = Cu, Ni, Co) and their catalytic activity in N2O decomposition

Abstract A series of M-AlO_xmixed oxides (M = Cu, Co, Ni) with the addition of high loadings of rare earth elements (REE, R = Ce, Nd, Pr; R_0.5M_0.8Al_0.2, molar ratio) were investigated in N₂O decomposition. The precursors were prepared by coprecipitation and subsequent calcination at 600 °C. The obtained mixed metal oxides were characterized by X-ray diffraction with Rietveld analysis, N₂sorption, and H₂temperature-programmed reduction. Depending on the nature of REE and the initial M-Al system, R cations could be separately segregated in oxide form or coordinated with the transition metal cations and form mixed structures. The addition of Ce³⁺consistently led to nanocrystalline CeO₂mixed with the divalent oxides, whereas the addition of Nd³⁺or Pr³⁺resulted in the formation of their respective oxide phases as well as perovskites/Ruddlesden–Popper phases. The presence of REE modified the textural and redox properties of the calcined materials. The rare earth element-induced formation of low-temperature reducible MO_xspecies that systematically improved the N₂O decomposition on the modified catalysts compared to the pristine M-Al materials by the order of Co > Ni > Cu. The Ce_0.5Co_0.8Al_0.2catalyst revealed the highest activity and remained stable (approximately 90% of N₂O conversion) for 50 h during time-on-stream in 1000 ppm N₂O, 200 ppm NO, 20 000 ppm O₂, 2500 ppm H₂O/N₂balance at WHSV = 16 L g⁻¹ h⁻¹.