Insight into the role of Co2C supported on reduced graphene oxide in Fischer-Tropsch synthesis and ethene hydroformylation

Abstract

The roles of Co2C supported on reduced graphene oxide (RGO) for both Fischer-Troprsch (FT) and ethene hydroformylation reactions have been studied for the first time. Two catalysts, cobalt supported by RGO (CG) and Rh promoted cobalt supported by RGO (RCG), have been successfully synthesized. A series of experiments were performed where the feed was switched between syngas and a syngas–ethene mixture. During H2 reduction: Metallic Co has been formed for the CG catalyst; However, Co2C was detected in RCG catalyst, which experimentally proved that the RGO was the carbon source for the formation of Co2C. After H2 reduction, both CG and RCG catalyst exhibited extremely low FT reactivity, which indicated that the interaction between the Co and RGO limited the FT chain growth reaction. The catalyst characterization results proved that the exposure of the CG and RCG catalysts to syngas or/and a syngas-ethene mixture could transform CoO or/and metallic Co to Co2C. It was found that the Co-Co2C interface derived from CG catalyst was inactive for FTS and exhibited low CO conversion with the main products being short chain alcohols and hydrocarbons (C1-C4). Nevertheless, exposing the Co-Co2C interface to CO/C2H4/H2 feed promoted the production of C3 oxygenates, which indicated the multi-phase of Co-Co2C was highly active for ethene hydroformylation. Moreover, a pure Co2C phase was obtained with the promotion of Rh, which was completely inactive for FTS but highly active for ethene hydroformylation. It is can be concluded that the interaction between RGO and cobalt species could suppress CO chain growth reaction, while promoting the CO insertion reaction to form aldehydes or alcohols.