Characterization and catalytic behavior of amorphous Ni-B/AC catalysts prepared in different impregnation sequences

Two supported amorphous Ni-B catalysts on active carbon (AC) were prepared by altering the impregnation sequence of the reductant, KBH4, and the nickel salt, NiCl2, The catalytic activities of the as-prepared catalysts were measured through liquid phase hydrogenation of 4,4'-dinitro-diphenylether under moderate pressure. It is found that conventional impregnation sequence (catalyst denoted as Ni-B/AC-2) led to considerable blockade of the pores of the support, while impregnating KBH4 first (catalyst denoted as Ni-B/AC-1) resulted in larger Ni-B grain size. The two factors coincidentally compensate each other, leading to identical active surface areas, However. the turn over frequency (TOF) value over Ni-B/AC-1 is triple that over Ni-B/AC-2, which is mainly attributed to the different reducing environment caused by different impregnation sequences leading to Ni-B alloys with different compositions and structures. (C) 2002 Elsevier Science B.V. All rights reserved.