Effect of Re promoter on the structure and catalytic performance of Ni–Re/Al2O3 catalysts for the reductive amination of monoethanolamine

Abstract

In this paper, Ni/Al₂O₃ catalysts (15 wt% Ni) with different Re loadings were prepared to investigate the effect of Re on the structure and catalytic performance of Ni–Re/Al₂O₃ catalysts for the reductive amination of monoethanolamine. Reaction results reveal that the conversion and ethylenediamine selectivity increase significantly with increasing Re loading up to 2 wt%. Ni–Re/Al₂O₃ catalysts show excellent stability during the reductive amination reaction. The characterization of XRD, DR UV-Vis spectroscopy, H₂-TPR, and acidity–basicity measurements indicates that addition of Re improves the Ni dispersion, proportion of octahedral Ni²⁺ species, reducibility, and acid strength for Ni–Re/Al₂O₃ catalysts. The Ni15 and Ni15–Re2 catalysts were chosen for in-depth study. The results from SEM-BSE, TEM, and CO-TPD indicate that smaller Ni⁰ particle size and higher Ni⁰ surface area are obtained in the reduced Ni–Re/Al₂O₃ catalysts. Results from in situ XPS and STEM-EDX line scan suggest that Re species show a mixture of various valances and have a tendency to aggregate on the surface of Ni⁰ particles. During reaction, the Ni⁰ particles on the Al₂O₃ support are stabilized and the sintering process is effectively suppressed by the incorporation of Re. It could be concluded that sufficient Ni⁰ sites, the collaborative effect of Ni–Re, and brilliant stability contribute to the excellent catalytic performance of Ni–Re/Al₂O₃ catalysts for the reductive amination of monoethanolamine.