Electron spin resonance and electron spin echo modulation studies on reducibility, location, and adsorbate interactions of N(I) in Ni(II)-exchanged SAPO-34

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 I-Ill by Ni(II). After dehydration at temperatures above 573 K as well as after gamma-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)-(H-2)(n) is also observed after hydrogen reduction at 573 K. Adsorption of water into reduced NiH-SAPO-34 forms an axially symmetric Ni(I)-(O-2)(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 ethylene adsorption onto reduced NiH-SAPO-34. Analysis of the C-13 hyperfine structure obtained after (CO)-C-13 adsorption showed a Ni(I)-(CO)(3) species. The location of Ni(I) in NiH-SAPO-34 was determined qualitatively by Al-27 ESEM which suggested that even though Ni is situated within 5 Angstrom of the framework aluminum, the two species are not in close proximity. A more quantitative analysis using P-31 ESEM showed that Ni(I) is at site II' in the chabazite cage near a six-ring window after both thermal and hydrogen reduction.