Process for continuous hydrogenation of aqueous levulinic acid to gamma-valerolactone and tandem conversion thereof to high octane gasoline range hydrocarbons

Abstract

Ru-supported carbon materials having characteristic surface chemistry (Bronsted acidic phosphate groups, Lewis basic N-groups selected from the group consisting of Lewis basic pyridine N-groups, pyrrole N-groups and quaternary N-groups, and oxygen functional groups), when hydrogenating aqueous levulinic acid (0.47 M and 0.95 M) to gamma-valerolactone with near stoichiometric H2 under mild conditions (80 DEG C to 95 DEG C), the Ru-supported carbon materials having surface chemical properties (Bronsted acidic phosphate groups, Lewis basic N-groups selected from the group consisting of Lewis basic pyridine N-groups, pyrrole N-groups, and quaternary N-groups). It is proved that the catalyst shows excellent activity, selectivity and stability. The material exhibits significant stability in a fixed bed reactor under continuous flow conditions, maintaining high activity and gamma-valerolactone selectivity at 3 bar to 5 bar, 80 DEG C to 95 DEG C, and a low H2 / levulinic acid ratio (4 to 17) for an operating time of about 1250 hours. The excellent catalytic performance and stability of the multi-functional Ru catalyst is attributed to the unique surface chemistry of the carbon support that stabilizes Ru nanoparticles over surface nitrogen and oxygen deficiencies and promotes the cyclization of 4-hydroxyvalerate over the acidic phosphate sites and RuOx / RuO2 sites.

Description

Technical Field

[0001] The present invention relates to a process for hydrogenating levulinic acid with H2 to γ-valerolactone. The present invention also relates to a catalyst for use in the process. If desired, the γ-valerolactone can be further converted into gasoline-range hydrocarbons. Background Art

[0002] Levulinic acid is a well-known product of hexose hydrolysis / dehydration and is inexpensively obtained by decomposing cellulose feedstock. Levulinic acid is an attractive platform material for producing, for example, gamma-valerolactone. Among the various levulinic acid derivatives, gamma-valerolactone is particularly commercially important due to its usefulness as a solvent, food additive, fuel component, and as a precursor for high-value chemicals (linear α-olefins, esters) and fuel-range synthetic hydrocarbons.

[0003] Traditionally, γ-valerolactone has been obtained via the tandem hydrogenation-dehydration of levulinic acid under pressurized H₂ (1 MPa to 3 MPa). Catalytic hydrogenation of levulinic acid or its derivatives has been demonstrated using both homogeneous and heterogeneous noble metal and non-noble metal catalysts. Ru (ruthenium) appears to be the most active due to its unique ability to selectively hydrogenate keto C=O groups. Even so, elevated temperatures (≥150°C) or acid promoters are required to promote the conversion of the intermediate hydroxy acid (4-hydroxyvaleric acid) and provide selective conversion of levulinic acid to γ-valerolactone. Consequently, the commercial usefulness of Ru-based catalysts has been plagued by deactivation problems caused by: (a) leaching of Ru species through the formation of Ru-carboxylate complexes with levulinic acid (pKa approximately 4.59) in the liquid phase, and (b) sintering and charring of Ru nanoparticles in gas-phase systems. Another disadvantage of processes operating at elevated H₂ pressures and reaction temperatures is the reduced selectivity for γ-valerolactone due to the formation of over-hydrogenated byproducts such as 2-methyltetrahydrofuran and pentane-1,4-diol. Similarly, at low temperatures, hydrogenation of levulinic acid produces the intermediate hydroxy acid (4-hydroxyvaleric acid) as the primary product; the dehydration step is kinetically less favorable at low temperatures relative to the hydrogenation step. Therefore, elevated temperatures or acid cocatalysts are required to provide high γ-valerolactone selectivity / yield in the liquid-phase hydrogenation conversion of levulinic acid (or its derivatives) [RSC Adv., 2017, 7, 44082, ACS Catal. 2014, 4, 4, 1171-1181]. In fact, given the benefits of low-temperature operation (low energy consumption and minimization of sintering and coking), researchers have used both mineral acids and solid acids (Amberlyst-15, Amberlyst-70, niobium phosphate and niobic acid, etc.) as co-catalysts for the energy-efficient hydrogenation of levulinic acid to γ-valerolactone [Green Chem., 2012, 14, 688-694, ChemSusChem. 10 (14) (2017) 2891-2896].

[0004] Therefore, to date, the development of practical, efficient, and stable bifunctional Ru catalysts for the selective low-temperature hydrogenation of aqueous levulinic acid to γ-valerolactone by incorporating non-reducible and stable acid sites remains a major technical challenge.

[0005] US 7,741,527 discloses a process for the dimerization of olefins, the process comprising using a solid phosphoric acid catalyst comprising phosphoric acid supported on a carrier, a compound that forms phosphoric acid by hydrolysis, or a mixture of the two.

[0006] US 8,148,553 discloses a process involving the conversion of levulinic acid to gamma-valerolactone by contacting levulinic acid with a heterogeneous catalyst comprising Ru / C.

[0007] CN 102658131 discloses a ruthenium-based catalyst for preparing γ-valerolactone from levulinic acid, comprising an active component and a catalyst support. The active component is 1 to 10 weight percent ruthenium. A promoter of up to 10 weight percent of a Group VIII element or a Group I element may be present. The catalyst support may be a carbon material (e.g., activated carbon, carbon black, carbon nanotubes, or carbon nanofibers), an oxide (e.g., alumina, silica, titania, or binary mixed oxides thereof), or a molecular sieve (e.g., MCM, ZSM, SBA, or faujasite). The catalyst can be prepared using a solvent-free microwave-assisted pyrolysis method. The catalytic reaction can be carried out at a temperature ranging from 70°C to 120°C for 1 to 10 hours using high-pressure hydrogen (1 MPa to 5 MPa).

[0008] CN 108745401 discloses a nitrogen- and phosphorus-doped porous carbon-rhodium phosphide catalyst, as well as its preparation method and application. A polyol, a rhodium source, and a substance containing nitrogen and phosphorus compounds are dispersed in water; stirred to form a mixed sol; and then calcined in a single step at high temperature to obtain a composite nanomaterial comprising rhodium phosphide supported on porous carbon, wherein the porous carbon support is modified with nitrogen and phosphorus in the compounds. Rhodium phosphide nanoparticles are supported on the nitrogen- and phosphorus-modified porous carbon, wherein the rhodium phosphide nanoparticles have a size of 4 to 8 nm.

[0009] CN 114433163 discloses an in-situ modified and pore-adjustable biochar-supported ruthenium catalyst, a preparation method of the in-situ modified and pore-adjustable biochar-supported ruthenium catalyst, and the use of the in-situ modified and pore-adjustable biochar-supported ruthenium catalyst in lignin. Summary of the Invention

[0010] It is an object of the present invention to obviate at least some of the disadvantages of the prior art and to provide an improved catalyst for the hydrogenation of aqueous levulinic acid streams to gamma-valerolactone.

[0011] In a first aspect, a catalytic material based on a carbon-containing material is provided, the catalytic material being loaded with Ru, wherein the surface of the catalytic material comprises: a) Bronsted acidic phosphate groups; b) Lewis basic N-groups selected from Lewis basic pyridinic N-groups, pyrrolic N-groups and quaternary N-groups; and c) oxygen functional groups.

[0012] In a second aspect, a system is provided, comprising a catalyst bed containing a catalytic material as described above, a heater and a thermocouple, a pump for feeding levulinic acid to the catalyst bed, a pressure regulator for regulating the pressure in the catalyst bed / system, and a valve for regulating the inflow of H2.

[0013] In a third aspect, there is provided a method for converting levulinic acid into γ-valerolactone comprising using the catalytic material according to any one of claims 1 to 7 or the system according to any one of claims 8 to 10, the method comprising the step of contacting the catalyst with an aqueous solution of levulinic acid and hydrogen (H2).

[0014] In a fourth aspect, there is provided γ-valerolactone or a γ-valerolactone / 4-hydroxyvaleric acid mixture produced using the catalytic material, system or method described above.

[0015] In a fifth aspect, there is provided a C prepared by the method described above. 8+ Olefins.

[0016] In a sixth aspect, a method for preparing a catalytic material as described above is provided, the method comprising the step of contacting an organic polymer comprising amine groups with phosphoric acid, followed by the step of carbonizing the material at an elevated temperature under an autogenous atmosphere to provide a carbon-based material, wherein the surface of the material comprises: a) Bronsted acidic phosphate groups; b) Lewis basic N-groups selected from Lewis basic pyridinic N-groups, pyrrolic N-groups and quaternary N-groups; and c) oxygen functional groups, followed by a final loading step wherein the material is mixed with an aqueous solution of a ruthenium salt, followed by reduction of the ruthenium salt so that small particles comprising elemental ruthenium are loaded on the carbon-based material.

[0017] Further embodiments of the invention are defined in the appended dependent claims, which are expressly incorporated herein.

[0018] One advantage is the extended stability. The long-term stability is due to the enhanced stabilization effect of the Ru nanoparticles on the highly nitrogen-doped carbon surface.

[0019] Conversion and selectivity are maintained and are comparable to or better than Ru catalysts according to the prior art.

[0020] There is the possibility of adjusting the levulinic acid conversion and γ-valerolactone yield / selectivity by simply adjusting the flow rate of the liquid feed (liquid hourly space velocity / weight hourly space velocity), the flow rate of gaseous H2 (H2 / levulinic acid molar ratio), and the reaction temperature and pressure.

[0021] Another advantage is the possibility to work with aqueous levulinic acid in a concentration range of about 0.5 M to 1.0 M, which is representative of actual levulinic acid feeds obtained from biomass processing.

[0022] The leaching of Ru from the catalyst material is very limited.

[0023] Temperature and operating pressure can be kept relatively low, resulting in low energy consumption and minimization of sintering and coking of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Aspects and embodiments will be described with reference to the following drawings, in which:

[0025] Figure 1 Shown is the experimental setup for the continuous hydrogenation of aqueous levulinic acid to γ-valerolactone.

[0026] Figure 2 Shown are the FE-SEM images and corresponding EDX trace element mapping (C, O, N, P, and Ru) of the Ru / CNP500 catalyst.

[0027] Figure 3 The effect of Ru loading (1 wt % to 5 wt %) on the NH 3 -TPD curves of Ru / CNP500 catalysts is shown (IW indicates Ru / CNP500 catalyst obtained by incipient wetness impregnation and H 2 treatment at 400° C.).

[0028] Figure 4 (a) Levulinic acid conversion of Ru / CNP500 as a function of Ru loading versus normalized time (time*mmol / g Ru ) and (b) conversion relative to γ-valerolactone selectivity. Reaction conditions: 0.25 g levulinic acid, 5 ml deionized H₂O, 15 mg catalyst (Ru / CNP500, Ru loading 1 wt% to 5 wt%), 5.5 ± 1 bar initial H₂, 400 rpm (stirring rate).

[0029] Figure 5 Shown are (a) the effect of catalyst acidity (phosphate) on catalytic performance (γ-valerolactone selectivity) at room temperature and (b) the effect of reaction temperature on γ-valerolactone selectivity. Reaction conditions: 0.25 g levulinic acid, 5 ml deionized H₂O, 15 mg catalyst, 5.5 ± 1 bar initial H₂, 400 rpm (stirring rate).

[0030] Figure 6Catalyst stability (γ-valerolactone yield) as a function of (a) reuse (batch experiments) and (b) run time (fixed-bed experiments) for the multifunctional Ru / CNP500 catalyst compared to physical mixtures of (Ru / Csigma + Amberlyst 15) and (Ru / Csigma + NbOPO4 / Amberlyst 15). Batch reaction conditions: 0.25 g levulinic acid, 5 ml deionized H2O, 15 mg catalyst (@0.34 mol% Ru, 5 wt% Ru loading), 5.5 ± 1 bar initial H2, 80°C, 4 hours, 400 rpm (stirring rate); fixed-bed reaction conditions: 80°C, 5 bar, 0.48 M aqueous levulinic acid, H2 / levulinic acid (molar) ratio ≥ 10, WHSV 0.11 hr-1 to 0.12 hr-1 (with respect to 0.48 M aqueous levulinic acid).

[0031] Figure 7 Shown are the catalytic performances of the Ru / CNP500 catalyst (5 wt % Ru) in the continuous hydrogenation of aqueous levulinic acid under different reaction conditions over a 52-day run time.

[0032] Figure 8 TEM images of 5 wt % Ru / CNP500 and the corresponding particle size distribution are shown (top - fresh and bottom - after 52 days of run time).

[0033] Figure 9 Shown are (a) NH3-TPD plot of 5 wt% Ru / CNP500 after 52 days of operation and (b) N2-adsorption-desorption isotherms and corresponding pore size distribution plots (inset) of Ru / CNP500 before and after 52 days of continuous operation.

[0034] Figure 10 High-resolution (a) C1s and Ru3d XPS spectra, (b) O1s XPS spectra, (c) N1s XPS spectra, and (d) P2p XPS spectra of fresh Ru / CNP500 and spent Ru / CNP500 (5 wt% Ru) after 52 days of operation are shown.

[0035] Figure 11 Shown is a simplified experimental setup for the tandem conversion of levulinic acid-derived aqueous γ-valerolactone to fuel-range hydrocarbons. The reactors include R0 (hydrogenation reactor, 80°C to 95°C, 3.5 to 5 bar), R1 (decarboxylation reactor, 380°C, 1 bar), and R2 (oligomerization reactor, 170°C to 200°C, 1 bar), along with an MFC (mass flow controller), S1, S2, and S3 (gas-liquid separators).

[0036] Figure 12 This document shows the conversion of a 9 wt% aqueous γ-valerolactone / 4-hydroxyvaleric acid mixture (85 to 96 mol% γ-valerolactone and 4 to 15 mol% 4-hydroxyvaleric acid) produced over a multifunctional Ru / CNP500 catalyst into fuel-range hydrocarbons (C8+ branched olefins) at atmospheric pressure using a single-pass, two-bed reactor system in series containing commercial silica-alumina (first bed) and commercial solid phosphoric acid (second bed) as the decarboxylation and oligomerization catalysts, respectively. Reaction conditions: 380°C (first bed, 10 g of pellets made with 30% alumina), 170°C to 200°C (second bed, 20 g of pellets), 1 bar, and a WHSV of 0.12 hr⁻¹ for both γ-valerolactone and 4-hydroxyvaleric acid fed to the first bed. DETAILED DESCRIPTION

[0037] Before the present invention is disclosed and described in detail, it should be understood that the present invention is not limited to the specific configurations, process steps and materials disclosed herein, and thus the configurations, process steps and materials may vary. It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting, as the scope of the present invention is limited only by the appended claims and their equivalents.

[0038] It must be noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0039] The following terminology is used throughout the specification and claims.

[0040] All percentages and ratios are by weight unless otherwise indicated.

[0041] In this paper, the “amount” of particles or other materials on a surface is usually expressed as µg / cm 2 This is a suitable way to express the amount because the applied layer is very thin. To calculate the amount, measure the area of ​​the object and calculate the amount per area.

[0042] A "Brønsted acid" is a molecule (or ion) that is capable of donating a proton.

[0043] A "Lewis base" is an atomic or molecular species in which the highest occupied molecular orbital (HOMO) is highly localized. Examples include, but are not limited to, conventional amines such as ammonia and alkylamines, and pyridine and its derivatives. Other examples include, but are not limited to, compounds of the formula NH 3-x R x (wherein R = alkyl or aryl) amines, pyridine and its derivatives, formula PR3-x A x Phosphines (where R = alkyl, A = aryl), compounds of O, S, Se and Te in oxidation state -2, including water, ethers and ketones.

[0044] "Nanoparticles" are particles of a substance with a diameter in the range of 1 nm to 100 nm. For irregular particles, the largest particle dimension is considered to be the diameter. For spheres, the largest dimension is the diameter.

[0045] Oxygen functional groups are chemical functional groups containing an oxygen atom and include, for example, alcohols, ethers, aldehydes, ketones, and carboxylic acids, as well as various derivatives of carboxylic acids, such as amides, esters, and acyl halides.

[0046] In one embodiment, a highly porous, multifunctional Ru / C catalyst incorporating unique surface features (oxygen functional groups, strongly Bronsted-acidic, non-reducible phosphate sites, and abundant Lewis-basic N-sites) is disclosed as a catalyst for the selective, low-temperature, tandem hydrogenation-dehydration of aqueous levulinic acid to γ-valerolactone. A low-cost, multifunctional Ru / C catalyst derived from chitin (biowaste) is disclosed, based on extended stability testing conducted in a continuous-flow fixed-bed reactor (approximately 1250 hours of run time) under mild conditions (3 to 3.5 bar and 80°C to 95°C) using a low H2:levulinic acid molar ratio (≤17).

[0047] In a first aspect, a catalytic material based on a carbon-containing material is provided, the catalytic material being loaded with Ru, wherein the surface of the catalytic material comprises: a) Bronsted acidic phosphate groups; b) Lewis basic N-groups selected from Lewis basic pyridinic N-groups, pyrrolic N-groups and quaternary N-groups; and c) oxygen functional groups.

[0048] In one embodiment, the content of Ru is from 0.1 wt% to 10 wt%. In one embodiment, the content of Ru is from 1 wt% to 6 wt%. In one embodiment, Ru is present in the form of nanoparticles comprising Ru, preferably having an average particle size d in the range of 1.5 nm to 5 nm as measured by H2 pulse chemisorption. p,H2 In another embodiment, Ru is present in an average particle size d as measured by H2 pulse chemisorption. p,H2 In another embodiment, Ru is present in the form of nanoparticles in the range of 1.5 nm to 3.75 nm. ... p,H2 It exists in the form of nanoparticles in the range of 1.7 nm to 3.7 nm.

[0049] In one embodiment, the NH3-acidity measured by NH3-TPD (temperature programmed desorption) (70°C to 450°C total) is greater than 1.5 mmol / g.

[0050] In one embodiment, the CO2-alkalinity measured by CO2-TPD (temperature programmed desorption) (30°C to 150°C total) is greater than 0.03 µmol / g.

[0051] In one embodiment, the specific surface area is at least 300 m 2 The specific surface area is measured by gas adsorption using the BET method according to ISA 9277:2010.

[0052] In one embodiment, the pore volume is at least 0.3 cm 3 / g.

[0053] In one embodiment, the catalytic material is based on carbonized organic material. In one embodiment, the catalytic material is based on carbonized chitin.

[0054] In one embodiment, the Bronsted acidic phosphate group comprises NbOPO4.

[0055] In one embodiment, the catalytic material comprises Bronsted acidic phosphate groups covalently bound to carbon (-OPO4 sites). In one embodiment, the catalytic material comprises 0.18 mmol / g Bronsted acidic phosphate groups covalently bound to carbon (-OPO4 sites).

[0056] It is intended that Bronsted acidic phosphate groups and oxygen functional groups are distinct. Thus, the oxygen functional groups under c) do not include the Bronsted acidic phosphate groups under a). It is intended that the oxygen functional groups in c) are not Bronsted acidic phosphate groups. The Bronsted acidic phosphate groups under a) are not oxygen functional groups in c). The oxygen functional groups in c) do not include Bronsted acidic phosphate groups.

[0057] In a second aspect, a system is provided, comprising a catalyst bed containing a catalytic material as described above, a heater and a thermocouple, a pump for feeding levulinic acid to the catalyst bed, a pressure regulator for regulating the pressure in the catalyst bed / system, and a valve for regulating the inflow of H2.

[0058] In one embodiment, the system includes a valve for regulating the inflow of N2.

[0059] In one embodiment, the system includes a gas-liquid separator for separating the obtained liquid product from unreacted H2.

[0060] In a third aspect, there is provided a method for converting levulinic acid into γ-valerolactone comprising using the catalytic material as described above or the system as described above, the method comprising the steps of contacting the catalyst with an aqueous solution of levulinic acid and hydrogen (H2).

[0061] In one embodiment, the H2 / levulinic acid molar ratio is in the range of 3 to 20, preferably 4 to 17.

[0062] In one embodiment, the pressure during the reaction is in the interval from 1.5 bar to 10 bar, preferably from 2 bar to 7 bar.

[0063] In one embodiment, the temperature is above 70°C but below the boiling point of the aqueous levulinic acid solution at the pressure at which the reaction is carried out, preferably in the range of 80°C to 95°C.

[0064] In one embodiment, the catalyst is contacted with an aqueous solution of levulinic acid and hydrogen gas in a reaction vessel in batches. In one embodiment, the catalyst is contacted with an aqueous solution of levulinic acid and hydrogen gas in a high pressure reaction vessel in batches.

[0065] In one embodiment, the catalyst is contacted in a fixed bed reactor under continuous flow conditions of an aqueous solution of levulinic acid and hydrogen.

[0066] In one embodiment, levulinic acid is produced from a raw material comprising cellulose.

[0067] In one embodiment, γ-valerolactone or a γ-valerolactone / 4-hydroxyvaleric acid mixture is further converted to C in a cascade process at atmospheric pressure using a single-pass dual-bed reactor system comprising commercial silica-alumina (first bed) and solid phosphoric acid (second bed). 8+ Olefins.

[0068] In a fourth aspect, there is provided gamma-valerolactone produced using a catalytic material as described in any one of the above aspects and embodiments.

[0069] In a fifth aspect, there is provided a C manufactured as described above 8+ Olefins.

[0070] In a sixth aspect, a method for preparing a catalytic material as described above is provided, the method comprising the step of contacting an organic polymer comprising amine groups with phosphoric acid, followed by the step of carbonizing the material at an elevated temperature under an autogenous atmosphere to provide a carbon-based material, wherein the surface of the material comprises: a) Bronsted acidic phosphate groups; b) Lewis basic N-groups selected from Lewis basic pyridinic N-groups, pyrrolic N-groups and quaternary N-groups; and c) oxygen functional groups, followed by a final loading step wherein the material is mixed with an aqueous solution of a ruthenium salt, followed by reduction of the ruthenium salt so that small particles comprising elemental ruthenium are loaded on the carbon-based material.

[0071] In one embodiment, the organic polymer comprising amine groups is chitin.

[0072] In one embodiment, the material is carbonized at an elevated temperature of at least 500° C. in an atmosphere comprising an elevated concentration of N 2 compared to standard atmospheric air, which is standard air having a content of about 78% by weight.

[0073] Other features of the present invention and their associated advantages will be apparent to those skilled in the art after reading the description and examples.It will be understood that the disclosed embodiments can be freely combined with all other embodiments as long as there is no obvious contradiction.

[0074] It should be understood that the invention is not limited to the specific embodiments shown herein.The following examples are provided for illustrative purposes and are not intended to limit the scope of the invention, since the scope of the present invention is limited only by the appended claims and their equivalents.

[0075] Example

[0076] Chemicals

[0077] NaOH (99%, Sigma-Aldrich), H3PO4 (85%, VWR), HCl (37%, Merck), chitin flakes (from shrimp shells, Sigma-Aldrich), ammonium dihydrogen phosphate (99.9%, Merck), Amberlyst® 15 (dried, H + Form, Sigma-Aldrich) Ru / C (5%, Sigma-Aldrich), levulinic acid (97%, Sigma-Aldrich), γ-valerolactone (99%, Sigma-Aldrich), niobium (V) chloride (99.8%, ACROS), ruthenium chloride (RuCl3.xH2O, abcr GmbH, 36% Ru) were obtained from commercial sources and used without further purification.

[0078] Catalytic materials

[0079] The bifunctional carbon support containing a nitrogen site and a phosphate site was obtained by the well-known one-step phosphoric acid activation described in the literature. This method is well known and widely practiced for obtaining high surface area nitrogen and phosphate self-doped carbons from nitrogen-rich biowaste including chitin, for example in [JP Mikkola, V Kent, W Siljebo, LJ Konwar,A Samikannu, Hydrothermal method for producing renewable paraffinic hydrocarbons, 2021, EP3841186A1; LJ Konwar, JP Mikkola, Carbon support effects on metal (Pd, Pt and Ru) catalyzed hydrothermal decarboxylation / deoxygenation of triglycerides Appl. Catal. A. General, 638,2022, 118611 and A Samikannu, LJ Konwar, P Mäki-Arvela, JP Mikkola, Renewable N-doped active carbons as efficient catalysts for direct synthesis of cyclic carbonates from epoxides and CO2 Appl. Catal. B, 241, 2019, 41-51]. In a typical synthesis process, 10 g of chitin flakes were soaked with 50 wt% aqueous phosphoric acid at a 1:2 (weight / weight) ratio and aged under ambient conditions for 24 hours. In the next step, the chitin-phosphoric acid mixture was transferred to an alumina crucible, loaded into a muffle furnace (Nabertherm, LT15), and activated at 500°C (heating rate 3°C / min) for 1 hour in an autogenous atmosphere. The obtained material was ground into a powder and thoroughly washed with hot deionized water (90°C) until a neutral pH was reached. It was then dried in an oven at 100°C for 24 hours to produce a bifunctional carbon support (CNP500) containing nitrogen (basic), oxygen, and phosphorus (acidic) functional groups.

[0080] According to the following procedure, a base carbon material (CN650) containing only nitrogen sites without phosphorus doping was obtained by directly carbonizing chitin sheets at 650°C. In a typical synthesis process, 10 grams of chitin sheets were loaded onto an alumina boat, transferred to a tube furnace (Carbolite), and carbonized at 350°C (heating rate 2.5°C / min) under a 50 ml / min N2 flow for 2 hours. The obtained carbon material was further carbonized at 650°C for 1.5 hours (heating rate 5°C / min, 50 ml / min N2). The resulting carbon material was powdered, washed with deionized water, and dried at 100°C overnight to obtain the base carbon support (CN650) functionalized with nitrogen functional groups.

[0081] Carbon supports containing oxygen functional groups and trace amounts of phosphate (CPcomm) were obtained by phosphoric acid washing of powdered activated carbon obtained from Fisher scientific. Ru-supported catalysts (Ru / CN650, Ru / CNP500, and Ru / CPcomm) were prepared by using methods described in the literature, for example, in Pham, TN, Samikannu, A., Rautio, AR. et al. Catalytic Hydrogenation of D-Xylose Over Ru Decorated Carbon Foam Catalyst in a SpinChem ® The catalyst was prepared using the well-known deposition-precipitation method described in Rotating Bed Reactor. Top Catal 59, 1165-1177 (2016). This deposition-precipitation method is well known and widely practiced. The synthesis process for the supported catalyst was as follows: 1 g of the support was added to 50 ml of deionized water at room temperature with stirring. After stirring for 1 hour, an appropriate amount of ruthenium chloride (aqueous) solution (2.5 mg / ml, corresponding to a metal loading of 1 wt % to 5 wt %) was added to the mixture / suspension and stirred at room temperature for 2 hours. Next, 0.1 M NaOH was slowly added to the reaction mixture to adjust the pH of the solution to approximately 9.5. After further stirring the resulting mixture for 1 hour, a calculated amount of freshly prepared NaBH4 solution (nNaBH4 / nRu = 15 / 1) was quickly added to the solution and stirred for a further 1 hour at room temperature. To obtain the desired catalytic material, the contents of the reaction mixture were filtered and washed extensively with deionized water until free of Cl. - ions and dried under N2 flow at 70°C for 24 hours. A reference catalyst Ru / CNP500_IW was also prepared according to the incipient wetness impregnation and H2 reduction technique.

[0082] The Nb-based support, NbP-bulk (NbOPO4), was prepared according to a literature procedure (niobium (V) chloride was hydrolyzed in 12 M HCl in the presence of a stoichiometric amount of ammonium dihydrogen phosphate, followed by calcination at 400°C) and the method described in [Samikannu A., Konwar LJ, Rajendran K., Lee CC, Shchukarev A., Virtanen P., Mikkola J-P. Highly dispersed NbOPO4 / SBA-15 as a versatile acid catalyst upon production of renewable jet-fuel from bio-based furanics via hydroxyalkylation-alkylation (HAA) and hydrodeoxygenation (HDO) reactions, Appl. Catal. B, 272, 2020, 118987]. The Ru-supported catalyst, Ru / NbP-bulk, was obtained by incipient wetness impregnation with RuCl3, according to a procedure described elsewhere. Prior to use, the catalytic material was reduced at 400°C under a stream of H2.

[0083] The actual metallic Ru loading measured by ICP-OES was the same as the designed loading in all catalysts.A commercial ruthenium catalyst (Ru / CSigma) with 5 wt% ruthenium loading and an oxygen-functionalized activated carbon support were obtained from Sigma Aldrich and used as received.

[0084] Catalytic reaction process

[0085] Batch experiments were conducted in a custom-made microautoclave (approximately 13 mL) assembled from Swagelok components and filled with a stoichiometric amount of H₂. The reactor was equipped with a pressure gauge, inlet valve, and outlet valve. In a typical experiment, after loading the reactor with the desired amount of catalyst (15 mg to 30 mg), levulinic acid (0.25 g), and water (5 g), the reactor was sealed and purged with pure H₂ gas up to five times. In the next step, the reactor was pressurized to the desired initial H₂ pressure (5.5 ± 1 bar or approximately 2.5 mmol H₂). To initiate the reaction, the reactor contents were heated in a sand bath with magnetic stirring (500 rpm) to the desired reaction temperature (85°C) for the appropriate duration. After the reaction was complete, the reactor was cooled under tap water, any residual H₂ was carefully released, and the liquid contents were centrifuged to separate the catalyst.

[0086] In a typical continuous experiment, dry catalyst powder (1 g to 1.6 g) was loaded into a custom-made tubular downflow micro-fixed bed reactor (12 mm OD, 10 mm ID, and 16 cm length) assembled from high-pressure 316 stainless steel tubing, fittings, and valves purchased from Swagelok ( Figure 1 The reactor temperature was maintained (80°C to 95°C) using an aluminum block heated by a band heater, and the total pressure was controlled (3 bar to 5 bar) using a back pressure regulator (Equilibar U3L series precision back pressure regulator). The liquid feed (0.47 M or 0.95 M levulinic acid) was continuously pumped into the reactor using an HPLC pump (Perkin Elmer series 200 micro pump) while the flow rate was controlled using a mass flow controller (Bronkhorst EL-FLOW ® In a typical experiment, the system was initially heated with 10 mL min -1 The reactor was degassed with N2 at a constant flow rate for 1 hour, then the flow was switched to H2 and the flow rate was adjusted to obtain the desired H2:levulinic acid (molar ratio), and the reactor was heated to the desired temperature before continuously pumping the liquid feed.

[0087] To determine conversion and selectivity, liquid aliquots / solutions collected from batch and continuous flow experiments were periodically analyzed by HPLC (Agilent Technologies 1200 Series, RID detector, Aminex HPX-87H column) and GC-FID (Agilent 7820A GC, HP-5MS capillary column, 30 m length, 0.25 mm i.d., 0.25 μm film thickness). Quantification of the individual components in the liquid mixture was based on calibration curves obtained with commercially available compounds. To examine Ru leaching, liquid aliquots were also periodically analyzed by ICP-OES with the aid of a PerkinElmer (OPTIMA 2000 DV) instrument.

[0088] Catalytic material characterization

[0089] Different Ru catalyst samples were prepared using porous supports with varying surface acidities. Table 1 summarizes the structural properties and surface acid-base characteristics of the various support materials used in this work. The data presented in Table 1 show that the NbP-based materials exhibit the most acidic surfaces, with abundant strong Brønsted sites (Nb2O5 and NbOPO4), while the carbon materials (CPcomm, CNP500, and CN650) exhibit highly functionalized surfaces containing neutral, weakly acidic, moderately Brønsted, and Lewis basic sites.

[0090] The carbon support (CN650) obtained by pyrolysis of chitin exhibits a surface containing natural sites, weakly acidic sites, and basic sites (attributed to the presence of -COOH, -OH, pyridinic nitrogen, pyrrolic nitrogen / pyridone nitrogen, and N-oxides of pyridinic nitrogen species), while the carbon material (CNP500) obtained by phosphoric acid activation of chitin exhibits a multifunctional surface chemistry containing neutral to weakly acidic oxygen functional groups, strongly Bronsted acidic phosphate sites, and basic pyridinic nitrogen sites, pyrrolic nitrogen sites / pyridone nitrogen sites, quaternary nitrogen sites, and N-oxides of pyridinic nitrogen sites (Table 1). In contrast, commercial activated carbon (CPcomm) exhibits an acidic surface containing only oxygen functional groups and trace amounts of phosphorus functional groups.

[0091] Table 2 summarizes the structural characteristics, dispersion, and average metal particle size of the supported Ru catalysts using the different supports discussed above, compared to commercial Ru / CSigma. The Ru / NbP-bulk catalysts were obtained by incipient wetness impregnation with RuCl3 according to the following procedure. In a typical synthesis, a calculated amount of ruthenium chloride precursor solution (the volume of the precursor solution was calculated to be equal to the pore volume of the NbP-bulk) was added to the support (NbP-bulk) under vigorous stirring. The impregnated sample was dried at 100°C overnight and then further reduced at 400°C for 3 hours (temperature ramp of 1°C / min) under a 10 ml / min H2 flow. In contrast, the carbon-based catalytic material was synthesized by standard deposition-precipitation of RuCl3 followed by reduction with NaBH4.

[0092] The importance of the carbon support surface chemistry on the dispersion and average metal particle size is clearly evident from the data presented in Table 2. The presence of surface functional groups, particularly Brønsted acidic sites (Nb2O5 and NbOPO4) and Lewis basic nitrogen sites, clearly favors the formation of uniformly dispersed and small metal (Ru) nanoparticles. The effect is evident for NbP-bulk, CN650, and CNP500, resulting in highly dispersed (37% to 76%) and ultrasmall Ru nanoparticles (1.76 nm to 3.63 nm) at Ru loadings ranging from 2.5 wt% to 5 wt% (Table 2). The presence of well-dispersed Ru species and the uniform distribution of surface functional groups including nitrogen, oxygen, and phosphate sites can be confirmed by EDX trace element (Ru, P, O, C, and N) mapping images ( Figure 2 ). In addition, from the NH3-acidity values ​​presented in Table 2 and Figure 3 The positive effect of Ru nanoparticle immobilization on the surface acidity of the catalyst is clearly observed in the NH3-TPD curves. The enhanced acidity of the Ru-supported catalyst can be attributed to the RuO2 / RuO x The presence of Lewis acidity of a substance.

[0093] Batch catalytic activity

[0094] To evaluate the impact of catalyst characteristics on the hydrogenation of aqueous levulinic acid, preliminary catalytic tests were performed in batch mode at 80°C using a near-stoichiometric amount of H2 (5.5 ± 1 bar or approximately 2.5 mmol). The results from the batch experiments, presented in Table 3, confirm the positive influence of catalyst acidity on γ-valerolactone selectivity. The activity / selectivity trends observed with multifunctional Ru catalysts incorporating phosphate sites (Ru / NbP-bulk, Ru / CNP500, and Ru / CPcomm) are comparable to those observed for Ru / Csigma-catalyzed levulinic acid hydrogenation promoted by Brønsted acids (Amberlyst 15 and NbOPO4), consistent with the role of strong / moderate Brønsted surface acid sites as co-catalysts for the dehydration of 4-hydroxyvaleric acid (Scheme 2). Interestingly, a positive correlation was observed between levulinic acid conversion and γ-valerolactone selectivity with increasing Ru loading ( Figure 4 ), which is consistent with Table 2 and Figure 3 The acidity trend and RuO2 / RuO x The Lewis acidity of the materials is consistent. In addition, the catalyst preparation method also has an impact on the acidity of the supported Ru catalyst, which in turn affects the catalyst activity (conversion, γ-valerolactone yield, and selectivity). In this work, the catalyst prepared by incipient wetness impregnation and H2 reduction (Ru / CNP500_IW) exhibits approximately half the activity of the Ru / CNP500 catalyst obtained by the deposition-precipitation technique. This is because the NH3 acidity of the former is 1 / 3.5 ( Figure 3 , Tables 2 and 3). RuO2 / RuO x The Lewis acidity of the species is also responsible for the rather high (90%) γ-valerolactone selectivity observed at 80°C for the Ru / Csigma catalyst incorporating only oxygen functional groups, whereas the presence of surface Lewis basic sites is clearly detrimental to γ-valerolactone production as observed for Ru / CN650 (entry 2, Table 3). The effect of catalyst surface acidity on γ-valerolactone selectivity is clearly more pronounced at room temperature, with Ru / Csigma exhibiting approximately 1 / 1.6 the γ-valerolactone selectivity of the multifunctional Ru / CNP500 and Ru / CPcomm catalysts incorporating phosphate sites ( Figure 5 (a) and Table 3). Figure 5The positive effect of reaction temperature on the selectivity for γ-valerolactone can also be observed in the graph in (b). It is also important to emphasize here that in all catalytic experiments, only a stoichiometric amount of H2 was consumed to produce γ-valerolactone and 4-hydroxyvaleric acid, which is consistent with the selective hydrogenation of levulinic acid under mild experimental conditions. The carbon-based multifunctional catalyst (Ru / CNP500) can also be reused without activity loss during multiple recycling, similar to the bifunctional mixtures of (Ru / Csigma+Amberlyst 15) and (Ru / Csigma+NbP-bulk). However, the bifunctional catalyst based on NbOPO4 (Ru / NbP-bulk) showed a steady loss of activity (about 3% to 3.5%) with each recycling, most likely due to sintering or loss of active Ru nanoparticles ( Figure 6 (a)).

[0095]

[0096] Scheme 2. Acid-promoted selective hydrogenation of levulinic acid to γ-valerolactone (preferred pathway is the descending pathway).

[0097] Catalytic activity in continuous flow

[0098] The low-temperature hydrogenation activity of a multifunctional Ru / CNP500 catalyst under continuous flow conditions was investigated. For comparison, the stability of bifunctional mixtures of (Ru / Csigma + Amberlyst 15) and (Ru / Csigma + NbP-bulk) was also explored (Ru loading was 5 wt% in all catalysts). Catalytic experiments were conducted in a custom downflow fixed-bed reactor that allowed for the parallel flow of H2 and the liquid feed (aqueous levulinic acid), maintaining reaction conditions similar to those of batch operations. Representative results from the fixed-bed experiments are summarized in Table 4, confirming the excellent catalytic performance of the multifunctional Ru / CNP500 catalyst for γ-valerolactone production, achieving conversion and selectivity comparable to a commercial bifunctional mixture of Ru / Csigma with an acid promoter. The data presented in Table 4 also confirm the possibility of adjusting the levulinic acid conversion and γ-valerolactone yield / selectivity by simply adjusting the flow rate of the liquid feed (liquid hourly space velocity / weight hourly space velocity), the flow rate of gaseous H2 (H2 / levulinic acid molar ratio), and the reaction temperature and pressure. GVL g Ru -1 Hour -1), although the blended catalytic system outperforms the multifunctional Ru / CNP500 (Table 4), the latter is more favorable in terms of long-term stability, which is caused by the enhanced stabilization effect of Ru nanoparticles on the highly nitrogen-doped carbon surface (see below) [19-21].

[0099] To assess the longevity / stability of the catalytic system, the catalytic reaction was continuously monitored under fixed-bed conditions at a fixed liquid hourly space velocity (LHSV), H2 / levulinic acid molar ratio, and temperature for at least 12 hours, or until stable deactivation (decay in γ-valerolactone selectivity or conversion) was observed. If no deactivation was observed during the approximately 120-hour run, reaction conditions such as temperature, LHSV, H2 / levulinic acid molar ratio, and liquid feed concentration were adjusted to assess the impact of these parameters on catalyst stability (see below). It is also important to emphasize that our process / catalyst operated at H2 / levulinic acid (molar) ratios of 4 to 17, significantly lower than the reported benchmark bifunctional catalyst (Ru@DOWEX) for continuous γ-valerolactone production, which operated at H2 / levulinic acid (molar) ratios of 54 to 95 under comparable conditions. Comparison of run time data obtained for the blended catalyst systems (Ru / Csigma+Amberlyst 15 and Ru / Csigma+NbP-bulk) with Ru / CNP500 for the hydrogenation of 0.48 M levulinic acid at 85°C further confirms the superiority of the multifunctional catalysts, which showed no signs of deactivation during the 120-hour run, compared to the bifunctional mixtures which showed significant activity loss at approximately 10 hours for (Ru / Csigma+NbP-bulk) and approximately 35 hours for (Ru / Csigma+Amberlyst 15). Figure 6 (b)). Due to the low pH of the feed, in this work, we chose to conduct deactivation studies at full conversion to eliminate Ru species leached through the formation of Ru-carboxylate complexes with levulinic acid (pKa approximately 4.59) in the liquid phase. However, the activity loss of the bifunctional mixture can be primarily attributed to sintering of the Ru nanoparticles and, in part, to the formation of metal sulfides under a reducing H2 atmosphere for the Ru / Csigma + Amberlyst 15 system, as ICP-OES analysis showed no leaching of Ru species.

[0100] For the Ru / CNP500 catalyst, an extended stability test was conducted with the same catalyst without any regeneration or pretreatment by varying the reaction conditions to further investigate the effects of reaction parameters and feed concentration on catalyst stability. From the data presented in Table 4 and Figure 7A run time plot for 5% Ru / CNP500 shows that levulinic acid conversion was stable and approached approximately 100% over the 1250 hours (52 days) of operation, regardless of reaction temperature, pressure, weight hourly space velocity, and liquid feed concentration. However, a slight decrease in γ-valerolactone selectivity (approximately 10%) was observed when switching from 0.48 M to 0.96 M levulinic acid feed. This selectivity could be improved to the desired level of ≥90% by increasing the reaction temperature or reducing the liquid feed weight hourly space velocity. This decrease in selectivity can be attributed to the lack of sufficient moderately acidic (phosphate) sites for cyclization of 4-hydroxyvaleric acid. However, the observed approximately 100% levulinic acid conversion is well consistent with the kinetically favorable hydrogenation of the carbonyl carbon of levulinic acid and the high activity of the small Ru nanoparticles (approximately 3.6 nm) deposited on the multifunctional carbon support CNP500 (Tables 2 and 3). However, upon decreasing the H2 / levulinic acid (molar) ratio to 4, the conversion of levulinic acid decreased to 85%, the γ-valerolactone selectivity approached the desired level (≥90%), and most importantly, both conversion and selectivity remained unaffected under these conditions over a run time of approximately 30 h ( Figure 7 ). As shown in Table 3 and Figure 7 As shown, reaction pressure was found to have a positive impact on the selectivity of the desired product (γ-valerolactone), however, H2 pressures greater than 5 bar were avoided in this study. Overall, the results of the extended stability testing confirm the excellent stability of the multifunctional Ru / CNP500 (Ru loading 5%) catalyst for the continuous hydrogenation of aqueous levulinic acid (0.48 M to 0.96 M) to γ-valerolactone under mild process conditions.

[0101] Without wishing to be bound by any particular scientific theory, the inventors believe that the excellent catalytic performance and durability of the Ru / CNP500 catalyst can be attributed to the enhanced stabilization of the Ru nanoparticles on nitrogen surface defects, which prevents nanoparticle aggregation and leaching, thereby inhibiting deactivation. Most importantly, unlike bifunctional Ru catalysts that incorporate unstable and reducible SO3H groups as acidic sites, the acidic phosphate sites of the multifunctional Ru / CNP500 catalyst are non-reducible and chemically stable under experimental conditions. In fact, it represents the most economical and stable Ru catalyst for the energy-efficient hydrogenation of levulinic acid. Furthermore, the catalyst's unique ability to operate under low-pressure H2 flow and low H2 / feed (molar) ratios may enable the development of small-scale hydrogenation reactors for γ-valerolactone production that can directly utilize renewable H2 from water electrolysis.

[0102] The observed activity, selectivity, and stability of the Ru / CNP500 catalyst were further supported by characterization of spent catalyst collected from the fixed bed after 1250 hours of run time, while no leaching of Ru species was confirmed by ICP-OES analysis of the liquid product collected at regular intervals. Comparison of TEM images showed that no aggregation or sintering of the nanoparticles was observed even after 52 days of continuous operation (approximately 1250 hours of run time) under different pressure, temperature, H2, and feed flow rates. Figure 8 However, the NH3-TPD pattern of the spent catalyst shows a slight shift of the medium-temperature desorption peak to higher temperatures, which can be attributed to the RuO x / RuO2 is partially reduced to metallic Ru( Figure 9 (a)). The deposition of carbonaceous impurities can also partially contribute to this shift in the desorption peak. Comparison of the structural characteristics obtained by N2 physical adsorption determined that, even after prolonged use (52 days) under different empirical conditions, the material retained its mesoporous structure, 53% of its specific surface area, and 62% of its pore volume. The slight decrease in porosity and specific surface area is most likely related to the strongly chemisorbed oxidized molecules on the catalyst surface functional groups, which hinder access to the smaller micropores (Tables 2 and Figure 9 (b)). Further confirmation of the hypothesis regarding the presence of adsorbed organic matter and the excellent stability of the immobilized Ru nanoparticles was obtained by XPS surface analysis. Comparison of the high-resolution XPS spectra of the spent Ru / CNP500 in the C1s, O1s, N1s, P2p, and Ru3d regions with the synthesized Ru / CNP500 also showed only minor compositional changes in the surface chemical characteristics of the CNP500 even after 52 days of continuous operation and γ-valerolactone production ( Figure 10 As expected, the C1s region shows a slight increase in the intensity of the C1s (C=O) peak, which is indicated by an increase in carbon content of about 4%, consistent with the strong adsorption of γ-valerolactone molecules ( Figure 10 (a)). Comparison of the O1s region shows a decrease in the intensity of the O1s (=O) peak, which can be attributed to the surface RuO2 / RuO x The material is reduced to metallic Ru, and considering the mild reaction conditions, it is unlikely to remove surface oxides (e.g., COOH, OH) ( Figure 10 (b)). The N1s region showed no significant changes and retained approximately 70% of its sites even after 52 days of continuous operation under reducing conditions ( Figure 10 (c)). Comparison of the P2p region shows a significant decrease in phosphate content (about 65%), which can be attributed to the hydrolytic cleavage of CP bonds or COP bonds under hydrothermal conditions ( Figure 10(d)). Even so, the material retains a sufficient amount of Bronsted acidic phosphate sites to promote the dehydration of 4-hydroxyvaleric acid to γ-valerolactone at approximately 1250 hours of run time. Most importantly, the acidic phosphate sites are non-reducible even in the presence of excess H2 at elevated temperatures (80°C to 95°C), which resolves the permanent deactivation phenomenon associated with bifunctional Ru catalysts based on sulfated supports. Finally, comparison of the Ru3d peaks of spent Ru / CNP500 and fresh Ru / CNP500 shows no net reduction in Ru content ( Figure 10 (a)), which is consistent with the findings of ICP-OES analysis, and the presence of metallic Ru(0) in the spent catalyst is attributed to the RuO2 / RuO x Based on the experimental findings, a reasonable mechanism for the hydrogenation of levulinic acid to γ-valerolactone catalyzed by Ru / CNP500 can be proposed, so the Bronsted acidic phosphate and Lewis acidic RuO2 / RuO x The substance promoted the lactonization of the intermediate hydrogenation product 4-hydroxyvaleric acid to γ-valerolactone under mild conditions (Scheme 3).

[0103]

[0104] Scheme 3. Schematic representation of the plausible mechanism for the selective hydrogenation of levulinic acid to γ-valerolactone

[0105] Furthermore, to determine the commercial / industrial applicability of the presented process, for example in the synthesis of synthetic hydrocarbons, we also examined the conversion of 9 wt% aqueous γ-valerolactone (or γ-valerolactone and 4-hydroxyvaleric acid) obtained over a multifunctional Ru / CNP500 catalyst into C in a cascade process similar to the procedures of US 8,410,326 B2 (Dumesic et al.) and US 8,975,461 B2 (Peters et al.). 8+ Branched olefins ( Figure 11 However, unlike previous processes that operated at high pressure (e.g., 36 bar) and with concentrated feeds (30% or higher), our process operates at atmospheric pressure with a single-pass dual-bed reactor system containing commercial silica-alumina (first bed) and solid phosphoric acid (second bed) ( Figure 12 ), which also used 9 wt% aqueous γ-valerolactone directly from the hydrogenation reactor without any pretreatment. Interestingly, as observed in US 8,410,326 B2 (Dumesic et al.), the use of lower pressure and diluted γ-valerolactone feed prevented deactivation of the silica-alumina catalyst ( Figure 11 ).

[0106] in conclusion

[0107] In summary, a biowaste (chitin)-derived multifunctional Ru catalyst (Ru / CNP500) incorporating moderately Brønsted acidic phosphate sites, Lewis basic N-sites, and surface oxides demonstrated excellent activity and stability in the selective hydrogenation of aqueous levulinic acid to γ-valerolactone under mild reaction conditions (80°C to 95°C, stoichiometric or low H₂ / feed ratio). The multifunctional catalyst outperformed a bifunctional Ru catalyst based on NbOPO₄ and a blended catalytic system comprising commercial Ru / carbon as the hydrogenation catalyst and NbOPO₄ / Amberlyst 15 as the cocatalyst / acid promoter. Most importantly, the catalytic material exhibited remarkable stability under continuous flow conditions in a fixed-bed reactor, maintaining high activity and γ-valerolactone selectivity over approximately 1250 hours of operation at 3 to 5 bar, 80 to 95°C, and low H₂ / levulinic acid ratios (4 to 17). The excellent catalytic performance and stability of the multifunctional Ru catalyst are attributed to the unique surface chemistry of the carbon support, which stabilizes the Ru nanoparticles at surface nitrogen and oxygen vacancies and promotes the cyclization of 4-hydroxyvaleric acid at acidic phosphate sites. Furthermore, unlike previously reported bifunctional Ru catalysts that incorporate unstable and reducible SO3H groups as acidic sites, the acidic phosphate sites of the multifunctional Ru / CNP500 catalyst are non-reducible and chemically stable under empirical conditions. In fact, it represents the most economical and stable Ru catalyst for the energy-efficient hydrogenation of levulinic acid. Furthermore, the catalyst's unique ability to operate under low-pressure H2 flow and low H2 / feed (molar) ratios could enable the development of small-scale hydrogenation reactors for γ-valerolactone production that can directly utilize renewable H2 from water electrolysis.

[0108]

[0109]

[0110]

[0111]

Claims

1. A catalytic material based on a carbon-containing material, the catalytic material being loaded with Ru, wherein the surface of the catalytic material comprises: a) Bronsted acidic phosphate groups; b) Lewis basic N-groups selected from Lewis basic pyridinic N-groups, pyrrolic N-groups and quaternary N-groups; and c) oxygen functional groups. 2 . The catalytic material according to claim 1 , wherein the content of Ru is 0.1 wt % to 10 wt %. The catalytic material according to claim 1 , wherein the content of Ru is 1 wt % to 6 wt %.

4. The catalytic material according to any one of claims 1 to 2, wherein the Ru is present in the form of Ru-containing nanoparticles, preferably having an average particle size d in the range of 1.5 nm to 5 nm as measured by H2 pulse chemisorption. p,H2 . 5 . The catalytic material according to claim 1 , wherein the NH 3 acidity measured by NH 3 -TPD (temperature programmed desorption) (70° C. to 450° C. in total) is greater than 1.5 mmol / g. 6 . The catalytic material according to claim 1 , wherein the CO 2 -alkalinity measured by CO 2 -TPD (temperature programmed desorption) (30° C. to 150° C. total) is greater than 0.03 μmol / g.

7. The catalytic material according to any one of claims 1 to 6, wherein the specific surface area is at least 300 m 2 / g.

8. The catalytic material according to any one of claims 1 to 7, wherein the pore volume is at least 0.3 cm 3 / g.

9. Catalytic material according to any one of claims 1 to 8, wherein the catalytic material is based on carbonized organic material.

10. Catalytic material according to any one of claims 1 to 9, wherein the catalytic material is based on carbonized chitin.

11. The catalytic material according to any one of claims 1 to 10, wherein the Bronsted acidic phosphate groups comprise NbOPO4.

12. A system comprising a catalyst bed containing the catalytic material according to any one of claims 1 to 10, a heater and a thermocouple, a pump for feeding levulinic acid to the catalyst bed, a pressure regulator for regulating the pressure in the catalyst bed / the system, and a valve for regulating the inflow of H2.

13. The system of claim 12, wherein the system comprises a valve for regulating the inflow of N2.

14. The system according to any one of claims 12 to 13, wherein the system comprises a gas-liquid separator for separating the obtained liquid product from unreacted H2.

15. A method for converting levulinic acid into γ-valerolactone, comprising using the catalytic material according to any one of claims 1 to 11 or the system according to any one of claims 12 to 14, the method comprising the step of contacting the catalyst with an aqueous solution of levulinic acid and hydrogen (H2).

16. The process according to claim 15, wherein the H2 / levulinic acid molar ratio is in the range of 3 to 20, preferably 4 to 17.

17. The process according to any one of claims 15 to 16, wherein the pressure during the reaction is in the interval from 1.5 bar to 10 bar, preferably from 2 bar to 7 bar.

18. The process according to any one of claims 15 to 17, wherein the temperature is higher than 70°C but lower than the boiling point of the aqueous levulinic acid solution at the pressure at which the reaction is carried out, preferably in the interval of 80 to 95°C.

19. The process of any one of claims 15 to 18, wherein the catalyst is contacted batchwise with the aqueous levulinic acid solution and the hydrogen gas in a reaction vessel.

20. The process of any one of claims 15 to 19, wherein the catalyst is contacted in a fixed bed reactor under continuous flow conditions of aqueous levulinic acid solution and hydrogen.

21. The method of any one of claims 15 to 20, wherein the levulinic acid is produced from a raw material comprising cellulose.

22. The process according to any one of claims 15 to 21, wherein the γ-valerolactone or γ-valerolactone / 4-hydroxyvaleric acid mixture is further converted to C in a cascade process at atmospheric pressure using a single-pass dual-bed reactor system comprising commercial silica-alumina (first bed) and solid phosphoric acid (second bed). 8+ Additional subsequent steps for olefins.

23. Gamma-valerolactone or a gamma-valerolactone / 4-hydroxyvaleric acid mixture produced using the catalytic material of any one of claims 1 to 11, or produced using the system of any one of claims 12 to 14, or produced using the method of any one of claims 15 to 21.

24. A C manufactured by the method according to claim 22 8+ Olefins.

25. A method for preparing a catalytic material according to any one of claims 1 to 11, the method comprising the step of contacting an organic polymer comprising amine groups with phosphoric acid, followed by the step of carbonizing the material at an elevated temperature under an autogenous atmosphere to provide a carbon-based material, wherein the surface of the material comprises: a) Bronsted acidic phosphate groups; b) Lewis basic N-groups selected from Lewis basic pyridinic N-groups, pyrrolic N-groups and quaternary N-groups; and c) oxygen functional groups, followed by a final loading step wherein the material is mixed with an aqueous solution of a ruthenium salt, which is then reduced so that small particles comprising elemental ruthenium are loaded onto the carbon-based material.

26. The method of claim 25, wherein the organic polymer comprising amine groups is chitin.

27. A method according to any one of claims 25 to 26, wherein the material is carbonised at an elevated temperature of at least 500°C in an atmosphere comprising an elevated concentration of N2 compared to standard atmosphere.

Images