Loading and promoter effects on the performance of nitrogen functionalized graphene nanosheets supported cobalt Fischer-Tropsch synthesis catalysts

Abstract

The effects of nitrogen functional groups on graphene surface and also the effects of cobalt loading and ruthenium promoter on the performance of nitrogen functionalized graphene nanosheets (N-GNS) supported cobalt catalysts in Fischer–Tropsch synthesis (FTS) are investigated. A 15 wt% Co/PGNS catalyst, a series of Co/N-GNS (15–30 wt% loading) and ruthenium promoted catalysts (25 wt% Co,0.5 wt% Ru/N-GNS and 25 wt% Co,0.5 wt% Ru/PGNS) were prepared by impregnation method. The purified GNS and functionalized GNS and all catalysts were characterized by Raman spectroscopy, FTIR, SEM, EDS, ICP, BET, TEM, XRD and TPR. The catalysts assessed in FTS in a fixed bed micro-reactor at 220 °C, 1.8 Mpa and H2/CO ratio of 2. Functionalization of GNS shifted the TPR reduction peaks to lower temperature, increased the dispersion of cobalt particles and increased the percentage CO conversion from 70.6% to 74.5%. Increasing the cobalt loading resulted in increasing the average cobalt cluster size, improvements in the reducibility of Co3O4. The maximum FTS activity for N-GNS supported catalyst is achieved at 30 wt % cobalt loading. The C5+ selectivity for the 30 wt % cobalt catalyst was higher than that of the 15 wt % Cobalt catalyst. Addition of 0.5 wt%Ru increased the FTS rate (gCH/(gcat·h)) from 0.377 to 0.412 and the liquid products selectivity from 86.5% to 91.2%.