The Role of Steric Effects and Acidity in the Direct Synthesis of iso-Paraffins from Syngas on Cobalt Zeolite Catalysts

This study focuses on the effects of the localization of Co species, zeolite structure, and acidity on the performance of Co bifunctional catalysts promoted with Pt for the direct synthesis of iso-paraffins from syngas. ZSM-5, MOR, and BEA were chosen as zeolites with different structures and pore diameters. The catalysts were prepared either by incipient wetness impregnation or by the mechanical mixing of the zeolite with a conventional silica-supported Co catalyst. The increase in the pore size and open character of the zeolite structure from ZSM-5 to BEA resulted in a higher fraction of Co located inside the pores of the catalysts prepared by impregnation. The catalytic performance was affected strongly by the zeolite acidity, pore structure, and Co distribution between the pores and the external surface. The selectivity to short-chain iso-paraffins is affected principally by the zeolite acidity, whereas the selectivity to long-chain branched hydrocarbons mostly depends on steric effects.