Method for preparing catalysts derived from lignocellulosic biomass for the conversion of organic compounds

Abstract

The method described in the present invention concerns the preparation of heterogeneous catalysts having low contents of metal, such as ruthenium, in the form of nanoparticles, and carbonaceous supports derived from lignocellulosic biomass waste for the conversion of organic compounds, such as levulinic acid, into gamma-valerolactone. The appropriate experimental method developed allows the production of heterogeneous catalysts that have excellent catalytic behaviour in mild reaction conditions, which, together with the low metal content of same, minimises the economic and energy cost of the overall process. Thus, the strategy followed allows the development of a process that encompasses the principles of the circular economy and which could be used to obtain molecules of great interest in the chemical industry.

Description

[0001] PROCEDURE FOR THE PREPARATION OF CATALYSTS DERIVED FROM LIGNOCELLULOSIC BIOMASS FOR THE CONVERSION OF ORGANIC COMPOUNDS

[0002] DESCRIPTION

[0003] FIELD OF INVENTION

[0004] The scope of the present invention focuses on the industrial sector, specifically on biomass conversion processes and the production of chemical products from biomass. The present invention relates to the preparation of heterogeneous catalysts based on low ruthenium content, in the form of nanoparticles, and carbonaceous supports derived from lignocellulosic biomass waste for the conversion of organic compounds, such as the conversion of levulinic acid to gamma-valerolactone using mild reaction conditions.

[0005] STATE OF THE ART

[0006] The current production and consumption system is based on finite raw materials, from which the desired products are prepared, used, and then discarded. This "linear economy" model, coupled with the growing demand driven by the growing world population, poses a major challenge in terms of sustainability. In contrast, the "circular economy," understood as a production and consumption model based on the use of biodegradable resources for the production of consumer goods that do not cause environmental damage at the end of their useful life, is an ideal model from a sustainability perspective. Therefore, significant efforts are being made to transition from a linear economy to a circular economy.

[0007] One of the objectives addressed in the circular economy is centered on the concept of the "bioeconomy," which is defined by the Food and Agriculture Organization of the United Nations (FAO) as the production, utilization, conservation, and regeneration of biological resources, including knowledge, science, technology, and innovation, to provide sustainable solutions (information, products, processes, and services) within and across all economic sectors and enable a transformation to a sustainable economy. Biorefineries are essential to the development of the bioeconomy, as they replace fossil resources with renewable ones, integrating processes to convert biomass into fuels, electricity, and chemicals.In this context, the importance of platform molecules, understood as molecules derived from biomass and serving as starting materials for the preparation of diverse chemical products, must be highlighted. In 2004, the United States Department of Energy (DOE) identified the 12 platform molecules that have traditionally been considered: 1,4-dicarboxylic acids (succinic, fumaric, and maleic), furan-2,5-dicarboxylic acid, 3-hydroxypropionic acid, aspartic acid, glucaric acid, glutamic acid, itaconic acid, levulinic acid, 3-hydroxybutyrolactone, glycerol, sorbitol, and xylitol / arabitol. Later, in 2010, the DOE updated this list to include molecules such as ethanol and furfural.

[0008] The reactivity of the ketone and carboxylic functional groups present in levulinic acid gives it great versatility, and a large number of molecules of great interest can be prepared from it, such as esters, acrylic acid, 1,4-pentanediol, α-angelica lactones, 2-methyltetrahydrofuran, and γ-valerolactone (GVL).

[0009] GVL can be obtained from the catalytic hydrogenation of levulinic acid, which can take place via two possible reaction pathways: (1) hydrogenation of levulinic acid to give 4-hydroxyvaleric acid, followed by dehydration to give GVL; (2) dehydration of levulinic acid to α-angelica lactone and subsequent hydrogenation to GVL [1],

[0010] GVL is a molecule of great interest, both for its properties (it is miscible with water, biodegradable and has very low volatility under normal conditions) [2], and for the wide range of applications in which it can be used, among which it is worth mentioning its use as an additive in food and cosmetic products, a green solvent as an alternative to solvents classified as hazardous (such as N-ethylpyrrolidone, N-methylpyrrolidone, ethyl acetate, etc.), a precursor in the synthesis of high added value molecules (butene, valeric acid, 2-methyltetrahydrofuran, 1,4-pentanediol, etc.), as well as the preparation of fuels or fuel additives, such as valerous esters [2].

[0011] The hydrogenation of levulinic acid to GVL can be carried out using homogeneous and heterogeneous catalysts. The most commonly used homogeneous catalysts are usually based on noble metals, such as ruthenium ([RuCh(PPh3)3], [RuH2(PPhs)4], [Ru(acac)s] / PnBu3, [Ru(acac)3] / TPPTS, [Ru(acac)3] / DPPB, [Ru(acac)3] / thphos, etc.), iridium ([lr(COE)2Cl2]2 / PNPtBu, [Ir-Bipy-OMe], etc.) and palladium ([Pd(DTBPE)CI2], etc.) [1], but the use of homogeneous catalysts with other compositions has also been reported. However, the high boiling point of GVL (208 °C) makes it difficult to separate it from the reaction medium using a distillation process, so it is usually preferred to use heterogeneous catalysts [3,4]. The heterogeneous catalysts most commonly used in the hydrogenation of levulinic acid to GVL are based, like the homogeneous systems, on ruthenium.Most of the heterogeneous catalysts studied contain relatively high amounts of ruthenium (generally between 1 and 5% by weight) and the catalytic reaction is carried out using temperatures above 100 °C, both of which are factors determining the high costs of the overall process, both from an economic and energetic point of view. Some of the ruthenium-based heterogeneous catalysts have been previously patented [5-7].

[0012] In relation to the reported works on ruthenium-based catalysts supported on carbonaceous materials, studies have been published using commercial catalysts (Ru / C with 3 wt.% ruthenium, from Evonik [8]), reduced graphene oxide and reduced graphene oxide functionalized with benzosulfonic groups (with ruthenium contents of 4.7 and 4.0 wt.%, respectively) [9], hollow carbon spheres (ruthenium contents of 1.18 wt.%)

[0010] , nitrogen-doped carbon spheres (ruthenium contents of 0.5, 1.5 and 3.0 wt.%)

[0011] , mesoporous carbon (ruthenium content of 1.96 wt.%)

[0012] , nitrogen-doped mesoporous carbon (ruthenium contents of 5 wt.%)

[0013] , carbon nanotubes and nitrogen- and sulfur-doped carbon nanotubes (ruthenium contents of 3.9, 1.3-4.0 and 4.2% by weight, respectively)

[0014] , nanodiamonds (ruthenium content of 2% by weight)

[0015] , core-shell structures formed by carbon fibers and graphitic carbon nitride (ruthenium content of 3% by weight)

[0016] , and other composite materials that involve the use of metal-organic frameworks as precursors (known as “Metal Organic Frameworks” or MOFs), such as carbon-ALOs (ruthenium contents of 3.1% by weight)

[0017] or T¡O2-nitrogen-doped carbon (ruthenium content of 0.13 and 0.23% by weight)

[0018] , in which, although in some cases the ruthenium content is not high, the final cost of the catalyst is high due to the use of the precursors used in the synthesis of the MOFs from which the catalysts were prepared, as well as the numerous synthesis stages required in the preparation of the final materials.

[0013] In recent years, studies have also been reported in which the carbonaceous material used as a catalytic support has been prepared from a biomass residue. Thus, the overall process of preparing the catalysts and their application to obtain a high added value product, such as GVL, from a biomass-derived molecule, such as levulinic acid, is perfectly aligned with the objectives of the circular economy. Rodríguez Vl et al., in their work entitled "Ruthenium catalysts supported on hydrothermally treated carbon from rice husk: the effect of reduction temperature on the hydrogenation reaction of levulinic acid to y-valerolactone"

[0019] , used rice husks to prepare carbonaceous materials, which were subsequently used to synthesize catalysts containing 2% by weight of ruthenium. Although mild reaction conditions (70 °C and 15 bar) were used in this case, the synthesis of the catalysts involved the reduction of the metallic phase at elevated temperatures (between 100 and 350 °C), and the resulting materials showed moderate levulinic acid conversions and selectivity toward LVG. In this sense, the levulinic acid conversion was 82% and the selectivity toward LVG was 90% for the catalyst with the best catalytic performance in the first reaction cycle, decreasing to 72% and 78%, respectively, in the third reaction cycle.

[0014] Ruiz-Bernal Z. et al., in their work entitled "Ru catalysts supported on commercial and biomass-derived activated carbons for the transformation of levulinic acid into y-valerolactone under mild conditions"

[0020] , used an almond shell residue for the preparation of an activated carbon that was used for the preparation of a catalyst with 1% by weight of ruthenium. In this case, the synthesis of the catalyst involved numerous experimental steps and long synthesis times, including the mechanical mixing of the carbon support with the solution of the ruthenium precursor for 24 h, ultrasonic treatment for 3 h, solvent removal, drying of the material at 115 °C and, in some cases, reduction of the metallic phase with 75 mL min -1of a hydrogen stream at 250 °C for 4 h. The multiple steps described in this reference entail consequent disadvantages in terms of economics and energy. The resulting catalyst was evaluated using a hydrogen pressure of 15 bar and two reaction temperatures (170 and 70 °C), achieving conversions of 96% and selectivities towards GVL of 84% at 170 °C, while at 70 °C, conversions are close to 100% and selectivities towards GVL are around 60%.

[0015] Bounoukta CE et al., in their work entitled “Functionalized biochars as supports for Ru / Catalysts: Tunable and efficient materials for y-valerolactone production"

[0021] prepared catalysts consisting of carbonized ruthenium nanoparticles, which were obtained from cotton stalks. In this case, the incorporation of the metallic phase (1, 2 and 5% by weight of ruthenium) was carried out by impregnation with the precursor salt and reduction in a hydrogen atmosphere at 400 °C. The catalytic tests were carried out for 2 h, at 100 °C and with a hydrogen atmosphere of 10 bar. Among the catalysts prepared in this work, the best performance was obtained for the one whose support was prepared by pretreating the starting biomass with HNO3 and ZnCh (an activating agent dangerous for the environment).

[0016] Subsequently, they carried out a heat treatment in a CO2 atmosphere at 780 °C. The ruthenium catalysts were prepared by impregnating the supports with the metallic precursor, evaporating the solvent in a rotary evaporator, drying the samples at 100 °C and, finally, reducing the metallic phases at 400 °C for 2 h in a hydrogen atmosphere. Therefore, the materials used in this work require numerous experimental steps, with the consequent associated economic and energy costs.

[0017] Furthermore, other authors have also studied the catalytic behavior of heterogeneous systems based on ruthenium and carbonaceous materials using hydrogen sources other than molecular hydrogen in the gas phase.

[0018] J^drzejczyk M. et al. in his work entitled “The influence of carbon nature on the catalytic performance of Ru / C in levulinic acid hydrogenation with internal hydrogen source"

[0022] used formic acid as a hydrogen source and evaluated the catalytic behavior of ruthenium catalysts supported on carbonaceous materials with different properties and using a reaction temperature of 190 °C. In this case, it was observed that, although formic acid conversions of 100% were achieved, levulinic acid conversions were relatively low (38-45%) in the absence of molecular hydrogen in the gas phase in the reaction medium.

[0019] Seenivasan K. et al., in their work entitled “Graphene oxide framework-confined Ru (Ru@GOF) as recyclable catalyst for hydrogenation of levulinic acid into y-valerolactone with formic acid'

[0023] They also used formic acid as a hydrogen source to carry out the hydrogenation of levulinic acid with catalysts based on ruthenium nanoparticles confined in graphene oxide structures and organic ligands. In this case, the catalysts had a ruthenium content of 3.3–3.5% by weight, and the reaction was carried out for 8 hours at 90 °C.

[0020] Therefore, taking into account the above, it is necessary to find a suitable procedure for the preparation of heterogeneous catalysts with low metal contents that can be used in procedures such as the selective hydrogenation of levulinic acid to GVL under mild reaction conditions, so that the economic and energy cost of the overall process is minimized and that they are aligned with the objectives of the circular economy.

[0021] The present invention is focused on the process for preparing heterogeneous catalysts consisting of an active metallic phase formed by low transition metal contents in the form of highly dispersed metallic nanoparticles and carbonaceous materials derived from lignocellulosic biomass waste for the conversion of organic compounds and, in particular, of levulinic acid to gamma-valerolactone.

[0022] Among other advantages, thanks to a reduction step of the metallic phase using a solution of a reducer, such as NaBH4, the process of the invention avoids the use of hydrogen gas at high temperatures.

[0023] Furthermore, the dispersion of the nanoparticles obtained according to the process of the present invention and the size of said nanoparticles give rise to better results in the reactions catalyzed by these heterogeneous catalysts.

[0024] DESCRIPTION OF THE INVENTION

[0025] The preparation procedure for heterogeneous catalysts based on carbonaceous materials derived from lignocellulosic biomass waste and low metal contents in the form of metal nanoparticles is detailed below.

[0026] The present invention relates to a process for preparing a heterogeneous catalyst comprising:

[0027] (i) preparation of a carbonaceous support from lignocellulosic biomass residues, by hydrothermal carbonization, with the addition of an aqueous solution of phosphoric acid (activating agent) in a concentration between 25% by weight and 15% by weight of the acid with respect to the weight of the aqueous solution, for a time between 6 and 20 hours, preferably between 6 and 12 hours, and more preferably, between 6 and 8 hours,

[0028] (i) heat treatment of the product obtained in step (i) at temperatures between 350 and 1000 °C, preferably at temperatures between 450 °C and 1000 °C, obtaining an activated carbon,

[0029] (iii) incorporation of a metallic phase into the activated carbon obtained in step (i), by mixing under stirring for a time between 1 and 4 hours a dispersion of the activated carbon obtained in step (i) with an aqueous solution containing a precursor of a transition metal and

[0030] (iv) a step of reducing the metallic phase to an active metallic phase using a solution of a reducer, obtaining the heterogeneous catalyst.

[0031] Step (i) comprises the preparation of a carbonaceous support from lignocellulosic biomass residues, by means of hydrothermal carbonization, with the addition of an aqueous solution of phosphoric acid in a concentration between 25% by weight and 15% by weight of the acid with respect to the weight of the aqueous solution, for a time between 6 and 20 hours, preferably between 6 and 12 hours, and more preferably, between 6 and 8 hours.

[0032] Lignocellulosic biomass residues can be any biomass (coconut shell, eucalyptus, almond shell (AS) or hemp, etc.) and are preferably selected from almond shell (AS) and hemp.

[0033] Phosphoric acid is present in the carbonization stage in a solution having a phosphoric acid concentration between 25% by weight and 15% by weight, both values ​​included, preferably, between 23% and 15%, more preferably, between 20% and 15%.

[0034] The terms “lignocellulosic biomass” and “biomass precursor” are used interchangeably.

[0035] H3PO4 / lignocellulosic biomass ratios between 1 / 2 and 2 / 1 are used, such as 1 / 2, 1 / 1 and 3 / 2, or 1 / 1.

[0036] According to particular embodiments, the lignocellulosic biomass residue is almond shell, and HsPCU / lignocellulosic biomass ratios equal to 1 / 2, 1 / 1, 3 / 2 and 2 / 1 are used, the latter (2 / 1) being the optimal ratio.

[0037] According to particular embodiments, the lignocellulosic biomass residue is hemp, and H3PO4 / lignocellulosic biomass ratios equal to 1 / 2, 1 / 1 and 3 / 2 are used, with 1 / 1 being the optimal ratio.

[0038] Biomass waste can be pre-milled and sieved to achieve optimal particle size. Particle sizes can range from 0.4 mm to 1.0 mm, for example.

[0039] Optionally, biomass waste can be subjected to a grinding process and subsequently to a washing process.

[0040] Washing of biomass residues can be carried out with an acid solution, such as a solution of H2SO4 in distilled water with a final sulfuric acid concentration of 2% by weight.

[0041] After washing the biomass residues with an aqueous acid solution, they are repeatedly washed with distilled water until a neutral pH is achieved. In particular embodiments, the biomass residues are dried in an oven, for example, between 100 and 140°C, for example, at 110°C. The drying time for the biomass residues ranges from 8 to 20 hours, for example, for 12 hours.

[0042] The hydrothermal carbonization stage in the presence of phosphoric acid can be carried out using an autoclave reactor, which can be made of Teflon lined with a stainless steel jacket.

[0043] The hydrothermal carbonization treatment in step (i) is carried out in a temperature range between 150 °C and 250 °C, preferably 200 °C.

[0044] Stage i) comprises performing a heat treatment of the product obtained in stage i) at temperatures between 350 and 1000 °C, obtaining activated carbon.

[0045] In step (i), according to particular embodiments, the heat treatment can be carried out at a temperature between 450 °C and 950 °C, inclusive.

[0046] In step (i), according to particular embodiments, the heat treatment can be carried out at a temperature between 350 °C and 400 °C, inclusive.

[0047] The heat treatment of carbon support activation can be carried out in a tubular furnace.

[0048] According to particular embodiments, the heat treatment for activating the carbon support is carried out at 450 °C. According to further particular embodiments, the lignocellulosic biomass residue is almond shells and the heat treatment of the carbon support is carried out at 450 °C.

[0049] The activation heat treatment of the carbon support can be carried out using a heating ramp of 5 °C min -1 until reaching the desired temperature and maintaining the final temperature for a time between 1 and 4 hours, for example, for 2 hours.

[0050] According to particular embodiments, the heat treatment for activating the carbon support is carried out at 550 °C. According to further particular embodiments, the lignocellulosic biomass residue is almond shells and the heat treatment of the carbon support is carried out at 550 °C.

[0051] According to particular embodiments, the heat treatment of the carbon support is carried out at 900 °C. According to further particular embodiments, the lignocellulosic biomass residue is almond shell and the heat treatment of the carbon support is carried out at 900 °C.

[0052] According to additional particular embodiments, the lignocellulosic biomass residue is almond shell and the heat treatment of the carbon support is carried out at 450 °C and then a heat treatment at 900 °C is carried out.

[0053] According to additional particular embodiments, the lignocellulosic biomass residue is hemp and the heat treatment of the carbon support is carried out at 550 °C.

[0054] In step (i), the resulting activated carbon may be washed with distilled water until a neutral pH is reached. The washings may be carried out, for example, between 50 and 80 °C, preferably at temperatures between 60 °C and 70 °C, and more preferably at 60 °C.

[0055] Once the resulting activated carbon has been washed, it can be dried at 100 to 130 °C, for example at 110 °C.

[0056] The drying time of activated carbon can be between 10 and 15 hours, for example, for 12 hours.

[0057] Step (iii) of the process comprises incorporating a metallic phase into the activated carbon obtained in step (ii) by mixing, under stirring for a time between 1 and 4 hours, preferably 2 hours, a dispersion of the activated carbon obtained in step (iii) with an aqueous solution containing a precursor of a transition metal.

[0058] In the process of the invention, the metallic phase (metal precursor) is an inorganic salt of a transition metal, such as ruthenium, palladium, iron, or rhenium. The metal is preferably ruthenium.

[0059] The inorganic salt of Ru is, for example, chloride, such as RuCh.x W.

[0060] According to a particular embodiment, step (iii) comprises dispersing the activated carbon support (for example 0.5 g) in distilled water (for example, in 50 mL), dissolving a salt of a transition metal (such as 0.01 g of ruthenium chloride (RuCh.x W)) in distilled water (for example, 10 mL), adding this volume to the prepared activated carbon dispersion to achieve a final metal content of 1% by weight and leaving the mixture under stirring at room temperature for 2 hours. Step (iv) of the process comprises reducing the metallic phase, using a solution of a reducing agent.

[0061] The reduction of the metal salt can be carried out with any reducing agent. Preferably, the reducing agent is a metal hydride, and most preferably, the reducing agent is NaBh.

[0062] The molar ratio between the reducing agent and the metal can be, for example, between 10 / 1 to 5 / 1, preferably 5 / 1.

[0063] According to particular embodiments, the metal is Ru, the reducing agent is NaBhL and the molar ratio of NaBhL / Ru is 10 / 1 and 5 / 1, preferably 5 / 1.

[0064] After the reduction, the catalyst obtained is filtered, washed with distilled water and dried at a temperature between 60 °C and 75 °C, preferably between 60 °C and 70 °C and more preferably at 60 °C for 12 hours. The low temperatures used in drying the catalyst prevent the electronic properties of the surface of the metal nanoparticles from changing substantially.

[0065] The catalyst obtained according to the process of the invention has an apparent surface area greater than 700 m 2 g -1 , more specifically between 715 and 2000 m 2 g -1 . It has been proven that the surface area of ​​even up to 715 m 2 g -1 does not affect catalytic activity.

[0066] The active metal phase of the heterogeneous catalyst obtained is in the form of nanoparticles. The metal nanoparticles have an average size of 1 to 10 nm, preferably 1.6 to 3 nm, for example, ruthenium nanoparticles with an average nanoparticle size of 1.8 nm.

[0067] Unlike what occurs according to reference

[0020] , in the case of the present invention, particle aggregates are not obtained. Furthermore, according to the present invention, the dispersion of the metallic phase is good on any support, while according to

[0020] a good dispersion is only obtained on one of the supports used.

[0068] The heat treatment in step (i) can be carried out in an inert atmosphere, preferably with N2. The final metal content in the heterogeneous catalyst obtained is between 0.15% and 0.60% by weight, for example, 0.55% by weight relative to the total weight of the catalyst.

[0069] For a given reaction and catalyst type, the catalytic response depends on the catalyst characteristics. The dispersion of the metal phase in the support and the size of the nanoparticles are two determining factors for achieving good catalytic performance. In this case, the experimental procedure employed has allowed the development of catalysts with very small average nanoparticle sizes (between 1.6 and 3 nm).

[0070] The catalysts of the invention with nanoparticles of such small and highly dispersed sizes result in many active sites being present for the reaction in which these catalysts are intended to be used.

[0071] According to particular embodiments, the process for obtaining the catalyst comprises the following steps: a) Biomass processing. The biomass residues are subjected to a grinding and sieving process in order to obtain an optimal particle size (between 0.4 mm and 1.0 mm). Subsequently, they are subjected to a washing process with a solution of H2SO4 in distilled water with a final concentration of 2% by weight, followed by repeated washes with distilled water until ensuring a neutral pH. Finally, the biomass residues are dried in an oven at 110 °C for 12 hours. b) Hydrothermal carbonization in the presence of an aqueous solution of phosphoric acid at concentrations between 25% by weight and 15% by weight, using a Teflon autoclave reactor lined with a stainless steel jacket. The autoclave is sealed and taken to an oven, where a heat treatment at 200 °C for 20 hours is carried out. c) Activation of the carbonized impregnated with phosphoric acid.The carbonization was subjected to an activation treatment in a tubular furnace using a heating ramp of 5 °C min. -1 until reaching the desired temperature (450 °C, 550 °C or 900 °C), which was maintained for 2 hours, except in the case of the temperature of 900 °C, which was maintained for only 15 minutes. The activation treatment was carried out in an inert atmosphere using a constant N2 flow of 100 mL min -1. d) Washing of the resulting activated carbon with distilled water until reaching a neutral pH. Washings were carried out at temperatures above 60 °C. e) Drying of the activated carbon. The activated carbon was dried at 110 °C for 12 hours. f) Impregnation of the activated carbon with the metal precursor. 0.5 g of the activated carbon support was dispersed in 50 mL of distilled water. On the other hand, 0.01 g of ruthenium chloride (RuCh.xFW) was dissolved in 10 mL of distilled water and this volume was added to the activated carbon dispersion to achieve a final metal content of 1% by weight. The mixture was left to stir at room temperature for 2 hours. g) Reduction of the metallic phase with a reducing agent. After impregnation, the metal precursor was reduced with NaBhL maintaining a NaBhL / Ru molar ratio of 5 / 1.To do this, an aqueous solution of NaBhL was added dropwise to the suspension containing the metal precursor and the carbon support while stirring. Stirring was continued for another hour, and the mixture was then filtered to remove the solvent (distilled water). h) The catalyst was dried at 60 °C for 12 hours.

[0072] Drying the catalyst at this low temperature compared to state-of-the-art procedures prevents the electronic properties of the surface of the metal nanoparticles from changing substantially.

[0073] Furthermore, the present invention relates to the use of the heterogeneous catalyst obtained according to the process defined above, in the conversion of organic compounds, such as selective hydrogenation of other organic molecules, the decomposition of hydrogen-bearing molecules and the production of ammonia.

[0074] A particular preferred use is the use of the heterogeneous catalyst obtained according to the procedure defined above, in the conversion of levulinic acid to gamma-valerolactone.

[0075] According to particular embodiments, in the conversion of levulinic acid to gamma-valerolactone a temperature of between 50 and 90 °C is used, preferably between 60 and 75 °C and more preferably 70 °C.

[0076] According to particular embodiments, in the conversion of levulinic acid to gamma-valerolactone a pressure of between 10 and 20 bar of H2, preferably between 12 and 18 bar of H2, and more preferably 15 bar of H2 is used.

[0077] According to particular embodiments, in the conversion of levulinic acid to gamma-valerolactone a temperature of 70 °C and a pressure of 15 bar of H2 are used.

[0078] The catalytic reaction can be carried out in a batch reactor.

[0079] According to a particular embodiment, the catalytic reaction of conversion of levulinic acid to gamma-valerolactone is carried out using a discontinuous reactor (batch reactor with a volume of 100 mL). For this purpose, 0.1 g of catalyst, 25 mL of distilled water and 0.5 g of levulinic acid were used. Before starting the catalytic test, the system was purged with helium (He) and finally filled with hydrogen (H2). Finally, the temperature was increased to 70 °C with a slow heating rate (~2 °C min -1 ) and maintained for 1 hour at a H2 pressure of 15 bar. After this time, the reactor was rapidly cooled using an ice bath, stirring was stopped, and the system was depressurized. To recover the sample, the mixture was filtered, separating the liquid for analysis, and the catalyst was dried at 60 °C for 12 hours.

[0080] At 70 °C the selectivities obtained with the catalysts of the invention are higher than those disclosed in the state of the art, in particular in reference

[0020] . The following advantages can be highlighted from the process for obtaining the heterogeneous catalyst:

[0081] 1) It comprises few stages, and is carried out at moderate temperatures, which also favors the formation of small metallic nanoparticles, offering many active sites for the reaction in which the catalyst is going to be used.

[0082] 2) The valorization of abundant biomass waste for the preparation of activated carbons used as catalyst supports in reactions of high industrial interest.

[0083] 3) The substantial reduction in the concentration of activating agent used in the chemical activation stage of carbonization compared to conventional activation of biomass-derived materials, which reduces costs and environmental impact.

[0084] 4) The simplicity of the method used to obtain activated carbons with a porosity development equal to, or even greater than, those prepared by conventional activation.

[0085] 5) Hydrothermal synthesis prior to activation with phosphoric acid fixes the organic matter, achieving higher yields in the activation process compared to chemical activation with other activating agents.

[0086] 6) The process carried out for the preparation of the catalytic supports is easily scalable to an industrial level.

[0087] 7) The versatility of the method used in the preparation of the supports allows starting from lignocellulosic biomass residues of various types, regardless of the composition of the lignocellulosic biomass and the degree of humidity.

[0088] 8) The low economic cost of the catalysts due to the low metallic content present compared to the metallic contents of the catalysts commonly used.

[0089] 9) The low economic cost of the catalytic process due to the mild reaction conditions used (low temperatures and pressures and short reaction times).

[0090] 10) The high conversions achieved with the obtained catalyst, of levulinic acid and high selectivities towards gamma-valerolactone.

[0091] 11) The high stability of the catalysts during several consecutive reaction cycles.

[0092] BRIEF DESCRIPTION OF THE FIGURES

[0093] Figure 1. N2 adsorption isotherms at -196 °C (a) Example 1, (b) Example 2, (c) Example 3, (d) Example 4, (e) Example 5 and (f) Example 6.

[0094] Figure 2. TEM micrographs of the catalysts described in the different examples.

[0095] Figure 3. LA conversion and selectivity to GVL obtained for the catalysts of the different examples in the hydrogenation reaction of levulinic acid to GVL at 70 °C.

[0096] Figure 4. Conversion of levulinic acid and selectivity to GVL obtained in the hydrogenation reaction of levulinic acid to GVL at 70 °C during cycles 1, 2 and 3 of the catalyst described in Example 2.

[0097] EXAMPLES

[0098] The methodology used in the synthesis of catalysts based on activated carbon derived from biomass residues for the hydrogenation of levulinic acid to gamma-valerolactone is described in detail below. In addition, examples are presented with the physicochemical characterization of the catalysts, as well as the results obtained in the catalytic tests. The synthesis methodology for the catalysts for the hydrogenation of levulinic acid to gamma-valerolactone is divided into the following stages:

[0099] 1. Biomass processing. The biomass residues are milled and sieved to obtain an optimal particle size (between 0.4 mm and 1.0 mm). They are then washed with a solution of H2SO4 in distilled water at a final concentration of 2% by weight, followed by repeated washes with distilled water to ensure a neutral pH. Finally, the biomass residues are dried in an oven at 110 °C for 12 hours.

[0100] 2. Preparation of the supports (activated carbon). Activated carbons were prepared from biomass residues, in this case, almond shell (AS), by a hydrothermal carbonization treatment with the addition of an aqueous solution of phosphoric acid (H3PO4) at the concentrations indicated in the description (between 25% by weight and 15% by weight). Initially, a solution of phosphoric acid in distilled water was prepared with a final concentration of 25% by weight. Subsequently, 2 g of AS and 16 g of the phosphoric acid solution were introduced into a Teflon autoclave lined with a stainless steel jacket with a volume of 50 mL, in order to obtain an impregnation ratio H3PO4 / AS- by weight equal to 2. The autoclave was sealed and placed in an oven, where a heat treatment was carried out at 200 °C for 20 hours.The carbonized product obtained was removed from the autoclave and subjected to an activation treatment in a tubular furnace using a heating ramp of 5 °C min. -1 until reaching the desired temperature (450 °C, 550 °C or 900 °C), which was maintained for 2 hours, except in the case of the temperature of 900 °C, which was maintained for only 15 minutes. The activation treatment was carried out in an inert atmosphere using a constant N2 flow of 100 mL min -1 The resulting activated carbon was washed with distilled water until a neutral pH was reached. The washes were carried out at temperatures above 60°C. Finally, the activated carbon was dried at 110°C for 12 hours.

[0101] 3. Heat treatment of activated carbons. Heat-treated activated carbon was prepared from activated carbon at 450 °C by heat treatment in a tube furnace. This treatment was carried out in an inert atmosphere using a constant N2 flow of 100 mL min-1. -1 and a heating rate or ramp of 5 °C min -1until reaching a temperature of 900 °C, which was maintained for 15 minutes. 4. Preparation of the catalysts for the hydrogenation of levulinic acid to gamma-valerolactone. The activated carbons prepared by the methodology described above were used as supports to prepare the ruthenium-based catalysts by a conventional impregnation method in excess moisture. For this, 0.5 g of the activated carbon support was dispersed in 50 mL of distilled water. On the other hand, 0.01 g of ruthenium chloride (RuCh.x W) was dissolved in 10 mL of distilled water and this volume was added to the activated carbon dispersion to achieve a final metal content of 1% by weight. The mixture was left to stir at room temperature for 2 hours. After this time, the metal precursor (RuCh.x W) was reduced with NaBhL maintaining a NaBhL / Ru molar ratio of 5 / 1.To do this, an aqueous solution of NaBhL was added dropwise to the dispersion containing the metal precursor and the carbon support while stirring. Stirring continued for another hour, followed by filtration to remove the solvent (distilled water). Finally, the catalysts were dried at 60°C for 12 hours.

[0102] The characterization of all the catalysts for the hydrogenation of levulinic acid to gamma-valerolactone, described later in the examples, was carried out using different characterization techniques. N2 adsorption at -196 °C was used to determine the porous texture of both the supports (activated carbons) and the catalysts. The morphology of the active metallic phase of the catalysts was analyzed using transmission electron microscopy (TEM), determining the average size of the nanoparticles. Regarding the final ruthenium content in each catalyst, this was determined by inductively coupled plasma optical emission spectroscopy (ICP-OES). In addition, X-ray photoelectron spectroscopy (XPS) was used to determine the different ruthenium species present in the catalysts, as well as their surface content.

[0103] Catalytic tests of the different catalysts were carried out in a stirred, high-pressure, high-temperature benchtop reactor (PARR 4566C). This reactor consists of a 100 mL stainless steel reactor body, a heating mantle, a gas inlet, a cooling system, and a pressure, temperature, and stirring controller. Initially, 0.1 g of catalyst was dispersed in 25 mL of distilled water, and this dispersion was immersed in an ultrasonic bath for 5 minutes. Afterwards, 0.5 g of LA was added, and the resulting mixture was again placed in the ultrasonic bath for 5 minutes to ensure homogeneity. This mixture was then introduced into the reactor, which was sealed with a metal safety cap secured with screws. The cooling pump and stirring were started, and the heating mantle was adjusted.Before starting the catalytic test, the system was purged by passing helium (He) through the reactor, and then the reactor was filled with hydrogen (H2). Finally, the temperature was increased to 70 °C with a low heating rate (~2 °C min). -1 ) and maintained for 1 hour at a H2 pressure of 15 bar. After this time, the reactor was rapidly cooled using an ice bath, stirring was stopped, and the system was depressurized. To recover the sample, the mixture was filtered, separating the liquid for analysis, and the catalyst was dried at 60 °C for 12 hours.

[0104] The catalytic activity was evaluated by analyzing the reaction liquid using a gas chromatograph. First, standards of both levulinic acid and GVL were prepared with different concentrations. In the case of levulinic acid, the standards had concentrations ranging from 150 ppm to 2500 ppm, while for GVL, the concentrations ranged from 5000 to 20000 ppm. For the analysis of both the standards and the samples, 0.5 pl was injected into the gas chromatograph, and the chromatogram was recorded for 10 minutes. The catalytic activity was measured in terms of levulinic acid conversion and selectivity toward the conversion of levulinic acid to GVL.

[0105] EXAMPLE 1: PREPARATION OF A RUTHENIUM-BASED CATALYST SUPPORTED ON ACTIVATED CARBON DERIVED FROM ALMOND SHELL (ACTIVATION TEMPERATURE OF 450 °C).

[0106] The activated carbon used as a catalyst support in this example was prepared from almond shells using the procedure described above.

[0107] Subsequently, the activated carbon was impregnated with a solution containing the active phase (Ru) using a conventional impregnation method in excess moisture to obtain the catalyst. To do this, 0.5 g of activated carbon was dispersed in 50 mL of distilled water. Then, 0.01 g of ruthenium chloride (RUCI3.XH2O) was dissolved in 10 mL of distilled water and this volume was added to the initial dispersion of activated carbon, trying to obtain a metal content of 1% by weight of ruthenium. The mixture was left stirring at room temperature for 2 hours. Subsequently, the metal precursor salt was reduced with NaBH4 with a NaBHVRu molar ratio of 5 / 1, adding an aqueous solution of the reducer to the suspension with the activated carbon and metal precursor salt and maintaining stirring for 1 more hour. After this time, it was filtered to remove the solvent. Finally, the catalyst was dried at 60 °C for 12 hours.

[0108] The N2 adsorption isotherms at -196 °C for both the activated carbon (support) and the catalyst show that both materials exhibit a high volume of adsorbed gas at low relative pressures, indicative of the presence of micropores. A hysteresis loop and an increase in the slope can also be clearly observed at relative pressures above 0.2, indicating the presence of mesoporosity. Therefore, these materials exhibit a combination of type I and type IV isotherms (Figure 1a). These materials have apparent surface areas greater than 1500 m 2 g -1 and it can be observed that the introduction of the active phase (Ru) does not affect the porous texture of the activated carbon.

[0109] Regarding the TEM analysis of the catalyst (see Figure 2), the micrograph corresponding to this catalyst shows that the ruthenium nanoparticles are well dispersed and homogeneously distributed throughout the catalyst. This can be attributed to the high surface area of ​​the activated carbon used as a support. This catalyst has an average nanoparticle size of 1.6 nm. ICP analysis confirmed that the final ruthenium content in this catalyst was 0.55% by weight.

[0110] The XPS spectrum of Ru 3p shows that this catalyst has Ru° and Ru species. 3+ in a relative proportion of 60% and 40%, respectively, indicating that, although both species are present on the surface of ruthenium nanoparticles, Ru° is the predominant species.

[0111] The catalytic activity of this catalyst in the hydrogenation of levulinic acid to LPG is shown in Figure 3. It can be observed that this catalyst has a levulinic acid conversion of 96.8% and a LPG selectivity of 91.8%. These results demonstrate excellent catalytic performance under the reaction conditions employed, with a levulinic acid conversion very close to 100% and a LPG selectivity above 90%. The results obtained represent an advance in the preparation of catalysts for the hydrogenation of levulinic acid to LPG, using a simple synthesis method from biomass waste and with low ruthenium contents. It is important to highlight that these catalysts exhibit very good catalytic activity at low reaction temperatures. Furthermore, based on these results, it is possible to make variations in the support used as described in the following examples.

[0112] EXAMPLE 2: PREPARATION OF A RUTHENIUM-BASED CATALYST SUPPORTED ON ACTIVATED CARBON DERIVED FROM ALMOND SHELL (ACTIVATION TEMPERATURE OF 550 °C).

[0113] The properties of the support used can influence the catalytic behavior towards the hydrogenation of levulinic acid to GVL. The activated carbon used as a support for this catalyst was prepared by the same procedure as that followed in the preparation of the support in Example 1, but modifying the temperature during the activation treatment of the precursor. In this example, the activation temperature was 550 °C. The activated carbon obtained was used for the preparation of the catalyst following the conventional method of impregnation in excess of moisture described in Example 1.

[0114] The result of the characterization of the porous texture of this support and the catalyst can be observed in Figure 1b. This shows no significant difference with respect to the isotherms of Example 1. Therefore, for this example the isotherms also correspond to a combination of type I and type IV isotherms. These materials have apparent surface areas greater than 1500 m 2 g -1 and it was also confirmed that the introduction of the active phase (Ru) did not affect the porous texture of the activated carbon.

[0115] The catalyst characterization by TEM is presented in Figure 2. The ruthenium nanoparticles are observed to be well dispersed and homogeneously distributed throughout the catalyst, with an average nanoparticle size of 3.0 nm. The final ruthenium content in this catalyst is the same as in Example 1 (0.55% by weight).

[0116] The ruthenium species present in this catalyst are Ru° and Ru 3+ in a relative proportion of 62% and 38%, respectively, with the Ru° species being again the most abundant on the surface of the nanoparticles.

[0117] Although no significant differences are observed in terms of the physicochemical characterization between the catalysts of Example 1 and the present example, the catalytic activity of this catalyst in the hydrogenation of levulinic acid to GVL in terms of selectivity to GVL improves significantly with respect to the catalyst of Example 1. These results are presented in Figure 3, in which it can be seen that this catalyst has a levulinic acid conversion of 96.4%, which is practically the same as that of Example 1. However, the catalyst of this example shows a selectivity to GVL of 98.2%, being higher than the catalyst of Example 1. These results are even more interesting, since they present values ​​of both levulinic acid conversion and selectivity to GVL very close to 100%.

[0118] Given the excellent catalytic performance of this catalyst, its stability under reaction conditions was studied by performing three consecutive catalytic cycles to verify its continued catalytic performance. These results are shown in Figure 4, which shows that, after three reaction cycles, the catalyst continues to display excellent catalytic performance, with only a slight decrease in levulinic acid conversion of approximately 1% and a decrease in selectivity to GVL of approximately 12%.

[0119] EXAMPLE 3: PREPARATION OF A RUTHENIUM-BASED CATALYST SUPPORTED ON ACTIVATED CARBON DERIVED FROM ALMOND SHELL (ACTIVATION TEMPERATURE OF 900 °C).

[0120] A catalyst was prepared by further increasing the activation temperature of the activated carbon used as a support. In this case, the activated carbon was prepared using the same methodology as in the previous examples, but increasing the activation temperature to 900 °C. Similarly, the conventional excess moisture impregnation method described in the previous examples was used to support the active phase (Ru).

[0121] Figure 1c shows the porous texture of the materials synthesized in this example. The isotherms correspond to a combination of type I and type IV isotherms, as in the previous cases. However, this activated carbon has a larger apparent surface area, very close to 2000 m 2 g -1 . In addition, these materials have a larger volume of both micropores and mesopores. The textural properties of this activated carbon are also unaffected by the introduction of the active phase (Ru).

[0122] Figure 2 shows the TEM image obtained for this catalyst, which shows the presence of ruthenium nanoparticles with an average nanoparticle size of 1.8 nm. ICP analysis for this catalyst shows a final ruthenium content of 0.28% by weight. This ruthenium content is significantly lower compared to the two previous examples.

[0123] Regarding the XPS spectrum of the Ru 3p level, no differences are observed with respect to the previous examples, observing the presence of Ru° and Ru species. 3+ in a relative proportion similar to those of the examples described previously (64% Ru° and 36% Ru 3+ ).

[0124] As in the previous examples, the catalyst prepared using activated carbon as a support at 900 °C exhibits very good activity toward the hydrogenation of levulinic acid to LPG (Figure 3). This catalyst has an LA conversion of 97.8%, which is slightly higher than the previous examples, while the LPG selectivity is 96.0%. Once again, catalytic behavior is observed, with levulinic acid conversion and LPG selectivity values ​​very close to 100%.

[0125] EXAMPLE 4: PREPARATION OF A RUTHENIUM-BASED CATALYST SUPPORTED ON ACTIVATED CARBON DERIVED FROM ALMOND SHELL (ACTIVATION TEMPERATURE OF 450 °C) AND SUBSEQUENT HEAT TREATMENT AT 900 °C

[0126] Another modification in the synthesis of the support was carried out by heat treatment to the activated carbon described in Example 1. For this, the activated carbon used as support in Example 1 was heat treated in a tubular furnace in an inert atmosphere using a constant flow of N2 of 100 mL min -1 and with a heating rate of 5 °C min -1 until reaching a temperature of 900 °C, which was maintained for 15 minutes. Once the heat-treated activated carbon was obtained, the active phase (Ru) was impregnated using the conventional excess moisture impregnation method described for the previous examples.

[0127] The characterization of the porous texture of the support and catalyst described in this example shows a combination of type I and type IV isotherms (Figure 1d), indicating the presence of both microporosity and mesoporosity. The heat treatment performed on the support leads to a decrease in the surface area compared to the activated carbon of Example 1, due to the porosity contraction. Despite this, this heat-treated activated carbon has a surface area greater than 1000 m 2 g' 1 . By introducing the active phase (Ru) no changes are observed in the textural properties of the support.

[0128] The TEM images (Figure 2) obtained for this catalyst confirm the presence of ruthenium nanoparticles with an average nanoparticle size of 2.0 nm. As for the final ruthenium content in this catalyst, determined by ICP analysis, it was 0.31% by weight. This ruthenium content is lower compared to Examples 1 and 2 and very similar to that obtained for the catalyst described in Example 3. In the XPS spectrum of the Ru 3p level obtained for the catalyst described in this example, the presence of Ru° and Ru species can be observed. 3+ in a relative proportion of 72% and 28%, respectively. As with the catalysts described in the previous examples, it is the Ru° species that appears in the highest proportion.

[0129] The results obtained for the catalyst described in this example are even better compared to the examples described above. This catalyst exhibits excellent catalytic performance toward the hydrogenation of levulinic acid to GVL (Figure 3), showing a levulinic acid conversion and GVL selectivity of 98.4% and 100%, respectively. It is important to highlight the low Ru content in this catalyst.

[0130] EXAMPLE 5: PREPARATION OF A RUTHENIUM-BASED CATALYST SUPPORTED ON ACTIVATED CARBON DERIVED FROM HEMP, WITH AN ACTIVATION TEMPERATURE OF 550 °C

[0131] To demonstrate the versatility of the synthesis method for ruthenium-based catalysts supported on activated carbon derived from biomass waste, a catalyst was prepared under the same conditions as in Example 2, but in this case using hemp as a precursor.

[0132] The N2 adsorption isotherms at -196 °C of the support and catalyst described in this example are presented in Figure 1e. These materials exhibit a high N2 adsorption capacity at low relative pressures, which is characteristic of microporous solids and correspond to type I isotherms. Activated carbon prepared from hemp residues has a surface area greater than 1300 m 2 g -1 The introduction of the active phase (Ru) does not significantly affect the porous texture of this activated carbon.

[0133] Figure 2 shows the TEM image of the catalyst described in this example. This image shows the presence of ruthenium nanoparticles with an average size of 1.8 nm, which are homogeneously distributed throughout the catalyst. The final metal content determined for this catalyst using ICP was 0.4% by weight.

[0134] The ruthenium species present in this catalyst were Ru° and Ru 3+ , were determined by XPS. The relative proportion of these species was 64% and 36%, respectively. As with all the catalysts described in the previous examples, the Ru° species is present in the greatest proportion on the catalyst surface.

[0135] The evaluation of the catalytic activity of this catalyst in the hydrogenation of levulinic acid to LPG in terms of LPG selectivity is shown in Figure 3. It can be seen that the results obtained with this example are just as promising as those obtained with the other catalysts described in each of the previous examples. This catalyst has a levulinic acid conversion of 97.8% and a LPG selectivity of 94.5%. These results confirm the versatility of the catalyst synthesis method for the hydrogenation of levulinic acid to LPG using different biomass residues, whether hard biomass (almond shells) or soft biomass (hemp).

[0136] EXAMPLE 6: PREPARATION OF A RUTHENIUM-BASED CATALYST SUPPORTED ON ACTIVATED CARBON DERIVED FROM ALMOND SHELL (ACTIVATION TEMPERATURE OF 450 °C AND ELIMINATING THE LIQUID PHASE AFTER HYDROTHERMAL CARBONIZATION).

[0137] The carbon support used in this example was prepared from almond shell using the same procedure as in Example 1, but in this case the liquid phase obtained from the hydrothermal carbonization step was removed, thereby eliminating part of the activating agent (H3PO4). The Ru-based catalyst was subsequently prepared using the resulting support. For this purpose, the same excess moisture impregnation method as in the previous examples was used.

[0138] The porous texture of the support and catalyst in this example was evaluated using N2 adsorption isotherms at -196 °C, and the results obtained are presented in Figure 1f. In both cases, IUPAC type I isotherms are observed, which are characteristic of microporous solids. The support prepared in this example has a specific surface area of ​​715 m 2 g -1and the presence of the active phase (Ru) does not considerably affect the textural properties of this activated carbon. To determine the size and distribution of Ru nanoparticles in this catalyst, a TEM characterization was performed and the results are presented in Figure 2. The average size of the nanoparticles present in this catalyst is 2.5 nm and, as can be seen in the micrograph of the catalyst, the ruthenium nanoparticles are well dispersed and homogeneously distributed. The final ruthenium content of this catalyst was 0.41 wt % and was determined by ICP analysis.

[0139] Analysis of this catalyst by XPS shows that the Ru species present correspond to Ru° and Ru 3+ and are found in a relative proportion of 75% and 25%, respectively.

[0140] Figure 3 presents the results of the catalytic activity of this catalyst in the hydrogenation of levulinic acid to GVL. It can be observed that this catalyst has a levulinic acid conversion of 96.5% and a selectivity to GVL of 100%. These results demonstrate that, even using a lower concentration of phosphoric acid for the preparation of the catalyst support, it still has a high specific surface area on which the Ru nanoparticles are homogeneously distributed, achieving a catalyst with excellent catalytic activity.

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Claims

CLAIMS 1. A process for preparing a heterogeneous catalyst comprising: (i) preparation of a carbonaceous support from lignocellulosic biomass residues, by hydrothermal carbonization with the addition of an aqueous solution of phosphoric acid in a concentration between 25% by weight and 15% by weight of the acid with respect to the weight of the aqueous solution, such that the hydrothermal carbonization is carried out for a time between 6 and 20 h, (i) heat treatment of the product obtained in step (i) at temperatures between 350 and 1000 °C, obtaining an activated carbon, (iii) incorporation of a metallic phase into the activated carbon obtained in step (i), by mixing under stirring for a time between 1 and 4 hours a dispersion of the activated carbon obtained in step (i) with an aqueous solution containing a precursor of a transition metal, and (iv) a stage of reduction of the metallic phase, using a solution of a reducing agent, obtaining the heterogeneous catalyst.

2. The method according to claim 1, wherein the lignocellulosic biomass residues are subjected to a grinding and sieving process in order to obtain a particle size between 0.4 mm and 1.0 mm.

3. The method according to claim 1, wherein the biomass residues are selected from almond shell (AS) and hemp.

4. The method according to claim 1, wherein H3PO4 / lignocellulosic biomass ratios equal to 1 / 2, 1 / 1, 3 / 2 and 2 / 1 are used.

5. The process according to claim 1, wherein the lignocellulosic biomass residue is almond shell, and HsPC / almond shell ratios equal to 1 / 2, 1 / 1, 3 / 2 and 2 / 1 are used.

6. The process according to claim 1, wherein the lignocellulosic biomass residue is hemp, and HsPC / hemp ratios equal to 1 / 2, 1 / 1 and 3 / 2 are used.

7. The method according to claim 1, wherein the hydrothermal carbonization treatment is carried out in a temperature range between 150 °C and 250 °C.

8. The method according to claim 1, wherein the lignocellulosic biomass residue is almond shell and the heat treatment of activation of the carbon support is carried out carried out at 450 °C.

9. The process according to claim 1, wherein the lignocellulosic biomass residue is almond shell and the heat treatment to activate the carbon support is carried out at 550 °C.

10. The process according to claim 1, wherein the lignocellulosic biomass residue is almond shell and the heat treatment to activate the carbon support is carried out at 900 °C.

11. The method according to claim 1, wherein the heat treatment of activation of the carbon support is carried out at 450 °C and then a heat treatment is carried out at 900 °C.

12. The process according to claim 1, wherein the metallic phase is an inorganic salt of a transition metal, preferably ruthenium, and more preferably, RuCh.x W.

13. The process according to claim 1, wherein the reduction of the metallic phase is carried out with NaBH4.

14. The method according to claim 1, wherein the molar ratio between the reducing agent and the metal is between 10 / 1 to 5 / 1, preferably 5 / 1.

15. A heterogeneous catalyst obtained according to the process defined in any one of claims 1 to 14.

16. A heterogeneous catalyst according to claim 15, having an apparent surface area greater than 700 m 2 g -1 .

17. Use of the heterogeneous catalyst obtained according to the process defined in any one of claims 1 to 14, in the conversion of organic compounds, preferably, in the selective hydrogenation of organic molecules, the decomposition of hydrogen-carrying molecules and the production of ammonia.

18. Use of the heterogeneous catalyst according to claim 17, wherein the conversion of organic compounds is selected from selective hydrogenation of organic molecules, decomposition of hydrogen-carrying molecules and the production of ammonia.

19. Use of the heterogeneous catalyst according to claim 17, in the conversion of the acid levulinic to gamma-valerolactone.

20. Use of the heterogeneous catalyst according to claim 19, comprising carrying out the conversion at a temperature of between 50 and 90 °C, preferably between 60 and 75 °C and more preferably at 70 °C.

21. Use of the heterogeneous catalyst according to claim 19, in the conversion of levulinic acid to gamma-valerolactone, comprising carrying out the conversion at a pressure of between 10 and 20 bar of H2, preferably between 12 and 18 bar of H2, and more preferably at 15 bar of H2.

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