Effect of Co-fed Water on a Co–Pt–Si/γ-Al2O3 Fischer–Tropsch Catalyst Modified with an Atomic Layer Deposited or Molecular Layer Deposition Overcoating

Niko Heikkinen,Matti Putkonen,Jasmiina Palo,Laura Keskiväli,Matti Reinikainen

doi:10.1021/acsomega.1c06512

Niko Heikkinen, Matti Putkonen + Show 3 more

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https://doi.org/10.1021/acsomega.1c06512

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Abstract

Atomic layer deposition (ALD) and molecular layer deposition (MLD) methods were used to prepare overcoatings on a cobalt-based Fischer–Tropsch catalyst. A Co–Pt–Si/γ-Al2O3 catalyst (21.4 wt % Co, 0.2 wt % Pt, and 1.6 wt % Si) prepared by incipient wetness impregnation was ALD overcoated with 30–40 cycles of trimethylaluminum (TMA) and water, followed by temperature treatment (420 °C) in an inert nitrogen atmosphere. MLD-overcoated samples with corresponding film thicknesses were prepared by using TMA and ethylene glycol, followed by temperature treatment (400 °C) in an oxidative synthetic air atmosphere. The ALD catalyst (40 deposition cycles) had a positive activity effect upon moderate water addition (PH2O/PH2 = 0.42), and compared with a non-overcoated catalyst, it showed resistance to irreversible deactivation after co-fed water conditions. In addition, MLD overcoatings had a positive effect on the catalyst activity upon moderate water addition. However, compared with a non-overcoated catalyst, only the 10-cycle MLD-overcoated catalyst retained increased activity throughout high added water conditions (PH2O/PH2 = 0.71). All catalyst variations exhibited irreversible deactivation under high added water conditions.

Highlights

Fischer−Tropsch (FT) synthesis is a versatile method for converting a wide variety of feedstocks into valuable chemical products
This paper addresses the effect of atomic layer deposition (ALD) and molecular layer deposition (MLD) overcoatings on FT catalysts
A catalyst with 21.4 wt % cobalt, 0.2 wt % platinum, and 1.6 wt % silicon on a γ-Al2O3 support was prepared by incipient wetness co-impregnation and overcoated with ALD and MLD

Summary

Introduction

Fischer−Tropsch (FT) synthesis is a versatile method for converting a wide variety of feedstocks into valuable chemical products. In many cases, such as with biomass gasification or CO2 utilization schemes, remarkable amount of water can be present in the feed of the FT step. In addition to a positive effect on the activity, the higher coverage of the reactive monomer species is suggested to increase C5+ selectivity through an enhanced polymerization rate without increasing chain termination probability. The increased activity has mainly been reported for TiO2- and SiO2-supported catalysts,[9,10] and decreased activity has mainly been reported for Al2O3-supported catalysts with narrow pores below 13 nm.[2,5,11] catalysts supported on narrow-pore γ-Al2O3 show a lower CO conversion rate, interestingly, selectivity is increased without exception.[11−13] the

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