Effects of lanthanum addition on Ni-B/γ-Al2O3 amorphous alloy catalysts used in anthraquinone hydrogenation

A series of amorphous Ni-B/gamma-Al2O3 catalysts with different La loadings were prepared by KBH4 reduction, characterized by inductively coupled plasma (ICP), DSC H-2-TPD, X-ray photoelectron spectroscopy (XPS) and H-2-chemisorption, and studied in the hydrogenation of anthraquinone (AQ). In comparison with the catalyst without La loadings, the presence of proper amounts of lanthanum in the supported amorphous alloy catalyst leads to more active centers, higher extents of H-2-chemisorption, the shift of H-2 desorption peaks to lower temperatures, the enhancement of thermal stability as well as higher reaction rates and higher TOF values. The effects of lanthanum were attributed to both its structure effect, dispersing Ni, leading to more active centers and enhancing the thermal stability, and its electronic effect, resulting in electron-rich Ni. weakening the adsorption of anthraquinone and the bond strength of Ni-H and therefore activating the adsorbed hydrogen. However. hi-her La loadings were harmful to the activity because too many surface Ni active centers might be covered by La3+ species. (C) 2003 Elsevier B.V. All rights reserved.