Precious metal catalysts, methods of making and using the same, and methods of making biomass-based carboxylic polymer monomers

Abstract

The application relates to the field of biomass conversion, and discloses a noble metal catalyst, a preparation method and application thereof, and a preparation method of a biomass-based carboxylic acid polymer monomer. The catalyst comprises a carrier and an active component loaded on the carrier, the active component comprises noble metal and rhenium, and the carrier is a carbon nanotube; wherein the dispersion degree of the noble metal is 40-60%. The noble metal catalyst has the advantages that the dispersion degree of the noble metal is high, the hydrogen reduction condition is mild, the catalyst is used for preparing adipic acid from saccharic acid under a water system, the saccharic acid conversion rate is high, the selectivity of the adipic acid is high, and the reaction is green and environment-friendly.

Description

Technical Field

[0001] This invention relates to the field of biomass conversion, specifically to a noble metal catalyst, its preparation method and application, and a method for preparing biomass-based carboxylic acid polymer monomers. Background Technology

[0002] Adipic acid, a white monoclinic crystal at room temperature, is widely used in plastics, resins, and other fields. It can be used to manufacture nylon 66, plasticizers, lubricants, and polyurethane foams. In smaller quantities, it is used as an acidulant in food and as a substitute for tartaric acid in baking powder. It also has applications in pharmaceuticals and fragrances. Currently, the annual production of adipic acid exceeds 3 million tons, and is increasing at a rate of 5% annually. The current industrial production method for adipic acid is mainly the nitric acid oxidation method using cyclohexanol and cyclohexanone (KA oil) as raw materials. This method uses highly oxidizing nitric acid, causing severe equipment corrosion, and the generated N2O is considered one of the pollutants contributing to global warming and ozone depletion, resulting in significant environmental pollution.

[0003] Developing green and low-carbon technologies for the synthesis of liquid fuels and chemicals is an important way to solve the current problems of fossil resource shortages and serious greenhouse gas emissions. Therefore, developing an efficient and green economical method for the synthesis of adipic acid has become a research goal for many scientists. Currently, the biomass-based adipic acid production route using glucose as a raw material is simple, has mild reaction conditions, and does not use nitric acid, making the process environmentally friendly. The complete reaction process involves the oxidation of glucose by a noble metal catalyst to obtain gluconic acid, which is then hydrogenated and deoxygenated to obtain adipic acid. The second step, the preparation of adipic acid from gluconic acid, is more difficult, requiring a high-quality catalyst. Using water as the reaction system, efficient and green catalytic preparation of adipic acid from gluconic acid is currently a key research focus. Existing catalysts have poor dispersion of active components and are prone to aggregation, resulting in high reduction and reaction temperatures. These catalytic reactions are costly and complex to operate. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned problems existing in the prior art and to provide a noble metal catalyst and its preparation method and application, as well as a method for preparing biomass-based carboxylic acid polymer monomers. The noble metal catalyst of this invention has high noble metal dispersion and mild hydrogen reduction conditions. It is used to catalyze the preparation of adipic acid from gluconic acid in an aqueous system. It has the advantages of high gluconic acid conversion rate and high adipic acid selectivity, and the reaction is green and environmentally friendly.

[0005] To achieve the above objectives, the present invention provides a noble metal catalyst, wherein the catalyst comprises a support and an active component supported on the support, the active component comprising a noble metal and rhenium, and the support being a carbon nanotube; The dispersion of precious metals is 40-60%.

[0006] Preferably, the dispersion of the precious metal is 50-60%.

[0007] Preferably, the XRD pattern of the noble metal catalyst does not contain characteristic peaks of noble metals.

[0008] A second aspect of the present invention provides a method for preparing a noble metal catalyst, wherein the method includes the following steps: (1) Carbon nanotubes were subjected to acidic pretreatment under an inert atmosphere to obtain pretreated carbon nanotubes. (2) Noble metals and rhenium are introduced onto the pretreated carbon nanotubes by strong electrostatic adsorption. (3) Reduce the product obtained in step (2).

[0009] A third aspect of the present invention provides a noble metal catalyst prepared by the method of the second aspect described above.

[0010] The fourth aspect of the present invention provides the application of the noble metal catalyst described in the first or third aspect above in the preparation of biomass-based carboxylic acid polymer monomers.

[0011] The fifth aspect of this invention provides a method for preparing biomass-based carboxylic acid polymer monomers, the method comprising: In the presence of hydrogen, the noble metal catalyst described in the first or third aspect above is contacted with gluconic acid for reaction.

[0012] Preferably, the reaction is carried out in the presence of water.

[0013] The solution provided by the present invention, through the above technical solution, has the following beneficial effects: (1) Loading noble metals and rhenium onto carbon nanotubes can enhance the catalytic activity of noble metal catalysts.

[0014] (2) The strong electrostatic adsorption method can make the active components in the prepared noble metal catalyst well dispersed, the noble metal dispersion is high, and the hydrogen reduction conditions are mild.

[0015] (3) The noble metal catalyst prepared by the present invention is used to catalyze the preparation of adipic acid from gluconic acid in an aqueous system. It has the advantages of high gluconic acid conversion rate and high adipic acid selectivity, and the reaction is green and environmentally friendly. Attached Figure Description

[0016] Figure 1 The XRD pattern of the noble metal catalyst prepared in Example 1; Figure 2 TEM image of the noble metal catalyst prepared in Example 1; Figure 3 TEM image of the noble metal catalyst prepared in Comparative Example 1; Figure 4 (a) XPS spectrum of Pd element in noble metal catalyst of Example 1; (b) XPS spectrum of Pd element in noble metal catalyst of Comparative Example 1; Figure 5 TEM image of the noble metal catalyst prepared in Comparative Example 2; Figure 6 The noble metal catalyst prepared in Example 1 was used to catalyze the preparation of adipic acid from gluconic acid. The liquid chromatogram of the product after the reaction is shown. Figure 7 The noble metal catalyst prepared in Example 2 was used to catalyze the preparation of adipic acid from gluconic acid. The liquid chromatogram of the product after the reaction is shown. Detailed Implementation

[0017] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0018] The first aspect of the present invention provides a noble metal catalyst, wherein the catalyst includes a support and an active component supported on the support, the active component including a noble metal and rhenium, and the support being a carbon nanotube; The dispersion of precious metals is 40-60%.

[0019] In this invention, loading noble metals and rhenium onto carbon nanotubes can enhance the catalytic activity of noble metal catalysts.

[0020] According to the present invention, preferably, the dispersion of the precious metal is 50-60%.

[0021] In this invention, when the dispersion of the noble metal in the noble metal catalyst meets the above-mentioned range, the resulting catalyst has better activity, milder catalyst reduction conditions, and more complete reduction.

[0022] In this invention, the dispersion of precious metals was determined using CO pulse adsorption. Specifically, the CO-TPD dispersion of precious metals in the sample was detected using an Autochem 2920 II chemisorption analyzer. A U-shaped quartz tube was used as the reaction tube. 50 mg of catalyst was weighed and filled to a suitable height using quartz sand. A thermocouple was placed in the middle of the bed. A nitrogen-hydrogen mixture of 10% H2 was then introduced at a flow rate of 50 ml / min. The temperature was increased to 200°C at a programmed rate of 10°C / min and maintained for 0.5 h for reduction. The atmosphere was then switched to pure He, and purging was continued for another 0.5 h. After purging, the temperature was lowered to 30°C. CO pulse adsorption was then initiated, and the CO peak area remained constant after multiple pulses before the process was stopped.

[0023] According to the present invention, preferably, the XRD pattern of the noble metal catalyst does not contain characteristic peaks of noble metals.

[0024] In this invention, when the characteristic peaks of noble metals are not present in the XRD spectrum of the noble metal catalyst, it indicates that the noble metals are well dispersed in the catalyst, which further enhances the activity of the catalyst.

[0025] In this invention, the specific conditions for X-ray diffraction (XRD) testing include: the equipment is Rigaku D / max-rC, the light source is Cu Kα 0.154 nm, the testing range is 5-75°, and the step size is 0.02°.

[0026] According to the present invention, preferably, the valence state of the precious metal is 0 to +2, more preferably 0 to +1, as determined by XPS analysis.

[0027] In this invention, when the valence state of the precious metal meets the above-mentioned range, the resulting catalyst has better activity and the catalyst reduction is more complete.

[0028] In this invention, the valence state of noble metals is determined by XPS. Specific testing conditions include: the sample valence state is detected using a ThermoESCALAB 250 photoelectron spectrometer. The X-ray excitation source used is monochromatic Al Kα with an energy of 1488.6 eV and a power of 160 W. The X-ray beam size is 500 μm, and the binding energy is corrected for carbon C1s (284.8 eV).

[0029] According to the present invention, preferably, based on the total amount of catalyst, the content of precious metal elements is 0.25-1 wt% and the content of rhenium is 1.5-4 wt%. Furthermore, based on the total amount of catalyst, the content of precious metal elements is 0.45-0.8 wt%, and the content of rhenium is 1.5-3 wt%.

[0030] In this invention, when the content of precious metal elements and rhenium elements meets the above-mentioned range, it is more conducive to further improving their conversion rate and selectivity in the preparation reaction of biomass-based carboxylic acid polymer monomers.

[0031] The inventors of this invention have discovered that a high content of precious metals may cause the active components to agglomerate during the catalyst preparation process, resulting in insufficient catalyst reduction, or that because precious metals occupy more active sites in the catalyst, the product undergoes further reactions, thereby reducing the product selectivity. Similarly, excessive Re occupies more effective active sites in the catalyst, hindering the reaction and making the target product more likely to undergo further reactions, leading to a decrease in product selectivity.

[0032] In this invention, the contents of precious metal elements and rhenium elements are determined by ICP method.

[0033] In this invention, the ICP testing method is as follows: 50 mg of catalyst is weighed, the sample is dissolved in an appropriate amount of nitric acid, and the solution is transferred to a volumetric flask with a concentration of 10 mg / L. The content of noble metal elements and rhenium elements in the catalyst is detected using a Varian 710 spectrometer.

[0034] According to the present invention, preferably, the noble metal is at least one selected from Pt, Pd, Rh and Ru.

[0035] Furthermore, the precious metal is preferably Pt or Pd.

[0036] Furthermore, the precious metal is preferably Pd. Using Pd in ​​combination with rhenium and carbon nanotubes is more beneficial for improving the catalytic performance of the catalyst.

[0037] In this invention, there is no particular limitation on the source of carbon nanotubes, which can be obtained through commercial purchase.

[0038] According to the present invention, preferably, the carbon nanotubes are carbon nanotubes with double walls and / or single walls, and the aforementioned carbon nanotubes have a large loaded specific surface area, so that the prepared catalyst has more active sites.

[0039] According to the present invention, preferably, the pore size of the carbon nanotubes is 2 nm or more, and more preferably 2-4 nm. This preferred embodiment is advantageous for loading the active component.

[0040] The present invention does not impose any particular limitation on the preparation method of the catalyst, as long as the catalyst with the above composition can be obtained.

[0041] A second aspect of the present invention provides a method for preparing a noble metal catalyst, the method comprising the following steps: (1) Carbon nanotubes were subjected to acidic pretreatment under an inert atmosphere to obtain pretreated carbon nanotubes. (2) Noble metals and rhenium are introduced onto the pretreated carbon nanotubes by strong electrostatic adsorption. (3) Reduce the product obtained in step (2).

[0042] In this invention, the use of strong electrostatic adsorption method enables the prepared noble metal catalyst to have good dispersion of active components, high dispersion of noble metals, and mild hydrogen reduction conditions.

[0043] In this invention, the strong electrostatic adsorption method is based on the principle of electrostatic adsorption. By adjusting the pH value of the system, the carbon nanotube support and the surface of the active component are made to carry opposite charges, which makes it easier for the active component to be adsorbed on the support. This is beneficial for the noble metal to be better dispersed and loaded on the surface of the support, thus making the reduction conditions during catalyst preparation milder, increasing the proportion of active sites on the noble metal catalyst, and improving the catalytic activity.

[0044] In this invention, the carbon nanotubes are acid-treated to remove excess impurities from the carrier surface and adjust the carrier's isoelectric point, which is beneficial for the uniform loading of noble metals onto the carrier surface during the strong electrostatic adsorption method.

[0045] According to the present invention, preferably, the acid used in the acidic pretreatment in step (1) is selected from at least one of nitric acid, sulfuric acid, hydrochloric acid and hydrofluoric acid, and more preferably nitric acid.

[0046] According to the present invention, preferably, the acidic pretreatment includes: contacting carbon nanotubes with an acid solution under an inert atmosphere, followed by calcination.

[0047] In one specific embodiment of the present invention, preferably, the concentration of the acid solution is 1-5 mol / L.

[0048] In this invention, preferably, the amount of acid solution used is 40-60 mL relative to 1 g of carbon nanotubes.

[0049] According to the present invention, preferably, the conditions for contacting carbon nanotubes with acid solution include: a temperature of 60-80°C and a time of 3-6 hours.

[0050] In this invention, step (1) further includes filtering the acid-pretreated carbon nanotubes before calcination. The filtering method is a well-known filtering operation in the art, such as using a Buchner funnel for filtering.

[0051] In this invention, step (1) further includes drying the filtered carbon nanotubes. The present invention does not have specific limitations on the drying conditions, as long as moisture can be removed. Preferably, the drying conditions include: a temperature of 60-80℃ and a time of 6-12 hours.

[0052] In this invention, there is no particular limitation on the roasting temperature. Preferably, the temperature is 400-550℃ and the roasting rate is 0.5-5℃ / min. The roasting time can be adjusted according to the actual situation, preferably 2-4h.

[0053] In one specific embodiment of the present invention, preferably, the roasting is carried out in a tube furnace, which will not be described in detail below.

[0054] In this invention, the range of types of inert atmospheres is relatively wide. Preferably, the inert atmosphere is selected from at least one of nitrogen, argon and helium.

[0055] In one specific embodiment of the present invention, preferably, the inert atmosphere is nitrogen, and the flow rate of nitrogen is 100-200 mL / min.

[0056] According to the present invention, preferably, the isoelectric point of the pretreated carbon nanotubes is lower than that of the untreated carbon nanotubes. This preferred embodiment is more advantageous for pH control of the solution during strong electrostatic adsorption.

[0057] In this invention, the isoelectric point has the conventional interpretation in the art, and can specifically be expressed as the pH value when the surface of a molecule is uncharged.

[0058] The present invention does not have any particular limitation on the specific implementation of introducing noble metals and rhenium onto the pretreated carbon nanotubes by strong electrostatic adsorption in step (2). It can be carried out according to various strong electrostatic adsorption methods commonly used in the art. Preferably, step (2) includes: providing an active component mixture containing a noble metal precursor and a rhenium precursor, providing a mixture containing pretreated carbon nanotubes, adjusting the pH of the active component mixture and the mixture containing pretreated carbon nanotubes to above the isoelectric point of the pretreated carbon nanotubes, and mixing the two.

[0059] In this invention, the range of sources for the precious metal precursor is relatively wide, as long as the precious metal required by this invention can be provided. Preferably, the precious metal precursor is at least one of chloroplatinic acid, platinum nitrate, chloropalladium acid, palladium chloride, palladium nitrate and their salts.

[0060] In this invention, the range of sources for the rhenium precursor is relatively wide, as long as the rhenium required by this invention can be provided. Preferably, the rhenium precursor is at least one of perrhenic acid, ammonium perrhenate, and their salts.

[0061] In this invention, the solvent in the active component mixture or the mixture containing pretreated activated carbon is not particularly limited; preferably, the solvent is deionized water. The amount of solvent used is also not particularly limited, as long as the components are sufficiently dispersed and mixed.

[0062] In this invention, the reagents used to adjust the pH of the active components and the mixture and the mixture containing pretreated carbon nanotubes are not particularly limited, and can be, for example, acids or bases, preferably nitric acid and / or hydrochloric acid.

[0063] According to the present invention, preferably, the pH of the active component mixture and the mixture containing the pretreated carbon nanotubes is adjusted to 0.5-4 above the isoelectric point of the pretreated carbon nanotubes, more preferably 1.5-2.5. Under the aforementioned preferred conditions, it is beneficial for the active components to undergo strong electrostatic adsorption, thereby enabling the noble metals to be better dispersed and loaded in the carbon nanotubes.

[0064] In this invention, there are no particular limitations on the mixing method. Preferably, the mixing includes adding the pH-adjusted active component mixture to the pH-adjusted mixture containing pretreated carbon nanotubes. Preferably, the pH-adjusted active component mixture is added dropwise to the pH-adjusted mixture containing pretreated carbon nanotubes at a rate of 2-4 mL / min using a peristaltic pump. This preferred drop rate ensures that the active components are evenly dispersed in the carbon nanotube mixture, avoiding precipitation or aggregation.

[0065] According to the present invention, preferably, the mixing time is 2-4 hours. It should be noted that the mixing time begins after the dripping is completed.

[0066] In this invention, there is no particular limitation on the amount of precious metal precursor and rhenium precursor used, as long as the content of precious metal and rhenium in the prepared catalyst meets the requirements of this invention. Preferably, the amount of precious metal and rhenium introduced in step (2) is such that, based on the total amount of catalyst, the content of precious metal element is 0.25-1wt% and the content of rhenium element is 1.5-4wt%.

[0067] Furthermore, based on the total amount of catalyst, the content of precious metal elements is 0.45-0.8 wt%, and the content of rhenium is 1.5-3 wt%.

[0068] In this invention, step (3) further includes filtration of the mixed product before reduction. The filtration method is a filtration operation well known to those skilled in the art, such as using a Buchner funnel for filtration.

[0069] In this invention, step (3) further includes drying the filtered product before reduction. This invention does not have any particular limitation on the drying conditions, as long as the solvent can be removed. Preferably, the drying temperature is 60-80℃ and the drying time is 6-12h.

[0070] In this invention, preferably, step (3) further includes calcining the dried product. This invention does not specifically limit the calcination conditions. Preferably, the calcination conditions include: heating to 400-550°C at a heating rate of 0.5-5°C / min under an inert atmosphere. The calcination time can be adjusted according to actual needs; preferably, the time is 2-4 hours.

[0071] In this invention, the range of inert atmospheres is relatively wide, and it can be at least one of nitrogen, argon and helium, with nitrogen being preferred. This invention does not have a particular limitation on the flow rate of nitrogen, but preferably, the flow rate of nitrogen is 40-80 mL / min.

[0072] In this invention, the product obtained in step (2) also needs to be reduced.

[0073] According to the present invention, preferably, the reduction conditions in step (3) include: being carried out in a hydrogen-containing atmosphere at a temperature of 20-400°C, preferably 20-50°C.

[0074] In this invention, the reduction time in step (3) is 0.5-6h, preferably 0.5-3h.

[0075] In this invention, preferably, the reduction in step (3) is carried out under normal pressure, the hydrogen reduction conditions are mild, and the reaction system is safer.

[0076] In this invention, the reduction temperature in step (3) is low, the hydrogen reduction conditions are mild, and the reaction system is safer.

[0077] In this invention, there is no particular limitation on the hydrogen-containing atmosphere, as long as hydrogen is present. Preferably, the hydrogen-containing atmosphere has a hydrogen volume percentage of 20-50%, and may also contain an inert atmosphere, preferably selected from at least one of nitrogen, argon, and helium. There is no particular limitation on the flow rate of the hydrogen-containing atmosphere. Preferably, the flow rate of the hydrogen-containing atmosphere is 50-300 mL / min, more preferably 50-100 mL / min. Using the aforementioned preferred flow rate can ensure sufficient contact of the catalyst and remove moisture during the reduction process, making the reaction safer.

[0078] A third aspect of the present invention provides a noble metal catalyst prepared by the method described in the second aspect above.

[0079] A fourth aspect of this invention provides the application of the noble metal catalysts described in the first and third aspects above in the preparation of biomass-based carboxylic acid polymer monomers. The noble metal catalysts of this invention are particularly suitable for the preparation reactions of biomass-based carboxylic acid polymer monomers, including but not limited to the preparation of carboxylic acid polymer monomers such as adipic acid, 2,5-dihydroxyadipic acid, or 2-hydroxyadipic acid. The noble metal catalysts of this invention have the advantages of high feed conversion rate and high product selectivity in this system.

[0080] In this invention, preferably, the raw material for preparing biomass-based carboxylic acid polymer monomers is gluconic acid.

[0081] The fifth aspect of this invention provides a method for preparing biomass-based carboxylic acid polymer monomers, the method comprising: In the presence of hydrogen, the noble metal catalyst described in the first or third aspect above is contacted with gluconic acid to react. According to the present invention, preferably, the reaction is carried out in the presence of water. More preferably, the amount of water used is such that the mass concentration of gluconic acid is 1-5 wt%. This preferred embodiment makes the method provided by the present invention green and environmentally friendly.

[0082] According to the present invention, preferably, the mass ratio of the gluconic acid to the noble metal catalyst is 1:1-1.5.

[0083] In this invention, there is no particular limitation on the reaction temperature, but it is preferably 100-150℃; the reaction time can be adjusted according to the actual situation, preferably 3-12h.

[0084] In this invention, there is no particular limitation on the reaction pressure, but it is preferably 0.1-2 MPa.

[0085] The present invention will be described in detail below through embodiments.

[0086] Unless otherwise specified, all raw materials used in the following embodiments are commercially available.

[0087] The specific conditions for CO pulse adsorption testing, XRD testing, and XPS testing are as described above and will not be repeated here.

[0088] The contents of precious metal elements and rhenium in the catalyst were determined by ICP method.

[0089] Example 1 (1) 5g of double-walled carbon nanotubes (pore size 2-3nm) were dispersed in 300mL of 2mol / L HNO3 and pretreated at 60℃ for 3h under N2 atmosphere. The pretreated product was filtered and dried at 60℃ for 12h, and then placed in a tube furnace under N2 atmosphere (nitrogen flow rate of 100mL / min) and heated to 500℃ for 3h at a heating rate of 4℃ / min to obtain pretreated carbon nanotubes. The isoelectric point of the pretreated double-walled carbon nanotubes was lower than that of the untreated double-walled carbon nanotubes, and the isoelectric point of the pretreated double-walled carbon nanotubes was 3.5.

[0090] (2) Pd and Re were introduced onto the pretreated double-walled carbon nanotubes by strong electrostatic adsorption. Specifically, 3g of pretreated double-walled carbon nanotubes were dispersed in 200mL of deionized water, and HReO4 containing 60mg Re and Pd(NO3)2 containing 15mg Pd were mixed and dispersed in 200mL of deionized water. The pH of the above active component mixture and the mixture containing the pretreated double-walled carbon nanotubes were adjusted to 6, and the active component mixture was added dropwise to the mixture containing the pretreated double-walled carbon nanotubes at a rate of 2mL / min using a peristaltic pump. After the addition was completed, the mixture was mixed and adsorbed for 4h.

[0091] (3) The product obtained above was filtered, dried at 60°C for 12 h, placed in a tube furnace under N2 atmosphere (nitrogen flow rate of 100 mL / min) and heated to 500°C for 3 h at a heating rate of 4°C / min. Then it was reduced at 30°C for 3 h in an atmosphere containing 80% N2 and 20% H2 (flow rate of 100 mL / min) to finally obtain the noble metal catalyst C1. Figure 1 The absence of characteristic peaks for Pd in ​​the XRD pattern of C1 indicates that the noble metal is well dispersed in the catalyst.

[0092] Figure 2 The TEM image of C1 shows that the active component is well dispersed.

[0093] Example 2 (1) Same as step (1) in Example 1.

[0094] (2) Pd and Re were introduced onto the pretreated double-walled carbon nanotubes (pore size 2-3 nm) by strong electrostatic adsorption. Specifically, 3 g of pretreated double-walled carbon nanotubes were dispersed in 200 mL of deionized water, and NH4ReO4 containing 60 mg Re and Pd(NO3)2 containing 15 mg Pd were mixed and dispersed in 200 mL of deionized water. The pH of the above active component mixture and the mixture containing the pretreated double-walled carbon nanotubes were adjusted to 5, and the active component mixture was added dropwise to the mixture containing the pretreated double-walled carbon nanotubes at a rate of 2 mL / min using a peristaltic pump. After the addition was completed, the mixture was mixed and adsorbed for 4 h.

[0095] (3) The product obtained above was filtered, dried at 60°C for 12 hours, placed in a tube furnace under N2 atmosphere (nitrogen flow rate of 100 mL / min) and heated to 450°C for 3 hours at a heating rate of 4°C / min. Then it was reduced at 30°C for 3 hours in an atmosphere containing 80% N2 and 20% H2 (flow rate of 50 mL / min) to finally obtain the noble metal catalyst C2. The XRD spectrum of C2 does not contain the characteristic peak of Pd.

[0096] Example 3 (1) Same as step (1) in Example 1, except that single-walled carbon nanotubes of equal mass (pore size 2-4 nm) are used. The isoelectric point of the pretreated single-walled carbon nanotubes is lower than that of the untreated single-walled carbon nanotubes, and the isoelectric point of the pretreated single-walled carbon nanotubes is 2.

[0097] (2) Pd and Re were introduced onto the pretreated double-walled carbon nanotubes by strong electrostatic adsorption. Specifically, 3g of pretreated double-walled carbon nanotubes were dispersed in 200mL of deionized water, and HReO4 containing 60mg Re and Pd(NO3)2 containing 22.5mg Pd were mixed and dispersed in 200mL of deionized water. The pH of the above active component mixture and the mixture containing the pretreated single-walled carbon nanotubes were adjusted to 4.5, and the active component mixture was added dropwise to the mixture containing the pretreated single-walled carbon nanotubes at a rate of 2mL / min using a peristaltic pump. After the addition was completed, the mixture was mixed and adsorbed for 4h.

[0098] (3) Following the same steps as in Example 1, a noble metal catalyst C3 was obtained. The XRD spectrum of C3 did not contain the characteristic peak of Pd.

[0099] Example 4 (1) Same as step (1) in Example 1.

[0100] (2) Pd and Re were introduced onto the pretreated double-walled carbon nanotubes (pore size 2-3 nm) by strong electrostatic adsorption. Specifically, 3 g of pretreated double-walled carbon nanotubes were dispersed in 200 mL of deionized water, and HReO4 containing 60 mg Re and Pd(NO3)2 containing 30 mg Pd were mixed and dispersed in 200 mL of deionized water. The pH of the above active component mixture and the mixture containing the pretreated single-walled carbon nanotubes were adjusted to 4, and the active component mixture was added dropwise to the mixture containing the pretreated single-walled carbon nanotubes at a rate of 2 mL / min using a peristaltic pump. After the addition was completed, the mixture was mixed and adsorbed for 4 h.

[0101] (3) Following the same steps as in Example 1, the noble metal catalyst C4 was obtained. The XRD spectrum of C4 did not contain the characteristic peak of Pd.

[0102] Example 5 (1) Same as step (1) in Example 1.

[0103] (2) Pd and Re were introduced onto the pretreated double-walled carbon nanotubes (pore size 2-3 nm) by strong electrostatic adsorption. Specifically, 3 g of pretreated double-walled carbon nanotubes were dispersed in 200 mL of deionized water, and HReO4 containing 120 mg Re and Pd(NO3)2 containing 30 mg Pd were mixed and dispersed in 200 mL of deionized water. The pH of the above active component mixture and the mixture containing the pretreated double-walled carbon nanotubes were adjusted to 5.5 respectively. The active component mixture was then added dropwise to the mixture containing the pretreated double-walled carbon nanotubes at a rate of 2 mL / min using a peristaltic pump. After the addition was completed, the mixture was mixed and adsorbed for 4 h.

[0104] (3) Following the same steps as in Example (1), the noble metal catalyst C5 was obtained. The XRD spectrum of C5 did not contain the characteristic peak of Pd.

[0105] Example 6 (1) 5g of double-walled carbon nanotubes (pore size 2-3nm) were dispersed in 300mL of 2mol / L hydrochloric acid and pretreated at 60℃ for 3h under N2 atmosphere. The pretreated product was filtered and dried at 60℃ for 12h, and then placed in a tube furnace under N2 atmosphere (nitrogen flow rate of 100mL / min) and heated to 500℃ for 3h at a heating rate of 4℃ / min to obtain pretreated carbon nanotubes. The isoelectric point of the pretreated double-walled carbon nanotubes was lower than that of the untreated double-walled carbon nanotubes, and the isoelectric point of the pretreated double-walled carbon nanotubes was 4.

[0106] (2) Pd and Re were introduced onto the pretreated double-walled carbon nanotubes by strong electrostatic adsorption. Specifically, 3g of pretreated double-walled carbon nanotubes were dispersed in 200mL of deionized water, and HReO4 containing 60mg Re and Pd(NO3)2 containing 15mg Pd were mixed and dispersed in 200mL of deionized water. The pH of the above active component mixture and the mixture containing the pretreated double-walled carbon nanotubes were adjusted to 6, and the active component mixture was added dropwise to the mixture containing the pretreated double-walled carbon nanotubes at a rate of 2mL / min using a peristaltic pump. After the addition was completed, the mixture was mixed and adsorbed for 4h.

[0107] (3) The product obtained above was filtered, dried at 60°C for 12 hours, placed in a tube furnace under N2 atmosphere (nitrogen flow rate of 100 mL / min) and heated to 500°C for 3 hours at a heating rate of 4°C / min. Then it was reduced at 50°C for 2 hours in an atmosphere containing 80% N2 and 20% H2 (flow rate of 50 mL / min) to finally obtain the noble metal catalyst C6. The XRD spectrum of C6 does not contain the characteristic peak of Pd.

[0108] Example 7 (1) 5g of double-walled carbon nanotubes (pore size 2-3nm) were dispersed in 300mL of 2mol / L HNO3 and pretreated at 60℃ for 3h under N2 atmosphere. The pretreated product was filtered and dried at 60℃ for 12h, and then placed in a tube furnace under N2 atmosphere (nitrogen flow rate of 100mL / min) and heated to 500℃ for 3h at a heating rate of 4℃ / min to obtain pretreated carbon nanotubes. The isoelectric point of the pretreated double-walled carbon nanotubes was lower than that of the untreated double-walled carbon nanotubes, and the isoelectric point of the pretreated double-walled carbon nanotubes was 3.5.

[0109] (2) Pd and Re were introduced onto the pretreated double-walled carbon nanotubes by strong electrostatic adsorption. Specifically, 3g of pretreated double-walled carbon nanotubes were dispersed in 200mL of deionized water, and HReO4 containing 60mg Re and Pd(NO3)2 containing 7.5mg Pd were mixed and dispersed in 200mL of deionized water. The pH of the above active component mixture and the mixture containing the pretreated double-walled carbon nanotubes were adjusted to 6, and the active component mixture was added dropwise to the mixture containing the pretreated double-walled carbon nanotubes at a rate of 2mL / min using a peristaltic pump. After the addition was completed, the mixture was mixed and adsorbed for 4h.

[0110] (3) The product obtained above was filtered, dried at 60°C for 12 hours, placed in a tube furnace under N2 atmosphere (nitrogen flow rate of 100 mL / min) and heated to 500°C for 3 hours at a heating rate of 4°C / min. Then it was reduced at 450°C for 3 hours in an atmosphere containing 80% N2 and 20% H2 (flow rate of 100 mL / min) to finally obtain the noble metal catalyst C7. The XRD spectrum of C7 does not contain the characteristic peak of Pd.

[0111] Comparative Example 1 (1) Same as step (1) in Example 1, except that the same mass of coconut shell activated carbon is used. The isoelectric point of the pretreated activated carbon is lower than that of the activated carbon before treatment. The isoelectric point of the pretreated activated carbon is 5.

[0112] (2) Pd and Re were introduced onto the pretreated activated carbon by equal volume impregnation. Specifically, HReO4 containing 60 mg Re and Pd(NO3)2 containing 15 mg Pd (total 1.8 mL solution) were added to 3 g of activated carbon and impregnated for 6 h.

[0113] (3) The product obtained above was filtered, dried at 60°C for 12 hours, placed in a tube furnace under N2 atmosphere (nitrogen flow rate of 27 mL / min) and heated to 500°C for 3 hours at a heating rate of 4°C / min. Then it was reduced at 300°C for 3 hours in an atmosphere containing 80% N2 and 20% H2 (flow rate of 100 mL / min) to finally obtain the noble metal catalyst D1.

[0114] Figure 3 The TEM image at D1 shows that the active components are poorly dispersed in the catalyst, exhibiting agglomeration.

[0115] Figure 4 It can be seen that the catalyst in Example 1 only reduces Pd to a lower valence state at room temperature, while the catalyst in Comparative Example 1 still has insufficient reduction at 300℃, with a large amount of high-valence Pd remaining. This proves that the strong electrostatic adsorption method can better disperse the active component in the preparation method of this catalyst.

[0116] Comparative Example 2 (1) Same as step (1) in Example 1, except that the same mass of coconut shell activated carbon is used. The isoelectric point of the pretreated activated carbon is lower than that of the activated carbon before treatment. The isoelectric point of the pretreated activated carbon is 5.

[0117] (2) Pd and Re were introduced onto the pretreated activated carbon by excess impregnation. Specifically, 30 mL of HReO4 containing 60 mg Re and Pd(NO3)2 containing 15 mg Pd were added to 3 g of activated carbon and impregnated for 6 h.

[0118] (3) The product obtained above was filtered, dried at 60°C for 12 hours, placed in a tube furnace under N2 atmosphere (nitrogen flow rate of 27 mL / min) and heated to 500°C for 3 hours at a heating rate of 4°C / min. Then it was reduced at 300°C for 3 hours in an atmosphere containing 80% N2 and 20% H2 (flow rate of 100 mL / min) to finally obtain the noble metal catalyst D2.

[0119] Figure 5 The TEM image of D2 shows that the active components are poorly dispersed in the catalyst, with a large amount of agglomeration.

[0120] Comparative Example 3 (1) 5g of coconut shell activated carbon carrier was dispersed in 300mL of 2mol / L HNO3 and pretreated at 60℃ for 3h under N2 atmosphere. The pretreated product was filtered and dried at 60℃ for 12h to obtain pretreated activated carbon. The isoelectric point of the pretreated activated carbon was lower than that of the untreated activated carbon, and the isoelectric point of the pretreated activated carbon was 4.

[0121] (2) Pd and Re were introduced onto the pretreated activated carbon by strong electrostatic adsorption. Specifically, 30 mL of HReO4 containing 60 mg Re and Pd(NO3)2 containing 15 mg Pd were added to 3 g of activated carbon and impregnated for 6 h.

[0122] (3) The product obtained above was filtered, dried at 60°C for 12 hours, placed in a tube furnace under N2 atmosphere (nitrogen flow rate of 27 mL / min) and heated to 500°C for 3 hours at a heating rate of 4°C / min. Then it was reduced at 300°C for 3 hours in an atmosphere containing 80% N2 and 20% H2 (flow rate of 100 mL / min) to finally obtain the noble metal catalyst D3.

[0123] The contents of active components, the dispersion of noble metals, and the valence state results of the noble metal catalysts prepared in the examples and comparative examples are shown in Table 1.

[0124] Table 1

[0125] Table 1 shows that the content of active components in the obtained noble metal catalysts is basically consistent with the theoretical values. The dispersion of noble metals in the noble metal catalysts prepared by the strong electrostatic adsorption method is greater than that in the noble metal catalysts prepared by the equal volume impregnation method and the excess impregnation method. The strong electrostatic adsorption method is beneficial to the full loading of active components and supports, which can further improve the activity of the catalyst.

[0126] Test case 200 mg of noble metal catalyst and 2 wt% gluconic acid aqueous solution (200 mg gluconic acid) were added to a high-pressure reactor. After purging the reactor three times with 1 MPa H2, a 0.2 MPa H2 atmosphere was introduced. The reactor was rotated at 500 rpm and the temperature was 100 °C for 9 h. After the reaction was completed, the pressure was released, the solution in the reactor was filtered, and the product was analyzed by high-performance liquid chromatography. The test results of each catalyst are shown in Table 2.

[0127] The catalysts prepared in the examples and comparative examples were used to catalyze the preparation of adipic acid from gluconic acid in an aqueous system. The conversion rate of gluconic acid and the selectivity of adipic acid were calculated using the external standard method, and the calculation formulas are defined as follows: Conversion rate of gluconic acid = (Initial gluconic acid content - gluconic acid content in product) / Initial gluconic acid content × 100% Adipic acid selectivity = (Adipic acid content in the product / Conversion to gluconic acid content) × 100% Table 2 catalyst Conversion rate of gluconic acid / % Selectivity of adipic acid / % C1 100 93 C2 100 89 C3 100 90 C4 100 86 C5 100 85 C6 100 81 C7 100 47 D1 93 20 D2 89 17 D3 100 23 Figure 6 The noble metal catalyst prepared in Example 1 was used to catalyze the preparation of adipic acid from gluconic acid. The liquid chromatogram of the product after the reaction shows that adipic acid was present at a retention time of 7.1 min.

[0128] Figure 7 The noble metal catalyst prepared in Example 2 was used to catalyze the preparation of adipic acid from gluconic acid. The liquid chromatogram of the product after the reaction shows that adipic acid was present at a retention time of 7.1 min.

[0129] As shown in Table 2, the noble metal catalyst prepared by this invention has the advantages of high gluconic acid conversion rate and high adipic acid selectivity when used in an aqueous system for the catalytic preparation of adipic acid from gluconic acid.

[0130] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A noble metal catalyst, characterized in that, The catalyst includes a support and an active component supported on the support, the active component including noble metals and rhenium, and the support being carbon nanotubes; The dispersion of precious metals is 40-60%.

2. The catalyst according to claim 1, wherein, The dispersion of precious metals is 50-60%; Preferably, the XRD pattern of the noble metal catalyst does not contain characteristic peaks of noble metals.

3. The catalyst according to claim 1 or 2, wherein, XPS analysis showed that the valence state of the precious metal was 0 to +2, preferably 0 to +1.

4. The catalyst according to any one of claims 1-3, wherein, Based on the total amount of catalyst, the content of precious metal elements is 0.25-1 wt%, and the content of rhenium is 1.5-4 wt%. Preferably, based on the total amount of catalyst, the content of precious metal elements is 0.45-0.8 wt%, and the content of rhenium is 1.5-3 wt%.

5. The catalyst according to any one of claims 1-4, wherein, The precious metal is at least one of Pt, Pd, Rh and Ru, preferably Pt and / or Pd, and more preferably Pd; Preferably, the carbon nanotubes are carbon nanotubes with double walls and / or single walls; Preferably, the pore size of the carbon nanotubes is above 2 nm, and more preferably 2-4 nm.

6. A method for preparing a noble metal catalyst, characterized in that, The method includes the following steps: (1) Carbon nanotubes were subjected to acidic pretreatment under an inert atmosphere to obtain pretreated carbon nanotubes. (2) Noble metals and rhenium are introduced onto the pretreated carbon nanotubes by strong electrostatic adsorption. (3) Reduce the product obtained in step (2).

7. The method according to claim 6, wherein, The acid used in the acid pretreatment is selected from at least one of nitric acid, sulfuric acid, hydrochloric acid and hydrofluoric acid, preferably nitric acid; Preferably, the acidic pretreatment includes: contacting the carbon nanotubes with an acid solution under an inert atmosphere, followed by calcination; Preferably, the conditions for contacting carbon nanotubes with acid solution include: a temperature of 60-80°C and a time of 3-6 hours; Preferably, the calcination conditions include: a temperature of 400-550℃ and a time of 2-4 hours; Preferably, the inert atmosphere is selected from at least one of nitrogen, argon and helium.

8. The method according to claim 6 or 7, wherein, The isoelectric point of pretreated carbon nanotubes is lower than that of untreated carbon nanotubes.

9. The method according to any one of claims 6-8, wherein, Step (2) includes: providing an active component mixture containing a noble metal precursor and a rhenium precursor, providing a mixture containing pretreated carbon nanotubes, adjusting the pH of the active component mixture and the mixture containing pretreated carbon nanotubes to above the isoelectric point of the pretreated carbon nanotubes, and mixing the two. Preferably, the pH of the active component mixture and the mixture containing the pretreated carbon nanotubes is adjusted to be 0.5-4 above the isoelectric point of the pretreated carbon nanotubes. Preferably, the mixing includes adding a pH-adjusted mixture of active components to a pH-adjusted mixture containing pretreated carbon nanotubes; Preferably, the mixing time is 2-4 hours.

10. The method according to any one of claims 6-9, wherein, In step (2), the amount of precious metal and rhenium introduced is such that, based on the total amount of catalyst, the content of precious metal is 0.25-1 wt% and the content of rhenium is 1.5-4 wt%. Preferably, based on the total amount of catalyst, the content of precious metal elements is 0.45-0.8 wt%, and the content of rhenium is 1.5-3 wt%.

11. The method according to any one of claims 6-10, wherein, The reduction conditions in step (3) include: being carried out in a hydrogen-containing atmosphere, at a temperature of 20-400℃, preferably 20-50℃, for a time of 0.5-6h, preferably 0.5-3h.

12. The noble metal catalyst prepared by the method according to any one of claims 6-11.

13. The use of the noble metal catalyst according to any one of claims 1-5 and 12 in the preparation of biomass-based carboxylic acid polymer monomers.

14. A method for preparing a biomass-based carboxylic acid polymer monomer, characterized in that, The method includes: In the presence of hydrogen, the noble metal catalyst according to any one of claims 1-5 and 12 is reacted with gluconic acid; Preferably, the reaction is carried out in the presence of water; Preferably, the mass ratio of the gluconic acid to the noble metal catalyst is 1:1-1.5; Preferably, the reaction conditions include: a temperature of 100-150℃, a pressure of 0.1-2MPa, and a time of 3-12h.

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