Materials containing iron nanoparticles embedded in carbon, methods for their production, and use as heterogeneous catalysts

Abstract

The present invention relates to a catalytically active material comprising grains of non-graphitizable carbon with iron nanoparticles dispersed therein, wherein dp, the average diameter of the iron nanoparticles in the non-graphitizable carbon grains, is in the range of 1 nm to 20 nm, D, the average distance between the iron nanoparticles in the non-graphitizable carbon grains, is in the range of 2 nm to 150 nm, and ω, the combined total mass fraction of metals in the non-graphitizable carbon grains, is in the range of 30 wt% to 70 wt% of the total mass of the non-graphitizable carbon grains, and dp, D, and ω obey the following relationship: 4.5 dp / ω > D ≥ 0.25 dp / ω. The present invention further relates to a method for producing the material according to the invention, and to its use as a catalyst.

Description

Technical Field

[0001] The present invention relates to a material comprising grains of graphitization-resistant carbon together with iron nanoparticles dispersed therein. The material according to the present invention is catalytically active in various chemical reactions and can be obtained by a straightforward procedure.

[0002] The carbon phase of the present invention is mainly amorphous and does not appear to be activated carbon, carbon black, graphite, graphitized carbon black or paracrystalline carbon.

[0003] Prior Art Considerable efforts in the prior art have been directed towards synthesizing transition metal nanoparticles, especially those with catalytic activity. However, since the nanoparticles themselves cannot be used in most heterogeneous catalyst-based methods, further efforts have been made to develop materials containing transition metal nanoparticles attached to a suitable support, substrate, or wafer. Prior art approaches for this have mainly been based on the impregnation or chemical vapor deposition of metal precursors onto porous or mesoporous supports (Sietsma, Jelle R. A., et al. “Highly active cobalt-on-silica catalysts for the fischer-tropsch synthesis obtained via a novel calcination procedure.” Studies in Surface Science and Catalysis (2007); Van Deelen, T. W., et al. “Assembly and activation of supported cobalt nanocrystal catalysts for the Fischer-Tropsch synthesis.” Chemical Communications (2018)) or using ligands clearly defined for those metal species and applying high-temperature treatments (Westerhaus, Felix A., et al. “Heterogenized cobalt oxide catalysts for nitroarene reduction by pyrolysis of molecularly defined complexes” Nature Chemistry (2013); Banerjee, Debasis, et al. “Convenient and Mild Epoxidation of Alkenes Using Heterogeneous Oxide Catalysts” Angewandte Chemie, International Edition (2014)).However, the interaction between the nanoparticles and the support has been found to impose significant limitations (Oschatz, M., et al. “Effects of calcination and activation conditions on ordered mesoporous carbon supported iron catalysts for production of lower olefins from synthesis gas” Catalysis Science & Technology (2016)). In particular, the prior art procedures have not been able to yield materials that exhibit high dispersion and uniform coordination of transition metal / metal oxide nanoparticles in combination with high metal loadings. Most prior art transition metal nanoparticle materials actually show either low active metal concentrations as a result of clustering and a corresponding loss of dispersion of the metal particles at higher metal concentrations (Hernandez Mejia, Carlos, Tom W. van Deelen and Krijn P de Jong. “Activity enhancement of cobalt catalysts by tuning metal-support interactions” Nature Communications (2018); Oschatz, M., et al. “Effects of calcination and activation conditions on ordered mesoporous carbon supported iron catalysts for production of lower olefins from synthesis gas.” Catalysis Science & Technology (2016)). While materials that exhibit high dispersion and uniform coordination of transition metal / metal oxide nanoparticles in combination with high metal loadings are not currently available, there is a need for technology that provides such materials and methods for their manufacture in order to obtain materials with high catalytic activity, in light of the fact that such properties are considered desirable.

[0004] The present invention provides materials exhibiting desired properties and a facile method for their production.

[0005] The present invention relates to a catalytically active material comprising grains of graphitizable carbon containing iron nanoparticles dispersed therein, where dp, the average diameter of the iron nanoparticles in the graphitizable carbon grains, is in the range of 1 nm to 20 nm, D, the average distance between the iron nanoparticles in the graphitizable carbon grains, is in the range of 2 nm to 150 nm, and ω, the total mass fraction of metal in the graphitizable carbon grains, is in the range of 30 wt% to 70 wt% of the total mass of the graphitizable carbon grains, dp and D are measured by TGZ-TEM as described herein, and dp, D and ω are in the following relationship: 4.5dp / ω > D ≥ 0.25dp / ω and follow.

[0006] The material according to the present invention is obtained by the following steps: (a) preparing an aqueous solution containing a metal precursor and an organic carbon source, where the metal precursor comprises one or a combination of more than one organic, at least partially water-soluble, iron salt, and the organic carbon source is one or a combination of more than one saturated, aliphatic dicarboxylic acid, tricarboxylic acid, or polycarboxylic acid, (b) spray-drying or freeze-drying the aqueous solution of the metal precursor and the organic carbon source, and thus obtaining an intermediate product P, (c) heat-treating the intermediate product P at a temperature in the range of 200 °C to 380 °C can be obtained by a method comprising.

[0007] As a result of the research underlying the present invention, grains of graphitizable carbon having iron nanoparticles dispersed therein are obtained from an aqueous solution of a metal precursor and an organic carbon source, (i) spray drying or freeze drying the aqueous solution, (ii) heat treatment of the intermediate obtained from step (i) at a suitable temperature, and It has been found that it can be obtained by combining them.

[0008] The final product has been found to exhibit catalytic activity in various chemical reactions. In the context of the present invention, any material or substance that reduces the activation energy of a chemical reaction and thus increases its rate at a specific temperature without being consumed itself by the catalytic reaction is considered to be catalytically active.

[0009] By varying the method conditions and investigating the resulting materials, the method conditions and material properties as described in the claims have been found.

[0010] It has been found that forming an aqueous solution of a metal precursor and an organic carbon source in a glass beaker and slowly drying these solutions overnight in a dryer does not result in an intermediate product that can be converted by heat treatment at a suitable temperature into grains of graphitizable carbon having iron nanoparticles dispersed therein. Specifically, it has been found that when the drying method is carried out too slowly, significant decomposition of the polycarboxylic acid and formation of carbon dioxide start too early, leading to an early loss of the oxygen functional groups of the carbon source. However, the early loss of oxygen functional groups seems to correlate with the agglomeration of the metal component and the segregation of the metal precursor and the carbon source, ultimately resulting in an irregular distribution of large-sized metal clusters within the carbon matrix. Without wishing to be bound by theory, it thus becomes apparent that being able to fully utilize the oxygen-containing functional groups during part of the drying procedure is essential for fixing the metal precursor within the carbon source in a highly dispersed and regular manner.

[0011] Furthermore, it has been found that heat treatment of intermediate product P at temperatures below 200°C and above 380°C does not result in grains of graphitization-resistant carbon according to the present invention having iron nanoparticles dispersed therein. In particular, it has been found that the proportion of the graphitization-resistant carbon phase itself according to the present invention decreases when the temperature selected for the heat treatment is too high. However, these phases are presumably related to favorable hydrogen conductivity, which is also essential for efficiently catalyzing reactions involving hydrogen conversion. On the other hand, when the temperature selected for the heat treatment is too low or the heat treatment period is too short, the level of residual oxygen in the resulting carbon phase is too high and the reduction of the metal precursor remains incomplete, resulting in reduced catalytic activity.

[0012] Moreover, in view of the prior art, it should be noted that, as a result of the method of the present invention, the formation of the graphitization-resistant carbon phase of the present invention may seem surprising. However, without wishing to be bound by theory, it is hypothesized that the formation of graphitization-resistant carbon under the low-temperature conditions of the method of the present invention is promoted by the high concentration of the metal precursor present in a highly dispersed manner in the intermediate product P before the subsequent heat treatment.

[0013] The method of the present invention yields a granular form of graphitization-resistant carbon material. Graphitization-resistant carbon can be identified by those skilled in the art using TEM analysis (see P.W. Albers, Neutron scattering study of the terminating protons in the basic structural units of non-graphitizing and graphitizing carbons, Carbon 109 (2016), 239-245, p.241, Figure 1c).

[0014] The experimental results obtained in connection with the present invention show that the catalytic activity of the material obtained by the method of the present invention correlates well with the content of the grains of graphitization-resistant carbon exhibiting the characteristics of the present invention.

[0015] Typically, 90% of the graphitization-resistant carbon grains obtained by the method of the present invention exhibit an appropriate size, i.e., a diameter of 2 μm to 200 μm. Generally, more than 95% of those moderately sized graphitization-resistant carbon grains obtained by the method of the present invention are related to the relationship 4.5d p / ω>D≧0.25d p / ω (where d p represents the average diameter of the iron nanoparticles in the graphitization-resistant carbon grains, D represents the average distance between the iron nanoparticles in the graphitization-resistant carbon grains, and ω represents the total mass fraction of the metals in the graphitization-resistant carbon grains) have been found to contain iron nanoparticles dispersed therein. The method of the present invention typically produces grains, where only a fraction of very small grains and a fraction of very large grains, i.e., the particle fraction outside the appropriate size range of 2 μm to 200 μm, contain a significant portion of the grains, where the iron nanoparticles are related to the relationship 4.5d p / ω>D≧0.25d p / ω. Accordingly, the method of the present invention generally produces a material having a high content of grains containing iron nanoparticles, where the iron nanoparticles are related to the relationship 4.5d p / ω>D≧0.25d p / ω. However, materials having a lower content of these grains can be obtained by dilution with other methods or other materials and are thus likewise included by the present invention.

[0016] Accordingly, in a preferred embodiment, the present invention relates to a catalytically active material comprising grains of graphitizable carbon with iron nanoparticles dispersed therein, wherein more than 90% of the graphitizable carbon grains of appropriate size, i.e., graphitizable carbon grains having a diameter of 2 μm to 200 μm, the iron nanoparticles follow the relationship 4.5dp / ω > D ≥ 0.25dp / ω, and further dp, the average diameter of the iron nanoparticles in the graphitizable carbon grains is in the range of 1 nm to 20 nm, D, the average distance between the iron nanoparticles in the graphitizable carbon grains is in the range of 2 nm to 150 nm, and ω, the total mass fraction of the metals in the graphitizable carbon grains is in the range of 30 wt% to 70 wt% of the total mass of the graphitizable carbon grains. In another preferred embodiment, the present invention relates to a catalytically active material comprising grains of graphitizable carbon with iron nanoparticles dispersed therein, wherein more than 95% of the graphitizable carbon grains of appropriate size, i.e., graphitizable carbon grains having a diameter of 2 μm to 200 μm, the iron nanoparticles follow the relationship 4.5dp / ω > D ≥ 0.25dp / ω, and further dp, the average diameter of the iron nanoparticles in the graphitizable carbon grains is in the range of 1 nm to 20 nm, D, the average distance between the iron nanoparticles in the graphitizable carbon grains is in the range of 2 nm to 150 nm, and ω, the total mass fraction of the metals in the graphitizable carbon grains is in the range of 30 wt% to 70 wt% of the total mass of the graphitizable carbon grains.

[0017] The iron nanoparticles in the graphitizable carbon material of the present invention are mainly composed of elemental iron, however, for example, iron oxide and / or dopant metal and / or a second metal may also be contained.

[0018] Computer-assisted analysis of TEM images (TEM = transmission electron microscopy) combined with the Degussa-derived TGZ method enables the determination of the diameter of individual iron nanoparticles and the statistical measures of their sets (see Parker et al. “The effect of particle size, morphology and support on the formation of palladium hydride in commercial catalysts” Chemical Science, 2019, 10, 480).

[0019] In connection with the present invention, the average diameter, d, of the iron nanoparticles p , and the mean distance D are determined by the TGZ-TEM method as described below: 1. Sample preparation In most cases, the samples to be tested are available as powders.

[0020] The powder is usually dispersed in a solvent under the application of ultrasound. The application of the ultrasound disintegrates the agglomerates into aggregates, and as a result, an aggregate distribution rather than a mixture of aggregates and agglomerates is obtained. A micropipette is then used to drop the liquid onto a film-coated grid on a piece of filter paper. Excess liquid is quickly absorbed through the filter paper, so agglomerate formation is prevented by this drying method. The suspended grains should not be too dense, because the shape and outer appearance of the nanoparticles cannot be clearly seen through the contact and overlap of the grains. The optimal dilution has to be determined by a pilot experiment using a dilution series.

[0021] In general, it can be stated that the type of production has little influence on the result of the primary nanoparticle size evaluation.

[0022] 2. Conducting the test Individual nanoparticles whose properties can be determined based on the TEM image must be imaged with a sufficiently sharp contour.

[0023] A not-too-dense distribution of the nanoparticles having particles that have little or as much separation from each other as possible on the TEM image facilitates the measurement with the TGZ3, but does not affect the measurement results.

[0024] After examining various image regions of the TEM specimen, a suitable region is selected accordingly. It should be noted that for each of the above samples, the ratios of small, medium, and large nanoparticles are representative and characteristic, and no selective preference for small or large particles is given by the operator.

[0025] The total number of primary nanoparticles that can be measured depends on the scattering range of the primary nanoparticle size: the larger the scattering range, the more particles must be measured to obtain sufficient statistics. For metal catalysts, about 1500 single particles are measured. For all TGZ analyses, a calibrated Hitachi H-7500 field transmission electron microscope equipped with a CCD camera and operated at 100 keV was used.

[0026] 3. Explanation of the measurement procedure The measurement procedure is carried out according to the TGZ3 manual by Carl ZEISS (“Teilchengroessenanalysator (particle size analyser) TGZ3”; manual of Carl ZEISS).

[0027] 4. Measurement data processing A detailed description of the measurement data processing is given in (F. Endter u. H. Gebauer, “Optik (Optics)” 13 (1956), 97) and (K. Seibold and M. Voll, “Distribution function for describing the particle size distribution of Soot and pyrogenic oxides”. Chemiker-Zeitung, 102 (1978), No. 4, 131-135).

[0028] The statistical summary can be presented in the form of a report. A detailed statistical description is given in (Lothar Sachs, “Statistical methods”, 5th edition, Springer-Verlag, Berlin (1982)).

[0029] 5. Evaluation and Display of Results a. Total number of particles (N) b. Evaluated particle size distributions q0(x) and q3(x) of 1500 isolated nanoparticles per sample c. Particle size d n , average diameter (d n ) [Number] n i = number of particles with diameter d i d. Average distance D in the rectangular plane [Number] a, b = length and width of the rectangular plane x, y, x * y * = particle coordinates.

[0030] ​The total mass fraction of the above-mentioned metals, ω, is defined as the fraction of the total mass of the considered materials that is the sum of the total mass of iron, all dopant metals, and the second metal: ω = (m(iron) + m(dopant metal) + m(second metal)) / m(material); where m(iron) is the total mass of elemental iron in the form of elemental iron itself and / or in the form of any compound of iron in the material, m(dopant metal) is the total mass of all dopant metals in elemental form contained in the material in the form of elemental dopant metal itself and / or in the form of any compound of the dopant metal, m(second metal) is the total mass of all second metals in elemental form contained in the material in the form of the above-mentioned elemental second metal itself and / or in the form of any compound of the second metal, and m(material) is the total mass of the considered material.

[0031] The total mass fraction of the above-mentioned metals, ω, can be determined by any method for quantitative elemental analysis, in particular by XRF (X-ray fluorescence) and ICP-AES (inductively coupled plasma atomic emission spectroscopy).

[0032] The appropriate selection of conditions in the method according to the invention makes it possible to control the total mass fraction of the above-mentioned metals, ω, in the resulting material: In step (a), a method of preparing a solution with a high metal content (combining iron, dopant metals, and the second metal) results in a material with a higher total mass fraction of metals, ω, than a method of preparing a solution with a lower metal content in step (a).

[0033] A method involving heat treatment in step (c) at a high temperature in the range of 200°C to 380°C results in a material with a higher total mass fraction of metals, ω, than a method involving heat treatment in step (c) at a lower temperature.

[0034] The method of the present invention results in a granular material. The size of the individual particles of this material as well as the statistical measures of their sets can be determined by laser diffraction analysis (e.g., Cilas 1190 Series), which is well known to those skilled in the art.

[0035] Typically, the method of the present invention yields a particulate material having the following particle size distribution: d10 = 5 μm, d50 = 40 μm, d90 = 150 μm.

[0036] In view of the fact that the material obtained by the method according to the present invention has been found to be extremely suitable for producing shaped catalysts, in a preferred embodiment, the present invention relates to a catalytically active material comprising grains of graphitizable carbon together with iron nanoparticles dispersed therein, d p wherein the average diameter of the iron nanoparticles in the graphitizable carbon grains is in the range of 1 nm to 20 nm, D, the average distance between the iron nanoparticles in the graphitizable carbon grains is in the range of 2 nm to 150 nm, and ω, the total mass fraction of metal in the graphitizable carbon grains is in the range of 30 wt% to 70 wt% of the total mass of the graphitizable carbon grains, and d p D and ω are in the following relationship: 4.5d p / ω > D ≧ 0.25d p / ω and and the graphitizable carbon grains exhibit the following particle size distribution: d10 = 5 μm, d50 = 40 μm, d90 = 150 μm.

[0037] There may be uses for the material according to the present invention when the presence of nitrogen is harmful. Accordingly, in a preferred embodiment, the present invention relates to a material according to the present invention, wherein the total mass fraction of nitrogen is less than 1 wt% of the total mass of the material.

[0038] Experimental results indicate that materials with relatively small iron nanoparticles can have particularly attractive catalytic properties. Accordingly, in a preferred embodiment, the present invention relates to a material according to the present invention, where d pis within the range of 4 nm to 18 nm. In a particularly preferred embodiment, the present invention relates to a material according to the present invention, where d p is within the range of 6 nm to 14 nm.

[0039] As shown by the experimental results, the addition of the dopant metal affects the catalytic activity of the material of the present invention. Accordingly, in a preferred embodiment, the present invention relates to a material according to the present invention, wherein the iron nanoparticles are doped with a dopant metal, and the dopant metal is selected from Na (sodium) or K (potassium) or Ca (calcium) or Mg (magnesium) or a mixture thereof, and the material exhibits a molar ratio RDM = n(iron):n(dopant metal) within the range of 5 to 1000.

[0040] In a particularly preferred embodiment, the present invention relates to a material according to the present invention, wherein the iron nanoparticles are doped with a dopant metal, and the dopant metal is selected from Na (sodium) or K (potassium) or Ca (calcium) or Mg (magnesium) or a mixture thereof, and the material exhibits a molar ratio RDM = n(iron):n(dopant metal) within the range of 10 to 500.

[0041] In another preferred embodiment, the present invention relates to a material according to the present invention, wherein the iron nanoparticles are combined with a second metal, and the said second metal is selected from Group 1 or Group 2, where Group 1 is defined as Mo (molybdenum) or W (tungsten) or a mixture thereof, and Group 2 is defined as Co (cobalt) or Cu (copper) or Mn (manganese) or a mixture thereof, and the material exhibits a molar ratio RSM = n(iron):n(second metal) within the range of 1 to 50.

[0042] The present invention further relates to a method for manufacturing the material of the present invention. As shown above, it has been found that the combination of two method steps is decisive: (i) Spray drying or freeze drying of an aqueous solution of the above-mentioned metal precursor and organic carbon source, and (ii) Heat treatment of the resulting intermediate at a suitable temperature.

[0043] Accordingly, in another aspect, the present invention further relates to a method for manufacturing a material according to the present invention, and the following steps: (a) A step of preparing an aqueous solution containing a metal precursor and an organic carbon source, wherein the metal precursor includes one or a combination of more than one organic, at least partially water-soluble iron salt, and the organic carbon source is one or a combination of more than one saturated aliphatic dicarboxylic acid, tricarboxylic acid, or polycarboxylic acid, (b) Spray drying or freeze drying the aqueous solution of the above-mentioned metal precursor and organic carbon source, and thus obtaining an intermediate product P, (c) A step of heat-treating the intermediate product P at a temperature within the range of 200 °C to 380 °C are included.

[0044] Each of these method steps may be carried out in a batch or continuous form.

[0045] In another aspect, the present invention further relates to a material obtainable by the method of the present invention.

[0046] As indicated above, the formation of the material of the present invention requires a combination of spray drying or freeze drying and a suitable heat treatment at a moderate temperature. Accordingly, it seems reasonable to assume that only the materials present in dissolved form in the solution, i.e., the solution prepared in step (a) of the process, can be converted into the materials according to the present invention. However, insoluble substances in solid form can be suspended in the solution prepared in step (a), provided that they do not interfere with the method of forming the material of the present invention. For example, such solids, which may be derived from undissolved metal precursors or organic carbon sources, can form solid diluents of the material of the present invention in the solid product obtained after step (c) of the method of the present invention. Similarly, organic solvents can be dissolved or emulsified in the solution prepared in step (a), provided that their presence does not interfere with the method of forming the material of the present invention. However, in order to avoid interference with the method of forming the material of the present invention, in a preferred embodiment, the method of the present invention is carried out using an aqueous solution prepared in step (a) that is free of insoluble substances in solid form and free of organic solvents.

[0047] When no dopant metal and no second metal are used, the metal precursor in the solution prepared in step (a) of the method of the present invention is one or a combination of more than one organic, at least partially water-soluble salts of iron. In this context, a salt is considered to be at least partially water-soluble if at least a part of the salt dissolves in the aqueous solution prepared in step (a) under the conditions used in the process. Preferably, when no dopant metal and no second metal are used, the metal precursor in the solution prepared in step (a) of the method of the present invention is one or a combination of more than one organic salts of iron, and the desired amount thereof that can be included in the solution is completely soluble in the aqueous solution of step (a).

[0048] In a preferred embodiment of the present invention, no dopant metal and no second metal are used.

[0049] In another preferred embodiment of the present invention, a dopant metal is used, but no second metal is used.

[0050] When a dopant metal is used, the metal precursor in the solution prepared in step (a) of the method of the present invention is a combination of one or more organic, at least partially water-soluble salts of iron and one or more organic, at least partially water-soluble salts of one or more dopant metals. Preferably, when a dopant metal is used, the metal precursor in the solution prepared in step (a) of the method of the present invention is a combination of one or more organic salts of iron and one or more organic salts of one or more dopant metals, and the desired amount thereof that can be contained in the solution is completely soluble in the aqueous solution of step (a).

[0051] When a second metal is used, the metal precursor in the solution prepared in step (a) of the method of the present invention is a combination of one or more organic, at least partially water-soluble salts of iron and one or more organic, at least partially water-soluble salts of one or more second metals. Preferably, when a second metal is used, the metal precursor in the solution prepared in step (a) of the method of the present invention is a combination of one or more organic salts of iron and one or more organic salts of one or more second metals, and the desired amount thereof that can be contained in the solution is completely soluble in the aqueous solution of step (a).

[0052] When a dopant and a second metal are used, the metal precursor in the solution prepared in step (a) of the method of the present invention is a combination of one or more organic, at least partially water-soluble salts of iron and one or more organic, at least partially water-soluble salts of one or more dopant metals and one or more organic, at least partially water-soluble salts of one or more second metals. Preferably, when a dopant and a second metal are used, the metal precursor in the solution prepared in step (a) of the method of the present invention is a combination of one or more organic salts of iron and one or more organic salts of one or more dopant metals and one or more organic, at least partially water-soluble salts of one or more second metals, and the desired amount thereof that can be contained in the solution is completely soluble in the aqueous solution of step (a).

[0053] Preferred organic anions of the metal precursor in the solution prepared in step (a) of the method of the present invention are acetate, carbonate, oxalate, citrate, malonate, tartrate and glutarate. When nitrogen need not be avoided, nitrate is another preferred anion of the metal precursor in the solution prepared in step (a).

[0054] Saturated aliphatic dicarboxylic acids, tricarboxylic acids, or polycarboxylic acids can be used, either alone or as part of a mixture, as the organic carbon source of the aqueous solution prepared in step (a) as long as they assist in the formation of the materials of the present invention. In a preferred embodiment, malonic acid, glutaric acid, citric acid or a mixture thereof is used as the organic carbon source of the aqueous solution prepared in step (a) of the method of the present invention. In a particularly preferred embodiment of the present invention, citric acid is used as the organic carbon source of the aqueous solution prepared in step (a) of the method of the present invention.

[0055] The aqueous solution prepared in step (a) is spray-dried or freeze-dried in step (b) of the method of the present invention. The resulting product is called intermediate product P in relation to the present invention. The method parameters for spray drying and freeze drying can be varied over a wide range as long as the drying method is carried out without interruption and the total content of water and organic solvent indicated by intermediate product P is less than 10% by weight. In a preferred embodiment of the present invention, the aqueous solution prepared in step (a) is spray-dried in step (b) of the method of the present invention.

[0056] The heat treatment according to step (c) of the method of the present invention is carried out under defined temperature conditions and an inert gas atmosphere, such as nitrogen, or air. A wide range of furnaces suitable for this purpose are commercially available. In a preferred embodiment, the heat treatment is carried out under an inert gas atmosphere, such as nitrogen. The heating rate during the heat treatment should be small enough to allow for a homogeneous distribution of heat, i.e., typically less than 15 K / min, preferably less than 10 K / min, and particularly preferably less than 5 K / min. The heat treatment of the intermediate product P is carried out at a temperature within the range of 200 °C to 380 °C. In a preferred embodiment of the present invention, the heat treatment of the intermediate product P is carried out at a temperature within the range of 255 °C to 375 °C. In a particularly preferred embodiment, the heat treatment of the intermediate product P is carried out at a temperature within the range of 300 °C to 350 °C. Typically, the heat treatment of the intermediate product P is carried out for a period of 1 to 4 hours, however, heat treatments for longer or shorter time intervals can equally be carried out. The heating and cooling intervals are not considered as causes when determining the duration of the heat treatment. In a preferred embodiment, the heat treatment of the intermediate product P is carried out for a period of 1 to 4 hours.

[0057] As indicated above, the material according to the present invention exhibits catalytic activity. Accordingly, in another aspect, the present invention further relates to the use of the material of the present invention as a catalyst.

[0058] The material according to the present invention can be used, for example, as a catalyst in the liquid-phase hydrogenation of organic compounds, specifically unsaturated compounds such as alkenes and alkynes, aldehydes and ketones, esters and imines, nitro compounds and nitriles. The material according to the present invention is furthermore a very active catalyst for the reductive amination of carbonyl compounds. Accordingly, in another aspect, the present invention further relates to the use of the material of the present invention as a catalyst for the hydrogenation of organic compounds and / or the reductive amination of carbonyl compounds.

[0059] The material according to the present invention can also be used as a catalyst in the conversion of carbon monoxide, carbon dioxide, or a mixture thereof, with hydrogen, into alkenes, alkanes, or a mixture thereof. Correspondingly, in another aspect, the present invention further relates to the use of the material of the present invention as a catalyst for the conversion of carbon monoxide, carbon dioxide, or a mixture thereof, with hydrogen, into alkenes, alkanes, or a mixture thereof.

[0060] The material according to the present invention can be used in its unmodified form as a catalyst or can be converted into a catalyst body by shaping methods (e.g., tabletting, pelletizing, extrusion, coating, 3D printing) well-known to those skilled in the art.

Examples

[0061] Example Production of Fe Nanoparticles Embedded in Fea,b - Carbon Fe nanoparticles embedded in carbon were produced by dissolving 14.4 g of citric acid (highest purity, Sigma Aldrich) in 75 mL of deionized water with constant stirring at room temperature. In a second beaker, 18.7 g of iron(II) acetate (Fe(CH3COO)2, Sigma Aldrich) was dissolved in 75 mL of deionized water with constant stirring at room temperature. The iron acetate solution was slowly added to the citric acid solution and stirred for another 30 min at room temperature. The resulting solution was spray-dried using a conventional mini spray dryer (Buechi, Mini Spray Dryer B - 290) at a constant inlet temperature of 220 °C, an outlet temperature of 120 °C, and a pump speed of 20%. The obtained powder was divided into two fractions having the same mass for final heat treatment.

[0062] The first sample was heat-treated in a tubular furnace under a nitrogen atmosphere with a gradient to 300 °C over 180 min, where the temperature was maintained for another 4 h and then allowed to cool naturally. The resulting catalyst powder was named FeCat. 1a.

[0063] The second sample was heat-treated in a nitrogen atmosphere in a similar manner. The sample was heated to 350 °C within 180 min, the temperature was maintained there for 4 h, and then it was naturally cooled. The resulting catalyst powder was named FeCat. 1b.

[0064] The material was determined to have the following properties by XRF (X-ray fluorescence) and TGZ analysis, using a calibrated Hitachi H-7500 field transmission electron microscope equipped with a CCD camera and operated at 100 keV: [Table 1]

[0065] Comparative Example For comparison, a high-loading catalyst having 20 wt% iron on a conventional Vulcan XC72R carbon support was prepared by incipient wetness impregnation and named FeCat. Ref.

[0066] The material was determined to have the following properties by XRF (X-ray fluorescence) and TGZ analysis, using a calibrated Hitachi H-7500 field transmission electron microscope equipped with a CCD camera and operated at 100 keV: [Table 2]

[0067] Test of Catalytic Activity Experiments to determine the catalytic activity and selectivity of the material were carried out batchwise using 200 mg of catalyst and 5 mmol of substrate in 5 ml of methanol. The autoclave was heated to the desired reaction temperature and stirred under a constant hydrogen pressure of 50 bar for all experiments. The reaction products were filtered and analyzed by GC-MS.

[0068] I. Hydrogenation of N-benzylidene-benzylamine [Chemical formula] [Table 3]

[0069] II. Hydrogenation of Methyl Crotonate to Methyl Butyrate

Chem.

Table 4

[0070] III. Hydrogenation of Dodecanenitrile

Chem.

Table 5

[0071] IV. Hydrogenation of Acetylnaphthalene

Chem.

Table 6

Claims

1. A catalytically active material comprising grains of graphitizable carbon together with iron nanoparticles dispersed therein, d ｐ , the average diameter of the iron nanoparticles in the graphitization-resistant carbon grains is in the range of 1 nm to 20 nm, D, wherein the average distance between iron nanoparticles in the graphitizable carbon grains is in the range of 2 nm to 150 nm, and ω, wherein the total mass fraction of metals in the graphitizable carbon grains is in the range of 30 wt% to 70 wt% of the total mass of the graphitizable carbon grains, d ｐ and D is measured by TGZ-TEM, and d ｐ , D, and ω have the following relationship: 4.5d ｐ / ω > D ≥ 0.25d ｐ / ω the catalytically active material according to.

2. The material according to claim 1, wherein the graphitizable carbon grains exhibit the following particle size distribution: d10 = 5 μm, d50 = 40 μm, d90 = 150 μm.

3. The material according to claim 1 or 2, wherein the total mass fraction of nitrogen in the graphitizable carbon grains is less than 1 wt% of the total mass of the graphitizable carbon grains.

4. d ｐ The material according to any one of claims 1 to 3, wherein d is in the range of 4 nm to 18 nm.

5. d ｐ The material according to any one of claims 1 to 4, wherein d is in the range of 6 nm to 14 nm.

6. The material is doped with a dopant metal, and the dopant metal is selected from Na (sodium), K (potassium), Ca (calcium), Mg (magnesium) or a mixture thereof, and the graphitizable carbon grains exhibit a molar ratio = n(iron) / n(dopant metal) in the range of 5 to 1000, the material according to any one of claims 1 to 5.

7. The material is combined with a second metal, and the second metal is selected from Group 1 or Group 2, where Group 1 is defined as Mo (molybdenum) or W (tungsten) or a mixture thereof, and Group 2 is defined as Co (cobalt) or Cu (copper) or Mn (manganese) or a mixture thereof, and the graphitizable carbon grains exhibit a molar ratio = n(iron) / n(second metal) in the range of 1 to 50, the material according to any one of claims 1 to 5.

8. A method for producing the material according to any one of claims 1 to 7, comprising the following steps: (a) preparing an aqueous solution comprising a metal precursor and an organic carbon source, wherein the metal precursor comprises one or a combination of more than one organic, at least partially water-soluble iron salt, and the organic carbon source is one or a combination of more than one saturated aliphatic dicarboxylic acid, tricarboxylic acid, or polycarboxylic acid, b) spray-drying or freeze-drying the aqueous solution of the metal precursor and the organic carbon source, and thus obtaining an intermediate product P, Step of heat-treating the intermediate product P at a temperature within the range of 200°C to 380°C The method as described above. **Claim 9** The method according to claim 8, wherein the organic carbon source is selected from malonic acid, tartaric acid, citric acid, and mixtures thereof. **Claim 10** The method according to claim 8 or 9, wherein the intermediate product P is heat-treated at a temperature within the range of 255°C to 375°C for 1 to 4 hours. **Claim 11** The method according to any one of claims 8 to 10, wherein the intermediate product P is heat-treated at a temperature within the range of 300°C to 350°C for 1 to 4 hours. **Claim 12** Use of the material according to any one of claims 1 to 7 as a catalyst. **Claim 13** The use according to claim 12, wherein the catalyst is a catalyst for hydrogenation of organic compounds and / or reductive amination of carbonyl compounds. **Claim 14** The use according to claim 12, wherein the catalyst is a catalyst for conversion of carbon monoxide, carbon dioxide, or a mixture thereof to an alkene, alkane, or a mixture thereof with hydrogen.

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