The kinetic study of temperature-programmed reduction of nickel oxide in hydrogen atmosphere

Abstract

The powder samples of nickel oxide were 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 ). Reaction kinetics parameters ( E a , ln A ) were determined using a few methods: Stationary point (SP), Kissinger, Friedman, Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose methods. The Málek's kinetic procedure was used for the determination of the most suitable kinetic model and calculation of a complete set of kinetic parameters. 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 E a = 90.8 kJ mol - 1 ; ln A = 19.50 ( A expressed in min - 1 ) and f ( α ) = α 0.63 ( 1 - α ) 1.39 . The reliability of kinetics parameters calculated from TPR data is tested by comparing calculated and experimental non-isothermal data. Comparing both experimental and calculated rate curves at constant heating rate assessed the adequate consistency of the kinetic triplet. In agreement with the obtained results, the mechanism of nickel oxide reduction by hydrogen was considered.