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Cobalt distribution between the external surface and micropores and acidity of the large pore BEA zeolite were controlled by choosing the sequence of impregnation and ion exchange procedures. Higher concentration of ion exchangeable cobalt was observed in the catalyst prepared by ion‐exchange of the zeolite proton form. The presence of Na+ instead of H+ ions in the exchange positions of zeolite favored deposition of cobalt on the external surface. The acid sites in the zeolite micropores can be then restored by subsequent ion exchange of sodium with ammonium nitrate and calcination. The catalytic performance of the cobalt zeolite catalysts prepared using different impregnation and ion exchange procedures was tested in the Fischer‐Tropsch synthesis. Higher reaction rates were observed over the catalysts, which did not contain cobalt ions in the cation sites of the zeolite. Lower methane selectivity, higher selectivity to long chain hydrocarbons and high fraction of isomerized products are observed when cobalt species are located on the zeolite outer surface and acid sites inside the BEA zeolite micropores. Ion launch sequence: Impregnation and ion exchange sequences control metal localization, acidity, diffusion and performance of cobalt‐BEA catalysts for Fischer‐Tropsch synthesis [ABSTRACT FROM AUTHOR]

This paper focuses on the effect of synthesis conditions on the structure of cobalt-ZSM-5 zeolites and the localization, dispersion, and reducibility of cobalt species and their catalytic performance in Fischer-Tropsch synthesis. The zeolite catalysts were prepared by using carbon nanotubes as sacrificial templates. Addition of pristine carbon nanotubes resulted only in a slight increase in the zeolite mesoporosity, whereas the presence of carbon nanotubes impregnated with cobalt drastically modified the zeolite morphology and texture. The zeolite mesoporous volume increased by 3-4 times. The catalysts prepared by using cobalt-impregnated carbon nanotubes as templates showed 5-8 times higher Fischer-Tropsch reaction rates normalized by reducible cobalt compared with the catalysts prepared by conventional impregnation. Higher selectivity to isomerized branched hydrocarbons on these zeolites was attributed to the enhanced diffusion favoring removal of isomerized products and avoiding their cracking. [ABSTRACT FROM AUTHOR]

The performance of supported cobalt and iron catalysts in low and high temperature Fischer–Tropsch synthesis was investigated in the presence of small amounts of ammonia in syngas. Ammonia was co-fed to the reactor either by in-situ hydrolysis of acetonitrile or by addition of aqueous ammonia. The addition of acetonitrile and ammonia resulted in significant irreversible deactivation of alumina supported cobalt catalysts. Lower methane and higher C 5+ hydrocarbon selectivities were observed. Iron based catalysts did not show any noticeable deactivation in the presence of acetonitrile or ammonia. Moreover, Fischer–Tropsch reaction rate slightly increased after addition of the nitrogen-containing compounds to silica and alumina supported samples. Lower methane selectivity and higher C 2 –C 4 olefin to paraffin ratio were observed in the presence of ammonia when the catalysts were reduced in hydrogen. Iron catalysts activated in carbon monoxide did not demonstrate any significant effect of ammonia on the selectivity. The catalytic data were explained by irreversible formation of inactive cobalt nitrides in cobalt catalysts and transformation of metallic iron and iron oxides in the presence of acetonitrile and ammonia into iron nitrides and iron carbides active in Fischer–Tropsch synthesis. [ABSTRACT FROM AUTHOR]

This study focuses on the effects of the localization of Co species, zeolite structure, and acidity on the performance of Co bifunctional catalysts promoted with Pt for the direct synthesis of iso-paraffins from syngas. ZSM-5, MOR, and BEA were chosen as zeolites with different structures and pore diameters. The catalysts were prepared either by incipient wetness impregnation or by the mechanical mixing of the zeolite with a conventional silica-supported Co catalyst. The increase in the pore size and open character of the zeolite structure from ZSM-5 to BEA resulted in a higher fraction of Co located inside the pores of the catalysts prepared by impregnation. The catalytic performance was affected strongly by the zeolite acidity, pore structure, and Co distribution between the pores and the external surface. The selectivity to short-chain iso-paraffins is affected principally by the zeolite acidity, whereas the selectivity to long-chain branched hydrocarbons mostly depends on steric effects. [ABSTRACT FROM AUTHOR]

Highlights: [•] Different cobalt and iron species as a function of Co/Fe ratio. [•] Higher dispersion of cobalt and iron in bimetallic catalysts. [•] Much easier iron and more difficult cobalt reducibilities in bimetallic catalysts. [•] Cobalt–iron mixed species in both calcined and reduced catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cobalt-bismuth nanoparticles in carbon nanotubes supported catalysts. • Noticeable increase in catalyst stability on the promotion. • Migration of metallic bismuth occurring leading to its redispersion. • Enhancement of cobalt reduction on the promotion. • Preferential bismuth localization at the steps and edges of cobalt nanoparticles. Metal nanoparticles on the surface of porous supports have found numerous applications in different areas of science. Fischer-Tropsch synthesis, which proceeds on the surface of cobalt metal nanoparticles, is an efficient way to convert renewables and fossil feedstocks into alternative fuels. The stability of cobalt catalysts is an essential and even crucial parameter and can be significantly improved by promotion. In this paper, a combination of operando Quick-XAS, NAP-XPS, high resolution electron microscopy imaging, DFT modeling alongside with Fischer-Tropsch catalytic experiments has provided deep insights into the evolution of bismuth promoter and structure of cobalt-bismuth nanoparticles in the catalysts supported by carbon nanotubes. We uncovered noticeable migration of metallic bismuth occurring during the reduction step, which leads to bismuth redispersion over the surface of cobalt nanoparticles. Cobalt reduction is facilitated in the presence of bismuth. The working Fischer-Tropsch catalyst contains cobalt-bismuth bimetallic nanoparticles, with bismuth located in the nanoparticle shell. The promotion with bismuth has resulted in a noticeable increase in catalyst stability. Characterization and DFT modeling suggest preferential localization of bismuth mobile promoter at the steps and edges of cobalt nanoparticles, which hinders cobalt sintering and carbon deposition and improves the catalyst stability. [ABSTRACT FROM AUTHOR]

This paper investigates the role of the carbon pre-coating of silica in controlling the structure and performance of silica supported cobalt catalysts for Fischer–Tropsch synthesis. It was found that coating silica support with carbon led to stabilization of highly dispersed cobalt oxide with partial cobalt reduction during thermal treatment in inert atmosphere. The size of cobalt oxide nanoparticles decreased from 10–15 nm over the conventional silica supported catalyst prepared without carbon pre-coating to 5–6 nm over samples with high carbon content. Calcination in air of the samples prepared using carbon pre-coating led to only partial increase in the cobalt oxide nanoparticle size to 7–8 nm with uniform particle size distribution. Deep encapsulation of cobalt nanoparticles was the major reason for low activity of the catalysts containing the carbon layer. Removal of carbon layer by calcination in air resulted in a major enhancement of the catalytic performance. Higher catalytic performance was observed with the catalysts prepared with higher carbon content and containing smaller cobalt particles. The maximum FT activity was almost twice higher compared to the reference uncoated catalysts. Higher selectivity to long chain hydrocarbons and low methane selectivity were also observed. [ABSTRACT FROM AUTHOR]

Cobalt nanoparticles in the range of 1.7–7 nm were synthesized in water using sodium borohydride as reducing agent and subsequently immobilized on TiO 2 . Both colloidal and TiO 2 supported NPs were characterized by TEM, XRD, HRTEM, XPS, TGA, ICP techniques and their catalytic performance of the supported catalysts evaluated in the Fischer–Tropsch synthesis. As a general trend, an increase in activity and TOF was observed when the particle size decreased. These results were rationalized by the higher reducibility of the catalysts bearing the smaller nanoparticles. The unconventional stability of these relatively small CoNPs in FTS was attributed to the promoting effect of boron on the stability of the cobalt nanocrystals. [ABSTRACT FROM AUTHOR]