CN115155639B - Ultralow-load ruthenium catalyst and preparation method and application thereof - Google Patents

Ultralow-load ruthenium catalyst and preparation method and application thereof Download PDF

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CN115155639B
CN115155639B CN202210839265.5A CN202210839265A CN115155639B CN 115155639 B CN115155639 B CN 115155639B CN 202210839265 A CN202210839265 A CN 202210839265A CN 115155639 B CN115155639 B CN 115155639B
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gamma
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valerolactone
ruthenium
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CN115155639A (en
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宋国勇
刘真真
高雪影
王水众
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Beijing Forestry University
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
    • B01J27/24—Nitrogen compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/20—Catalysts, in general, characterised by their form or physical properties characterised by their non-solid state
    • B01J35/23—Catalysts, in general, characterised by their form or physical properties characterised by their non-solid state in a colloidal state
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B01J35/391—Physical properties of the active metal ingredient
    • B01J35/393—Metal or metal oxide crystallite size
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/30—Catalysts, in general, characterised by their form or physical properties characterised by their physical properties
    • B01J35/396—Distribution of the active metal ingredient
    • B01J35/399—Distribution of the active metal ingredient homogeneously throughout the support particle
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
    • B01J35/61—Surface area
    • B01J35/615—100-500 m2/g
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
    • B01J35/64—Pore diameter
    • B01J35/647—2-50 nm
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07D—HETEROCYCLIC COMPOUNDS
    • C07D307/00—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom
    • C07D307/02—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom not condensed with other rings
    • C07D307/26—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom not condensed with other rings having one double bond between ring members or between a ring member and a non-ring member
    • C07D307/30—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom not condensed with other rings having one double bond between ring members or between a ring member and a non-ring member with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms
    • C07D307/32—Oxygen atoms
    • C07D307/33—Oxygen atoms in position 2, the oxygen atom being in its keto or unsubstituted enol form

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Abstract

The invention relates to an ultra-low load ruthenium catalyst expressed as Ru/M a O b NC, the active metal Ru is uniformly dispersed on the nitrogen-doped carbon carrier in the form of monoatoms and/or nanoparticles and has a metal oxide M a O b As the acid center, NC represents a nitrogen-doped carbon support, and M is selected from at least one of Al, zn, co, fe. The method for preparing the ultralow-load ruthenium catalyst has the advantages of simple process, abundant raw material sources, low cost, simple equipment and suitability for large-scale production. The prepared ultralow-load ruthenium catalyst can realize high-efficiency catalysis of levulinic acid hydrogenation to prepare gamma-valerolactone under the relatively mild condition of a solvent-free system, has excellent stability and reusability, and provides a feasible path for realizing industrial application.

Description

Ultralow-load ruthenium catalyst and preparation method and application thereof
Technical Field
The invention belongs to the field of biomass catalytic conversion, and particularly relates to an ultralow-load ruthenium catalyst, and a preparation method and application thereof.
Background
In the context of carbon neutralization and energy safety, there is a need for efficient conversion of renewable biomass resources into fuels and high value-added chemicals in biomass refining processes. Among biomass-derived platform molecules and end products, gamma valerolactone has excellent physical and chemical properties, and is widely used as a resin solvent, a fuel additive, a plasticizer, various chemical intermediates, and the like. Therefore, the efficient catalytic hydrogenation of the cellulose-derived platform compound levulinic acid to prepare gamma-valerolactone has important significance.
A common reaction path for converting levulinic acid into gamma-valerolactone is that the carbonyl group of levulinic acid is first catalytically hydrogenated to produce the unstable intermediate gamma-hydroxyvaleric acid, which is then dehydrated by intramolecular esterification to gamma-valerolactone. The ligand-based transition metal homogeneous catalyst can efficiently catalyze the conversion of the hydro-levulinic acid into gamma-valerolactone. At present, organometallic complexes based on Ru, ir and Fe show good catalytic activity for preparing gamma-valerolactone by hydrogenation of levulinic acid and esters thereof, and the conversion number TONs is as high as 10 4 -10 5 . However, homogeneous catalysts suffer from difficult recovery and recycling, which severely limits their use in large-scale industrialization. Heterogeneous catalysts with supported active metal centers are easy to separate from the reaction system and can be recycled, and are widely focused by people. Up to now, the application of a plurality of supported metal catalysts such as Ru, pt, pd, ir, cu, co, ni in preparing gamma-valerolactone by hydrogenating levulinic acid has been reported. The active metal Ru has higher carbonyl hydrogenation capability and is considered to be one of catalysts with highest activity and selectivity in the reaction of preparing gamma-valerolactone by hydrogenating levulinic acid. Patent CN108047171B discloses a heterogeneous catalyst (Ru, 2.0-2.5 wt%) with silica, alumina, magnesia, activated carbon or aza activated carbon as carrier and with Ru, pt or Pd as supported metal. Mixing levulinic acid, a solvent, formic acid, an alkaline substance and a heterogeneous catalyst according to the mass ratio of 114:5000:92:0-53:20, reacting for 1-8 hours in a closed container at 90-150 ℃ in a nitrogen atmosphere, centrifugally separating reaction liquid, and extracting by using an organic solvent to obtain the product gamma-valerolactone. The heterogeneous catalyst involved in the method has high noble metal load, which affects the atom economy of noble metal; the use of organic solvents and alkaline substances presents the risks of high management costs and environmental pollution during use, and complex operating steps. Patent CN109395723A discloses a Ru-Al catalytic system for preparing gamma-valerolactone by catalyzing levulinic acid hydrogenation, and the recycling problem of a catalyst is not mentioned in the system, so that industrial application is difficult to realize. The use of Ru/C (Ru, 5 wt.%) Ru/gamma-Al is reported in the literature (ACS Sustin. Chem. Eng.2016,4, 2939-2950) 2 O 3 (Ru, 0.3 wt.%) and Ru/TiO 2 (Ru, 1 wt%) catalyst was reacted at a reaction temperature of 90℃under a hydrogen pressure of 4.5MPa in the presence of water as solvent for 6 hours, the yields of levulinic acid into gamma-valerolactone were 81.3mol%,9.6mol% and 14.0mol%, respectively, with the concomitant formation of a large amount of by-products. When the catalyst uses water as a solvent, ru aggregation and leaching phenomena occur, so that the stability of the catalyst is reduced. Document (ACS Catal.2021,11, 2669-2675) reports an anchor on carbon-nitrogen substrates containing WO x Clustered Ru monoatomic catalystRu1@WO x CN (Ru, 4.7 wt%) uses notch-like polyoxometallates to stabilize the Ru atoms and prevent them from aggregating during pyrolysis. The reaction is carried out for 2 hours at 100 ℃ and 2MPa in a solvent-free system, the yield of converting levulinic acid into gamma-valerolactone is over 99 percent, and the superior catalytic performance is attributed to active metal Ru and an acid center WO x The synergy of the clusters and the carbon-nitrogen substrate. However, in the reaction of levulinic acid to gamma valerolactone, the TONs of heterogeneous catalysts are far from being homogeneous. Therefore, a heterogeneous catalyst which is equivalent to a homogeneous catalyst in high activity and has high stability and recycling property in the levulinic acid hydrogenation process should be constructed, and the heterogeneous catalyst has great significance and great challenges.
The structure of the heterogeneous catalyst has important influence on the preparation of gamma-valerolactone by high-efficiency hydrogenation of levulinic acid and esters thereof. For example, 1) the active metal with ultra-low load is uniformly dispersed, and an effective catalytic active site is provided for catalytic reaction and cooperates with the second metal acid center, so that the conversion efficiency of unit active metal is improved. 2) The active metal is anchored by nitrogen coordination, so that the active metal is not easy to aggregate and leach, and the stability of the catalyst is improved.
Disclosure of Invention
To overcome the defects and shortages of the prior art, the invention provides an ultra-low load ruthenium catalyst Ru/M with high activity and stability for preparing gamma-valerolactone by hydrogenating levulinic acid or levulinate a O b /NC，M a O b NC represents the nitrogen-doped carbon in transit, being a metal oxide. The catalyst takes ultralow-load Ru as hydrogenation active metal, and takes metal oxide (such as Al 2 O 3 ZnO) is an acid center, and the biomass raw material chitosan with rich sources is used as a nitrogen-doped carbon carrier, so that the N atoms with rich electrons can stabilize Ru species, and the stability of the catalyst is improved. Wherein Ru/M a O b The NC catalyst can efficiently catalyze levulinic acid to hydrogenate into gamma-valerolactone under the condition of no solvent, and the temperature is 150 ℃ and the pressure is 4MPa H 2 The yield of gamma-valerolactone in 3h of reaction under the condition is 99.7% (TON, 4.8X10) 4 ) The method comprises the steps of carrying out a first treatment on the surface of the When the reaction time was prolonged to 60 hours, the yield of gamma-valerolactone was 91.5% (TON, 1.7X10) 5 ). The catalyst has excellent stability and reusability in the levulinic acid hydrogenation reaction, can still keep high catalytic activity in 22 times of cyclic reactions, and can accumulate TON to a million level.
The technical problems to be solved by the invention are as follows: the existing catalyst has the disadvantages of large noble metal loading, poor catalyst stability, difficult catalyst recovery and recycling and low catalytic activity. Therefore, the preparation method of the ultra-low load ruthenium catalyst with high activity and stability is provided, and the catalyst is applied to the preparation of gamma-valerolactone by the catalytic hydrogenation of levulinic acid in a solvent-free system. The catalyst provided by the invention has the advantages of low active metal loading, high catalytic activity, good stability, contribution to reactant diffusion, active site exposure and the like, and simultaneously expands the application of the ultra-low-load noble metal catalyst in the field of catalytic conversion of biomass and biomass platform compounds.
In order to achieve the above purpose, the present invention is realized by the following technical scheme:
the first object of the present invention is to provide an ultra-low supported ruthenium catalyst expressed as Ru/M a O b NC, the active metal Ru is uniformly dispersed on the nitrogen-doped carbon carrier in the form of monoatoms and/or nanoparticles and has a metal oxide M a O b As the acidic center, NC represents a nitrogen-doped carbon support, M is at least one selected from Al, zn, co, fe, and a and b satisfy the valence of the metal oxide.
Further, in the ultra-low load ruthenium catalyst, the active metal ruthenium loading is 0.05-0.20wt%, and the acidic center accounts for 15-40wt% according to metal.
The N content in the nitrogen-doped carbon carrier is 1-4%, and the C content is 30-45%.
Preferably, the metal oxide is selected from Al 2 O 3 、ZnO、Co 3 O 4 And Fe (Fe) 3 O 4 At least one of when the metal oxide is selected from Al 2 O 3 When the Al loading is 15-25 wt%; when the metal oxide is selected from ZnO, the Zn loading is 30 to 40wt% (because Zn volatilizes when pyrolyzed at 850 ℃ C., losses are relatively large, to ensure the finalZn content, so that the addition amount of Zn is more in the earlier stage); when the metal oxide is selected from Co 3 O 4 When Co is supported, the Co loading is 15-25 wt%. When the metal oxide is selected from Fe 3 O 4 When the Fe loading is 15-25 wt%.
Further, the specific surface area of the ultra-low load ruthenium catalyst is 150-400 m 2 g -1 Has a mesoporous structure, and the average pore diameter is 2.0-6.0 nm.
Furthermore, ru in the ultra-low load ruthenium catalyst is uniformly dispersed on the nitrogen-doped carbon carrier in the form of nano particles/single atoms, so that a high-efficiency catalytic active center is provided, and the ultra-low load ruthenium catalyst also has high atom economy. The average grain diameter of the Ru nano-particles is 1.0-2.0 nm, and the Ru nano-particles have lattice fringe spacing of 0.22nm and correspond to the (100) crystal face of the Ru nano-particles. In the hydrogenation reaction of levulinic acid, on a single atom with metal-metal bond nano particles and nitrogen-metal bond, hydrogen molecules can form active hydrogen species through two modes of homolytic cleavage and isosplitting, and meanwhile, the surface of the catalyst has enough acid sites to adsorb levulinic acid, so that the efficient catalytic conversion of levulinic acid is easier to realize.
Further, the ultra-low supported ruthenium catalyst has at least one of the following spectral features:
1) In Ru/Al 2 O 3 In the X-ray diffraction pattern of the NC catalyst, metal oxide gamma-Al exists 2 O 3 Is located at 31 + -0.5 deg., 37 + -0.5 deg., 56 + -0.5 deg., 60 + -0.5 deg., and 66 + -0.5 deg.; gamma-Al exists in solid-phase nuclear magnetic spectrum of Al element 2 O 3 Octahedral (10 ppm), pentahedral (38 ppm) and tetrahedral (70 ppm) Al 3+ Binding of cations. Metal oxide gamma-Al 2 O 3 The presence of (2) can provide an acidic site to enhance the catalytic performance of the catalyst.
2) In Ru/Al 2 O 3 In the N1s high resolution spectrum of the X-ray photoelectron spectrum of the NC catalyst, a peak of 399.2 +/-0.2 eV exists, which indicates that Ru monoatoms form Ru-N by being anchored on a carbon substrate through coordination with N x . In addition, N exists in the forms of pyridine N, pyrrole N, graphite N and oxidized N, and the corresponding energy is 39 respectively8.2.+ -. 0.4eV, 400.5.+ -. 0.4eV, 401.1.+ -. 0.4eV and 403.+ -. 0.4eV; four characteristic peaks exist in the Ru 3p high-resolution spectrogram, corresponding to Ru 0 (462.1±0.5eV，Ru3p 3/2 The method comprises the steps of carrying out a first treatment on the surface of the 484.3.+ -. 0.5eV, ru 3p 1/2) and Ru n+ The signal peaks of (464.0.+ -. 0.5eV, ru 3p3/2; 486.6.+ -. 0.5eV, ru 3p 1/2) indicate that Ru nanoparticles or clusters coexist with Ru monoatoms.
3) In Ru/Al 2 O 3 In the normalized Fourier transform spectrum of the NC catalyst X-ray absorption spectrum, the following exists Ru-N major peak and +.>The Ru-Ru scattering peak.
The second object of the present invention is to provide a preparation method of the ultra-low supported ruthenium catalyst, which comprises the following steps:
(1) Dispersing chitosan in acetic acid aqueous solution, slowly dropwise adding ruthenium salt aqueous solution and metal M salt aqueous solution, and performing hydrothermal reaction;
(2) And (3) rotary evaporating, freeze drying and roasting reduction are carried out on the mixed solution obtained in the step (1) in an inert gas atmosphere, and then the ultra-low load ruthenium catalyst is obtained.
The concentration of the chitosan in the acetic acid aqueous solution in the step (1) is 5-20 mg/mL, preferably 8-14 mg/mL; the concentration of the acetic acid aqueous solution is 0.5-2.0wt%. The hydrothermal reaction is carried out for 12-24 h under stirring at 60-80 ℃.
The ruthenium salt in the step (1) is selected from ruthenium trichloride hydrate and/or ruthenium nitrosylnitrate; the metal M salt is selected from at least one of a halide, nitrate, acetate of the metal M, and in one embodiment, the metal M salt is selected from at least one of a nitrate, acetate, and halide of the metal M. Examples of salts of metal M include, but are not limited to, aluminum nitrate, zinc acetate.
The freezing temperature in the step (2) is-50 to-30 ℃ and the drying time is 48 to 72 hours; the inert gas is nitrogen or argon; the roasting temperature is 700-900 ℃, preferably 750-850 ℃, and the roasting time is 8-10 h.
The ultralow-load ruthenium catalyst provided by the invention has the advantages that the preparation method is simple, the raw materials are cheap and easy to obtain, the chitosan widely existing in the nature and the low in price is used as the raw material of the nitrogen-doped carbon carrier.
The third object of the invention is to provide a method for preparing gamma-valerolactone by hydrogenating levulinic acid or levulinate esters, wherein the ultra-low load ruthenium catalyst is used as a catalyst.
Further, the reaction conditions for preparing gamma-valerolactone by hydrogenating levulinic acid or levulinate esters are as follows: after the air is exhausted from the closed container, hydrogen is introduced, and the reaction is carried out at the temperature of 140-160 ℃ and the hydrogen partial pressure of 3-4 MPa for 3-24 h.
Further, the mol ratio of the levulinic acid or levulinate to Ru in the catalyst is 40000-200000 mol/mol;
further, the method for preparing gamma-valerolactone by hydrogenating levulinic acid or levulinate further comprises the step of recovering the ultralow-load ruthenium catalyst: and centrifuging, filtering and separating the reaction liquid after the reaction is finished and the catalyst, collecting the catalyst, and washing and drying the catalyst for the next catalytic reaction.
The invention provides an ultralow-load ruthenium catalyst with high activity and stability, active metal ruthenium is low in load, uniformly dispersed on a nitrogen-doped carbon carrier in the form of single atoms and nano particles, and has stronger interaction with the carrier, and meanwhile, a second metal provides an acidic site, so that the catalyst can realize hydrogenation of levulinic acid to prepare gamma-valerolactone under the conditions of relative mild and no solvent, and compared with a conventional load metal heterogeneous catalyst, the catalyst has high catalytic efficiency and durability.
Compared with the prior art, the invention has the beneficial effects that:
(1) The metal providing an acidic site in the catalyst prepared by the invention can capture the carboxyl of levulinic acid, and active metal Ru is added to hydrogenate carbonyl; active metal Ru coexists in the form of nano particles and single atoms, and hydrogen is activated and dissociated to form hydrogen species through two modes of homolytic and heterolytic, so that the catalytic activity of the catalyst is improved.
(2) The catalyst takes the biomass derivative chitosan with abundant natural sources and low price as the nitrogen doped carrier, the molecular structure of the catalyst contains abundant amino groups, the N atoms with rich electrons can anchor low-load Ru species, the stability of the catalyst is improved, the dispersion of metal components is promoted, the preparation method is simple, the production cost is low, and the catalyst meets the requirements of industrial large-scale production.
(3) The catalyst prepared by the invention can be recycled for multiple times, has satisfactory stability of catalytic activity, and has obvious industrial production advantages and prospects.
(4) When the catalyst prepared by the invention is applied to levulinic acid for preparing gamma-valerolactone, the reaction condition is mild, a solvent-free system is adopted, the problem of environmental pollution caused by using an organic solvent is avoided, the energy consumption is reduced, and meanwhile, the economical efficiency and the safety of an industrial production system are improved.
Drawings
For a clearer understanding of the technical solutions of the embodiments of the present invention, the following description of the preferred embodiments of the present invention will be made with reference to the accompanying drawings, which should not be construed as limiting the invention.
FIG. 1 is Ru/Al prepared according to example 1 2 O 3 Morphology photograph of NC catalyst precursor (before being calcined without carbon after freeze-drying).
FIG. 2 shows Ru/Al prepared according to example 1 2 O 3 Scanning electron microscopy of NC catalyst precursor (FIG. 2 a) and element maps (FIG. 2 b-f).
FIG. 3 shows Ru/Al prepared according to example 1 2 O 3 Scanning Electron Microscope (SEM) spectrogram of NC catalyst precursor.
FIG. 4 shows Ru/Al prepared according to example 1 2 O 3 N of NC catalyst 2 Adsorption-desorption isotherms (fig. 4 a) and pore size distribution curves (fig. 4 b).
FIG. 5 shows Ru/Al prepared according to example 1 2 O 3 High angle annular dark field scanning transmission map of NC catalyst (FIGS. 5 a-b), element map (FIG. 5 c).
FIG. 6 is a Ru/Al mixture prepared according to example 1 2 O 3 High resolution transmission electron microscopy of NC catalyst (fig. 6b is a partial high resolution transmission electron microscopy of fig. 6 a).
FIG. 7 is Ru/Al prepared according to example 1, comparative example 1 and comparative example 2 2 O 3 NC, ru/NC and Al 2 O 3 X-ray diffraction pattern of NC catalyst.
FIG. 8 shows Ru/Al prepared according to example 1 2 O 3 Solid-phase nuclear magnetic spectrum of Al element in NC catalyst.
FIG. 9 is Ru/Al prepared according to example 1 2 O 3 Raman spectra of NC catalyst.
FIG. 10 shows Ru/Al prepared according to example 1 2 O 3 X-ray electron energy full spectrum (FIG. 10 a), N1s (FIG. 10 b) and Ru 3p (FIG. 10 c) high resolution X-ray electron energy spectrum of NC catalyst.
FIG. 11 shows Ru/Al prepared according to example 1 2 O 3 Ru K-side X-ray absorption near-side structure spectrum (FIG. 11 a), extended X-ray absorption fine structure spectrum (FIG. 11 b) and wavelet transformation spectrum (FIG. 11 c) of NC catalyst.
FIG. 12 shows Ru/Al prepared according to example 1 2 O 3 H of NC catalyst 2 Temperature programmed reduction map (FIG. 12 a), NH 3 Ru/Al prepared by temperature-programmed release chart (FIG. 12 b) and example 1, comparative example 2 2 O 3 /NC、Al 2 O 3 Pyridine infrared spectrum of NC catalyst (fig. 12 c).
FIG. 13 is a chart of Ru/Al cycling 22 times for example 9 2 O 3 High angle annular dark field scan transmission plot of NC catalyst.
Detailed Description
The present invention is further illustrated below in conjunction with specific embodiments, which are intended only to provide a better understanding of the present invention to those of ordinary skill in the art, and are not intended to limit the scope of the present invention.
The experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials, unless otherwise specified, are commercially available.
Chitosan was purchased from saen chemical technology (Shanghai) limited under the model of medium viscosity, about 300mpa.s.
Example 1
1. High activity and high stability Ru/Al 2 O 3 Preparation of NC catalyst
1g of chitosan was weighed and added to 50mL of an aqueous acetic acid solution (1 wt%) under magnetic stirring, and RuCl was slowly added dropwise respectively after complete dissolution 3 ·3H 2 O aqueous solution (0.08 mg/mL,25 mL) and Al (NO) 3 ) 3 ·9H 2 O aqueous solution (65.5 mg/mL,25 mL) was stirred at a reaction temperature of 60℃for 24 hours to obtain a mixed solution. Removing part of water from the mixed solution by rotary evaporation at 60 ℃, freeze-drying for 48 hours to obtain a catalyst precursor, placing the catalyst precursor in a tube furnace, heating from room temperature to 350 ℃ at 2 ℃/min under nitrogen atmosphere, then heating from 350 ℃ to 800 ℃ at 5 ℃/min, roasting for 2 hours, and cooling to obtain Ru/Al 2 O 3 NC catalyst. Ru/Al by ICP-AES 2 O 3 Ru and Al contents in the NC catalyst were 0.18wt% and 27.7wt%, respectively.
2. Ru/Al in solvent-free systems 2 O 3 Preparation of gamma-valerolactone by hydrogenation of levulinic acid under catalysis of NC catalyst
Levulinic acid (5 g) and Ru/Al 2 O 3 NC catalyst (50 mg) was added to a 100mL parr autoclave, sealed and then treated with N at room temperature 2 And (3) performing air extraction, removing air in the reaction kettle, then flushing with hydrogen for 3 times, controlling the pressure of the hydrogen at room temperature to be 4MPa, setting the rotating speed to be 400r/min, and reacting for 3 hours at the reaction temperature of 150 ℃. After the reaction is finished and cooled to room temperature, the product gamma-valerolactone is obtained with the yield of 99.7 percent. And washing and drying the catalyst after centrifugal separation by water and ethanol, and drying in a drying oven at 65 ℃ for the next catalysis experiment.
For Ru/Al prepared in example 1 2 O 3 The morphology of the NC catalyst is characterized. Ru/Al prepared 2 O 3 NC catalyst precursor is light, is in loose porous lamellar shape, contains elements C,o, N, ru and Al are uniformly dispersed on the nitrogen-doped carbon support (FIGS. 1,2 and 3). Through N 2 Adsorption-desorption curves found Ru/Al 2 O 3 Specific surface area of NC catalyst is 280m 2 g -1 Has a mesoporous structure with an average pore size distribution of about 4nm (FIG. 4). From the high-angle annular dark field scanning transmission diagram, it can be seen that Ru nanoparticles are dispersed on a nitrogen-doped carbon carrier, the average particle diameter is 1.5nm, the lattice fringe spacing of the Ru nanoparticles is 0.22nm, and the Ru nanoparticles belong to Ru (100) crystal faces (large circles in FIGS. 5 a-b); in addition, a large number of bright spots are uniformly distributed on the nitrogen-doped carbon carrier, which indicates that Ru monoatoms exist (small circles in fig. 5 a-b); some dimly disordered lattices can also be observed, ascribed to Al 2 O 3 Species (fig. 5a-b boxes). Ru/Al 2 O 3 The Ru, al, N, C and O elements in the NC catalyst are homogeneously distributed, with Ru species coexisting in nanoparticle and monoatomic form (FIG. 5C). A high resolution transmission electron microscope image (FIG. 6) is shown at Ru/Al 2 O 3 The structural edges of the NC catalyst are present in the form of graphite carbon which is randomly distorted.
Ru/Al prepared in example 1, comparative example 1 and comparative example 2 2 O 3 NC, ru/NC and Al 2 O 3 The X-ray diffraction patterns of the three catalysts/NC are shown in FIG. 7. The three catalysts exhibit two broad peaks at-23 ° and-45 °, respectively attributed to the (002) and (100) crystal planes of graphitic carbon. In Ru/Al 2 O 3 No diffraction peaks of Ru were observed in the/NC and Ru/NC catalysts, probably because the loading of Ru was extremely low and highly uniformly dispersed on the nitrogen-doped carbon support. Ru/Al 2 O 3 NC and Al 2 O 3 The X-ray diffraction patterns of the NC catalyst have obvious diffraction peaks at-31 degrees, -37 degrees, -56 degrees, -60 degrees and-66 degrees, and the diffraction peaks correspond to gamma-Al 2 O 3 (JCPDS No. 50-0741). Such as Ru/Al 2 O 3 Solid phase nuclear magnetic spectrum of Al element in NC catalyst (figure 8) shows Ru/Al 2 O 3 The NC catalyst exhibited characteristic peaks at 10ppm,38ppm and 70ppm chemical shifts, respectively due to gamma-Al 2 O 3 Mesooctahedral, pentahedral and tetrahedral Al 3+ Cation binding, a phenomenon in whichVerification was made in X-ray diffraction pattern analysis. FIG. 9 is Ru/Al 2 O 3 Raman spectra of NC catalyst. Ru/Al 2 O 3 NC catalyst at 1335cm -1 (peak D) and 1590cm -1 The apparent Raman peak exists at (G peak), the area ratio of D peak to G peak (I D /I G ) 2.7, indicating the presence of defects and disordered structures on the carbon support. At 3000cm -1 The Raman peak at (2D peak) indicates Ru/Al 2 O 3 The number of graphite carbon layers in the NC catalyst is smaller. Ru/Al pair using high resolution X-ray electron spectroscopy 2 O 3 Characterization analysis was performed on the surface element composition and chemical state of the NC catalyst (fig. 10). As can be seen from the full spectrum of X-ray electron energy (FIG. 10 a), ru/Al 2 O 3 The NC catalyst had characteristic peaks of Al 2p (75.1 eV), al 2s (118.1 eV), C1 s (284.8 eV), N1s (400.1 eV) and O1s (532.1 eV), and no characteristic peak of Ru element was detected, possibly due to extremely low Ru content. XPS results showed Ru/Al 2 O 3 N content in NC is 1.6%, C content is 37%. Ru/Al 2 O 3 The N1s high resolution spectrum of the NC catalyst is shown in FIG. 10b, and the N element is Ru/Al 2 O 3 Pyridine N (398.2 eV), ru-N in NC catalyst x (399.2 eV), pyrrole N (400.5 eV), graphite N (401.1 eV) and oxidized N (403 eV) exist in five forms, and the coordination of Ru and N increases the stability of the catalyst. In Ru/Al 2 O 3 Four characteristic peaks exist in the Ru 3p high-resolution spectrogram of the/NC catalyst (FIG. 10 c), corresponding to Ru 0 (462.1 eV，Ru 3p 3/2 ；484.3 eV，Ru 3p 1/2 ) And Ru (Rust) n+ (464.0 eV，Ru 3p 3/2 ；486.6 eV，Ru 3p 1/2 ) Indicating that the Ru nanoparticles or clusters coexist with Ru monoatoms. To further explore Ru/Al 2 O 3 And (3) carrying out X-ray absorption fine structure spectrum analysis on the K side of the Ru species in the electronic structure and coordination environment of the Ru species in the NC catalyst. In Ru/Al 2 O 3 In the X-ray absorption near-edge structure spectrum of the NC catalyst (FIG. 11 a), the absorption energy intensity of Ru species is located at Ru foil and RuO 2 In between, ru is stated to have a positive valence. To further confirm the distribution of Ru atoms, ru/Al is disclosed 2 O 3 The exact Ru coordination environment in the NC catalyst, normalized Fourier transform of the extended X-ray absorption spectrum (FIG. 11 b), was performed, the presenceRu-N major peak and +.>The Ru-Ru scattering peak shows that Ru species are dispersed in nano-particle or cluster and monoatomic form. Based on the analysis of the wavelet transformation spectrum (FIG. 11 c), two intensity signal peaks are shown in the contour plot, respectively due to Ru-N coordination +.>Coordination with Ru-RuThe analysis result is consistent with the high-angle annular dark field scanning transmission and the X-ray electron spectrum analysis, and fully proves Ru/Al 2 O 3 Ru is present in the NC catalyst as nanoparticles or clusters and in monoatomically dispersed form.
By H 2 Temperature programmed reduction technique for Ru/Al 2 O 3 The reducibility of the NC catalyst and the interaction of the metal with the support are characterized (fig. 12 a). The results show that, at H 2 During the temperature programmed reduction, hydrogen consumption peaks appear at 193 ℃,278 ℃ and 430 ℃. The reduction peak in the low temperature region (193 ℃) correlates with the reduction of highly dispersed Ru species and with the strong interactions between the support; the reduction peak at 278 ℃ is due to weak interactions between Ru species and the carrier; the reduction peak in the high temperature zone (430 ℃) is related to the oxygen on the support. By NH 3 Ru/Al is examined in temperature programming reduction experiment 2 O 3 NC catalyst surface acid properties (fig. 12 b). The characteristic peak at 145 ℃ of adsorption temperature is a weak acid peak, and the stronger characteristic peak exists at 440 ℃ of adsorption temperature, which shows that Ru/Al 2 O 3 The NC catalyst has strong acid sites. Ru/Al analysis by pyridine infrared spectroscopy 2 O 3 NC and Al 2 O 3 NC catalyst tableThe facial acid type (Lewis acid and Bronsted acid) (FIG. 12 c), both catalysts were found to be of the 1556. 1556 cm wavelength -1 And 1645 cm -1 The absorption peak of (2) is due to weak Bronsted acid sites at a wavelength of 1446 cm -1 ，1577cm -1 And 1597 cm -1 Is assigned to the Lewis acid site and, in addition, 1491 cm -1 Weak absorption peaks are associated with lewis acid and bronsted acid sites.
Example 2
Example 2 procedure was followed as in example 1, but with the difference that RuCl was added dropwise 3 ·3H 2 The O aqueous solution was 0.06mg/mL and 25mL. Ru/Al by ICP-AES 2 O 3 Ru and Al contents in the NC catalyst were 0.13wt% and 27.8wt%, respectively. The yield of gamma valerolactone obtained was 79.3%.
Comparative example 1
Comparative example 1 the procedure was as in example 1, except that NO Al (NO 3 ) 3 ·9H 2 O aqueous solution. Ru content in Ru/NC catalyst was 0.19wt% as measured by ICP-AES. The gamma valerolactone yield was 2.3%.
Comparative example 2
Comparative example 2 the procedure was as in example 1, except that RuCl was not added 3 ·3H 2 O aqueous solution. Al was measured by ICP-AES 2 O 3 The Al content in the NC catalyst was 27.8wt%. No gamma valerolactone product was detected.
Comparative example 3
Ru/γ-Al 2 O 3 The catalyst is prepared by adopting a wet impregnation method: 0.5g Al 2 O 3 (200-300 mesh) is dispersed in 50mL of aqueous solution under the magnetic stirring state, and RuCl is slowly added dropwise 3 ·3H 2 O aqueous solution (0.1 mg/mL,25 mL) was stirred at a reaction temperature of 60℃for 24 hours to obtain a catalyst precursor. Removing part of water from the catalyst precursor by rotary evaporation at 60 ℃, freeze-drying for 48 hours, placing the catalyst precursor in a tube furnace, heating from room temperature to 350 ℃ at 2 ℃/min under nitrogen atmosphere, heating from 350 ℃ to 500 ℃ at 5 ℃/min, roasting for 2 hours, and cooling to obtain Ru/gamma-Al 2 O 3 A catalyst. Ru/gamma-Al by ICP-AES 2 O 3 The Ru content in the catalyst was 0.19wt%.
Ru/gamma-Al 2 O 3 Catalyst was used in the levulinic acid hydrogenation procedure of example 1, but no gamma valerolactone product was detected.
Example 3
Example 3 the procedure is as in example 1, except that Al (NO 3 ) 3 ·9H 2 O aqueous solution (65.5 mg/mL,25 mL) was replaced with Zn (OAc) 2 The Ru/ZnO/NC catalyst contained in the aqueous solution (40 mg/mL,25 mL) was found to have Ru and Zn contents of 0.17wt% and 9.44wt%, respectively, as measured by ICP-AES. The gamma valerolactone yield was 67.4%.
The catalysts prepared in the above examples and comparative examples are used for catalyzing levulinic acid hydrogenation to prepare gamma valerolactone in a solvent-free system, and the catalyst and the amount of levulinic acid used are the same as those in example 1 except for the different types of catalysts, and the results of converting levulinic acid in each of the examples and comparative examples to gamma valerolactone are shown in Table 1 below. First, the Ru/Al prepared in example 1 was investigated 2 O 3 The activity of the NC catalyst for the catalytic hydrogenation of levulinic acid is compared with a series of other catalysts for analysis. In a solvent-free system, 150 ℃ and 4MPa H 2 The reaction is carried out for 3 hours under the condition that the yield of gamma valerolactone is 99.7 percent, TON and TOF are 48170 and 16057 hours respectively -1 . Ru/Al prepared by reducing Ru content 2 O 3 NC catalyst (example 2) in the hydrogenation of levulinic acid, the gamma valerolactone yields were 79.3%, respectively. Comparative example 2 Al prepared 2 O 3 The NC catalyst has almost no reactivity in the levulinic acid catalytic hydrogenation reaction, which shows that Ru is a main active center. Under the action of the Ru/NC catalyst prepared in comparative example 1, the gamma-valerolactone yield was low, only 2.3%, indicating that the presence of Lewis acidic centers has a significant effect on the activity of the catalyst. The activity of ultra-low supported ruthenium catalysts with Zn species as lewis acid centers was further investigated. Under the same reaction conditions, the Ru/ZnO/NC catalyst prepared in example 3 has 67.4% of gamma-valerolactone yield prepared by hydrogenating levulinic acid, which is higher than the reactivity of the Ru/NC catalyst. Indicating that the introduction of Lewis acid centers is advantageousHydrogenation of levulinic acid to gamma valerolactone. In addition, comparative example 3 was prepared with Al 2 O 3 Ru/gamma-Al for support preparation 2 O 3 The catalyst is non-reactive to levulinic acid hydrogenation. The results show that chitosan is taken as a nitrogen doped carrier, ru species is anchored through N atoms, and a primer Al 2 O 3 Ru/Al prepared as acid center in equal regulation and control mode 2 O 3 The NC catalyst has incomparable advantages in the application of preparing gamma-valerolactone by hydrogenating levulinic acid.
TABLE 1
Note that: a gamma valerolactone yield calculation was quantified using a gas chromatograph with N-methylpyrrolidone as an internal standard.
b Number of molar conversions (TON) =n GVL /n Ru 。n GVL Represents the number of moles (mol) of GVL of the obtained product, n Ru The number of moles (mol) of Ru in the catalyst is expressed.
c Conversion frequency (TOF) =n GVL /(n Ru X t). t represents a reaction time (h).
d N.d. means no gamma valerolactone was detected.
Example 4
Example 4 Ru/Al prepared by example 1 2 O 3 The NC catalyst was used to catalyze the hydrogenation of levulinic acid to prepare gamma valerolactone, and the reaction conditions were the same as those in example 1 except that different solvents were added in the catalytic reaction, and the specific reaction solvents and the results of converting levulinic acid into gamma valerolactone in each example were shown in Table 2 below. Examine solvent-free system and Ru/Al pair of different solvents 2 O 3 The NC catalyst is used for catalyzing the effect of levulinic acid hydrogenation to prepare gamma-valerolactone. At 150 ℃,4MPa H 2 The reaction is carried out for 3 hours under the condition that the levulinic acid is catalytically hydrogenated to be converted into the gamma valerolactone with the yield of 99.7 percent and 96.6 percent in a solvent-free system or with water as a solvent. In organic solvents such as tetrahydrofuran, methyl acetateIn benzene, 1, 4-dioxane system, levulinic acid does not react. In methanol, isopropanol organic solvent, levulinic acid reacted to methyl levulinate (91%) and isopropyl levulinate (79%), no gamma valerolactone product was detected. From the economic efficiency of industrial practical application, a solvent-free system is a preferred choice for preparing gamma-valerolactone by catalytic hydrogenation of levulinic acid.
TABLE 2
Example 5
Example 5 Ru/Al prepared by example 1 2 O 3 The NC catalyst was used for catalyzing methyl levulinate and ethyl levulinate to prepare gamma-valerolactone by hydrogenation, and the reaction conditions were the same as those in example 1 except that the catalyst amount, methyl levulinate amount, ethyl levulinate amount, solvent and reaction time were different, and the results of converting methyl levulinate and ethyl levulinate into gamma-valerolactone are shown in the following table 3. Ru/Al research by using methyl levulinate and ethyl levulinate as typical substrates 2 O 3 Catalytic hydrogenation performance of NC catalysts in solvent-free systems and aqueous solutions. Ru/Al 2 O 3 The NC catalyst is not catalytically active to methyl levulinate and ethyl levulinate in a solvent-free system, and the gamma valerolactone yield is close to 100% in aqueous solution.
TABLE 3 Table 3
Example 6
Example 6 Ru/Al prepared by example 1 2 O 3 The NC catalyst was used to catalyze the hydrogenation of levulinic acid to gamma valerolactone, and the reaction conditions were the same as those in example 1, except that the reaction temperature was varied, and the results of converting levulinic acid to gamma valerolactone at the different reaction temperatures were shown in Table 4 below. As the reaction temperature increased from 120℃to 1The gamma-valerolactone yield is improved from 39.2% to 99.7% at 50 ℃. The temperature was further raised to 160℃and the gamma valerolactone yield was slightly varied.
TABLE 4 Table 4
Example 7
EXAMPLE 7 Ru/Al prepared according to example 1 2 O 3 The reaction conditions were the same as in example 1 except that the hydrogen pressure at room temperature was different, and the results of converting levulinic acid into gamma valerolactone at different hydrogen pressures were shown in Table 5 below. With the increase of the hydrogen pressure, the yield of the gamma-valerolactone is gradually increased (8.9-99.7%), and the highest yield of the gamma-valerolactone can reach 99.7% when the hydrogen pressure is 4 MPa.
TABLE 5
Example 8
Example 8 Ru/Al prepared by example 1 2 O 3 The NC catalyst was used to catalyze levulinic acid to prepare gamma valerolactone, and the reaction conditions were the same as those in example 1 except that the catalyst and the amount of levulinic acid used were different, and the results of converting levulinic acid into gamma valerolactone at different catalyst and levulinic acid amounts and reaction times were shown in Table 6 below. The amount of catalyst is a key parameter in evaluating the catalyst activity and achieving commercial viability. Exploration of Ru/Al 2 O 3 Different amounts of NC catalyst are used in a solvent-free system at 150 ℃ and 4MPa H 2 Influence of reaction for 3h on gamma-valerolactone yield under the condition of Ru/Al 2 O 3 The gamma valerolactone yield was highest (99.7%) and TON was 48170 at 0.05g (example 1) of NC catalyst. Ru/Al 2 O 3 When the amount of the NC catalyst was reduced to 0.03g, the gamma valerolactone yield was reduced (88.2%), but TON was increased to 71022. ContinuingRu/Al reduction 2 O 3 The gamma valerolactone yield was lower, only 3.2%, with a NC catalyst dosage of 0.0125g, i.e. levulinic acid/Ru molar ratio of 195455. We further kept the catalyst usage low and improved gamma valerolactone yield by extending the reaction time. The results showed that with the extension of the reaction time, the gamma valerolactone yield was 91.5% at 60h and TON was as high as 176831. Indicating Ru/Al 2 O 3 The NC catalyst can realize the efficient catalysis of levulinic acid hydrogenation to prepare gamma-valerolactone.
TABLE 6
Example 9
Example 9 use of the Ru/Al recovered from example 1 2 O 3 The NC catalyst is used for catalyzing levulinic acid to prepare gamma-valerolactone through hydrogenation, and the reaction conditions are exactly the same as those in the example 1. After the reaction, ru/Al is added 2 O 3 After the NC catalyst is washed by water and ethanol and dried, ru/Al is measured by ICP-AES after one-time use 2 O 3 Ru and Al contents in the NC catalyst were 0.18wt% and 27.2wt%, respectively; ru/Al after 22 times of use 2 O 3 Ru and Al contents in the NC catalyst were 0.16wt% and 3.24wt%, respectively. As can be clearly seen from the high angle annular dark field scanning transmission diagram (FIG. 13), ru/Al after 22 cycles 2 O 3 The Ru nanoparticles and monoatoms in the NC catalyst are still uniformly dispersed on the nitrogen-doped carbon support. The results of the conversion of levulinic acid to gamma valerolactone for each example are set forth in Table 7 below. The results in Table 7 show that the yield of gamma-valerolactone prepared by catalyzing the hydrogenation of levulinic acid can still reach 91.8% after 22 times of circulation experiments, and the accumulated TON exceeds a million. Indicating Ru/Al 2 O 3 The NC catalyst not only has high catalytic efficiency, but also has excellent stability and reusability.
TABLE 7
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Claims (9)

1. The preparation method of the ultralow-load ruthenium catalyst is characterized by comprising the following steps of:
(1) Dispersing chitosan in acetic acid aqueous solution, slowly dropwise adding ruthenium salt aqueous solution and metal M salt aqueous solution, and performing hydrothermal reaction; the hydrothermal reaction is carried out for 12-24 hours under stirring at 60-80 ℃;
(2) Performing rotary evaporation, freeze drying and roasting reduction on the mixed solution obtained in the step (1) in an inert gas atmosphere to obtain an ultralow-load ruthenium catalyst; the roasting temperature is 700-900 ℃, and the roasting time is 8-10 hours;
the ultra-low load ruthenium catalyst is expressed as Ru/M a O b NC, the active metal Ru is uniformly dispersed on the nitrogen-doped carbon carrier in the form of monoatoms and nano-particles and has a metal oxide M a O b NC represents a nitrogen-doped carbon support as an acidic center; m is M a O b Is Al 2 O 3 ；
The metal ruthenium loading is 0.05-0.20wt%; the nitrogen-doped carbon carrier contains 1-4% of N and 30-45% of C; the loading amount of Al is 15-25 wt%;
the specific surface area of the ultra-low load ruthenium catalyst is 150-400 m 2 And/g, the mesoporous structure is provided, and the average pore diameter is 2.0-6.0 nm; the average particle diameter of Ru nanoparticles is 1.0-2.0 nm.
2. The preparation method of claim 1, wherein the concentration of chitosan in the acetic acid aqueous solution in the step (1) is 5-20 mg/mL, and the concentration of the acetic acid aqueous solution is 0.5-2.0 wt%; the ruthenium salt in the step (1) is selected from ruthenium trichloride hydrate and/or ruthenium nitrosylnitrate; the metal M salt is selected from at least one of halide, nitrate and acetate of metal M.
3. The preparation method of claim 2, wherein the concentration of chitosan in the acetic acid aqueous solution in the step (1) is 8-14 mg/mL.
4. The method of claim 2, wherein the metal salt M is aluminum nitrate.
5. The preparation method of claim 1, wherein the freezing temperature in the step (2) is-50 to-30 ℃ and the drying time is 48-72 hours; the inert gas is argon; the roasting temperature is 750-850 ℃.
6. A process for the hydrogenation of levulinic acid or levulinate esters to gamma valerolactone, characterized in that an ultra low supported ruthenium catalyst obtainable by the process according to any one of claims 1-5 is used.
7. The process of claim 6, wherein the reaction conditions for the hydrogenation of levulinic acid or levulinate esters to gamma valerolactone are: after the air is exhausted from the closed container, introducing hydrogen, and reacting for 3-24 hours at the temperature of 140-160 ℃ and the partial pressure of the hydrogen of 3-4 MPa.
8. The method of claim 7, wherein the molar ratio of levulinic acid or levulinate to Ru in the catalyst is 40000-200000 mol/mol.
9. The method of claim 7, further comprising the step of recovering the ultra-low supported ruthenium catalyst: and centrifuging, filtering and separating the reaction liquid after the reaction is finished and the catalyst, collecting the catalyst, and washing and drying the catalyst for the next catalytic reaction.
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