Process for the continuous hydrogenation of aqueous levulinic acid to γ-valerolactone and its tandem conversion to high-octane gasoline range hydrocarbons

Abstract

Ru-loaded carbon materials with distinctive surface chemistry (Brønsted acidic phosphate groups, Lewis basic pyridine N-groups, pyrrolic N-groups, and quaternary N-groups, as well as oxygen functional groups) have been shown to exhibit excellent activity, selectivity, and stability in the hydrogenation of aqueous levulinic acid (0.47 M and 0.95 M) to γ-valerolactone using near-stoichiometric H2 under mild conditions (80-95 °C). The materials demonstrated excellent stability in a fixed-bed reactor under continuous flow conditions, maintaining high activity and γ-valerolactone selectivity over a period of approximately 1250 hours on-stream operating at 3-5 bar, 80-95 °C, and low H2 / levulinic acid ratios (4-17). The exceptional catalytic performance and stability of this multifunctional Ru catalyst are due to the stabilization of Ru nanoparticles on surface nitrogen and oxygen vacancies and the formation of acidic phosphate sites and RuO. x This was attributed to the unique surface chemistry of the carbon support, which promoted the cyclization of 4-hydroxypentanoic acid across the / RuO2 moieties.

Description

[Technical Field]

[0001] The present invention relates to a process for the hydrogenation of levulinic acid to γ-valerolactone with H2. The present invention further relates to a catalyst for use in said process. γ-Valerolactone can be further converted to gasoline range hydrocarbons, if desired. [Background technology]

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

[0003] Traditionally, γ-valerolactone has been obtained by tandem hydrogenation-dehydration of levulinic acid under pressurized H2 (1–3 MPa). Catalytic hydroconversion of levulinic acid or its derivatives has been demonstrated using both homogeneous and heterogeneous catalysts, both noble and non-noble. Ru (ruthenium) is considered the most active due to its unique ability to selectively hydrogenate the ketonic C=O group. Nevertheless, elevated temperatures (≥150 °C) or acid cocatalysts are required to promote the conversion of the intermediate hydroxy acid (4-hydroxypentanoic acid) and result in the selective conversion of levulinic acid to γ-valerolactone. As a result, the commercial utility of Ru-based catalysts has been hampered by deactivation issues due to (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 coking of Ru nanoparticles in the gas phase. Another drawback of processes operating under pressurized H2 and elevated reaction temperatures is reduced selectivity to γ-valerolactone due to the formation of overhydrogenation by-products such as 2-methyltetrahydrofuran and pentane-1,4-diol. Similarly, at low temperatures, the hydrogenation of levulinic acid produces an intermediate hydroxy acid (4-hydroxypentanoic acid) as the main product; the dehydration step is kinetically less favorable at low temperatures than the hydrogenation step. Therefore, elevated temperatures or an acid as a cocatalyst are required to achieve high selectivity / yield of γ-valerolactone in the liquid-phase hydroconversion of levulinic acid (or its derivatives) [RSC Adv., 2017, 7, 44082, ACS Catal. 2014, 4, 4, pp. 1171-1181]. In fact, given the advantages of low-temperature operation (low energy consumption and minimized sintering and coking), researchers have employed both mineral acids and solid acids (such as Amberlyst-15, Amberlyst-70, niobium phosphate, and niobic acid) as cocatalysts for the energy-efficient hydrogenation of levulinic acid to γ-valerolactone [Green Chem., 2012, 14, pp. 688-694, ChemSusChem. 10(14)(2017) pp. 2891-2896].

[0004] Therefore, the development of practical, efficient, and stable bifunctional Ru catalysts by incorporating nonreducing and stable acid sites for the selective low-temperature hydrogenation of aqueous levulinic acid to γ-valerolactone has remained a major technical challenge until now.

[0005] U.S. Pat. No. 7,741,527 discloses a process for the dimerization of olefins, which involves the use of a solid phosphoric acid catalyst supported on a support, which catalyst comprises phosphoric acid, a compound that produces phosphoric acid upon hydrolysis, or a mixture of both.

[0006] US Pat. No. 8,148,553 discloses a process involving the conversion of levulinic acid to gamma-valerolactone by contacting the acid with a heterogeneous catalyst comprising Ru / C.

[0007] Chinese Patent No. 102658131 discloses a ruthenium-based catalyst for preparing gamma-valerolactone from levulinic acid, including an active component and a catalyst carrier. The active component is 1-10% by weight of ruthenium. Up to 10% by weight of a cocatalyst such as a Group VIII or Group I element may be present. The catalyst support can be a carbon material (e.g., activated carbon, carbon black, carbon nanotubes, or carbon nanofibers), an oxide (e.g., alumina, silica, titania, or their binary mixed oxides), or a molecular sieve (e.g., MCM, ZSM, SBA, or faujasite). The catalyst can be prepared using a solventless microwave-assisted pyrolysis method. The catalytic reaction can be carried out using high-pressure hydrogen (1-5 MPa) at temperatures ranging from 70 to 120°C for 1 to 10 hours.

[0008] Chinese Patent No. 108745401 discloses a nitrogen- and phosphorus-doped porous carbon-rhodium phosphide catalyst, as well as its preparation and application. A substance containing a polyhydric alcohol, a rhodium source, and a nitrogen and phosphorus compound is dispersed in water; stirring is performed to form a mixed sol; and a one-step high-temperature calcination is used to prepare a composite nanometer material with rhodium phosphide loaded on porous carbon, where the porous carbon carrier is modified with nitrogen and phosphorus in the compound. Rhodium phosphide nanoparticles are loaded on the nitrogen- and phosphorus-modified porous carbon, where the rhodium phosphide nanoparticles have a size of 4-8 nm.

[0009] Chinese Patent No. 114433163 discloses an in-situ modified and pore-tunable biochar-loaded ruthenium catalyst, a method for preparing the in-situ modified and pore-tunable biochar-loaded ruthenium catalyst, and the application of the in-situ modified and pore-tunable biochar-loaded ruthenium catalyst in lignin. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] U.S. Patent No. 7,741,527 [Patent Document 2] U.S. Patent No. 8,148,553 [Patent Document 3] Chinese Patent No. 102658131 [Patent Document 4] Chinese Patent No. 108745401 [Patent Document 5] Chinese Patent No. 114433163 [Patent Document 6] JP Mikkola, V Kent, W Siljebo, LJ Konwar, A Samikannu, Hydrothermal method for producing renewable paraffinichydrocarbons, 2021, EP3841186A1 [License 7] US8,410,326B2(Dumesicら) [License 8] US8,975,461B2(Petersら) [Non-licensed literature]

[0011] [Non-licensed Document 1] RSC Adv., 2017, 7, 44082 [Non-licensed Document 2] ACS Catal. 2014.4.4, pp. 1171-1181 [Non-licensed Document 3] Green Chem., 2012, 14, pp. 688-694. [Non-licensed Document 4] ChemSusChem. 10(14)(2017) 2891~2896 [Non-licensed Document 5] LJKonwar,JP Mikkola,Carbon support effects on metal (Pd,Pt and Ru)catalyzed hydrothermal decarboxylation / deoxygenation of triglycerides Appl.Catal.A.General,638,2022,118611 [Non-licensed Document 6] A Samikannu, LJ Konwar, P Maki-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, pp. 41-51 [Non-Patent Document 7] Pham, TN, Samikannu, A., Rautio, AR. et al. Catalytic Hydrogenation of D-Xylose Over Ru Decorated Carbon Foam Catalyst in a SpinChem® Rotating Bed Reactor. Top Catal 59, pp. 1165-1177 (2016) [Non-patent document 8] Samikannu A., Konwar LJ, Rajendran K., Lee CC, Shchukarev A., Virtanen P., Mikkola JP. 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 Summary of the Invention [Problem to be solved by the invention]

[0012] One object of the present invention is to overcome at least some of the shortcomings of the prior art and to provide an improved catalyst for the hydrogenation of an aqueous levulinic acid stream to gamma valerolactone. [Means for solving the problem]

[0013] In a first aspect, a catalytic material based on a carbon-containing material is provided, the catalytic material being supported on Ru, and the surface of the catalytic material comprising a) Bronsted acidic phosphate groups, b) Lewis basic N-groups selected from the group consisting of Lewis basic pyridine N-groups, pyrrolic N-groups, and quaternary N-groups, and c) oxygen functional groups.

[0014] In a second aspect, there is provided a system comprising a catalyst bed comprising the above-described catalyst material, a heater and thermocouple, a pump for supplying 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.

[0015] In a third aspect, there is provided a method for converting levulinic acid to γ-valerolactone, comprising the use of a catalytic material according to any one of claims 1 to 7 or a system according to any one of claims 8 to 10, the method comprising contacting the catalyst with an aqueous solution of levulinic acid and hydrogen gas (H).

[0016] In a fourth aspect, there is provided γ-valerolactone or a γ-valerolactone / 4-hydroxypentanoic acid mixture produced using the catalytic material, system or method described above.

[0017] In a fifth aspect, C produced by the above method 8+ An olefin is provided.

[0018] In a sixth aspect, there is provided a method for preparing the above catalytic material, comprising the steps of contacting an organic polymer comprising amine groups with phosphoric acid, followed by a subsequent step of carbonizing the material at elevated temperature in a self-generating atmosphere to provide a carbon-based material, the surface of which comprises a) Brønsted acidic phosphate groups, b) Lewis basic N-groups selected from the group consisting of Lewis basic pyridine N-groups, pyrrolic N-groups and quaternary N-groups, and c) oxygen functional groups, after which a final loading step is carried out in which 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 on the carbon-based material.

[0019] Further embodiments of the invention are defined in the appended dependent claims, which are expressly incorporated into this specification.

[0020] One advantage is the extended stability, which is attributed to the enhanced stability of Ru-nanoparticles on the highly nitrogen-doped carbon surface.

[0021] Conversion and selectivity are maintained and according to the current state of the art are comparable or better than Ru catalysts.

[0022] The conversion of levulinic acid and the yield / selectivity of γ-valerolactone may be controlled by simple adjustment of the liquid feed flow rate (liquid / mass space velocity), gaseous H2 (H2 / levulinic acid molar ratio), and reaction temperature and pressure.

[0023] Another advantage is the possibility to operate using aqueous levulinic acid in the concentration range of about 0.5-1.0 M, which is a realistic levulinic acid feed obtained from biomass processing.

[0024] Leaching of Ru from the catalyst material is very limited.

[0025] Temperatures and operating pressures can be kept relatively low, resulting in low energy consumption and minimal sintering and coking of the catalyst.

[0026] Aspects and embodiments are described with reference to the following drawings. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 shows the experimental setup for the continuous hydrogenation of aqueous levulinic acid to γ-valerolactone. [Figure 2] FIG. 2 shows the FE-SEM image and corresponding EDX trace element mapping (C, O, N, P, and Ru) of the Ru / CNP500 catalyst. [Figure 3] Figure 3 shows the effect of Ru loading (1–5 wt%) on the NH3-TPD profile of Ru / CNP500 catalyst (IW indicates Ru / CNP500 catalyst obtained by incipient wetness impregnation and H2 treatment at 400 °C). [Figure 4] Figure 4 shows (a) levulinic acid conversion versus normalized time (hours * mmol / g Ru) and (b) conversion versus γ-valerolactone selectivity as a function of Ru loading on Ru / CNP500. Reaction conditions: 0.25 g levulinic acid, 5 ml deionized H2O, 15 mg catalyst (Ru / CNP500, Ru loading 1-5 wt%), initial H2 5.5 ± 1 bar, 400 rpm (stirring speed). [Figure 5] Figure 5 shows (a) the effect of catalyst acidity (phosphate groups) on catalyst 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 HO, 15 mg catalyst, initial H 5.5±1 bar, 400 rpm (stirring speed). [Figure 6]Figure 6 shows the catalyst stability (γ-valerolactone yield) as a function of (a) reuse (batch experiment) and (b) time on stream (fixed-bed experiment) for the multifunctional Ru / CNP500 catalyst compared to the physical mixtures (Ru / Csigma + Amberlyst 15) and (Ru / Csigma + NbOPO4 / Amberlyst 15). Batch reaction conditions: 0.25 g levulinic acid, 5 ml deionized HO, 15 mg catalyst (@ 0.34 mol% Ru, 5 wt% Ru loading), initial H2 pressure 5.5 ± 1 bar, 80 °C, 4 h, 400 rpm (stirring speed); fixed-bed reaction conditions: 80 °C, 5 bar, 0.48 M aqueous levulinic acid, H2 / levulinic acid (molar) ratio ≥ 10, WHSV 0.11–0.12 h-1 (relative to 0.48 M aqueous levulinic acid). [Figure 7] FIG. 7 shows the catalytic performance of Ru / CNP500 catalyst (5 wt. % Ru) in the continuous hydrogenation of aqueous levulinic acid over a 52-day on-stream time course under various reaction conditions. [Figure 8] Figure 8 shows TEM images of 5 wt% Ru / CNP500 and the corresponding particle size distribution (top - fresh and bottom - after 52 days on-stream time). [Figure 9] Figure 9 shows (a) the NH-TPD pattern of 5 wt% Ru / CNP500 after 52 days of on-stream time, and (b) the N-adsorption-desorption isotherms and corresponding pore size distribution plots (inset) of Ru / CNP500 before and after 52 days of continuous operation. [Figure 10] FIG. 10 shows high-resolution (a) C1s and Ru3d, (b) O1s, (c) N1s, and (d) P2p XPS spectra of fresh Ru / CNP500 and used Ru / CNP500 after 52 days on-stream time (5% wtRu). [Figure 11]Figure 11 shows a simplified experimental setup for the tandem conversion of aqueous γ-valerolactone from levulinic acid to fuel-range hydrocarbons. R0 (hydrogenation reactor, 80-95 °C, 3.5-5 bar), R1 (decarboxylation reactor, 380 °C, 1 bar), and R2 (oligomerization reactor, 170-200 °C, 1 bar), MFC (mass flow controller), S1, S2, and S3 (gas-liquid separators). [Figure 12] Figure 12 illustrates the tandem conversion of a 9 wt% aqueous γ-valerolactone / 4-hydroxypentanoic acid mixture (85-96 mol% γ-valerolactone and 4-15 mol% 4-hydroxypentanoic acid) produced over a multifunctional Ru / CNP500 catalyst to fuel-range hydrocarbons (C8+ branched olefins) at atmospheric pressure using a single-pass, two-bed reactor system 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 pellets made of 30% alumina), 170-200 °C (second bed, 20 g pellets), 1 bar, WHSV 0.12 h-1 for γ-valerolactone and 4-hydroxypentanoic acid fed to the first bed. DETAILED DESCRIPTION OF THE INVENTION

[0028] Before the present invention is disclosed and described in detail, it is to be understood that this invention is not limited to the particular configurations, method steps, and materials disclosed herein, as such configurations, method steps, and materials may vary to some extent. It is also to 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 will be limited only by the appended claims and their equivalents.

[0029] It should 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.

[0030] The following terms are used throughout the detailed description and claims.

[0031] Unless otherwise stated, all percentages and ratios are calculated by weight.

[0032] The "amount" of particles or other material on a surface is referred to herein in μg / cm 2 This is an appropriate way to express the quantity because the applied layer is very thin. To calculate the quantity, the area of ​​the object is measured and the amount per area is calculated.

[0033] A "Bronsted acid" is a molecule (or ion) that can donate a proton.

[0034] A "Lewis base" is an atomic or molecular species whose highest occupied molecular orbital (HOMO) is highly localized. Examples include, but are not limited to, conventional amines such as ammonia and alkylamines, as well as pyridine and its derivatives. Further examples include, but are not limited to, compounds of the formula NH 3-X R X amines of the formula (wherein R=alkyl or aryl), pyridine and its derivatives, 3-x A x (where R=alkyl, A=aryl), phosphines, water, ethers and ketones, as well as compounds of O, S, Se and Te in the oxidation state -2.

[0035] A "nanoparticle" is a particle of a substance with a diameter in the range of 1-100 nm. For irregular particles, the diameter is the largest particle size. For spherical particles, the largest dimension is the diameter.

[0036] Oxygen functional groups are chemical functional groups that contain an oxygen atom, and examples of oxygen functional groups include alcohols, ethers, aldehydes, ketones, and carboxylic acids, as well as various derivatives of carboxylic acids, such as amides, esters, and acid halides.

[0037] In one embodiment, a highly porous multifunctional Ru / C catalyst incorporating unique surface properties (oxygen functional groups, strongly Brønsted acidic sites, non-reducing 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 from extended stability studies conducted in a continuous-flow fixed-bed reactor (approximately 1250 hours on-stream time) and under mild conditions (3-3.5 bar and 80-95°C) using a low H:levulinic acid molar ratio (≦17).

[0038] In a first aspect, a catalytic material based on a carbon-containing material is provided, the catalytic material being supported on Ru, and the surface of the catalytic material comprising a) Bronsted acidic phosphate groups, b) Lewis basic N-groups selected from the group consisting of Lewis basic pyridine N-groups, pyrrolic N-groups, and quaternary N-groups, and c) oxygen functional groups.

[0039] In one embodiment, the Ru content is 0.1 to 10 wt %. In one embodiment, the Ru content is 1 to 6 wt %. In one embodiment, Ru is present in the form of Ru-containing nanoparticles, the particles preferably having an average particle size d between 1.5 and 5 nm as measured by H pulse chemisorption. p,H2 In another embodiment, the Ru is present in the form of nanoparticles comprising Ru, the nanoparticles having an average particle size d between 1.5 and 3.75 nm as measured by H pulse chemisorption. p,H2 In yet another embodiment, the Ru is present in the form of nanoparticles having an average particle size d between 1.7 and 3.7 nm as measured by H pulse chemisorption. p,H2 The compound is present in the form of nanoparticles comprising:

[0040] In one embodiment, the NH3-acidity is greater than 1.5 mmol / g as measured by NH3-TPD (Temperature Programmed Desorption) (total 70-450°C).

[0041] In one embodiment, the CO2-basicity is greater than 0.03 μmol / g as measured by CO2-TPD (Temperature Programmed Desorption) (total 30-150° C.).

[0042] 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 in accordance with ISA9277:2010.

[0043] In one embodiment, the pore volume is at least 0.3 cm 3 / g.

[0044] In one embodiment, the catalytic material is based on a carbonized organic material. In one embodiment, the catalytic material is based on carbonized chitin.

[0045] In one embodiment, the Bronsted acidic phosphate group comprises NbOPO4.

[0046] In one embodiment, the catalytic material comprises Bronsted acid phosphate (-OPO4 moieties) groups covalently bonded to carbon. In one embodiment, the catalytic material comprises 0.18 mmol / g of Bronsted acid phosphate (-OPO4 moieties) groups covalently bonded to carbon.

[0047] It is intended that the Bronsted acid phosphate group and the oxygen functional group are different. Thus, the oxygen functional group based on c) does not include the Bronsted acid phosphate group based on a). It is intended that the oxygen functional group in c) is not a Bronsted acid phosphate group. The Bronsted acid phosphate group based on a) does not fall under the category of the oxygen functional group in c). The oxygen functional group in c) does not include the Bronsted acid phosphate group.

[0048] In a second aspect, there is provided a system comprising a catalyst bed comprising the above-described catalyst material, a heater and thermocouple, a pump for supplying 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.

[0049] In one embodiment, the system includes a valve to regulate the inflow of N2.

[0050] In one embodiment, the system includes a gas-liquid separator for separating the resulting liquid product from unreacted H2.

[0051] In a third aspect, there is provided a method for converting levulinic acid to γ-valerolactone comprising the use of the above-described catalytic material or the above-described system, the method comprising contacting the catalyst with an aqueous solution of levulinic acid and hydrogen gas (H).

[0052] In one embodiment, the molar ratio of H2 / levulinic acid is between 3 and 20, preferably between 4 and 17.

[0053] In one embodiment, the pressure during the reaction process is between 1.5 and 10 bar, preferably between 2 and 7 bar.

[0054] 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 between 80 and 95°C.

[0055] In one embodiment, the catalyst is contacted with an aqueous solution of levulinic acid and hydrogen gas in a reactor vessel in a batch mode. In one embodiment, the catalyst is contacted with an aqueous solution of levulinic acid and hydrogen gas in a high-pressure reactor vessel in a batch mode.

[0056] 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 gas.

[0057] In one embodiment, levulinic acid is produced from raw materials comprising cellulose.

[0058] In one embodiment, γ-valerolactone or a γ-valerolactone / 4-hydroxypentanoic acid mixture is purified by a single-pass, two-bed reactor system containing commercially available silica-alumina (first bed) and solid phosphoric acid (second bed) in a cascade process at atmospheric pressure. 8+ It is further converted to olefins.

[0059] In a fourth aspect, there is provided gamma valerolactone produced using the catalyst material according to any of the above aspects and embodiments.

[0060] In a fifth aspect, the C prepared above 8+ An olefin is provided.

[0061] In a sixth aspect, there is provided a method for preparing the above catalytic material, comprising the steps of contacting an organic polymer comprising amine groups with phosphoric acid, followed by a subsequent step of carbonizing the material at elevated temperature in a self-generating atmosphere to yield a carbon-based material, the surface of which comprises a) Brønsted acidic phosphate groups, b) Lewis basic N-groups selected from the group consisting of Lewis basic pyridine N-groups, pyrrolic N-groups and quaternary N-groups, and c) oxygen functional groups, before a final loading step is carried out, in which 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 on the carbon-based material.

[0062] In one embodiment, the organic polymer containing amine groups is chitin.

[0063] In one embodiment, the material is carbonized at an elevated temperature of at least 500° C. in an atmosphere containing an elevated concentration of N2 compared to a normal atmosphere, where the normal atmosphere is normal air with an N2 content of about 78% by weight.

[0064] Other features and attendant advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the detailed description and examples of the present invention. It is understood that the disclosed embodiments may be freely combined with all other embodiments unless clearly inconsistent.

[0065] It should be understood that the present 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 present invention, which is limited only by the appended claims and equivalents thereof. [Example]

[0066] <Chemical substances> 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 (dry form, H + Ru / C (5%, Sigma-Aldrich), levulinic acid (97%, Sigma-Aldrich), γ-valerolactone (99%, Sigma-Aldrich), niobium(V) chloride (99.8%, ACROS), and ruthenium chloride (RuCl, xHO, abcr GmbH, 36% Ru) were obtained from commercial sources and used without further purification.

[0067] <Catalyst materials> Bifunctional carbon supports containing nitrogen and phosphate moieties were obtained by a well-known one-step phosphoric acid activation method described in the literature. This method is well known and widely practiced to obtain high surface nitrogen and phosphate self-doped high surface from nitrogen-rich biowastes, including chitin, and is widely practiced in the following, for example: 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 Maki-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, pp. 41-51]. In a typical synthesis procedure, 10 g of chitin flakes were immersed in a 50% by weight aqueous phosphoric acid solution in a 1:2 (w / w) ratio and aged for 24 hours under ambient conditions. In the next step, the chitin-phosphate mixture was transferred to an alumina crucible, placed in a muffle furnace (Nabertherm, LT15), and activated at 500 °C (heating rate 3 °C / min) for 1 hour in a self-generated atmosphere. The resulting material was ground into powder, thoroughly washed with hot deionized water (90 °C) until a neutral pH was reached, and dried in an oven at 100 °C for 24 hours to produce a bifunctional carbon support (CNP500) with nitrogen (basic), oxygen, and phosphorus (acidic) functional groups.

[0068] A basic carbon material (CN650) bearing only nitrogen sites without phosphorus doping was obtained by direct carbonization of chitin flakes at 650 °C according to the following procedure. In a typical synthesis procedure, 10 g of chitin flakes were placed on an alumina boat and transferred to a tube furnace (Carbolite) and carbonized at 350 °C (heating rate 2.5 °C / min) for 2 h under a 50 ml / min N2 flow. The resulting carbon material was further carbonized at 650 °C for 1.5 h (heating rate 5 °C / min, 50 ml / min N2). The resulting carbon material was powdered, washed with deionized water, and dried overnight at 100 °C to obtain a nitrogen-functionalized basic carbon support (CN650).

[0069] Carbon supports (CPcomm) bearing oxygen functional groups and trace amounts of phosphate groups were obtained by washing powdered activated carbon (Fisher Scientific) with phosphoric acid. Ru-supported catalysts (Ru / CN650, Ru / CNP500, and Ru / CPcomm) were prepared using a well-known deposition-precipitation method described in the literature, e.g., Pham, TN, Samikannu, A., Rautio, AR. et al., "Catalytic Hydrogenation of D-Xylose Over Ru Decorated Carbon Foam Catalyst in a SpinChem® Rotating Bed Reactor." Top Catal. 59, pp. 1165-1177 (2016). This deposition-precipitation method is well known and widely practiced. The synthesis procedure for the supported catalysts was as follows: 1 g of support was added to 50 ml of deionized water with stirring at room temperature. After stirring for 1 hour, an appropriate amount of ruthenium chloride (aqueous) solution (2.5 mg / ml, corresponding to a metal loading of 1-5 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 stirring the resulting mixture for an additional hour, a calculated amount of freshly prepared NaBH4 solution (nNaBH4 / nRu=15 / 1) was quickly added to the solution and stirred for an additional hour at room temperature. To obtain the desired catalyst material, the contents of the reaction mixture were filtered and Cl was added. -It was thoroughly washed with deionized water until free of ions and dried under N2 flow at 70 °C for 24 h. The reference catalyst Ru / CNP500_IW was also prepared according to the incipient wetness impregnation and H2 reduction method.

[0070] The Nb-based support, NbP-bulk (NbOPO4), was prepared according to a literature procedure (hydrolysis of niobium(V) chloride in 12 M HCl in the presence of a stoichiometric amount of ammonium dihydrogen phosphate, followed by calcination at 400 °C) as described in [Samikannu A., Konwar LJ, Rajendran K., Lee CC, Shchukarev A., Virtanen P., Mikkola JP. 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 catalyst, was obtained by incipient wetness impregnation with RuCl3 according to a procedure described elsewhere. Prior to use, the catalyst material was reduced at 400 °C under a stream of H 2 .

[0071] The actual metallic Ru loadings measured by ICP-OES were the same as the designed loadings for all catalysts. A commercial ruthenium catalyst (Ru / CSigma) with a 5 wt% ruthenium loading and an oxygen-functionalized activated carbon support was obtained from Sigma-Aldrich and used as received.

[0072] <Catalytic reaction procedure> Batch tests were conducted in a custom-built mini-autoclave (approximately 13 mL) assembled from Swagelok parts using a stoichiometric amount of H2. The reactor was equipped with a pressure gauge, inlet valves, and outlet valves. In a typical test, the reactor was charged with the desired amount of catalyst (15–30 mg), levulinic acid (0.25 g), and water (5 g), then 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 to the desired reaction temperature (85 °C) in a sand bath with magnetic stirring (500 rpm) for an appropriate duration. After completion of the reaction, the reactor was cooled under tap water, the remaining H2 was carefully released, and the liquid contents were centrifuged to separate the catalyst.

[0073] In a typical continuous run, dry catalyst powder (1–1.6 g) was loaded into a custom-built tubular, downflow, mini-fixed-bed reactor (12 mm OD, 10 mm ID, and 16 cm long) assembled from high-pressure 316 stainless steel tubing, tube fittings, and valves purchased from Swagelok (Figure 1). The reactor temperature was maintained (80–95 °C) using an aluminum block heated by a band heater, and the total pressure (3–5 bar) was controlled using a back-pressure regulator (Equilibar U3L Series Precision Back Pressure Regulator). A liquid feed (0.47 M or 0.95 M levulinic acid) was continuously delivered to the reactor using an HPLC pump (Perkin Elmer Series 200 Micro Pump), while H2 was simultaneously delivered using a mass flow controller (Bronkhorst EL-FLOW® Select). In a typical run, the system was operated at a 10 mL min -1 The reactor was first degassed with N2 at a flow rate of 0.05 ml for 1 hour, then the flow was switched to H2, the flow rate was adjusted to obtain the desired H2:levulinic acid (molar ratio), the reactor was heated to the desired temperature, and then the liquid feed was continuously pumped.

[0074] To determine conversion and selectivity, liquid aliquots / solutions taken 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 internal diameter, 0.25 μm film thickness). Quantification of individual components in the liquid-phase mixture was based on calibration curves obtained with commercially available compounds. To confirm Ru leaching, liquid aliquots were also periodically analyzed by ICP-OES on a PerkinElmer (OPTIMA 2000 DV) instrument.

[0075] <Analysis and evaluation of catalyst material properties> Different samples of Ru catalysts were prepared using porous supports with varying surface acidity. A summary of the textural and surface acid-base properties of the different support materials used in this evaluation is shown in Table 1. From the data shown in Table 1, it can be seen that NbP bulk exhibited the most acidic surface with abundant strong Brønsted sites (Nb2O5 and NbOPO4), while the carbon materials (CPcomm, CNP500, and CN650) presented highly functionalized surfaces composed of neutral, weakly acidic, moderately Brønsted, and Lewis basic sites.

[0076] The carbon support (CN650) obtained by pyrolysis of chitin exhibited a surface composed of naturally occurring weakly acidic and basic sites (due to the presence of -COOH, -OH, pyridine nitrogen, pyrrole / pyridone nitrogen, and N-oxides of pyridine nitrogen species), whereas the carbon material (CNP500) obtained by phosphoric acid activation of chitin exhibited a multifunctional surface chemistry composed of neutral to weakly acidic oxygen functional groups, strongly Brønsted acidic phosphate sites, and basic pyridine nitrogen sites, pyrrole / pyridone nitrogen sites, quaternary nitrogen sites, and N-oxides of pyridine nitrogen sites (Table 1). In contrast, the commercially available activated carbon (CPcomm) exhibited an acidic surface composed only of oxygen functional groups and traces of phosphorus functional groups.

[0077] The textural characteristics, dispersion, and average metal particle size of supported Ru catalysts using the various supports discussed above, compared with the commercially available Ru / CSigma, are summarized in Table 2. Ru / NbP bulk catalysts were obtained by incipient wetness impregnation with RuCl 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 overnight at 100 °C, followed by further reduction at 400 °C for 3 h (ramp 1 °C / min) under a 10 ml / min H flow. In contrast, carbon-based catalyst materials were synthesized by standard RuCl precipitation followed by reduction with NaBH.

[0078] The data presented in Table 2 clearly demonstrate the importance of the surface chemistry of the carbon support on metal particle dispersion and average metal particle size. The presence of surface functional groups, especially Brønsted acidic sites (NbO and NbOPO) and Lewis basic nitrogen sites, clearly favored the formation of uniformly dispersed and small metal (Ru) nanoparticles. This effect was clearly evident for NbP-bulk, CN650, and CNP500, where highly dispersed (37–76%) and very small Ru nanoparticles (1.76–3.63 nm) were obtained with Ru loadings of 2.5–5 wt% (Table 2). The presence of well-dispersed Ru species and the uniform distribution of surface functional groups consisting of nitrogen, oxygen, and phosphate sites were confirmed by EDX trace element (Ru, P, O, C, and N) mapping images (Figure 2). Furthermore, the positive effect of immobilizing Ru nanoparticles on the acidity of the catalyst surface is clearly observed from the NH3-acidity values ​​shown in Table 2 and the NH3-TPD profiles in Figure 3. The enhanced acidity of the Ru-supported catalysts is due to the RuO2 / RuO x This could be attributed to the presence of Lewis acidity in the species.

[0079] <Batch catalytic activity> To evaluate the effect of catalyst properties on the hydrogenation of aqueous levulinic acid, preliminary catalytic tests were conducted in batch mode using a near-stoichiometric amount of H (5.5 ± 1 bar or approximately 2.5 mmol) at 80 °C. The results of the batch experiments, shown in Table 3, confirm the positive effect of catalyst acidity on γ-valerolactone selectivity. The activity / selectivity trends observed for multifunctional Ru catalysts incorporating phosphate sites (Ru / NbP-bulk, Ru / CNP500, and Ru / CPcomm) were comparable to the selectivity trends for the levulinic acid hydrogenation of the Brønsted acid (Amberlyst 15 and NbOPO4)-promoted Ru / Csigma catalysts, consistent with the role of strong / moderate Brønsted surface acid sites as cocatalysts for the dehydration of 4-hydroxypentanoic acid (Scheme 2). Interestingly, we observed a positive correlation between levulinic acid conversion and γ-valerolactone selectivity with increasing Ru loading (Figure 4), which is consistent with the acidity trends shown in Table 2 and Figure 3, as well as the RuO / RuO x This was consistent with the Lewis acidity of the species. In addition, the catalyst preparation method also had an impact on the acidity of the supported Ru catalyst, which in turn affected the catalytic activity (conversion, γ-valerolactone yield, and selectivity). In this study, the catalyst prepared by incipient wetness impregnation and H2 reduction (Ru / CNP500_IW) showed approximately 2 times lower activity than the Ru / CNP500 catalyst obtained by the deposition-precipitation method, which is attributed to the 3.5 times lower NH3 acidity of the former (Figure 3, Tables 2 and 3). Also, the RuO2 / RuO xThe Lewis acidity of the species explains the rather high (90%) γ-valerolactone selectivity observed at 80 °C for the Ru / Csigma catalyst, which incorporates only oxygen functional groups, whereas the presence of surface Lewis basic sites was 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 was more clearly evident at room temperature, where Ru / Csigma exhibited approximately 1.6-fold lower γ-valerolactone selectivity than the multifunctional Ru / CNP500 and Ru / CPcomm catalysts, both of which incorporate phosphate sites (Figure 5(a) and Table 3). The positive effect of reaction temperature on γ-valerolactone selectivity could also be observed from the plot in Figure 5(b). It is also important to emphasize that in all catalytic tests, only the stoichiometric amount of H was consumed to produce γ-valerolactone and 4-hydroxypentanoic acid, consistent with the selective hydrogenation of levulinic acid under mild experimental conditions. The carbon-based multifunctional catalyst (Ru / CNP500) was also reusable without loss of activity over multiple recycling processes, as were the bifunctional mixtures (Ru / Csigma + Amberlyst 15) and (Ru / Csigma + NbP-bulk). However, the NbOPO4-based bifunctional catalyst (Ru / NbP-bulk) demonstrated a steady loss of activity (approximately 3–3.5%) with each recycling, most likely due to sintering or loss of the active Ru nanoparticles (Figure 6(a)).

[0080] [ka] Scheme 2. Acid-promoted selective hydrogenation of levulinic acid to γ-valerolactone (preferred route is the lower route).

[0081] <Catalytic activity in continuous flow> The low-temperature hydrogenation activity of the multifunctional Ru / CNP500 catalyst under continuous-flow conditions was investigated. The stability of the bifunctional mixtures (Ru / Csigma + Amberlyst 15) and (Ru / Csigma + NbP-bulk) was also investigated for comparison (Ru loading was 5 wt% for all catalysts). Catalytic testing was carried out in a custom-built, flow-through fixed-bed reactor that allowed the co-flow of H2 and a liquid feed (aqueous levulinic acid) to maintain reaction conditions similar to those of batch operation. Representative results from the fixed-bed experiments are summarized in Table 4 and confirm the exceptional catalytic performance of the multifunctional Ru / CNP500 catalyst for γ-valerolactone production, which was comparable in terms of conversion and selectivity to a commercial bifunctional mixture of Ru / Csigma with an acid cocatalyst. The data shown in Table 4 also confirm the possibility of balancing the conversion of levulinic acid and the yield / selectivity of γ-valerolactone by simply adjusting the flow rate of the liquid feed (liquid / mass hourly space velocity), the gaseous H2 (H2 / levulinic acid molar ratio), and the reaction temperature and pressure. [ka] Although the blended catalytic system outperformed the multifunctional Ru / CNP500 in terms of catalytic activity (Table 4), the latter had more advantages in terms of long-term stability brought about by the enhanced stabilization of Ru-nanoparticles over the highly nitrogen-doped carbon surface (see below) [19-21].

[0082] To evaluate the lifetime / stability of the catalytic system, the catalytic reaction under fixed-bed conditions was continuously monitored at a fixed liquid hourly space velocity, H2 / levulinic acid molar ratio, and temperature for at least 12 hours or until steady deactivation (decay in γ-valerolactone selectivity or conversion) was observed. If no deactivation was observed over the course of approximately 120 hours of operation, reaction conditions such as temperature, liquid hourly space velocity, H2 / levulinic acid molar ratio, and liquid feed concentration were adjusted to evaluate the effect of these parameters on catalyst stability (see below). It is also important to note that our method / catalyst operated at H2 / levulinic acid (molar) ratios of 4 to 17, which was much lower than the benchmark bifunctional catalyst (Ru@DOWEX) reported for continuous γ-valerolactone production, which operated at H2 / levulinic acid (molar) ratios of 54 to 95 under comparable conditions. Comparison of the on-stream time data obtained for the hydrogenation of 0.48 M levulinic acid at 85 °C for the blended catalyst systems (Ru / Csigma + Amberlyst 15 and Ru / Csigma + NbP-bulk) with Ru / CNP500 further confirms the superiority of the multifunctional catalyst, which shows no signs of deactivation over the course of 120 h of operation, in contrast to the bifunctional mixture, which showed significant activity losses at approximately 10 and 35 h for (Ru / Csigma + NbP-bulk) and (Ru / Csigma + Amberlyst 15), respectively (Figure 6(b)). Due to the low pH of the feed, in this study we opted for deactivation tests at full conversion to exclude leaching of Ru species through the formation of Ru carboxylate complexes with levulinic acid (pKa ca. 4.59) in the liquid phase. Nevertheless, the activity loss of the bifunctional mixtures can be mainly attributed to the sintering of Ru nanoparticles, but also partly to the formation of metal sulfides under a reducing H2 atmosphere for the Ru / Csigma+Amberlyst 15 system, since ICP-OES analysis did not reveal any leaching of Ru species.

[0083] For the Ru / CNP500 catalyst, extended stability tests were conducted using the same catalyst by varying the reaction conditions without any regeneration or pretreatment to further investigate the effects of reaction parameters and feed concentration on catalyst stability. The data shown in Table 4 and the plot of on-stream time for 5% Ru / CNP500 in Figure 7 indicate that over the course of 1250 hours (52 days), levulinic acid conversion remained stable and near 100%, regardless of reaction temperature, pressure, mass space velocity, and liquid feed concentration. Nevertheless, a slight decrease (approximately 10%) in γ-valerolactone selectivity was observed when the levulinic acid feed was switched from 0.48 M to 0.96 M. However, selectivity could be improved to the desired level of ≥90% by either increasing the reaction temperature or decreasing the mass space velocity of the liquid feed. The decrease in selectivity was likely due to a lack of sufficient medium-sized acid (phosphate group) sites for the cyclization of 4-hydroxypentanoic acid. Nevertheless, the observed approximately 100% conversion of levulinic acid was 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, when the H2 / levulinic acid (molar) ratio was reduced to 4, the conversion of levulinic acid decreased to 85%, and the selectivity of γ-valerolactone approached the desired level (>90%). Most importantly, both conversion and selectivity remained unaffected over the course of approximately 30 hours of operation under these conditions (Figure 7). As shown in Table 3 and Figure 7, respectively, reaction pressure was found to have a positive effect on the selectivity of the desired product (γ-valerolactone); however, the use of H2 pressures above 5 bar was avoided in this study. Overall, the results of the extended stability study confirm the exceptional stability of the multifunctional Ru / CNP500 (Ru loading was 5%) catalyst toward the continuous hydrogenation of aqueous levulinic acid (0.48 M–0.96 M) to γ-valerolactone under mild process conditions.

[0084] While not wishing to be bound by any particular scientific theory, the inventors believe that the exceptional catalytic performance and durability of the Ru / CNP500 catalyst can be attributed to the enhanced stability of the Ru nanoparticles across the nitrogen surface defects, which prevents nanoparticle aggregation and leaching and thus suppresses 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 the test conditions. In fact, this catalyst is the most economical and stable Ru catalyst for the energy-efficient hydrogenation of levulinic acid. Furthermore, the catalyst's unique ability to operate at low-pressure H2 flow and low H2 / feed (molar) ratio may enable the development of a small-scale hydrogenation reactor for the production of γ-valerolactone that can directly utilize renewable H2 from water electrolysis.

[0085] The experimentally observed activity, selectivity, and stability of the Ru / CNP500 catalyst were further supported by the characterization of the spent catalyst sampled from the fixed-bed after 1250 hours on-stream, while ICP-OES analysis of the liquid product sampled at regular intervals confirmed the absence of leaching of Ru species. Comparison of TEM images shows that even after 52 days of continuous operation (approximately 1250 hours on-stream) under various conditions of pressure, temperature, H2, and feed flow rate, no aggregation or sintering of nanoparticles could be observed (Figure 8). However, the NH3-TPD pattern of the spent catalyst revealed a slight shift of the intermediate-temperature desorption peak to higher temperatures, which was attributed to the conversion of RuO to metallic Ru. xThis could be due to the partial reduction of RuO2 species (Figure 9(a)). The deposition of carbonaceous impurities may also partially contribute to this shift in the desorption peak. Comparison of the textural characteristics obtained from N2 physisorption confirms that even after prolonged use (52 days) under various experimental conditions, the material retained its mesoporous structure, its specific surface area of ​​53%, and its pore volume of 62%. The slight decrease in porosity and specific surface area is most likely related to oxygenated molecules strongly chemisorbed to functional groups on the catalyst surface, blocking access to smaller micropores (Table 2 and Figure 9(b)). Further confirmation of the hypothesis regarding the presence of adsorbed organic species and the exceptional stability of the immobilized Ru-nanoparticles was obtained from XPS surface analysis. Comparison of the high-resolution XPS spectra C1s, O1s, N1s, P2p, and Ru3d regions of as-synthesized and used Ru / CNP500 revealed only minor compositional changes to the surface chemistry of CNP500, even after 52 days of continuous operation and γ-valerolactone production (Figure 10). As expected, the C1s region revealed a slight increase in the intensity of the C1s (C=O) peak, reflected by an approximately 4% increase in carbon content, consistent with the strong adsorption of γ-valerolactone molecules (Figure 10(a)). Comparison of the O1s region revealed a decrease in the intensity of the O1s (=O) peak, which is consistent with the surface RuO2 / RuO xThis may be due to the reduction of species to metallic Ru, and the removal of surface oxygenates (e.g., COOH, OH) is unlikely given the mild reaction conditions (Figure 10(b)). The N1s region retained approximately 70% of its sites without significant change even after 52 days of continuous operation under reducing conditions (Figure 10(c)). Comparison of the P2p region revealed a significant decrease in phosphate group content (approximately 65%), which may be due to hydrolytic cleavage of CP or COP linkages in the hydrothermal environment (Figure 10(d)). Nevertheless, the material retained a moderate amount of Brønsted acidic phosphate sites to promote the dehydration of 4-hydroxypentanoic acid to produce γ-valerolactone at approximately 1250 hours on-stream time. Most importantly, the acidic phosphate sites were nonreducible at elevated temperatures (80–95 °C) even in the presence of excess H, addressing the phenomenon of permanent deactivation associated with bifunctional Ru catalysts based on sulfated supports. Finally, a comparison of the Ru 3d peaks of spent and virgin Ru / CNP500 did not reveal a net decrease in Ru content (Fig. 10(a)), which was consistent with the findings of ICP-OES analysis, whereas the presence of metallic Ru(0) in the spent catalyst was due to the reduction of RuO2 / RuO2 under reducing conditions. x Based on the findings from these studies, a plausible mechanism can be proposed for the hydrogenation of levulinic acid catalyzed by Ru / CNP500 to γ-valerolactone, namely, the reduction of Brønsted acid phosphate species and Lewis acidic RuO / RuO x The species promoted the intramolecular esterification of the intermediate hydrogenation product, 4-hydroxypentanoic acid, to γ-valerolactone under mild conditions (Scheme 3 ).

[0086] [ka] Scheme 3. A plausible mechanism illustrating the selective hydrogenation of levulinic acid to γ-valerolactone

[0087] Furthermore, to confirm the commercial / industrial utility of the above-proven method, for example, in the synthesis of synthetic hydrocarbons, the present inventors have demonstrated the C 0 of 9 wt. % aqueous γ-valerolactone (or γ-valerolactone and 4-hydroxypentanoic acid) obtained over a multifunctional Ru / CNP500 catalyst in a cascade process following procedures similar to those described in U.S. Pat. No. 8,410,326 B2 (Dumesic et al.) and U.S. Pat. No. 8,975,461 B2 (Peters et al.). 8+ Tandem conversion to branched olefins was also investigated (Figure 11). However, unlike previous methods operating at high pressure (e.g., 36 bar) and concentrated feed (30% or more), our method was operated at atmospheric pressure using a single-pass, two-bed reactor system consisting of commercial silica-alumina (first bed) and solid phosphoric acid (second bed) (Figure 12). Furthermore, our method directly used 9% by mass aqueous γ-valerolactone obtained from the hydrogenation reactor without any pretreatment. Interestingly, the use of lower pressure and diluted γ-valerolactone feed prevented the deactivation of the silica-alumina catalyst observed in U.S. Pat. No. 8,410,326 B2 (Dumesic et al.) (Figure 11).

[0088] <Conclusion> In conclusion, a biowaste (chitin)-derived multifunctional Ru catalyst (Ru / CNP500) with moderate incorporation of Brønsted acidic phosphate sites, Lewis basic N-sites, and surface oxygenates has been shown to exhibit exceptional activity and stability for the selective hydrogenation of aqueous levulinic acid to γ-valerolactone under mild reaction conditions (80–95 °C, stoichiometric or low H2 / feed ratios). This multifunctional catalyst outperformed a bifunctional Ru catalyst based on NbOPO4 and a blended catalyst system consisting of commercial Ru / carbon as the hydrogenation catalyst and NbOPO4 / Amberlyst 15 as the cocatalyst / acid promoter. Most importantly, this catalytic material demonstrated excellent stability in a fixed-bed reactor under continuous-flow conditions, maintaining high activity and γ-valerolactone selectivity over approximately 1250 hours of on-stream time operating at 3–5 bar, 80–95°C, and low H2 / levulinic acid ratios (4–17). The exceptional catalytic performance and stability of this multifunctional Ru catalyst were attributed to the unique surface chemistry of the carbon support, which stabilized Ru nanoparticles on surface nitrogen and oxygen vacancies and promoted the cyclization of 4-hydroxypentanoic acid on the acidic phosphate sites. Furthermore, the acidic phosphate sites of this multifunctional Ru / CNP500 catalyst were non-reducing and chemically stable under the test conditions, unlike previously reported bifunctional Ru catalysts that incorporate unstable and reducing SO3H groups as acidic sites. Indeed, this catalyst is the most economical and stable Ru catalyst for the energy-efficient hydrogenation of levulinic acid. Furthermore, the unique ability of the catalyst to operate at low pressure H2 flow and low H2 / feed (molar) ratios may enable the development of a small-scale hydrogenation reactor for the production of γ-valerolactone that can directly utilize renewable H2 derived from water electrolysis.

[0089] [Table 1]

[0090] [Table 2]

[0091] Table 3

[0092] Table 4

Claims

1. A catalytic material based on a carbon-containing material, the catalytic material supporting Ru, the surface of the catalytic material comprising a) Bronsted acidic phosphate groups, b) Lewis basic N-groups selected from the group consisting of Lewis basic pyridine N-groups, pyrrolic N-groups and quaternary N-groups, and c) oxygen functional groups.

2. 2. The catalytic material according to claim 1, wherein the Ru content is 0.1 to 10 mass %.

3. 2. The catalytic material according to claim 1, wherein the Ru content is 1 to 6 mass %.

4. The Ru is present in the form of nanoparticles containing Ru, and preferably the nanoparticles are H ２ Average particle size d between 1.5 and 5 nm as measured by pulse chemisorption ｐ，Ｈ２ 3. The catalytic material according to claim 1 or 2, comprising:

5. NH ３ -Acidity is NH ３ A catalytic material according to any one of claims 1 to 4, having a SiO2 content greater than 1.5 mmol / g, as measured by TPD (Temperature Programmed Desorption) (total 70-450°C).

6. CO ２ -Basicity is CO ２ A catalytic material according to any one of claims 1 to 5, having a solubility of greater than 0.03 μmol / g, as measured by TPD (Temperature Programmed Desorption) (total 30-150°C).

7. Specific surface area is at least 300m ２ The catalytic material according to any one of claims 1 to 6, wherein the Molecular Weight of the catalyst material is 1000 ppm / g.

8. Pore ​​volume of at least 0.3 cm ３ The catalytic material according to any one of claims 1 to 7, wherein the Mo is 0.01g / g.

9. 9. The catalytic material according to any one of claims 1 to 8, which is based on carbonized organic material.

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

11. The Bronsted acidic phosphate group is NbOPO ４ The catalytic material according to any one of claims 1 to 10, comprising:

12. A catalyst bed comprising the catalyst material of any one of claims 1 to 10, a heater and a thermocouple, a pump for supplying levulinic acid to the catalyst bed, a pressure regulator for adjusting the pressure in the catalyst bed / system, H ２ a valve for regulating the inflow of

13. N ２ 13. The system of claim 12, further comprising a valve for regulating the inflow of

14. The resulting liquid product was treated with unreacted H ２ 14. The system of claim 12 or 13, comprising a gas-liquid separator for separating the liquid from the gas.

15. A method for converting levulinic acid to gamma-valerolactone, comprising the use of a catalytic material according to any one of claims 1 to 11 or a system according to any one of claims 12 to 14, wherein the catalyst is reacted with an aqueous solution of levulinic acid and hydrogen gas (H ２ ) contacting the

16. H ２ 16. The process according to claim 15, wherein the molar ratio of hydroxybenzoate to levulinic acid is between 3 and 20, preferably between 4 and 17.

17. 17. The process according to claim 15 or 16, wherein the pressure during the reaction is between 1.5 and 10 bar, preferably between 2 and 7 bar.

18. 18. A process according to any one of claims 15 to 17, wherein 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 between 80 and 95°C.

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

20. 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 an aqueous solution of levulinic acid and hydrogen gas.

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

22. γ-valerolactone or a γ-valerolactone / 4-hydroxypentanoic acid mixture is produced in a cascade process at atmospheric pressure using a single-pass, two-bed reactor system containing commercially available silica-alumina (first bed) and solid phosphoric acid (second bed). ８＋ 22. The process of any one of claims 15 to 21, comprising a further subsequent step of further conversion to olefins.

23. γ-valerolactone or a γ-valerolactone / 4-hydroxypentanoic 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. C produced by the method of claim 22. ８＋ Olefin.

25. 12. A method for preparing a catalytic material according to any one of claims 1 to 11, comprising the step of contacting an organic polymer comprising amine groups with phosphoric acid, followed by a subsequent step of carbonizing said material at elevated temperature in a self-generated atmosphere to yield a carbon-based material, the surface of which comprises a) Bronsted acidic phosphate groups, b) Lewis basic N-groups selected from the group consisting of Lewis basic pyridine N-groups, pyrrolic N-groups and quaternary N-groups, and c) oxygen functional groups, after which a final support step is carried out, in which said material is mixed with an aqueous solution of a ruthenium salt, which is then reduced so that small particles comprising elemental ruthenium are supported on the carbon-based material.

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

27. The material is in a high concentration of N compared to the normal atmosphere. ２ 27. The method of claim 25 or 26, wherein the carbonization is carried out at an elevated temperature of at least 500°C in an atmosphere containing

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