Abstract: Diphenyl-sulfide (Ph2S) modified Pd/C catalysts (Pd-Ph₂S_x/C) were prepared and studied for "one-step" and "two-step" reductive alkylation of N-phenyl-p-phenylenediamine (PADPA) and methyl isobutyl ketone (MIBK) to obtain N-(1, 3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (DBPPD).The structure of the Pd-Ph₂S_x/C catalysts was characterized by X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).The results show that the Pd-Ph₂S_x/C catalysts have remarkable selectivity for DBPPD synthesis in both "one-step" and "two-step" methods.DBPPD selectivity can reach up to 96.3% in one-pot process by changing Ph2S content, temperature and pressure.However, PADPA is difficult to be completely transformed due to the formation of H₂O from PADPA and MIBK condensation in the "one-step" route at low temperature (413~433 K), where the "two-step" reaction process can overcome this problem.PADPA and MIBK were first dehydrated to form imines on activated carbon catalysts, and then the imines were reduced to prepare DBPPD with the Pd-Ph₂S_x/C catalysts.The results show that PADPA conversion of 100% can be obtained at 413 K and H₂ pressure of 3 MPa using the "two-step" method.Meanwhile, DBPPD selectivity over 97.4% can also be obtained.Additionally, the reusability of the Pd-Ph₂S_x/C catalyst was studied.It is found that the Pd-Ph₂S_x/C catalyst can be reused for 3 times without distinctly loss of activity, which shows a wide application potential in industry.