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

摘要

In this paper, Ni/Al _(2) O _(3) 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/Al _(2) O _(3) 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/Al _(2) O _(3) catalysts show excellent stability during the reductive amination reaction. The characterization of XRD, DR UV-Vis spectroscopy, H _(2) -TPR, and acidity–basicity measurements indicates that addition of Re improves the Ni dispersion, proportion of octahedral Ni ~(2+) species, reducibility, and acid strength for Ni–Re/Al _(2) O _(3) 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 Ni ~(0) particle size and higher Ni ~(0) surface area are obtained in the reduced Ni–Re/Al _(2) O _(3) 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 Ni ~(0) particles. During reaction, the Ni ~(0) particles on the Al _(2) O _(3) support are stabilized and the sintering process is effectively suppressed by the incorporation of Re. It could be concluded that sufficient Ni ~(0) sites, the collaborative effect of Ni–Re, and brilliant stability contribute to the excellent catalytic performance of Ni–Re/Al _(2) O _(3) catalysts for the reductive amination of monoethanolamine.