Ni-ru-ce catalyst and use thereof in catalytic applications

Abstract

The present invention relates to a highly active and selective catalyst comprising a mixture of cerium oxide, nickel oxide and ruthenium, of formula Ru / NiO-CeO2, wherein the nickel cations are inside the cerium particles, forming a mixed oxide, and wherein the ruthenium is dispersed on the surface of the NiO-CeO2 particles. The invention also relates to the use thereof in product conversion, such as the production of synthetic natural gas or hydrogen, in particular using starting materials selected from resins and plastics or using ethanol.

Description

[0001] Ni-Ru-Ce catalyst and its use in catalytic applications

[0002] DESCRIPTION

[0003] The present invention relates to a highly active and selective catalyst containing Ni, Ru, and Ce, prepared by a specific method. The present invention also relates to the process for obtaining said catalyst, which consists, firstly, of preparing an intimate mixture of NiO-CeC₂ using a combination of solvents and subsequently incorporating Ru by impregnation.

[0004] Therefore, the present invention can be classified in the area of ​​catalysis.

[0005] BACKGROUND OF THE INVENTION

[0006] Catalytic processes have multiple applications. Examples include the production of synthetic natural gas, the production of hydrogen from polymer waste, and the production of hydrogen from (bio)alcohols.

[0007] Natural gas is a mixture of carbon dioxide (CO2) and methane (CH4), and it is a naturally occurring energy resource. Although its use is less polluting than that of other hydrocarbons derived from petroleum or coal, the use of natural gas also generates greenhouse gas emissions. The environmental problems stemming from the use of these carbonaceous fuels are driving a global shift in the energy model, seeking to reduce the use of fossil fuels in favor of environmentally friendly renewable energy sources.

[0008] One of the challenges with renewable energy sources is that energy production is intermittent, making storage technologies essential to utilize surplus energy generated during periods of low production. The technology gaining traction involves using surplus renewable energy to hydrolyze water and produce hydrogen (H2). H2 produced using renewable energy is called green hydrogen, and it's a way to chemically store energy. This energy can be recovered by reacting green H2 with oxygen (O2), a completely clean process that produces only water as a byproduct.H2, however, has technical storage and transport problems, since it is a flammable, light gas that cannot be liquefied at room temperature, so it is necessary to store and transport it at high pressure, which is dangerous and in some cases unfeasible.

[0009] One alternative is to use green hydrogen to produce synthetic natural gas by hydrogenating CO2, which has several benefits. The renewable energy invested in producing green hydrogen is stored as CH4, and existing natural gas infrastructure can be used for its storage and transport. Furthermore, CO2 is consumed, contributing to a reduction in the atmospheric concentration of this greenhouse gas. The mixture of CO2 and CH4 obtained through hydrogenation is called synthetic natural gas.

[0010] One of the technological challenges for making the production of synthetic natural gas from CO2 and green hydrogen profitable is minimizing the energy consumption needed to carry out the reaction, and this is achieved by using a suitable catalyst.

[0011] Numerous catalysts capable of accelerating the hydrogenation reaction of CO2 to CH4 are known, typically operating between 300 °C and 450 °C. However, designing catalysts that can function below these temperatures is a complex challenge that is rarely achieved. For a catalyst to be active and selective at low temperatures, it is necessary not only to select the most appropriate components but also to optimize its composition and synthesis method to control its composition, morphology, and surface structure at the molecular level [1-11].

[0012] On the other hand, thermochemical processes for the valorization of waste consisting of polymer resins focus on two techniques: pyrolysis and gasification. These technologies are highly developed, and their main difference lies in the temperature ranges and the atmosphere used in the process.

[0013] Pyrolysis processes are carried out at a medium temperature range, typically between 350-900 °C, depending on the nature of the resin, and employ inert (non-oxidizing) atmospheres. The pyrolysis of polymer resins produces a mixture of gases, a liquid fraction (condensable gases), and a solid fraction. The gases obtained are mostly oxygenated aromatic compounds and, in much smaller proportions, light compounds such as alkanes, diphenyls, alcohols, and other light gases (H2, CO, CO2, and CH4) [12-13]. Gasification, on the other hand, is a process carried out at high temperatures (700-1000 °C) using an oxidizing atmosphere, which can be air, O2, CO2, or H2O.In this process, the gasifying gas reacts with the polymer - or resin - and produces mainly CO, H2, CO2, CH4 and other light hydrocarbons in different proportions depending on the operating parameters, such as residence time, ratio between oxidizing agent and residue, reaction temperature and pressure and catalyst.

[0014] There is a history of treating fiber-resin composite materials, such as glass fiber reinforced plastic (GFRP), by a thermochemical pyrolysis process at high temperatures (500 - 900 °C), obtaining as main products a gaseous mixture of H2, CO, CO2 and CH4, with a higher proportion of hydrogen and in a lower proportion the other gases

[0014] . Similar studies, in temperature ranges between 500 - 700 °C, indicate that a mixture of solid (40%), liquid (20%) and gaseous products (40%, composed mainly of CH4 and H2) is obtained.

[0015] Similar materials, such as glass-reinforced polyester (GRP) and sheet molding compounds (SMC and DMC), have been treated and characterized after subjecting them to a pyrolysis process at 450 °C. In this type of process, the resin separates from the fiber and decomposes into solid, liquid, and gaseous products. The solid product (including waxes and the solid formed by pyrolysis) represents 54% by weight of the total products, while the liquid represents 40% and the gaseous 6%, the latter composed mainly of CO and CO2, and to a lesser extent H2, CH4, and C2-C4 hydrocarbons.

[0016] ,

[0015] Some processes combine pyrolysis in a first stage and gasification in a second. However, the gasification stage requires higher temperatures than those used in the pyrolysis stage, and catalysts are added to increase the yield of energy-rich gases such as CH4, CO, and H2.

[0017] This field has been explored and evaluated primarily for the treatment of plastic waste. The pyrolysis process is carried out at a medium temperature between 350 and 500 °C, depending on the type of plastic. The gases and vapors produced from the thermal decomposition of the polymer resin are heat-treated in an oxidizing atmosphere using a catalyst to increase the yield of H₂ and CO₂.

[0018] within a temperature range of 600 °C to 900 °C. H2 production yields typically range from 20 to 40 millimoles H2 per gram of waste, depending on the treatment conditions, reaction, catalyst, oxidizing agent, and the nature of the waste. Thermochemical conversion in the valorization of plastic waste is a promising solution for the treatment and management of this type of waste due to its high carbon content and calorific value. Pyrolysis and gasification are among the most suitable technologies for its treatment. Pyrolysis has the potential to generate a gas mixture, a liquid fraction (condensable gases), and a solid fraction, while plastic gasification produces a hydrogen-rich mixture of light gases (H2, CO, CO2, and CH4CO). These technologies are highly developed, and their main differences lie in the temperature ranges and the atmosphere used in the process.

[0016] Pyrolysis processes are carried out within a temperature range, typically between 300 and 650 °C, depending on the nature of the polymer, and employ inert (non-oxidizing) atmospheres. Gasification, on the other hand, is a process performed at high temperatures (700–1000 °C) using an oxidizing atmosphere, which can be air, O2, CO2, or H2O. In this process, the gasifying gas reacts with the plastic polymer and produces mainly CO, H2, CO2, CH4, and other light hydrocarbons in varying proportions depending on the operating parameters, such as residence time, the ratio of oxidizing agent to residue, reaction temperature and pressure, and the catalyst.

[0017] Currently, the treatment of plastic waste in two stages (pyrolysis - gasification) for hydrogen production is being explored and evaluated with a greater focus. The pyrolysis process is carried out at medium temperatures, between 500 and 650 °C, depending on the nature of the plastic, while the gases and vapors produced from the thermal decomposition of the polymer are heat-treated in an oxidizing atmosphere using a catalyst to increase the yield towards the production of H2 and CO in a temperature range from 700 °C to 900 °C.

[0017] The H2 production yield per gram of waste used varies between 10 and 219 depending on the treatment conditions, reaction, catalyst, oxidizing compound, and nature of the waste.

[0018] Additionally, it should be mentioned that ethanol is a renewable fuel produced primarily from the fermentation of sugars present in plants such as corn, sugarcane, and beets, among others. This biofuel has various applications and advantages. Currently, it is used as a gasoline additive to improve its octane rating and reduce polluting emissions. It can also be used in engines specifically designed to run on ethanol blends, such as E85 (85% ethanol and 15% gasoline), and is compatible with fuel cells for generating electricity.

[0019] The use of ethanol as fuel reduces emissions of greenhouse gases and other pollutants, since its origin is biological and not derived from petroleum.

[0020] Ethanol can play an important role in a future based on the use of hydrogen as an energy carrier. As a renewable resource derived from biomass, ethanol can be used to produce green hydrogen through various methods, the most common being steam reforming.

[0021] This reforming process involves heating a mixture of ethanol and steam in a reactor at high temperatures (typically around 700 °C), producing hydrogen and other byproducts such as carbon monoxide (CO), carbon dioxide (CO2), and methane (CH4). The main reaction is:

[0022] C2H5OH + 3H2O = 2CO2+6H2

[0023] For this reaction to be effective and to lower the temperature at which it occurs, a catalyst is necessary. Some of the most common catalysts include transition metals (nickel and cobalt), noble metals (palladium, platinum, rhodium, and ruthenium), and mixed oxides of cerium, zirconium, and cobalt.

[0024] This paper describes a catalyst containing nickel, ruthenium, and cerium, which improves upon the state-of-the-art results in the treatment of resins and subsequent hydrogen production, as well as in the treatment of plastics, resulting in better yields in hydrogen production.

[0025] The catalyst is also capable, for example, of very actively and selectively accelerating the hydrogenation of CO2 to CH4 from 190 °C, being, as far as the inventors know, the most active and selective one reported for obtaining synthetic natural gas at low temperature.

[0026] The catalyst has also proven efficient in catalyzing the reaction for the production of H2 from (bio)ethanol. Bibliography

[0027] [1] X. Jia, X. Zhang, N. Rui, X. Hu, C.-jun Liu. Structural effect of Ni / ZrC>2 catalyst on CO2 methanation with enhanced Activity. Appl. Catal. B: Environ. 244 (2019) 159-169.

[0028] [2] T. Zhang, W. Wang, F. Gu, W. Xu, J. Zhang, Z. Li, T. Zhu, G. Xu, Z. Zhong, F. Su. Enhancing the low-temperature CO2 methanation over Ni / La-CeO2 catalyst: The effects of surface oxygen vacancy and basic site on the catalytic performance. Appl. Catal. B: Environ. 312 (2022) 121385.

[0029] [3] H. Liu, X. Zou, X. Wang, X. Lu, W. Ding. Effect of CeÜ2 addition on Ni / AhOs catalysts for methanation of carbon dioxide with hydrogen. J. Nat. Gas Chem. 21 (2012) 703-707.

[0030] [4] J. Ashok, M.L. Ang, S. Kawi. Enhanced activity of CO2 methanation over Ni / CeO2- ZrÜ2 catalysts: Influence of preparation methods. Catal. Today 281 (2017) 304- 311.

[0031] [5] L. Ma, R. Ye, Y. Huang, T. Ramirez Reina, X. Wang, C. Li, X. L. Zhang, M. Fan, R. Zhang, J. Liu. Enhanced low-temperature CO2 methanation performance of N¡ / ZrÜ2 catalysts via a phase engineering strategy. Chem. Eng. J. 446 (2022) 137031.

[0032] [6] F. Wang, S. He, H. Chen, B. Wang, L. Zheng, M. Wei, D. G. Evans, X. Duan. Active Site Dependent Reaction Mechanism over Ru / CeÜ2 Catalyst toward CO2 Methanation J. Am. Chem. Soc. 138 (2016) 6298-6305.

[0033] [7] B. Mutz, H. W.P. Carvalho, S. Mangold, W. Kleist, J.-D. Grunwaldt. Methanation of CO2: Structural response of a Ni-based catalyst under fluctuating reaction conditions unraveled by operando spectroscopy. J. Catal. 327 (2015) 48-53.

[0034] [8] S. He, C. Li, H. Chen, D. Su, B. Zhang, X. Cao, B. Wang, M. Wei, D. G. Evans, X. Duan. A Surface Defect-Promoted Ni Nanocatalyst with Simultaneously Enhanced Activity and Stability. Chem. Mater. 25 (2013) 1040-1046.

[0035] [9] S. Renda, A. Ricca, V. Palma. Precursor salts influence in Ruthenium catalysts for CO2 hydrogenation to methane. Appl. Energy 279 (2020) 115767.

[0036]

[0010] Q. Liu, S. Wang, G. Zhao, H. Yang, M. Yuan, X. An, H. Zhou, Y. Qiao, Y. Tian. CO2 methanation over ordered mesoporous NiRu-doped CaO-AhOs nanocomposites with enhanced catalytic performance! nt. J. Hydrog. Energy 43 (2018) 239-250

[0037]

[0011] R.-Yu Chein, C. -Chang Wang. Experimental Study on CO2 Methanation over Ni / ALOs, RU / AI2O3, and Ru-Ni / AhOs Catalysts. Catalysts 10 (2020) 1112.

[0038]

[0012] D. Saebea, P. Ruengrit, A. Arpornwichanop, Y. Patcharavorachot. Gasification of plastic waste for synthesis gas production. Energy Rep 6 (2020) 202.

[0039]

[0013] K. G. Burra, A. K. Gupta. Kinetics of synergistic effects in co-pyrolysis of biomass with plastic wastes. Appl. Energy 220 (2018) 408.

[0040]

[0014] R. Miandad, M. A. Barakat, A. S. Abuhazaiza, M. Rehan, A. S. Nizami. Catalytic pyrolysis of plastic waste: A review. Process Safety and Environmental Protection 102 (2016) 822.

[0041]

[0015] D. Saebea, P. Ruengrit, A. Arpornwichanop, Y. Patcharavorachot. Gasification of plastic waste for synthesis gas production. Energy Reports 6 (2020) 202.

[0042]

[0016] A. D. A. B. A. Sofian, H. R. Lim, K. W. Chew, K. S. Khoo, I. S. Tan, Z. Ma, P. L. Show. Hydrogen production and pollution mitigation: Enhanced gasification of plastic waste and biomass with machine learning & storage for a sustainable future. Environmental Pollution 342 (2024) 123024.

[0043]

[0017] A. S. Al-Fatesh, N. Y. AL-Garadi, A. I. Osman, F. S. Al-Mubaddel, A. Ibrahim, W. II. Khan, O. Y. Alothman. From plastic waste pyrolysis to Fuel: Impact of process parameters and material selection on hydrogen production. Fuel 344 (2023) 128107.

[0044]

[0018] S. Wang, R. Shan, J. Gu, T. Huhe, X. Ling, H. Yuan, Y. Chen. High-yield H2 production from polypropylene through pyrolysis-catalytic reforming over activated carbon based nickel catalyst. Journal of Cleaner Production 352 (2022) 131566.

[0045] DESCRIPTION OF THE INVENTION

[0046] The present invention relates to a catalyst comprising a mixture of cerium oxide, nickel oxide and ruthenium, of formula Ru / N₂O-CeO₂, wherein the nickel cations are inside the cerium particles forming a mixed oxide, and wherein the ruthenium is dispersed on the surface of the N₂O-CeO₂ particles.

[0047] The presence of the N cations 2+The presence of fluorite-type crystalline structures within ceria is evident in X-ray diffractograms due to the absence of diffraction patterns attributable to nickel species. The catalyst of the invention exhibits an X-ray diffractogram containing only the diffraction bands characteristic of ceria with a fluorite structure.

[0048] The X-ray diffractogram shows the following relative intensity of the bands, normalized by dividing the intensity of each peak by the intensity of the CeÜ2 peak (111).

[0049] The catalyst of the invention comprises a ruthenium content of at most 2% by weight of the total catalyst weight. According to particular embodiments, it may comprise a ruthenium content of between 1% and 2%, preferably 2% by weight of the total catalyst weight.

[0050] The catalyst of the invention comprises a proportion of Ni between 5% and 20% by weight, with respect to the total weight of the catalyst, preferably between 5% and 15%, and more preferably the proportion of Ni is 10% by weight with respect to the total weight of the catalyst.

[0051] The catalyst of the invention comprises a proportion of ceria that corresponds to the difference between the proportion of nickel oxide and ruthenium oxide until reaching 100% of the weight of the catalyst.

[0052] The NiO-CeO2 mixed oxide and the catalyst of the invention have particle sizes ranging from 4 to 14 nm, with the predominant particles being 7–8 nm. This size is similar in all cases, i.e., both in the NiO-CeO2 particles and in the final catalyst after the inclusion of Ru. The particle sizes measured for the described examples can be seen using TEM microscopy. The term “predominant” has its usual meaning, i.e., that more than 50% of the particles are between 7 and 8 nm in size.

[0053] Impregnation with ruthenium salt and subsequent drying and heat treatment does not change the particle size.

[0054] In the case of the catalyst of the invention, the terms “crystal” and “particle” of NiO-CeC2 mixed oxide are equivalent. This is because the method used to obtain the catalyst ensures that each particle is a single crystal.

[0055] The present invention also relates to a process for preparing the catalyst defined above, comprising: a) dissolving a nickel precursor salt and a fennel precursor salt in water; b) adding to the above solution a mixture of an alkane of 5 to 10 carbon atoms, a linear monohydric alkanol of 2 to 8 carbon atoms, and a non-ionic surfactant, for example, a mixture of n-heptane, hexanol, and Triton X-100, while stirring the mixture; c) dissolving an alkali compound in water, such as an ammonium hydroxide salt, such as tetraalkylammonium hydroxide, where “alkyl” means an alkyl group of 1 to 6 carbon atoms, such as tetramethylammonium hydroxide.d) Add to the previous solution a mixture of an alkane with 5 to 10 carbon atoms, a linear monohydric alkanol with 2 to 8 carbon atoms, and a non-ionic surfactant, for example, a mixture of n-heptane, hexanol, and Triton X-100, keeping the mixture under stirring; e) Mix both solutions and stir, for example, for 24 hours, obtaining a solid; f) Separate the solid and subject it to washing, drying, and calcination at a temperature between 450 and 700 °C; g) Add ruthenium to the solid obtained in the previous step by impregnating the solid with a ruthenium salt; h) Dry it and heat treat it in a non-oxidizing atmosphere at a temperature above 250 °C.

[0056] An example of a nickel precursor salt is Ni(NOs)₂·6H₂O. The concentration, for example, can be between 25 and 99 g per liter of water, and preferably between 30 and 55 g / liter, and more preferably 49 g per liter of water. An example of a cerium precursor salt is Ce(NOs)₃·6H₂O. The concentration, for example, can be between 236 and 188 g per liter of water, and preferably between 236 and 215 g / liter, and more preferably between 236 and 218 g / liter, and even more preferably 220 g per liter of water.

[0057] The ratio of Ni and Ce in the catalyst is controlled by modifying the ratio of the precursor salts used, such as Ce(NOs)3-6H2O and Ni(NO3)2'6H2O.

[0058] According to a further particular embodiment, the weight ratio of solvents and surfactants is within the following ranges: 0.5-1 : 5-6: 1-2 : 1-2 for water : alkane : non-ionic surfactant : alkanol.

[0059] According to a further particular embodiment, the weight ratio of solvents and surfactants is within the following ranges: 0.7-1 : 5, 5-5, 8: 1 ,8-2 : 1 ,4-1 ,6 for water : alkane : non-ionic surfactant : alkanol.

[0060] According to a further particular embodiment, the weight ratio of solvents and surfactants is 1 : 5.7: 1 .9 : 1 .5 for water : n-heptane : Triton X-100 : hexanol.

[0061] An example of an alkali compound is a tetraalkylammonium hydroxide in which the alkyl group has between 1 and 5 carbon atoms, and in which the alkyl radicals can be the same or different. A specific example is tetramethylammonium hydroxide.

[0062] The required proportion of alkaline compound, for example, tetraalkylammonium hydroxide, can range from 300 to 400 g per liter of water, preferably from 320 to 380 g per liter of water. In one specific example, it is used in a proportion of 340 g per liter of water.

[0063] The calcination of the cene and nickel solid can be carried out between 450 and 700 °C, preferably between 500 and 600 °C.

[0064] The solvent for the ruthenium salt must be capable of solubilizing the ruthenium salt (which is insoluble in water, acetone, ethanol, and others). It must also be capable of wetting the NiO-CeC₂ particles (organic solvents that dissolve the Ru precursor generally wet NiO-CeC₂ particles poorly). The solvent can be toluene.

[0065] In specific embodiments, the ruthenium salt can be a soluble salt that does not contain chlorides, for example, ruthenium(III) acetylacetonate (RuCsHyjs), and the solvent can be toluene. The resulting catalyst can be dried in air between 50 and 150 °C, preferably between 50 and 110 °C, for example, at 100 °C.

[0066] The heat treatment after impregnation with the ruthenium salt, in a non-oxidizing atmosphere, can be done in nitrogen at a temperature between 250 and 400 °C, preferably between 250 and 360 °C, for example, at 350 °C.

[0067] According to specific embodiments, the procedure comprises: preparing an intimate mixture of nickel and cene oxides with a predominant particle size of 7-8 nm. To prepare this material, the nickel and cene precursor salts are dissolved in water, and then a mixture of n-heptane, hexanol, and a surfactant (Triton X-100) is added while the mixture is stirred. Similarly, an alkali compound (tetramethyl ammonium hydroxide) is dissolved in water, and n-heptane, hexanol, and Triton X-100 are added to this solution while it is stirred. Both solutions (the tetramethyl ammonium hydroxide solution and the nickel and cene metal solution) are mixed and vigorously stirred, and the resulting solid is separated from the solution, washed, dried, and calcined at a moderate temperature, i.e., between 450 °C and 700 °C, followed by the addition of ruthenium.The solid obtained in the previous stage is impregnated with a ruthenium salt using toluene as a solvent and, after drying, is thermally treated in a non-oxidizing atmosphere at 350 °C.

[0068] Following this synthesis method, a catalyst is obtained that selectively accelerates the hydrogenation of CO2 to CH4, achieving a synthetic natural gas synthesis reaction rate at low temperatures, for example, between 190 °C and 300 °C (250 °C in specific embodiments). To the inventors' knowledge, this rate is higher than that of any other catalyst of the same or different composition reported in the literature. At temperatures above 300 °C, the catalyst of the invention also selectively accelerates the hydrogenation of CO2 to CH4, but the results are no better than those of other catalysts published in the literature.

[0069] According to preferred realizations:

[0070] In preparing the intimate mixture of cene and nickel oxides, the combination of solvents and additives used (water, n-heptane, hexanol, and surfactant) is maintained. The metal precursors and tetraalkylammonium hydroxide are dissolved separately in water. Once the remaining solvents and surfactant are added to each of the aqueous solutions, they are mixed.

[0071] The calcination temperature of the resulting nickel and cene solid is between 450 and 700 °C.

[0072] Ruthenium is subsequently introduced by impregnation and the heat treatment to stabilize it is carried out in the absence of oxygen.

[0073] The present invention also relates to the use of the catalyst described above in various product conversion processes, for example, for obtaining gases.

[0074] One particular use of the catalyst involves the conversion of products to obtain hydrogen. These products can be waste materials, such as resin waste or plastic waste.

[0075] According to particular embodiments, the conversion of products comprises obtaining hydrogen from starting materials selected from resins, such as resins derived from a fiber-resin waste, and plastics, such as polyethylene, polypropylene or polystyrene.

[0076] The catalyst of the invention allows a reduction in the amount of liquid products obtained in hydrogen production compared to the uncatalyzed thermal process, produces no solid waste, and promotes hydrogen production in the gas mixture.

[0077] The present invention also relates, according to particular embodiments, to the use of the catalyst described above for obtaining synthetic natural gas.

[0078] The method for obtaining synthetic natural gas involves contacting the catalyst with a stream of CO2 and H2 with a carrier gas, such as nitrogen.

[0079] The catalyst of the invention allows the production of synthetic natural gas at lower temperatures than conventional catalysts.

[0080] The present invention also relates, according to specific embodiments, to the use of the catalyst described above for obtaining hydrogen by reforming (bio)alcohols. BRIEF DESCRIPTION OF THE FIGURES

[0081] Figure 1. Catalytic conversion of CO2 to CH4 using 200 mg of Ru / N₂O-CeO2 (NP1) catalyst (example 1), as well as using other prepared and tested reference catalysts (example 2), and a gas mixture of 200 ml / min with 10% C₂O and 40% H₂ with nitrogen as the carrier gas. The catalysts compared were named Ru / N₂O-CeO2(NP1), NiO-CeO2(NP2), Ru / CeO2(NP3), Ru / N₂O-CeO2(NP4) and Ru / N₂O-CeO2(REF).

[0082] Figure 2. Reaction rate measured at low temperatures in catalytic experiments of hydrogenation of CO2 to CH4 using 200 mg of catalyst and a gas mixture of 200 ml / min with 10%CC>2 and 40%H2 with nitrogen as carrier gas.

[0083] Figure 3. Hydrogenation rate of CO2 to CH4 at 250 °C of the catalyst of the invention and the most active catalysts reported in the literature.

[0084] Figure 4. TEM photographs of the optimal catalyst prepared according to the procedure of the invention and of other catalysts prepared for comparative purposes, (a) CeO2 (NP), (b) NiO-CeO2(NP2), (c) Ru / CeO2(NP3), (d) Ru / NiO-CeO2(NP1) and (e) Ru / NiO-CeO2(REF).

[0085] Figure 5. X-ray diffractograms of the optimum catalyst prepared following the procedure described according to the invention and of other catalysts prepared for comparative purposes.

[0086] Figure 6. N2 adsorption isotherms at -196 °C of the optimum catalyst prepared according to the procedure described in the invention and of other catalysts prepared for comparative purposes.

[0087] Figure 7. Temperature Programmed Reduction with H2 of the optimum catalyst prepared following the procedure described according to the invention and of other catalysts prepared for comparative purposes.

[0088] Figure 8. DRIFT spectra obtained at 300 °C by permuting the gas composition between methanation conditions (H2 / N2 + CO2 / N2) and mixtures with only one of the reactants (H2 / N2 and CO2 / N2) (a) NiO-CeO2(NP2), (b) Ru / CeO2(NP3) and (c) Ru / NiO-CeO2(NP1). Figure 9: Graphs showing the hydrogen production obtained according to example 4.

[0089] Figure 10: Fiber-resin waste from a wind turbine (left) and fiber (center) and resin (right) recovered using the method described in Patent P201531174, corresponding to example 5.

[0090] Figure 11. Distribution of gaseous products for the uncatalyzed reaction according to example 5.

[0091] Figure 12. Distribution of gaseous products for the catalyzed reaction according to example 5.

[0092] EXAMPLES

[0093] Examples 1 and 2 describe, respectively, a synthesis of a catalyst according to the invention and catalysts prepared for comparative purposes. In total, five catalysts are compared, designated Ru / N₂O-CeO₂ (NP1), N₂O-CeO₂ (NP2), Ru / CeO₂ (NP3), Ru / N₂O-CeO₂ (NP4), and Ru / N₂O-CeO₂ (REF).

[0094] The catalysts designated NP were prepared using the method described herein, but with selected components. Specifically, Ru / NiO-CeC₂ (NP1) contains all the components (Ru, NiO, and Ce₂) and is therefore referred to as the catalyst of the invention. NiO-CeC₂ (NP2) contains only Ni and Ce, and Ru / Ce₂ (NP3) contains only Ru and Ce. The Ru-NiO-CeC₂ (NP4) catalyst has a composition similar to the catalyst of the invention, but all its components (Ru, Ni, and Ce) are introduced simultaneously by dissolving the precursor salts of these metals together in water and then coprecipitating them according to the procedure of the invention. Therefore, the difference between the catalyst of the invention (Ru / N¡O-CeC>2 (NP1)) and the catalyst Ru-N¡O-CeC>2 (NP4) is that the catalyst of the invention is obtained by impregnating N¡O-CeC>2 (NP2) with a Ru salt, while in Ru-N¡O-CeC>2 (NP4) Ru is introduced along with Ni and Ce.

[0095] Finally, the Ru / NiO-CeC₂ (REF) catalyst was prepared by a conventional direct calcination method of a mixture of nickel nitrates and cenotes, and Ru was subsequently incorporated as described in this document (see Example 1). In all cases, the Ce₂ and NiO-CeC₂ were calcined in air at 500 °C, and the nickel content was 11 ± 1 wt% relative to the total mass of the catalyst. In the catalysts containing Ru (2 wt% relative to the total mass of the catalyst), this metal was introduced by impregnation and heat treatment in N₂ at 350 °C.

[0096] Example 1

[0097] Obtaining the Ru / N₂O-CeC₂ catalyst (NP₁)

[0098] 1.18 g of Ni(NOs)2-6H2O and 4.27 g of Ce(NOs)3-6H2O were dissolved in 20 mL of water.

[0099] To the resulting solution, a mixture of 114 g of heptane, 37 g of Triton X, and 29 g of hexanol was added, and the mixture was stirred while preparing the second mixture described below. Separately, 6.8 g of tetramethyl ammonium hydroxide was dissolved in 20 mL of water, and to this solution, a mixture of 114 g of heptane, 37 g of Triton X, and 29 g of hexanol was also added, stirring to obtain a homogeneous mixture.

[0100] Both solutions (the one containing the nickel and zinc salts, and the one containing the tetramethylammonium compound) were mixed and stirred for 24 hours. The resulting solid was separated from the solution by centrifugation, washed with ethanol, and dried in an air oven at 100 °C for 24 hours. It was then calcined at 500 °C for 1 hour.

[0101] The solid obtained in the previous step was impregnated with 0.16 g of ruthenium(III) acetylacetonate dissolved in 2.7 g of toluene. After drying in air at 110 °C, it was heat-treated in a nitrogen atmosphere at 350 °C for 3 hours.

[0102] 2 g of Ru / NiO-CeC>2 (NP1) were obtained.

[0103] Example 2

[0104] Preparation of catalysts for comparative purposes

[0105] The catalyst called Ru / NiO-CeC>2 (NP1) is the catalyst of the invention. According to the invention, nickel is first introduced into the structure of the nickel, and then Ru is impregnated, remaining on the surface of the NiO-CeC>2 particles. The catalyst called Ru / NiO-CeC>2 (REF) was prepared by direct calcination of a mixture of nickel nitrates and nickel (1.18 g of Ni(NOs)2-6H2O and 4.27 g of Ce(NOs)3-6H2O). Calcination was carried out in air at 500 °C for 1 hour, and Ru was subsequently incorporated as described herein (see example 1).

[0106] The catalysts containing only one of the metals Ru or Ni were prepared as indicated in Example 1, but in each case omitting the operations involving the missing metal with respect to the catalyst of the invention.

[0107] The catalyst called Ru-N₂O-CeC₂ (NP4) has a composition similar to that of the invention (Ru / N₂O-CeC₂ (NP1)), but all its components (Ru, Ni, and Ce) are introduced simultaneously by dissolving the precursor salts of these metals together in water and then proceeding to their coprecipitation following the procedure of the invention. Therefore, the difference between the catalyst of the invention (Ru / N₂O-CeC₂ (NP1)) and the Ru-N₂O-CeC₂ (NP4) catalyst is that the catalyst of the invention is obtained by impregnating N₂O-CeC₂ (NP2) with a Ru salt, while in Ru-N₂O-CeC₂ (NP4) the Ru is introduced together with the Ni and Ce.

[0108] Table 1 shows the surface areas determined by N2a adsorption - 196 °C, and the crystal sizes determined by X-ray Diffraction, of the prepared catalysts, as well as of a pure, nickel- and ruthenium-free CeÜ2 (NP) prepared by the method of the invention.

[0109] Table 1

[0110] As can be seen in the table, the catalyst of the invention Ru / NiO-CeC2 (NP1) has a much larger surface area and a much smaller crystal size than the reference catalyst Ru / NiO-CeC2 (REF), which has a similar composition but is prepared using a conventional method. The other catalysts prepared according to the method of the invention, but with modified composition (NiO-CeC2 (NP2) and Ru / CeC2 (NP3)), as well as the pure cerium prepared according to the method of the invention (CeC2 (NP)), also have larger surface areas and smaller particle sizes than the reference catalyst.

[0111] Example 3

[0112] Use of the Ru / N₂O-CeC₂ (NP₁) catalyst in the synthesis of synthetic natural gas.

[0113] The catalytic tests were performed using a steel reactor placed inside a horizontal furnace to control the reaction temperature. A stoichiometric gas mixture with a composition of CO₂:H₂ 1:4 was used, with a total flow rate of 200 ml / min and using N₂ as the carrier gas. The tests were carried out using 200 mg of powdered catalyst. The composition of the gases during the reaction was monitored using specific NDIR-UV (non-dispersive infrared) analyzers for CO, CO₂, and CH₄, and an electrochemical sensor for H₂.

[0114] Figure 1 shows the CO2 to CH4 conversion curves obtained with a catalyst of the invention, prepared according to the procedure of the invention (called Ru / N¡O-CeO2 (NP1)) (example 1), as well as with other catalysts prepared and tested as a reference (example 2).

[0115] The catalysts compared in this Figure 1 were named NiO-CeC>2 (NP2), Ru / CeO2(NP3), Ru / N¡O-CeO2(NP1), Ru-N¡O-CeO2(NP4) and Ru / N¡O-CeO2(REF).

[0116] The catalyst of the invention (Ru / NiO-CeC>2 (NP1)) begins to produce methane at 190 °C, and production increases rapidly with temperature until the reaction equilibrium is reached, which cannot be exceeded for thermodynamic reasons. This catalyst is 100% selective for the formation of CH4, without producing any other byproducts. Figure 1 shows results for two catalysts containing only two of the components (catalysts designated Ru / CeC>2 (NP3) and NiO-CeC>2 (NP2)) and two catalysts of similar composition to the optimum Ru / NiO-CeC>2 (NP1), one prepared by a conventional method based on impregnation and calcination (designated Ru / NiO-CeC>2 (REF)) and the other prepared by the method of the invention, but introducing Ru at the same time as Ni and Ce (designated Ru / NiO-CeC>2 (NP4)).All these catalysts have a lower activity than the catalyst of the invention (Ru / NiO-CeC>2 (NP1)), being in line with other values ​​commonly reported in the literature.

[0117] The catalyst of the invention was synthesized using the inventive synthesis method, optimizing the proportions of the various components (2% Ru, 10% Ni, and the remainder Ce₂). Figure 2 shows the reaction rate for obtaining synthetic natural gas achieved at low temperatures with catalysts prepared using the synthesis method described herein (Ru / NiO-CeC₂ (NP1)) by modifying the amounts of Ru and Ni. The highest rates of synthetic natural gas production are achieved with 2% Ru and 10% Ni, although all catalysts prepared using the method described herein perform better than the reference catalysts. With catalysts prepared according to the inventive method with a lower Ru content than the optimum (2%), the reaction rate for obtaining synthetic natural gas decreases, and the amount cannot be increased above 2% because unstable volatile ruthenium compounds are generated.The amount of Ni can also be modified, but values ​​below 10% decrease the activity of the catalyst and higher values ​​result in a price increase without achieving an improvement in activity.

[0118] Figure 2 also includes reference materials of similar composition to the optimum but prepared by methods different from that of the invention and with a different structure and physicochemical properties:

[0119] • Ru / N¡O-CeC>2 catalyst (REF), prepared by a conventional impregnation and calcination method.

[0120] • Ru-NiO-CeC2 (NP4) catalyst: The portion of the method of the invention used to obtain NiO-CeC2 was employed, but in this case, Ru, Ni, and Ce were added simultaneously. It was prepared by mixing all the components to obtain an intimate Ru-Ni-Ce mixture; that is, the ruthenium was introduced at the same time as the nickel, instead of impregnating it subsequently as described in the invention.

[0121] These reference materials, despite having a composition very similar to that of the catalyst of the invention, achieve lower reaction rates because the synthesis methods are worse than that of the invention and the structure and physicochemical properties of the catalyst are different.

[0122] Table 2 includes comparative data for the optimized catalyst prepared according to the method of the invention and the best catalysts reported in the literature. It is concluded that the optimized catalyst prepared according to the method described in this invention is the most effective for accelerating the hydrogenation of CO2 to CH4 at low temperatures.

[0123] Table 2 Figure 3 includes a graph showing the reaction rate achieved at 250 °C by the eight most active catalysts at this temperature, according to the data in Table 2. This graph illustrates the considerable improvement achieved with the optimal catalyst prepared according to the method of the invention. This catalyst is 22% more active than the next most active catalyst reported in the literature, and 70% more active than the reference catalyst of similar composition but prepared by a conventional method.

[0124] To analyze why the optimal catalyst Ru / NiO-CeC>2 (NP1), prepared following the procedure of the invention, presents the best catalytic results, a physicochemical characterization of this catalyst and the rest of the reference catalysts included in Figure 1 has been carried out.

[0125] Figure 4 shows the temperature-programmed reduction profiles with H2, obtained using 5% H2 / Ar and monitoring H2 consumption with a thermal conductivity detector (TCD). Catalyst reduction is a key step in the catalytic hydrogenation mechanism of CO2 to CH4, as this reaction is catalyzed by a redox cycle where CO2 acts as the oxidant and H2 as the reductant. Two main regions can be distinguished in the reduction curves in all cases. Reduction events occurring below 600 °C are attributed to surface processes, while those occurring above this temperature are due to mass reduction of the catalyst.

[0126] The Ce₂ (NP) reduction profile indicates that surface reduction of the carbon occurs around 500 °C, and the incorporation of Ni and / or Ru accelerates this reduction to lower temperatures. The catalyst with the best reduction capacity (Ru / N₂O-Ce₂ (NP₁)) is the one that has shown the best catalytic activity. This catalyst exhibits three surface reduction events. The first, around 100 °C, is attributed to the reduction of ruthenium oxide along with some of the carbon and nickel oxide located in the vicinity of the ruthenium, and the double peak between 150 and 400 °C is due to the reduction of Ni 2+and from the surface dinner. These same events are also observed in the Ru / N₂O-CeCl₂ (REF) catalyst, of the same composition but prepared without size control, but the low-temperature reduction of ruthenium oxides and their surroundings is much less effective. Likewise, the monometallic catalysts (in catalysis, a catalyst containing a minor metallic component (in this case Ru or Ni) dispersed on a major support (in this case CeCl₂)) Ru / CeCl₂ (NP3) and N₂O-CeCl₂ (NP2) show the reduction of Ru and Ni oxides, respectively, and their catalytic effect on cerium reduction, but their reducibility is worse than that of the Ru + Ni catalysts. In summary, the catalyst prepared by the method of the invention is the best reduced at low temperature due to a synergistic effect between Ru and Ni that is not achieved by a conventional synthesis method.

[0127] The X-ray diffractograms, included in Figure 5, provide additional information that helps explain the optimal catalytic behavior of the catalyst prepared by the method of the invention. The diffractograms show characteristic peaks of NiO and / or Ce₂, with no evidence of Ru species observed in any case due to their low concentration and high dispersion. In the NiO-CeC₂ (NP2) and Ru / NiO-CeC₂ (NP1) catalysts, the characteristic NiO peaks are either not observed or are of very low intensity due to the insertion of NiO cations. 2+ within the ceria structure, forming a mixed oxide. Conversely, the characteristic NiO peaks are very prominent in the Ru / NiO-CeO2 (REF) catalyst, indicating poorer NiO-CeO2 contact, which would explain its reduced reducibility and catalytic activity. It is known that the oxygen vacancies generated at the Ni interfaces +2 -O-Ce 4+They are very effective active sites for CO2 chemisorption.

[0128] To analyze the diffractograms quantitatively, the intensity of all peaks was determined and normalized by dividing it by the intensity of the most intense peak of the ceria, corresponding to the crystal plane identified by the Miller indices (111). Table 3 shows the normalized intensities, confirming that the peaks corresponding to NiO in the reference catalyst Ru / NiO-CeO2 (REF) are even higher than those of the ceria, reaching normalized intensities well above 1 in some cases. However, in the catalyst of the invention Ru / NiO-CeO2 (NP1), the NiO peaks are negligible.

[0129] Table 3. Relative intensity of the dCe(Ne X-ray diffraction peaks as a function of the maximum intensity peak of ceria (111). aThe numbers (hk I) indicated in parentheses are the Miller indices that identify each crystal plane.

[0130] From the X-ray diffractograms, the crystal sizes were determined using the Scherrer and Williamson-Hall methods, and the results are included in Table 1. The results confirm that the method according to the invention generates crystals of a much smaller average size than those obtained by a conventional calcination method.

[0131] In summary, the diffractograms indicate that one of the causes of the optimal performance of the catalyst of the invention is the intimate contact achieved between the Ni and Ce species.

[0132] The differences observed using XRD are also evident in the porosity of the materials, as shown in Figure 6 and Table 1. These graphs include the N2 adsorption isotherms at -196 °C, and from these isotherms, the surface areas were determined using the BET method and the pore volume using the XRD method. It should be noted that, since a reaction between gases is being catalyzed on the surface of a solid, having a solid with a high surface area is advantageous.

[0133] The adsorption isotherm of the catalyst prepared by a conventional method, Ru / N₂O-CeC₂ (REF), shows a very low adsorption capacity compared to that of the materials of the invention, presenting the smallest surface area (20 m²). 2 / g). The remaining materials have a much larger surface area, and nickel significantly affects this area, possibly because it promotes cross-linking of the primary crystals. The materials that do not contain nickel have a surface area of ​​around 110 m². 2 / g, and the incorporation of nickel decreases this value to 54-64 m 2 / g. In any case, the method of the invention allows obtaining materials with a higher surface area than the conventional method.

[0134] The TEM photographs, included in Figure 7, confirm that the particle size of the catalyst synthesized by the conventional method, Ru / NiO-CeCl₂ (REF), is much larger than that observed in the catalyst prepared according to the method of the invention. In this material, particles of size 7–8 nm are observed, where it is not possible to distinguish the different components of the catalyst, while in the reference catalyst Ru / NiO-CeCl₂ (REF), large crystals of very diverse sizes attributable to NiO and CeCl₂ are observed, along with small ruthenium oxide crystals of 2–3 nm coating the larger crystals.

[0135] Looking at the Ru / NiO-CeC>2 (NP1) diffractogram, it can be said that all the Ni is within the structure of the cinque.

[0136] In summary, the characterization results confirm that the method of the invention allows obtaining small crystals of mixed NiO-CeC2 oxide, where the nickel is embedded in the structure of the support, and that subsequent ruthenium impregnation achieves good metal-support contact, generating a synergy between the catalyst components (Ru, Ni, and Ce) that facilitates their reducibility. This reducibility is necessary to accelerate the methanation of CO2, since the oxygen vacancies generated by reducing the catalyst surface favor CO2 chemisorption, and the formation of reduced Ru species favors the dissociation of the H2 molecule. This Ru-Ni-Ce synergy is not achieved by a conventional synthesis method without structural control, due to the poorer contact between the catalyst components.

[0137] The role assigned to each component of the optimal Ru / N₂O-CeC₂ (NP₁) catalyst was confirmed by DRIFTS (Diffuse Reflectance Infrared Fourier Transform Spectroscopy) infrared spectroscopy, with measurements performed at 300 °C in a controlled atmosphere by modifying the nature of the feed gas mixture. The spectra were obtained using an infrared spectroscope with a reaction chamber, where the catalyst is placed inside a heated reactor designed so that the reaction gas mixture passes through the powdered catalyst bed while the powder surface is irradiated by infrared radiation. The gas mixtures used were CO₂ + H₂ (10% CO₂ + 40% H₂ + 50% N₂), H₂ (40% H₂ + 60% N₂), and CO₂ (10% CO₂ + 90% N₂).This method allows for the identification of species formed on the surface of the catalysts during the methanation reaction, thus enabling the identification of intermediate species during the catalytic transformation of CO2 to CH4. The presence of CO2 and CH4 in the gas phase can also be identified in the spectra. The spectra obtained with the catalysts N₂O-CeC₂ (NP2), Ru / CeC₂ (NP3), and Ru / N₂O-CeC₂ (NP1) are shown in Figure 8.

[0138] The spectra obtained with the NiO-CeC>2 (NP2) catalyst show the presence of CO2 and CH4 in the gas phase and the formation of monodentate and bidentate carbonates when the methanation gas mixture (CO2 + H2 + N2) is fed. The bidentate carbonates disappear when only H2 + N2 is fed, suggesting that they are being hydrogenated. These spectra demonstrate the high CO2 chemisorption capacity of this catalyst, which can be explained by the presence of a Ni interface.2+ -O-Ce 4+ easily reducible, which favors the creation of oxygen vacancies that act as chemisorption sites.

[0139] The Ru / Ce₂ catalyst (NP3), when fed with CO₂ + N₂ or the methanation mixture CO₂ + H₂ + N₂, shows evidence of the formation of ruthenium bicarbonates and carbonyls, with intensities lower than those observed with the NiO-Ce₂ catalyst (NP2). This confirms that the incorporation of nickel into ceria is more effective at promoting CO₂ chemisorption than the incorporation of ruthenium. However, when H₂ + N₂ is fed to the Ru / Ce₂ catalyst (NP), all bands assigned to species formed by CO₂ chemisorption disappear, and even negative bands are observed. This indicates that ruthenium is much more effective than nickel at accelerating the hydrogenation of surface carbonaceous species, even hydrogenating species that were originally present in the catalyst at the beginning of the experiment, when the baseline was taken and subsequently subtracted from all spectra.

[0140] In the spectra obtained with the optimal catalyst Ru / NiO-CeC>2 (NP1), a combined effect of the roles attributed to nickel and ruthenium is observed. When feeding the methanation mixture, a significant amount of bicarbonates is formed due to the high CO2 chemisorption capacity promoted by the presence of nickel in close contact with the ceria. Likewise, when feeding H2 + N2, very good hydrogenation of the surface carbonaceous species is observed, also with the formation of negative absorption bands, which can be attributed to the catalytic effect of ruthenium.

[0141] In conclusion, the Ru / NiO-CeC>2 catalyst (NP1), prepared according to the inventive process, combines the effect of nickel in promoting CO2 chemisorption with the effect of ruthenium in accelerating the hydrogenation of the chemisorbed species. For this synergy to be effective, it is important to ensure adequate contact between the catalyst components, and optimal results have been achieved by following the inventive process, which yields mixed NiO-CeC>2 oxide nanoparticles onto which ruthenium is subsequently deposited.

[0142] Example 4

[0143] Use of the Ru / NiO-CeC>2 (NP1) catalyst for the production of H2 from ethanol

[0144] An H2 production trial was carried out by decomposition and catalytic reforming of ethanol (EtOH) using different FW / EtOH ratios. (a) FW / EtOH =0, (b) H2O / EtOH =1 , (c) H2O / EtOH =2, (d) H2O / EtOH =3.

[0145] The Ru / NiO-CeC>2 catalyst (NP1) (200 mg) is pretreated in situ at 400 °C in 50% H2 / He (200 mL / min), then pure He is introduced and the temperature is stabilized at 300 °C. A reactive mixture of H2O / EtOH (0.04 mL / min) mixed with He (200 mL / min) is introduced, and the gas composition is measured once steady state is reached. The temperature is increased in 50 °C steps at a rate of 10 °C / min, and the steady-state gas composition is determined at each temperature.

[0146] The results demonstrate that it is possible to obtain H2 by decomposition and reforming of ethanol using the Ru / NiO-CeC>2 (NP) catalyst. The highest H2 production yield in the temperature range of 300–500°C, and under the conditions of these experiments, is obtained using an H2O / EtOH ratio of 3.

[0147] Figure 9 shows the hydrogen production obtained.

[0148] Example 5

[0149] Use of the Ru / NiO-CeC>2 (NP1) catalyst for the production of H2 from resins

[0150] The process of producing hydrogen from resins is carried out in a catalyzed system under an oxidizing atmosphere (H2O) and a constant temperature of around 370 °C.

[0151] In one particular example, the resin recovered from a fiber-resin waste from a wind turbine has been treated. Figure 10 shows a fiber-resin waste from a wind turbine (left) and the fiber (center) and resin (right) recovered using the method described in Patent P201531174.

[0152] The recovered resin is gasified with H2O to produce H2 in a plug flow reactor under the following conditions:

[0153] - Resin mass: Catalyst mass 1 : 1 (1 g of resin mixed with 1 g of catalyst).

[0154] - Catalyst: Ru / N₂O-CeO₂ (NP1), prepared as described in example 1.

[0155] - Reaction atmosphere: H2O / N2.

[0156] - N2 flow: 90 mL / min.

[0157] - H2O flow: 0.17 mL / min.

[0158] - Reaction temperature: heating at 5 °C / min from ambient temperature to 370 °C and holding at this temperature.

[0159] - System pressure: 1 atm.

[0160] The results obtained in the catalyzed gasification process are shown in the following table, comparing them with those of a similar process carried out in the absence of a catalyst:

[0161] Table 4. Product distribution during the catalyzed gasification of resin recovered from a fiber-resin waste from a wind turbine using the method described in Patent P201531174.

[0162] Figures 11 and 12 show the distribution of gaseous products (considering the concentration of the carrier gas N2) for the uncatalyzed and catalyzed reaction, respectively, as a function of time and temperature.

[0163] Uncatalyzed gasification produces a low proportion of gases (9% compared to 74% for catalyzed gasification), and the small amount of gas generated contains mainly CO2 and some CO.

[0164] Catalyzed gasification completely eliminates the amount of solid residue obtained (0% compared to 58% in the uncatalyzed reaction), with the gaseous fraction predominating. The gas composition consists mainly of H2, with CO2 in a smaller proportion and small amounts of CO and CH4.

[0165] The advantages of the catalyzed gasification process described in this document compared to other thermal gasification processes for polymer waste are:

[0166] • Oxidation process at low reaction temperatures.

[0167] • Reduction in the amount of solid, liquid, and gaseous products other than hydrogen obtained.

[0168] • Hydrogen production in a high proportion.

[0169] Example 6

[0170] Use of the Ru / NiO-CeC>2 (NP1) catalyst for the production of H2 from waste

[0171] A hydrogen production process was carried out from plastic waste (polypropylene, polyethylene and polystyrene), in a catalyzed system under an oxidizing atmosphere (H2O) and variable temperature depending on the nature of the polymer.

[0172] In several particular experiments, polypropylene (Sigma-Aldrich particle size 4 mm), polyethylene (Sigma-Aldrich particle size 2 - 4 mm) and polystyrene (Sigma-Aldrich with average molecular weight 280,000 gr / mol) and a commercial residue used for food packaging (composed of polypropylene) were treated in a single-stage catalytic system at temperatures between 450 °C and 550 °C depending on the type of polymer.

[0173] The polymers are gasified with H2O to produce H2 in a plug flow reactor under the following conditions:

[0174] • Polymer mass: Catalyst mass 1 : 0.7 (1 g of polymer mixed with 0.7 g of catalyst).

[0175] • Ru / NiO-CeC>2 catalyst (NP1), prepared as described in Example 1.

[0176] • Reaction atmosphere: N2 - H2O.

[0177] • N2 flow: 90 mL / h.

[0178] • H2O flow: 10 mL / h.

[0179] • Reaction temperature: heating at 5 °C / min from ambient temperature to (450-550) °C and holding at this temperature.

[0180] • System pressure: 1 atm.

[0181] The results obtained in the catalyzed gasification process are shown in the following table, comparing them with those of a similar process carried out in the absence of a catalyst: Table 5. Distribution of products during the catalyzed gasification of the polymers.

[0182] Uncatalyzed gasification produces a majority liquid fraction and a minor gaseous fraction as reaction products.

[0183] Catalyzed gasification decreases the amount of the liquid fraction and increases the proportion of the gaseous fraction. The gas composition consists mainly of H2, with CO2 in a smaller proportion and small amounts of CO and CH4.

[0184] The advantages of the described catalyzed gasification process compared to other thermal processes for gasifying polymeric waste are:

[0185] • Low temperature reaction oxidation process using a Ni-Ru-Ce, Ru / NiO-CeO2 (NP1) catalyst, described in the present invention.

[0186] • High-volume hydrogen production. • Single-stage process.

Claims

1. CLAIMS 1. A catalyst comprising a mixture of cerium oxide, nickel oxide and ruthenium, of formula Ru / N₂O-CeO₂, wherein the nickel cations are inside the cerium particles forming a mixed oxide, and wherein the ruthenium is dispersed on the surface of the N₂O-CeO₂ particles.

2. A catalyst according to claim 1, comprising a Ru proportion of between 1% and 2%, preferably the Ru proportion being 2% by weight relative to the total weight of the catalyst.

3. A catalyst according to claim 1, comprising a Ni proportion between 5% and 20%, preferably the Ni proportion being 10% by weight relative to the total weight of the catalyst.

4. A catalyst according to claim 1, 2 or 3, having a predominant particle size of 7-8 nm.

5. A catalyst according to any one of claims 1 to 4 having an X-ray diffractogram which only contains the characteristic diffraction bands of fluorite-structured cinnabar.

6. A catalyst according to claim 5 wherein the X-ray diffractogram shows the following relative band intensities, normalized by dividing the intensity of each peak by the intensity of the CeÜ2 peak (111).

7. A process for preparing the catalyst defined in any one of the preceding claims, comprising a) dissolving a nickel precursor salt and a zinc precursor salt in water. b) add to the previous solution a mixture of: - an alkane with 5 to 10 carbon atoms, - a linear monohydric alkanol of 2 to 8 carbon atoms, - and a non-ionic surfactant, obtaining a first solution, c) dissolve an alkali compound in water, d) add to the solution obtained in step c) a mixture of: - an alkane with 5 to 10 carbon atoms, - a linear monohydric alkanol of 2 to 8 carbon atoms, and - a non-ionic surfactant, keeping the mixture under agitation, obtaining a second solution, e) mix both solutions, first and second, and stir, obtaining a solid. f) separate the solid obtained in step e) and subject it to washing, drying and calcination at a temperature between 450 and 700 °C, g) add ruthenium to the solid obtained in step f) by impregnating it with a ruthenium salt, h) dry the resulting catalyst and heat treat it in a non-oxidizing atmosphere at a temperature above 250 °C.

8. A process according to claim 7, wherein the nickel precursor salt is Ni(NO3)2-6H2O.

9. A process according to claim 7, wherein the precursor salt is Ce(NO3)3-6H2O.

10. A process according to claim 7, wherein the alkali compound is a tetraalkylammonium hydroxide in which the alkyl moiety has between 1 and 5 carbon atoms, and in which the alkyl radicals are the same or different.

11. A process according to claim 7, wherein the calcination of the nickel solid is carried out between 450 and 700 °C, preferably between 500 and 600 °C.

12. A process according to claim 7, wherein the ruthenium salt is ruthenium(III) acetylacetonate (Ru(O2CsH7)3) and the solvent is toluene.

13. A process according to claim 7, wherein the alkaline compound is used in a proportion of between 300 and 400 g per liter of water, preferably between 320 and 380 g per liter of water.

14. A process according to claim 7, comprising: a) dissolving a nickel precursor salt and a cene precursor salt in water, b) adding to the above solution a mixture of n-heptane, hexanol and Triton X-100 while keeping the mixture under stirring, obtaining a first solution, c) dissolving tetramethyl ammonium hydroxide in water, d) adding to the above solution a mixture of n-heptane, hexanol and Triton X-100 while keeping the mixture under stirring, obtaining a second solution, e) mixing both the first and second solutions, and stirring, obtaining a solid. f) separate the solid obtained in step e) and subject it to washing, drying and calcination at a temperature between 450 and 700 °C, g) add ruthenium to the solid obtained in step f) by impregnation with a ruthenium salt using toluene as a solvent h) dry the resulting catalyst and heat treat it in a non-oxidizing atmosphere at 250 °C.

15. Use of the catalyst defined in any one of the preceding claims 1 to 6, for the conversion of products.

16. Use of the catalyst according to the preceding claim wherein the conversion of products is obtaining hydrogen.

17. Use of the catalyst according to claim 16 wherein the product conversion comprises obtaining hydrogen from starting materials selected from resins and plastics.

18. Use of the catalyst according to claim 17 wherein the resins are derived from a fiber-resin residue.

19. Use of the catalyst according to claim 17 wherein the plastics are selected from polyethylene, polypropylene and polystyrene.

20. Use of the catalyst according to claim 16 wherein the hydrogen is obtained from ethanol.

21. Use of the catalyst according to claim 15 for obtaining synthetic natural gas.

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