Electron Spin Resonance and Electron Spin Echo Modulation Studies on Reducibility, Location, and Adsorbate Interactions of Ni(I) in Ni(II)-Exchanged SAPO-34

Abstract

Electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopies were used to study the reducibility, location, and adsorbate interactions of Ni(I) in NiH−SAPO-34, in which Ni(II) was introduced into extraframework sites of SAPO-34 by partial ion exchange of H(I) by Ni(II). After dehydration at temperatures above 573 K as well as after γ-irradiation at 77 K, one nickel species assigned as isolated Ni(I) by ESR is observed. Along with the isolated Ni(I) species, a second species assigned to Ni(I)−(H2)n is also observed after hydrogen reduction at 573 K. Adsorption of water into reduced NiH−SAPO-34 forms an axially symmetric Ni(I)−(O2)n complex indicating water decomposition by Ni(I). Adsorption of methanol into reduced NiH−SAPO-34 forms two Ni(I)-methanol complexes suggested to be located at two different sites in the chabazite structure. Similarly, two Ni(I)−(C2D4)n complexes, the predominant one exhibiting axial symmetry and the other one having rhombic symmetry, are formed after eth...