OXIDATIVE LEACHING OF CU ATOMS FROM PDCU PARTICLES IN ZEOLITE-Y

NaY-supported PdCu samples of various Cu/Pd ratios were prepared by ion exchange with Pd(NH3)42+ and Cu(NH3)42+ precursors. Reduction of Cu is enhanced by Pd; however, after calcination at 500°C the bare ions have migrated into sodalite cages, and reduction is only enhanced for those Cu2+ ions which happen to share their cage with a Pd2+ ion. Reduction with HZ results in bimetallic PdCu particles and protons of high Brønsted acidity. At 280°C, and in an inert atmosphere, these protons selectively reoxidize surface Cu atoms to Cu+ ions, which are still attached to the surface of the bimetal particles; they can be reduced at 210°C. Complete oxidation of the Cu component takes place at 500°C; the Cu2+ ions leached from PdCu particles migrate to small zeolite cages, as indicated by EXAFS and a peak at 290°C in the profile of subsequent TPR. After complete leaching of Cu, the monometallic Pd particles are discerned from the original particles in PdCu/NaY and PdCu2/NaY by their propensity to form hydrides that are detectable by TPD. No hydride is formed with bimetal particles with Cu/Pd > 0.5; particles in Pd2Cu/NaY do form a hydride which is, however, distinguished from Pd hydride by its TPD peak position. © 1991.