Patent Application
20090197760
The present invention relates to metallic catalysts containing nanoparticles of transition metals, and to a method for their preparation. More particularly the invention relates to catalysts possessing nanoparticles of metals selected from the group comprising Co, Ru, Fe, Pd, and Rh, which are contained in pure ionic liquids, or impregnated on supports selected from zeolites, silicas, aluminas and oxides, forming catalytic systems. In another aspect, the invention also relates to a method for the preparation of the catalysts.
The reaction between carbon monoxide and molecular hydrogen for producing hydrocarbons and oxygen-containing compounds, also known as the Fischer-Tropsch process, is catalysed by a wide range of transition metals such as cobalt, iron and ruthenium immobilized on the most varied types of supports such as silicas, zeolites and oxides (Chernavskii, P. A., Kinetics and Catalysis 2005, 46, 634-640).
It is also known that ionic liquids, also known as fused salts, are constituted of salts derived from tetraalkyl ammonium or phosphonium cations or, more often, from heteroaromatic cations, associated with anions, for example BF4, PF6, CF3SO3, (CF3SO2)2N, CF3CO2 (P. Wasserscheid, T. Welton; Ionic Liquids in Synthesis, VCH-Wiley, Weinheim, 2002; J. Dupont; R. F. De Souza, P. A. Z. Suarez; Chem. Rev.; 2002, 102, 3667; P. Wasserscheid, W. Keim; Angew. Chem. Int. Ed.; 2000, 39, 3773; T. Welton; Chem. Rev.; 1999, 99, 2071), are employed extensively as liquid supports for catalysts based on transition metals.
The ionic liquids most studied and used are those based on 1,3-dialkyl-imidazolium cations as they have unique physicochemical properties such as:
Said catalysts can be employed in conventionally known refining processes, such as hydrocracking, hydroisomerization, or hydrofining; Fischer-Tropsch synthesis, or can be employed in novel processes.
The Fischer-Tropsch process can be carried out with supported catalysts (dissolved or dispersed) in appropriate ionic liquids or immobilized on classical supports such as zeolites or even in the presence of a mixture of ionic liquids with the other supports.
The process of preparation of these catalysts is carried out in two stages that can be sequential or not, for example:
1. Decomposition of compounds of cobalt, iron and/or ruthenium dissolved in ionic liquids followed by direct use in the Fischer-Tropsch reaction;
2. Decomposition of compounds of cobalt, iron and/or ruthenium dissolved in ionic liquids followed by isolation of nanoparticles and re-dispersion of said nanoparticles in the liquids and use in the Fischer-Tropsch reaction;
3. Decomposition of compounds of cobalt, iron and/or ruthenium dissolved in ionic liquids in the presence of the supports or followed by addition of the supports (zeolites, silicas, aluminas or oxides) and use in the Fischer-Tropsch reaction;
4. Decomposition of compounds of cobalt, iron and/or ruthenium dissolved in ionic liquids in the presence of the supports or followed by addition of the supports (zeolites, silicas, aluminas or oxides) and later removal of the ionic liquid and use in the Fischer-Tropsch reaction.
In a series of articles, J. Dupont and co-workers present the preparation of nanoparticles of transition metals in ionic liquids, derived from reaction of transition metal chloride ligands and derivatives of 1,3-dialkyl-imidazolium.
The simple reduction of complexes or salts of iridium (J. Am. Chem. Soc. 2002, 124, 4228-4229), rhodium (Chem.-Eur. J. 2003, 9, 3263-3269), ruthenium (Catal. Lett. 2004, 92, 149-155) or palladium (J. Am. Chem. Soc. 2005, 127, 3298-3299, Adv. Synth. Catal. 2005, 347, 1404-1412) dissolved in ionic liquids derived from 1,3-dialkyl imidazolium, for example, 1-butyl-3-methyl imidazolium tetrafluoroborate, by molecular hydrogen, hydrides or olefins, produces nanoparticles of these metals in the ionic liquids, which are employed as catalysts for reactions of hydrogenation, hydroformylation and C—C coupling.
The decomposition of organometallic complexes of Pt(O) (Inorg. Chem. 2003, 42, 4738-4742) or Ru(O) (Chem.-Eur. J. 2004, 10, 3734-3740) in these ionic liquids also produces nanoparticles of the respective metals that are employed in catalytic processes, principally in the hydrogenation of olefins and arenes.
There are also articles that describe the preparation of nanoparticles of Pd in functionalized ionic liquids (Zhao, D.; Fei, Z.; Geldbach Tilmann, J.; Scopelliti, R; Dyson Paul, J., J. Am. Chem. Soc. 2004, 126, 15876-82) or of Rh in polymeric ionic liquids (Mu, X. D.; Meng, J. Q.; Li, Z. C; Kou, Y., J. Am. Chem. Soc. 2005, 127, 9694-9695).
The present invention relates to a method of synthesis of catalysts constituted of nanoparticles of cobalt, ruthenium and/or iron prepared in ionic liquids preferably derived from the 1-alkyl (C1-C20), 3-alkyl (C1-C20)-imidazolium cation associated with anions of the halide, carboxylate, sulphate, nitrate, sulphonate, phosphate, PF6, BF4, CF3SO3, (CF3SO2)2N and (CF3CF2)2PF3 type, for the Fischer-Tropsch process.
The nanoparticles of Co, Fe and Ru of the present invention were prepared by the decomposition of compounds of Co, Fe or Ru, preferably compounds in oxidation state zero such as metal carbonyls of the type Co2(CO)5, Co4(CO)12, Fe(CO)5, Fe2(CO)8, Fe3(CO)12, Ru3(CO)12, Ru(cod)(cot) where cod=1,5-cyclooctadiene and cot=1,3,5-cyclooctatriene or mixed such as [Ru(Co)3]12—N+ (where N=quaternary ammonium salt), dissolved in ionic liquids preferably derived from the 1-alkyl (C1-C20), 3-alkyl (C1-C20)-imidazolium or 1-alkyl (C1-C20), 2-alkyl (C1-C20), 3-alkyl (C1-C20)-imidazolium cation associated with anions of the halide, carboxylate, sulphate, nitrate, sulphonate, phosphate; PF6, BF4, CF3SO3, (CF3SO2)2N and (CF3CF2)2PF3 type in the absence or presence of hydrogen at various pressures (preferably between 400 and 5000 kPa, i.e., 4 and 50 bar), at temperatures between 30° C. and 300° C. (preferably between 50° C. and 100° C.) for a period between 10 minutes and 72 hours.
The dark mixture obtained containing metallic nanoparticles of the respective metals (Co, Ru, Fe, Pd, Rh, etc.) can be used directly in the Fischer-Tropsch process or mixed with supports such as zeolites, silicas, aluminas or oxides followed or not by removal of the ionic liquid and subsequent use in the Fischer-Tropsch process.
The nanoparticles prepared in the ionic liquids can be isolated preferably by centrifugation and re-dispersed in the ionic liquids or immobilized on the supports and used in the Fischer-Tropsch process.
It should be pointed out that the innovative process for preparation of catalysts proposed here can be used in the preparation of supported catalysts containing more than one active metal, with or without a promoter.
Another embodiment would be combination of the innovative technology disclosed here, with usual techniques of dry impregnation, precipitation of metals, etc.
The examples of the present invention, presented below, illustrate the methodology employed in the preparation of the nanoparticles (Example 1), of the nanoparticles supported on zeolites (Example 2), as well as the performance of a novel catalytic process (Example 3).
Co4(CO)12 (57 mg, 0.1 mmol) dissolved in 10 mL of n-pentane is added to 1 mL of 1-n-decyl-3-methylimidazolium tetrafluoroborate at 15000 with mechanical stirring and under an argon stream. After addition, stirring was maintained for two hours at 150° C. for decomposition of the cobalt precursor.
After this time the stirring was stopped and the dark mixture containing cobalt nanoparticles was cooled to room temperature.
X-ray diffraction patterns were obtained in a SIEMENS D1500 instrument using Bragg-Brentano geometry. The radiation used was copper (Cukα=1.5418 Å). The monochromator used was a graphite crystal, and the equipment was operated using a voltage of 30 kV and a current of 25 mA in a range from 10° C. to 100° C. The solid samples were dispersed in a layer on the glass support and were then analysed.
The diffraction pattern in
Measurements of magnetization were carried out using a field gradient magnetometer, AGM, for nanoparticles isolated from the ionic liquid and a SQUID Quantum Design magnetometer for nanoparticles soaked in ionic liquid.
The analyses were performed with a small aliquot withdrawn directly from the reaction medium of nanoparticles of cobalt, ruthenium and iron prepared in ionic liquids derived from the 1-alkyl (C1-C20), 3-alkyl (C1-C20)-imidazolium or 1-alkyl (C1-C20), 2-alkyl (C1-C20), 3-alkyl (C1-C20)-imidazolium cation associated with anions of the halide, carboxylate, sulphate, nitrate, sulphonate, phosphate, PF6, BF4, CF3SO3, (CF3SO2)2N and (CF3CF)2PF3 type.
The suspensions of the nanoparticles were diluted in the respective ionic liquid (1/10) and the new solution was placed under a copper grating (300 mesh) covered with carbon in such a way that a thin film of this solution, of the order of 100 nm, adheres on the carbon film, providing better visualization in the microscope.
The size distribution of the nanoparticles was determined from the original negative, digitized and expanded to 470 pixel/cm for more precise resolution and measurement.
The histogram of size distribution was obtained by counting approximately 300 particles. The diameter of the particles in the micrographs was measured using Sigma Scan Pro 5 software.
Zeolites Y with the characteristics presented below in Table 1 were used.
a= Surface area, determined by the BET method.
b= Pore diameter, determined by the BJH method.
c= SiO2/Al2O3 ratio, determined by infrared (IV) and X-ray fluorescence (FRX).
d= Size of unit cell determined by X-ray diffraction (DRX).
e= Percentage crystallinity determined by (DRX).
A Fischer-Tropsch reactor was charged with 150 mg of zeolite; 20 mg (0.1 mmol) of RhCl3 hydrate dissolved in 2 mL of methanol and 1 mL BMI.BF4.
The methanol was removed by means of reduced pressure (0.1 mbar) at room temperature for 30 minutes.
The system was immersed in silicone oil and maintained at 75° C., stirring continuously, and 4 atm of pressure of molecular hydrogen was admitted to the system. After the system had darkened, the dark solution containing the nanoparticles supported on the substrate was centrifuged at 3500 rpm and then washed with acetone for various times to remove the ionic liquid. The supernatant was drawn off and the black solid residue was put in a Schlenk tube and dried at reduced pressure and was then characterized.
It is important to note that the two diffraction patterns correspond to the same sample of nanoparticles of Rh supported on zeolite (designated HDT9729).
a= BET Method
b= BJH Method
The surface areas, pore volume and average pore diameter of the commercial zeolites and supported with metallic rhodium nanoparticles (Rh 3.1 wt. %) are presented in Table 2, and were obtained from the nitrogen adsorption-desorption isotherms by the BET method, using the Micrometrics Gemini system at a temperature of 77 K. The samples were preheated at 110° C. under a pressure of 10-1 Pa for 6 hours, and the average pore size distribution was found using the BJH mathematical model based on the nitrogen desorption isotherms.
The test was carried out using a 25 mL batch reactor, which was charged with recently prepared cobalt nanoparticles suspended in 1-butyl-3-methylimidazolium tetrafluoroborate, and pressurized to 50 bar (5000 kPa) solely with a mixture of hydrogen and carbon monoxide (2:1 molar).
The reactor was heated to a temperature of 200° C., with mechanical stirring. After 48 h of testing, it was observed that the initial pressure had dropped by approximately 50%.
The results demonstrate that it is possible to carry out a novel process, where Fischer-Tropsch synthesis would be carried out in a homogeneous medium.
The catalytic mixture can be reused after removing the extraction solvent under reduced pressure.
Although the present invention has been presented according to its preferred embodiments, a person skilled in the art will be aware that conceivable variations and modifications can be made in the present invention, while remaining within its spirit and scope, which are defined by the claims presented below.
| Number | Date | Country | Kind |
|---|---|---|---|
| PI 0800207-0 | Jan 2008 | BR | national |
