MATERIALS COMPRISING IRON NANOPARTICLES EMBEDDED IN CARBON, PROCESSES FOR THEIR MANUFACTURE, AND USE AS A HETEROGENEOUS CATALYST

Abstract

The present invention relates to a catalytically active material comprising non-graphitizing carbon grains with iron nanoparticles dispersed therein, wherein dp, the average diameter of the iron nanoparticles in the non-graphitizing carbon grains, is in the range of 1 nm to 20 nm, D, the average distance between iron nanoparticles in the non-graphitizing carbon grains, is in the range of 2 nm to 150 nm, and Δ, the combined total mass fraction of metal in the non-graphitizing carbon grains, is in the range of 30 wt% to 70 wt% of the total mass of the non-graphitizing carbon grains, and wherein dp, D, and Δ conform to the following relationship: 4.5 dp / Δ > D = 0.25 dp / Δ. Furthermore, the present invention relates to a process for manufacturing the material according to the invention, as well as its use as a catalyst.

Description

MATERIALS COMPRISING IRON NANOPARTICLES EMBEDDED IN CARBON, PROCESSES FOR THEIR MANUFACTURE, AND USE AS A HETEROGENEOUS CATALYST FIELD OF INVENTION The present invention relates to a material comprising non-graphitizing carbon grains with iron nanoparticles dispersed therein. The material according to the invention is catalytically active in a variety of chemical reactions and can be obtained by a simple process. The carbon phase of the invention is largely amorphous and does not appear to be activated carbon, black carbon, graphite, graphitized black carbon, or paracrystalline carbon. BACKGROUND OF THE INVENTION Significant prior art efforts have been directed toward synthesizing transition metal nanoparticles, including transition metal nanoparticles with catalytic activity in particular. However, since the nanoparticles themselves cannot be used in most heterogeneously catalyzed processes, further efforts have been made to develop materials containing transition metal nanoparticles bonded to suitable supports, substrates, or wafers. Prior art approaches for this purpose were mainly based on impregnation or chemical vapor deposition of metal precursors onto porous or mesoporous supports (Sietsma, Jelle RA, et al.).“Highly active cobalt-on-silica catalysts for the fischer-tropsch synthesis obtained via a novel calcination procedure”, (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, TW, et al. “Assembly and activation of supported cobalt nanocrystal catalysts for the Fischer-Tropsch synthesis”, (Assembly and activation of supported cobalt nanocrystal catalysts for the Fischer-Tropsch synthesis). Chemical Communications (2018).) or using well-defined ligands for the metal species and applying high-temperature treatment (Westerhaus, Félix A., et al.“Heterogenized cobalt oxide catalysts for nitroarene reduction by pyrolysis of molecularly defined complexes”, (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”, (Convenient and Mild Epoxidation of Alkenes Using Heterogeneous Oxide Catalysts), Angewandte Chemie, International Edition (2014).) However, it was found that nanoparticle-support interactions lead to 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”, (Effects of calcination and activation conditions on iron catalysts supported by ordered mesoporous carbon for the production of lower olefins from synthesis gas), Catalysis Science & Technology (2016).) In particular, the procedures of the prior art failed to produce materials exhibiting high dispersion and uniform coordination of transition metal / metal oxide nanoparticles in combination with a high metal content.In fact, most transition metal nanoparticle materials from the previous pcoznn / zznz / E / Yi technique exhibit very low active metal concentrations of less than 20 wt% as a result of aggregation and a corresponding loss of metal particle dispersion at higher metal concentrations (Hernández Mejía, 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).Given that materials exhibiting high dispersion and uniform coordination of transition metal / metal oxide nanoparticles in combination with a high metal content are not currently available, while such properties are considered desirable in order to obtain material with high catalytic activity, there is a need in the art to provide such materials as well as processes for their manufacture. The present invention provides materials that exhibit the desired properties and a simple process for their manufacture. DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a catalytically active material, comprising non-graphitizing carbon grains with iron nanoparticles dispersed therein. where: dp, the average diameter of iron nanoparticles in non-graphitizing carbon grains, is in the range of 1 nm to 20 nm, D, the average distance between iron nanoparticles in non-graphitizing carbon grains, is in the range of 2 nm to 150 nm, and ω, the combined total mass fraction of metal in non-graphitizing carbon grains, is in the range of 30 wt% to 70 wt% of the total mass of non-graphitizing carbon grains, wherein dp and D are measured by TGZ-TEM as described herein, and wherein dp, D and ω are adjusted to the following relationship: 4.5dp / ω>D>0.25dp / ω. The material according to the present invention can be obtained by means of a process comprising the following steps: (a) providing 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 iron salt, at least partially soluble in water, and wherein the organic carbon source is one or a combination of more than one saturated aliphatic di-, tri- or polycarboxylic acid, (b) spray-drying or freeze-drying the aqueous solution of the metal precursor and the organic carbon source and thereby obtaining the intermediate product P, pcoznn / zznz / E / Yi, (c) heat-treating the intermediate product P at a temperature in the range of 200°C to 380°C. As a result of the research underlying the present invention, it was discovered that non-graphitizing carbon grains with iron nanoparticles dispersed therein can be obtained from aqueous solutions of metal precursors and organic carbon sources by combining (i) spray drying or freeze drying of the aqueous solution, with (ii) heat treatment at moderate temperatures of the intermediate obtained from step (i). The final product was found to exhibit catalytic activity in a variety of chemical reactions. In the context of the present invention, any material or substance that lowers the activation energy of a chemical reaction and thereby increases its rate at a particular temperature, without being consumed by the catalyzed reaction itself, is considered to be catalytically active. Variation of process conditions and examination of the materials obtained, process conditions discovered and material properties as claimed in this document. It was discovered that forming aqueous solutions of metal precursors and organic carbon sources in beakers and slowly drying these solutions overnight in a drying cabinet did not produce intermediate products that could be transformed into non-graphitizing carbon grains with iron nanoparticles dispersed within them by heat treatment at moderate temperatures. Specifically, it was found that if the drying process was carried out too slowly, significant decomposition of the polycarboxylic acids and the formation of carbon dioxide began too early, leading to an early loss of the oxygen functionalities of the carbon source.However, an early loss of oxygen functionalities appears to be correlated with agglomeration of metal components and segregation of the metal precursor from the carbon source, ultimately resulting in an irregular distribution of large metal groups within the carbon matrix. Therefore, without intending to be constrained by theory, it seems that sufficient availability of oxygen-containing functional groups during parts of the drying process is essential for fixing the metal precursors within the carbon source in a highly dispersed and regular manner. Furthermore, it was discovered that heat-treating the intermediate product P at temperatures below 200°C and above 380°C did not produce non-graphitizing carbon grains according to the invention with iron nanoparticles dispersed therein. In particular, it was found that the proportion of the non-graphitizing carbon phase according to the invention decreased when the selected heat-treating temperatures were too high. However, these phases are supposedly related to the appropriate hydrogen conductivity, which, in turn, is essential for efficiently catalyzing reactions involving hydrogen conversion.If, on the other hand, the temperatures selected for the heat treatment were too low or the duration of the heat treatment was too short, the level of residual oxygen in the carbon phase obtained was too high and the reduction of the metal precursors was incomplete, leading to decreased catalytic activity as a result. Additionally, it should be noted that, in view of the prior art, the formation of the non-graphitizing carbon phase of the invention, as a result of the process of the present invention, may seem surprising. However, without intending to be limited by theory, it is assumed that the formation of non-graphitizing carbon under the low-temperature conditions of the process of the present invention is facilitated by the presence of high concentrations of metal precursors in a highly dispersed manner in the intermediate product P prior to subsequent heat treatment. The process of the invention produces non-graphitizing carbon material in granular form. Non-graphitizing carbon can be identified by a person experienced in TEM analysis (see PW Albers, “Neutron scattering study of the terminating protons in the basic structural units of non-graphitizing and graphitizing carbons”, Carbon 109 (2016), 239-245, page 241, figure 1c). The experimental results obtained in conjunction with the present invention indicate that the catalytic activity of the material obtained by means of the process of the invention correlates well with its content of non-graphitizing carbon grains that exhibit the characteristics of the invention. Generally, 90% of the non-graphitizing carbon grains obtained by the process of the present invention exhibit moderate size, i.e., diameters between 2 pm and 200 pm. It has now been discovered that, generally, more than 95% of these moderately sized non-graphitizing carbon grains obtained by the process of the present invention contain iron nanoparticles dispersed therein that conform to the relationship 4.5 dp / ω > D > 0.25 dpI ω (with dp denoting the average diameter of the iron nanoparticles in the non-graphitizing carbon grains, D denoting the average distance between the iron nanoparticles in the non-graphitizing carbon grains, and ω denoting the combined total mass fraction of metal in the non-graphitizing carbon grains).Generally, the process of the present invention produces grains in which only the very small grain fraction and the very large grain fraction—that is, the particle fractions outside the moderate size range between 2 µm and 200 µm—contain significant portions of grains where the iron nanoparticles do not conform to the ratio 4.5 dp / ω > D > 0.25 dpI ω. Consequently, the process of the present invention generally produces materials with a high content of grains containing iron nanoparticles where the iron nanoparticles conform to the ratio 4.5 dp / ω > D > 0.25 dp / ω. However, materials with lower contents of these grains can be obtained by other processes or by dilution with other materials and are therefore also covered by the present invention. Accordingly, in a preferred embodiment, the present invention relates to a catalytically active material comprising non-graphitizing carbon grains with iron nanoparticles dispersed therein, wherein the iron nanoparticles in more than 90% of moderately sized non-graphitizing carbon grains, i.e., non-graphitizing carbon grains with a diameter between 2 pm and 200 pm, conform to the ratio 4.5 dp / ω > D > 0.25 dp / ω, and wherein furthermore dp, the average diameter of the iron nanoparticles in the non-graphitizing carbon grains, is in the range of 1 nm to 20 nm, D, the average distance between iron nanoparticles in the non-graphitizing carbon grains, is in the range of 2 nm to 150 nm, and ω, the combined total mass fraction of metal in the non-graphitizing carbon grains, is in the range of 30 wt% to 70 wt% of the total mass of the pcQznn / zznz / B / Yi grains of non-graphitizing carbon. In another preferred embodiment, the present invention relates to a catalytically active material comprising non-graphitizing carbon grains with iron nanoparticles dispersed therein, wherein the iron nanoparticles in more than 95% of moderately sized non-graphitizing carbon grains, i.e., non-graphitizing carbon grains with a diameter between 2 pm and 200 pm, conform to the ratio 4.5 dp / ω > D > 0.25 dp / ω, and wherein furthermore dp, the average diameter of the iron nanoparticles in the non-graphitizing carbon grains, is in the range of 1 nm to 20 nm, D, the average distance between iron nanoparticles in the non-graphitizing carbon grains, is in the range of 2 nm to 150 nm, and ω, the combined total mass fraction of metal in the non-graphitizing carbon grains, is in the range of 30 wt% to 70 wt% of the mass total of non-graphitizing carbon grains. The iron nanoparticles in the non-graphitizing carbon material of the invention are composed mainly of elemental iron but may also contain, for example, iron oxide and / or dopant metal and / or secondary metal. Computer-assisted analysis of transmission electron microscopy (TEM) images together with the TGZ method derived from Degussa allows the determination of the diameters of individual iron nanoparticles as well as statistical measures of sets of them (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). In the context of the present invention, the average diameter of the iron nanoparticles, dp, and the average 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. The powders are typically dispersed in solvents under ultrasonic application. The ultrasonic application breaks down agglomerates into aggregates, resulting in a distribution of aggregates rather than a mixture of aggregates and agglomerates. A micropipette is then used to drop a single drop onto a film-coated mesh placed over a piece of filter paper. Excess liquid is quickly drawn through the filter paper to prevent agglomeration from drying. The suspended grains should not be too dense, as the shape and contour of the nanoparticles will not be clearly visible due to contact and overlapping of the grains. An optimal dilution should be determined through trial experiments with a series of dilutions. In general, it can be stated that the type of preparation has little effect on the result of the evaluation of the size of the primary nanoparticles. 2. Test performance The individual nanoparticles to be characterized based on TEM images must be photographed with sufficiently sharp outlines. pcQznn / zznz / B / Yi A distribution of nanoparticles that is not very dense with few overlaps or particles that are as far apart as possible in TEM images facilitates measurement in the TGZ3, but does not influence the measurement result. After examining different image sections of a TEM preparation, suitable areas are selected accordingly. It should be noted that the proportion of small, medium, and large nanoparticles for the respective sample is representative and characteristic, and the operator does not selectively favor small or large particles. The total number of primary nanoparticles to be measured depends on the size dispersion range of the primary nanoparticles: the wider the dispersion range, the more particles must be measured to obtain an adequate statistical statement. For metallic catalysts, approximately 1500 individual particles are measured. A calibrated Hitachi H-7500 field transmission electron microscope, operated at 100 keV and equipped with a CCD camera, was used for all TGZ analyses. 3. Description of the measurement procedure The measurement procedure is performed in accordance with the TGZ3 manual by Carl ZEISS (TeilchengróBenanalysator TGZ3, (TGZ3 Particle Size Analyzer); Manual Fa. Carl ZEISS). 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 und M. Voll, “Distribution function for describing the particle size distribution of Soot and pyrogenic oxides”, (Distribution function for describing the particle size distribution of soot and pyrogenic oxides). Chemiker-Zeitung, 102 (1978), Nr. 4,131-135). The statistical summary is compiled in the form of a report. A detailed statistical description is given in (Lothar Sachs, “Statistical methods”, 5th Edition, Springer-Verlag, Berlin (1982)). 5. Evaluation and visualization of results a. Total number of particles (N) b. Particle size distributions q0(x) and q3(x) evaluated from 1500 isolated nanoparticles per sample c. Particle diameter dn, mean diameter (dn) n¡ = number of particles with diameter d¡ d. Average distance D in rectangular plane D= ¿7dy* ídy Γdx* C / (.X* -x / + (y* -y / dx a, b = length, width of the rectangular plane x, y, x*, y* = particle coordinates. The combined total mass fraction of metal, ω, is defined as the fraction of the combined total masses of iron and all dopant and secondary metals, of the total mass of the material under consideration: ω = (m(iron) + m(dopant metals) + m(secondary metals)) / m(material);with m(iron) = total mass of elemental iron contained in the material in the form of elemental iron itself and / or in the form of any iron compound, m(dopant metals) = total combined mass of all elemental dopant metals contained in the material in the form of elemental dopant metals themselves and / or in the form of any compound of dopant metals, m(secondary metals) = total combined mass of all elemental secondary metals contained in the material in the form of elemental secondary metals themselves and / or in the form of any compound of secondary metals, and m(material) = total mass of the material under consideration. The total combined mass fraction of metal, ω, can be determined by all methods for quantitative elemental analysis, in particular X-ray fluorescence (XRF) and inductively coupled plasma atomic emission spectroscopy (ICP-AES). A suitable choice of process conditions according to the present invention allows control of the combined total mass fraction of metal, ω, in the resulting material: Processes that provide in step (a) solutions with a high metal content (iron and combined dopant and secondary metals) produce materials with a total combined metal mass fraction, ω, greater than processes that provide in step (a) solutions with a lower metal content. Heat treatment processes in step (c) at high temperatures in the range of 200°C to 380°C produce materials with a combined total mass fraction of metal, ω, greater than heat treatment processes in step (c) at lower temperatures. The process of the present invention produces granular material. The size of the individual particles of this material, as well as statistical measurements of assemblies thereof, can be determined by means of laser diffraction analysis (e.g., Ollas 1190 Series), a method well known to those experienced in this field. Generally, the process of the present invention produces granular material exhibiting the following particle size distribution: d10 = 5pm, d50 = 40pm, d90 = 150pm. In view of the fact that the material obtained by the process according to the present invention was found to be very suitable for manufacturing shaped catalysts, in a preferred embodiment, the present invention relates to a catalytically active material comprising non-graphitizing carbon grains with iron nanoparticles dispersed therein, wherein: dp, the average diameter of iron nanoparticles in non-graphitizing carbon grains, is in the range of 1 nm to 20 nm, D, the average distance between iron nanoparticles in the non-graphitizing carbon grains, is in the range of 2 nm to 150 nm, and pcQznn / zznz / B / Yi ω, the combined total mass fraction of metal in the non-graphitizing carbon grains, is in the range of 30 wt% to 70 wt% of the total mass of the non-graphitizing carbon grains, and wherein dp, D and ω are adjusted to the following relationship: 4.5dp / ω>D >0.25dp / ω, and where the non-graphitizing carbon grains exhibit the following particle size distribution: d10 = 5pm, d50 = 40 pm, d90 = 150 pm. There may be applications for materials according to the present invention where the presence of nitrogen is detrimental. Accordingly, in a preferred embodiment, the present invention relates to the material according to the invention wherein the total mass fraction of nitrogen is less than 1% by weight of the total mass of the material. Experimental results indicate that materials with relatively small iron nanoparticles can exhibit particularly attractive catalytic properties. Accordingly, in a preferred embodiment, the present invention relates to the material according to the invention, wherein the particle size (dp) is in the range of 4 nm to 18 nm. In a particularly preferred embodiment, the present invention relates to the material according to the invention, wherein the particle size (dp) is in the range of 6 nm to 14 nm. As indicated by experimental results, the addition of dopant metals affects the catalytic activity of the materials of the present invention. Accordingly, in a preferred embodiment, the present invention relates to the material according to the invention wherein the iron nanoparticles have been doped with a dopant metal, and wherein the dopant metal is selected from Na (sodium), K (potassium), Ca (calcium), Mg (magnesium), or mixtures thereof, and wherein the material exhibits a molar ratio RDM = n(iron):n(dopant metal) in the range of 5 to 1000. In a particularly preferred embodiment, the present invention relates to the material according to the invention wherein the iron nanoparticles have been doped with a dopant metal, and wherein the dopant metal is selected from Na (sodium) or K (potassium) or Ca (calcium) or Mg (magnesium) or mixtures thereof, and wherein the material exhibits a molar ratio RDM = n(iron): n(dopant metal) in the range of 10 to 500. In another preferred embodiment, the present invention relates to the material according to the invention, wherein the iron nanoparticles have been combined with a secondary metal, and wherein the secondary metal is selected from group 1 or group 2, with group 1 defined as: Mo (molybdenum) or W (tungsten) or mixtures thereof, and with group 2 defined as: Co (cobalt) or Cu (copper) or Mn (manganese) or mixtures thereof, and wherein the material exhibits a molar ratio RSM = n(iron): n(secondary metal) in the range of 1 to 50. Furthermore, the present invention relates to a process for manufacturing the materials of the invention. As previously stated, a combination of the two process steps was found to be crucial: (i) spray drying or freeze drying of the aqueous solution of the metal precursor and the organic carbon source and pcQznn / zznz / B / Yi (i) heat treatment at moderate temperatures of the resulting intermediate. Accordingly, in another aspect, the present invention is also directed to a process for manufacturing material according to the invention, comprising the following steps: (a) providing 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 iron salt, at least partially soluble in water, and wherein the organic carbon source is one or a combination of more than one saturated aliphatic di-, tri- or polycarboxylic acid, (b) spray-drying or freeze-drying the aqueous solution of the metal precursor and the organic carbon source and thereby obtaining the intermediate product P, (c) heat-treating the intermediate product P at a temperature in the range of 200°C to 380°C. Each of the process steps can be carried out in a batch or continuous format. Furthermore, in another aspect, the present invention is directed to materials that can be obtained by means of the process of the invention. As previously stated, the formation of the materials of the present invention requires a combination of spray drying or freeze-drying and suitable heat treatment at moderate temperatures. Consequently, it seems reasonable to assume that only the material present in solution, i.e., dissolved in the solution provided in step (a) of the process, can be transformed into the material according to the invention. However, undissolved matter in solid form can be suspended in the solution provided in step (a) as long as it does not interfere with the process of forming the material of the present invention. For example, such solids, which may originate from the undissolved metal precursor or organic carbon source, can form solid diluents of the material of the invention in the solid product obtained after step (c) of the process of the invention.Similarly, organic solvents may be dissolved or emulsified in the solution provided in step (a) as long as their presence does not interfere with the process forming the material of the present invention. However, in order to avoid interference with the process forming the material of the present invention, in preferred embodiments, the process of the invention is carried out with aqueous solutions, provided in step (a), that are free from undissolved matter in solid form as well as free from organic solvents. If no dopant metal and no secondary metal are used, the metal precursor in the solution provided in step (a) of the process of the present invention is one or a combination of more than one organic iron salt, at least partially soluble in water. In the present context, a salt is considered to be at least partially soluble in water if at least a fraction of the salt dissolves in the aqueous solution provided in step (a) under the conditions employed in the process. Preferably, if no dopant metal and no secondary metal are used, the metal precursor in the solution provided in step (a) of the process of the present invention is one or a combination of more than one organic iron salt, of which the desired amounts ecaznn / zznz / E / Yii to be included in the solution are completely soluble in the aqueous solution of step (a). In a preferred embodiment of the present invention, no dopant metal and no secondary metal are used. In another preferred embodiment of the present invention, the dopant metal is used but the secondary metal is not used. If a dopant metal is used, the metal precursor in the solution provided in step (a) of the process of the present invention is a combination of one or more organic iron salts, at least partially soluble in water, with one or more organic salts of one or more dopant metals, at least partially soluble in water. Preferably, if a dopant metal is used, the metal precursor in the solution provided in step (a) of the process of the present invention is a combination of one or more organic iron salts with one or more organic salts of one or more dopant metals, the desired amounts of which are completely soluble in the aqueous solution of step (a). If a secondary metal is used, the metal precursor in the solution provided in step (a) of the process of the present invention is a combination of one or more organic iron salts, at least partially soluble in water, with one or more organic salts of one or more secondary metals, at least partially soluble in water. Preferably, if a secondary metal is used, the metal precursor in the solution provided in step (a) of the process of the present invention is a combination of one or more organic iron salts with one or more organic salts of one or more secondary metals, the desired amounts of which are completely soluble in the aqueous solution of step (a). If a secondary dopant metal is used, the metal precursor in the solution provided in step (a) of the process of the present invention is a combination of one or more organic iron salts, at least partially soluble in water, with one or more organic salts of one or more dopant metals, at least partially soluble in water, and one or more organic salts of one or more secondary metals, at least partially soluble in water. Preferably, if a secondary dopant metal is used, the metal precursor in the solution provided in step (a) of the process of the present invention is a combination of one or more organic iron salts with one or more organic salts of one or more dopant metals and one or more organic salts of one or more secondary metals, at least partially soluble in water, the desired amounts of which are to be included in the solution being completely soluble in the aqueous solution of step (a). The preferred organic anions of the metal precursors in the solution provided in step (a) of the process of the present invention are acetate, carbonate, oxalate, citrate, malonate, tartrate, and glutarate. If nitrogen must not be avoided, nitrate is another preferred anion of the metal precursors in the solution provided in step (a). Saturated aliphatic di-, tri-, or polycarboxylic acids, alone or as part of a mixture, may be used as sources of organic carbon in the aqueous solution provided in step (a), provided they support the formation of the materials of the present invention. In preferred embodiments, malonic acid, glutaric acid, citric acid, or mixtures thereof are used as sources of organic carbon in the aqueous solution provided in step (a) of the process of the present invention. In a particularly preferred embodiment of the present invention, citric acid is used as the source of organic carbon in the aqueous solution provided in step (a) of the process of the present invention. The aqueous solution provided in step (a) is spray-dried or freeze-dried in step (b) of the process of the present invention. The resulting product is referred to as intermediate product P in the context of the present invention. The process parameters for spray drying and freeze-drying can be varied over a wide range, provided that the drying process is carried out without interruption and the combined water and organic solvent content of intermediate product P is below 10% by weight. In a preferred embodiment of the present invention, the aqueous solution provided in step (a) is spray-dried in step (b) of the process of the present invention. The heat treatment according to step (c) of the process of the present invention is carried out under defined temperature and inert gas atmosphere conditions, for example, nitrogen or air. A wide range of ovens suitable for this purpose are commercially available. In preferred embodiments, the heat treatment is carried out under an inert gas atmosphere, for example, nitrogen. The heating rates during the heat treatment must be sufficiently small to allow for homogeneous heat distribution, i.e., generally 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 in the range of 200°C to 380°C. In preferred embodiments of the present invention, the heat treatment of the intermediate product P is carried out at a temperature in the range of 255°C to 375°C.In particularly preferred embodiments, the heat treatment of intermediate product P is carried out at a temperature in the range of 300°C to 350°C. Generally, the heat treatment of intermediate product P is carried out over a period of 1 to 4 hours, but heat treatment for longer or shorter periods may also be acceptable. Heating and cooling intervals are not considered when determining the duration of the heat treatment. In preferred embodiments, the heat treatment of intermediate product P is carried out over a period of 1 to 4 hours. As previously stated, the materials according to the present invention exhibit catalytic activity. Consequently, in another aspect, the present invention also relates to the use of materials of the present invention as catalysts. The materials according to the present invention can be used, for example, as catalysts in liquid-phase hydrogenations of organic compounds, specifically unsaturated compounds such as alkenes and alkynes, aldehydes and ketones, esters and amines, nitro compounds and nitriles. The materials according to the present invention are also highly active catalysts for the reductive amination of carbonyl compounds. Accordingly, in another aspect, the present invention further relates to the use of the materials of the invention as catalysts for the hydrogenation of organic compounds and / or the reductive amination of carbonyl compounds. The materials according to the present invention can also be used as catalysts in the conversion of carbon monoxide, carbon dioxide, or mixtures thereof, with hydrogen, to alkenes, alkanes, or mixtures thereof. Accordingly, in another aspect, the present invention also relates to the use of materials of the invention as catalysts for the conversion of carbon monoxide, carbon dioxide, or mixtures thereof, with hydrogen, to alkenes, alkanes, or mixtures thereof. The materials according to the present invention can be used as catalysts in unmodified form or can be transformed into catalyst bodies by means of shaping processes (e.g., tableting, granulation, extrusion, coating, 3D printing), well known to people experienced in the field. Examples Examples Fe a,b - Preparation of Fe nanoparticles embedded in carbon Carbon-embedded Fe nanoparticles were prepared by dissolving 14.4 g of citric acid (Puriss, Sigma Aldrich) in 75 mL of deionized water under 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 under constant stirring at room temperature. The iron(II) 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 (Büchi, Mini Spray Dryer B-290) with a constant inlet temperature of 220°C, an outlet temperature of 120°C, and a pump speed of 20%. The resulting powder was divided into two fractions of equal mass for final heat treatment. The first sample was heat-treated in a tubular furnace under a nitrogen atmosphere, with a gradual increase over 180 min to 300°C, where the temperature was maintained for another 4 h followed by natural cooling. The resulting catalyst powder was labeled FeCat. 1a. The second sample was heat-treated in a similar manner under a nitrogen atmosphere. The sample was heated to 350°C for 180 min, where the temperature was maintained for 4 h, followed by natural cooling. The resulting catalyst powder was labeled FeCat. 1b. The materials exhibit the following characteristics, which were determined by XRF (X-ray fluorescence) and TGZ analysis using a calibrated Hitachi H-7500 field transmission electron microscope, operated at 100 keV, equipped with a CCD camera: ecaznn / zznz / E / Yii ID dp ω D FeCat. 1a 10 nm 0.56 17 nm FeCat. 1b 12nm 0.61 14nm Comparative Examples For comparison, a highly loaded catalyst containing 20 wt% iron on a conventional Vulcan XC72R carbon support was prepared by incipient moisture impregnation and labeled FeCat. Ref. The materials exhibit the following characteristics, which were determined by XRF (X-ray fluorescence) and TGZ analysis using a calibrated Hitachi H-7500 field transmission electron microscope, operated at 100 keV, equipped with a CCD camera: ecaznn / zznz / E / Yii ID ω D FeCat. Ref 72 nm 0.20 nd* Catalytic activity test Batch experiments were conducted to determine the catalytic activity and selectivity of the materials using 200 mg of catalyst and 5 mmol of substrate in 5 mL of methanol. Autoclaves were 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. I. Hydrogenation of N-benzylidene-benzylamine H2 / Cat Meoh ID Cat. ID Duration h TempT°C Reagent % product % secondary product % 1 FeCat. 1 to 20.00 100.00 66.1 29.5 4.40 2 FeCat. 1 b 20.00 100.00 64.0 31.9 4.10 3 FeCat. Ref 20.00 100.00 89.8 0 10.2 II. Hydrogenation of methyl crotonate to methyl butyrate H2 / Cat OMe 102.07ΟΜθ MeOH θ5^ιοθ2: ID Cat. ID Duration h Temp. T °C reactant % product % 4 FeCat. 1 a 20.00 80.00 5.00 95.00 5 FeCat. 1 b 20.00 80.00 0.00 100.00 6 FeCat. Ref 20.00 80.00 38.7 61.3 III. Hydrogenation of dodecanitrile H2 / Cat CN -------+(C12H27)2NH MeOH ID Cat. ID Duration h Temp. T°C Reagent % product % secondary product % 7 FeCat. 1 a 20.00 80.00 85.9 7.60 6.40 8 FeCat. 1 b 20.00 80.00 73.0 16.7 10.3 9 FeCat. Ref 20.00 80.00 98.0 0.00 2.00 IV. Hydrogenation of acetylnaphthalene ID Cat. ID Duration h Temp. T°C Reagent % product % secondary product % 10 FeCat. 1 a 20.00 80.00 62.6 37.4 0.00 11 FeCat. 1 b 20.00 80.00 51.6 48.4 0.00 12 FeCat. Ref 20.00 80.00 100.0 0.00 0.00

Claims

1. A catalytically active material comprising non-graphitizing carbon grains with iron nanoparticles dispersed therein, wherein: dp, the average diameter of the iron nanoparticles in the non-graphitizing carbon grains, is in the range of 1 nm to 20 nm, D, the average distance between the iron nanoparticles in the non-graphitizing carbon grains, is in the range of 2 nm to 150 nm, and ω, the combined total mass fraction of metal in the non-graphitizing carbon grains, is in the range of 30 wt% to 70 wt% of the total mass of the non-graphitizing carbon grains, wherein dp and D are measured by TGZ-TEM as described herein, and wherein dp, D and ω are adjusted to the following relationship: 4.5dp / ω>D >0.25dp / ω.

2. The material according to claim 1, wherein the non-graphitizing carbon grains exhibit the following particle size distribution: d10 = 5 μm, d50 = 40 μm, d90 = 150 μm 3. The material according to any of claims 1 to 2, wherein the total mass fraction of nitrogen in the non-graphitizing carbon grains is less than 1% by weight of the total mass of the non-graphitizing carbon grains.

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

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

6. The material according to any one of claims 1 to 5, wherein the material has been doped with an occupying metal, and wherein the dopant metal is selected from Na (sodium), K (potassium), Ca (calcium), Mg (magnesium) or mixtures thereof, and wherein the non-graphitizing carbon grains exhibit a molar ratio RDM = n(iron): n(dopant metal) in the range of 5 to 1000.

7. The material according to any one of claims 1 to 5, wherein the material has been combined with secondary metal, and wherein the secondary metal is selected from group 1 or group 2, with group 1 defined as: Mo (molybdenum) or W (tungsten) or mixtures thereof, and with group 2 defined as: Co (cobalt) or Cu (copper) or Mn (manganese) or mixtures thereof, pcQznn / zznz / B / Yi, and wherein the non-graphitizing carbon grains exhibit a molar ratio RSM = n(iron) : n(secondary metal) in the range of 1 to 50.

8. A process for manufacturing material according to any of claims 1 to 7, comprising the following steps: (a) providing 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 iron salt, at least partially soluble in water, and wherein the organic carbon source is one or a combination of more than one saturated aliphatic di-, tri- or polycarboxylic acid, (b) spray-drying or freeze-drying the aqueous solution of the metal precursor and the organic carbon source and thereby obtaining the intermediate product P, (c) heat-treating the intermediate product P at a temperature in the range of 200°C to 380°C.

9. The process according to claim 8, wherein the organic carbon source is selected from malonic acid, tartaric acid, citric acid and mixtures thereof.

10. The process according to any of claims 8 to 9, wherein the intermediate product P is heat-treated at a temperature in the range of 255°C to 375°C for 1 to 4 hours.

11. The process according to any of claims 8 to 10, wherein the intermediate product P is heat-treated at a temperature in the range of 300 °C to 350 °C for 1 to 4 hours.

12. A use of the material according to any of claims 1 to 7 as a catalyst.

13. Use according to claim 12, wherein the catalyst is a catalyst for the hydrogenation of organic compounds and / or the reductive amination of carbonite compounds.

14. Use according to claim 12, wherein the catalyst is a catalyst for the conversion of carbon monoxide, carbon dioxide, or mixtures thereof, with hydrogen, to alkenes, alkanes, or mixtures thereof. ecaznn / zznz / E / Yii