Abstract
The present work explores the technical feasibility of passivating a Co/γ-Al2O3 catalyst by atomic layer deposition (ALD) to reduce deactivation rate during Fischer–Tropsch synthesis (FTS). Three samples of the reference catalyst were passivated using different numbers of ALD cycles (3, 6 and 10). Characterization results revealed that a shell of the passivating agent (Al2O3) grew around catalyst particles. This shell did not affect the properties of passivated samples below 10 cycles, in which catalyst reduction was hindered. Catalytic tests at 50% CO conversion evidenced that 3 and 6 ALD cycles increased catalyst stability without significantly affecting the catalytic performance, whereas 10 cycles caused blockage of the active phase that led to a strong decrease of catalytic activity. Catalyst deactivation modelling and tests at 60% CO conversion served to conclude that 3 to 6 ALD cycles reduced Co/γ-Al2O3 deactivation, so that the technical feasibility of this technique was proven in FTS.
Highlights
Nowadays, Fischer–Tropsch synthesis (FTS) has regained interest motivated by the development of two concepts
The results reported in these works suggest that alternative stabilization methods, such as atomic layer deposition (ALD), may give positive results in terms of preventing FTS cobalt catalyst from deactivation
It is observed that the incorporation of Al2 O3 on the catalyst by ALD cycles did not lead to significant morphology changes, neither in textural properties nor in the cobaltCactive phase (Co) crystallite size
Summary
Fischer–Tropsch synthesis (FTS) has regained interest motivated by the development of two concepts. Despite being discovered more than a century ago, FTS is still facing some economic and technical challenges, which hinder its consolidation as a viable alternative to producing synthetic fuels from renewable sources. In this regard, catalyst deactivation is a major technical issue. The main causes of cobalt catalyst deactivation could be: poisoning due to the presence of S, N and alkali metals, reoxidation of cobalt species, coke deposition, sintering of cobalt crystallites, metal-support solid state reactions and particle attrition Some of these phenomena, such as poisoning by sulfur compounds, can
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