Nitrogen-doped carbon-loaded PdBi bimetallic catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of catalysis, and particularly relates to a nitrogen-doped carbon-loaded PdBi bimetallic catalyst as well as a preparation method and application thereof. After the carbon black is acidified, oxygen-containing functional groups on the surface are increased, so that adsorption and anchoring of metal components are facilitated; acidified carbon black and melamine are subjected to co-pyrolysis to prepare nitrogen-doped carbon, and the doping of N further strengthens the interaction between the carrier and the active component, improves the stability of the catalyst and prevents the active component from agglomerating; in the pyrolysis process, an additional reducing atmosphere is not needed, ammonia gas generated through melamine decomposition is only needed to be used for reduction of a Pd source and a Bi source, Pd and Bi in the active nanoparticles exist in an alloy form, and the synergistic effect between metal Pd and Bi can regulate and control surface charges of Pd and enhance the catalytic activity of the Pd center, so that the catalyst can keep high activity under the condition of low Pd loading capacity, and the catalytic activity of the catalyst is improved. The catalysis cost is reduced.

Description

Technical Field

[0001] The present invention belongs to the field of catalysis technology, and in particular relates to a nitrogen-doped carbon-supported PdBi bimetallic catalyst, a preparation method and applications thereof. Background Art

[0002] Benzyl esters are important fine chemical intermediates with widespread applications in pharmaceuticals, fragrances, and polymer materials. Compared to the classic synthetic route based on the nucleophilic substitution reaction of carboxylic acid derivatives (carboxylic acids, acyl halides, anhydrides, or active esters) with benzyl alcohol under acid-catalyzed conditions, the direct oxidative esterification of alcohols starts with the alcohol and directly converts it into an ester via the action of an oxidant. This eliminates the need for the pre-synthesis step of the carboxylic acid or its derivatives, shortening the reaction path while reducing byproduct formation and significantly improving atom economy.

[0003] The core of this reaction lies in the development of catalysts and catalytic systems. Various noble metal-based homogeneous catalytic systems have been developed so far, including palladium, rhodium, iridium, gold, and combinations thereof with other transition metal co-catalysts. However, homogeneous reaction systems typically require a large amount of expensive ligands, additives, and bases, and the noble metals are difficult to recycle, resulting in high catalytic costs. In addition, esters are typically obtained at relatively high temperatures and / or high pressures, with the reactor configuration accounting for a large proportion of the total cost. Therefore, designing cost-effective and reusable heterogeneous catalysts for direct oxidative esterification of alcohols under mild conditions is more attractive and challenging for academia and industry.

[0004] Pd-based catalysts are widely used in the direct oxidative esterification of alcohols. However, traditional supported palladium catalysts (such as Pd / C, with Pd loadings typically exceeding 10 wt.%) suffer from issues such as active site aggregation and deactivation, as well as insufficient surface electronic state control, resulting in insufficient catalytic activity at the Pd active center. This results in a 30-50% decrease in catalytic efficiency compared to homogeneous systems. Therefore, current research focuses on effectively enhancing the catalytic activity of the Pd center while controlling the precious metal content to promote its industrial application. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a nitrogen-doped carbon-supported PdBi bimetallic catalyst in the first aspect. x Bi y / NC t Catalyst, wherein x is 0 to 20, y is 0 to 20, and t is 600 to 1000, and x and y cannot be 0 at the same time.

[0006] In some embodiments, x is 1 to 12, y is 1 to 12, and t is 700 to 1000.

[0007] The second aspect of the present invention provides a method for preparing the nitrogen-doped carbon-supported PdBi bimetallic catalyst, the preparation method comprising the following steps: (1) Treating the carbon black material with acid at high temperature to obtain acidified carbon black powder; (2) mixing acidified carbon black powder, melamine, Bi(NO3)3·5H2O and Pd(NO3)2 in a solvent, removing the solvent, and drying to obtain a precursor; (3) The precursor is calcined in an inert atmosphere to obtain a nitrogen-doped carbon-loaded PdBi bimetallic catalyst.

[0008] In some embodiments, the acid in step (1) is concentrated nitric acid, the high temperature is 80-120° C., and the treatment time is 4-24 hours.

[0009] In some embodiments, the mass proportions of melamine, acidified carbon black powder, Bi(NO3)3·5H2O and Pd(NO3)2 in step (2) are 10 to 300 parts of melamine, 150 to 210 parts of acidified carbon black powder, 0 to 100 parts of Bi(NO3)3·5H2O and 0 to 91 parts of Pd(NO3)2.

[0010] In some embodiments, the solvent in step (2) is any one of water, ethanol, methanol, isopropanol, dichloromethane, and acetonitrile.

[0011] In some embodiments, the calcination temperature in step (3) is 600-1000°C.

[0012] A third aspect of the present invention provides an application of a nitrogen-doped carbon-supported PdBi bimetallic catalyst for catalyzing the oxidative esterification of benzyl alcohol and fatty alcohols to prepare ester compounds. Benzyl alcohol, fatty alcohol, base, and the nitrogen-doped carbon-supported PdBi bimetallic catalyst are thoroughly mixed and reacted at 30-90°C for 1-10 hours under normal pressure air or oxygen atmosphere.

[0013] In some embodiments, the benzyl alcohol is benzyl alcohol and its derivatives, the fatty alcohol is methanol, the base additive is any one of Na2CO3, K2CO3, Cs2CO3, and potassium tert-butoxide, and the molar ratio of the benzyl alcohol to the base additive is 32 to 1:1.

[0014] In some embodiments, the ratio of the nitrogen-doped carbon-supported PdBi bimetallic catalyst to the benzyl alcohol is 1.0 to 20.0 g / mol.

[0015] Beneficial effects: (1) After acidification, the surface oxygen-containing functional groups of carbon black increase, which is beneficial to the adsorption and anchoring of metal components. Nitrogen-doped carbon is prepared by co-pyrolysis of acidified carbon black and melamine. The nitrogen doping further strengthens the interaction between the support and the active component, improves the catalyst stability, and prevents the agglomeration of the active component. (2) The pyrolysis process does not require an additional reducing atmosphere. Only ammonia generated by the decomposition of melamine is needed to reduce the Pd and Bi sources. Pd and Bi exist in the active nanoparticles in the form of an alloy. The synergistic effect between metallic Pd and Bi can regulate the surface charge of Pd and enhance the catalytic activity of the Pd center, so that the catalyst can maintain high activity even at low Pd loading, thereby reducing the catalytic cost. (3) Based on the heterogeneous catalytic system, the oxidative esterification reaction of benzyl alcohol was carried out by simple filtration to separate the solid and liquid phases, which achieved efficient recovery and reuse of the catalyst. The activity decay of the catalyst was less than 5% after 5 cycles, showing excellent cyclic stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Pd5Bi5 / NC prepared in Example 3 800 TEM image of the catalyst; Figure 2 Pd5Bi5 / NC prepared in Example 3 800 Catalyst Mapping diagram; Figure 3 Pd5Bi5 / NC prepared in Example 3 800 Line scan of element distribution of catalyst nanoparticles; Figure 4 Pd5Bi5 / NC prepared in Example 3, Comparative Example 3 and Comparative Example 4 800 、Pd 10 / NC 800 、Bi 10 / NC 800 XRD pattern of the catalyst; Figure 5 Pd5Bi5 / NC prepared in Example 3 800 Cyclic performance diagram of the catalyst in catalyzing the oxidative esterification of benzyl alcohol and methanol to produce methyl benzoate. DETAILED DESCRIPTION

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. In the event of a conflict, the definitions in this specification shall prevail.

[0018] Unless otherwise indicated, all percentages, parts, ratios, etc. are by weight.

[0019] As used herein, the terms "comprises," "includes," "has," "having," "containing," or any other variations thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may also include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0020] When quantity, weight part or other numerical value or parameter is given as range, preferred range or a series of upper preferred value and lower preferred value, it should be understood that it specifically discloses all ranges formed by any pair of numerical values ​​of any larger range limit or preferred value and any smaller range limit or preferred value, and no matter whether scope is disclosed respectively.For example, when describing the scope of "1 to 5", described scope should be understood as including the scope of "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc.Unless otherwise stated, when describing numerical range herein, described range is intended to include range end value and all integers, fractions, decimals etc. within the range.

[0021] In addition, the indefinite articles "a" and "an" before the elements or components of the present disclosure are intended to indicate that the number of occurrences (i.e., occurrences) of the elements or components is not limited. Therefore, "a" or "an" should be understood to include one or at least one, and unless it is clearly indicated that the number is singular, the elements or components in the singular also include plural cases.

[0022] Unless otherwise specified, the materials, methods, and examples described herein are illustrative only and not limiting. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure, suitable methods and materials are described herein.

[0023] The present disclosure is described in detail below.

[0024] Pd x Bi y / NC t Here, t can also be understood as the calcination temperature.

[0025] Example 1 Pd1Bi9 / NC 800 Preparation of catalyst: (1) A 1000 mL flask was used for the reaction. 400 mL of concentrated nitric acid (Shanghai test, GR, 65%-68%) was added to 60.0 g of Vulcan XC-72 carbon black provided by Guangzhou Jingyi New Materials Co., Ltd., and then ultrasonicated and stirred until no carbon black adhered to the wall of the flask and all the carbon black was evenly dispersed. The flask and the mixture were placed in a 100°C oil bath and refluxed for 12 h. After cooling to room temperature, the mixture was transferred to a beaker, diluted with water, and allowed to settle. The supernatant was removed. After repeated several times, the mixture containing black particles in the lower layer was poured into a dialysis bag, sealed, and dialyzed in deionized water until neutral. The solid was filtered and dried to obtain acidified carbon black powder (CB).

[0026] (2) 200.0 mg of CB prepared in step (1) and 200.0 mg of melamine were mixed and dispersed in 30 mL of ethanol at room temperature and ultrasonically treated for 30 min to form a dispersion A. 41.8 mg of Bi(NO3)3·5H2O (Shanghai test, 99.9%) and 86.6 mg of Pd(NO3)2 (palladium nitrate dihydrate, Aladdin, w / w 4-5% (cont. Pd)) were ultrasonically dispersed in 20 mL of ethanol to form a dispersion B. Dispersion B was added dropwise to dispersion A under stirring and stirring was continued for 30 min. Subsequently, the mixture was rotary evaporated at 60 °C for 30 min, and the solid residue was transferred to a vacuum oven and dried at 80 °C for 8 h to obtain a black mixture powder Pd1Bi9 / CBM.

[0027] (3) The obtained Pd1Bi9 / CBM powder was calcined in a tube furnace in a N2 atmosphere at a temperature of 800°C for 2 h at a heating rate of 5°C / min. After calcination, the mixture was naturally cooled to room temperature to obtain Pd1Bi9 / NC 800 catalyst.

[0028] Example 2 Pd3Bi7 / NC 800 Preparation of catalyst: (1) 200.0 mg of CB prepared in step (1) of Example 1 and 200.0 mg of melamine were mixed and dispersed in 30 mL of ethanol at room temperature and ultrasonically treated for 30 min to form a dispersion A. 32.5 mg of Bi(NO3)3·5H2O (Shanghai test, 99.9%) and 259.8 mg of Pd(NO3)2 (palladium nitrate dihydrate, Aladdin, w / w 4-5% (cont. Pd)) were ultrasonically dispersed in 20 mL of ethanol to form a dispersion B. Dispersion B was added dropwise to dispersion A under stirring and stirring was continued for 30 min. Subsequently, the mixture was rotary evaporated at 60 °C for 30 min, and the solid residue was transferred to a vacuum oven and dried at 80 °C for 8 h to obtain a black mixture powder Pd3Bi7 / CBM.

[0029] (2) The obtained Pd3Bi7 / CBM powder was calcined in a tube furnace in a N2 atmosphere at a temperature of 800°C for 2 h at a heating rate of 5°C / min. After calcination, the powder was naturally cooled to room temperature to obtain Pd3Bi7 / NC 800 catalyst.

[0030] Example 3 Pd5Bi5 / NC 800 Preparation of catalyst: (1) 200.0 mg of CB prepared in step (1) of Example 1 and 200.0 mg of melamine were mixed and dispersed in 30 mL of ethanol at room temperature and ultrasonically treated for 30 min to form a dispersion A. 23.2 mg of Bi(NO3)3·5H2O (Shanghai test, 99.9%) and 433.3 mg of Pd(NO3)2 (palladium nitrate dihydrate, Aladdin, w / w 4-5% (cont. Pd)) were ultrasonically dispersed in 20 mL of ethanol to form a dispersion B. Dispersion B was added dropwise to dispersion A under stirring and stirring was continued for 30 min. Subsequently, the mixture was rotary evaporated at 60 °C for 30 min, and the solid residue was transferred to a vacuum oven and dried at 80 °C for 8 h to obtain a black mixture powder Pd5Bi5 / CBM.

[0031] (2) The obtained Pd5Bi5 / CBM powder was calcined in a tube furnace in a N2 atmosphere at a temperature of 800°C for 2 h at a heating rate of 5°C / min. After calcination, the powder was naturally cooled to room temperature to obtain Pd5Bi5 / NC 800 catalyst.

[0032] Pd5Bi5 / NC prepared in Example 3 800 TEM images of the catalysts are shown in Figure 2. Figure 1As shown, the Pd and Bi active components exist in the form of nanoparticles with a particle size of less than 30 nm.

[0033] The element distribution diagram of the catalyst is shown in Figure 2 As shown in the figure, the blue nitrogen element is evenly distributed, indicating that melamine, used as a nitrogen source, can be successfully incorporated into the carbon black skeleton through high-temperature pyrolysis. The Pd and Bi elements are concentrated in the same locations. Considering that the catalyst preparation process involves simultaneous high-temperature reduction of Pd and Bi and their immobilization on the carbon black skeleton, it can be inferred that the active PdBi nanoparticles in the catalyst are an alloy structure.

[0034] Figure 3 Pd5Bi5 / NC prepared in Example 3 800 Line scan image of a single nanoparticle of the catalyst. In the image, it can be seen that Pd and Bi exist simultaneously at each point along the line scan path, and the content remains basically unchanged, which also intuitively reflects that the PdBi metal active component is an alloy structure.

[0035] Example 4 Pd7Bi3 / NC 800 Preparation of catalyst: (1) 200.0 mg of CB prepared in step (1) of Example 1 and 200.0 mg of melamine were mixed and dispersed in 30 mL of ethanol at room temperature and ultrasonically treated for 30 min to form a dispersion A. 13.9 mg of Bi(NO3)3·5H2O (Shanghai test, 99.9%) and 606.3 mg of Pd(NO3)2 (palladium nitrate dihydrate, Aladdin, w / w 4-5% (cont. Pd)) were ultrasonically dispersed in 20 mL of ethanol to form a dispersion B. Dispersion B was added dropwise to dispersion A under stirring and stirring was continued for 30 min. Subsequently, the mixture was rotary evaporated at 60 °C for 30 min, and the solid residue was transferred to a vacuum oven and dried at 80 °C for 8 h to obtain a black mixture powder Pd7Bi3 / CBM.

[0036] (2) The obtained Pd7Bi3 / CBM powder was calcined in a tube furnace in a N2 atmosphere at a temperature of 800°C for 2 h at a heating rate of 5°C / min. After calcination, the mixture was naturally cooled to room temperature to obtain Pd7Bi3 / NC 800 catalyst.

[0037] Example 5 Pd9Bi1 / NC 800 Preparation of catalyst: (1) 200.0 mg of CB prepared in step (1) of Example 1 and 200.0 mg of melamine were mixed and dispersed in 30 mL of ethanol at room temperature and ultrasonically treated for 30 min to form a dispersion A. 4.6 mg of Bi(NO3)3·5H2O (Shanghai test, 99.9%) and 779.5 mg of Pd(NO3)2 (palladium nitrate dihydrate, Aladdin, w / w 4-5% (cont. Pd)) were ultrasonically dispersed in 20 mL of ethanol to form a dispersion B. Dispersion B was added dropwise to dispersion A under stirring and stirring was continued for 30 min. Subsequently, the mixture was rotary evaporated at 60 °C for 30 min, and the solid residue was transferred to a vacuum oven and dried at 80 °C for 8 h to obtain a black mixture powder Pd9Bi1 / CBM.

[0038] (2) The obtained Pd9Bi1 / CBM powder was calcined in a tube furnace in a N2 atmosphere at a temperature of 800 °C for 2 h at a heating rate of 5 °C / min. After calcination, the mixture was naturally cooled to room temperature to obtain Pd9Bi1 / NC 800 catalyst.

[0039] Comparative Example 1 Preparation of acidified carbon black (CB): The reaction was carried out in a 1000 mL flask. 400 mL of concentrated nitric acid (Shanghai test, GR, 65%-68%) was added to 60.0 g of Vulcan XC-72 carbon black supplied by Guangzhou Jingyi New Materials Co., Ltd. The mixture was then ultrasonically treated and stirred until no carbon black adhered to the flask walls and all the carbon black was evenly dispersed. The flask and mixture were placed in a 100°C oil bath for 12 hours of condensation and reflux. After cooling to room temperature, the mixture was transferred to a beaker, diluted with water, and allowed to settle. The supernatant was removed. This was repeated several times, and the mixture containing the black particles was poured into a sealed dialysis bag. The bag was then dialyzed in deionized water until neutral. The solid was filtered and dried to obtain acidified carbon black powder (CB).

[0040] Comparative Example 2 Preparation of nitrogen-doped carbon black (NC): 200 mg of the CB prepared in Control Example 1 and 200 mg of melamine were mixed and dispersed in 30 mL of ethanol at room temperature and sonicated for 30 minutes until uniformly dispersed. The mixture was then rotary evaporated at 60°C for 30 minutes. The solid residue was transferred to a vacuum oven and dried at 80°C for 8 hours to obtain a black CBM powder.

[0041] Finally, the CBM powder was calcined in a tube furnace under a nitrogen atmosphere at 800°C for 2 hours at a heating rate of 5°C / min. After calcination, the powder was naturally cooled to room temperature to obtain nitrogen-doped carbon black (NC).

[0042] Comparative Example 3 Pd 10 / NC 800 Preparation of catalyst: (1) At room temperature, 200.0 mg of CB prepared in Control Example 1 and 200.0 mg of melamine were mixed and dispersed in 30 mL of ethanol and ultrasonically treated for 30 min to form a dispersion A. 866.1 mg of Pd(NO3)2 (palladium nitrate dihydrate, Aladdin, w / w 4-5% (cont. Pd)) was ultrasonically dispersed in 20 mL of ethanol to form a dispersion B. Dispersion B was added dropwise to dispersion A under stirring and stirring was continued for 30 min. Subsequently, the mixture was rotary evaporated at 60 °C for 30 min, and the solid residue was transferred to a vacuum oven and dried at 80 °C for 8 h to obtain a black mixture powder Pd 10 / CBM.

[0043] (2) The obtained Pd 10 The / CBM powder was calcined in a tube furnace in a N2 atmosphere at 800 °C for 2 h at a heating rate of 5 °C / min. After calcination, it was naturally cooled to room temperature to obtain Pd 10 / NC 800 catalyst.

[0044] Comparative Example 4 Bi 10 / NC 800 Preparation of catalyst: (1) At room temperature, 200.0 mg of CB prepared in Control Example 1 and 200.0 mg of melamine were mixed and dispersed in 30 mL of ethanol and ultrasonically treated for 30 min to form a dispersion A. 46.4 mg of Bi(NO3)3·5H2O (99.9% in Shanghai test) was ultrasonically dispersed in 20 mL of ethanol to form a dispersion B. Dispersion B was added dropwise to dispersion A under stirring and continued stirring for 30 min. Subsequently, the mixture was rotary evaporated at 60 °C for 30 min, and the solid residue was transferred to a vacuum oven and dried at 80 °C for 8 h to obtain a black mixture powder Bi 10 / CBM.

[0045] (2) Get Bi 10The / CBM powder was calcined in a tube furnace in a N2 atmosphere at 800 °C for 2 h at a heating rate of 5 °C / min. After calcination, it was naturally cooled to room temperature to obtain Bi 10 / NC 800 catalyst.

[0046] Figure 4 Pd5Bi5 / NC prepared in Example 3, Comparative Example 3 and Comparative Example 4 800 、Pd 10 / NC 800 and Bi 10 / NC 800 XRD pattern of catalyst. Pd 10 / NC 800 Catalyst 2 θ The diffraction peaks at 40.1°, 46.7° and 68.1° correspond to the (111), (200) and (220) crystal planes of face-centered cubic structure Pd. 800 The diffraction peaks of the catalyst are mainly those of Pd, and they are closely related to the Pd 10 / NC 800 In comparison, the diffraction peak is 2 θ According to the Bragg equation, the diffraction peak decreases and the corresponding interplanar spacing increases. Since the atomic radius of Bi is larger than that of Pd, when Bi atoms enter the Pd lattice, they will stretch the original Pd lattice, resulting in an increase in the interplanar spacing, which is consistent with the XRD results. Therefore, the XRD results reflect the Pd5Bi5 / NC 800 The active metal components in the catalyst exist in the form of PdBi alloy.

[0047] Comparative Example 5 Pd5Bi5 / NC 700 Preparation of catalyst: (1) 200.0 mg of CB prepared in Control Example 1 and 200.0 mg of melamine were mixed and dispersed in 30 mL of ethanol at room temperature and ultrasonically treated for 30 min to form a dispersion A. 23.2 mg of Bi(NO3)3·5H2O (Shanghai test, 99.9%) and 433.3 mg of Pd(NO3)2 (palladium nitrate dihydrate, Aladdin, w / w 4-5% (cont. Pd)) were ultrasonically dispersed in 20 mL of ethanol to form a dispersion B. Dispersion B was added dropwise to dispersion A under stirring and stirring was continued for 30 min. Subsequently, the mixture was rotary evaporated at 60 °C for 30 min. The solid residue was transferred to a vacuum oven and dried at 80 °C for 8 h to obtain a black mixture powder Pd5Bi5 / CBM.

[0048] (2) The obtained Pd5Bi5 / CBM powder was calcined in a tube furnace in a N2 atmosphere at a temperature of 700°C for 2 h at a heating rate of 5°C / min. After calcination, the powder was naturally cooled to room temperature to obtain Pd5Bi5 / NC 700 catalyst.

[0049] Comparative Example 6 Pd5Bi5-NC 800 -0.1 Preparation of catalyst: (1) 200.0 mg of CB prepared in Control Example 1 and 20.0 mg of melamine were mixed and dispersed in 30 mL of ethanol at room temperature and ultrasonically treated for 30 min to form a dispersion A. 23.2 mg of Bi(NO3)3·5H2O (Shanghai test, 99.9%) and 433.3 mg of Pd(NO3)2 (palladium nitrate dihydrate, Aladdin, w / w 4-5% (cont. Pd)) were ultrasonically dispersed in 20 mL of ethanol to form a dispersion B. Dispersion B was added dropwise to dispersion A under stirring and stirring was continued for 30 min. Subsequently, the mixture was rotary evaporated at 60 °C for 30 min, and the solid residue was transferred to a vacuum oven and dried at 80 °C for 8 h to obtain a black mixture powder Pd5Bi5 / CBM-0.1.

[0050] (2) The obtained Pd5Bi5 / CBM-0.1 powder was calcined in a tube furnace in a N2 atmosphere at a temperature of 700 °C for 2 h at a heating rate of 5 °C / min. After calcination, the mixture was naturally cooled to room temperature to obtain Pd5Bi5-NC 800 The difference between this comparative example and Example 3 lies in the ratio of melamine to CB in the feed, and the rest of the operation steps are exactly the same.

[0051] Comparative Example 7 Pd 0.5 Bi 0.5 -NC 800 Preparation of catalyst: (1) At room temperature, 200.0 mg of CB prepared in step (1) of Example 1 and 200.0 mg of melamine were mixed and dispersed in 30 mL of ethanol and ultrasonically treated for 30 min to form a uniform dispersion A. 2.32 mg of Bi(NO3)3·5H2O (Shanghai test, 99.9%) and 43.3 mg of Pd(NO3)2 (palladium nitrate dihydrate, Aladdin, w / w 4-5% (cont. Pd)) were ultrasonically dispersed in 20 mL of ethanol to form a dispersion B. Dispersion B was added dropwise to dispersion A under stirring and stirring was continued for 30 min. Subsequently, the mixture was rotary evaporated at 60 °C for 30 min, and the solid residue was transferred to a vacuum oven and dried at 80 °C for 8 h to obtain a black mixture powder Pd 0.5 Bi 0.5 / CBM.

[0052] (2) The obtained Pd 0.5 Bi 0.5 The / CBM powder was calcined in a tube furnace in a N2 atmosphere at 800 °C for 2 h at a heating rate of 5 °C / min. After calcination, it was naturally cooled to room temperature to obtain Pd 0.5 Bi 0.5 -NC 800 The difference between Comparative Example 7 and Example 3 lies in the amount of Pd and Bi sources fed, and the rest of the preparation methods are the same.

[0053] The catalytic effects of the supported catalysts prepared in the above examples and control examples were tested in sequence, and the testing methods were: 0.05 g of supported catalyst (or CB in Control Example 1 or NC in Control Example 2, serving as a blank control), 1.08 g (10 mmol) of benzyl alcohol, 20 mL of methanol, and 0.173 g (1.25 mmol) of K2CO3 were added to a 150 mL reactor and dispersed evenly by ultrasonication. The mixture was stirred at 60°C under an atmosphere of industrial oxygen (95%) for 8 h. After the reaction, it was naturally cooled to room temperature. After removing the catalyst through membrane filtration of the organic phase, the remaining reaction solution was directly analyzed by GC. The benzyl alcohol conversion, methyl benzoate yield, and selectivity were calculated using the normalization method as follows: The results are shown in Table 1.

[0054] Table 1 Catalytic performance of the catalysts for the oxidative esterification of benzyl alcohol and methanol to methyl benzoate

[0055] Reaction conditions: catalyst 0.05 g, benzyl alcohol (10 mmol) 1.08 g, potassium carbonate (1.25 mmol) 0.173 g, reaction temperature 60°C, standard atmospheric pressure, atmosphere of 95.0% industrial oxygen, reaction time 8 h.

[0056] As shown in Table 1, CB and NC supports have almost no catalytic activity for oxidative esterification (Comparative Example 1, Comparative Example 2). 10 -NC 800 The oxidative esterification reaction also showed no catalytic activity (Comparative Example 4). 10 -NC 800 , the selectivity and yield were only 82.5% (Comparative Example 3). In contrast, when Bi(NO₃)₃·5H₂O and Pd(NO₃)₂ were present simultaneously, the prepared catalysts showed significant improvements in conversion, selectivity, and yield. The catalysts in Examples 1–5 were able to achieve nearly complete conversion of the feedstock, exhibiting good selectivity and yield. Lowering the pyrolysis temperature resulted in insufficient catalytic activity (Comparative Example 5); reducing the mass ratio of melamine to M resulted in insufficient ammonia generation, making it difficult to completely reduce Pd and Bi, similarly leading to insufficient conversion (Comparative Example 6). Furthermore, too little Pd content also reduced the catalyst's reactivity, preventing the intermediate benzaldehyde from further reaction.

[0057] The above results show that in Pd x Bi y / NC t In the oxidative esterification reaction catalyzed by the catalyst, Pd serves as the catalytic active center and benefits from a synergistic effect with Bi, significantly enhancing catalytic activity. Nitrogen doping in the support improves the interaction between the active component and the support, further modulating the surface charge characteristics of the catalyst, anchoring the active component, and enhancing catalytic activity. Furthermore, the support effect effectively prevents nanoparticle agglomeration and improves catalyst stability.

[0058] Cyclic performance test of Pd5Bi5 / NC catalyst, the test method is: 0.05 g of supported catalyst, 1.08 g (10 mmol) of benzyl alcohol, 20 mL of methanol, and 0.173 g (1.25 mmol) of K₂CO₃ were added to a 150 mL reactor and ultrasonically dispersed. The mixture was stirred at 60°C under an industrial oxygen atmosphere for 8 h and then cooled to room temperature. The catalyst was recovered by filtration through an organic filter membrane, washed with methanol and water, and used in the next reaction. The filtrate was filtered through a syringe filter and directly analyzed by GC. The benzyl alcohol conversion, methyl benzoate yield, and selectivity were calculated using normalization.

[0059] Figure 5 This is the cyclic performance diagram of the Pd5Bi5-NC catalyst. After 5 cycles, the conversion rate, yield, and selectivity did not change significantly, and all were maintained above 90%. It can be seen that the Pd3Bi7 / NC catalyst has excellent cyclic stability.

[0060] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A nitrogen-doped carbon-supported PdBi bimetallic catalyst, characterized in that: The catalyst is Pd x Bi y / NC t Catalyst, wherein x is 0 to 20, y is 0 to 20, and t is 600 to 1000, and x and y cannot be 0 at the same time.

2. The nitrogen-doped carbon-supported PdBi bimetallic catalyst according to claim 1, characterized in that: The x is 1 to 12, the y is 1 to 12, and the t is 700 to 1000.

3. A method for preparing the nitrogen-doped carbon-supported PdBi bimetallic catalyst according to any one of claims 1 or 2, characterized in that: The preparation method comprises the following steps: (1) The carbon black material is treated with acid at high temperature and condensation reflux to obtain acidified carbon black powder; (2) mixing acidified carbon black powder, melamine, Bi(NO3)3·5H2O and Pd(NO3)2 in a solvent, removing the solvent, and drying to obtain a precursor; (3) The precursor is calcined in an inert atmosphere to obtain a nitrogen-doped carbon-loaded PdBi bimetallic catalyst.

4. The method for preparing a nitrogen-doped carbon-supported PdBi bimetallic catalyst according to claim 3, wherein: In the step (1), the acid is concentrated nitric acid, the high temperature is 80-120° C., and the treatment time is 4-24 hours.

5. The method for preparing nitrogen-doped carbon-supported PdBi bimetallic catalyst according to claim 4, characterized in that: In the step (2), the mass proportions of melamine, acidified carbon black powder, Bi(NO3)3·5H2O and Pd(NO3)2 are 10 to 300 parts of melamine, 150 to 210 parts of acidified carbon black powder, 0 to 100 parts of Bi(NO3)3·5H2O and 0 to 91 parts of Pd(NO3)2.

6. The method for preparing a nitrogen-doped carbon-supported PdBi bimetallic catalyst according to claim 5, characterized in that: The solvent in step (2) is any one of water, ethanol, methanol, isopropanol, dichloromethane, and acetonitrile.

7. The method for preparing a nitrogen-doped carbon-supported PdBi bimetallic catalyst according to claim 6, characterized in that: The calcination temperature in step (3) is 600-1000°C.

8. Use of the nitrogen-doped carbon-supported PdBi bimetallic catalyst according to claim 1 or 2 in catalyzing the oxidative esterification of benzyl alcohol and fatty alcohol to prepare ester compounds, characterized in that: After fully mixing benzyl alcohol, fatty alcohol, base and the nitrogen-doped carbon-supported PdBi bimetallic catalyst according to claim 1 or 2, react at 30-90° C. for 1-10 h under normal pressure air or oxygen atmosphere.

9. Use of the nitrogen-doped carbon-supported PdBi bimetallic catalyst according to claim 8 in catalyzing the oxidative esterification of benzyl alcohol and fatty alcohol to prepare ester compounds, characterized in that: The benzyl alcohol is benzyl alcohol and its derivatives, the fatty alcohol is methanol, the base additive is any one of Na2CO3, K2CO3, Cs2CO3, and potassium tert-butoxide, and the molar ratio of the benzyl alcohol to the base additive is 32 to 1:

1.

10. Use of the nitrogen-doped carbon-supported PdBi bimetallic catalyst according to claim 9 in catalyzing the oxidative esterification of benzyl alcohol and fatty alcohol to prepare ester compounds, characterized in that: The amount ratio of the nitrogen-doped carbon-supported PdBi bimetallic catalyst to the benzyl alcohol is 1.0 to 20.0 g / mol.

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