Identification of the site locations of two Pd(I) species in PdH-SAPO-5 and PdH-SAPO-11 molecular sieves from phosphorus-31 nuclear modulation

Activation of PdH-SAPO-5 and PdH-SAPO-11 molecular sieves, in which the palladium ion is incorporated by ion exchange, generates two different paramagnetic Pd(I) species distinguished by g_∥ = 2.9 for species A and 2.6 for species B with a common value of g_⊥ = 2.1. Based largely on absorbate interactions, these two species have been tentatively assigned to a hexagonal prism site location for species A and a site near a 6-ring window for species B. In this work phosphorus-31 nuclear modulation has been observed by electron spin echo methods for these two Pd(I) species. Simulation of the nuclear modulation in terms of the geometry of nearby phosphorus nuclei unambiguously identifies Pd(I) species A as located in site I in a hexagonal prism site and Pd(I) species B as located at site II* near a 6-ring window bordering the large channels of the molecular sieve structures.