Post doped nitrogen-decorated hollow carbon spheres as a support for Co Fischer-Tropsch catalysts

Abstract

In this study the outer surface of porous hollow carbon spheres (HCSs) materials were functionalized by N-doping using a post-synthesis method and they were used as a Fischer-Tropsch catalyst support. Melamine was used as the nitrogen source, and carbonization was performed at diff erent temperatures (600 and 900 °C) to introduce variable levels of N into the HCSs, with diff erent bonding configurations. This procedure allowed for the incorporation of up to 13% N. Our results show that post-synthesis N-doping introduced marginal defects into the carbon framework and this did not aff ect the thermal stability of the materials. XPS studies revealed that the surface content on these materials varied and provided evidence for temperaturetunable bonding configurations. Eff ects associated with post-synthesis N-doping were apparent on the Co catalyst (˜10 wt.%) properties such as the inhibited reduction caused by a metal-support interaction observed by the H2-TPR and in situ PXRD techniques. As a consequence the Fischer-Tropsch performance was influenced as both the activity and stability were improved on the catalysts supported on the N-doped materials. TEM analysis of the spent catalysts demonstrated the influence of N-doping on the sintering characteristics of Co, with particles > 30 nm measured on the N-free catalyst while Ndoped samples had sizes < 15 nm.

Cobalt catalysts on carbon-based materials for Fischer-Tropsch synthesis: a review

“…In order to improve Co dispersion on carbon supports, recent studies evidenced that the introduction of nitrogen functional groups on/in the carbon materials can alter the electronic structure and thus improve Co dispersion [20,131,238]. More specifically, this doping: (i) increases the local basicity and/or the local electron density of the carbon support; (ii) modifies the nucleation and growth kinetics during metal particle deposition, favoring the formation of small particles and therefore increases Co dispersion; (iii) increases the MSI, which can lead to improved catalyst stability during the reaction, and (iv) modifies the electronic structure of catalyst particles and can consequently enhance the FTS performances [20,160,[239][240][241].…”

“…Furthermore, the Co particles were well-dispersed on N-GNS surface with a size within the 4-11 nm range, while a broader particle size distribution was observed for Co/GNS (3-15 nm). In addition, anchoring or defect sites created by the presence of nitrogen functional groups reinforce MSI [240], and prevent Co particle agglomeration and sintering. In FTS (T = 220 °C, P = 18 bar, H2/CO = 2, GHSV = 5143 mL g -1 h -1 ), the Co/N-GNS catalyst exhibited better activity, stability and lower particle growth rate than Co/GNS, which was explained by the improvement of Co species reducibility by nitrogen functional groups [155].…”

Carbon-based catalysts for Fischer–Tropsch synthesis

“…Porous hollow carbon spheres (HCSs) materials were functionalized by N doping through a post-synthesis method with melamine as the nitrogen source. 134 Various levels of N doping and different bonding configurations of HCSs were obtained through performing carbonization at different temperatures. Marginal defects of the carbon framework of HCSs were found.…”

Vapour phase hydrogenation of cinnamaldehyde using cobalt supported inside and outside hollow carbon spheres

“…Continuing from earlier studies by others working in our research group on the use of Co supported on carbon in catalysis [19][20][21] we herein report on their use for the vapour phase CALD hydrogenation reaction using hollow carbon spheres (HCSs) as a support. HCSs contain a mesoporous shell that allows for the loading of Co both inside and outside HCSs; the structure can support a high loading of small metal nanoparticles.…”