Palladium on carbon catalyst, process for its preparation and use

Abstract

The present application provides a palladium-carbon catalyst, a preparation method and application thereof. The palladium-carbon catalyst comprises an activated carbon carrier and metal palladium and metal ruthenium supported on the carrier, wherein the atomic proportion of exposed Pd(111) crystal faces in the catalyst is 25%-75%. When the palladium-carbon catalyst is applied to crude terephthalic acid hydrogenation refining, the content of residual p-carboxybenzaldehyde can be effectively reduced.

Description

Technical Field

[0001] This invention belongs to the field of catalysts, specifically relating to a palladium-on-carbon catalyst, its preparation method, and its application. Background Technology

[0002] Purified terephthalic acid, commonly known as PTA, is a basic raw material for the synthesis of polyethylene terephthalate (PET). Crude terephthalic acid (CTA) contains a small amount of impurity p-carboxybenzaldehyde (4-CBA), which affects the subsequent esterification performance of PTA. An effective industrial method for removing 4-CBA from CTA involves hydrogenating it with a palladium catalyst to convert it into water-soluble hydroxymethylbenzoic acid and p-methylbenzoic acid, followed by multiple crystallization and centrifugation processes to separate and purify the CTA. Currently, palladium-on-carbon catalysts are the main industrial catalysts. During the hydrogenation catalysis process, only a few surface-active atoms of Pd nanoparticles participate in the reaction, resulting in a significant reduction in Pd atom utilization. Therefore, the catalyst preparation method and the distribution of palladium on the support have a significant impact on catalyst performance. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides a palladium-on-carbon catalyst and a method for preparing the palladium-on-carbon catalyst. When the palladium-on-carbon catalyst provided by this invention is applied in the hydrogenation purification of crude terephthalic acid, it can effectively reduce the content of residual p-carboxybenzaldehyde.

[0004] In a first aspect, the palladium-on-carbon catalyst provided by the present invention comprises an activated carbon support and metallic palladium and metallic ruthenium supported on the support, wherein the atomic percentage of exposed Pd(111) crystal planes in the catalyst is 25%-75%, for example, 27%, 30%, 33%, 35%, 37%, 40%, 43%, 45%, 47%, 49%, 50%, 51%, 53%, 55%, 57%, 59%, 60%, 61%, 63%, 65%, 67%, 69%, 70%, 72%, 74% or any value between them. This invention simultaneously loads palladium and ruthenium onto an activated carbon support and controls the atomic percentage of exposed Pd(111) crystal faces within the aforementioned range. On one hand, the presence of ruthenium provides a confined platform for the growth of Pd nanoparticles, limiting the atomic percentage of the (111) facets of Pd nanoparticles to a suitable range. This ensures sufficient active sites on the surface of the Pd nanoparticles for reactant adsorption and desorption, while minimizing the loss of non-reacting atoms within the particles, thus improving Pd utilization under the same loading conditions. On the other hand, the hydrogen spillover effect of Pd allows Ru atoms, which have relatively low hydrogenation activity, to also possess high activity, resulting in better overall catalyst reaction performance and lower cost.

[0005] In some embodiments, the proportion of atoms exposing the Pd(111) crystal plane in the catalyst is 30%-75%.

[0006] In some embodiments, the proportion of atoms exposing the Pd(111) crystal plane in the catalyst is 45%-65%.

[0007] In some embodiments, the mass content of palladium is 0.1%-0.5% based on the mass of the catalyst. In some embodiments, the mass content of palladium is 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, or any value between them.

[0008] In some embodiments, the ruthenium content is 0.1%-0.5% by mass, based on the mass of the catalyst. In some embodiments, the ruthenium content is 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, or any value between them.

[0009] Secondly, the method for preparing the palladium-on-carbon catalyst provided by the present invention includes:

[0010] S1: Activated carbon carrier for acid pretreatment;

[0011] S2: The activated carbon support is mixed with a solution containing a ruthenium source to obtain a first mixture;

[0012] S3: The first mixture is mixed with a complexing agent and then mixed with a solution containing a palladium source to obtain a second mixture;

[0013] S4: Allow the second mixture to stand, dry, and reduce.

[0014] The method of the present invention effectively constructs a suitable atomic exposure ratio on the surface of Pd grains by first loading ruthenium on an activated carbon support and then loading palladium, thus efficiently utilizing Pd active sites and successfully achieving the goal of reducing the content of the noble metal Pd and efficiently removing 4-CBA.

[0015] In some embodiments, in S1, the acid pretreatment includes reacting activated carbon with an oxidizing acid followed by calcination. Pre-treating the activated carbon with acid before loading can enrich the carbon layer surface with more carboxyl and carbonyl functional groups. These functional groups can electrostatically adsorb Ru cations within the corresponding pH range, constructing a more dispersed RuO particle platform, which then allows for more uniform and controlled growth of Pd nanoparticles.

[0016] In some embodiments, the oxidizing acid includes at least one of nitric acid, sulfuric acid, and perchloric acid. In some embodiments, the oxidizing acid is selected from nitric acid with a concentration of 40%-60%, for example, 50% or 55%.

[0017] In some embodiments, the calcination temperature is 400°C-600°C, for example, 450°C, 500°C, or 550°C. In some embodiments, the calcination is carried out under the protection of an inert gas. In some embodiments, the inert gas is selected from nitrogen and / or argon.

[0018] In some embodiments, mixing in S2 is carried out at room temperature, for example, 5°C-35°C.

[0019] In some embodiments, the mixing of the first mixture with the complexing agent in step S3 is carried out at room temperature, for example, 5°C-35°C. In some embodiments, after the first mixture with the complexing agent in step S3 is mixed, it is allowed to stand at room temperature, for example, 5°C-35°C for a certain period of time, for example, 2h-10h, before being mixed with a solution containing a palladium source. Preferably, the mixing is carried out at room temperature, for example, 5°C-35°C.

[0020] In some embodiments, the activated carbon carrier is selected from one or more of coal-based charcoal, wood-based charcoal, or fruit shell charcoal. In some embodiments, the activated carbon carrier is selected from coconut shell activated carbon.

[0021] In some embodiments, the specific surface area of ​​the activated carbon is preferably 800 μm. 2 / g-1600m 2 / g, for example, but not limited to, the activated carbon with a specific surface area of ​​900m² 2 / g, 1000m 2 / g、1100m 2 / g、1200m 2 / g、1300m 2 / g, 1400m 2 / g, 1500m 2 / g etc.

[0022] In some embodiments, the activated carbon has a pore volume of 0.35 mL / g to 0.80 mL / g, for example, but not limited to, 0.4 mL / g, 0.45 mL / g, 0.5 mL / g, 0.55 mL / g, 0.6 mL / g, 0.65 mL / g, 0.75 mL / g, etc.

[0023] In some embodiments, the mass ratio of palladium to ruthenium in the solution containing the ruthenium source and the solution containing the palladium source is (0.2-4):1. In some embodiments, the mass ratio of palladium to ruthenium is 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, or any value between them.

[0024] In some embodiments, the ruthenium source is selected from RuCl3 and its ammonia complex. In some embodiments, the pH of the solution containing the ruthenium source is 1-12, for example, 2, 4, 6, 7, 8.5, 9, 9.5, 10, 10.5, 11, or 11.5. In some embodiments, the pH of the solution containing the ruthenium source is 8-12. Alkaline solutions containing the ruthenium source are beneficial for the synthesis of the catalyst of the present invention.

[0025] In some embodiments, the palladium source is selected from H₂PdCl₄ and its hydrochloric acid complex. In some embodiments, the pH of the solution containing the palladium source is 1-12, for example, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 9, or 11. In some embodiments, the pH of the solution containing the palladium source is 1-6. Acidic solutions containing palladium and ruthenium sources are beneficial for palladium dispersion. In some embodiments, the mass of the ruthenium source in the solution containing the ruthenium source, based on the mass of ruthenium, is 0.1%-0.5% of the acid-pretreated activated carbon support, for example, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, or any value between these values.

[0026] In some embodiments, the palladium source in the solution contains 0.1% to 0.5% of the acid-pretreated activated carbon support by mass of palladium, for example, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, or any value between therewith.

[0027] In some embodiments, the complexing agent is selected from at least one of 8-hydroxyquinoline, ethylenediaminetetraacetic acid, and pyromellitic acid.

[0028] In some embodiments, the mass ratio of the complexing agent to the acid-pretreated activated carbon carrier is (0.5-15):50, for example, 1.5:50, 2:50, 3:50, 4:50, 5:50, 6:50, 7:50, 8:50, 9:50, 9.5:50, 11:50, 12:50, 14:50, or any value between them. In some embodiments, the mass ratio of the complexing agent to the acid-pretreated activated carbon carrier is (1-10):50. In some embodiments, in S4, the settling temperature is 10°C-30°C, for example, 15°C, 20°C, or 25°C. In some embodiments, in S4, the settling time is 1h-10h, for example, 2h, 3h, 4h, 5h, 6h, 7h, 8h, or 9h.

[0029] In some embodiments, in S4, the drying temperature is 50°C-150°C, for example, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C or 140°C.

[0030] In some embodiments, in S4, the reduction conditions include reduction in a mixed atmosphere of hydrogen and argon, wherein the volume concentration of hydrogen is 0.5%-5%. In some embodiments, the volume concentration of hydrogen is 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or any value between them.

[0031] In some embodiments, the flow rate of the hydrogen and argon mixture is 1 mL / min to 40 mL / min, for example, 5 mL / min, 10 mL / min, 15 mL / min, 20 mL / min, 25 mL / min, 30 mL / min or 35 mL / min.

[0032] In some embodiments, the reduction time in S4 is 1-5 hours, for example, 2 hours, 3 hours, or 4 hours. In some embodiments, the reduction temperature in S4 is 150°C-300°C, for example, 180°C, 200°C, 220°C, 240°C, 260°C, or 280°C.

[0033] In some embodiments, the method includes purging with a mixture of oxygen and argon after the reduction reaction. In some embodiments, the oxygen volume concentration in the oxygen and argon mixture is 0.5%-5%. In some embodiments, the oxygen volume concentration is 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or any value between them.

[0034] In some embodiments, the flow rate of the mixed gas is 1 mL / min to 40 mL / min, for example, 5 mL / min, 10 mL / min, 15 mL / min, 20 mL / min, 25 mL / min, 30 mL / min or 35 mL / min.

[0035] In some embodiments, the purging temperature is 80°C-150°C, for example, 90°C, 100°C, 110°C, 120°C, 130°C, or 140°C. In some embodiments, the purging time is 0.5h-3h, for example, 1h, 1.5h, 2h, or 2.5h.

[0036] In some embodiments, the preparation method of the palladium-on-carbon catalyst includes the following specific steps:

[0037] (a) Activated carbon is reacted with an oxidizing acid and then calcined to obtain a pretreated support.

[0038] (b) Provide a solution A containing a ruthenium source and a solution B containing a palladium source;

[0039] (c) First, add solution A dropwise to the pretreated carrier, add a complexing agent, then add solution B, let stand at room temperature, and then heat to dry;

[0040] (d) After reducing the dry solid hydrogen, the catalyst is purged in an oxygen mixture to obtain the final product.

[0041] Thirdly, the present invention provides the application of the palladium-on-carbon catalyst described in the first aspect or the palladium-on-carbon catalyst prepared by the preparation method described in the second aspect in the hydrogenation purification of crude terephthalic acid.

[0042] Fourthly, the present invention provides a method for hydrogenating and refining crude terephthalic acid, which includes using water as a solvent, crude terephthalic acid containing 4-CBA and hydrogen as raw materials, and reacting in the presence of the palladium-on-carbon catalyst described in the first aspect or the palladium-on-carbon catalyst prepared by the preparation method described in the second aspect to remove 4-CBA from the crude terephthalic acid.

[0043] In some embodiments, the hydrorefining reaction temperature can be 250°C-295°C, for example, 265°C-290°C. In some embodiments, the hydrorefining reaction pressure can be 6.5 MPa-10.0 MPa, for example, 7.0 MPa-9.0 MPa. In some embodiments, the hydrogen partial pressure can be 0.5 MPa-1.0 MPa.

[0044] In some implementations, the reaction can be carried out in a batch or a continuous manner.

[0045] Beneficial technical effects of the present invention:

[0046] By adjusting the loading methods of Pd and Ru elements, a suitable ratio of exposed atoms on the surface of Pd grains was effectively constructed, efficiently utilizing Pd active sites and successfully achieving the goal of reducing the content of the precious metal Pd and efficiently removing 4-CBA. Compared with the traditional palladium-carbon catalyst with a loading of 0.5 wt%, this significantly reduces costs and improves economic efficiency. Attached Figure Description

[0047] Figure 1 The image shows the HAADF-STEM image of the palladium-on-carbon catalyst in Example 1 of this invention. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. The specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention in any way. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of this disclosure. Such structures and techniques have also been described in many publications.

[0049] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0050] The present invention will be described in detail below through embodiments.

[0051] In this invention, the positions of Pd nanoparticles were determined by EDS surface scanning using HAADF-STEM. Then, the atomic percentage of exposed Pd(111) crystal planes in the palladium-on-carbon catalyst was determined by randomly analyzing the particle size and morphology of 200 Pd nanoparticles. The specific method for calculating the number of crystal plane atoms is as follows:

[0052]

[0053] The diameter d of a Pd atom Pd The diameter is 0.276 nm, and the relationship between the number of Pd atoms in a cubic octahedron and the average particle size of its nanoparticles is as follows:

[0054] d = 1.105 × N T 1 / 3 ×d Pd atom

[0055] The percentage of atoms on the Pd(111) surface = N 111 / N S

[0056] Example 1

[0057] 1. Catalyst Preparation

[0058] (a) Weigh 50 grams of 4-8 mesh flake activated carbon from coconut shells, which has a specific surface area of ​​1100 μm. 2 / g, with a pore volume of 0.6mL / g. The above activated carbon was mixed with 500mL of concentrated nitric acid (50%) in a stirred tank for 1 hour under sealed conditions. It was then filtered and washed with a large amount of pure water until the filtrate was neutral. After drying in an oven at 100℃ for 6 hours, it was calcined in an inert gas furnace at 500℃, denoted as AC-D.

[0059] (b) Prepare RuCl3 aqueous solution (0.01 g / mL as Ru) and H2PdCl4 aqueous solution (0.01 g / mL as Pd). Take 7.5 mL of RuCl3 solution and add pure water to make up to 50 mL, then add ammonia to adjust the pH to 12, and record this as solution A; take 17.5 mL of H2PdCl4 aqueous solution and add pure water to make up to 50 mL, then adjust the pH to 1 with HCl (0.5 mol / L) solution, and record this as solution B;

[0060] (c) Solution A was then added dropwise to 50g AC-D while stirring continuously for 1 hour, followed by the addition of 5g 8-hydroxyquinoline, and then allowed to stand at 25°C for 6 hours. Solution B was then immediately added dropwise to the solid while stirring continuously for 1 hour, followed by drying at 25°C for 6 hours and then drying at 120°C for 12 hours.

[0061] (d) The dried solid was placed in a tube furnace and H2 / Ar (1%) mixture was introduced at a rate of 20 mL / min. The mixture was reduced at 280 °C for 1 h. The temperature was then lowered to 100 °C, and the gas was switched to O2 / Ar mixture for 1 h.

[0062] The preparation conditions are listed in Table 1.

[0063] 2. Catalyst Evaluation

[0064] The evaluation was conducted using a batch stirred tank reactor, under the following conditions:

[0065] Catalyst loading weight: 2g;

[0066] The reaction raw materials consist of 30g crude terephthalic acid, pure water, and 10g 4-CBA.

[0067] Reaction pressure: 7.5 MPa;

[0068] Reaction temperature: 280℃;

[0069] Reaction time: 30 min;

[0070] Catalyst evaluation methods:

[0071] The catalyst activity was evaluated in a 2L batch reactor. The reactants were added to the reactor, and the catalyst was loaded into a rotating frame inside the reactor. The reaction conditions were as described above, with a hydrogen partial pressure of 1 MPa. After the reaction, the hydrogenated terephthalic acid was washed with ultrapure water, filtered, dried, and samples were taken to determine the 4-CBA content. The 4-CBA content was determined using an HP1100 HPLC system, and the experimental results are listed in Table 2.

[0072] Example 2

[0073] 1. Catalyst Preparation

[0074] (a) Weigh 50 grams of 4-8 mesh flake activated carbon from coconut shells, which has a specific surface area of ​​1100 μm. 2 / g, pore volume 0.6mL / g. It was mixed with 500mL concentrated nitric acid (50%) in a stirred tank for 1h under sealed conditions, followed by filtration and washing with a large amount of pure water until the filtrate was neutral. After drying in an oven at 100℃ for 6h, it was calcined in an inert gas furnace at 500℃, denoted as AC-D;

[0075] (b) Prepare RuCl3 aqueous solution (0.01 g / mL as Ru) and H2PdCl4 aqueous solution (0.01 g / mL as Pd). Take 7.5 mL of RuCl3 solution and add pure water to make up to 50 mL, then add HCl (0.5 mol / L) dropwise to adjust the pH to 1, and record this as solution A; take 17.5 mL of H2PdCl4 aqueous solution and add pure water to make up to 50 mL, then adjust the pH to 12 with ammonia, and record this as solution B;

[0076] (c) Solution A was then added dropwise to 50g AC-D while stirring continuously for 1 hour, followed by the addition of 5g 8-hydroxyquinoline, and then allowed to stand at 25°C for 6 hours. Solution B was then immediately added dropwise to the solid while stirring continuously for 1 hour, followed by drying at 25°C for 6 hours and then drying at 120°C for 12 hours.

[0077] (d) The dried solid was placed in a tube furnace and H2 / Ar (1%) mixture was introduced at a rate of 20 mL / min. The mixture was reduced at 280 °C for 1 h. The temperature was then lowered to 100 °C, and the gas was switched to O2 / Ar mixture for 1 h.

[0078] The preparation conditions are listed in Table 1.

[0079] 2. Catalyst Evaluation

[0080] The evaluation was conducted using a batch stirred tank reactor, under the following conditions:

[0081] Catalyst loading weight: 2g;

[0082] The reaction raw materials consist of 30g crude terephthalic acid, pure water, and 10g 4-CBA.

[0083] Reaction pressure: 7.5 MPa;

[0084] Reaction temperature: 280℃;

[0085] Reaction time: 30 min;

[0086] The catalyst evaluation method is the same as in Example 1.

[0087] The experimental results are listed in Table 2.

[0088] Example 3

[0089] 1. Catalyst Preparation

[0090] (a) Weigh 50 grams of 4-8 mesh flake activated carbon from coconut shells, which has a specific surface area of ​​1100 μm. 2 / g, with a pore volume of 0.6mL / g. The above activated carbon was mixed with 500mL of concentrated nitric acid (50%) in a stirred tank for 1 hour under sealed conditions. It was then filtered and washed with a large amount of pure water until the filtrate was neutral. After drying in an oven at 100℃ for 6 hours, it was calcined in an inert gas furnace at 500℃, denoted as AC-D.

[0091] (b) Prepare RuCl3 aqueous solution (0.01 g / mL as Ru) and H2PdCl4 aqueous solution (0.01 g / mL as Pd). Take 7.5 mL of RuCl3 solution and add pure water to make up to 50 mL, then add ammonia to adjust the pH to 9, and record this as solution A; take 17.5 mL of H2PdCl4 aqueous solution and add pure water to make up to 50 mL, then adjust the pH to 4 with HCl (0.5 mol / L) solution, and record this as solution B;

[0092] (c) Solution A was then added dropwise to 50g AC-D while stirring continuously for 1 hour, followed by the addition of 5g 8-hydroxyquinoline, and then allowed to stand at 25°C for 6 hours. Solution B was then immediately added dropwise to the solid while stirring continuously for 1 hour, followed by drying at 25°C for 6 hours and then drying at 120°C for 12 hours.

[0093] (d) The dried solid was placed in a tube furnace and H2 / Ar (1%) mixture was introduced at a rate of 20 mL / min. The mixture was reduced at 280 °C for 1 h. The temperature was then lowered to 100 °C, and the gas was switched to O2 / Ar mixture for 1 h.

[0094] The preparation conditions are listed in Table 1.

[0095] 2. Catalyst Evaluation

[0096] Same as Example 1.

[0097] Example 4

[0098] 1. Catalyst Preparation

[0099] (a) Weigh 50 grams of 4-8 mesh flake activated carbon from coconut shells, which has a specific surface area of ​​1100 μm. 2 / g, with a pore volume of 0.6mL / g. The above activated carbon was mixed with 500mL of concentrated nitric acid (50%) in a stirred tank for 1 hour under sealed conditions. It was then filtered and washed with a large amount of pure water until the filtrate was neutral. After drying in an oven at 100℃ for 6 hours, it was calcined in an inert gas furnace at 500℃, denoted as AC-D.

[0100] (b) Prepare RuCl3 aqueous solution (0.01 g / mL as Ru) and H2PdCl4 aqueous solution (0.01 g / mL as Pd). Take 7.5 mL of RuCl3 solution and add pure water to make up to 50 mL, then add ammonia to adjust the pH to 12, and record this as solution A; take 17.5 mL of H2PdCl4 aqueous solution and add pure water to make up to 50 mL, then adjust the pH to 1 with HCl (0.5 mol / L) solution, and record this as solution B;

[0101] (c) Solution A was then added dropwise to 50g AC-D while stirring continuously for 1 hour, followed by the addition of 10g 8-hydroxyquinoline, and then allowed to stand at 25°C for 6 hours. Solution B was then immediately added dropwise to the solid while stirring continuously for 1 hour, followed by drying at 25°C for 6 hours and then drying at 120°C for 12 hours.

[0102] (d) The dried solid was placed in a tube furnace and H2 / Ar (1%) mixture was introduced at a rate of 20 mL / min. The mixture was reduced at 280 °C for 1 h. The temperature was then lowered to 100 °C, and the gas was switched to O2 / Ar mixture for 1 h.

[0103] The preparation conditions are listed in Table 1.

[0104] 2. Catalyst Evaluation

[0105] Same as Example 1.

[0106] Comparative Example 1

[0107] 1. Catalyst Preparation

[0108] (a) Weigh 50 grams of 4-8 mesh flake activated carbon from coconut shells, which has a specific surface area of ​​1100 μm. 2 / g, pore volume 0.6mL / g. It was mixed with 500mL concentrated nitric acid (50%) in a stirred tank for 1h under sealed conditions, followed by filtration and washing with a large amount of pure water until the filtrate was neutral. After drying in an oven at 100℃ for 6h, it was calcined in an inert gas furnace at 500℃, denoted as AC-D;

[0109] (b) Prepare RuCl3 aqueous solution (0.01 g / mL as Ru) and H2PdCl4 aqueous solution (0.01 g / mL as Pd). Take 7.5 mL of RuCl3 solution and add pure water to make up to 50 mL, then add ammonia water dropwise to adjust the pH to 12, and record this as solution A; take 17.5 mL of H2PdCl4 solution... l4 The aqueous solution was diluted to 50 mL with pure water and the pH was adjusted to 1 with HCl (0.5 mol / L) solution. This solution is denoted as solution B.

[0110] (c) Solution B was then added dropwise to 50g AC-D while stirring continuously for 1 hour, followed by the addition of 5g 8-hydroxyquinoline, and then allowed to stand at 25°C for 6 hours. Immediately afterwards, solution A was added dropwise to the solid while stirring continuously for 1 hour, followed by drying at 25°C for 6 hours and then drying at 120°C for 12 hours.

[0111] (d) The dried solid was placed in a tube furnace and H2 / Ar (1%) mixture was introduced at a rate of 20 mL / min. The mixture was reduced at 280 °C for 1 h. The temperature was then lowered to 100 °C, and the gas was switched to O2 / Ar mixture for 1 h.

[0112] The preparation conditions are listed in Table 1.

[0113] 2. Catalyst Evaluation

[0114] The evaluation was conducted using a batch stirred tank reactor, under the following conditions:

[0115] Catalyst loading weight: 2g;

[0116] The reaction raw materials consist of 30g crude terephthalic acid, pure water, and 10g 4-CBA.

[0117] Reaction pressure: 7.5 MPa;

[0118] Reaction temperature: 280℃;

[0119] Reaction time: 30 min;

[0120] The catalyst evaluation method is the same as in Example 1.

[0121] The experimental results are listed in Table 2.

[0122] Comparative Example 2

[0123] 1. Catalyst Preparation

[0124] (a) Weigh 50 grams of 4-8 mesh flake activated carbon from coconut shells, which has a specific surface area of ​​1100 μm. 2 / g, with a pore volume of 0.6mL / g. The above activated carbon was mixed with 500mL of concentrated nitric acid (50%) in a stirred tank for 1 hour under sealed conditions. It was then filtered and washed with a large amount of pure water until the filtrate was neutral. After drying in an oven at 100℃ for 6 hours, it was calcined in an inert gas furnace at 500℃, denoted as AC-D.

[0125] (b) Prepare RuCl3 aqueous solution (0.01 g / mL as Ru) and H2PdCl4 aqueous solution (0.01 g / mL as Pd). Take 7.5 mL of RuCl3 solution and add pure water to make up to 50 mL, then add HCl (0.5 mol / L) dropwise to adjust the pH to 1, and record this as solution A; take 17.5 mL of H2PdCl4 aqueous solution and add pure water to make up to 50 mL, then adjust the pH to 12 with ammonia, and record this as solution B;

[0126] (c) Solution B was then added dropwise to 50g AC-D while stirring continuously for 1 hour, followed by the addition of 1g 8-hydroxyquinoline, and then allowed to stand at 25°C for 6 hours. Immediately afterwards, solution A was added dropwise to the solid while stirring continuously for 1 hour, followed by drying at 25°C for 6 hours and then drying at 120°C for 12 hours.

[0127] (d) The dried solid was placed in a tube furnace and a H2 / Ar (1%) mixture was introduced at a rate of 20 mL / min. The mixture was reduced at 280 °C for 1 h. The temperature was then lowered to 100 °C, and the gas was switched to an O2 / Ar mixture for 1 h. The preparation conditions are listed in Table 1.

[0128] 2. Catalyst Evaluation

[0129] Same as Example 1.

[0130] Comparative Example 3

[0131] 1. Catalyst Preparation

[0132] (a) Weigh 50 grams of 4-8 mesh flake activated carbon from coconut shells, with a specific surface area of ​​1100 μm. 2 / g, pore volume 0.6mL / g. It was mixed with 500mL concentrated nitric acid (50%) in a stirred tank for 1h under sealed conditions, followed by filtration and washing with a large amount of pure water until the filtrate was neutral. After drying in an oven at 100℃ for 6h, it was calcined in an inert gas furnace at 500℃, denoted as AC-D;

[0133] (b) Prepare RuCl3 aqueous solution (0.01 g / mL as Ru) and H2PdCl4 aqueous solution (0.01 g / mL as Pd). Take 7.5 mL of RuCl3 solution and add pure water to make up to 50 mL, then add ammonia to adjust the pH to 1, and record this as solution A; take 17.5 mL of H2PdCl4 aqueous solution and add pure water to make up to 50 mL, then adjust the pH to 12 with HCl (0.5 mol / L) solution, and record this as solution B;

[0134] (c) Then, solutions A and B were added dropwise to 50g AC-D and stirred continuously for 2h. Then, 5g of 8-hydroxyquinoline was added, and the mixture was allowed to stand at 25℃ for 6h and dried at 120℃ for 12h.

[0135] (d) The dried solid was placed in a tube furnace and H2 / Ar (1%) mixture was introduced at a rate of 20 mL / min. The mixture was reduced at 280 °C for 1 h. The temperature was then lowered to 100 °C, and the gas was switched to O2 / Ar mixture for 1 h.

[0136] The preparation conditions are listed in Table 1.

[0137] 2. Catalyst Evaluation

[0138] The evaluation was conducted using a batch stirred tank reactor, under the following conditions:

[0139] Catalyst loading weight: 2g;

[0140] The reaction raw materials consist of 30g crude terephthalic acid, pure water, and 10g 4-CBA.

[0141] Reaction pressure: 7.5 MPa;

[0142] Reaction temperature: 280℃;

[0143] Reaction time: 30 min;

[0144] The catalyst evaluation method is the same as in Example 1.

[0145] The experimental results are listed in Table 2.

[0146] Comparative Example 4

[0147] 1. Catalyst Preparation

[0148] (a) Prepare RuCl3 aqueous solution (0.01 g / mL as Ru) and H2PdCl4 aqueous solution (0.01 g / mL as Pd). Take 7.5 mL of RuCl3 solution and add pure water to make up to 50 mL, then add ammonia to adjust the pH to 12, and record this as solution A; take 17.5 mL of H2PdCl4 aqueous solution and add pure water to make up to 50 mL, then adjust the pH to 1 with HCl (0.5 mol / L) solution, and record this as solution B;

[0149] (b) Solution A was then added dropwise to 50g of activated carbon and stirred continuously for 1 hour, followed by the addition of 10g of 8-hydroxyquinoline, and then allowed to stand at 25°C for 6 hours. Solution B was then immediately added dropwise to the solid and stirred continuously for 1 hour, followed by drying at 25°C for 6 hours and then drying at 120°C for 12 hours.

[0150] (c) The dried solid was placed in a tube furnace and H2 / Ar (1%) mixture was introduced at a rate of 20 mL / min and reduced at 280 °C for 1 h; the temperature was then lowered to 100 °C and the gas was switched to O2 / Ar mixture and introduced for 1 h.

[0151] The preparation conditions are listed in Table 1.

[0152] 2. Catalyst Evaluation

[0153] Same as Example 1.

[0154] Comparative Example 5

[0155] 1. Catalyst Preparation

[0156] (a) Weigh 50 grams of 4-8 mesh flake activated carbon from coconut shells, which has a specific surface area of ​​1100 μm. 2 / g, with a pore volume of 0.6mL / g. The above activated carbon was mixed with 500mL of concentrated nitric acid (50%) in a stirred tank for 1 hour under sealed conditions. It was then filtered and washed with a large amount of pure water until the filtrate was neutral. After drying in an oven at 100℃ for 6 hours, it was calcined in an inert gas furnace at 500℃, denoted as AC-D.

[0157] (b) Prepare an aqueous solution of H₂PdCl₄ (0.01 g / mL, calculated as Pd). Take 17.5 mL of the H₂PdCl₄ aqueous solution and add pure water to make up to 50 mL. Adjust the pH to 1 with HCl (0.5 mol / L) solution. This solution is denoted as solution B.

[0158] (c) Solution B was then added dropwise to 50g AC-D and stirred continuously for 1 hour, then allowed to stand at 25°C for 6 hours and dried at 120°C for 12 hours.

[0159] (d) The dried solid was placed in a tube furnace and H2 / Ar (1%) mixture was introduced at a rate of 20 mL / min. The mixture was reduced at 280 °C for 1 h. The temperature was then lowered to 100 °C, and the gas was switched to O2 / Ar mixture for 1 h.

[0160] The preparation conditions are listed in Table 1.

[0161] 2. Catalyst Evaluation

[0162] Same as Example 1.

[0163] Table 1

[0164]

[0165] Table 2

[0166]

[0167] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing a palladium-on-carbon catalyst, wherein, The palladium-on-carbon catalyst comprises an activated carbon support and metallic palladium and metallic ruthenium supported on the support, wherein the proportion of atoms exposing the Pd(111) crystal facets in the catalyst is 25%-75%. Specifically, based on the mass of the catalyst, the mass content of palladium is 0.1%-0.5%; the mass content of ruthenium is 0.1%-0.5%. The preparation method includes: S1: Provides an activated carbon carrier that has undergone acid pretreatment; the acid pretreatment includes reacting the activated carbon with an oxidizing acid followed by calcination. S2: The activated carbon support is mixed with a solution containing a ruthenium source to obtain a first mixture; S3: The first mixture is mixed with a complexing agent and then mixed with a solution containing a palladium source to obtain a second mixture; S4: Allow the second mixture to stand, dry, and reduce.

2. The preparation method according to claim 1, characterized in that, The oxidizing acid includes at least one of nitric acid, sulfuric acid, and perchloric acid.

3. The preparation method according to claim 1, characterized in that, The roasting temperature is 400℃-600℃.

4. The preparation method according to any one of claims 1-3, characterized in that, In the solutions containing ruthenium and palladium sources, the mass ratio of palladium to ruthenium is (0.2-4):1; and / or The ruthenium source is selected from RuCl3 and its ammonia complex, and the palladium source is selected from H2PdCl4 and its hydrochloric acid complex; and / or The pH of the solution containing the ruthenium source is 1-12; and / or The pH of the solution containing the palladium source is 1-12; and / or The complexing agent is selected from at least one of 8-hydroxyquinoline, ethylenediaminetetraacetic acid, and pyromellitic acid.

5. The preparation method according to claim 4, characterized in that, The pH of the solution containing the ruthenium source is 8-12.

6. The preparation method according to claim 4, characterized in that, The solution containing the palladium source has a pH of 1-6.

7. The preparation method according to any one of claims 1-3, characterized in that, In S4, the settling temperature is 10℃-30℃, and the settling time is 1h-10h; and / or The drying temperature is 50℃-150℃.

8. The preparation method according to any one of claims 1-3, characterized in that, In S4, the reduction conditions include: reduction in a mixed atmosphere of hydrogen and argon, wherein the volume concentration of hydrogen is 0.5%-5%, the reduction time is 1h-5h, and the reduction temperature is 150℃-300℃.

9. The preparation method according to any one of claims 1-3, characterized in that, The percentage of atoms exposing the Pd(111) crystal plane is 30%-75%.

10. The preparation method according to claim 9, characterized in that, The percentage of atoms exposing the Pd(111) crystal plane is 45%-65%.

11. A method for hydrogenating and refining crude terephthalic acid, comprising using water as a solvent, crude terephthalic acid containing 4-CBA and hydrogen as raw materials, and reacting in the presence of a palladium-carbon catalyst to remove 4-CBA from the crude terephthalic acid. in, The palladium-on-carbon catalyst comprises an activated carbon support and metallic palladium and metallic ruthenium supported on the support, wherein the proportion of atoms exposing the Pd(111) crystal facets in the catalyst is 25%-75%. Wherein, based on the mass of the catalyst, the mass content of palladium is 0.1%-0.5%; and the mass content of ruthenium is 0.1%-0.5%.

12. The method for hydrogenating and refining crude terephthalic acid according to claim 11, characterized in that, The percentage of atoms exposing the Pd(111) crystal plane is 30%-75%.

13. The method for hydrogenating and refining crude terephthalic acid according to claim 12, characterized in that, The percentage of atoms exposing the Pd(111) crystal plane is 45%-65%.

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