Catalytic combustion of methane on La2–xSrxNiO4–λ(x= 0.00–1.50) perovskites prepared via the nitrate and citrate routes

Abstract

The catalytic combustion of CH₄ with stoichiometric amounts of oxygen to CO₂ and H₂O has been studied over two series of perovskite solids La_2–xSr_xNiO_4–λ(x= 0.00, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50) prepared via the nitrate and citrate methods. The reaction rate consists of two rate components, one suprafacial employing oxygen from the gas phase and active at low temperatures and another intrafacial, employing oxygen from the perovskite lattice and apparent mainly at high temperatures. The reaction is first order relative to CH₄ for the two series and over the whole range of reaction temperature. The reaction order for oxygen decreases from 0.5 to 0.2 as the temperature increases. The Arrhenius-type temperature dependence of the reaction rate for the suprafacial and the intrafacial process have been determined for the La_1.25Sr_0.75NiO₄ samples to be 47.4 and 110.8 kJ mol^–1 for the nitrate solid and 61.5 and 52.5 kJ mol^–1 for the citrate solid, showing that the oxygen is much more strongly bound on the catalyst of nitrate origin. The catalytic activity of both series is uniquely related to %Ni³⁺ in the perovskite.