The Pd-B/SiO2 amorphous catalyst was prepared by regular impregnation following the chemical reduction with KBH4 solution. Its amorphous structure was confirmed by X-ray diffraction XRD patterns. The as-prepared Pd-B/SiO2 amorphous catalyst exhibited higher activity than the corresponding Pd/SiO2 and crystallized Pd-B/SiO2 catalysts during the liquid phase nitrobenzene hydrogenation to aniline, indicating the promoting effect of the alloying B. The fact that the activity per g Pd of the Pd-B/SiO2 amorphous catalyst was higher than that of the unsupported Pd-B amorphous catalyst also demonstrated the promoting effect of the silica support. Based on various characterizations, such as inductively coupled plasma (ICP), (XRD), diffraction scanning calorimetry (DSC), X-ray photoelectron spectroscopy (XPS), Raman spectra, and hydrogen chemisorption, we concluded that the promoting effect of alloying B was mainly attributed to the formation of the amorphous structure and the modification of the surface electronic state of the Pd active sites, while the promoting effect of silica support was ascribed to its high dispersion of the Pd active sites and its stabilization of the amorphous structure.