Influence of the silica support on the activity of Ni and Ni2P based catalysts in the hydrodechlorination of chlorobenzene. Study of factors governing catalyst deactivation

Abstract

Ni and Ni2P based catalysts supported on two different silica supports (Cab-O-Sil commercial silica and SBA-15 mesoporous silica) have been studied in the hydrodechlorination (HDC) of chlorobenzene (CB). Ni catalysts have been prepared from nickel(II) citrate in order to favour the formation of highly dispersed Ni particles. Ni2P based systems have been prepared from a phosphite-type precursor, Ni(HPO3H)2, where a great P excess is present in the catalyst surface. Thus, the role of the active phase, the preparation method and the silica support employed on the activity of the prepared catalysts are detailed. Characterization results reveal that the usage of nickel citrate provides catalysts with a small particle size, regardless of the material support used, although they suffer from deactivation in the HDC reaction due to the agglomeration of the active phase. Ni2P based catalysts prepared from nickel(II) dihydrogenphosphite, also form small particles that are more stable than Ni ones due to the weaker interaction with Cl species and the greater presence of hydrogen spillover species on the support and hydrogen species on the metal–support interface. These hydrogen species in the metal–support interface are ascribed to the P excess present in the catalyst surface. Moreover Cab-O-Sil based catalysts are more active than SBA-ones due to the higher stability of the active phase in the former.