Manufacturing AAl₂O₄ (A=Cu, Co, Ni, Zn) Spinel Catalysts for Toluene Combustion: Elucidating the A‐site Replacement Effect on the Reactivity

Abstract

To decode the A‐site substitution effect on the reactivity of Al‐based spinel complex oxides, a series of AAl2O4 (A = Cu, Co, Ni, Zn) compounds were manufactured and tested by toluene combustion. It was confirmed that a pure spinel crystalline phase has been successfully synthesized for all the catalysts. The toluene and CO oxidation activity are sequenced as CuAl2O4 > CoAl2O4 > NiAl2O4 > ZnAl2O4. As discovered, both active surface O2‐ and acid sites are the two critical factors to determine the reactivity, which can adsorb and activate the reactants effectively to form active intermediates, possibly following a Mars‐van‐Krevelen pathway. The activity improves positively with the amount increasing of these two kinds of active sites, thus showing an evident A‐site replacement effect. CuAl2O4 owns the biggest numbers of these two kinds of active sites, thereby exhibiting the optimal catalytic activity. Moreover, it also shows good stability in a dry feed, and considerable ability to resist water vapor and sulfur poisoning. In‐situ DRIFTS results have indicated that benzyl, benzoate, benzaldehyde and benzoquinone might be the major reaction intermediates.