A series of silica supported nickel catalysts promoted by lanthanumozide were prepared by using the incipient wetness co-impregnation and sequential impregnation methods.The effect of La2O3 introducing method on the activity and selectivity of Ni/SiO2 catalyst for m-dinitrobenzene hydrogenation to m-phenylenediamine was studied

and the physical and chemical properties of the catalysts were investigated by the techniques of X-ray diffraction (XRD)

temperature-programmed reduction (TPR)

and X-ray photoelectron spectroscopy (XPS).The results showed that the addition sequence of La promoter played a substantial role in determining the catalytic hydrogenation properties of the nickel-based catalysts.When stepwise incipient impregnation method was used and La component was firstly impregnated on support before nickel component

the interaction between nickel and support was obviously weakened

the particle size of nickel crystallites was significantly reduced

and the nickel species were well dispersed

thus the activity of catalyst was apparently improved.In hydrogenation of m-dinitrobenzene under the conditions of hydrogen pressure 2.6 MPa

temperature 373 K and reaction time for 1 h

the conversion of m-dinitrobenzene and the yield of m-phenylenediamine on the above catalyst were up to 97.1% and 93.5%

respectively.The sample prepared by the La-Ni co-impregnation method also positively affected the catalytic performance of catalyst

but not as good as the former.When La component was impregnated after nickel component

however

the particle size of nickel crystallites increased apparently

thus resulting in dramatic decrease of catalyst activity.