Bismuth mobile promoter and cobalt-bismuth nanoparticles in carbon nanotube supported Fischer-Tropsch catalysts with enhanced stability

Metal nanoparticles on the surface of porous supports have found numerous applications in different areas of science. Fischer-Tropsch synthesis, which proceeds on the surface of cobalt metal nanoparticles, is an efficient way to convert renewables and fossil feedstocks into alternative fuels. The stability of cobalt catalysts is an essential and even crucial parameter and can be significantly improved by promotion. In this paper, a combination of operando Quick-XAS, NAP-XPS, high resolution electron microscopy imaging, DFT modeling alongside with Fischer-Tropsch catalytic experiments has provided deep insights into the evolution of bismuth promoter and structure of cobalt-bismuth nanoparticles in the catalysts supported by carbon nanotubes. We uncovered noticeable migration of metallic bismuth occurring during the reduction step, which leads to bismuth redispersion over the surface of cobalt nanoparticles. Cobalt reduction is facilitated in the presence of bismuth. The working Fischer-Tropsch catalyst contains cobalt-bismuth bimetallic nanoparticles, with bismuth located in the nanoparticle shell. The promotion with bismuth has resulted in a noticeable increase in catalyst stability. Characterization and DFT modeling suggest preferential localization of bismuth mobile promoter at the steps and edges of cobalt nanoparticles, which hinders cobalt sintering and carbon deposition and improves the catalyst stability. (c) 2021 Elsevier Inc. All rights reserved.

Automated summary

Metal nanoparticles on porous supports have wide applications in various scientific areas. This study demonstrates that bismuth promoter can enhance the stability of cobalt catalysts, leading to migration and redisersion of bismuth over the surface of cobalt nanoparticles during the reduction step. The preferential localization of mobile bismuth promoter at the steps and edges of cobalt nanoparticles hinders cobalt sintering and carbon deposition, resulting in improved catalyst stability.