Precious metal-based catalyst as well as preparation method and application thereof

Abstract

The invention discloses a noble metal-based catalyst as well as a preparation method and application thereof, and belongs to the technical field of methanol steam reforming hydrogen production and catalysts. The noble metal-based catalyst comprises a carrier, an auxiliary agent metal and an active metal, the carrier comprises CeO2, and the shape of the carrier is a polyhedral nanoparticle accumulation body; the active metal comprises Pt; the auxiliary agent metal comprises In2O3; the active sites of the noble metal-based catalyst comprise less than 30% of Pt < 0 >, 60-90% of Pt < delta + > and less than 30% of Pt < 2 + >. According to the preparation method, the size of the polyhedral particles is controlled, so that the dispersity and the particle size of the active metal and the auxiliary metal are adjusted, Pt, the path and the performance are adjusted and controlled, and the methanol conversion rate is effectively increased.

Description

Technical Field

[0001] This application relates to the technical fields of hydrogen production by methanol steam reforming and catalysts, and particularly relates to a noble metal-based catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Due to its high efficiency and flexibility, the methanol steam reforming hydrogen production technology shows broad application prospects in the field of distributed hydrogen production. However, with the diversification of hydrogen demand scenarios, the requirements for the hydrogen production process and hydrogen purity are becoming increasingly strict. Although traditional copper-based catalysts have high catalytic activity, problems such as high pyrophoricity and poor stability limit their further development. Noble metal-based catalysts, especially platinum-based catalysts, have become potential alternative solutions due to their excellent stability and reactivity. However, the methanol conversion rate of traditional Pt-based catalysts still needs to be improved. Summary of the Invention

[0003] The main purpose of this application is to provide a noble metal-based catalyst, a preparation method thereof, and an application thereof, aiming to effectively improve the methanol conversion rate.

[0004] To achieve the above purpose, an embodiment of this application provides a noble metal-based catalyst, including: a carrier, a promoter metal, and an active metal;

[0005] The carrier includes CeO2, and the morphology of the carrier is a polyhedron nanoparticle aggregate;

[0006] The active metal includes Pt;

[0007] The promoter metal includes In2O3;

[0008] The active sites of the noble metal-based catalyst include: Pt 0 , Pt δ+ and Pt 2+ , where Pt 0 is less than 30%, Pt δ+ is 60-90%, and Pt 2+ is less than 30%.

[0009] In one embodiment, the specific surface area of the carrier is 35-70 m 2 g -1 ;

[0010] and / or, the pore volume of the carrier is 0.1-0.3 m 3 g -1 .

[0011] In one embodiment, the noble metal-based catalyst includes: 2-10 wt.% promoter metal and 0.5-2 wt.% active metal.

[0012] In one embodiment, the particle size of the carrier is 15 to 100 nm.

[0013] In one embodiment, the main exposed crystal plane of the carrier is (111);

[0014] and / or, the oxygen vacancy O of the noble metal-based catalyst v is 20 to 30%.

[0015] The embodiment of the present application further provides a preparation method of a noble metal-based catalyst, which is applied to prepare the noble metal-based catalyst as described above, and includes the following steps:

[0016] Prepare the carrier by a hydrothermal method, wherein the carrier includes CeO2, and the morphology of the carrier is a polyhedron nanoparticle aggregate;

[0017] Load the active metal and the promoter metal on the carrier to obtain the noble metal-based catalyst, wherein the promoter metal includes In2O3, the active metal includes Pt, and the active sites of the noble metal-based catalyst include: Pt 0 、Pt δ+ and Pt 2+ , wherein, Pt 0 is less than 30%, Pt δ+ is 60 to 90%, and Pt 2+ is less than 30%.

[0018] In one embodiment, the step of preparing the carrier by a hydrothermal method includes:

[0019] Mix the NaOH solution and the cerium nitrate solution to obtain a solid-liquid mixture;

[0020] Heat the solid-liquid mixture and centrifuge and wash to obtain the carrier.

[0021] In one embodiment, the heating temperature when heating the solid-liquid mixture is 100 to 200 °C, and the heating duration is 5 to 35 h.

[0022] In one embodiment, the step of loading the active metal and the promoter metal on the carrier to obtain the noble metal-based catalyst includes:

[0023] Prepare the active metal solution and the promoter metal solution;

[0024] Mix the active metal solution and the promoter metal solution to obtain a mixed solution;

[0025] Place the carrier in the mixed solution, take out the carrier loaded with the active metal and the promoter metal and calcine to obtain the noble metal-based catalyst.

[0026] The embodiment of the present application further provides an application of the above-mentioned noble metal-based catalyst in the methanol steam reforming reaction for hydrogen production.

[0027] One or more technical solutions proposed in the present application have at least the following technical effects: providing a noble metal-based catalyst, including: a carrier, a promoter metal, and an active metal; the carrier includes CeO2, and the morphology of the carrier is a polyhedral nanoparticle aggregate; the active metal includes Pt; the promoter metal includes In2O3; the active sites of the noble metal-based catalyst include: Pt 0 , Pt δ+ and Pt 2+ , where Pt 0 is less than 30%, Pt δ+ is 60-90%, and Pt 2+ is less than 30%. By using CeO2 with a polyhedral nanoparticle aggregate morphology as the carrier and adding In2O3 as the promoter metal, it is possible to promote the better dispersion of Pt, thereby regulating the valence states of the active sites of Pt to: Pt 0 , Pt δ+ and Pt 2+ , while Pt 0 is less than 30%, Pt δ+ is 60-90%, and Pt 2+ is less than 30%; furthermore, it promotes the reaction path of Pt in the noble metal-based catalyst to include: the direct path of Pt δ+ , the Pt δ+ -In2O3, Pt δ+ -CeO2, Pt 0 -Pt 2+ and Pt 0 -Pt δ+ 's synergistic path, and taking the direct path of Pt δ+ as the main reaction path. Furthermore, when the noble metal-based catalyst is applied to methanol steam reforming (MSR) for hydrogen production, the Pt metal site (Pt δ+ ) will be used as an efficient active center, thereby effectively promoting methanol dissociation and water molecule activation, accelerating the methanol steam reforming reaction, and improving the methanol conversion rate. The synergistic effect of the Pt δ+ -In2O3, Pt δ+ -CeO2, Pt 0 -Pt 2+ and Pt 0 -Pt δ+ 's synergistic path can further improve the reaction selectivity and efficiency, especially by enhancing the adsorption and conversion of intermediates and reducing the generation of CO in by-products. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the reaction path of the noble metal-based catalyst involved in the solution of the embodiment of the present application Figure 1 ;

[0029] Figure 2 Schematic diagram of the reaction path of the noble metal-based catalyst involved in the solution of the embodiment of the present application Figure 2 ;

[0030] Figure 3 Schematic diagram of the reaction path of the noble metal-based catalyst involved in the solution of the embodiment of the present application Figure 3 ;

[0031] Figure 4 Schematic flow chart of the preparation method of the noble metal-based catalyst involved in the solution of the embodiment of the present application;

[0032] Figure 5 Schematic diagram of the TEM result involved in the solution of the embodiment of the present application;

[0033] Figure 6 Schematic diagram of the XPS result involved in the solution of the embodiment of the present application;

[0034] Figure 7 Schematic diagram of the infrared result involved in the solution of the embodiment of the present application.

[0035] The realization of the purpose of the present application, functional features and advantages will be further described in conjunction with the embodiments with reference to the accompanying drawings. Detailed implementation manners

[0036] To make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. Those reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0037] Hereinafter, embodiments of the noble metal-based catalyst, its preparation method and application of the present application are specifically disclosed with appropriate reference to the accompanying drawings in detail. However, there will be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application, and are not intended to limit the subject matter described in the claims.

[0038] The "ranges" disclosed in this application are defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise specified, the numerical range "a-b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are fully listed herein, and "0-5" is only an abbreviated representation of these numerical combinations. In addition, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0039] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined with each other to form new technical solutions.

[0040] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0041] Unless otherwise specified, all steps of this application can be carried out sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, it is mentioned that the method may further include step (c), which means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0042] Unless otherwise specified, the "including" and "comprising" mentioned in this application mean open-ended or can also be closed-ended. For example, the "including" and "comprising" can mean that other components not listed can also be included or comprised, or can only include or comprise the listed components.

[0043] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0044] To make the above objects, features, and advantages of this application more obvious and understandable, the technical solutions of this application will be further described below in conjunction with the accompanying drawings and embodiments. However, this application is not limited to the listed embodiments, and should also include any other well-known changes within the scope of the rights required by this application.

[0045] As used herein, the term "one embodiment" or "embodiment" refers to a specific feature, structure, or characteristic that may be included in at least one implementation of this application. The phrase "in one embodiment" that appears in different places in this specification does not necessarily refer to the same embodiment, nor is it an embodiment that is separate from or mutually exclusive of other embodiments.

[0046] To better understand the technical solutions of this application, the following will be described in detail in conjunction with the accompanying drawings of the specification and specific implementation manners.

[0047] In conventional technologies, traditional Pt-based catalysts mainly promote the cracking reaction of methanol. Due to the lack of water dissociation active sites on the carrier, it is difficult to decompose water, and the main products are CO and H2. It is difficult to further convert CO into CO2, resulting in a relatively high proportion of CO in the products.

[0048] In the embodiments of this application, by using CeO2 with a polyhedral nanoparticle-packed morphology as the carrier and adding In2O3 as a promoter metal, it is possible to promote the better dispersion of Pt, thereby regulating the valence states of the active sites of Pt to be: Pt 0 、Pt δ+ and Pt 2+ , while Pt 0 is less than 30%, Pt δ+ is 60-90%, and Pt 2+ is less than 30%; furthermore, it promotes the reaction paths of Pt in the noble metal-based catalyst to include: the direct path of Pt δ+ , the Pt δ+ -In2O3, Pt δ+ -CeO2, Pt 0 -Pt 2+ and Pt 0 -Pt δ+ synergistic paths, and with Pt δ+The direct path is the main reaction path. When a noble metal-based catalyst is further applied to methanol steam reforming (MSR), the Pt metal sites (Pt δ+ ) will serve as efficient active centers, thus effectively promoting methanol dissociation and water molecule activation, accelerating the methanol steam reforming reaction, and increasing the methanol conversion rate. And Pt δ+ -In2O3, Pt δ+ -CeO2, Pt 0 -Pt 2+ and Pt 0 -Pt δ+ synergistic paths can further improve the selectivity and efficiency of the reaction, especially by enhancing the adsorption and conversion of intermediates and reducing the formation of CO in by-products.

[0049] In the first aspect of the embodiments of the present application, a noble metal-based catalyst is provided, including: a carrier, a promoter metal, and an active metal;

[0050] The carrier includes CeO2, and the morphology of the carrier is a polyhedron nanoparticle aggregate;

[0051] The active metal includes Pt;

[0052] The promoter metal includes In2O3;

[0053] The active sites of the noble metal-based catalyst include: Pt 0 , Pt δ+ and Pt 2+ , where Pt 0 is less than 30%, Pt δ+ is 60-90%, and Pt 2+ is less than 30%.

[0054] In a feasible embodiment, Pt (platinum) is a highly efficient catalytic active center, showing extremely high catalytic activity for key steps such as methanol dissociation and water molecule activation. It can effectively reduce the reaction activation energy, enabling the MSR reaction to proceed smoothly at a relatively low temperature. This not only improves the energy utilization efficiency but also reduces the demand for high-temperature equipment and lowers the operating cost. In addition, there is a strong metal-support interaction (SMSI) between Pt and the carrier material, and this interaction is particularly obvious under MSR conditions. Through this interaction, Pt can be stably dispersed on the surface of the carrier, preventing its sintering or aggregation, thus maintaining a high specific surface area and the number of active sites, and ensuring that the catalyst maintains high performance throughout the reaction process.

[0055] In a feasible embodiment, the introduction of In2O3 can enhance the interaction between the support and the active metal, especially through strong metal-support interaction (SMSI); this interaction helps to stabilize Pt particles and prevent them from sintering and aggregating during high-temperature or long-term reactions, thus maintaining the high dispersion and large specific surface area of the catalyst and ensuring continuous and efficient catalytic activity. In addition, the presence of In2O3 can also regulate the electronic properties of the Pt surface, change its adsorption ability and activation efficiency for reactant molecules, and further improve the selectivity and rate of the MSR reaction. Moreover, the introduction of In2O3 helps to enhance the thermal stability and anti-poisoning ability of the catalyst. In practical applications, the MSR reaction may face challenges in high-temperature environments and various impurity gases (such as sulfides, chlorides, etc.), which are likely to cause the inactivation of ordinary catalysts. However, In2O3 can effectively resist the above adverse effects and maintain long-term stable catalytic performance by changing the chemical composition and structural characteristics of the catalyst surface.

[0056] In a feasible embodiment, as an excellent support material, CeO2 has excellent thermal stability and mechanical strength, can maintain its structural integrity under high-temperature and high-pressure conditions, ensure the long-term operation of the catalyst without inactivation, and thus reduce the replacement frequency of the catalyst during actual application, lower the maintenance cost, and improve the production efficiency. In addition, there is a strong metal-support interaction between CeO2 and noble metals (e.g., Pt), and this interaction is crucial for optimizing the catalyst performance. It helps to stabilize metal nanoparticles and prevent them from sintering or aggregating at high temperatures, thus maintaining a high dispersion and specific surface area. At the same time, SMSI can also change the electronic structure of the metal surface, making the catalyst more selective for specific reaction paths and further improving the catalytic efficiency. Exemplarily, in a system containing CeO2, Pt nanoparticles can obtain better reducibility and higher catalytic activity through interaction with CeO2, which is particularly beneficial for the MSR reaction.

[0057] Exemplarily, the morphology of the support includes: octahedron.

[0058] Exemplarily, the dispersion state and particle size of In2O3 include: a small amount of highly dispersed In2O3 small particles or an In2O3 surface nanolayer, In2O3 particles with a size similar to that of the support particles but not firmly anchored, and a small amount of In2O3 bulk particles that are difficult to disperse. The present application can regulate the dispersion state of In2O3 by carrier regulation or the loading amount of the promoter metal, and then regulate Pt and the path and performance.

[0059] In a feasible embodiment, the specific surface area of the support is 35-70 m 2 g -1 ; for example, 35 m 2 g-1 、36 m 2 g -1 、37 m 2 g -1 、38 m 2 g -1 、39 m 2 g -1 、40 m 2 g -1 、41 m 2 g -1 、42 m 2 g -1 、43 m 2 g -1 、44 m 2 g -1 、45 m 2 g -1 、46 m 2 g -1 、47 m 2 g -1 、48 m 2 g -1 、49 m 2 g -1 、50 m 2 g -1 、51 m 2 g -1 、52 m 2 g -1 、53 m 2 g -1 、54 m 2 g -1 、55 m 2 g -1 、56 m 2 g -1 、57 m 2 g -1 、58 m 2 g -1 、59 m 2 g -1 、60 m 2 g -1 、61 m 2 g -1 、62 m 2 g -1 、63 m 2 g -1 、64 m 2 g -1 、65 m 2 g -1 、66 m 2 g -1 、67 m 2 g -1, 68 m 2 g -1 , 69 m 2 g -1 , 70 m 2 g -1 etc.

[0060] In a feasible embodiment, the pore volume of the carrier is 0.1 - 0.3 m 3 g -1 ; 0.1 m 3 g -1 , 0.11 m 3 g -1 , 0.12 m 3 g -1 , 0.13 m 3 g -1 , 0.14 m 3 g -1 , 0.15 m 3 g -1 etc.

[0061] In a feasible example, the morphology of the CeO2 carrier in the embodiment of the present application is a polyhedron nanoparticle aggregate, having a moderate specific surface area and pore volume; the polyhedron nanoparticle aggregate has a small particle size, which can promote the dispersion of the promoter In2O3, making it form smaller particles and preventing agglomeration into bulk particles, thereby promoting the dispersion of Pt and the formation of oxygen vacancies. In addition, metal nanoparticles can be more selectively anchored on the promoter or the carrier, enhancing their thermal stability and anti-poisoning ability. Secondly, the moderate oxygen vacancy concentration can regulate the valence state of the active sites of Pt to be: Pt 0 , Pt δ+ and Pt 2+ , where Pt 0 is less than 30%, Pt δ+ is 60 - 90%, and Pt 2+ is less than 30%; thus optimizing the reaction path, and promoting the reaction path of Pt in the noble metal-based catalyst to include: the direct path of Pt δ+ , the Pt δ+ -In2O3, Pt δ+ -CeO2, Pt 0 -Pt 2+ and Pt 0 -Pt δ+ synergistic paths, and taking the direct path of Pt δ+ as the main reaction path, the presence of Pt 0 can promote the decomposition of methanol, thereby generating more formaldehyde intermediates, and formaldehyde can diffuse and migrate to Pt δ+ or Pt 2+react with -OH, thereby promoting the conversion rate and reducing the production of CO. When the noble metal-based catalyst is applied to MSR, Pt metal sites (Pt δ+ ) will serve as efficient active centers, thus effectively promoting methanol dissociation and water molecule activation, accelerating the methanol steam reforming reaction, and improving the methanol conversion rate. And Pt δ+ -In2O3, Pt δ+ -CeO2, Pt 0 -Pt 2+ and Pt 0 -Pt δ+ synergistic effects of the synergistic pathways can further improve the selectivity and efficiency of the reaction, especially by enhancing the adsorption and conversion of intermediates and reducing the formation of CO in by-products.

[0062] In a feasible embodiment, the main exposed crystal plane of the carrier is (111).

[0063] In a feasible embodiment, the oxygen vacancies O v of the noble metal-based catalyst are 20-30%.

[0064] In a feasible example, since CeO2 with a polyhedral nanoparticle-packed morphology is selected as the carrier, the main exposed crystal plane of the carrier is (111). The (111) crystal plane provides a moderate oxygen vacancy concentration and good oxygen migration ability, which means that the energy required to generate oxygen vacancies is relatively small, so that oxygen vacancies are more likely to form, but not too many, remaining at a moderate level, that is, the oxygen vacancies O v are 20-30%. Such an oxygen vacancy distribution helps to improve the activity of the catalyst surface while avoiding structural instability caused by excessive oxygen vacancies. Secondly, the (111) crystal plane is rich in cerium ions (Ce 4+ ) with unsaturated coordination. These ions can more easily lose or gain electrons, thereby promoting the adsorption and dissociation of oxygen molecules on it and the interaction with reactants, providing more active sites for catalytic reactions.

[0065] Optionally, the active sites of the noble metal-based catalyst include: Pt 0 , Pt δ+ and Pt 2+ , where Pt 0 is less than 30%, Pt δ+ is 60-90%, and Pt 2+ is less than 30%. Based on the valence states and ratios of the above activities, the reaction pathways of the noble metal-based catalyst in the embodiments of the present application include: the direct pathway of Pt δ+ , Pt δ+ -In2O3, Pt δ+-CeO2, Pt 0 -Pt 2+ and Pt 0 -Pt δ+ synergistic paths, and the direct path of Pt δ+ is the main reaction path.

[0066] Exemplarily, in the noble metal-based catalyst, the reaction paths include: Pt δ+ direct path (mainly Pt δ+ -In2O3, and a small part of Pt δ+ -CeO2), Pt 0 -Pt 2+ synergistic paths and Pt 0 -Pt δ+ synergistic paths. The distance between the oxygen vacancy and Pt δ+ determines whether the -OH generated by the decomposition of water by the oxygen vacancy needs to migrate.

[0067] Exemplarily, referring to Figure 1 , it is the direct path of Pt δ+ ; when Pt δ+ is adjacent to small In2O3 particles, oxygen vacancies can be generated at the adjacent position of Pt δ+ . Therefore, methanol is adsorbed on Pt δ+ and gradually decomposes to generate adsorbed HCHO. If there are oxygen vacancies at the adjacent position of Pt δ+ , water is adsorbed on the -OH generated by the oxygen vacancy. Without migrating to Pt δ+ , it can directly dehydrogenate with *H2CO on Pt δ+ to generate *H2COO, and then the O of the hydroxyl group detaches to form monodentate m-*HCOO, and the oxygen vacancy is restored. The energy barrier for the decomposition of m-*HCOO into CO2 and H2 is lower and can proceed quickly, and this path is the direct path of Pt δ+ .

[0068] Exemplarily, referring to Figure 2 , it is the synergistic path of Pt δ+ ; when Pt δ+ is adjacent to large particles, it is difficult to ensure the generation of oxygen vacancies at the adjacent position of Pt δ+ . And when the oxygen vacancy is far from Pt δ+ , the -OH generated in the oxygen vacancy needs to migrate to Pt δ+ and then dehydrogenate with *H2CO to generate bi-*HCOO, and the decomposition is slower, and the path is the synergistic path of Pt δ+ . Although methanol is more easily adsorbed on Pt δ+ , decomposing methanol requires the supply of electrons, so Pt 0Decompose methanol faster, generating a large amount of HCHO. And HCHO is more likely to adsorb on the positively charged Pt. Therefore, Pt 0 and Pt δ+ active sites can undergo a synergistic reaction.

[0069] Exemplarily, referring to Figure 3 for Pt 0 -Pt 2+ synergistic path; Pt 0 and Pt 2+ coexist together. Therefore, the HCHO generated by Pt 0 can also migrate to Pt 2+ to react with -OH to form monodentate formate, which is more easily decomposed to form H2 and CO2. But Pt 0 and Pt 2+ are contradictions and it is difficult to coexist in large quantities at the same time. Therefore, the probability of this path occurring is very small.

[0070] Optionally, in the catalytic system composed of In2O3 and Pt δ+ oxygen vacancies are easily formed and affect the specific path of formaldehyde (HCHO) oxidation reaction. When the oxygen vacancy is adjacent to Pt δ+ , a direct and efficient reaction path is activated. In this path, the -OH (hydroxyl group) adsorbed on the oxygen vacancy can directly react with the formaldehyde molecule without long-distance migration, quickly generating monodentate m-*HCOO as an intermediate product. And "monodentate" means that the intermediate product is anchored on the catalyst surface only through one connection point (oxygen atom), reflecting the efficiency and directness of the reaction. However, when the distance between the oxygen vacancy and Pt δ+ is relatively far, the reaction follows a more complex synergistic path. In this situation, the -OH generated by decomposing water in the oxygen vacancy needs to undergo a migration process until it reaches the Pt δ+ site to combine with the formaldehyde molecule, and then generate bidentate bi-*HCOO formate as an intermediate product. And "bidentate" means that the intermediate product forms a stable anchor with the catalyst surface through two connection points (possibly two oxygen atoms), reflecting the complexity and synergy of the intermolecular interaction during the reaction process.

[0071] In a feasible embodiment, the noble metal-based catalyst comprises: 2-10 wt.% of a promoter metal and 0.5-2 wt.% of an active metal. For example, the loading amount of the promoter metal is 2 wt.%, 3 wt.%, 4 wt.%, 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, etc. The loading amount of the active metal is 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, 1 wt.%, 1.1 wt.%, 1.2 wt.%, 1.3 wt.%, 1.4 wt.%, 1.5 wt.%, 1.5 wt.%, 1.7 wt.%, 1.8 wt.%, 1.9 wt.%, 2 wt.%, etc.

[0072] In a feasible embodiment, when the loading amount of the active metal is too high, it may lead to agglomeration between the active metals, forming larger particles. This not only reduces the effective surface area of the active metal but also decreases the number of active sites provided by the active metal per unit mass, thereby weakening the catalytic efficiency. Secondly, a high loading amount may cause too high a coverage on the surface of the support, hindering the contact of reactant molecules with important active centers such as promoters or oxygen vacancies on the support, and thus affecting the synergistic effect. On the contrary, when the loading amount of the active metal is too low, although it can save costs and avoid the above-mentioned agglomeration problem, it also means that there are insufficient active sites on the catalyst surface, which is not enough to fully activate the reactant molecules, resulting in a decrease in the catalytic reaction rate. Therefore, the embodiments of the present application determine that the loading amount of the active metal in the noble metal-based catalyst is 0.5-2 wt.%.

[0073] In a feasible embodiment, when the loading amount of the promoter metal is too high, it may lead to partial shielding of the active sites on the catalyst surface. Since the promoter metal particles are relatively large, too much promoter metal will cover the surface of the active metal, reducing the exposed effective active sites, thereby reducing the overall activity of the catalyst. In addition, too high a loading of the promoter metal may change the electronic properties of the catalyst, affecting the strong metal-support interaction between the active metal and the promoter metal, and thus weakening the synergistic effect between the two, ultimately affecting the catalytic efficiency and selectivity. On the contrary, when the loading amount of the promoter metal is too low, although the above problems can be avoided, a lower content of the promoter metal means that the provided oxygen vacancies and additional active centers are insufficient, which is not conducive to promoting the adsorption, activation of reactant molecules, and the formation of intermediate products. For example, in the MSR process, an appropriate amount of the promoter metal helps to stabilize the hydroxyl species and promote their migration to the Pt active center to generate a bidentate-bound formate intermediate. If the content of the promoter metal is too low, this process will be inhibited, resulting in a decrease in the efficiency of the catalytic path. Therefore, the embodiments of the present application determine that the loading amount of the promoter metal in the noble metal-based catalyst is 2-10 wt.%.

[0074] In a feasible embodiment, the particle size of the carrier is 15 to 100 nm; for example, the particle size of the carrier is 15 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, etc. Larger particles have greater internal mass transfer resistance, and the diffusion paths of reactant molecules and product molecules inside the particles become longer, which may lead to a decrease in the reaction rate. On the contrary, if the particle size of the carrier is too low, it may increase the tendency of agglomeration between carrier particles, affecting its stability and utilization rate. Therefore, the embodiments of the present application determine that the particle size of the carrier in the noble metal-based catalyst is 15 to 100 nm.

[0075] Optionally, the noble metal-based catalyst of the embodiments of the present application can be used in the methanol steam reforming reaction for hydrogen production.

[0076] In this embodiment, by using CeO2 with a polyhedral nanoparticle-packed morphology as the carrier and adding In2O3 as a promoter metal, it is possible to promote the better dispersion of Pt, thereby regulating the valence state of the active sites of Pt to: Pt 0 、Pt δ+ and Pt 2+ , while Pt 0 is less than 30%, Pt δ+ is 60 to 90%, Pt 2+ is less than 30%; furthermore, it promotes the reaction paths of Pt in the noble metal-based catalyst to include: the direct path of Pt δ+ , the Pt δ+ -In2O3, Pt δ+ -CeO2, Pt 0 -Pt 2+ and Pt 0 -Pt δ+ synergistic paths, and the direct path of Pt δ+ is the main reaction path. Furthermore, when the noble metal-based catalyst is applied to methanol steam reforming for hydrogen production (methanol steam reforming, MSR), the Pt metal sites (Pt δ+ ) will be used as efficient active centers, thereby effectively promoting methanol dissociation and water molecule activation, accelerating the methanol steam reforming reaction, and improving the methanol conversion rate. And Pt δ+ -In2O3, Pt δ+ -CeO2, Pt 0 -Pt 2+ and Pt 0 -Pt δ+The synergy of the synergy path can further improve the selectivity and efficiency of the reaction, especially by enhancing the adsorption and conversion of intermediates and reducing the generation of CO in by-products. In the catalyst of this application, the oxygen vacancies account for 20% - 30%, and the main exposed crystal plane is the (111) plane. The (111) crystal plane is generally considered the most stable surface, with relatively strong Ce-O bonds, and the binding of surface Ce ions to oxygen ions is relatively stable. It has the lowest surface energy, a relatively close atomic arrangement, fewer surface atoms exposed, and a relatively flat surface. The (111) crystal plane has a relatively high activation energy. Therefore, the catalyst has a high methanol conversion rate, low CO selectivity, and good stability.

[0077] Furthermore, referring to Figure 4 , the embodiments of this application also provide a preparation method of a noble metal-based catalyst. The preparation method of the noble metal-based catalyst includes the following steps:

[0078] Step S10, preparing a support by a hydrothermal method, wherein the support includes CeO2, and the morphology of the support is a polyhedron nanoparticle aggregate;

[0079] In a feasible embodiment, a CeO2 support with a polyhedron nanoparticle aggregate morphology is prepared by a hydrothermal method.

[0080] In a feasible embodiment, step S10, the step of preparing a support by a hydrothermal method includes:

[0081] Step S11, mixing a NaOH solution and a cerium nitrate solution to obtain a solid-liquid mixture;

[0082] Step S12, heating the solid-liquid mixture and centrifuging and washing to obtain the support.

[0083] In a feasible embodiment, a 0.002 - 3M NaOH solution and a 0.2 - 0.6M cerium nitrate solution are provided. The NaOH solution and the cerium nitrate solution are mixed to generate a precipitate, and a solid-liquid mixture is obtained. The solid-liquid mixture is heated at a temperature of 100 - 200 °C for 5 - 35 h to carry out a hydrothermal reaction, and then through centrifuging and washing, a CeO2 support with a polyhedron nanoparticle aggregate morphology is obtained after drying. Among them, the particle size of the support is 15 - 100 nm, the specific surface area is 35 - 70 m 2 g -1 , and the pore volume is 0.1 - 0.3 m 3 g -1 .

[0084] Optionally, the concentration of NaOH can be 0.002M, 0.5M, 1M, 1.5M, 2M, 2.5M, 3M, etc.

[0085] Optionally, the concentration of cerium nitrate can be 0.2M, 0.3M, 0.4M, 0.5M, 0.6M, etc.

[0086] Optionally, the heating temperature of the solid-liquid mixture is 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, 200°C, etc.

[0087] Optionally, the heating duration of the solid-liquid mixture is 5h, 10h, 15h, 20h, 25h, 30h, 35h, etc.

[0088] In this embodiment, by controlling the hydrothermal reaction conditions, a CeO2 support with a polyhedral nanoparticle-packed morphology is prepared. Among them, the particle size of the support is 15 - 100nm, the specific surface area is 35 - 70m 2 g -1 , and the pore volume is 0.1 - 0.3m 3 g -1 . This support helps to regulate the valence state and proportion of the active sites of the active metal in the noble metal-based catalyst, thereby promoting methanol dissociation and water molecule activation, accelerating the methanol steam reforming reaction, increasing the methanol conversion rate, and reducing the generation of CO in the products.

[0089] Step S20: Load the active metal and the promoter metal on the support to obtain a noble metal-based catalyst. Among them, the promoter metal includes In2O3, the active metal includes Pt, and the active sites of the noble metal-based catalyst include: Pt 0 、Pt δ+ and Pt 2+ , where Pt 0 is less than 30%, Pt δ+ is 60 - 90%, and Pt 2+ is less than 30%.

[0090] In a feasible embodiment, an active metal including Pt is provided, and a promoter metal including In2O3 is provided; the active metal and the promoter metal are loaded on the support to obtain a noble metal-based catalyst. Among them, the active sites of the noble metal-based catalyst include: Pt 0 、Pt δ+ and Pt 2+ , where Pt 0 is less than 30%, Pt δ+ is 60 - 90%, and Pt 2+ is less than 30%.

[0091] In a feasible embodiment, step S20, the step of loading the active metal and the promoter metal on the support to obtain a noble metal-based catalyst includes:

[0092] Step S21: Configure the active metal solution and the promoter metal solution;

[0093] Step S22: Mix the active metal solution and the promoter metal solution to obtain a mixed solution;

[0094] Step S23: Place the carrier in the mixed solution, take out the carrier loaded with the active metal and the promoter metal, and calcine it to obtain the noble metal-based catalyst.

[0095] In a feasible embodiment, an active metal solution and a promoter metal solution are configured and mixed to obtain a mixed solution; the carrier is placed in the mixed solution, ultrasonicated, then left for impregnation, and dried and calcined to obtain a Pt-In2O3 / CeO2-c noble metal-based catalyst.

[0096] Optionally, the calcination temperature is 300 - 550 °C and the calcination duration is 2 - 10 h.

[0097] Optionally, the noble metal-based catalyst prepared in the embodiments of the present application can be used in the methanol steam reforming reaction for hydrogen production.

[0098] In this embodiment, by using CeO2 with a polyhedral nanoparticle-packed morphology as the carrier and adding In2O3 as the promoter metal, it is possible to promote the better dispersion of Pt, thereby regulating the valence states of the active sites of Pt to be: Pt 0 、Pt δ+ and Pt 2+ , while Pt 0 is less than 30%, Pt δ+ is 60 - 90%, and Pt 2+ is less than 30%; furthermore, it promotes the reaction paths of Pt in the noble metal-based catalyst to include: the direct path of Pt δ+ , the Pt δ+ -In2O3, Pt δ+ -CeO2, Pt 0 -Pt 2+ and Pt 0 -Pt δ+ synergistic paths, with the direct path of Pt δ+ as the main reaction path. Furthermore, when the noble metal-based catalyst is applied to methanol steam reforming (MSR), it will use the Pt metal sites (Pt δ+ ) as efficient active centers, thereby effectively promoting methanol dissociation and water molecule activation, accelerating the methanol steam reforming reaction, and improving the methanol conversion rate. And Pt δ+ -In2O3, Pt δ+ -CeO2, Pt 0 -Pt 2+and Pt 0 -Pt δ+ The synergy of the synergy path with Pt can further improve the selectivity and efficiency of the reaction, especially by enhancing the adsorption and conversion of intermediates and reducing the generation of CO in by-products.

[0099] To enable those skilled in the art to clearly understand the details and operations of the above embodiments of the present application, and to significantly reflect the progressive performance of the embodiments of the present application, the above technical solutions will be illustrated by multiple embodiments below.

[0100] Example 1

[0101] (1) Weigh cerium nitrate and dissolve it in deionized water to prepare a 0.3M cerium nitrate solution; weigh NaOH and dissolve it in deionized water to prepare a 0.1M NaOH solution; mix the NaOH solution and the cerium nitrate solution to obtain a solid-liquid mixture;

[0102] (2) Transfer the solid-liquid mixture to a polytetrafluoroethylene liner, place it in a stainless steel hydrothermal autoclave and tighten the seal; place the hydrothermal autoclave in an oven at 190 °C and heat for 24 h to obtain a polyhedral nanoparticle aggregate CeO2 support (CeO2-p);

[0103] (3) Prepare a chloroplatinic acid solution, where the concentration of Pt 4+ is 0.21M; prepare an In(NO3)3 solution, where the concentration of In 3+ is 0.56M;

[0104] (4) Pipette an appropriate amount of the chloroplatinic acid solution and the In(NO3)3 solution, and weigh the CeO2-p support obtained in step (2), add them to the solution, shake well while slowly adding, and sonicate for 30 min; then impregnate at room temperature for 12 h, dry and calcine in air at 450 °C for 4 h to obtain a Pt-In2O3 / CeO2-p catalyst, where the theoretical loading of Pt is 1 wt.%, and the theoretical loading of In2O3 is 7 wt.%.

[0105] Example 2

[0106] The experimental steps are the same as those in Example 1, except that:

[0107] In step (2), place the hydrothermal autoclave in an oven at 190 °C and heat for 12 h to obtain a polyhedral nanoparticle aggregate CeO2 support (CeO2-p1).

[0108] Example 3

[0109] The experimental steps are the same as those in Example 1, except that:

[0110] In step (2), the hydrothermal reactor was placed in an oven at 200 °C and heated for 24 h to obtain a polyhedral nanoparticle-packed CeO2 support (CeO2-p2).

[0111] Comparative Example 1

[0112] The experimental procedure was the same as in Example 1, except that the preparation steps of the CeO2 support included:

[0113] (1) Weigh 4.4 g of cerium nitrate and dissolve it in 70 mL of deionized water; weigh 7.2 g of urea and dissolve it in 70 mL of deionized water. Mix the two and place them in a hydrothermal reactor at 130 °C for 24 h.

[0114] (2) Centrifuge, wash, and dry to obtain a relatively regular particle CeO2 support, where the particle size is 200 nm.

[0115] Comparative Example 2

[0116] The experimental procedure was the same as in Example 1, except that:

[0117] CTAB surfactant was selected, and sol-gel method was used to prepare nanoparticle-packed CeO2. Among them, the heating rate was controlled at 10 °C / min, heated to 450 °C, and calcined for 4 h to obtain particle-packed CeO2 (CTAB-10 °C / min).

[0118] Comparative Example 3

[0119] The experimental procedure was the same as in Example 1, except that only the active metal Pt was loaded, and the promoter metal In2O3 was not loaded.

[0120] The specific surface area, pore volume, and loading amount of the catalysts in Examples 1 to 3 and Comparative Examples 1 to 3 were tested, and the experimental results are shown in Table 1 below; according to Table 1, it can be seen that for the support CeO2-p prepared in the examples of the present application, after loading Pt and In2O3, the specific surface area and pore volume changed little, and the theoretical loading amount and actual loading amount of Pt and In2O3 were close.

[0121] Table 1

[0122]

[0123]

[0124] TEM test was carried out on Example 1, and the results are referred to Figure 5 , where Figure 5 a to d are characterization diagrams at different magnification factors. It can be seen that the CeO2 nanoparticle sizes in the polyhedral nanoparticle-packed body are relatively uniform, and the average particle diameter is mainly about 17 nm. Pt was not observed significantly in the TEM0 Large particles, and atomically dispersed Pt 2+ . The particles of In2O3 are similar to those of the polyhedral nanoparticle aggregates, and some unanchored ones are observed.

[0125] Perform XPS characterization on Example 1, and the results are referred to Figure 6 and Table 2 below; it can be seen that in Example 1, Pt is mainly δ+ dominant, with a small amount of zero-valent Pt 0 and divalent Pt 2+ ; there are oxygen vacancies in O, and Pt in In2O3 2+ -In2O3-CeO2 is very little. Among them, the proportions of Pt 0 , Pt δ+ and Pt 2+ are 7%, 70% and 23% respectively, the oxygen vacancies mainly account for 22%, while Pt in In2O3 2+ -In2O3-CeO2 is only 6%.

[0126] Table 2

[0127]

[0128] Apply the catalysts prepared in Examples 1 to 2 and Comparative Examples 1 to 3 to the hydrogen production by steam reforming of methanol; evaluate the performance of the catalysts for hydrogen production by steam reforming of methanol through a micro fixed-bed quartz tube reactor. The reaction is carried out at atmospheric pressure. When the reaction temperature is 260 - 340 °C, the ratio of methanol to water in the raw material is 1:1 (mol / mol), WHSV is 3 h-1, and nitrogen is used as the carrier gas during the reaction. After the tail gas is condensed, the gas phase enters the on-line chromatograph for detection. The experimental results are shown in Table 3 below:

[0129] Table 3

[0130]

[0131]

[0132] According to the above experimental results, it can be known that the noble metal-based catalysts prepared in Examples 1 to 3 of the present application have good methanol conversion rate and H2 yield, and at the same time have outstanding stability. The stability of each catalyst is characterized by testing the duration during which the methanol conversion rate of each catalyst remains above 80%, and it is further found that the stability of Examples 1 and 2 is outstanding, and at the same time, a relatively low CO selectivity (<2%) can be maintained. And according to the experimental results of Example 1 and Comparative Example 3, after adding In2O3, due to its easy agglomeration, the methanol conversion rate and stability will decrease to some extent, but if In2O3 is not added, the CO content in the product will be too high.

[0133] The catalyst of Example 1 was subjected to in-situ infrared MSR reaction to detect the generation of intermediate products during the MSR reaction, and the results are referred to Figure 7 ; According to Figure 7 It can be seen that the intermediate products during the MSR reaction in Example 1 include: monodentate m-*HCOO, bidentate bi-*HCOO, CO, and CO2. According to the adsorption and decomposition capabilities of different Pt species for reactants and intermediate products, at low temperatures, the Pt 0 -Pt δ+ path may be mainly carried out. Pt 0 is more likely to decompose CH3OH, which can avoid the rate-determining step of Pt δ+ (the dehydrogenation of methoxy to form formaldehyde), and formaldehyde reacts with -OH on Pt δ+ to form m-*HCOO and then decompose, which can avoid the rate-determining step of Pt 0 (the decomposition of bi-*HCOO). As the temperature increases, CH3OH is more likely to be adsorbed on Pt δ+ and decomposes rapidly. The direct Pt δ+ path is greatly enhanced. Therefore, m-*HCOO increases rapidly, and the peak of t-*OCH3 appears, indicating that Pt active sites with different valence states all rapidly break the C-H bond of methanol to form methoxy, which is strongly adsorbed on the Pt active sites. This reaction path has a faster conversion rate, but there is very little Pt 0 in the system. Therefore, this path is not the main reaction path.

[0134] The above are only the preferred embodiments of the present application, and do not limit the patent scope of the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the patent protection scope of the present application.

Claims

1. A noble metal-based catalyst, characterized in that The noble metal-based catalyst comprises: a carrier, a promoter metal and an active metal; The carrier includes CeO2, and the morphology of the carrier is a polyhedral nanoparticle stack; The active metal includes Pt; The auxiliary metal includes In2O3; The active sites of the noble metal-based catalyst include: Pt 0 , Pt δ+ and Pt 2+ , where Pt 0 Less than 30%, Pt δ+ 60~90%, Pt 2+ Less than 30%.

2. The noble metal-based catalyst according to claim 1, characterized in that The specific surface area of ​​the carrier is 35 to 70 m 2 g -1 ; And / or, the pore volume of the carrier is 0.1 to 0.3 m 3 g -1 .

3. The noble metal-based catalyst according to claim 1, characterized in that The noble metal-based catalyst comprises: 2-10 wt.% of promoter metal and 0.5-2 wt.% of active metal.

4. The noble metal-based catalyst according to claim 1, characterized in that The particle size of the carrier is 15 to 100 nm.

5. The noble metal-based catalyst according to claim 1, characterized in that The main exposed crystal face of the carrier is (111); And / or, the oxygen vacancies O of the noble metal-based catalyst v It is 20 to 30%.

6. A method for preparing a noble metal-based catalyst, characterized in that: The method is used to prepare the noble metal-based catalyst according to any one of claims 1 to 5, and the method comprises the following steps: The carrier is prepared by a hydrothermal method, wherein the carrier comprises CeO2 and the morphology of the carrier is a polyhedral nanoparticle stack; Active metal and auxiliary metal are loaded on the carrier to prepare a noble metal-based catalyst, wherein the auxiliary metal includes In2O3, the active metal includes Pt, and the active sites of the noble metal-based catalyst include: Pt 0 , Pt δ+ and Pt 2+ , where Pt 0 Less than 30%, Pt δ+ 60~90%, Pt 2+ Less than 30%.

7. The method for preparing a noble metal-based catalyst according to claim 6, characterized in that: The step of preparing the carrier by hydrothermal method comprises: mixing the NaOH solution and the cerium nitrate solution to prepare a solid-liquid mixture; The solid-liquid mixture is heated and centrifuged for washing to obtain the carrier.

8. The method for preparing a noble metal-based catalyst according to claim 7, characterized in that: The solid-liquid mixture is heated at a temperature of 100 to 200° C. and for a heating time of 5 to 35 hours.

9. The method for preparing a noble metal-based catalyst according to claim 6, characterized in that: The step of loading active metal and promoter metal on the carrier to prepare a noble metal-based catalyst comprises: Prepare active metal solution and auxiliary metal solution; Mixing the active metal solution and the auxiliary metal solution to obtain a mixed solution; The carrier is placed in the mixed solution, and the carrier loaded with active metal and auxiliary metal is taken out and calcined to obtain the noble metal-based catalyst.

10. Use of the noble metal-based catalyst according to any one of claims 1 to 5 for hydrogen production by methanol steam reforming.

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