Fischer-Tropsch synthesis: Effect of nitric acid pretreatment on graphene-supported cobalt catalyst

Abstract

As a support for cobalt Fischer-Tropsch synthesis catalyst, graphene needs to be pretreated to modify its surface properties for desired catalytic performance. Graphene was pretreated by thermal reflux using 20–60 % nitric acid. The pretreated graphene and catalysts were characterized with TPR, TEM, SEM, XRD, XPS and Raman spectroscopy to study the effect of treatment on microstructures of the materials. This work showed that cobalt metal uniformly dispersed on graphene, and with increasing pretreating acid concentration, surface defects increased and the cobalt particle size decreased, suggesting alleviated agglomeration of cobalt particles on graphene. Pretreating improved the reduction of the catalyst due to the increased defect sites, improved support-metal interaction and cobalt dispersion. Pretreated catalyst yielded better activity, higher C5+, but lower methane selectivity than unpretreated catalyst. Therefore, acid pretreatment of graphene can be an effective approach to modify the microstructure of the material, and can thus enhance the performance of the prepared catalyst.