In the presence of supported Pd nanoparticle catalysts, e.g., Pd/Al₂O₃, various diphenylamines could be synthesized through acceptorless formal arylation using NH₃ or its surrogates, e.g., urea, as nitrogen sources and cyclohexanones as arylation sources. The observed catalysis was truly heterogeneous, and the catalyst was reusable with retention of its high catalytic performance.