High-dispersity palladium carbon catalyst and preparation method thereof

Abstract

The invention provides a high-dispersity palladium-carbon catalyst and a preparation method thereof, and belongs to the field of hydrogenation catalysts. According to the preparation method, fructose is taken as a bio-based carbon source, fructose-based carbon aerogel is synthesized under the action of cyano ionic liquid, then the fructose-based carbon aerogel is added into an aqueous solution of a palladium-containing compound, and the palladium-carbon catalyst taking the fructose-based carbon aerogel as the carrier is obtained through freeze drying, high-temperature carbonization and reduction treatment. On one hand, fructose as a carbon source has the characteristics of wide source, reproducibility and greenness; on the other hand, 1, 1 '-dimethyl-1H, 1' H-[2, 2 '] biimidazole and 4-chlorobutyronitrile are used as main reactants to prepare cyano ionic liquid, cyano is an active unsaturated group and can be subjected to a coupling reaction with fructose to obtain a crosslinking monomer with positive charges, and electrostatic repulsion can inhibit agglomeration of a palladium-carbon catalyst, so that the ionic liquid can be used for preparing a high-molecular polymer; therefore, the prepared palladium-carbon catalyst has good dispersity.

Description

Technical Field

[0001] The invention relates to the technical field of hydrogenation catalysts, and in particular to a highly dispersed palladium-carbon catalyst and a preparation method thereof. Background Art

[0002] Palladium-carbon (Pd / C) catalyst is a commonly used hydrogenation catalyst, which can be widely used in the field of hydrogenation of double bonds, nitro groups, nitroso groups and carbonyl groups. Traditional palladium-carbon catalyst refers to a catalyst that uses activated carbon as a carrier and loads palladium on activated carbon. Among them, activated carbon has a large surface area, a good pore structure and a relatively rich surface group, which makes the palladium-carbon catalyst have good catalytic activity as a whole, and has attracted extensive attention from scientific researchers.

[0003] Although the traditional palladium-carbon catalyst with activated carbon as the carrier has many excellent properties mentioned above and has mature applications, there are still some unresolved defects. For example, the main role in the palladium-carbon catalyst is the palladium active component, and the dispersion performance of palladium is crucial to improving the activity of the catalyst. However, the porosity and specific surface area of ​​activated carbon are limited, which makes it difficult for the palladium active component to be highly dispersed in the activated carbon; and the interaction between palladium and the activated carbon carrier is mainly physical, and the interaction is not strong, resulting in poor stability of the palladium-carbon catalyst.

[0004] The patent with publication number CN 104549255B discloses a palladium carbon catalyst and its preparation method. The palladium carbon catalyst prepared in the application includes an activated carbon carrier and Pd, an alkaline earth metal and a lanthanide metal, which can better solve the problem of poor sulfur resistance of the catalyst and easy growth of palladium particles. However, it does not solve the problem that the active component of palladium cannot be highly dispersed in the activated carbon due to limited porosity and specific surface area.

[0005] The patent with publication number CN 1457922A discloses a hydrogenation catalyst for terephthalic acid refining, wherein the carrier activated carbon of the hydrogenation catalyst is granular or shaped coconut shell carbon, the active component is metal Pd, and the catalyst has a suitable pore structure so that the active component is evenly dispersed. However, the problem of poor interaction between activated carbon and metal Pd is not mentioned and solved, which may affect the service life of the catalyst.

[0006] In view of this, it is necessary to design a highly dispersed palladium-carbon catalyst and a preparation method thereof to solve the above problems. Summary of the invention

[0007] In view of the technical problems existing in the background technology, the present application provides a highly dispersible palladium-carbon catalyst and a preparation method thereof, wherein the preparation method replaces activated carbon with fructose-based carbon aerogel, and optimizes the synthesis steps and reaction conditions, thereby solving the problem of poor dispersibility and stability of the palladium-carbon catalyst. Specifically, the preparation method uses fructose as a bio-based carbon source, and synthesizes fructose-based carbon aerogel under the action of a cyanide ionic liquid, and then adds the fructose-based carbon aerogel to an aqueous solution containing a palladium compound, and after freeze drying, high-temperature carbonization, and reduction treatment, a palladium-carbon catalyst with fructose-based carbon aerogel as a carrier is prepared.

[0008] In a first aspect, the present invention provides a method for preparing a highly dispersed palladium-carbon catalyst, comprising the following steps:

[0009] S1, adding fructose to the cyanide ionic liquid, heating to 65-75°C, stirring, transferring to a reaction vessel, heating to 190-210°C, keeping warm for 23-25h, cooling to room temperature, obtaining a fructose-based carbon aerogel, and setting aside;

[0010] S2, adding the fructose-based carbon aerogel obtained in step S1 to an aqueous solution containing a palladium compound, stirring for 10-12 hours, adding tert-butanol, soaking, freezing at -25 to -15°C for 2-4 hours, freeze drying, high temperature carbonization, and reduction treatment to obtain a highly dispersed palladium-carbon catalyst.

[0011] In the embodiment of the present application, natural and environmentally friendly fructose is used as a bio-based carbon source, and fructose-based carbon aerogel is synthesized under the action of cyanide ionic liquid. The fructose-based carbon aerogel is then added to an aqueous solution containing a palladium compound, and after freeze-drying, high-temperature carbonization, and reduction treatment, a palladium-carbon catalyst with fructose-based carbon aerogel as a carrier is prepared.

[0012] Furthermore, in step S1, the mass ratio of the fructose to the cyanide ionic liquid is 1:(3.5-4.5), preferably 1:4.

[0013] Furthermore, in step S1, the method for preparing the cyanide ionic liquid comprises the following steps:

[0014] 1,1'-dimethyl-1H,1'H-[2,2']biimidazole and 4-chlorobutyronitrile are mixed, heated to 80-100° C., and stirred to obtain a cyanide ionic liquid.

[0015] Furthermore, the molar ratio of the 1,1'-dimethyl-1H,1'H-[2,2']biimidazole to the 4-chlorobutyronitrile is 1:(0.5-0.6), preferably 1:0.5.

[0016] On the one hand, fructose is used as a carbon source, which has the characteristics of wide sources, renewable and green; on the other hand, 1,1'-dimethyl-1H,1'H-[2,2']biimidazole and 4-chlorobutyronitrile are used as the main reactants to prepare cyanide ionic liquids. Cyano is an active unsaturated group that can undergo a coupling reaction with fructose to obtain a cross-linked monomer with a positive charge. The electrostatic repulsion can inhibit the aggregation of the palladium carbon catalyst, so that the prepared palladium carbon catalyst has good dispersibility.

[0017] Furthermore, by controlling the reaction molar ratio of 1,1'-dimethyl-1H,1'H-[2,2']biimidazole and 4-chlorobutyronitrile, the cyanide ionic liquid still contains a certain content of free imidazole groups. Imidazole can form a certain coordination effect with palladium ions, so that the palladium ions can be stably loaded in the fructose-based carbon aerogel carrier, thereby improving the stability and dispersibility of the palladium-carbon catalyst.

[0018] Furthermore, in step S2, the palladium-containing compound in the aqueous solution of the palladium-containing compound is palladium nitrate or palladium chloride, preferably palladium nitrate.

[0019] Furthermore, in step S2, the concentration of the aqueous solution containing the palladium compound is 0.8-3 wt%.

[0020] Preferably, the concentration of the aqueous solution containing the palladium compound is 1-2 wt %.

[0021] More preferably, the concentration of the aqueous solution containing the palladium compound is 1.5 wt %.

[0022] Furthermore, in step S2, the mass ratio of the fructose-based carbon aerogel to the aqueous solution containing the palladium compound is 1:(1.05-1.21).

[0023] Preferably, the mass ratio of the fructose-based carbon aerogel to the aqueous solution containing the palladium compound is 1:1.1.

[0024] Furthermore, in step S2, the freeze-drying treatment temperature is -60 to -50°C, and the treatment time is 46 to 50 hours. Preferably, the freeze-drying temperature is -55°C, and the treatment time is 48 hours.

[0025] Furthermore, in step S2, the temperature of the high temperature carbonization treatment is 800-1000°C, and the treatment time is 2-3 hours. Preferably, the temperature of the high temperature carbonization is 900°C, and the treatment time is 2.5 hours.

[0026] In a second aspect, the present invention provides a highly dispersed palladium-carbon catalyst prepared by the aforementioned technical solution, wherein the BET specific surface area of ​​the palladium-carbon catalyst is not less than 750 m 2 ·g -1; The average grain size of palladium is not more than 6nm.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (1) The present invention provides a method for preparing a highly dispersed palladium-carbon catalyst, in which activated carbon is replaced by fructose-based carbon aerogel, and the synthesis steps and reaction conditions are optimized. Through the synergistic effect of the components, the prepared palladium-carbon catalyst has the characteristics of high dispersion and high stability.

[0029] (2) The present invention selects natural and environmentally friendly fructose as a synthetic bio-based carbon source, and synthesizes fructose-based carbon aerogel under the action of cyanide ionic liquid, and then adds the fructose-based carbon aerogel into a palladium-containing impregnation solution, and after freeze-drying, high-temperature carbonization, and reduction treatment, a palladium-carbon catalyst with fructose-based carbon aerogel as a carrier is prepared. While improving the dispersibility of the palladium-carbon catalyst, it also improves the interaction between palladium and the carrier, thereby improving the stability of the palladium-carbon catalyst.

[0030] (3) The BET specific surface area of ​​the palladium-carbon catalyst obtained by the preparation method of the present invention is not less than 750 m 2 ·g -1 The average grain size of palladium is no more than 6nm, and it has the characteristics of high dispersibility and high stability.

[0031] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. DETAILED DESCRIPTION

[0032] The following is a detailed description of the embodiments of the technical solution of the present application. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the description and claims of this application and any variations thereof are intended to cover non-exclusive inclusions.

[0034] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0035] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0036] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0037] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0038] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0039] At present, most of the palladium-carbon catalysts on the market are prepared by loading palladium on activated carbon using activated carbon as a carrier. However, there is a common problem of poor dispersion of palladium on activated carbon due to the limited porosity of activated carbon and insufficient specific surface area.

[0040] Compared with activated carbon, carbon aerogel has the advantages of large specific surface area, high porosity, high strength and high temperature resistance, making it an excellent substitute for activated carbon. Currently, most carbon aerogels are made from inexpensive resorcinol and formaldehyde, but they are difficult to recycle and have poor environmental protection.

[0041] The present invention provides a method for preparing a highly dispersed palladium-carbon catalyst, comprising the following steps:

[0042] S1, adding fructose to the cyanide ionic liquid, heating to 65-75°C, stirring, transferring to a reaction vessel, heating to 190-210°C, keeping warm for 23-25h, cooling to room temperature, obtaining a fructose-based carbon aerogel, and setting aside;

[0043] Wherein, the mass ratio of fructose to the cyanide ionic liquid is 1:(3.5-4.5).

[0044] The preparation method of the cyano ionic liquid comprises the following steps:

[0045] 1,1'-dimethyl-1H,1'H-[2,2']biimidazole and 4-chlorobutyronitrile are mixed, heated to 80-100° C., and stirred to obtain a cyanide ionic liquid.

[0046] The molar ratio of 1,1'-dimethyl-1H,1'H-[2,2']biimidazole to the 4-chlorobutyronitrile is 1:(0.5-0.6).

[0047] S2, adding the fructose-based carbon aerogel obtained in step S1 to an aqueous solution containing a palladium compound, stirring for 10-12 hours, adding tert-butanol, soaking, freezing at -25 to -15°C for 2-4 hours, freeze drying, high temperature carbonization, and reduction treatment to obtain a highly dispersed palladium-carbon catalyst.

[0048] The concentration of the aqueous solution containing palladium compounds is 0.8-3 wt %. The aqueous solution containing palladium compounds contains palladium nitrate or palladium chloride.

[0049] The mass ratio of the fructose-based carbon aerogel to the aqueous solution containing the palladium compound is 1:(1.05-1.21).

[0050] In step S2, the freeze-drying treatment temperature is -60 to -50°C, and the treatment time is 46 to 50 hours.

[0051] In step S2, the temperature of the high temperature carbonization treatment is 800-1000°C, and the treatment time is 2-3h.

[0052] In the embodiment of the present application, natural and environmentally friendly fructose is selected as a bio-based carbon source, and fructose-based carbon aerogel is synthesized under the action of cyanide ionic liquid. The fructose-based carbon aerogel is then added to an aqueous solution containing a palladium compound, and after freeze-drying, high-temperature carbonization, and reduction treatment, a palladium-carbon catalyst with fructose-based carbon aerogel as a carrier is prepared.

[0053] On the one hand, the present application selects fructose as a carbon source, which has the characteristics of wide source, renewable and green; on the other hand, the present application uses 1,1'-dimethyl-1H,1'H-[2,2']biimidazole and 4-chlorobutyronitrile as main reactants to prepare a cyanide ionic liquid. The cyanide group is an active unsaturated group that can undergo a coupling reaction with fructose to obtain a cross-linked monomer with a positive charge. The electrostatic repulsion can inhibit the agglomeration of the palladium-carbon catalyst, thereby making the prepared palladium-carbon catalyst have good dispersibility.

[0054] Furthermore, the present application controls the reaction molar ratio of 1,1'-dimethyl-1H,1'H-[2,2']biimidazole and 4-chlorobutyronitrile so that the cyanide ionic liquid still contains a certain amount of free imidazole groups. The imidazole can form a certain coordination effect with the palladium ions, so that the palladium ions can be stably loaded in the fructose-based carbon aerogel carrier, thereby improving the stability and dispersibility of the palladium-carbon catalyst.

[0055] The present application also provides a highly dispersed palladium-carbon catalyst prepared by the above-mentioned preparation method, wherein the BET specific surface area of ​​the palladium-carbon catalyst is not less than 750 m 2 ·g -1 ; The average grain size of palladium is not more than 6nm.

[0056] Some specific embodiments are listed below. It should be noted that the embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application.

[0057] In the following examples, except for the cyanide ionic liquid, the other compound monomers and related reagents used can be purchased from the market.

[0058] Preparation Example 1

[0059] The synthesis method of cyano ion liquid A comprises the following steps:

[0060] 0.2 mol of 1,1'-dimethyl-1H,1'H-[2,2']biimidazole and 0.1 mol of 4-chlorobutyronitrile were mixed, heated to 90° C., and stirred for 7 h to obtain cyanide ionic liquid A.

[0061] That is, the molar ratio of 1,1'-dimethyl-1H,1'H-[2,2']biimidazole to 4-chlorobutyronitrile is 1:0.5.

[0062] Preparation Example 2

[0063] The synthesis method of cyanide ion liquid B is the same as that of cyanide ion liquid A, except that the molar number of 4-chlorobutyronitrile is replaced by 0.08 mol.

[0064] That is, the molar ratio of 1,1'-dimethyl-1H,1'H-[2,2']biimidazole to 4-chlorobutyronitrile is 1:0.4.

[0065] Preparation Example 3

[0066] The synthesis method of cyanide ion liquid C is the same as that of cyanide ion liquid A, except that the molar number of 4-chlorobutyronitrile is replaced by 0.14 mol.

[0067] That is, the molar ratio of 1,1'-dimethyl-1H,1'H-[2,2']biimidazole to 4-chlorobutyronitrile is 1:0.7.

[0068] Preparation Example 4

[0069] The synthesis method of cyanide ion liquid D is the same as that of cyanide ion liquid A, except that the molar number of 4-chlorobutyronitrile is replaced by 0.12 mol.

[0070] That is, the molar ratio of 1,1'-dimethyl-1H,1'H-[2,2']biimidazole to 4-chlorobutyronitrile is 1:0.6.

[0071] Example 1

[0072] A method for preparing a highly dispersed palladium-carbon catalyst comprises the following steps:

[0073] S1, add 6 g of fructose to 24 g of cyanide ionic liquid A, heat to 70°C, stir for 1.5 h, transfer to a polytetrafluoroethylene-lined reaction vessel, heat to 200°C, keep warm for 24 h, cool to room temperature, and obtain fructose-based carbon aerogel for use; that is, the mass ratio of fructose to cyanide ionic liquid is 1:4.

[0074] S2, add 20g of the fructose-based carbon aerogel obtained in step S1 to 22g of a 1.5wt% palladium nitrate aqueous solution, stir for 11h, add 40ml of tert-butanol, soak for 24h, centrifuge, add 40ml of tert-butanol, soak for 24h, centrifuge, add 40ml of tert-butanol again, soak for 24h, freeze at -20℃ for 3h, freeze-dry at -55℃ for 48h, high-temperature carbonize at 900℃ for 2.5h, and perform reduction treatment (cool down to 200℃ in a nitrogen atmosphere, introduce hydrogen, reduce at a pressure of 5MPa for 4h, and cool to room temperature) to obtain a highly dispersed palladium-carbon catalyst.

[0075] Comparative Example 1

[0076] This comparative example provides a method for preparing a highly dispersed palladium-carbon catalyst. The specific implementation method is the same as that of Example 1, except that the mass of the cyanide ion liquid A in step S1 is 19.5 g.

[0077] Comparative Example 2

[0078] This comparative example provides a method for preparing a highly dispersed palladium-carbon catalyst. The specific implementation method is the same as that of Example 1, except that the mass of the cyanide ion liquid A in step S1 is 28.5 g.

[0079] Comparative Example 3

[0080] This comparative example provides a method for preparing a highly dispersed palladium-carbon catalyst. The specific implementation method is the same as that of Example 1, except that the mass of the aqueous palladium nitrate solution in step S2 is 17 g.

[0081] Comparative Example 4

[0082] This comparative example provides a method for preparing a highly dispersed palladium-carbon catalyst. The specific implementation method is the same as that of Example 1, and the main difference is that the mass of the palladium nitrate aqueous solution in step S2 is 25 g.

[0083] Comparative Example 5

[0084] This comparative example provides a method for preparing a highly dispersed palladium-carbon catalyst. The specific implementation method is the same as that of Example 1, and the main difference is that the cyanide ion liquid A is replaced by the cyanide ion liquid B in equal amounts.

[0085] Comparative Example 6

[0086] This comparative example provides a method for preparing a highly dispersed palladium-carbon catalyst. The specific implementation method is the same as that of Example 1, except that the cyanide ion liquid A is replaced by an equal amount of cyanide ion liquid C.

[0087] In summary, the differences between Comparative Examples 1-6 and Example 1 mainly lie in that the mass ratio of fructose to cyanide ionic liquid in step S1, the mass ratio of fructose-based carbon aerogel to the aqueous solution of palladium-containing compound in step S2, and the molar ratio of 1,1'-dimethyl-1H,1'H-[2,2']biimidazole to 4-chlorobutyronitrile are changed, and the other experimental parameters and conditions are substantially the same as those in Example 1.

[0088] For ease of comparison, the main differences between Comparative Examples 1-6 and Example 1 are summarized as shown in the following table.

[0089]

[0090] Comparative Example 7

[0091] This comparative example provides a method for preparing a highly dispersed palladium-carbon catalyst. The specific implementation method is the same as that of Example 1, except that the cyanide ionic liquid A is replaced by an equal amount of a commercially available conventional ionic liquid.

[0092] The commercially available conventional ionic liquid in this comparative example is 1-ethyl-3-methylimidazolium bromide.

[0093] Example 2

[0094] A method for preparing a highly dispersed palladium-carbon catalyst comprises the following steps:

[0095] S1, add 6g fructose to 21g cyanide ionic liquid A, heat to 65°C, stir for 2h, transfer to a polytetrafluoroethylene-lined reaction vessel, heat to 190°C, keep warm for 25h, cool to room temperature, and obtain fructose-based carbon aerogel for use;

[0096] S2, add 20g of the fructose-based carbon aerogel obtained in step S1 to 21g of 0.8wt% palladium nitrate aqueous solution, stir for 10h, add 40ml of tert-butanol, soak for 24h, centrifuge, add 40ml of tert-butanol, soak for 24h, centrifuge, add 40ml of tert-butanol again, soak for 24h, freeze at -25℃ for 2h, freeze-dry at -60℃ for 46h, high-temperature carbonize at 800℃ for 3h, and reduce (cool down to 200℃ in a nitrogen atmosphere, introduce hydrogen, reduce at a pressure of 5MPa for 4h, and cool to room temperature) to obtain a highly dispersed palladium-carbon catalyst.

[0097] Example 3

[0098] A method for preparing a highly dispersed palladium-carbon catalyst comprises the following steps:

[0099] S1. Add 6 g of fructose to 27 g of cyanide ionic liquid A, heat to 75°C, stir for 1 h, transfer to a polytetrafluoroethylene-lined reaction vessel, heat to 210°C, keep warm for 23 h, and cool to room temperature to obtain fructose-based carbon aerogel for use;

[0100] S3. Add 20 g of the fructose-based carbon aerogel of step S1 to 24.2 g of a 3 wt% aqueous solution of palladium nitrate, stir for 12 h, add 40 ml of tert-butanol, soak for 24 h, centrifuge, add 40 ml of tert-butanol, soak for 24 h, centrifuge, add 40 ml of tert-butanol again, soak for 24 h, freeze at -15 ° C for 4 h, freeze-dry at -50 ° C for 50 h, high-temperature carbonize at 1000 ° C for 2 h, and reduce (cool down to 200 ° C in a nitrogen atmosphere, pass hydrogen, reduce at a pressure of 5 MPa for 4 h, and cool to room temperature) to obtain a highly dispersed palladium-carbon catalyst.

[0101] Example 4

[0102] This embodiment provides a method for preparing a highly dispersed palladium-carbon catalyst. The specific implementation method is the same as that of Example 1, and the main difference is that the cyanide ion liquid A is replaced by an equal amount of cyanide ion liquid D.

[0103] For ease of comparison, the main differences between Examples 1-4 are summarized as shown in the following table.

[0104]

[0105] Performance Testing

[0106] The BET specific surface area and the average crystal size of palladium of the palladium carbon catalysts prepared in the above Examples 1-4 and Comparative Examples 1-7 were tested, and the test results are shown in Table 1 below.

[0107] The test of BET specific surface area refers to ASTM B922-2010.

[0108] The test of average grain size of palladium refers to GB / T 6394-2002.

[0109] Table 1

[0110]

[0111] It can be seen from Table 1 that the palladium-carbon catalysts in Examples 1-4 of the present invention have the characteristics of high BET specific surface area and small average crystal size of palladium as a whole, which proves that the prepared palladium-carbon catalysts have good dispersibility and stability.

[0112] Among them, in Comparative Example 1-2, the mass ratio of fructose to cyanide ionic liquid in step S1 was changed, so that the fructose-based carbon aerogel could not be well formed, resulting in the failure to improve the pore size and specific surface area of ​​the fructose-based carbon aerogel, thereby causing the dispersibility and stability of the palladium-carbon catalyst to decrease, that is, the BET specific surface area decreased and the average crystal size of palladium increased.

[0113] In Comparative Example 3-4, the ratio of the aqueous palladium nitrate solution to the fructose-based carbon aerogel in step S2 was changed, so that the palladium ions could not be stably loaded in the carrier, thereby causing the BET specific surface area of ​​the palladium-carbon catalyst and the average grain size of palladium to deteriorate.

[0114] Comparative Examples 5-6, when preparing the cyanide ionic liquid, the ratio between the main reactants 1,1'-dimethyl-1H,1'H-[2,2']biimidazole and 4-chlorobutyronitrile was changed. When the molar ratio between the reactants 1,1'-dimethyl-1H,1'H-[2,2']biimidazole and 4-chlorobutyronitrile was 1:(0.5-0.6), the cyanide ionic liquid still contained a certain amount of free imidazole groups, and imidazole could form a certain coordination effect with palladium ions, so that Palladium ions can be stably loaded in the fructose-based carbon aerogel carrier, thereby improving the stability and dispersibility of the palladium-carbon catalyst; when the molar ratio between the reactants 1,1'-dimethyl-1H,1'H-[2,2']biimidazole and 4-chlorobutyronitrile exceeds 1:(0.5-0.6), cyanide ionic liquid produces by-products, resulting in a decrease in the porosity and specific surface area of ​​the fructose-based carbon aerogel, which in turn leads to a decrease in the BET specific surface area of ​​the palladium-carbon catalyst and an increase in the average crystal size of palladium.

[0115] Comparative Example 7 is to replace cyanide ionic liquid A with commercially available conventional ionic liquid. Tests show that the BET specific surface area and the average crystal size of palladium in the prepared palladium carbon catalyst both show poor results, that is, it has poor dispersibility and stability.

[0116] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for preparing a highly dispersed palladium-carbon catalyst, characterized in that: The following steps are involved: S1, adding fructose to the cyanide ionic liquid, heating to 65-75°C, stirring, transferring to a reaction vessel, heating to 190-210°C, keeping warm for 23-25h, cooling to room temperature, obtaining fructose-based carbon aerogel, and setting aside; the mass ratio of the fructose to the cyanide ionic liquid is 1:(3.5-4.5); S2, adding the fructose-based carbon aerogel obtained in step S1 to an aqueous solution containing a palladium compound, stirring for 10-12 hours, adding tert-butanol, soaking, freezing at -25 to -15°C for 2-4 hours, freeze-drying, high-temperature carbonization, and reduction treatment to obtain a highly dispersed palladium-carbon catalyst; wherein the mass ratio of the fructose-based carbon aerogel to the aqueous solution containing the palladium compound is 1:(1.05-1.21).

2. The preparation method of a highly dispersible palladium-carbon catalyst according to claim 1, wherein In step S1, the method for preparing the cyanide ionic liquid comprises the following steps: 1,1'-dimethyl-1H,1'H-[2,2']biimidazole and 4-chlorobutyronitrile are mixed, heated to 80-100° C., and stirred to obtain a cyanide ionic liquid.

3. The preparation method of a highly dispersible palladium-carbon catalyst according to claim 2, wherein The molar ratio of the 1,1'-dimethyl-1H,1'H-[2,2']biimidazole to the 4-chlorobutyronitrile is 1:(0.5-0.6).

4. The preparation method of a highly dispersible palladium-carbon catalyst according to claim 1, wherein In step S2, the palladium-containing compound in the aqueous solution of the palladium-containing compound is palladium nitrate or palladium chloride.

5. The preparation method of a highly dispersible palladium-carbon catalyst according to claim 1, wherein In step S2, the concentration of the aqueous solution containing the palladium compound is 0.8-3 wt%.

6. The preparation method of a highly dispersible palladium-carbon catalyst according to claim 1, wherein In step S2, the freeze-drying treatment temperature is -60 to -50°C, and the treatment time is 46 to 50 hours.

7. The preparation method of a highly dispersible palladium-carbon catalyst according to claim 1, wherein In step S2, the temperature of the high temperature carbonization treatment is 800-1000°C, and the treatment time is 2-3h.

8. A highly dispersed palladium-carbon catalyst, characterized in that Prepared by the preparation method according to any one of claims 1 to 7, the BET specific surface area of ​​the palladium carbon catalyst is not less than 750m 2 ·g -1 ; The average grain size of palladium is not more than 6nm.

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