Pd Segregation to the Surface of Bimetallic Pt–Pd Particles Supported on H-β Zeolite Evidenced with X-Ray Photoelectron Spectroscopy and Argon Cation Bombardment

Bimetallic PtPd/H-β hydrocracking catalyst samples with 1.75 and 3.5 wt% metals, Pt:Pd atomic ratio of 3:1, and metal particle size of 1.7 nm were prepared using impregnation and cation exchange of Pt2+ and Pd2+ tetrammine complexes, oxidation, and hydrogen reduction at 400°C. The dispersed metal phases were characterized using XPS. The formation of bimetallic Pt–Pd particles with segregation of the palladium to the particles surfaces was evidenced by intensity changes of the Pd 3d and Pt 4d photolines upon bombardment with argon cations and by comparison with a physical mixture of monometallic Pd/H-β and Pt/H-β catalysts, subjected to the same treatment.