The kinetic analysis of non-isothermal nickel oxide reduction in hydrogen atmosphere using the invariant kinetic parameters method

The powder sample of nickel oxide was synthesized by sol–gel procedure. The non-isothermal reduction of nickel oxide using hydrogen, was investigated by temperature-programmed reduction (TPR) at four different heating rates (2.5, 5, 10 and 20 °C min−1). The kinetics parameters (Ea, lnA) were determined using Friedman (FR) isoconversional method and the invariant kinetic parameters method (IKP). The IKP method was applied in the conversion range of 0.20 ≤ α ≤ 0.60. The activation energy value obtained by the IKP method (Ea = 96.4 kJ mol−1) is somewhat higher than the value obtained by Friedman's method (Ea = 90.8 kJ mol−1). The values of invariant kinetic parameters were used for numerical evaluation of conversion function, f(α). The kinetic model of the investigated reduction process was determined, and this model corresponds to the empirical two-parameter Šesták–Berggren equation, which gives a more quantitative description. The kinetic triplet obtained for the investigated process is: Ea = 96.4 kJ mol−1; A = 1.04 × 108 min−1 and f(α) = α0.63(1 − α)1.39. In agreement with the obtained results, the mechanism of nickel oxide reduction by hydrogen was considered.