Fischer–Tropsch synthesis on a Co/Al2O3 catalyst with CO2 containing syngas

Abstract

Abstract Hydrogenation of CO, CO 2 and their mixtures has been comparatively studied in this work on a representative cobalt-based catalyst under typical Fischer–Tropsch synthesis conditions ( T = 220 °C, P = 20 bar, GHSV = 4800 cm 3 (STP)/h/g cat , H 2 /CO x = 2.45–4.9 mol/mol). In addition, the interactions of the adopted catalyst with CO, CO 2 and their mixtures have been studied by FT-IR spectroscopy. When used alone, both CO and CO 2 are easily hydrogenated over the adopted catalyst, with CO 2 showing a reactivity higher then CO. However the selectivity of the two processes is extremely different, with over 90% of the products represented by methane in the case of CO 2 hydrogenation. No evidence has been found for the involvement of different surface species in CO and CO 2 hydrogenation, suggesting that the observed reaction products originate from the same intermediate. It is speculated that the different reactivity of the mixtures CO/H 2 and CO 2 /H 2 is due to the different adsorption ability of CO and CO 2 , which strongly affects the H/C atomic ratio on the catalyst surface. The higher H/C ratio resulting upon CO 2 hydrogenation inhibits the chain growth, hence favoring the methanation reaction. In the presence of CO, CO 2 is hardly hydrogenated and behaves as an inert species: this has been ascribed to a competition between CO and CO 2 for the adsorption on the catalyst active sites.