| The formation of Ni(I) in NiAPSO-34 where Ni(II) is incorporated into the framework of chabazite-like SAPO-34 and its interaction with selected adsorbates are compared to Ni(I) species formed in NiH-SAPO-34 where Ni(II) is incorporated into extraframework sites using electron spin resonance (ESR) and electron spin echo modulation (ESEM) spectroscopies. ESEM results supported by ESR results indicate that the specific location of Ni(I) after reduction is in the chabazite cage near a six ring window for NiH-SAPO-34 and at framework phosphorus sites for NiAPSO-34.; The same techniques are used to study erionite-like SAPO-17 and levyne-like SAPO-35, in which Ni(II) ions were ion-exchanged. The interaction of NiH-SAPO-17 with ethylene and carbon monoxide produces two Ni(I)-C2D4 complexes and one Ni(I)-(CO)n complex. Nitric oxide adsorption on NiH-SAPO-17 generates one Ni(I)-(NO)+ complex, a NO radical and NO2 while on NiH-SAPO-35 it generates two Ni(I)-(NO) + complexes and a NO radical. Upon dehydration, Ni ions in NiH-SAPO-17 seem to migrate from the erionite supercage to the smaller cancrinite cage while in dehydrated NiH-SAPO-34 and NiH-SAPO-35 Ni ions remain in the large chabazite and levyne cages respectively.; Finally the selectivity of SAPO-34, SAPO-35, SAPO-17, and SAPO-18 (AEI) towards light olefins for the methanol to olefins reaction is studied using gas chromatography. The relationship between the catalyst performance on one hand and the structural type, the presence and location of Ni ions, and the amount of incorporated Ni(II) on the other hand is investigated. H-SAPO-34 yields the highest combined distribution of light olefins (C2-C 4) among the four H-SAPO-n samples while H-SAPO-18 is the best catalyst in terms of lifetime. Compared to H-SAPO-n, NiAPSO-n samples yield an increase in the lifetime, a larger overall distribution of C2-C4 olefins and better selectivity towards ethylene while NiH-SAPO-n samples only yield an increase in ethylene selectivity. Also, the increase in ethylene selectivity is more prominent in synthesized than in ion-exchanged samples. Among the Ni-loaded samples, NiAPSO-34 is the best catalyst both in terms of ethylene selectivity and lifetime. Finally, plotting ethylene selectivity versus the Ni(II) amount for NiAPSO-34 shows an optimum Ni(II) concentration for which the ethylene selectivity reaches a maximum. This optimum concentration is the same that was found to yield the strongest Ni(I) signal observed by ESR. |
