Catalytic Study of Methanol-to-Olefins Conversion in Four Small-Pore Silicoaluminophosphate Molecular Sieves: Influence of the Structural Type, Nickel Incorporation, Nickel Location, and Nickel Concentration

Abstract

The selectivity of four small-pore silicoaluminophosphate molecular sieves, including SAPO-34 (CHA), SAPO-35 (LEV), SAPO-17 (ERI), and SAPO-18 (AEI), toward light olefins in general and ethylene in particular has been investigated for the methanol-to-olefins reaction using gas chromatography. This study was prompted by earlier electron spin resonance and electron spin−echo modulation results on nickel-modified SAPO materials in which Ni(I) was incorporated into both framework and ion-exchanged sites. These seemingly similar materials behaved significantly differently with respect to reducing agents and adsorbates. Attention was focused on whether the catalyst performance is influenced by the structural type, the presence of a transition metal ion (Ni) either in the framework or at ion-exchanged positions, or the amount of incorporated transition metal ion. Our results show that these factors indeed play an important role in the catalytic behavior. Among the protonated H−SAPO-n materials, the highest combi...