The effect of Mg location on Co-Mg-Ru/γ-Al ₂ O ₃ Fischer–Tropsch catalysts

Abstract

The effectiveness of Mg as a promoter of Co-Ru/γ-Al2O3 Fischer–Tropsch catalysts depends on how and when the Mg is added. When the Mg is impregnated into the support before the Co and Ru addition, some Mg is incorporated into the support in the form of MgxAl2O3+x if the material is calcined at 550°C or 800°C after the impregnation, while the remainder is present as amorphous MgO/MgCO3 phases. After subsequent Co-Ru impregnation MgxCo3−xO4 is formed which decomposes on reduction, leading to Co(0) particles intimately mixed with Mg, as shown by high-resolution transmission electron microscopy. The process of impregnating Co into an Mg-modified support results in dissolution of the amorphous Mg, and it is this Mg which is then incorporated into MgxCo3−xO4. Acid washing or higher temperature calcination after Mg impregnation can remove most of this amorphous Mg, resulting in lower values of x in MgxCo3−xO4. Catalytic testing of these materials reveals that Mg incorporation into the Co oxide phase is severely detrimental to the site-time yield, while Mg incorporation into the support may provide some enhancement of activity at high temperature.

Inhibition by Inorganic Dopants of γ‐Alumina Chemical Weathering under Hydrothermal Conditions: Identification of Reactive Sites and their Influence in Fischer–Tropsch Synthesis

“…From these observations, we assume that the different catalytic activities measured on these five systems are related to the amount of metallic Co obtained upon reduction, which stems from the reducibility of CoO and is hampered significantly on 3 %Mg/γ‐Al 2 O 3 ‐500 °C and 3 %Si/γ‐Al 2 O 3 ‐CLD. Mg 2+ has been reported previously to decrease the reducibility and, consequently, the activity of Co catalysts in the FT reaction, supposedly by the insertion of Mg 2+ ions into cobalt oxide . This would explain why the catalyst supported on 3 %Mg/γ‐Al 2 O 3 ‐900 °C, in which Mg 2+ is located deep in the support is more active than its counterpart calcined at 500 °C, in which surface Mg 2+ is available for reaction with Co phases during impregnation or calcination in good agreement with the results of Gallagher et al .…”

“…Mg 2+ has been reported previously to decrease the reducibility and, consequently, the activity of Co catalysts in the FT reaction, supposedly by the insertion of Mg 2+ ions into cobalt oxide . This would explain why the catalyst supported on 3 %Mg/γ‐Al 2 O 3 ‐900 °C, in which Mg 2+ is located deep in the support is more active than its counterpart calcined at 500 °C, in which surface Mg 2+ is available for reaction with Co phases during impregnation or calcination in good agreement with the results of Gallagher et al . A similar decrease of the Co reducibility induced by the pollution of cobalt oxide with Si can be postulated for Co/3 %Si/γ‐Al 2 O 3 ‐CLD.…”

Biofuels and Bioproducts from Wet and Gaseous Waste Streams: Challenges and Opportunities

“…There are also a number of proposals regarding reactor design and process conditions (Okeson et al 2016;Savchenko et al 2016;Todic et al 2016). Catalyst morphology, including nanoparticles, pore sizes, and effective surface area, seems to be another active area of research (Gallagher et al 2016;Ligthart et al 2016;Nikparsa et al 2016). The bottom line is that there seems to be a great deal of interesting work on catalyst development, but it is not clear how the peer-reviewed literature is advancing the cause of making Fischer-Tropsch economically feasible at distributed scales.…”

Summarizing comments on the discussion and a prospectus for urgent future action

“…Rosseinsky and colleague's paper [14] was divided into two parts: (i) high-throughput methods of investigating the optimum sizes of cobalt-based Fischer-Tropsch catalysts using robots to prepare numerous different candidates and (ii) a computational modular assembly approach to the design of a new cathode for the solid oxide fuel cells. Interesting results were achieved in both of these studies.…”