COMPARISON OF PD(NH3)(4)(2+) DECOMPOSITION AND PD2+ REDUCTION IN ZEOLITES NAY, NAX AND CSX

The decomposition of Pd(NH3)(4)(2+) and further reduction to Pd-0 in Pd6.4NaY and three zeolites differing in alkalimetal cation or Pd loading (Pd(2.9)NaX, Pd(7.4)NaX and Pd(8.2)CsX) are investigated by TPO, TPR and UV-VIS-NIR spectroscopy. With regard to the temperature, the order for the decomposition of the ammine complex is PdCsX < PdNaX < PdNaY and that for the reduction of bare Pd2+ ions located in the same type of cage within the zeolites is PdCsX < PdNaX approximate to PdNaY. These orders depend an the stabilization of the various intermediate Pd complexes. It is shown that NaX favours the location of Pd2+ ions in the inner sites (i.e. sodalite and hexagonal prism). Parameters important for the various locations of Pd complexes are discussed in terms of the zeolite basicity and steric hindrance for migration of Pd(NH3)(x)(2+) complexes or Pd2+ ions in the inner cavities.