A single-component multi-center catalyst with spatial confinement within metal nanoislands and its preparation method

Abstract

A single-component multi-center catalyst with spatial confinement within metal nanoislands and its preparation method belong to the field of catalysts. The catalyst is denoted as M. 1+n @X / MMO, the noble metal M exists as a single atom (M1) and a cluster (M2). n The coexisting form is anchored in non-noble metal X to form nanoparticles, which are then uniformly dispersed on an oxide support (MMO). M accounts for 0.1%–5% of the total catalyst mass; the average particle size of X is 10–30 nm. First, the non-noble metal is introduced into the hydrotalcite layer, then the noble metal component is uniformly loaded via electrostatic adsorption. Under a reducing atmosphere, M is diluted by X to achieve redispersion, yielding M... 1+n @X / MMO catalyst. This catalyst is used in tandem reactions and can provide advantageous active sites for different reactants. It has a mass specific activity 1.5 times higher than that of a single atom, outstanding catalytic performance, good stability, and is easy to recover and reuse.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a single-component multi-center catalyst with spatial confinement of metal nanoislands and its preparation method. This catalyst is mainly used for tandem reactions. Background Technology

[0002] Currently, over 85% of reactions in chemical production involve catalysis, making catalysis the engine of the chemical industry. Innovations in modern heterogeneous catalysis technology have driven the development of industries such as petroleum, power, chemicals, and environmental remediation, and play a crucial role in chemical processes such as renewable energy utilization and carbon neutrality. Because catalysis is a surface reaction, the bulk atoms of metal-based catalysts are far less important than the surface atoms. Especially when a reaction requires precious metals as active ingredients, given the scarcity and high price of precious metals in my country, improving the utilization efficiency of precious metals and reducing the cost of catalysts is imperative.

[0003] Single-atom catalysts have become a hot research area in recent years due to their highly dispersed active sites and 100% atom utilization efficiency. However, such a single active center can only create one type of active site. For complex co-adsorption involving reactants, the optimal performance of the overall reaction usually requires the participation of at least two types of active sites. Therefore, in such complex reactions, a single type of catalytic site may not provide optimal catalytic activity for all molecules / steps of the entire reaction, necessitating new catalyst design strategies. Integrating both single atoms and clusters into the same catalyst can provide multiple active sites for the adsorption, activation, and transformation of different reactant molecules or different steps in the catalytic reaction while maintaining high atom utilization efficiency. This is an ideal approach for developing high-performance catalysts and has attracted widespread attention in recent years. Reference 1, in *Importance of Species Heterogeneity in Supported Metal Catalysts* [J]. J. Am. Chem. Soc. 2022, 144, 5108-5115, splits the Rh element into Rh single atoms and Rh clusters. The authors found that in the tandem reaction of cyclohexanol dehydrogenation to phenol, Rh single atoms promote the first step of cyclohexanol dehydrogenation to cyclohexanone, while Rh clusters promote the dehydrogenation of cyclohexanone to phenol. Reference 2, in *Modulating adsorbed hydrogen drive selectrochemical CO2-to-C2 products* [J]. Nat Commun 14, 4615 (2023), splits Cu into Cu single atoms and Cu clusters. This catalyst exhibits excellent activity in a typical electrocatalytic CO2 reduction reaction involving two reactant molecules (CO2 and H2O). The authors found that Cu single atoms promote H2O dissociation, while Cu clusters promote the conversion of *CHO. The synergy of the two active sites determines the excellent performance of the catalyst.

[0004] However, currently reported single-component bicentric catalysts do not consider the distance between the two sites. Maintaining the intimacy between sites while constructing two different scales is quite difficult. Therefore, it is necessary to find a method for the controllable preparation of highly efficient catalysts containing multiple atomic-level sites with a reasonable distribution. In this patent, we develop such a method for preparing single-component multicentric catalysts confined by metal nanoislands. Summary of the Invention

[0005] The purpose of this invention is to provide a spatially confined noble metal single-atom and nanocluster synergistic supported metal catalyst, its preparation method, and its application. This type of catalyst exhibits excellent activity and selectivity in tandem reactions involving the co-adsorption of multiple reactants, and has a higher mass-to-specific-activity ratio than single-atom catalysts. Furthermore, to control the spatial distribution of sites at different scales, different sites are anchored on nanoparticles to form a nanoreaction island.

[0006] This invention provides a metal catalyst in which a noble metal is anchored in non-noble metal nanoparticles in the form of both single atoms and clusters. These non-noble metal nanoparticles are then uniformly dispersed on an oxide support, denoted as M. 1+n @X / MMO, where M is the active ingredient, M 1+n Represents single atoms (M1) and clusters (M) formed from noble metal M. n X is a non-noble metal that provides confinement space for M in the catalyst, forming the space between M1 and M2. n It provides site intimacy, and the distribution and ratio of M1 and Mn can be adjusted by regulating the particle size of X; MMO (mixed metal oxide) is a mixed metal oxide carrier, and the nanoparticles formed by X are uniformly loaded on MMO.

[0007] In the above catalyst, the noble metal M can be Rh, Pd, Ru, Ir, Au, or Pt. The content of the noble metal in the catalyst, by mass percentage, can be 0.1% to 5%.

[0008] In the above catalyst, the non-noble metal X can be at least one of Ni, Co, Cu, Fe, and Zn. The size of the nanoparticles formed by X can be 10–30 nm.

[0009] The specific preparation steps of the catalyst provided by this invention are as follows:

[0010] A: Dissolve metal salts X, Mg, and Al in deionized water to prepare a mixed salt solution; wherein the molar ratio of (X+Mg):Al is 2–4; the molar ratio of X to Mg is 1–5, and the total concentration of the three metal ions is 0.5–1.5 mol / L. Dissolve the alkali in an equal volume of deionized water to the metal salt ions, with a total concentration of 0.5–2.0 mol / L.

[0011] The X salt is one of several nitrates or chlorides of Ni, Co, Cu, Fe, Zn, Mg, and Al; the alkaline solution is a mixed solution of NaOH and Na2CO3.

[0012] B: The salt mixture and alkali mixture obtained in step A are simultaneously injected into a stirred reactor using a syringe pump, and the solution is kept between 8 and 10. Crystallize at 50 to 80°C for 12 to 36 hours, and allow to cool naturally to room temperature. Filter and wash the precipitate until the pH of the supernatant solution is neutral. Filter again and place the obtained solid in an oven at 40 to 80°C for 12 to 24 hours to obtain XMgAl-LDHs.

[0013] C: Dissolve the noble metal M salt in deionized water to prepare an impregnation solution with a concentration of 10-50 mmol / L. The M salt used can be any one of RhCl3·3H2O, H2PdCl6, RuCl3·3H2O, H2PtCl6, H2IrCl6·6H2O, or HAuCl4·3H2O.

[0014] D: Grind the XMgAl-LDHs sample prepared in step B into powder, and then uniformly disperse it in deionized water to obtain a suspension with a solid content of 0.01-0.1 g / mL; add the noble metal M impregnation solution prepared in C, so that the loading of M is 0.1-5 wt%, continue stirring and heating to 70-90℃ until the deionized water is completely evaporated, and place the obtained solid in an oven at 40-80℃ to dry for 1 h to obtain the M-XMgAl-LDHs precursor.

[0015] E: The M-XMgAl-LDHs precursor obtained in step D is ground, heated to 500-700℃ in a reducing atmosphere at a heating rate of 2-10℃ / min, and held for 2-4 hours to prepare M 1+n @X / MMO catalyst.

[0016] The key feature of this preparation method is that, utilizing the dilution effect, the noble metal M is diluted by the guest metal X to form a highly dispersed state. Based on the adjustable elemental ratio and confinement effect of LDHs, by adjusting the contents of M and X, different degrees of dilution of M by X are achieved, resulting in M ​​structures with different degrees of dispersion: 1. Increasing or decreasing the content of the guest metal X while keeping M constant, the particle size of X increases or decreases, thus lowering or increasing the degree of dispersion of M; 2. Increasing or decreasing the content of the host metal M while keeping the guest metal X constant, thus lowering or increasing the degree of dispersion of M.

[0017] The beneficial effects of this invention are:

[0018] This invention utilizes a dilution method to prepare a catalyst with coexisting active sites of different scales, leveraging the dilution effect of guest metal X on noble metals. Guest metal X acts as an anchoring agent for the noble metal, enhancing the catalyst's stability. The different scale sites are confined on the nanoparticles formed by X, creating nano-reaction islands, increasing site intimacy, and preventing restricted mass transfer of active species. This catalyst exhibits excellent catalytic activity and selectivity when applied to tandem reactions. Attached Figure Description

[0019] Figure 1 High-resolution transmission electron microscope (TEM) images and particle size distribution diagrams of the catalyst prepared in Example 4 are shown. It can be seen that the X metal particles are uniformly dispersed on the surface of the oxide support, with a particle size ranging from 15 to 30 nm.

[0020] Figure 2 The image shown is a spherical aberration electron microscope image of the catalyst prepared in Example 2, which shows that the noble metal is uniformly dispersed on the surface of M nanoparticles as single atoms and clusters.

[0021] Figure 3 The CO infrared characterization of the catalyst prepared in Example 4 shows linear adsorption peaks and bridged adsorption peaks, which are attributed to the adsorption of CO in single atoms and clusters, respectively, indicating that M exists in the catalyst in one or both forms of single atoms and clusters.

[0022] Figure 4 The results show the evaluation of the stability of the catalyst in the series reaction in the application example.

[0023] Figure 5 The graph shows the product formation rates of single-component single-center and single-component multi-center catalysts in the application examples. Detailed implementation method:

[0024] Example 1

[0025] A. Dissolve 0.01 mol Al(NO3)3·9H2O, 0.005 mol Mg(NO3)2·6H2O, 0.025 mol Ni(NO3)2·6H2O and 100 mL deionized water under ultrasonic stirring until a stable and transparent mixed salt solution is formed.

[0026] B. Dissolve 0.045 mol Na₂CO₃, 0.03 mol NaOH, and 100 mL of deionized water thoroughly under ultrasonic stirring to form a stable and transparent alkaline solution. Simultaneously add the mixed alkaline solution and the mixed salt solution A prepared in step A dropwise to a flask equipped with a stir bar using a syringe pump until a suspension is formed, maintaining the solution pH at 9 ± 0.2. Control the crystallization temperature of the suspension at 80°C, the stirring rate at 400 rpm, and the crystallization time at 3 hours. Then, centrifuge the suspension, wash the solid with deionized water until the supernatant pH reaches 7, and dry the solid in an oven at 60°C for 12 hours to obtain NiMgAl-LDHs.

[0027] C. Dissolve RuCl3·3H2O in deionized water to prepare a Ru solution of 37.65 mmol / L. 3+ Impregnation solution C;

[0028] D. Under continuous stirring at 30℃, 0.5g of NiMgAl-LDHs powder from step B was added to 10mL of deionized water to prepare a suspension with a solid content of 0.05g / mL; then Ru was added according to a noble metal loading of 2wt%. 3+ The impregnation solution was continuously stirred and heated to 80°C until the deionized water was completely evaporated, yielding a catalyst precursor of 2wt% Ru-NiMgAl-LDHs loaded with noble metals.

[0029] E. The Ru-NiMgAl-LDHs obtained in step D were subjected to a 10:1 N2 / H2 atmosphere at 10 °C·min. -1 The temperature was increased to 600℃ at a certain rate, held for 2 hours, and then cooled to room temperature to obtain the catalyst. Analysis confirmed its expression as Ru. (1+n) @Ni / NiMgAlO x The catalyst (1 represents a Ru single atom, n represents a Ru cluster) is dispersed on the surface of Ni nanoparticles in the form of single atoms and clusters.

[0030] Example 2

[0031] A. Dissolve 0.01 mol Al(NO3)3·9H2O, 0.005 mol Mg(NO3)2·6H2O, 0.025 mol Ni(NO3)2·6H2O and 100 mL deionized water under ultrasonic stirring until a stable and transparent mixed salt solution is formed.

[0032] B. Dissolve 0.045 mol Na₂CO₃, 0.03 mol NaOH, and 100 mL of deionized water thoroughly under ultrasonic stirring to form a stable and transparent alkaline solution. Simultaneously add the mixed alkaline solution and the mixed salt solution A prepared in step A dropwise to a flask equipped with a stir bar using a syringe pump until a suspension is formed, maintaining the solution pH at 9 ± 0.2. Control the crystallization temperature of the suspension at 80°C, the stirring rate at 400 rpm, and the crystallization time at 3 hours. Then, centrifuge the suspension, wash the solid with deionized water until the supernatant pH reaches 7, and dry the solid in an oven at 60°C for 12 hours to obtain NiMgAl-LDHs.

[0033] C. Dissolve H₂PtCl₆ in deionized water to prepare a Pt solution of 17.60 mmol / L. 4+ Impregnation solution C;

[0034] D. Under continuous stirring at 30℃, 0.5 g of NiMgAl-LDHs powder from step B was added to 10 mL of deionized water to prepare a suspension with a solid content of 0.05 g / mL; then, Pt was added according to a noble metal loading of 2 wt%. 4+The impregnation solution was continuously stirred and heated to 80°C until the deionized water was completely evaporated, yielding a catalyst precursor of 2wt% Pt-NiMgAl-LDHs loaded with noble metals.

[0035] E. The Pt-NiMgAl-LDHs obtained in step D were subjected to a 10:1 N2 / H2 atmosphere at 10 °C·min. -1 The temperature was increased to 600℃ at a rate of [missing information], held for 2 hours, and then cooled to room temperature to obtain the catalyst. Analysis confirmed its expression as Pt. (1+n) @Ni / NiMgAlO x The catalyst (1 represents a single Pt atom, n represents a Pt cluster) is dispersed on the surface of Ni nanoparticles in the form of single atoms and clusters.

[0036] Example 3

[0037] A. Dissolve 0.01 mol Al(NO3)3·9H2O, 0.015 mol Mg(NO3)2·6H2O, 0.01 mol Co(NO3)2·6H2O and 100 mL of deionized water under ultrasonic stirring until a stable and transparent mixed salt solution is formed.

[0038] B. Dissolve 0.045 mol Na₂CO₃, 0.03 mol NaOH, and 100 mL of deionized water thoroughly under ultrasonic stirring to form a stable and transparent alkaline solution. Add the mixed alkaline solution and the mixed salt solution A prepared in step A dropwise to a flask equipped with a stir bar using a syringe pump until a suspension is formed, maintaining the solution pH at 10 ± 0.2. Control the crystallization temperature of the suspension at 50°C, the stirring rate at 400 rpm, and the crystallization time at 24 hours. Then, centrifuge the suspension, wash the solid with deionized water until the supernatant pH reaches 7, and dry the solid in an oven at 60°C for 12 hours to obtain CoMgAl-LDHs.

[0039] C. Dissolve H₂PtCl₆ in deionized water to prepare a Pt solution of 17.60 mmol / L. 4+ Impregnation solution C;

[0040] D. Under continuous stirring at 30℃, add 0.5g of CoMgAl-LDHs powder from step B to 10mL of deionized water to prepare a suspension with a solid content of 0.05g / mL; then add Pt according to a noble metal loading of 2wt%. 4+ The impregnation solution was continuously stirred and heated to 80°C until the deionized water was completely evaporated, yielding a catalyst precursor of 2wt% Pt-CoMgAl-LDHs loaded with noble metals.

[0041] E. The Pt-CoMgAl-LDHs obtained in step D were subjected to a 10:1 N2 / H2 atmosphere at 10 °C·min. -1 The temperature was increased to 600℃ at a rate of [missing information], held for 2 hours, and then cooled to room temperature to obtain the catalyst. Analysis confirmed its expression as Pt. (1+n) @Co / CoMgAlO x The catalyst (1 represents a single Pt atom, n represents a Pt cluster) is dispersed on the surface of Co nanoparticles in the form of single atoms and clusters.

[0042] Example 4

[0043] A. Dissolve 0.01 mol Al(NO3)3·9H2O, 0.015 mol Mg(NO3)2·6H2O, 0.01 mol Co(NO3)2·6H2O and 100 mL of deionized water under ultrasonic stirring until a stable and transparent mixed salt solution is formed.

[0044] B. Dissolve 0.045 mol Na₂CO₃, 0.03 mol NaOH, and 100 mL of deionized water thoroughly under ultrasonic stirring to form a stable and transparent alkaline solution. Add the mixed alkaline solution and the mixed salt solution A prepared in step A dropwise to a flask equipped with a stir bar using a syringe pump until a suspension is formed, maintaining the solution pH at 10 ± 0.2. Control the crystallization temperature of the suspension at 50°C, the stirring rate at 400 rpm, and the crystallization time at 24 hours. Then, centrifuge the suspension, wash the solid with deionized water until the supernatant pH reaches 7, and dry the solid in an oven at 60°C for 12 hours to obtain CoMgAl-LDHs.

[0045] C. Dissolve RuCl3·3H2O in deionized water to prepare a Ru solution of 37.65 mmol / L. 3+ Impregnation solution C;

[0046] D. Under continuous stirring at 30℃, 0.5g of CoMgAl-LDHs powder from step B was added to 10mL of deionized water to prepare a suspension with a solid content of 0.05g / mL; then Ru was added according to a noble metal loading of 2wt%. 3+ The impregnation solution was continuously stirred and heated to 80°C until the deionized water was completely evaporated, yielding a catalyst precursor loaded with 2wt% Ru-CoMgAl-LDHs containing noble metals.

[0047] E. The Ru-CoMgAl-LDHs obtained in step D were subjected to a 10:1 N2 / H2 atmosphere at 10 °C·min. -1 The temperature was increased to 600℃ at a certain rate, held for 2 hours, and then cooled to room temperature to obtain the catalyst. Analysis confirmed its expression as Ru. (1+n)@Co / CoMgAlO x The catalyst (1 represents a Ru single atom, n represents a Ru cluster) is dispersed on the surface of Co nanoparticles in the form of single atoms and clusters.

[0048] Application Example 1:

[0049] The performance of the catalysts prepared in the examples was evaluated using a tandem reductive amination reaction to produce primary amines as a probe reaction.

[0050] The evaluation device is a high-pressure reactor, and the operating steps are as follows:

[0051] A 50 mL high-pressure reactor was prepared by adding 1 mmol of methanol solution, 1 mmol of HMF, and the catalyst to a 50 mL high-pressure reactor, with a HMF to noble metal molar ratio of 500:1 and an HMF to NH3 molar ratio of 5:1. H2 was then introduced to replace the air in the reactor. The reactor temperature was raised to 100 °C, and H2 was introduced while maintaining the pressure at 1.5 MPa. Samples were taken for analysis every 1 hour, for a total reaction time of 6 hours. The products were detected using an Agilent gas chromatograph, and the data were processed using the internal standard method. The results are shown in Table 1.

[0052] Table 1

[0053]

[0054] As shown in Table 1, the catalyst prepared in this invention, when applied to a tandem reductive amination reaction, achieves 100% conversion within 1 hour, and the primary amine selectivity reaches its maximum value of 80-97% after 6 hours of reaction. Furthermore, the catalyst exhibits good stability and recyclability. Figure 4 .

Claims

1. A catalyst with spatially confined single-component multi-center metal nanoislands, characterized in that: Represented as M 1+n @X / MMO, the noble metal M exists as a single atom M1 and a cluster M. n The coexisting form is anchored in non-precious metal X nanoparticles, which are uniformly dispersed on the oxide support MMO; M accounts for 0.1% to 5% of the total catalyst mass; the average particle size of X is 10 to 30 nm. The catalyst was prepared using the following steps: A: Dissolve metal X salt, Mg salt, and Al salt in deionized water to prepare a mixed salt solution; wherein the molar ratio of (X+Mg):Al is 2~4; the molar ratio of X to Mg is 1~5, and the total concentration of the three metal ions is 0.5~1.5 mol / L; dissolve an alkali in the same volume of deionized water as the mixed salt solution to form an alkaline solution; the alkaline solution is a mixed solution of NaOH and Na2CO3; The X salt is a nitrate or chloride salt of at least one of Ni, Co, Cu, Fe, and Zn; B: The mixed salt solution and alkaline solution obtained in step A are simultaneously injected into a stirred reactor using a syringe pump, and the solution is kept between 8 and 10. Crystallize at 50 to 80°C for 12 to 36 hours, cool naturally to room temperature, filter and wash the precipitate until the pH of the supernatant solution is neutral, filter again, and place the obtained solid in an oven at 40 to 80°C for 12 to 24 hours to obtain XMgAl-LDHs; C: Dissolve the noble metal M precursor in deionized water to prepare an impregnation solution with a concentration of 10~50 mmol / L. The M precursor used is any one of RhCl3·3H2O, H2PdCl6, RuCl3·3H2O, H2PtCl6, H2IrCl6·6H2O, and HAuCl4·3H2O. D: Grind the XMgAl-LDHs sample prepared in step B into powder, and then uniformly disperse it in deionized water to obtain a suspension with a solid content of 0.01~0.1 g / mL; add the noble metal M impregnation solution prepared in C, so that the loading of M in the catalyst is 0.1~5 wt%, continue stirring and heating to 70~90℃ until the deionized water is completely evaporated, and place the obtained solid in an oven at 40~80℃ to dry for 1 h to obtain the M-XMgAl-LDHs precursor; E: The M-XMgAl-LDHs precursor obtained in step D is ground, heated to 500-700℃ in a reducing atmosphere at a heating rate of 2-10℃ / min, and held for 2-4 hours to prepare M 1+n @X / MMO catalyst.

2. A method for preparing a spatially confined, single-component, multi-center catalyst with metal nanoislands as described in claim 1, characterized in that... Prepared using the following steps: A: Dissolve metal X salt, Mg salt, and Al salt in deionized water to prepare a mixed salt solution; wherein the molar ratio of (X+Mg):Al is 2~4; the molar ratio of X to Mg is 1~5, and the total concentration of the three metal ions is 0.5~1.5 mol / L; dissolve an alkali in the same volume of deionized water as the mixed salt solution to form an alkaline solution; the alkaline solution is a mixed solution of NaOH and Na2CO3; The X salt is a nitrate or chloride salt of at least one of Ni, Co, Cu, Fe, and Zn; B: The mixed salt solution and alkaline solution obtained in step A are simultaneously injected into a stirred reactor using a syringe pump, and the solution is kept between 8 and 10. Crystallize at 50 to 80°C for 12 to 36 hours, cool naturally to room temperature, filter and wash the precipitate until the pH of the supernatant solution is neutral, filter again, and place the obtained solid in an oven at 40 to 80°C for 12 to 24 hours to obtain XMgAl-LDHs; C: Dissolve the noble metal M precursor in deionized water to prepare an impregnation solution with a concentration of 10~50 mmol / L. The M precursor used is any one of RhCl3·3H2O, H2PdCl6, RuCl3·3H2O, H2PtCl6, H2IrCl6·6H2O, and HAuCl4·3H2O. D: Grind the XMgAl-LDHs sample prepared in step B into powder, and then uniformly disperse it in deionized water to obtain a suspension with a solid content of 0.01~0.1 g / mL; add the noble metal M impregnation solution prepared in C, so that the loading of M in the catalyst is 0.1~5 wt%, continue stirring and heating to 70~90℃ until the deionized water is completely evaporated, and place the obtained solid in an oven at 40~80℃ to dry for 1 h to obtain the M-XMgAl-LDHs precursor; E: The M-XMgAl-LDHs precursor obtained in step D is ground, heated to 500-700℃ in a reducing atmosphere at a heating rate of 2-10℃ / min, and held for 2-4 hours to prepare M 1+n @X / MMO catalyst.

3. The method according to claim 2, characterized in that: Increasing or decreasing the content of the guest metal X while keeping M constant, the size of the X metal particles increases or decreases, thereby reducing or increasing the dispersion of M.

4. The method according to claim 2, characterized in that: Increase or decrease the content of the host metal M while keeping the guest metal X constant, thereby reducing or increasing the dispersion of M.

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