Enhancement of cobalt catalyst stability in Fischer–Tropsch synthesis using graphene nanosheets as catalyst support

Abstract

The effect of morphology and structure of graphene nanosheets (GNS) and carbon nanotubes (CNT) as support on the stability of cobalt catalyst for Fischer–Tropsch synthesis (FTS) was investigated using a fixed bed micro-reactor.15.0wt.% of cobalt was loaded on the supports by impregnation method. The deactivation of the two catalysts was studied at 220°C, 1.8MPa and 45 STP mL/min feed flow rate. Characterization of the supports, calcined fresh and used catalysts were studied by Raman spectroscopy, BET, XRD, TEM, TPR and H2 chemisorption techniques. XRD confirmed formation of cobalt oxides on the used catalysts. According to the TEM and H2 chemisorption tests, 480h continuous FT synthesis increased the average cobalt particle size from about 6 to 6.8nm for Co/GNS catalyst and from about 7.5 to 9.5nm for Co/CNT catalyst. The initial CO conversion of the Co/GNS catalyst was 12% higher than that of the Co/CNT. For the Co/GNS, 480h continuous FT synthesis decreased the CO conversion by 3.9%, whereas, under the same reaction conditions the CO conversion for Co/CNT decreased by 20.7%. Regeneration of the Co/GNS and Co/CNT recovered 99.3 and 92.8% of the initial activities of the catalysts, respectively. Significant stability of Co/GNS catalyst in FT synthesis, introduces graphene as an excellent support for the cobalt catalysts.