Catalysts For FT Synthesis Research Articles

Correlation of metal–organic framework structures and catalytic performance in Fischer–Tropsch synthesis process

Two typical metal–organic frameworks (MOFs), i.e. tris(pyridine-2-carboxylato)-cobalt(III) monohydrate (MOF-1) and (μ2-pyridine 2,6-dicarboxylato)(pyridine 2,6-dicarboxylato) pentaaqua dicobalt(II)dihydrate (MOF-2) were employed for preparation of cobalt Fischer–Tropsch catalysts. Both MOF-derived catalysts were obtained by direct pyrolysis in N2 atmosphere at 500 °C. The pyrolysis of desired MOFs resulted nanoparticles embedded in the porous carbon matrix. Such catalysts can serve as useful catalysts for FT synthesis. Co-MOF-1 derived catalyst exhibited carbon monoxide conversion of 74.8% and selectivity towards long-chain hydrocarbons (C5+) of 49.2%. Also, it showed selectivity for short-chain hydrocarbons (C2–C4) of 36.19% for 50 h on steam while Co-MOF-2 derived catalyst displayed CO conversion of 81.6% and selectivity for long-chain hydrocarbons (C5+) and short-chain hydrocarbons of 56.8% and 28.2%. The superb activity and catalytic efficiency can be ascribed to the MOF precursors structures. This study investigated the relationship between MOF structure and catalytic performance and presented a new approach to design novel super active catalysts with preferable selectivity for Fischer–Tropsch synthesis by opting the suitable MOF precursors.

Iron Fischer-Tropsch Catalysts Prepared by Solvent-Deficient Precipitation (SDP): Effects of Washing, Promoter Addition Step, and Drying Temperature

A novel, solvent-deficient precipitation (SDP) method for catalyst preparation in general and for preparation of iron FT catalysts in particular is reported. Eight catalysts using a 23 factorial design of experiments to identify the key preparation variables were prepared. The catalysts were characterized by electron microprobe, N2 adsorption, TEM, XRD, and ICP. Results show that the morphology of the catalysts, i.e., surface area, pore volume, pore size distribution, crystallite sizes, and promoter distribution are significantly influenced by (1) whether or not the precursor catalyst is washed, (2) the promoter addition step, and (3) the drying condition (temperature). Consequently, the activity, selectivity, and stability of the catalysts determined from fixed-bed testing are also affected by these three variables. Unwashed catalysts prepared by a one-step method and dried at 100 °C produced the most active catalysts for FT synthesis. The catalysts of this study prepared by SDP compared favorably in activity, productivity, and stability with Fe FT catalysts reported in the literature. It is believed that this facile SDP approach has promise for development of future FT catalysts, and also offers a potential alternate route for the preparation of other catalysts for various other applications.

Cobalt-supported carbon and alumina co-pillared montmorillonite for Fischer–Tropsch synthesis

The natural Na-type montmorillonite (Na-MMT) was co-pillared by aluminium polycation and cetyltrimethylammonium bromide (CTAB), and then carbonized in an argon atmosphere to obtain carbon and alumina modified MMT (C-Al-MMT). 20wt.% cobalt was loaded on C-Al-MMT via the impregnation method by using Co(NO3)2·6H2O as a precursor. The materials were characterized by XRD, H2-TPR, H2-TPD, NH3-TPD, O2 titration, TEM, and N2 adsorption–desorption at low temperature. From the composition of different C-Al-MMT, a competitive exchange between CTAB and aluminium polycation during the co-pillaring process was clearly found, leading to a significant change of the textural properties of C-Al-MMT with increasing the content of carbon. Moreover, the introduction of carbon clearly decreased interactions between cobalt and the support, leading to an increased extent of reduction of cobalt. As a result, an active Co/C-Al-MMT catalyst for FT synthesis was obtained by optimizing the content of carbon.

Fischer–Tropsch synthesis over alumina supported cobalt catalyst: Effect of promoter addition

In order to improve the activity of Co/Al2O3 catalyst for FT synthesis, loading effect of metal promoter on Al2O3 support was examined. In this study, total 13 kinds of metal (Mg, Ca, Sr, Ba, Y, La, Ce, Ti, V, Mn, Zn, Zr and Mo) were employed as promoters and θ-Al2O3 prepared by the calcination of commercial boehmite was used as support. Co/Al2O3 catalysts loaded with various metal promoters were prepared by a sequential impregnation method. Loading of Mn, V and Mo on Al2O3 support decreased Co reducibility and surface area of Co metal, but increased intrinsic activity per active Co metal sties (i.e. TOF). On the other hand, metal additives other than Mn, V and Mo varied Co reducibility and Co surface area, but did not influence TOF. High overall activity was obtained over Co/Al2O3 catalysts loaded with rare earth elements (e.g. La and Ce), which was due to the high surface area of Co metal. We also examined the co-loading of La and V promoters on Al2O3 support. Co/Al2O3 catalysts loaded with both La and V (Co/La+V/Al2O3) showed higher activity than those loaded with either La or V. CO conversion rate over the best Co/La(2)+V(0.5)/Al2O3 catalyst was 1.6 times as high as that over bare Co/Al2O3 catalyst. Over the Co/La+V/Al2O3 catalyst, La and V promoters cooperatively improved Co reducibility, Co surface area and TOF, resulting in an increase of overall catalytic activity.

Fischer–Tropsch synthesis over alumina supported cobalt catalyst: Effect of crystal phase and pore structure of alumina support

Effect of crystal phase and pore structure of Al2O3 support was examined in order to improve the activity of Co/Al2O3 catalysts for FT synthesis. Total 18 kinds of Al2O3 supports having different crystal phase and pore structures were prepared by the calcination of commercial boehmite and gibbsite under various conditions. Cobalt was loaded on these Al2O3 supports by the impregnation, drying and calcination. Activity of Co/Al2O3 catalyst for FT synthesis was evaluated with a continuously stirred tank reactor. Structure of Co particles and activity of Co/Al2O3 catalysts strongly depended on the pore structure (i.e. surface area and pore size) of Al2O3 support rather than the crystal phase. Among the examined samples, the highest activity was obtained over the catalyst, which was prepared from θ-Al2O3 having the moderate surface area (84m2g−1). When Al2O3 supports having the moderate surface area were used, the formation of Co particles having high dispersion and relatively uniform size was promoted by pores of suitable size and led to the enhancement of overall catalytic activity.

Use of in situ Mossbauer Spectroscopy and X-Ray Diffraction Techniques for the Characterization of Activated Fe-Ce Catalysts Employed in Fischer-Tropsch Synthesis

Several Fe-Ce catalysts for FT synthesis were prepared following two different methods: coprecipitation from Fe and Ce nitrate solutions and a physical mixture of pure Fe and Ce oxide precursors. Previously to CO hydrogenation, catalysts were activated in syngas (50 ml/min, H2/CO = 2) at 553 K for 1 h at atmospheric pressure. The iron phases de- veloped after activation pretreatment were identified by XRD and in situ Mossbauer spectroscopy with the objective to study the effect of the addition of cerium on the reduction behavior and catalytic properties of Fe systems. A good correla- tion between iron phases detected by both techniques was found. The results revealed that the cerium oxide in the samples prepared by coprecipitation produces two effects: (i) lower reduction rate leading to the metastable Fe1-xO species, and (ii), a decrease in the crystallite size of the iron species upon increasing Ce-contents, as inferred from an increase in su- perparamagnetic species detected by in situ Mossbauer spectroscopy. Since iron carbides are the real active phases in FT synthesis, the stabilization of Fe1-xO phase after activation is suggested to be responsible for the drop in catalytic activ- ity in Fe-Ce catalysts prepared by coprecipitation during FT synthesis.

95/04595 Effects of promoters on the Fe-Mn catalyst for FT synthesis

95/04595 Effects of promoters on the Fe-Mn catalyst for FT synthesis

95/00319 Effect of promoters on the co-precipitated [formula omitted] catalyst for FT synthesis. IV. Study on performance of the catalysts for FT synthesis

95/00319 Effect of promoters on the co-precipitated [formula omitted] catalyst for FT synthesis. IV. Study on performance of the catalysts for FT synthesis

95/00320 Effect of promoters on the co-precipitated [formula omitted] catalysts for FT synthesis. III. MES analysis of the catalysts

95/00320 Effect of promoters on the co-precipitated [formula omitted] catalysts for FT synthesis. III. MES analysis of the catalysts