Abstract
The effect of support material pretreatment temperature, prior to adding the active phase and promoters, on Fischer–Tropsch activity and selectivity was explored. Four iron catalysts were prepared on silica-stabilized alumina (AlSi) supports pretreated at 700 °C, 900 °C, 1100 °C or 1200 °C. Addition of 5% silica to alumina made the AlSi material hydrothermally stable, which enabled the unusually high support pretreatment temperatures (>900 °C) to be studied. High-temperature dehydroxylation of the AlSi before impregnation greatly reduces FeO·Al2O3 surface spinel formation by removing most of the support-surface hydroxyl groups leading to more effectively carbided catalyst. The activity increases more than four-fold for the support calcined at elevated temperatures (1100–1200 °C) compared with traditional support calcination temperatures of <900 °C. This unique pretreatment also facilitates the formation of ε′-Fe2.2C rather than χ-Fe2.5C on the AlSi support, which shows an excellent correlation with catalyst productivity.
Highlights
Fisher–Tropsch synthesis (FTS) is a catalytic process that converts carbon sources like natural gas, coal and biomass into more valuable hydrocarbon fuels
We explore the effect of support pretreatment temperature on the catalytic performance of iron catalysts supported on AlSi
To 1200 ◦ C, i.e., surface area decreases from 331 m2 /g to 76 m2 /g and pore volume decreases from
Summary
Fisher–Tropsch synthesis (FTS) is a catalytic process that converts carbon sources like natural gas, coal and biomass into more valuable hydrocarbon fuels. The FTS industry uses supported cobalt and unsupported iron catalysts [1,2]. Iron catalysts are preferred over cobalt for FTS from coal or biomass because of their low cost, low methane selectivity and high water–gas shift (WGS). Unsupported iron FT catalysts are limited by their weak mechanical strength making them a poor option for slurry-bubble column reactors, the most thermally efficient and economical FT reactors [3]. Supported iron FT catalysts have historically had poor activities and selectivities making them commercially unavailable [4,5,6]. Potassium and copper are structural promoters often used in industrial iron FT catalysts. Copper reduces the temperature required for the reduction of iron oxides through enhanced H2 dissociation [7,8,10]
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