Electron Spin Resonance and Electron Spin Echo Modulation Studies on the Formation and Adsorbate Interactions of Ni(Ι) in Synthetic Clinoptilolite

Abstract

Electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopies were used to study the formation of Ni(Ι) by various reduction methods and various adsorbate interactions of Ni(Ι) in synthetic clinoptilolite, in which Ni(ΙΙ) was ion-exchanged into extraframework sites of clinoptilolite. Thermal reduction by dehydration at 573 K shows a single species assigned to Ni(Ι) ions. Two isolated Ni(Ι) ions are observed after hydrogen reduction at 623 K. Adsorption of methanol on hydrogen-reduced NiNaK−Clino forms a Ni(Ι)−(CD3OH)n complex resulting from the interaction of methanol with one of the isolated Ni(Ι) ions. Adsorption of ammonia on hydrogen-reduced NiNaK−Clino produces a prominent Ni(Ι)−(ND3)n complex by interaction with both Ni(Ι) ions. The 13C hyperfine structure and ESEM analysis parameters after 13CO adsorption indicate that Ni(Ι) interacts with one CO molecule and forms a Ni(Ι)−(CO)1 complex. Two Ni(Ι)−(C2D4)n complexes are generated after adsorption of ethylene on dehydrated Ni(II)NaK−Clino and subsequent heating below 623 K. At higher temperature, these species disappear with the concomitant formation of two Ni(Ι)−(C4D8)n complexes, indicating ethylene dimerization. 2D ESEM confirms the coordination of Ni(Ι) with butene. Adsorption of NO on dehydrated Ni(II)NaK−Clino produces two Ni(Ι)−NO+ complexes formed by transfer of the odd electron from NO to Ni(ΙΙ) ions. Along with two Ni(Ι)−NO+ species, another species assigned to the NO radical is also observed in NiNaK−Clino after NO adsorption on Ni(II)NaK−Clino and NaK−Clino.