Co–Rh Nanoparticles for the Hydrogenation of Carbon Monoxide: Catalytic Performance Towards Alcohol Production and Ambient Pressure X-Ray Photoelectron Spectroscopy Study

Abstract

5 nm Co–Rh bimetallic nanoparticles with narrow size distributions and three different atomic compositions (2, 10, and 16 % Rh) were synthesized using a colloidal method. The bimetallic nanoparticles were loaded into mesoporous silica support MCF-17 and utilized in the catalytic hydrogenation of CO (Fischer–Tropsch synthesis). As compared to the pure 5 nm Co/MCF-17 catalyst, the bimetallic Co–Rh catalysts showed a similar activity while enhancing the selectivity towards alcohols, as evidenced by an increased ratio of alcohol to hydrocarbon products. Furthermore, larger alcohols such as propanol were formed with the addition of Rh, which is not observed with the pure Co/MCF-17 catalyst. In situ synchrotron based Ambient Pressure X-ray Photoelectron Spectroscopy studies on the Co–Rh samples revealed that Rh is segregated to the surface of the nanoparticles under reaction conditions, which plays an important role in altering the selectivity towards alcohol production. An optimum surface Rh concentration exists at ~9 at.%, where a fivefold enhancement in the alcohol-to-hydrocarbon ratio was achieved.