CN114308107A - Graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst and preparation method and application thereof - Google Patents
Graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst and preparation method and application thereof Download PDFInfo
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- KDLHZDBZIXYQEI-UHFFFAOYSA-N Palladium Chemical compound [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 title claims abstract description 116
- 239000003054 catalyst Substances 0.000 title claims abstract description 76
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- 238000002360 preparation method Methods 0.000 title abstract description 7
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- KZEVSDGEBAJOTK-UHFFFAOYSA-N 1-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)-2-[5-[2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidin-5-yl]-1,3,4-oxadiazol-2-yl]ethanone Chemical compound N1N=NC=2CN(CCC=21)C(CC=1OC(=NN=1)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F)=O KZEVSDGEBAJOTK-UHFFFAOYSA-N 0.000 description 1
- HMUNWXXNJPVALC-UHFFFAOYSA-N 1-[4-[2-(2,3-dihydro-1H-inden-2-ylamino)pyrimidin-5-yl]piperazin-1-yl]-2-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)ethanone Chemical compound C1C(CC2=CC=CC=C12)NC1=NC=C(C=N1)N1CCN(CC1)C(CN1CC2=C(CC1)NN=N2)=O HMUNWXXNJPVALC-UHFFFAOYSA-N 0.000 description 1
- VZSRBBMJRBPUNF-UHFFFAOYSA-N 2-(2,3-dihydro-1H-inden-2-ylamino)-N-[3-oxo-3-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)propyl]pyrimidine-5-carboxamide Chemical compound C1C(CC2=CC=CC=C12)NC1=NC=C(C=N1)C(=O)NCCC(N1CC2=C(CC1)NN=N2)=O VZSRBBMJRBPUNF-UHFFFAOYSA-N 0.000 description 1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/52—Improvements relating to the production of bulk chemicals using catalysts, e.g. selective catalysts
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Abstract
The invention discloses a graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst which comprises the following components in parts by mass: 0.5 part of palladium element, 99.5 parts of graphene-based nitrogen-doped hierarchical pore carbon and 6-14 parts of nitrogen element, wherein the nitrogen element is doped in the graphene-based nitrogen-doped hierarchical pore carbon; the preparation method of the catalyst comprises the following steps: firstly, preparing graphene-based nitrogen-doped phenolic resin by adopting a sol-gel method; secondly, preparing graphene-based nitrogen-doped hierarchical porous carbon by carbonization; thirdly, carrying palladium precursor and then reducing; the invention also discloses the application of the catalyst in the hydrofining of crude terephthalic acid. The nitrogen doped in the catalyst carrier improves the surface chemical property of the catalyst carrier, improves the dispersion degree of palladium and improves the catalytic activity of the catalyst; the invention adopts a sol-gel method combined with carbonization and reduction, and solves the problems of low utilization rate of Pd in the catalyst and poor catalyst activity; the catalyst of the invention has higher activity for hydrofining crude terephthalic acid.
Description
Technical Field
The invention belongs to the technical field of catalysts, and particularly relates to a graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst, and a preparation method and application thereof.
Background
Purified Terephthalic Acid (PTA) is an important organic dibasic acid and is widely used for producing polyester fibers, polyester bottle flakes and polyester films. The typical process of PTA industrial production is a two-step PTA refining process, which is to oxidize Paraxylene (PX) serving as a raw material under the action of a catalyst to prepare crude terephthalic acid. Since the crude terephthalic acid contains 4-carboxybenzaldehyde (4-CBA) as a by-product, the product quality of PTA and the processing performance of subsequent polyester are affected, and a hydrofining step is required for removing the by-product. The PTA hydrorefining reaction is that 4-CBA in crude terephthalic acid is reduced into p-toluic acid which is easy to dissolve in water under the conditions of 270-290 ℃ of temperature and 7.0-8.0 MPa of pressure under the action of palladium-carbon catalyst, and then fiber-grade PTA is prepared through crystallization, separation and drying.
Palladium is the most widely used active component for crude terephthalic acid hydrofinishing at present, and the catalyst commonly used in industrial production at present is an activated carbon supported palladium catalyst, but has some challenges. On the one hand, activated carbon is not favorable for molecular diffusion due to the huge microporous structure therein. Therefore, the porous structure of the carbon material must be carefully designed to enhance mass transfer to improve catalytic efficiency. On the other hand, since activated carbon is chemically inert at its surface and weakly interacts with metals, active metal species show a greater tendency to aggregate and leach on activated carbon, resulting in the leaching and agglomeration of active metal particles, and researchers have attempted to modify carriers to enhance this interaction.
Chinese patent publication No. CN104549239A discloses a catalyst using graphene as a carrier, wherein the catalyst carrier is obtained by reducing graphene oxide, the reduction of a palladium-containing compound and the reduction of graphene oxide are simultaneously carried out by reducing agent microwave method, which has good hydrogenation activity on 4-CBA, but the adopted graphene carrier has a low specific surface area, only 300m2(g), the active surface after loading is smaller.
Chinese patent publication No. CN112237946A discloses a palladium catalyst supported on nitrogen-doped activated carbon, which comprises the following components: 0.1-2 parts of palladium element, 98-100 parts of activated carbon and 1-6 parts of nitrogen element. The nitrogen-doped active carbon-supported palladium-carbon catalyst has high palladium dispersion degree, and the hydrogenation efficiency is obviously improved compared with that of common palladium-carbon when the catalyst is used in the crude terephthalic acid hydrofining reaction. However, the nitrogen content of the carrier is only 6%, and the nitrogen doping effect is not fully exerted.
Disclosure of Invention
The technical problem to be solved by the present invention is to provide a graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst, aiming at the above-mentioned deficiencies of the prior art. The surface chemical property of the carrier is improved by the carrier-doped nitrogen in the graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst, the dispersity of active component metal palladium is improved, the mass transfer performance of the carrier is improved by the hierarchical pore channel structure, and the catalytic activity of the catalyst relative to commercial Pd/C is improved together.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows: the graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst is characterized by comprising the following components in parts by mass: 0.5 part of palladium element, 99.5 parts of graphene-based nitrogen-doped hierarchical pore carbon and 6-14 parts of nitrogen element, wherein the nitrogen element is doped in the graphene-based nitrogen-doped hierarchical pore carbon.
The carrier in the graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst is graphene-based nitrogen-doped hierarchical porous carbon, the surface chemical property of the carrier is improved by the doped nitrogen, the dispersion degree of active component metal palladium is improved, the mass transfer performance of the carrier is improved by the hierarchical pore channel structure, and the catalytic activity of the catalyst relative to commercial Pd/C is improved together.
The graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst is characterized in that the dispersion degree of palladium elements in the catalyst is 33% -55%. The catalyst has high palladium element dispersion degree which is far higher than 23.9 percent of the palladium element dispersion degree in the commercial Pd/C catalyst, thereby having high catalytic activity.
In addition, the invention also discloses a method for preparing the graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst, which is characterized by comprising the following steps:
preparing graphene-based nitrogen-doped phenolic resin by using graphene oxide as a structure directing agent, resorcinol-formaldehyde-melamine as a precursor and a nitrogen source and adopting a sol-gel method;
carbonizing the graphene-based nitrogen-doped phenolic resin prepared in the step one to prepare graphene-based nitrogen-doped hierarchical porous carbon;
and step three, reducing the graphene-based nitrogen-doped hierarchical porous carbon supported palladium precursor prepared in the step two to obtain the graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst.
According to the method, graphene oxide is used as a structure directing agent, resorcinol-formaldehyde-melamine is used as a precursor (namely, a formaldehyde mixed solution of resorcinol and melamine), the melamine is used as a nitrogen source, a sol-gel method is adopted to prepare graphene-based nitrogen-doped phenolic resin, then, the graphene-based nitrogen-doped phenolic resin is carbonized in sequence to obtain three-dimensionally stacked graphene-based nitrogen-doped hierarchical porous carbon nanosheets with nanoscale thickness and high nitrogen content, and the graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst is obtained by reduction after a palladium precursor is supported. The preparation process organically combines the structural advantages of graphene and the chemical advantages of nitrogen doping, improves the mass transfer performance and the surface chemical performance of the carbon carrier, increases the specific surface area of the catalyst, improves the nitrogen doping content in the catalyst, further improves the dispersion degree of active component metal palladium, increases the activity of the catalyst, and solves the problems of low utilization rate of Pd in the catalyst and poor activity of the catalyst in the prior art.
The method is characterized in that the specific process of the sol-gel method in the step one is as follows: firstly, respectively preparing resorcinol-formaldehyde solution, melamine-formaldehyde solution and graphene oxide aqueous dispersion, then mixing and carrying out polymerization reaction under the stirring of water bath; the molar ratio of resorcinol to formaldehyde in the resorcinol-formaldehyde solution is 0.5: 1, the molar ratio of melamine to formaldehyde in the melamine-formaldehyde solution is 0.33: 1, the molar ratio of melamine to resorcinol in the mixed system is 0.5-2: 1, the mass ratio of resorcinol-formaldehyde-melamine to graphene oxide in the mixed system is 40-100: 1; the temperature of the water bath is 80 ℃, and the time of the polymerization reaction is 24 h.
The method as described above, wherein said carbonizing in step two is performed in N2The carbonization is carried out in the atmosphere, the temperature of the carbonization is 800 ℃, and the time of the carbonization is 3 h.
The method is characterized in that in the third step, the palladium precursor is at least one of palladium oxide, palladium acetate, palladium nitrate, chloropalladic acid and sodium chloropalladate, and the reducing agent used for reduction is at least one of formic acid, sodium formate, formaldehyde, hydrazine hydrate, glucose and hydrogen.
The method is characterized in that the palladium precursor is sodium chloropalladate, and the reducing agent is sodium formate.
The invention also discloses an application of the graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst in hydrofining of crude terephthalic acid. The graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst has the advantages of large specific surface area, high nitrogen content, high activity for hydrofining crude terephthalic acid and high application value.
Compared with the prior art, the invention has the following advantages:
1. the surface chemical property of the carrier is improved by the carrier-doped nitrogen in the graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst, the dispersity of active component metal palladium is improved, the mass transfer performance of the carrier is improved by the hierarchical pore channel structure, and the catalytic activity of the catalyst relative to commercial Pd/C is improved together.
2. The catalyst of the invention has the advantages of the thickness of a catalyst sheet layer of only 20nm, the nitrogen content of nearly 13.5 percent, the dispersion degree of surface palladium of 55 percent and the average grain diameter of only 2.0 nm.
3. According to the preparation method, graphene oxide is used as a structure directing agent, resorcinol-formaldehyde-melamine is used as a precursor and a nitrogen source, and carbonization and reduction are combined by adopting a sol-gel method to obtain the graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst, so that the structural advantages and the nitrogen-doped chemical advantages of graphene are organically combined, the specific surface area and the nitrogen-doped content of the catalyst are increased, the activity of the catalyst is increased, and the problems of low utilization rate of Pd in the catalyst and poor activity of the catalyst are solved.
4. According to the invention, the nitrogen content and the thickness of the sheet layer of the carrier are regulated and controlled by changing the molar ratio of the precursor melamine to the resorcinol and the mass ratio of the resorcinol-formaldehyde-melamine to the graphene oxide.
5. The graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst has the advantages of large specific surface area, high nitrogen content, high activity for hydrofining crude terephthalic acid and high application value.
The technical solution of the present invention is further described in detail by examples below.
Detailed Description
Examples 1 to 6 of the present invention and comparative example 1 employ H2-O2The dispersion degree of Pd in each catalyst is measured by a titration method, and the specific measurement process is as follows: the method comprises the steps of adopting an AutoChemII2920 chemical adsorption instrument of Michman instruments company in America as detection equipment, reducing a catalyst sample in a hydrogen atmosphere at 200 ℃, switching to an inert gas atmosphere to blow until a baseline is stable, switching to oxygen to oxidize, reducing an oxide by using pulse hydrogen, calculating the atomic number of surface metal palladium according to the hydrogen consumption, and further calculating to obtain the dispersion degree of Pd.
Nitrogen content in each catalyst was measured using an Elemental analyzer (Elemental variance EL III) in examples 1 to 6 of the present invention and comparative example 1; the surface morphology of each catalyst sample was observed using a JEOL 7100F field emission Scanning Electron Microscope (SEM) to estimate the catalyst lamella thickness.
Example 1
The graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst comprises the following components in parts by mass: 0.5 part of palladium element, 99.5 parts of graphene-based nitrogen-doped hierarchical pore carbon and 9.1 parts of nitrogen element, wherein the nitrogen element is doped in the graphene-based nitrogen-doped hierarchical pore carbon.
The preparation method of the graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst comprises the following steps:
step one, fixing the volume of 7.5g of Graphene Oxide (GO) water dispersion mother liquor of 12mg/mL to 50mL by using deionized water, and ultrasonically dispersing for 1h to obtain a GO dispersion liquid; mixing 2.85g of resorcinol (R) and 4.2g of formaldehyde (F) solution with the mass concentration of 37%, fixing the volume to 50mL by using deionized water, and then carrying out water bath at 40 ℃ for 30min to obtain a mixture with the molar ratio of R to F of 0.5: 1 RF solution; 3.26g of melamine (M) and 6.3g of a 37% formaldehyde (F) solution are mixed, deionized water is used for metering to 50mL, and then water bath is carried out at 80 ℃ for 15min, so that the molar ratio of M to F is 0.33: 1 in MF solution;
mixing the GO dispersion liquid, the RF solution and the MF solution, stirring in a water bath at 80 ℃ for 24 hours, filtering, and drying at 80 ℃ to obtain the material with the RMF/GO mass ratio of 40: 1. the molar ratio of M/R is 1: 1 graphene-based nitrogen-doped phenolic resin;
step two, adding the graphene-based nitrogen-doped phenolic resin prepared in the step one into N2Under the protection of airflow, heating to 800 ℃ at a heating rate of 1 ℃/min, and standing for 3 hours for carbonization to prepare graphene-based nitrogen-doped hierarchical porous carbon;
and step three, taking the graphene-based nitrogen-doped hierarchical porous carbon prepared in the step two as a carrier, soaking the carrier by adopting an aqueous solution of sodium chloropalladate, and reducing the carrier by sodium formate to obtain the graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst.
The palladium precursor in this embodiment may be replaced with at least one of palladium oxide, palladium acetate, palladium nitrate, chloropalladic acid, and sodium chloropalladate other than sodium chloropalladate, and the reducing agent used for reduction may be replaced with at least one of formic acid, sodium formate, formaldehyde, hydrazine hydrate, glucose, and hydrogen other than sodium formate.
Examples 2 to 6
According to the steps and the operation conditions of example 1, the graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst is prepared by only changing the molar ratio of melamine to resorcinol and the mass ratio of resorcinol-formaldehyde-melamine to graphene oxide, and the specific numerical values are shown in table 1.
TABLE 1
| Catalyst and process for preparing same | Molar ratio of M/R | Mass ratio RMF/GO |
| Example 1 | 1：1 | 40：1 |
| Example 2 | 1：1 | 60：1 |
| Example 3 | 1：1 | 80：1 |
| Example 4 | 1：1 | 100：1 |
| Example 5 | 0.5：1 | 40：1 |
| Example 6 | 2：1 | 40：1 |
Detecting the nitrogen content, the Pd dispersion degree and the lamella thickness of the graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst prepared in the embodiments 1 to 6 of the invention; the graphene-based nitrogen-doped hierarchical porous carbon supported Pd catalysts prepared in embodiments 1 to 6 of the present invention and commercial porous carbon supported Pd catalysts (abbreviated as Pd/C, palladium loading 0.5%) purchased in the market are applied to the hydrofining of crude terephthalic acid (4-CBA), respectively, and the specific processes and conditions are as follows: the catalyst loading was 2.0g, crude terephthalic acid 30.0g, 4-CBA1.0 g, and aqueous solution 900.0mL, catalytic reduction was carried out in a stainless steel stirred batch autoclave at a pressure of 7.5MPa and a temperature of 280 deg.C, quantitative analysis was carried out on the reacted liquid product using high performance liquid chromatography with an ultraviolet detector, the catalyst activity was evaluated by calculating the residual 4-CBA content, the lower the residual 4-CBA content, indicating the higher the catalytic hydrogenation efficiency of the catalyst, and the results are shown in Table 2.
TABLE 2
As can be seen from table 2, the nitrogen content of the graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst prepared in examples 1 to 6 of the present invention is significantly higher than that of the commercial product Pd/C not doped with nitrogen, the dispersion degree of Pd is greatly increased, the thickness of the sheet layer is small, and the activity of the catalyst applied to the hydrofining of crude terephthalic acid (4-CBA) is as high as 99.6%, which is improved compared with that of the commercial product Pd/C.
The above description is only for the preferred embodiment of the present invention, and is not intended to limit the present invention in any way. Any simple modification, change and equivalent changes of the above embodiments according to the technical essence of the invention are still within the protection scope of the technical solution of the invention.
Claims (8)
1. The graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst is characterized by comprising the following components in parts by mass: 0.5 part of palladium element, 99.5 parts of graphene-based nitrogen-doped hierarchical pore carbon and 6-14 parts of nitrogen element, wherein the nitrogen element is doped in the graphene-based nitrogen-doped hierarchical pore carbon.
2. The graphene-based nitrogen-doped hierarchical porous carbon-supported palladium catalyst according to claim 1, wherein the dispersion degree of palladium elements in the catalyst is 33% to 55%.
3. A method of preparing the graphene-based nitrogen-doped hierarchical porous carbon-supported palladium catalyst of claim 1 or 2, comprising the steps of:
preparing graphene-based nitrogen-doped phenolic resin by using graphene oxide as a structure directing agent, resorcinol-formaldehyde-melamine as a precursor and a nitrogen source and adopting a sol-gel method;
carbonizing the graphene-based nitrogen-doped phenolic resin prepared in the step one to prepare graphene-based nitrogen-doped hierarchical porous carbon;
and step three, reducing the graphene-based nitrogen-doped hierarchical porous carbon supported palladium precursor prepared in the step two to obtain the graphene-based nitrogen-doped hierarchical porous carbon supported palladium catalyst.
4. The method according to claim 3, wherein the sol-gel method in the first step comprises the following specific processes: firstly, respectively preparing resorcinol-formaldehyde solution, melamine-formaldehyde solution and graphene oxide aqueous dispersion, then mixing and carrying out polymerization reaction under the stirring of water bath; the molar ratio of resorcinol to formaldehyde in the resorcinol-formaldehyde solution is 0.5: 1, the molar ratio of melamine to formaldehyde in the melamine-formaldehyde solution is 0.33: 1, the molar ratio of melamine to resorcinol in the mixed system is 0.5-2: 1, the mass ratio of resorcinol-formaldehyde-melamine to graphene oxide in the mixed system is 40-100: 1; the temperature of the water bath is 80 ℃, and the time of the polymerization reaction is 24 h.
5. The method of claim 3, wherein the carbonizing in step two is at N2The carbonization is carried out in the atmosphere, the temperature of the carbonization is 800 ℃, and the time of the carbonization is 3 h.
6. The method of claim 3, wherein the palladium precursor in step three is at least one of palladium oxide, palladium acetate, palladium nitrate, chloropalladic acid and sodium chloropalladate, and the reducing agent used for the reduction is at least one of formic acid, sodium formate, formaldehyde, hydrazine hydrate, glucose and hydrogen.
7. The method of claim 6, wherein the palladium precursor is sodium chloropalladate and the reducing agent is sodium formate.
8. Use of the graphene-based nitrogen-doped hierarchical porous carbon-supported palladium catalyst of claim 1 or 2 in hydrofinishing of crude terephthalic acid.
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