Stability Of Cobalt Catalysts Research Articles

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.

Enhancement of performance and stability of Graphene nano sheets supported cobalt catalyst in Fischer–Tropsch synthesis using Graphene functionalization

Graphene nano sheets (GNS) were functionalized and used as cobalt Fischer–Tropsch synthesis (FTS) catalyst support. The effects of nitrogen functional groups on graphene surface on the activity, selectivity and stability of cobalt catalyst in FTS was investigated using a fixed bed micro-reactor. 15wt.% of cobalt was loaded on the supports by impregnation method. Physico-chemical properties of pure and functionalized graphene, calcined fresh and used catalysts were studied by Raman spectroscopy, FTIR, BET, XRD, TEM, TPR and H2chemisorption techniques. According to the TEM and H2chemisorption tests, 480hrs continuous FT synthesis increased the average cobalt particle size from about 7.8 to 8.8nm for Co/GNS catalyst and from about 6.8 to 7.2nm for Co/N-GNS catalyst. The proposed cobalt catalyst supported on functionalized GNS increased the initial %CO conversion from 70.6 to 74.5. The CO conversion over the Co/N-GNS after 480hrs on stream decreased by 4.3% and that for Co/GNS decreased by 6.2%. For the Co/N-GNS catalyst 0.6% of total activity loss and for the Co/GNS catalyst 3.1% of total activity loss cannot be recovered after regeneration of the catalyst at the same conditions of the first regeneration step.Catalysts supported on functionalized GNS showed better stability.

Prediction of stability of cobalt catalysts for hydrocarbon synthesis from CO and H2 in terms of resistance of cobalt crystallites against high-temperature agglomeration

The effect of temperature of calcination of Co catalysts reduced at 400°C on their characteristics (the surface area, degree of reduction, particle size, and average crystallite diameter), was investigated. It was found that an increase in the calcination temperature from 400 to 500°C significantly affects the size of cobalt crystallites. Based on these data, a method for predicting the catalyst stability is proposed.