Method for high-selectivity catalytic synthesis of biodiesel precursor

Abstract

The invention discloses a method for high-selectivity catalytic synthesis of a biodiesel precursor, which comprises the following steps: (1) aldol condensation reaction based on levulinic acid and furfural to prepare an oxygen-containing compound in a diesel carbon number range; (2) under the catalytic action of a composite catalyst system consisting of Pd / C and boric acid, carrying out hydrodeoxygenation reaction on an oxygen-containing compound to obtain a biodiesel precursor in the form of carboxylic acid; wherein in the hydrodeoxygenation reaction, the hydrogen pressure is 2-3 MPa, the reaction temperature is 250-255 DEG C, the reaction time is 12-16 h, and the mass ratio of the total addition amount of the composite catalyst system to the oxygen-containing compound is (3-3.5): 2. According to the method disclosed by the invention, a Pd / C and boric acid composite catalyst system with high catalytic activity is selected in the hydrodeoxygenation reaction process, and meanwhile, the hydrogen pressure, the reaction temperature and the reaction time in the hydrodeoxygenation reaction process are cooperatively controlled, so that the yield and the yield of a biodiesel precursor capric acid are greatly improved while the reaction efficiency is greatly improved; the high selectivity of a target product in the hydrodeoxygenation reaction process is realized.

Description

Technical Field

[0001] The present invention relates to a method for highly selective catalytic synthesis of a biodiesel precursor. Background Art

[0002] Diesel is a very important strategic energy material. Its main components are hydrocarbons such as alkanes, cycloalkanes and aromatic hydrocarbons, containing a small amount of sulfur, and it is divided into light diesel (about 0.8 - 0.85 g / cm -3 ) and heavy diesel (about 0.88 - 0.98 g / cm -3 ). Light diesel is suitable for high-speed diesel engines (such as cars and light trucks); heavy diesel has high viscosity and is mainly used in ships, power plants and heavy machinery.

[0003] As one of the most abundant renewable organic resources on the earth, biomass originates from the metabolic activities of plants, animals and microorganisms, and is an important raw material for biomanufacturing, biofuels and high-value chemicals. Currently, the methods for preparing biodiesel from biomass are as follows: (1) depolymerization of cellulose, lignin and hemicellulose to prepare biomass platform compounds, such as furfural, levulinic acid and 5-methylfurfural, etc.; (2) carbon-carbon coupling of biomass platform compounds to obtain oxygen-containing compounds within the diesel carbon number range, and then using a hydrodeoxygenation catalyst to catalyze to obtain alkanes or fatty acids; (3) converting fatty acids into long-chain fatty acid esters through an esterification reaction to finally obtain diesel. In the above methods, the current technical bottlenecks in selective hydrodeoxygenation are: on the one hand, the hydrodeoxygenation catalytic system selected in the hydrodeoxygenation reaction process mostly relies on noble metal / solid acid bifunctional catalysts, and this catalyst system has problems such as high preparation cost, difficult separation of products from the catalyst, and easy loss of active components; on the other hand, the hydrodeoxygenation process cannot be precisely controlled during the hydrodeoxygenation reaction, resulting in side reactions of hydrogenolysis (C-C bond cleavage) and over-hydrogenation, thereby leading to a decrease in the selectivity of the target product (biodiesel precursor). Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a method for highly selective catalytic synthesis of a biodiesel precursor. This method can greatly improve the selectivity of the target product (biodiesel precursor) during the hydrodeoxygenation reaction by selecting a specific highly reactive hydrodeoxygenation catalyst system and synergistically controlling the reaction conditions.

[0005] Technical Solution: The method for highly selective catalytic synthesis of a biodiesel precursor according to the present invention includes the following steps:

[0006] (1) Based on the aldol condensation reaction of levulinic acid and furfural, prepare an oxygen-containing compound (condensation product) within the diesel carbon number range;

[0007] (2) Under the catalytic action of a composite catalyst system composed of Pd / C and boric acid, the oxygen-containing compound is subjected to a hydrodeoxygenation reaction to obtain a biodiesel precursor in the form of a carboxylic acid; wherein, in the hydrodeoxygenation reaction, the hydrogen pressure is 2 to 3 MPa, the reaction temperature is 250 to 255°C, the reaction time is 12 to 16 h, and the mass ratio of the total amount of the composite catalyst system added to the oxygen-containing compound is 3 to 3.5:2.

[0008] Wherein, in step (2), in the composite catalyst system composed of Pd / C and boric acid, the composite mass ratio of Pd / C and boric acid is 1:2 to 2.5.

[0009] The Pd / C is prepared by the following method: PdCl2 and activated carbon are dispersed in ultrapure water, stirred thoroughly and dried at high temperature overnight, and the obtained solid is reduced at high temperature in a H2 atmosphere to obtain a Pd / C catalyst.

[0010] Among them, the added mass ratio of PdCl2 to activated carbon is 0.013-0.015:1.

[0011] The stirring temperature is 70-80°C and the stirring time is 5-6h.

[0012] Among them, the drying temperature is 80-100°C and the drying time is 12-24h.

[0013] The reduction temperature is 500-550°C, the heating rate is 5°C / min, and the reduction time is 2.5-3.0h.

[0014] Wherein, in the Pd / C catalyst, the loading amount of metal Pd on the activated carbon is 0.5-2% of the mass of the catalyst (the mass of metal Pd accounts for 0.5-2% of the total mass of the catalyst).

[0015] The Pd / C is carboxyl-modified Pd / C, and the specific modification method is: in the process of preparing Pd / C, acetic acid is added to the mixed solution of PdCl2 and activated carbon, wherein the mass ratio of the added acetic acid to the activated carbon is 0.3-0.5:1; the rest of the reaction process is the same as that of preparing Pd / C, and a carboxyl-modified Pd / C catalyst is obtained.

[0016] The carboxyl-modified Pd / C uses activated carbon as a carrier, and Pd reaction active sites are loaded on the activated carbon, and Pd atoms are embedded in the pores of the activated carbon; the carboxyl groups are connected to the activated carbon in the form of CC covalent bonds. Activated carbon provides a higher carbon specific surface area, porous structure and defect sites, and Pd atoms are physically embedded in the pores of the activated carbon; the carboxyl groups are connected to the activated carbon in the form of CC covalent bonds.

[0017] In the composite catalyst system of the present invention, Pd / C activates H2, activates the double bond or carbonyl group in the substrate, and realizes selective deoxygenation with the acidic sites provided by boric acid; boric acid provides appropriate acidic sites and proton H+, promoting the deoxygenation reaction. During the reaction process, boric acid will embed into the pores of activated carbon, thereby expanding the specific surface area of the carrier and enhancing the dispersion of Pd particles, achieving effective inhibition of catalyst coking while improving the hydrogenation activity of Pd metal particles, and further enabling the catalytic system to have good catalytic activity and reaction stability, ultimately realizing the high-selectivity preparation of the biodiesel precursor capric acid (the obtained capric acid is further processed through existing traditional esterification processes to obtain high-quality biodiesel).

[0018] Advantages: Compared with the prior art, the present invention has the following remarkable advantages: In the method of the present invention, a composite catalyst system of Pd / C and boric acid with high catalytic activity is selected during the hydrodeoxygenation reaction process, and at the same time, the hydrogen pressure, reaction temperature, and reaction time of the hydrodeoxygenation reaction process are synergistically controlled, achieving a significant increase in the reaction efficiency while significantly increasing the yield and production rate of the biodiesel precursor capric acid, and realizing high selectivity for the target product during the hydrodeoxygenation reaction process; in addition, since boric acid is in a liquid state above 180°C, effective contact between liquid boric acid and the reactants can be achieved. After the reaction ends and the product cools, boric acid re-solidifies to form a natural physical isolation layer, thereby realizing the simple separation of the catalyst and the product. Brief Description of the Drawings

[0019] Figure 1 is a flow chart of the method of the present invention;

[0020] Figure 2 is a gas chromatogram of the condensation product synthesized by the aldol condensation of furfural and levulinic acid in Example 1;

[0021] Figure 3 is a mass spectrum of the condensation product synthesized by the aldol condensation of furfural and levulinic acid in Example 1;

[0022] Figure 4 is a comparison chart of the products after the hydrodeoxygenation reaction of the condensation product catalyzed by different catalysts in Example 1 and Comparative Examples 11 - 13;

[0023] Figure 5 is a mass spectrum of the biodiesel precursor capric acid obtained after the hydrodeoxygenation reaction of the condensation product in Example 1;

[0024] Figure 6 is a mass spectrum of γ-decalactone obtained after the hydrodeoxygenation reaction of the condensation product in Example 1. Detailed Embodiments

[0025] Example 1

[0026] The method for highly selectively catalytically synthesizing a biodiesel precursor of the present invention comprises the following steps:

[0027] (1) Preparation of the condensation product from furfural and levulinic acid:

[0028] Place anhydrous sodium carbonate (36 g) and levulinic acid (LA, 27.8 g) in a three-necked flask, add 150 mL of ultrapure water thereto, and heat in a water bath to 90 °C; slowly add dropwise a mixed solution of furfural (FA, 11.52 g) and ethanol (24 mL) to carry out an aldol condensation reaction; after the reaction, add dilute HCl for acidification to obtain a yellow granular product, then wash with 2 - 3 L of ultrapure water and filter; freeze-dry the obtained solid to obtain the condensation product; the qualitative analysis of the product is carried out by an Agilent 7890A gas chromatography system equipped with an HP-5 capillary column and an FID detector, the vaporization chamber is maintained at 280 °C, the column oven temperature ranges from 40 °C (held for 3 minutes) to 280 °C (held for 3 minutes) at a rate of 10 °C / min; at the same time, NMR (nuclear magnetic resonance, Bruker AVANCE500 MHz) is also used for the qualitative analysis of the target product, and the gas chromatogram and mass spectrum of the target product are as Figures 2 - 3 shown;

[0029] (2) Charge 0.1 g of the condensation product, 0.05 g of Pd / C catalyst (in the Pd / C catalyst, the Pd loading is 0.8 wt.%), 0.1 g of boric acid, and 10 mL of cyclohexane into a 50 mL batch reactor. The reactor is purged with hydrogen three times and filled with 3 MPa H2, and the reactor is heated to 250 °C under vigorous stirring and reacted for 12 h; after the reaction, remove the composite catalyst (the composite catalyst composed of Pd / C catalyst and boric acid) by filtration; quantitatively analyze the product on an Agilent7890A gas chromatography system equipped with an HP-5 capillary column and an FID detector, using dodecane as the internal standard substance and the internal standard method as the quantitative method; the mass spectrum of the obtained product is as Figures 5 - 6 shown.

[0030] In this example, the Pd / C catalyst is prepared by the following method: Disperse 0.0134 g of PdCl2 and 1 g of activated carbon in 30 mL of ultrapure water; stir magnetically at 70 °C for 5 h; then dry the sample overnight at 100 °C, and finally carry out a reduction reaction in a H2 atmosphere at 550 °C at a heating rate of 5 °C / min for 3 hours.

[0031] In this example, the yield of capric acid is 41.9%, the yield of alkane is 3.2%, and the yield of γ-decalactone is 20.9%.

[0032] The reaction degree of hydrodeoxygenation is reflected by the production amounts of alkane and γ-decalactone. The alkane yield represents complete hydrodeoxygenation, and γ-decalactone represents insufficient hydrodeoxygenation.

[0033] Example 2

[0034] The method for highly selective catalytic synthesis of biodiesel precursors in the present invention comprises the following steps:

[0035] (1) Preparation of a condensation product based on furfural and levulinic acid:

[0036] Place anhydrous sodium carbonate (36 g) and levulinic acid (LA, 27.8 g) in a three-necked flask, add 150 mL of ultrapure water thereto, and heat in a water bath to 90 °C; slowly dropwise add a mixed solution of furfural (FA, 11.52 g) and ethanol (24 mL) to carry out an aldol condensation reaction; after the reaction, add dilute HCl for acidification to obtain a yellow granular product, then wash with 2 - 3 L of ultrapure water and filter; freeze-dry the obtained solid to obtain the condensation product;

[0037] (2) Charge 0.1 g of the condensation product, 0.05 g of Pd / C catalyst (in the Pd / C catalyst, the loading amount of Pd is 0.8 wt.%), 0.1 g of boric acid, and 10 mL of cyclohexane into a 50 mL batch reactor. The reactor is purged with hydrogen three times and filled with 3 MPa H2. Heat the reactor to 250 °C under vigorous stirring and react for 12 h; after the reaction, remove the composite catalyst (the composite catalyst composed of Pd / C catalyst and boric acid) by filtration; quantitatively analyze the product on an Agilent 7890A gas chromatography system equipped with an HP-5 capillary column and an FID detector, using dodecane as the internal standard substance and the internal standard method as the quantitative method.

[0038] In this example, the Pd / C catalyst is prepared by the following method: Disperse 0.0134 g of PdCl2 and 1 g of activated carbon in 30 mL of ultrapure water, and then add 0.5 g of acetic acid thereto; magnetically stir at 70 °C for 5 h; then dry the sample overnight at 100 °C, and finally carry out a reduction reaction in a H2 atmosphere at 550 °C at a heating rate of 5 °C / min for 3 hours.

[0039] In this example, the yield of capric acid is 55.7%, the yield of alkane is 4.0%, and the yield of γ-decalactone is 12.0%.

[0040] Example 3

[0041] The method for preparing capric acid in Example 3 is exactly the same as that in Example 1, and the only difference is that: in the Pd / C catalyst, the loading amount of Pd is 0.5 wt.%, and the obtained yield of capric acid is 40.6%, the yield of alkane is 4.1%, and the yield of γ-decalactone is 22%.

[0042] Example 4

[0043] Example 4 was exactly the same as Example 1 in the method for preparing capric acid, and the only difference was that in the Pd / C catalyst, the loading amount of Pd was 2 wt.%, the yield of capric acid obtained was 42.4%, the yield of alkane was 4.6%, and the yield of δ-decalactone was 17.4%.

[0044] Comparative Example 1

[0045] Comparative Example 1 was exactly the same as Example 1 in the method for preparing capric acid, and the only difference was that in the Pd / C catalyst, the loading amount of Pd was 0.3 wt.%, the yield of capric acid obtained was 35.5%, the yield of alkane was 2.2%, and the yield of δ-decalactone was 20.4%.

[0046] Comparative Example 2

[0047] Comparative Example 2 was exactly the same as Example 1 in the method for preparing capric acid, and the only difference was that in the Pd / C catalyst, the loading amount of Pd was 3 wt.%, the yield of capric acid obtained was 34.3%, the yield of alkane was 21.7%, and the yield of δ-decalactone was 17.6%.

[0048] When the loading amount of Pd is too high, it will cause excessive cleavage of C-C bonds, resulting in an increase in the yield of alkanes.

[0049] It can be seen from the comparison of Example 1, 3, 4 and Comparative Examples 1-2 that there is a synergistic effect between Pd / C and H3BO3, which can achieve high selectivity for the formation of capric acid under the condition of low Pd loading. As the Pd loading increases, the selectivity of capric acid slightly increases, and the yield remains at about 40%. And δ-decalactone is further hydrogenolyzed and transformed due to the increase in the content of hydrogenation metal (Pd); when the loading amount is too high, it will lead to the intensification of the hydrogenolysis reaction, causing the cleavage of C-C bonds and an increase in the yield of alkanes.

[0050] Comparative Example 3

[0051] Comparative Example 3 was exactly the same as Example 1 in the method for preparing capric acid, and the only difference was that during the hydrodeoxygenation reaction, the reaction temperature was 230 °C, the yield of capric acid obtained was 30.2%, the yield of alkane was 1.2%, and the yield of δ-decalactone was 26.6%.

[0052] Comparative Example 4

[0053] Comparative Example 4 was exactly the same as Example 1 in the method for preparing capric acid, and the only difference was that during the hydrodeoxygenation reaction, the reaction temperature was 270 °C, the yield of capric acid obtained was 31.6%, the yield of alkane was 2.0%, and the yield of δ-decalactone was 15.7%.

[0054] It can be seen from the comparison between Example 1 and Comparative Examples 3 to 4 that as the reaction temperature increases, the yield of capric acid increases significantly, the yields of δ-decalactone and alkanes increase slightly, while too high a temperature results in a significant decrease in the yields of all three.

[0055] Example 5

[0056] The method for preparing capric acid in Example 5 is exactly the same as that in Example 1, with the only difference being that during the hydrodeoxygenation reaction, the hydrogen pressure is 2 MPa. The yield of capric acid obtained is 42.4%, the yield of alkanes is 2.1%, and the yield of δ-decalactone is 20.6%.

[0057] Comparative Example 5

[0058] The method for preparing capric acid in Comparative Example 5 is exactly the same as that in Example 1, with the only difference being that during the hydrodeoxygenation reaction, the hydrogen pressure is 1 MPa. The yield of capric acid obtained is 34.9%, the yield of alkanes is 1.5%, and the yield of δ-decalactone is 17.5%.

[0059] Comparative Example 6

[0060] The method for preparing capric acid in Comparative Example 6 is exactly the same as that in Example 1, with the only difference being that during the hydrodeoxygenation reaction, the hydrogen pressure is 4 MPa. The yield of capric acid obtained is 23.9%, the yield of alkanes is 1.2%, and the yield of δ-decalactone is 20.9%.

[0061] It can be seen from the comparison between Example 1, 5 and Comparative Examples 5 to 6 that the adjustment of hydrogen pressure can effectively control the progress of the hydrogenation reaction, enabling the oxygenated compounds to exactly react to the state of the biodiesel precursor in the form of carboxylic acid during the hydrogenation reaction without over-hydrogenation.

[0062] Example 6

[0063] The method for preparing capric acid in Example 6 is exactly the same as that in Example 1, with the only difference being that during the hydrodeoxygenation reaction, the reaction time is 16 h. The yield of capric acid obtained is 38.6%, the yield of alkanes is 2.7%, and the yield of δ-decalactone is 18.7%.

[0064] Comparative Example 7

[0065] The method for preparing capric acid in Comparative Example 7 is exactly the same as that in Example 1, with the only difference being that during the hydrodeoxygenation reaction, the reaction time is 8 h. The yield of capric acid obtained is 30.9%, the yield of alkanes is 1.4%, and the yield of δ-decalactone is 24.1%.

[0066] Comparative Example 8

[0067] The method for preparing capric acid in Comparative Example 8 was exactly the same as that in Example 1, and the only difference was that during the hydrodeoxygenation reaction, the reaction time was 20 h, the yield of capric acid was 35.2%, the yield of alkane was 3.6%, and the yield of γ-decalactone was 14.1%.

[0068] It can be seen from the comparison of Example 1, Example 6 and Comparative Examples 7-8 that as the reaction time prolongs, the yield of capric acid gradually increases. However, after 12 h, the yield of capric acid decreases significantly, indicating that excessive hydrodehydrogenation side reactions will occur when the reaction time is too long.

[0069] Comparative Example 9

[0070] The method for preparing capric acid in Comparative Example 9 was exactly the same as that in Example 1, and the only difference was that during the hydrodeoxygenation reaction, the mass ratio of Pd / C catalyst to boric acid added was 1:1. The yield of capric acid obtained was 19.9%, the yield of alkane was 30.5%, and the yield of γ-decalactone was 17.1%.

[0071] Comparative Example 10

[0072] The method for preparing capric acid in Comparative Example 10 was exactly the same as that in Example 1, and the only difference was that during the hydrodeoxygenation reaction, the mass ratio of Pd / C catalyst to boric acid added was 1:3. The yield of capric acid obtained was 20.7%, the yield of alkane was 17.0%, and the yield of γ-decalactone was 18.5%.

[0073] It can be seen from the comparison of Example 1 and Comparative Examples 9-10 that an appropriate metal / acid ratio can improve the yield of capric acid by balancing the synergistic effect of surface active sites and acidic sites. When the amount of acid is low, the deoxygenation activity of the reaction system is insufficient and the hydrodeoxygenation performance is poor. When the amount of acid is too high, coking will occur, resulting in a decrease in the activity of the Pd / C catalyst and being unfavorable for the reaction to proceed.

[0074] Comparative Example 11

[0075] The method for preparing capric acid in Comparative Example 11 was exactly the same as that in Example 1, and the only difference was that during the hydrodeoxygenation reaction, the catalyst was Pd / C catalyst, and the hydrodeoxygenation performance was poor, and the main products were furan compounds such as 2-n-butyltetrahydrofuran.

[0076] Comparative Example 12

[0077] The method for preparing capric acid in Comparative Example 12 was exactly the same as that in Example 1, and the only difference was that during the hydrodeoxygenation reaction, the catalyst was a composite catalyst composed of C and boric acid, in which the mass ratio of C to boric acid added was 1:2, the substrate conversion rate was low, and the main products were furan compounds such as 2-n-butyltetrahydrofuran.

[0078] Comparative Example 13

[0079] The method for preparing capric acid in Comparative Example 13 was exactly the same as that in Example 1, with the only difference being that during the hydrodeoxygenation reaction, the catalyst was composed of boric acid, and the substrate conversion rate was extremely low, and no target product was formed.

[0080] From the comparison between Example 1 and Comparative Examples 11 to 13, it can be seen that there is a synergistic effect between Pd / C and boric acid. Pd / C has the function of activating H2 and has weak acidity, which can carry out partial hydrodeoxygenation reaction on the substrate. H3BO3 provides appropriate acidic sites for the system to promote the formation of capric acid.

[0081] Comparative Example 14

[0082] The method for preparing capric acid in Comparative Example 14 was exactly the same as that in Example 2, with the only difference being that during the preparation of the Pd / C catalyst, the addition amount of acetic acid was 0.3 g, and the obtained yield of capric acid was 32.6%, the yield of alkane was 1.1%, and the yield of γ-decalactone was 36.1%.

[0083] Comparative Example 15

[0084] The method for preparing capric acid in Comparative Example 15 was exactly the same as that in Example 2, with the only difference being that during the preparation of the Pd / C catalyst, the addition amount of acetic acid was 0.7 g, and the obtained yield of capric acid was 23.0%, the yield of alkane was 1.0%, and the yield of γ-decalactone was 32.9%.

[0085] From the comparison between Example 2 and Comparative Examples 14 to 15, it can be seen that after modification with acetic acid, carboxyl groups are connected to the surface of Pd / C, increasing the acidic sites on the surface of the Pd / C catalyst and promoting the formation of capric acid. If the content of acetic acid is too high, it will promote the reaction to proceed to side reactions, generating decanol, decyl capric acid ester, decyl ether, etc., and instead reducing the yield of capric acid.

Claims

1. A method for highly selective catalytic synthesis of biodiesel precursors, characterized in that: The steps include: (1) preparing oxygenated compounds within the diesel carbon number range based on the aldol condensation reaction of levulinic acid and furfural; (2) Under the catalytic action of a composite catalyst system composed of Pd / C and boric acid, the oxygen-containing compound is subjected to a hydrodeoxygenation reaction to obtain a biodiesel precursor in the form of a carboxylic acid; wherein, in the hydrodeoxygenation reaction, the hydrogen pressure is 2 to 3 MPa, the reaction temperature is 250 to 255°C, the reaction time is 12 to 16 h, and the mass ratio of the total amount of the composite catalyst system added to the oxygen-containing compound is 3 to 3.5:

2.

2. The method according to claim 1, characterized in that: In step (2), in the composite catalyst system composed of Pd / C and boric acid, the composite mass ratio of Pd / C to boric acid is 1:2 to 2.

5.

3. The method according to claim 2, characterized in that: The Pd / C is prepared by the following method: specifically, PdCl2 and activated carbon are dispersed in ultrapure water, fully stirred and dried at high temperature overnight, and the obtained solid is reduced at high temperature in a H2 atmosphere to obtain a Pd / C catalyst.

4. The method according to claim 3, characterized in that: The added mass ratio of PdCl2 to activated carbon is 0.013-0.015:

1.

5. The method according to claim 3, characterized in that: The stirring temperature is 70-80°C and the stirring time is 5-6h.

6. The method according to claim 3, characterized in that: The drying temperature is 80-100°C and the drying time is 12-24h.

7. The method according to claim 3, characterized in that: The reduction temperature is 500-550°C, the heating rate is 5°C / min, and the reduction time is 2.5-3.0h.

8. The method according to claim 3, characterized in that: In the Pd / C catalyst, the loading amount of metal Pd on the activated carbon is 0.5-2% of the mass of the Pd / C catalyst.

9. The method according to claim 2, characterized in that: The Pd / C is carboxyl-modified Pd / C, and the specific modification method is: in the process of preparing Pd / C, acetic acid is added to a mixed solution of PdCl2 and activated carbon, wherein the mass ratio of the added acetic acid to the activated carbon is 0.3-0.5:1; and a carboxyl-modified Pd / C catalyst is obtained.

10. The method according to claim 9, characterized in that: The carboxyl-modified Pd / C uses activated carbon as a carrier, on which Pd reaction active sites are loaded, and Pd atoms are embedded in the pores of the activated carbon; the carboxyl group is connected to the activated carbon in the form of a CC covalent bond.

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