Preparation and Formation Mechanism of New PdH_x-Pd/C Catalyst through Hy drazine-reducing Method under Atmospheric Pressure and H_2-free Conditions

PdHx is an important reactive species for the Pd/C catalyst.Without H2,it can not exist stably at room temperature.This species is usually prepared through reaction of Pd with H2 under certain pressure.PdHx-Pd/C catalyst was prepared through hydrazine-reducing method under atmospheric pressure and H2-free conditions.The microstructure,morphology and chemical state of PdHx and Pd particles were investigated by XRD,TEM and XPS characterization methods.The formation mechanism of PdHx particles in the hydrazine-reducing method was proposed.Experimental results show that the average particle size of PdHx is 3.9 nm,and the d spacing of PdHx(111) is slightly larger than that of Pd(111).The PdHx particles derive from the reduction process of PdO by hydrazine.Their particle size is closely related to the particle size and structural imperfection of PdO.The PdHx-Pd/C catalyst demonstrates better catalytic performance than the conventional Pd/C catalyst in the amination reaction to produce 2,6-dimethylaniline under H2-free condition.