Influence of the Ni/Al ratio on Ni–Al mixed oxides and their catalytic properties for ethanol decomposition

Abstract

The relationship between the properties with the composition of nickel–aluminium mixed oxides was investigated in this work. Ni–Al materials with Ni/Al molar ratios between 0.5 and 9 were synthesised via co-precipitation. The samples were characterised using the following techniques: surface area measurements (S BET), thermogravimetry, X-ray diffraction and temperature-programmed reduction, desorption and oxidation (H2-TPR, NH3-TPD and TPO/DTA). Samples with Ni/Al ratio = 0.5 primarily formed the Al2O3 phase, whereas Ni/Al ratio = 9 mainly led to the bulk NiO phase. However, Ni/Al ratios between 1 and 3 favoured the formation of the mixed oxide phase with increased thermal stability and specific surface area and decreased crystallite sizes. The lower Ni/Al ratios led to the production of ethylene, which is likely related to the higher number of sites with stronger acidity. The samples with Ni/Al ratios of 2 and 3 promoted selectivity towards synthesis gas. For higher Ni/Al ratios, low thermal stability leading to sintering and deactivation due to coke formation was observed.