Role of surface carboxylate deposition on the deactivation of cobalt on titania Fischer-Tropsch catalysts

Prasad Gonugunta,A Iulian Dugulan,G Leendert Bezemer,Ekkes Brück

doi:10.1016/j.cattod.2020.04.037

Prasad Gonugunta, A Iulian Dugulan + Show 2 more

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https://doi.org/10.1016/j.cattod.2020.04.037

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Abstract

Operando spectroscopic techniques (Diffusive Reflective Infrared Fourier-Transform and Mössbauer emission spectroscopy) were combined to investigate the role of oxygenates deposition on deactivation of cobalt on titania Fischer-Tropsch catalysts at high pressure. Clear formation of carboxylates was seen for catalysts prepared via both impregnation and precipitation, but more and heavier carboxylates were seen on the impregnated catalyst. This effect is related to a higher olefin content in the products obtained with the impregnated sample, resulting to increased formation of oxygenates through the hydroformylation side reaction. The combined gas chromatography/infrared spectroscopy data demonstrated that the surface carboxylate species are not involved in the catalyst deactivation, being most likely spectator species on the titania support.

Highlights

Fischer-Tropsch synthesis (FTS) is a catalytic process that converts synthesis gas obtained from natural gas, coal and biomass into liquid fuels [1,2]
We have investigated two catalysts prepared by incipient wetness impregnation (IWI) and homogeneous deposition precipitation (HDP) methods, uniquely monitoring the surface species with operando diffusive reflective infrared Fourier-Transform (DRIFT) and the state of the cobalt with operando Mossbauer emission
Morales et al [15] studied a Co/TiO2 catalysts containing Mn promoter prepared by IWI and HDP methods and they found that the HDP catalyst was more active than the catalyst prepared by the IWI method, due to the better distribution of the Co phase

Summary

Introduction

Fischer-Tropsch synthesis (FTS) is a catalytic process that converts synthesis gas obtained from natural gas, coal and biomass into liquid fuels [1,2]. Formation of different types of carbon compounds on the catalyst surface and their role on deactivation of Co-based FTS catalysts has been reported [4,5,6]. Scalbert et al [9] found build-up of oxygenated compounds with time on a Co/Al2O3 catalyst using XRD-DRIFT spectroscopy They proposed that these strongly adsorbed species are responsible for catalyst deactivation by covering the active sites. TPH-IR of the spent catalyst indicated that complete removal of carboxylate species required temperatures above 600 ◦C. They proposed that carboxylates on the catalyst surface cause deactivation, but the exact role of the carboxylates on the catalyst surface is not yet fully understood. The main aim of this research is to investigate the role of carboxylates in the deactivation mechanism of titania based FTS catalysts

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