Effect of zeolite on the activity of Ru/MnCO3 catalysts for Fischer–Tropsch reaction

Abstract

The zeolite-containing Ru/MnCO3 3Ru(NO)-Mn catalysts were investigated on the Fischer–Tropsch synthesis (FTS) in a low pressure fixed-bed reactor. The catalytic activity and i/n ratio of C4 hydrocarbons were found to be a little higher than those of non-zeolite systems such as 3Ru(NO)-Mn alone and 3Ru(NO)-Mn with MnCO3 as a diluents, while the α-value and olefin/paraffin ratio of C2–C4 hydrocarbons were lower for the zeolite system than those of non-zeolite. The hydrocarbon cracking ability could be improved for all-in-one type Ru-Z-B as well as 3Ru(NO)-Mn physically mixed with zeolite, compared with 3Ru(NO)-Mn with MnCO3. In fact, the Ru-Z-B catalyst gives a narrower carbon distribution than the 3Ru(NO)-Mn with MnCO3 catalyst. The Ru crystallite sizes of used catalysts after 120h- and 720h-reaction were close to those of fresh catalysts, indicating no aggregation occurred. The origin of catalyst deactivation could depend on the extent of hydrocarbon deposition, even in zeolite-containing catalyst systems. The longer reaction time, the more condensed wax materials were formed and, even after a gentle calcination of the used Ru-Z-B catalyst at 350°C, the inorganic-like carbons still remain, as ascertained by TPR-Q-mass analysis. The proposed deactivation mechanism would be consistent with other analytical evidences such as thermogravimetric analysis (TGA), CO adsorption, transmission electron micrograph (TEM) of used catalysts as well as NH3-TPD of the used zeolites.