Influence of calcination and pretreatment temperature on the activity of Ni-B/SiO2 amorphous catalyst in acrylonitrile hydrogenation

The Ni-B/SiO2 amorphous catalyst was prepared by impregnation of silica sup port with NiCl2 aqueous solution following the chemical reduction with KBH4 . The influence of calcination and pretreatment temperature on its activity was investigated by using acrylonitrile hydrogenation as a probe. On the o ne hand, it was found that the activity of the Ni-B/SiO2 amorphous catalyst first increased and then decreased when the precursor (Ni2+/SiO2) was calc ined at the temperature from 273 to 773 K in Ar flow. The optimum calcinati on temperature was then determined as 473 K. On the other hand, when the as -prepared Ni-B/SiO2 amorphous catalyst was pretreated at the temperature fr om 273 to 873 K in Ar flow, the activity of the catalyst first remained alm ost unchanged up to 573 K and then decreased abruptly with the further incr ease of temperature. According to various characterizations, such as induct ively coupled plasma (ICP), differential scanning calorimetry (DSC), X-ray photoelectron spectra (XPS), X-ray diffraction (XRD) and extended X-ray abs orption fine structure (EXAFS), it was concluded that the effect of the cal cination temperature on the activity should mainly be attributed to the sur face density of metallic nickel; while the effect of the pretreatment tempe rature on the activity was caused by the transformation from amorphous stru cture to crystalline structure. (C) 2001 Elsevier Science B.V. All rights r eserved.