Electron spin resonance and electron spin echo modulation studies of ion-exchanged NiH-SAPO-17 and NiH-SAPO-35 molecular sieves: Comparison with ion-exchanged NiH-SAPO-34 molecular sieve

Erionite-like silicoaluminophosphate molecular sieve SAPO-17 and levyne-lik e SAPO-35, in which Ni ions were incorporated via solid-state ion-exchange into known extraframework sites, have been studied by electron spin resonan ce (ESR) and electron spin echo modulation (ESEM). The Ni ion reducibility, location, and interaction with several adsorbates have been investigated. Among these adsorbates, the interaction with nitric oxide was emphasized an d compared to that of Ni ion with NO in the previously studied chabazite-li ke SAPO-34. Room-temperature adsorption of C2D4 on NiH-SAPO-17 after dehydr ation at 573 K, oxygen treatment at 823 K, evacuation, and subsequent hydro gen treatment at 573 K produces two Ni-ethylene complexes. Carbon monoxide adsorption gives rise to a Ni(I)-(CO)(n) complex with unresolved C-13 hyper fine lines. Following the kinetics of nitric oxide adsorption on NiH-SAPO-1 7 shows that initially, a Ni(I)(NO)(+) complex, a NO radical, and a new spe cies which appears to be another NO species are generated. After a reaction time of 24 h, NO2 is observed. As the adsorption time further increases, N O: becomes stronger while Ni(I)-(NO)(+) decays, and after 5 days only NO2 r emains. NO adsorption on NiH-SAPO-35 shows different features. Initially, t wo Ni(I)-(NO)(+) complexes along with a NO radical are seen. As the adsorpt ion time increases, one of the Ni(I)-(NO)(+) complexes decreases in intensi ty while the other one increases, and after a few days only one Ni(I)-(NO)( +) complex remains. Simulation of the P-31 ESEM spectrum: supplemented by A l-27 modulation, suggests that, upon dehydration, Ni ions in NiH-SAPO-17 mi grate from the erionite supercage to the smaller cancrinite cage. In dehydr ated NiH-SAPO-34 and NiH-SAPO-35, Ni ions remain in the large chabazite and levyne cages, respectively. As a consequence, Ni(II) in NiH-SAPO-17 is les s sensitive to reduction by hydrogen than it is in NiH-SAPO-34 and NiH-SAPO -35.