Oxidative dehydrogenation of propane by non-stoichiometric nickel molybdates

A series of catalysts represented by the formula Ni_1+δM_1-oδ/3O₄, where-1/5 ≤ δ ≤ 1/3, were investigated for activity towards oxidative dehydrogenation of propane. The catalysts were synthesized from layered ammonium nickel molybdate materials having a general formula (NH₄)H_2xNi_3-xp(OH)(MoO₄) ₂, where 0 ≤ x ≤ 3/2. The location of the nickel atoms on a crystallographic site of variable occupancy allowed for the careful manipulation of chemical composition of these precursors. The nickel/molybdenum ratio of the precursor was inherited by the catalyst, enabling the synthesis of non-stoichiometric molybdates. These catalysts were tested for the catalytic oxidative dehydrogenation of propane to elucidate the effect of the extent of non-stoichiometry (δ) on catalytic performance. The activities of the catalysts are highly sensitive to the catalyst composition and increase with decreasing Ni content. Selectivity towards propene is independent of the Ni content when the Ni/Mo ratio is less than unity, but decreases linearly with increasing amounts of Ni when Ni/Mo > 1.