Influence Of Steam Treatment On Structure And Performance Of Ni₂P/SiO₂Catalyst For Hydrodechlorination Of Chlorobenzene

Ni₂P/SiO₂catalyst was prepared by the temperature-programmed reduction （TPR）method, and it was then treated with steam at different conditions. The effect of steamtreatment on the structure and performance of Ni₂P/SiO₂catalyst for thehydrodechlorination of chlorobenzene was investigated by means of N2adsorption-desorption, ICP-AES, XRD, TEM, H2-TPR, H2-TPD, NH3-TPD, in situDRIFTS, CO chemisorption and the activity evaluation.The steam treatment did not influence the BET specific surface area, porestructure, the Ni₂P crystallite size, the Ni content and the Ni/P ratio for the Ni₂P/SiO₂catalyst. However, the surface properties of the Ni₂P/SiO₂catalyst greatly changedafter the treatment. The treatment at30℃did not influence the density of exposed Nisites on Ni₂P/SiO₂, while the treatment temperature above240℃decreased theexposed Ni sites. During the steam treatment, the new P-OH groups were formed onNi₂P/SiO₂, leading to the increase of surface acid sites.The steam treatment remarkably promoted the activity of Ni₂P/SiO₂. Comparingwith the influences of the treatment time and the steam concentration, the treatmenttemperature had more remarkable effect on the chlorobenzene conversion. As thetreatment temperature increased, the initial activity of catalyst decreased. Under theconditions of513K, the chlorobenzene space velocity of3.75mlCB·gcat^-1·h^-1and theH2/CB molar ratio of9.0, the chlorobenzene conversions on the catalysts treatedbelow270℃exceeded93.8%, which was about17times more than that on theuntreated catalyst.We suggest that the promoting effect of steam treatment on the activity ofNi₂P/SiO₂may be related to the decrease of nickel electron density and the synergismbetween the Ni sites and the P-OH groups.