Activity and deactivation nature of Ru/MnCO3 catalysts for Fischer–Tropsch reaction

The catalytic activities and different behaviors for catalyst deactivation by forming surface hydrocarbon deposits were investigated on the Cl-free Ru/MnCO3 Fischer–Tropsch synthesis (FTS) catalysts in a low pressure fixed-bed reactor. Catalytic activity of LT-Ru(NO) was found to be a little higher than that of Ru(NO). The differences seem to stem mainly from ruthenium particle sizes and reduction behavior of adsorbed CO on the catalysts, which would be consistent with the results of CH4 formation from temperature-programmed reduction (TPR) of pre-adsorbed CO, as well as Ru particle sizes, as ascertained by H2 and CO adsorptions and TEM measurements. The Ru particle sizes of used catalysts obtained after 120 h-reaction were approximately close to those of fresh catalysts and no ruthenium aggregation occurred. The origin of catalyst deactivation was investigated in terms of the extent of hydrocarbon deposition. The adsorbed atomic carbon at the peak temperature around 250–350 °C was eliminated by H2 treatment, but the more heavy hydrocarbons at peak temperature over 400 °C such as polymeric and graphitic carbons were not removed by any treatment. The nature of hydrocarbon deposition would be suggested by measuring the deposited carbon with the help of the characterizations, such as thermo-gravimetric analysis, temperature-programmed reduction and diffuse reflectance infrared Fourier transform (FT-IR) measurements.

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► Chloride-free Ru/MnCO3 was synthesized as catalysts for Fischer–Tropsch synthesis (FTS).
► Ru/MnCO3 shows high activity under low pressure conditions below 1 MPa.
► Metallic Ru particle sizes remained constant after 120 h-FTS reaction.
► The origin of catalyst deactivation was explained in terms of the extent of hydrocarbon deposition.