Characterization and catalytic properties of cobalt supported on delaminated ITQ-6 and ITQ-2 zeolites for the Fischer–Tropsch synthesis reaction

Cobalt catalysts (ca. 20 wt% Co) supported on all-silica delaminated ITQ-2 and ITQ-6 zeolites have been prepared by impregnation with aqueous Co(NO3)3 solutions. The catalysts have been characterized by X-ray diffraction (XRD), nitrogen adsorption, transmission electron microscopy (TEM), temperature-programmed reduction (TPR), and infrared spectroscopy of adsorbed CO. The catalytic properties for the Fischer–Tropsch synthesis (FTS) reaction under typical FTS conditions (493 K, 20 bar, H2/CO = 2) have been evaluated, and the results compared with those obtained over a conventional Co/SiO2 and a mesoporous Co/MCM-41 catalyst with comparable cobalt loading. Co/ITQ-6 was the most active catalyst, with a FTS reaction rate which was about 1.5 and 1.8 times higher than that of Co/MCM-41 and Co/SiO2, respectively. The high activity of Co/ITQ-6 is ascribed both to a relatively good dispersion (as observed by TEM) and to a high reducibility (determined by TPR) of the supported Co3O4 particles. The dispersion and reducibility of cobalt particles in Co/ITQ-2 were very close to those in Co/SiO2. Consequently, both catalysts presented similar FTS reaction rates. In addition, Co/ITQ-6 and Co/ITQ-2 presented a higher selectivity toward the formation of C5+ hydrocarbons than Co/SiO2 and Co/MCM-41. The higher C5+ selectivity of the catalysts based on the delaminated zeolites was ascribed to a higher concentration of coordinatively unsaturated Co0 sites which are characterized by a band at 1897 cm−1 in the infrared spectrum of adsorbed CO. This type of site having an enhanced electron density might stabilize surface hydrocarbon intermediates favoring chain growth processes.