Pd segregation to the surface of bimetallic Pt-Pd particles supported on H-beta zeolite evidenced with X-ray photoelectron spectroscopy and argon cation bombardment

Bimetallic PtPd/H-beta 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 degrees C. The dispers ed metal phases were characterized using XPS, The formation of bimetallic P t-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 b ombardment with argon cations and by comparison with a physical mixture of monometallic Pd/H-beta and Pt/H-beta catalysts, subjected to the same treat ment. (C) 2000 Academic Press.