Abstract
Fischer–Tropsch synthesis (FTS) is a promising technology to convert syngas derived from non-petroleum-based resources to valuable chemicals or fuels. Selectively producing target products will bring great economic benefits, but unfortunately it is theoretically limited by Anderson–Schulz–Flory (ASF) law. Herein, we synthesize size-uniformed cobalt nanocrystals embedded into mesoporous SiO2 supports, which is likely the structure of water-melon seeds inside pulps. We successfully tune the selectivity of products from diesel-range hydrocarbons (66.2%) to gasoline-range hydrocarbons (62.4%) by controlling the crystallite sizes of confined cobalt from 7.2 to 11.4 nm, and modify the ASF law. Generally, larger Co crystallites increase carbon-chain growth, producing heavier hydrocarbons. But here, we interestingly observe a reverse phenomenon: the uniformly small-sized cobalt crystallites can strongly adsorb active C* species, and the confined structure will inhibit aggregation of cobalt crystallites and escape of reaction intermediates in FTS, inducing the higher selectivity towards heavier hydrocarbons.
Highlights
Fischer–Tropsch synthesis (FTS) is a promising technology to convert syngas derived from non-petroleum-based resources to valuable chemicals or fuels
The results of transmission electron microscopy (TEM) (Supplementary Fig. 1) and X-ray diffraction (XRD; Supplementary Fig. 2) of the tetradecyltrimethlammonium bromide (TTAB)-capped Co3O4 nanocrystals reveal that the sizes of the Co3O4 nanocrystals increase with the prolonged hydrothermal duration
It is demonstrated that the embedment of cobalt into mesoporous silica support, likely water-melon seeds inside pulps, is a promising strategy to precisely control the crystallite size of the cobalt based FTS catalysts
Summary
Fischer–Tropsch synthesis (FTS) is a promising technology to convert syngas derived from non-petroleum-based resources to valuable chemicals or fuels. We successfully tune the selectivity of products from diesel-range hydrocarbons (66.2%) to gasoline-range hydrocarbons (62.4%) by controlling the crystallite sizes of confined cobalt from 7.2 to 11.4 nm, and modify the ASF law. Cobalt will gradually aggregate with proceeding of FTS reactions, which probably brings conflict results on function of crystallite sizes of cobalt on selectivity of products. We can successfully tune the selectivity of the FTS products from the diesel fraction (66.2%) to the gasoline fraction (62.4%) by controlling the crystallite sizes from 7.2 to 11.4 nm of the confined cobalt catalysts. It should be noticed that the small-sized cobalt crystallites with the confined structure interestingly give the large chain growth probability (α) and the high selectivity towards heavy hydrocarbons
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