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Title: 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-like SAPO-35, in which Ni ions were incorporated via solid-state ion-exchange into known extra framework sites, have been studied by electron spin resonance (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 and compared to that of Ni ion with NO in the previously studied chabazite-like SAPO-34. Room-temperature adsorption of C{sub 2}D{sub 4} on NiH-SAPO-17 after dehydration at 573 K, oxygen treatment at 823 K, evacuation, and subsequent hydrogen treatment at 573 K produces two Ni-ethylene complexes. Carbon monoxide adsorption gives rise to a Ni(I)-(CO){sub n} complex with unresolved {sup 13}C hyperfine lines. Following the kinetics of nitric oxide adsorption on NiH-SAPO-17 shows that initially, a Ni(I)-(NO){sup +} complex, a NO radical, and a new species which appears to be another NO species are generated. After a reaction time of 24 h, NO{sub 2} is observed. As the adsorption time further increases, NO{sub 2} becomes stronger while Ni(I)-(NO){sup +} decays, and after 5 days only NO{sub 2} remains. NO adsorption on NiH-SAPO-35 shows different features. Initially, two Ni(I)-(NO){sup +} complexes along with amore » NO radical are seen. As the adsorption time increases, one of the Ni(I)-(NO){sup +} complexes decreases in intensity while the other one increases, and after a few days only one Ni(I)-(NO){sup +} complex remains. Simulation of the {sup 31}P ESEM spectrum, supplemented by {sup 27}Al modulation, suggests that, upon dehydration, Ni ions in NiH-SAPO-17 migrate from the erioinite supercage to the smaller cancrinite cage. In dehydrated NiH-SAPO-17 migrate from the erionite supercage to the smaller cancrinite cage. In dehydrated 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 less sensitive to reduction by hydrogen than it is in NiH-SAPO-34 and NiH-SAPO-35.« less
Authors:
; ; ;  [1]
  1. Univ. of Houston, TX (United States). Dept. of Chemistry
Publication Date:
OSTI Identifier:
696651
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical; Journal Volume: 103; Journal Issue: 34; Other Information: PBD: 26 Aug 1999
Sponsoring Org:
National Science Foundation, Washington, DC (United States);Welch (Robert A.) Foundation, Houston, TX (United States);USDOE, Washington, DC (United States)
Country of Publication:
United States
Language:
English
Subject:
40 CHEMISTRY; 32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION; MOLECULAR SIEVES; CATALYSTS; TRANSITION ELEMENTS; ELECTRON SPIN RESONANCE; ACOUSTIC ESR; NICKEL; REDUCTION; ION EXCHANGE