An Experimental Study of the Performance of Isomorphically Zirconium-Substituted Mesoporous Alumina Supported Cobalt Catalysts in Fischer-Tropsch Synthesis

Sabar Simanungkalit,Zhezi Zhang,Gia Hung Pham,Mingming Zhu,Dongke Zhang

doi:10.4236/aces.2022.121004

Abstract

A series of mesoporous alumina (MA) supported cobalt (Co/MA) catalysts with MA isomorphically substituted by zirconium (Zr) were synthesised and evaluated for their performance in the Fischer-Tropsch synthesis. The Zr/(Zr + Al) atomic ratios varied from 1% - 15%. A zirconium-impregnated Co/MA catalyst prepared by wet impregnation with a Zr/(Zr + Al) atomic ratio of 5% was also evaluated to examine Zr incorporation’s effect method. The catalysts synthesised were characterised using N2 adsorption-desorption, X-ray Powder Diffraction (XRD), Transmission Electron Microscopy (TEM), and X-Ray Photoelectron Spectroscopy (XPS). It was found that Zr4+ ions were incorporated into the framework of MA and kept intact up to a Zr/(Zr + Al) atomic ratio of 5%. The cobalt dispersion and reducibility were improved as the Zr/(Zr + Al) atomic ratio increased to 50%. The performance of these catalysts for Fischer-Tropsch synthesis was evaluated using a fixed bed reactor at temperature and pressure of 493 K and 20 bar, respectively. The feed syngas had an H2/CO ratio of 2, diluted with 10% Ar. For isomorphically Zr-substituted Co/MA, the CO conversion and selectivity of diesel (C10 - C20) increased first and then decreased with increasing the Zr/(Zr + Al) atomic ratio. The maximum 38.9% CO conversion and 34.6% diesel (C10 - C20) selectivity were obtained at Zr/(Zr + Al) atomic ratio of 5%. The isomorphic substitution method was better than the wet impregnation method in CO conversion and diesel selectivity.

Highlights

The development of liquid fuel production technology becomes one of the pathways devoted to sustainable energy [1]
The catalysts were evaluated in Fischer-Tropsch (FT) synthesis in terms of CO conversion and selectivity in a high-pressure fixed-bed reactor
The C5+ products collected in the ethyl acetate trap were analysed by another off-line Agilent 7890 A gas chromatograph equipped with an HP-5 column and an flame ionisation detector (FID)

Summary

Introduction

The development of liquid fuel production technology becomes one of the pathways devoted to sustainable energy [1]. Zr promoted Co catalysts have been reported to enhance the catalytic activity and C5+ selectivity for the F-T synthesis compared with the non-promoted counterparts. The effects of different promoter incorporation methods on the catalytic performance in the F-T synthesis reactions have been extensively investigated and reported in the literature. Zirconium’s introduction into SBA-15 using four methods, impregnation, co-precipitation, isomorphic substitution (IS) and chemical grafting have been studied [9] [10] They found that when IS was used to prepare zirconium modified SBA-15 supports, the cobalt catalysts showed higher activity than the one prepared by impregnation but lower activity than prepared by grafting. A range of cobalt catalysts supported on the isomorphically Zr-substituted mesoporous SBA-15 with different Zr/Si ratios have been investigated to elucidate the influence of Zr content [11]. Zr incorporated Co/MA catalysts with a Zr/(Zr + Al) ratio of 5% prepared by wet impregnation method was used as a comparison to test the effects of Zr incorporation method on the catalyst performance

Catalyst Preparation

Material Characterisation

Evaluation of Catalyst Performance

Results and Discussion

Conclusion