Catalyst supports made from silicon carbide with TIO2 for Fischer-Tropsch synthesis

Catalyst supports to silicon carbide coated ti0₂ for the Fischer-Tropsch synthesis

The present invention relates to heterogeneous catalysis, and more particularly to supports for catalysts and the catalysts that can be used in heterogeneous catalysis. It particularly relates to a novel catalyst support and a new catalyst for the Fischer-Tropsch reaction. The novel catalyst carrier belongs to the supports based porous silicon carbide (SiC-), in particular containing SiC, modified by a surface deposition ti0₂ .

The Fischer-Tropsch reaction converts a mixture of CO and hydrogen to hydrocarbons. There are two types of catalysts for the Fischer-Tropsch reaction: the iron-based catalysts, which operate optimally at a temperature of approximately 350 °c (called "catalyst ft high temperature"), and the cobalt catalysts, which operate at a lower temperature, typically below 250 °c. They are mainly composed of an active phase and an oxidic support. An overview of the state of the technique on the catalysts for the reaction TFs cobalt based is given in the article " Tea is a cobalt-based on selectivity d' Fischer Tropsch catalysts: demonstration of Common responsable zu zu-menthane and longterm program chain hydrocarbon sensor " by S. Lôgdberg and Al, released in 2010 in J ridges (DOI of: 10.1016/jcat 2010.06.007.). The supports oxides are mainly formed of alumina, silica and optionally titanium dioxide. The supports oxides are excellent for making catalysts active for the reaction and ft, but they also suffer from drawbacks such as their very low thermal conductivity, a low hydrothermal strength, the presence of acid sites surface (alumina), low mechanical strength especially for extruded (silica and titania) and low resistance to attrition for microbeads used in an ebullated bed (especially for silica and ti0₂ ).

In order to enhance the mechanical stability and hydrothermal supports oxides, has been to modify these supports. Include alumina promoted lanthanum oxide the₂ 0₃ (U.S. patents 5,537,945 and US 6,255,358 (the ENERGY International TX), U.S. 7,163,963 (Conoco that Phillips CO)), Si (request US Patent 2005/0124490 (rafter Texaco or TX), US Patent 7,365,040 (Sasol's Hub)) and at Ti or Zr (US Patent 6, 975, 7209 (Sasol's Hub)). Supports spinel were also provided (requests to WO 2006/067285 (Institute French petroleum) and US 2007/0161714), as well as carriers in amorphous silica (US Patent request 2010/0311570) for increasing the resistance to attrition. The alumina used is in general largely L'alumine Y, but was also used alumina supports comprising a majority of α alumina (US Patent 7,351,679 (Statoil in the ASA)).

It has been reported in the literature that the carriers in ti0₂ enable the manufacture of cobalt catalysts extremely selective (C._{+ 5} ) for a ft (see the publications in the review of ridges Today of, 100 (2005) v., e. 343 - 347 and in the eyes of ridges, flight. 236 (2005), p 139, as well as in the Amazon has ridges: generally, flight. 210 P (2001) 137 - 150). However, the authors indicate that their mechanical strength is too low.

The ti0₂ is normally used to increase interaction with the particles of the active phase. It has been reported in the literature that a silica support covered with a layer of ti0₂ has been found to increase the activity and selectivity of a silica support. The results obtained on such a siliceous support promoted with the ti0₂ (see Publication " Preparing supporting OC influences patterning methods have Catalytic activity consisted d' co/ti0 NDA₂ - Hf0.001₂ zu Fischer Tropsch constraint " S. mu and Al, issued in 2009 in the review Catal. Mutat. 133, e. 341 - 345, and publishing S. Hinchiranan and Al issued in 2008 in the review process for fuel oil. Carcinog. 89, e. 455 - 459) show significant enhancement of catalytic activity in T-synthesis. Introducing the ti0₂ in the holder also modifies the selectivity to liquid hydrocarbons. However, depending on the mode of deposition and the configuration of the test TFs, fixed bed or bed bullant, the influence is different, G.C.. an improvement in the case of a test a ft fixed bed mode and a slight drop in the case of a test mode stirred bed. In all cases, the enhancement of the catalytic activity in ft is attributed to an improved dispersion particles of cobalt to a smaller size in the presence of the ti0₂ .

Finally, fixed beds in tubular reactors, the use of supported catalysts on β - θ ΐΟ allows tempering the thermal variations in the catalytic bed due to the high thermal conductivity of material 8 ΐ β - (3. All of these advantages help operate the T synthesis under more stringent conditions in order to improve the productivity.

However, a catalyst supported on a material in β - δ ΐΟ is less active than its peer supported on oxides.

The present invention aims at producing a new type of support based on silicon carbide (SiC-) for the reaction of Fischer-Tropsch synthesis (STF) with improved stability and efficiency as well as selectivity.

According to the invention, the problem is solved by depositing the active phase on a titanium oxide layer (ti0₂ ) very finely divided, comprised of nanoparticles, which at least partially covers the surface of the macroporous and meso-porous SiC porous support. The silicon carbide is preferably p-SiC at least macroporosity and a meso-porosity. It may be for example granules, beads or a foam of P-SiC composite. The ti0₂ is preferably anatase.

The inventors have observed that when cobalt is deposited on a support according to the invention based on silicon carbide (and in particular on a cellular foam into P-SiC composite) coated ti0₂ , this increases significantly the activity in T synthesis, while maintaining a relatively high selectivity to liquid hydrocarbons greater than 90%. The method of deposition of the surface layer of ti0₂ is easy to implement and that for all types and forms of support.

This mixed support has the advantageous properties from both polytype beta of silicon carbide SiC-^ -) and titanium dioxide in particular in its anatase form. Among these properties, it may be mentioned for the β - ε ΐΟ its excellent heat conductivity, porosity bimodal meso and macroporous, excellent chemical resistance and hydrothermal and high mechanical strength. The titanium dioxide in anatase form allows the fine dispersion of particles of active phase.

The method of synthesis according to the present invention freely controls the morphology and size of media depending on the configuration of the reactors used. The catalysts prepared from these cell-coated supports ti0₂ in STF have high activity as compared to that measured on a catalyst deposited on homologous β - θ ti0 layer 10 without₂ . In addition, the catalytic performance of the catalysts supported on 10 covered ti0 β - θ₂ are very stable over time.

According to an essential aspect of the invention, the deposition of ti0₂ is formed by a sol-gel method using a liquid phase precursor ti0₂ . This gives better results compared to a deposition of crystals of ti0₂ , e.g. from a powder dispersion ti0₂ (known method leading to a deposit called "wash"). More particularly, this invention involves the following steps:

(has) is fed with a support the P-SiC high porosity,

(d) preparing a solution of at least one precursor ti0₂ ,

(d) impregnating said support by said solution,

(D.) drying said impregnated support,

(I) said impregnated support is calcined to convert the precursor ti0₂ in ti0₂ .

This process, which forms the first object of the present invention, leads to the formation of crystallites ti0₂ on the macroporous and mesoporous surface. This avoids the formation of a crust on the macroporous surface which prevents access of the reaction gas to the mesopore and micropore. This is reflected by the fact that the pore distribution of the support is not significantly altered by depositing crystallites ti0₂ on the macroporous and mesoporous surface of the support.

In this method, said support into P-SiC composite can in particular be in the form of extrudates, pellets, beads, microbeads, or cellular foam.

The surface area of the support resulting from the method of the invention is at least 15 meters²/ gm, and preferably at least 20 M.²/ gm,

The contribution microporous to the surface area of said support is advantageously less than 5 M.²/ grams, and even more preferably less than 3.5 M.²/ gm.

Said calcination (step (I)) is preferably performed at a temperature of between 400 °c and 1000 °c, and preferably between 900 °c and 500 °c. The rise in temperature is advantageously carried out with a slope of between 1.5 °c/min and 3.5 °c/minute, and preferably between 1.5 °c/min. et2, 5 °C/minute.

A second object of the invention is a catalyst carrier which is obtainable by the process according to the invention, described above. Advantageously, its mass content (% therein) in ti0₂ relative to that (100 Y) SiC is between 3% and 30%, and preferably between 5% and 20%.

A third object is a catalyst obtained by depositing an active phase on the catalyst support according to the invention, characterized in that said active phase is cobalt metal, metallic iron or a mixture of both, finely divided.

Advantageously, it comprises between 5% and 40% and preferably between 10% by mass and 25% mass (expressed relative to the weight of the carrier) of cobalt on a support whose mass ti0₂ SiC is comprised between 5% / 20% and.

Advantageously, the content ti0₂ is less than 0.02 grams per m² of SiC surface area of the support, and preferably less than 0,013 grams per m² specific surface of the support member made of SiC.

A fourth object of the invention is the use of a catalyst support according to the invention or of a catalyst according to the invention for the Fischer-Tropsch reaction.

A final object of the invention is a process for catalytic conversion of co and hydrogen to hydrocarbons, characterized in that it employs a catalyst according to the invention.

In Figures 1 to 10 illustrate embodiments of the invention.

The fig. 1 shows curves of pore distribution by sorptométrie to nitrogen. The fig. 1a watch these curves for three samples: P-SiC(diamonds); 10% ti0₂ the P-SiC / 2 (squares) for example; 21% ti0₂ 79% β - ΘΟ //according to the example 4 (triangle). The fig. 1b watch, expanded in abscissa, these curves for P-SiC composite (diamonds) and 10% ti0₂/ β-according to the example 2 (squares), these two samples being the same as in Figure 1a, and in addition to the curve corresponding to 10% co/10% ti0₂/ P-SiC(cross) according to example 7.

The fig. 2 shows the X-ray diffraction diagrams of cobalt catalysts supported on P-SiC and 10% ti0₂/ P SiC after calcination in air at 350 °c during 2 hours and to a reduction under h₂ to 300 °c. For comparison the diagrams of the carrier alone, pure and covered ti0₂ , are also presented on the same figure. The insert: enlargement on the diffraction peak cobalt metal showing a widening of the half-value width in the presence of the ti0₂ . Samples: (has)P-SiC; (d) 10% of TiO₂/ P-SiC(according to the example 2); (d) 10% cosolvent/P-SiC(according to the example 5); 10% co/10% of TiO (D.)₂/ P-SiC(according to the example 7).

The fig. 3 shows micrographs obtained by scanning electron microscopy (SEM) at different magnifications of two samples: (has) and (b.): 10% cosolvent/P-SiC(according to the example 5). (C.) and (D.): 10% co/10% ti0₂/ P-SiC(according to the example 7). The length of the bars is indicated at the bottom right of each micrograph: 1 MW (has) and

(C.), 200 nm (d) and (D.).

The fig. 4 shows a micrograph obtained by transmission electron microscopy (TEMs) of an area of the support 10% ti0₂/ p sic obtained according to example 2. The fig. 4 (has) shows the TEM images, the fig. 4 (d) mapping the obtained chemical energy filtering mode for identifying the areas containing Ti (white) and those containing Si (darkly).. It is observed that the layer of ti0₂ covers much the SiC particles. The length of the bar corresponds to 50 nm.

The fig. 5 shows two views obtained by transmission electron microscopy filtering mode energy (EFTEM) and in three-dimensional representation of an area of the catalyst 10% co/21% ti0₂ 79% - the P-SiC example 9 (comparative) chemical in mapping mode (the two images correspond to the front and back of the same area). See the distribution of the ti0₂ (white) and SiC (gray) which are distributed in the surface of the solid. Content of cobalt particles (black): large particles deposited on the areas of SiC and a few rare particles, considerably smaller, deposited on the areas of ti0₂ .

The fig. 6 watch other two micrographs obtained by transmission electron microscopy in cross-section of two particles (Figure 6 (has) and (d)) catalyst 10% co/21% ti0₂ 79% - the P-SiC example 9 (comparative). The images were taken mode energy loss spectroscopy (EELS) electrons. Color: white=coextruded; black=Tl; gray=if.

The fig. 7 a catalyst 10% co/10% TiO2₂/ SiC. It shows a micrograph obtained by transmission electron microscopy (TEMs) (fig. 7 (has)) and filtering mode energy (EFTEM) (Figure 7 (d), 7 (d), 7 (d-) respectively for mapping of Si, Ti and CO)) of an area of the catalyst 10% co/10% TiO2₂ the P-SiC / example 7. The fig. 7 (D.) estimating an average particle size of 20 nm to about cobalt, the length of the bar being of 100 nm. Figures 7 (I) and 7 (e) show the same images that Figures 7 (has) and 7 (d);

they are slightly enlarged. (1) The area marks and (2) on the Figure 7 (I) and 7 (e) are enlarged in Figures 7 (gm) and (hr) for the zone (1) and Figure 7 (the I) and g) for the area (2), wherein the Figures 7 (gm) and (I-) are micrographs EMT and Figures 7 (hr) and g) micrographs EFTEM titanium; the length of the bar is 50 nm.

The fig. 8 shows the activity and selectivity (MSR) into liquid hydrocarbons (sc5 +) obtained with the catalyst 10% co/10% TiO2₂ the P-SiC / example 7 depending on the duration of the test. The ratio H_2/ CO was of 2, the reaction temperature was 215 °c, the total pressure 40 atmospheres, the volume velocity (GHSV of) 2850 hourly space of H '¹ .

The fig. 9 shows the activity and selectivity (MSR) into liquid hydrocarbons (sc5 +) obtained on the catalyst 10% co/10% ti0₂ the P-SiC / example 7 depending on the reaction temperature. The ratio H₂/ CO was of 2, the total pressure 40 atmospheres, the volume velocity (GHSV of) hourly space=3800 hours'¹ .

The fig. 10 shows a second area of the same sample that Figure 7. Figures 10 (has), (d) and (I) are micrographs TEMs, Figures 10 (d), and (d-) (F.) micrographs EFTEM titanium. Figures 10 (a c) and (d-) correspond to the area (1), (I) Figures 10 and

(F.) to the area (2).

1. Definitions

In the context of the present invention, the term "specific surface area" means the specific surface area determined according to the method of Brunauer, Emmett and Teller (BET), well known to those skilled in the and described particularly in the standard NF X-11 - 621.

The porosity of a material is usually defined by reference to three categories of pores which are distinguished by their size: the microporosity (diameter less than 2 nm), the mesoporosity (diameter between 2 nm and 50 nm) and the macroporosity (diameter greater than about 50 nm).

In some embodiments of the present invention, use is made of a foam which is present as a cellular foam having open porosity. We herein by "cellular foam" a foam that has both a very low density and pore volumes. The size of the cell opening is variable and ranges typically from about 800 and 6000 MW. Such a foam can be prepared using known techniques. It has a very low microporosity. The mesoporosity is related essentially to the bridges which form the cells. The macroporosity open of such foam may vary from 30 to 95%, especially 50 to 90%, and its bulk density may be between 0.05 gm/cm.³ 0.5 grams/cm. and³ . In general, for its use as a catalyst carrier or catalyst, below a 0.05 gm/cm in density³ , there are problems of mechanical strength of the foam, then qu'au above 0.5 gm/cm.³ , the foam pore volume will be decreased and the pressure loss will increase without giving an operational benefit. Advantageously, the density is between 0.1 and 0.4 grams/cm.³ .

In other embodiments of the present invention use is made of the P-SiC composite in the form of extrudates, pellets, microspheres or grain. This material can be prepared using known techniques.

In one embodiment, a carrier of high porosity is impregnated with an organic solution of a precursor of ti0₂ . Said precursor ti0₂ may be an organic precursor, such as an alkoxide. Preferred Ti (I-OC₃H₇ )₄ (abstract TIPP) the solvent may be an alcohol, for example ethanol or isopropanol. Advantageously used an ethanol solution (preferably anhydride to avoid hydrolysis of the TIPP) containing Ti (I-OC₃H₇ )₄ (distributed for example by company Acros).

In an advantageous embodiment, the mole ratio of Ti/Si is between 2.5% and 10% (either a load in ti0₂ between 5% and 20% by mass relative to the total mass of SiC). After impregnation the solid is dried, for example in an oven at 110 °c for 8 hours. Advantageously, allowing the solid after impregnation at room temperature (for example during 4 hours) prior to drying. The transformation of the precursor into ti0₂ is performed by calcination (advantageously under air), preferably at a temperature between about 400 °c to about 1000 °c). The ramp rate is advantageously between 1.5 °c/min and 3.5 °c/minutes, and preferably about 2 °c/minute. By way of example, the calcination temperature may be 600 °c, and treatment time at this temperature may be of 5 hours.

By contrast, can also be prepared a hybrid material containing contents ti0₂ siC and the like, but in which the two phases are distributed in the entire solid mass, as opposed to the preferred materials herein in which a core of SiC is covered by a layer of ti0₂ ; such a hybrid carrier does not come within the scope of the present invention.

To avoid confusion in the notations, it should be noted in the following " the X % ti0₂ The SiC / " the solids formed by a surface layer of ti0₂ (or at least by particles individual ti0₂ ) deposited on a support of SiC to a content of X % by weight of SiC, and "% ti0 therein₂ The SiC - " the mixed solid (also referred to herein as:

"hybrid") containing Y % of ti0₂ and (100 Y)% SiC distributed in the bulk material, wherein X and Y express weight percentages.

The inventive method provides good dispersion of fine particles of ti0₂ all over macro-porous and meso-porous, outer and inner, of the support. Avoids formation of thick film or crust. Depositing crystallites of ti0₂ from a dispersion liquid according to the state of the technique (forming a layer that the skilled person calls "for wash-coat") does not allow a dispersion as thin in depth of the support of P-SiC composite.

The support P-SIC can have any geometric shape. It includes in particular extruded granules. It can also be foam of P-SiC composite. These supports are known as such and may be prepared by one of the known methods, namely: (I-) impregnating a polyurethane foam with a suspension of silicon powder in an organic resin (method chestnut, see the EP 0,624 560 b1, the EP and EP 1,007 207 a1 0,836 882 b1); (III) the reaction between vapors SiO with carbon reagent at a temperature of between 1100 °c and 1400 °c (method Ledoux sylvie.ledoux@civilization.ca, see the EP 0,313 480 b1); or (II) the cross-linking, carbonization and carburizing a mixture of prepolymer liquid or pasty and a silicon powder (method Dubots, see the EP 0,440 569 b1 and EP 0,952 889 b1).

On the support ti0₂/ SiC, then depositing an active phase consisting of one or more transition metals. It is preferable to use iron, cobalt or a mixture of both. This deposition is preferably produced by means of the method of impregnating the porous volume by a solution of a precursor of the active phase, which is known to the skilled person. Said precursor may be a solution of at least one organometallic compound of the metal that forms the active phase, or organic salt thereof. After impregnation, the solid is dried (preferably at a temperature between 100 °c and 140 °c) and calcined (preferably in air at a temperature between 250 °c and 450 degrees, and preferably at a slope of heats of between 0.6 °c/min and 1.6 °c/min.) to obtain an oxide of said metal. The active phase is obtained by reducing the precursor oxide, preferably at a temperature of between 200 °c and 380 °c (and preferably with an inclination of heats of between 2 °c/min and 4 °c/min.).

The average size (D.) particles of active phase (i.e. polyethoxylated their average diameter) is advantageously between 15 nm and 40 nm. Either it can be estimated from the size of the precursor oxide, which is chemically stable and therefore easier to manipulate for further characterization (for iron and cobalt, the particle size is approximately 0.75 times that oxide particles), either from the widening of the diffraction peak of the formula of Sherrer, well known: D. = for Ka/(T-. the cos θ) where λ represents the wavelength of the incident radiation, τ the half-value width of the diffraction peak, the K is a constant and θ is half the deflection of the wave.

In an advantageous embodiment of this step, after impregnating the solid is dried at ambient air during 4 hours and then in an oven at 110 °c for 8 hours. The solid is dried and calcined in air at 350 °c (1 °c/min to slope) during 2 hours to provide the precursor oxide catalyst, cocatalyst₃ 04/xti0₂ The SiC /. The catalyst is obtained by reducing the precursor oxide under hydrogen flow at 300 °c (3 °c/min at slope) during 6 hours. The catalyst is then noted yCo/xNb0.024₂ The SiC / with Y representing the load (in percent) of cobalt on the catalyst ([coextruded] / [ti0₂ The SiC +] and X representing the load (in per cent) of the ti0₂ on the support of SiC ([ti0₂ ] /). The average particle size of about 20 nm is CO.

4. Use of the catalyst

The catalyst according to the invention is especially adapted for the Fischer-Tropsch reaction. The support may have any geometric shape, and can in particular be in the form of granules, beads, microspheres, extruded, or otherwise shaped as plates or foam cylinders.

5. Advantages

The added benefits in the use of such a catalyst system relative to those plotted at present in the literature are as follows:

(I-) easy shaping of the support depending on the nature of the reactor involved,

(ii) a perfect distribution control meso - and macro-porous carrier for improved accessibility of reagents and improved evacuation of the intermediate reaction product,

(iii) a higher thermal conductivity of the carrier, relative to the silica or alumina, for reducing the formation of hot spots on the surface of the catalyst, where hot spots can induce degradation of the selectivity and also promote sintering of the particles of the active phase.

(iv) a superior mechanical strength relative to the supports ti0 macroscopic in₂ (extruded, foam, rings, balls and so on) and better resistance to attrition, because the ti0₂ is in the porosity of the carrier and not on its surface. This attrition resistance property is particularly important if the catalyst is used in the form of microbeads in a reactor type "slurry".

Examples no. 1 to 3 (inventive): ti0 deposition₂ on the SiC substrate

Has been provisioned SiC grains having a specific surface area of porous 40 M.²/ g and a pore distribution free of micropores. The pore volume of the grains has been impregnated with an ethanol solution containing Ti (I-OC₃H₇ )₄ in amount necessary to deposit a charge corresponding to 5% of Ti ti0₂ , 10% of ti0₂ and 15% of ti0₂ the weight of SiC, respectively for the materials of examples no. 1.2 and 3.

After impregnation the solids have been left at room temperature for 4 hours and then dried in oven at 110 °c for 8 hours. The transformation of the precursor salt in ti0₂ was then performed by calcination in air at 600 °c to 5 during hours with a ramp rate of 2 °c/minute. The resulting materials specific surfaces respectively of 38 M.²/ gm, 41 M.² the m / g and 41²/ g for the examples 1, 2 and 3. The pore distribution of the starting SiC and holder 10% TiO2₂/ SiC are plotted in Figure 1a.

Figure 4 (d) shows a picture EFTEM (transmitting donate businesses on the ENERGY Filtered) obtained on the support 10% TiO2₂ The SiC /. The picture no. 4 (has) to left is a sectional TEM images which provide an overview of the sample. The picture of Figure 4 (d) clearly shows the presence of a thin layer of ti0₂ covering the surface of SiC porous grain.

Example no. 4 (comparative): preparing a mixed support ti0₂ - SiC with 21% of ti0₂ and 79% SiC

A mixed material ti0₂ - The SiC was prepared as follows:

Has been provisioned 1620 g of silicon powder, 1520 g of resin solid phenolic novolac, 600 g of powder ti0₂ (Degussa-to-Evonik p25, BET surface area about 50 M.²/ gm, average particle size of about 20 nm), 78 g of Hexamethylènetetramine (TDH), 30 g of powdered plasticizer Zusoplast ps1,200 g of a 35% solution of polyvinyl alcohol and 1195 g of water.

The powders were mixed. The polyvinyl alcohol is diluted in the quantity of water. We prepared an extrudable mixture under stirring by introducing the liquid mixture on the powders. The mixture is extruded to form pellets of 3 mm diameter. After drying in ambient air and then to 150 °c during 4:00, have been processed to 1360 °c under a flow of argon for one hour. The solid obtained has 83.7% 16.3% mass of SiC and tic mass (either a molar fraction of 11.5% Ti relative to the sum of Ti + if).

The X-ray diffraction pattern indicated that the solid is a mixture of SiC and tic ("SiC composite Tic-"). BET surface was 54 M.²/ gm, whose 27 M.²/ g of microporous surface.

Then, the SiC composite Tic-has been oxidized in air to 400 °c during 8:00. It was achieved then a composite mass ti0 20.6%₂ - 79.4% mass of SiC (either a molar fraction of 11.5% Ti relative to the sum of Ti + if) having a mechanical strength of the n/mm to 59. Its specific surface area is 83 M.²/ gm, whose 53 M.²/ g of microporous surface. Figure 5 shows that the surface of the material is made of SiC and juxtaposed areas ti0₂ in equivalent amounts.

This material therefore has a composition similar to that of the example 2, but its porous properties on the one hand and its surface composition on the other hand make it catalytic appear similar.

Example 5 (comparative): preparation of a coextruded a SiC/10% catalyst

10% Cobalt catalyst not containing titanium was prepared from SiC raw already used in the examples 1 to 3.

Prepared an aqueous solution of cobalt nitrate which is impregnated on the SiC in the manner of the pore volume. The concentration of cobalt nitrate is calculated to achieve the desired charge cobalt in the final catalyst. The solid was then dried in ambient air during 4:00, and then oven à110 °C during 8:00. It has undergone then a calcination in air at 350 °c (1 °c/min to slope) during 2 hours to provide the precursor oxide catalyst, cocatalyst₃ 0₄ The SiC /. The catalyst 10% CO has been obtained by reduction of the precursor oxide under hydrogen flow at 300 °c (3 °c/min at slope) during 6 hours. Its specific surface area was 33 M.²/ gm. The average particle size of CO is estimated 40 - 50 nm (see table 1).

Examples 6 to 8 (inventive): preparation of catalysts to 10% of TiO/OC₂ The SiC /

The example 5 was reproduced by replacing the support SiC by the solids prepared according to examples 1 to 3. Was obtained then respectively the catalysts of examples 6, 7 and 8, all containing a load of 10% CO the specific surface area and the average particle diameter measured coextruded on these catalysts are reported in table 1.

With respect to the surfaces of the supports specific initial, 10% CO catalysts deposited on the supports of CMOS ti0₂ do not exhibit any meaningful change in surface area, while it decreases of 40 M.² the m / g to 33²/ g after deposition of CO on sic.

The presence of the ti0₂ influence significantly the average particle size of cobalt. Indeed, it passes and about 40 - 50 nm on SiC at 20 nm when the support has been previously coated with a layer to 10% by weight of ti0₂ .

The X-ray diffraction patterns of the catalysts is presented in Figure 2. The diffraction peaks of the phase ti0₂ are clearly visible on the diffraction patterns. The diffraction also indicates that the reduction is (relatively) complete because not observed diffraction peaks corresponding to the phase cobalt oxide, COO and/or CO₃ 0₄ . The enlargement of the diffraction peak cobalt (insert Figure 2) on the diagrams shows that there is an increase in the half-value width of the peak indicating that the particle size of cobalt participating in the coherent diffraction is smaller in the presence of the ti0₂ .

The images SEM catalysts the example 5 and 7 (10% / 10% co/10% SiC and coextruded of TiO₂ The SiC /) are presented in Figure 3 and indicates a significant decrease in the size of the cobalt particles in the presence of the ti0₂ . These results are in agreement with those obtained by the X-ray diffraction presented previously: the dispersion particles of cobalt therefore is highly improved by the presence of the surface layer of ti0₂ .

The images EFTEM (transmitting donate businesses on the ENERGY Filtered) obtained on the catalyst 10% co/10% TiO2₂/ SiC are presented in Figure 7. Figures 7 (d) and 7 (d-) show the dispersion particles of cobalt layer on the ti0₂ . It is found on the mapping of Figure 7 (D.) that the average particle size of cobalt is relatively small (on the order of 20 nm) and homogeneous. This result is in good agreement with those obtained from the broadening of XRD peaks cobalt (table 1) previously presented. Figure 10, which refers to another area of the same sample, validates these results and conclusions.

Example 9 (comparative): preparation of a catalyst 10% co/21% of TiO₂ The SiC -

A catalyst 10% co was produced according to the example 5 by replacing the support SiC by the mixed solid 21% ti0₂ The SiC - prepared in the example 4. Figures 5 and 6 show that the resulting catalyst has two populations of active phase: very large particles of CO localized surface areas of SiC and a few very small particles of co deposited on areas ti0₂ .

Example 10 (comparative): preparing and testing a catalyst 10% of SiC/OC

We prepared a catalyst comprising an active phase cobalt (deposited by the method described in the example 5) on a SiC support microporous about 100 M.²/ gm.

Example 11 : Evaluation of catalytic performance of different catalysts according to the invention or according to the comparative examples.

The performances of the catalysts prepared according to examples 5, 6, 7 and 9 were evaluated in the Fischer-Tropsch reaction. The results are reported in table 2. Observed a doubling of catalytic activity for the catalyst comprising a continuous layer of ti0₂ on the SiC relative to catalyst prepared on the SiC alone. The catalyst prepared from a support partially coated ti0₂ has an intermediate activity, little enhanced relative to that of the catalyst not containing ti0₂ .

The stability of the catalytic performance of the catalyst of example 7 (10% co/10% TiO2₂ The SiC /) was also evaluated and the results are presented in Figure 8. It appears clearly on the character that the activity and selectivity of the catalyst to hydrocarbon liquids are extremely stable over time test.

The influence of reaction temperature on the activity of the catalyst of example 7 (10% co/10% TiO2₂ The SiC /) during testing Fischer Tropsch was also evaluated and the results are presented in Figure 9. It should be noted that in these tests the hourly volume space velocity was increased 2850 hr '¹ to 3800 hours'¹ . In order to avoid reaching conversions too high which could induce problems of thermal runaway in the catalyst bed. These thermal runaway would alter the characteristics of the active phase by sintering of the particles of the active phase. The activity in STF increases significantly with the reaction temperature while the selectivity of liquid hydrocarbons remains high and stable. The mass-specific activity (MSR) reaches about 0.6 gc5 + / gcatai_yn €/ H with a selectivity to hydrocarbon liquids around 90% to 225 °c. It should be noted also that the catalyst has a relatively high stability and none deactivation was observed at each bearing test.

By contrast, the catalyst prepared according to example 9 by depositing a mixed material CO 21% ti0₂ The SiC -, has specific activity far below that measured over catalysts forming the subject of the invention.

These results demonstrate that the catalysts prepared according to the invention have very good catalytic performance for the reaction and ft, excellent stability over time.

Table 1

Characteristics of the supports and catalysts used for F-T synthesis

Table 2

Catalytic performance in F-T synthesis on the catalysts based on cobalt supported on SiC-SiC and promoted with the ti0₂ .

Reaction conditions: cobalt concentration=10% by weight, ratio H₂/ Co=2, reaction temperature=215 °c, total pressure=40 atmospheres, hourly space velocity (GHSV of) volume=2850 hr '¹ (2750 hr '¹ for the catalyst of example no. 9).

^<b> Mass-specific activity (MSR): mass-specific activity (MSR) represents the mass of hydrocarbon (>C.₅ ) formed per gram of catalyst per hour (the GCS - ^ the FH/gcataiyseu]).

Table 3

Catalytic performance in F-T synthesis on the catalyst 10co/10tio₂ The SiC - depending on the reaction temperature.

Reaction conditions: cobalt concentration=10% by weight, of H₂ : Co=2, total pressure=40 atmatm., hourly space velocity (GHSV of) volume=3800 hours'¹ .

^(has) Coextruded Time of yield (suites): yield per site cobalt represents the number of moles of CO converted per unit mass of cobalt per hour (i. e. : OC / coextruded /].

^(b.) Mass-specific activity (MSR): mass-specific activity (MSR) represents the mass of hydrocarbon (>C.₅ ) formed per gram of catalyst per hour (+ / gcatai gc5_yn / €).