Active Fischer-Tropsch Catalysts Research Articles

Preparation of a Novel Active Fischer–Tropsch Co–Ni Catalyst Derived from Metal-Organic Framework

In the present study, a typical metal-organic framework has been employed for preparation of a novel active Fischer–Tropsch Co–Ni catalyst. Co–Ni catalyst was prepared by glycine–MOF combustion method and was heated in a tube furnace (2°C min–1) under air at 750°C for 6 h. Scanning electron micrograph of metal-organic framework shows regularly cubic shaped crystals and they were being deformed into a low density, loose and porous material after it was calcined in the tube furnace. BET surface area and pore volume are 276 m2/g and 0.31 cm3/g respectively. This active catalyst showed selectivity for long-chain hydrocarbons $$\left( {{\text{C}}_{5}^{ + }} \right)$$ of ~52% and for short-chain hydrocarbons (C2–C4) 30%. The relatively high activity (TOF of 2.08 s–1 at 340°C) was ascribed to its high porous structure and large pore size of the catalyst which facilitated the diffusion of hydrocarbons. The unique features of this catalyst, including structural tailor ability such as high surface area, porosity, homogeneity and stability enable it to be an active Fischer–Tropsch catalyst.

Influence of Promotion on the Growth of Anchored Colloidal Iron Oxide Nanoparticles during Synthesis Gas Conversion.

Using colloidal iron oxide nanoparticles with organic ligands, anchored in a separate step from the supports, has been shown to be beneficial to obtain homogeneously distributed metal particles with a narrow size distribution. Literature indicates that promoting these particles with sodium and sulfur creates an active Fischer–Tropsch catalyst to produce olefins, while further adding an H-ZSM-5 zeolite is an effective way to obtain aromatics. This research focused on the promotion of iron oxide colloids with sodium and sulfur using an inorganic ligand exchange followed by the attachment to H-ZSM-5 zeolite crystals. The catalyst referred to as FeP/Z, which consists of iron particles with inorganic ligands attached to a H-ZSM-5 catalyst, was compared to an unpromoted Fe/Z catalyst and an Fe/Z-P catalyst, containing the colloidal nanoparticles with organic ligands, promoted after attachment. A low CO conversion was observed on both FeP/Z and Fe/Z-P, originating from an overpromotion effect for both catalysts. However, when both promoted catalysts were washed (FeP/Z-W and Fe/Z–P-W) to remove the excess of promoters, the activity was much higher. Fe/Z-P-W simultaneously achieved low selectivity toward methane as part of the promoters were still present after washing, whereas for FeP/Z-W the majority of promoters was removed upon washing, which increased the methane selectivity. Moreover, due to the addition of Na+S promoters, the iron nanoparticles in the FeP/Z(-W) catalysts had grown considerably during catalysis, while those in Fe/Z-P(-W) and Fe/Z(-W) remained relatively stable. Lastly, as a large broadening of particle sizes for the used FeP/Z-W was found, where particle sizes had both increased and decreased, Ostwald ripening is suggested for particle growth accelerated by the presence of the promoters.

Solvent-free anchoring nano-sized zeolite on layered double hydroxide for highly selective transformation of syngas to gasoline-range hydrocarbons

Nano-sized zeolites (NZs) were anchored on the layered double hydroxide consisting of cobalt and aluminum (Co-Al-LDH) using a solvent-free synthesis method (denoted as Co-Al-LDO-NZs). During the synthesis process, Co-Al-LDH was not only employed as a substrate for the growth of nano-sized zeolites but also acting as Al sources to participate in the formation of acid sites in the zeolite. The well-designed catalyst was used as a bifunctional catalyst for highly selective production of gasoline-range hydrocarbons from syngas through Fischer-Tropsch (FT) synthesis. Benefiting from the unique architecture of Co-Al-LDO-NZs, long-chain hydrocarbons formed on the active FT catalyst could diffuse to the zeolites surface, where hydrocracking and isomerization occurred. Furthermore, different from the traditional zeolite-supported FT catalyst, the nanoscale zeolite in Co-Al-LDO-NZs efficiently suppressed the over-cracking of hydrocarbons, lowering the selectivity of undesirable light hydrocarbons (CH4 and C2–C4 alkanes).

Study of temperature-programmed calcination of cobalt-based catalysts under NO-containing atmosphere

Temperature-programmed calcination (TPC) experiments were performed under NO containing atmosphere for alumina supported cobalt catalyst. During these experiments the NO and NO2 concentration of the effluent was measured continuously. It was observed that NO concentrations below 1vol% significantly influence the TPC profile. With increasing NO content in the gas phase from 0 to 1vol% an increasing amount of NO2 evolves at temperatures below 100°C, which is correlated with consumption of NO. These results indicate decomposition of cobalt nitrate forming cobalt hydroxynitrates at low temperatures in the presence of NO. In agreement with literature, increased cobalt dispersion was obtained for materials calcined in NO containing atmosphere. Thus, the present method seems to be interesting for preparation of highly active Fischer–Tropsch catalysts.

Cobalt dispersion, reducibility, and surface sites in promoted silica-supported Fischer–Tropsch catalysts

Cobalt particle size, cobalt reducibility, and metal surface sites in a series of ruthenium- and rhenium-promoted cobalt silica-supported Fischer–Tropsch catalysts were studied by X-ray diffraction, UV–vis spectroscopy, in situ X-ray absorption, in situ magnetic method, X-ray photoelectron spectroscopy, DSC-TGA thermal analysis, and propene chemisorption. The catalysts were prepared by co-impregnation; in several catalyst syntheses, sucrose was added to the impregnating solutions. Mononuclear octahedral cobalt complexes were observed in the catalysts after impregnation and drying. Cobalt repartition on silica in the impregnated and dried catalysts depended primarily on the pH of the impregnating solution. Cobalt repartition was uniform on the silica surface if the pH of the impregnating solution was higher than the point of zero charge (PZC) of silica, but was less uniform at pH below that of the PZC of silica. Cobalt dispersion proceeded during catalyst calcination in air. Decomposition of cobalt nitrate and crystallization of cobalt oxide seemed to be the crucial steps in the preparation of highly dispersed cobalt catalysts. Promotion with noble metals resulted in greater cobalt dispersion, probably due to higher concentrations of cobalt oxide crystallization sites. Addition of sucrose modified the structure of supported cobalt complexes and led to higher temperatures of crystallization of cobalt oxide and to catalysts with extremely high cobalt dispersion. In situ magnetization measurements show that promotion with Ru moderated the temperature of reduction of cobalt oxide to metal phases, whereas the effect was less significant for Re-promoted catalysts. The addition of sucrose during impregnation, although significantly enhancing cobalt dispersion, did not diminish cobalt reducibility. Due to a combination of high cobalt dispersion and reducibility, the ruthenium- and rhenium-promoted catalysts prepared using sucrose had the highest number of cobalt metal surface sites. Fischer–Tropsch reaction rates were determined principally by the number of cobalt surface sites, with high cobalt dispersion and easy reducibility resulting in more active Fischer–Tropsch catalysts.

Support effects in cobalt-based fischer-tropsch catalysis

A range of cobalt catalysts supported on kieselguhr, silica, alumina, bentonite, zeolite Y, mordenite and ZSM-5 was examined for catalytic activity and product selectivity in the Fischer-Tropsch reaction. These results were correlated with catalyst reducibility and adsorptive properties, as well as support acidity, surface area and structure. It was found that high surface area supports give high cobalt dispersions and tend to produce highly active Fischer-Tropsch catalysts, as long as the reducibility of the cobalt is not hindered by metal-support interactions or ion exchange, or that pore diffusion or blocking effects are not taking place. All supports produced catalysts with similar methane, carbon dioxide and higher hydrocarbon selectivities, with carbon dioxide selectivity being low in all cases. The nature of the higher hydrocarbons depended strongly upon support acidity, with the non-zeolitic, low acidity supports producing the classic straight chained Fischer-Tropsch product. Of the zeolite supported catalysts, the most strongly acidic ZSM-5 supported catalyst produced the most highly branched product, followed by the zeolite Y supported catalyst. The straight chained character of the product from the mordenite supported catalyst was explained by the inaccessibility of the primary Fischer-Tropsch products to the mordenite acid sites, due to the mordenite channel system and ion exchange properties, thereby preventing secondary reactions such as isomerisation from occurring.

Anchoring of hydridic clusters by acid–base reactions: new method for the preparation of highly active Fischer–Tropsch catalysts

Hydridic complexes such as HFeCo3(CO)12 can be effectively supported on basic supports such as silica modified by amino donor functions in an acid–base reaction to give highly active Fischer–Tropsch catalysts which give rise to an unusual product distribution.

Utility of the MÖssbauer Effect in the Assessment of Chemical Transformations in Unsupported Catalyst Systems as a Function of the Metal Salt

ABSTRACTThis paper is presented to illustrate the utility of Fe-57 Mössbauer spectroscopy in the physical and chemical characterization of metallic catalysts as a function of preparation and subsequent treatment. The particular example chosen for investigation is the Ru-Fe bimetallic salt system which has significant potential as an active Fischer-Tropsch catalyst. The interpretation of the resulting Mössbauer parameters provides information on the chemical state of the metals as a function of treatment and initial salt properties and allows certain deductions to be made about particle size and solid state properties.