ELECTRON-SPIN-RESONANCE AND ELECTRON-SPIN ECHO MODULATION STUDY OF NI(I) IN SILICOALUMINOPHOSPHATE TYPE-5 - ADSORBATE INTERACTIONS AND EVIDENCE FOR THE FRAMEWORK INCORPORATION OF NI(I)

The various Ni(I) species formed by reduction and adsorbate interactions in silicoaluminophosphate-5 (SAPO-5), in which (a) Ni(II) was incorporated into framework positions by incorporation of Ni(II) into the SAPO-5 synthesis mixture (NiAPSO-5) and (b) Ni(II) was incorporated into extraframework positions by partial ion exchange of Hf in H-SAPO-5 by Ni2+ (NiH-SAPO-5), were studied by electron spin resonance (ESR) and electron spin echo modulation (ESEM). After dehydration at temperatures above 673 K one Ni(I) species is observed in NiAPSO-5 and in NiH-SAPO-5. Two distinct Ni(I) species, assigned as isolated Ni(I) and Ni(I)-(H-2)(n), are also observed in hydrogen-reduced NiAPSO-5 and NiH-SAPO-5. The difference between Ni(I) in NiH-SAPO-5 and NiAPSO-5 can be shown by their P-31 modulation. Adsorption of D2O on both types of materials at 77 K leads to the formation of a Ni(I)-(D2O), complex at low temperature; at room temperature the complex decomposes with water decomposition. Ammonia adsorption on NiH-SAPO-5 leads to two different ammonia complexes Ni(I)-(ND3)(4) with hyperfine splitting constants of 7.4 and 14.4 G, respectively, whereas in NiAPSO-5 only the Ni(I)-(ND3)(4) complex with a 7.4 G splitting is seen. Ni(I) complexes with methanol show differences in the ESR g parameters and in the ESEM between NiAPSO-5 and NiH-SAPO-5. The adsorption of ethylene onto NiH-SAPO-5 produces a Ni(I)-(C2D4)(1) complex compared to a Ni(I)-(C2D4)(2) species formed in NiAPSO-5. The contrasting ESR and ESEM characteristics of Ni(I) in NiAPSO-5 and NiH-SAPO-5 suggest that Ni is indeed in a framework site in NiAPSO-5. The effect of an increase of the channel size between SAPO-11 (10-ring channel) and SAPO-5 (12-ring channel) is seen by an increase in the number of coordinated methanol and ethylene molecules in SAPO-5.