A study of Ni–Al–O mixed oxides as catalysts for the oxidative conversion of ethane to ethylene

• Investigation of Ni–Al–O mixed oxides as effective catalysts in ethane ODH.
• The use of organic Al precursor led to a catalyst with 85% ethylene selectivity.
• Reduction of oxygen excess leads to less active but more selective catalysts.
• Reduction of catalyst oxygen lability leads to enhanced ethylene selectivity.

A series of Ni–Al–O mixed oxides with different aluminum content ranging from 1% to 50% (metal atomic content) were synthesized via a facile co-evaporation route and tested in ethane oxidative dehydrogenation. In samples with Al loading up to 30%, the crystal structure of NiO is retained and the interaction between nickel oxide and alumina leads to smaller crystal sizes, higher surface areas and decreased reducibility, along with a gradual decrease in the amount of desorbed oxygen observed by O2-TPD measurements. At higher aluminum loadings the formation of an amorphous spinel-like precursor phase is evidenced. Correlation between the catalytic performance of Ni–Al–O mixed oxide and their oxygen desorption properties showed that as the excess oxygen per catalyst surface area decreases, the catalysts become less active in the activation of ethane, but more selective toward ethylene. The catalyst containing 30% aluminum represents the optimum composition among Ni–Al–O mixed oxides studied in this work. Further optimization of the catalyst preparation method with the use of an organic aluminum precursor led to the development of a catalyst presenting up to 85% selectivity toward ethylene. The enhanced performance of this material was correlated with the further reduction of catalyst over-stoichiometry and oxygen lability induced by the organic precursor, according to O2-TPD and isotopic oxygen exchange experiments respectively.

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