Design of Cobalt Fischer–Tropsch Catalysts for the Combined Production of Liquid Fuels and Olefin Chemicals from Hydrogen-Rich Syngas

Abstract

Adjusting hydrocarbon product distributions in the Fischer–Tropsch (FT) synthesis is of notable significance in the context of so-called X-to-liquids (XTL) technologies. While cobalt catalysts are selective to long-chain paraffin precursors for synthetic jet- and diesel-fuels, lighter (C 10– ) alkane condensates are less valuable for fuel production. Alternatively, iron carbide-based catalysts are suitable for the coproduction of paraffinic waxes alongside liquid (and gaseous) olefin chemicals; however, their activity for the water–gas-shift reaction (WGSR) is notoriously detrimental when hydrogen-rich syngas feeds, for example, derived from (unconventional) natural gas, are to be converted. Herein the roles of pore architecture and oxide promoters of Lewis basic character on CoRu/Al 2 O 3 FT catalysts are systematically addressed, targeting the development of catalysts with unusually high selectivity to liquid olefins. Both alkali and lanthanide oxides lead to a decrease in turnover frequency . The latter, particularly PrO x , prove effective to boost the selectivity to liquid (C 5–10 ) olefins without undesired WGSR activity. In situ CO-FTIR spectroscopy suggests a dual promotion via both electronic modification of surface Co sites and the inhibition of Lewis acidity on the support, which has direct implications for double-bond isomerization reactivity and thus the regioisomery of liquid olefin products. Density functional theory calculations ascribe oxide promotion to an enhanced competitive adsorption of molecular CO versus hydrogen and olefins on oxide-decorated cobalt surfaces, dampening (secondary) olefin hydrogenation, and suggest an exacerbated metal surface carbophilicity to underlie the undesired induction of WGSR activity by strongly electron-donating alkali oxide promoters. Enhanced pore molecular transport within a multimodal meso-macroporous architecture in combination with PrO x as promoter, at an optimal surface loading of 1 Pr at nm –2 , results in an unconventional product distribution, reconciling benefits intrinsic to Co- and Fe-based FT catalysts, respectively. A chain-growth probability of 0.75, and thus >70 C% selectivity to C 5+ products, is achieved alongside lighter hydrocarbon (C 5–10 ) condensates that are significantly enriched in added-value chemicals (67 C%), predominantly α-olefins but also linear alcohols, remarkably with essentially no CO 2 side-production (<1%). Such unusual product distributions, integrating precursors for synthetic fuels and liquid platform chemicals, might be desired to diversify the scope and improve the economics of small-scale gas- and biomass-to-liquid processes.

Auto-tandem catalytic reductive hydroformylation with continuous multiphase catalyst recycling

“…1–3 One pathway to synthetic fuels is the biogas to olefin-selective Fischer–Tropsch (FT) concept. 4 By subsequent functionalization of the FT-derived olefins, tailor-made fuel properties are accessible. The hydroformylation/hydrogenation sequence to alcohols of FT olefins allows for further utilization of bio-derived syngas for the production of alcohols.…”

Direct Conversion of Syngas to Higher Alcohols via Tandem Integration of Fischer–Tropsch Synthesis and Reductive Hydroformylation

“…It has been recently shown by us that the design of cobalt-based FTS catalysts with multimodal porosities enables the conversion of syngas into synthetic linear hydrocarbons with unconventionally high shares of C 3 + olefins. [18,21] Here, these previous findings have been Scheme 1. Production of higher alcohols from syngas via the integration of Fischer-Tropsch synthesis (FTS) and reductive hydroformylation (RHF) in a tandem process.…”

Auto-Tandem Catalytic Reductive Hydroformylation in a CO2-Switchable Solvent System

“… 1 − 3 One pathway toward renewable fuels is olefin-selective Fischer–Tropsch (FT) synthesis with bio-syngas. 4 The FT-derived olefins allow for subsequent upgrading of such fuels and enable tailor-made fuel properties. Potential additives to biosynthetic fuels are alcohols, which are able to reduce emissions and improve combustion characteristics while aiding to achieve drop-in capability.…”