Dynamics of bimetallic Ni–Cu catalysts

Abstract

A series of unsupported nickel–copper catalysts with various Ni/Cu ratios has been prepared by coprecipitation and characterized by thermomagnetometry, (TM), temperature programmed reduction (TPR) and oxidation (TPO) and scanning electron microscopy (SEM). It was found that the magnetization of the nickel–copper catalyst depends significantly on both the Ni/Cu ratio and the reduction temperature. The magnetization is found to decrease linearly with a decrease in the Ni/Cu ratio or an increase in the reduction temperature. This is attributed to ferromagnetic decoupling between two neighbouring nickel atoms when a copper atom is introduced between them. Furthermore, magnetization of the nickel–copper catalysts decreases exponentially with the annealing time, which is a result of the structural reconstruction of nickel–copper samples during annealing. Rates of this reconstruction process are calculated to be 3.72 × 10^–4 s^–1(Ni/Cu = 0.96) and 1.17 × 10^–4 s^–1(Ni/Cu = 1.95) at 673 K; in addition, the activation energy is found to be ca. 49.0 kJ mol^–1 in samples with Ni/Cu = 0.96 and 1.95.