Abstract
Abstract A series of M-AlO x mixed oxides (M = Cu, Co, Ni) with the addition of high loadings of rare earth elements (REE, R = Ce, Nd, Pr; R 0.5 M 0.8 Al 0.2 , molar ratio) were investigated in N 2 O 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, N 2 sorption, and H 2 temperature-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 Ce 3+ consistently led to nanocrystalline CeO 2 mixed with the divalent oxides, whereas the addition of Nd 3+ or Pr 3+ 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 x species that systematically improved the N 2 O decomposition on the modified catalysts compared to the pristine M-Al materials by the order of Co > Ni > Cu. The Ce 0.5 Co 0.8 Al 0.2 catalyst revealed the highest activity and remained stable (approximately 90% of N 2 O conversion) for 50 h during time-on-stream in 1000 ppm N 2 O, 200 ppm NO, 20 000 ppm O 2 , 2500 ppm H 2 O/N 2 balance at WHSV = 16 L g −1 h −1 .