Atomic-scale dispersion transition metal M-based catalyst as well as preparation method and application thereof

Abstract

The invention provides an atomic-scale dispersion transition metal M-based catalyst as well as a preparation method and application thereof, and belongs to the field of chemical engineering. According to the invention, LDHs is used as an innovative platform, and rich oxygen vacancies which are uniformly distributed are formed through topological transformation in a high-temperature reducing atmosphere, so that M nano-particles formed in a sol fixing process can be promoted to be re-dispersed and anchored in situ, thereby obtaining the M1-YOx-MgAlO catalyst. The active metal M of the catalyst is dispersed in an atomic scale and is anchored by an oxygen vacancy adjacent to an unsaturated coordination Y atom, so that electron interaction between M and Y is initiated, and an electron-deficient and stable M1 delta < + >-YOx synergistic active center is formed. The prepared atomic-scale dispersion transition metal M-based catalyst can be used in a selective hydrogenation reaction, shows excellent hydrogenation activity and selectivity, has outstanding catalytic performance, is easy to recover and reuse, and has good stability.

Description

Technical Field

[0001] The present invention belongs to the field of chemical industry, and specifically relates to an atomically dispersed transition metal M-based catalyst, a preparation method and an application thereof. The catalyst is mainly used for the selective hydrogenation reaction of reactants containing unsaturated functional groups such as alkynes, alkynols and conjugated dienes. Background Art

[0002] The most commonly used selective hydrogenation catalyst in industry is the Lindlar catalyst, which improves selectivity by adding Pb or organic bases to poison some Pd sites at the expense of some activity. However, this also increases the difficulty of subsequent product separation and purification. In addition, precious metal resources have become scarce and expensive in recent years, and the total demand and total supply gap have widened year by year. Therefore, it is crucial to reduce the use of precious metals and develop atomically dispersed supported catalysts. For example, single-atom catalysts have been at the forefront of selective catalytic hydrogenation due to their highest atomic utilization and nearly 100% metal dispersion. However, isolated single atoms have poor stability and must be anchored and isolated with the help of suitable supports or co-metals.

[0003] Mixed metal oxides with topologically transformed layered double hydroxides (LDHs) are often used as supports in the preparation of supported metal catalysts for thermal catalysis due to their large specific surface area and high thermal stability. However, when loaded with active metals, these mixed metal oxides lack stable anchoring sites on their surfaces, leading to migration and aggregation of the active metals and difficulty maintaining a high dispersion during thermal catalysis.

[0004] Based on this, the present invention proposes a new technology of sol fixation-LDHs precursor-high temperature reducing atmosphere induction coupling, which promotes the redispersion of active metal particles formed in the sol fixation process during the topological transformation of LDHs, and prepares atomically dispersed M1-YO x -MgAlO catalyst. Since M atoms are replaced by YO x The uniformly distributed and abundant oxygen vacancies in the MgAlO mixed metal oxides are anchored and interact electronically with the neighboring Y atoms to form atomically dispersed and electron-deficient M1 δ+ -YO x Synergistic active centers promote the joint enhancement of selective hydrogenation activity and selectivity. Summary of the Invention

[0005] The purpose of the present invention is to provide an atomically dispersed transition metal M-based catalyst and a preparation method and application thereof.

[0006] The atomically dispersed transition metal M-based catalyst provided by the present invention is represented by M1-YO x-MgAlO, wherein M is an active metal, which is one of Pd, Pt, Rh, Ru, Ir, Ag, Au, Ni, Cu, Co, and Fe, with Pd and Pt being the most preferred; the active metal M accounts for 0.01 to 1.00 wt.% of the catalyst mass; the metal oxide of Y is reducible, which is one of Ga, Ce, Zr, Co, Fe, and Mn, YO x -MgAlO represents a mixed metal oxide with oxygen vacancies. The structural characteristics of this catalyst are: the oxygen vacancies adjacent to the Y atoms promote the redispersion and anchoring of the M nanoparticles formed during the sol fixation process, generating electronic interactions to form atomically dispersed and electron-deficient M1 δ+ -YO x Synergistic active center.

[0007] The method for preparing the atomically dispersed transition metal M-based catalyst provided by the present invention is characterized by being prepared according to the following specific steps:

[0008] Step A: Dissolve Mg(NO3)2·6H2O, Al(NO3)3·9H2O and reducible Y salt in deionized water to prepare a mixed salt solution with a concentration of 0.2-0.4 mol L -1 , wherein the molar ratio of Mg:Al:Y is 2-5:0.1-0.9:0.9-0.1; NaOH and Na2CO3 are dissolved in deionized water to prepare an alkaline solution with a concentration of 0.4-1.0 mol L -1 , where OH - The molar ratio of CO3 to total metal ions is 1 to 2:1. 2- With Al 3+ The molar ratio of the salt solution and the alkali solution is 1.5 to 3:1; the salt solution and the alkali solution are mixed dropwise, and the pH of the mixed solution is maintained between 9 and 10 by controlling the dropwise acceleration rate, followed by crystallization reaction at 25 to 80°C. After crystallization for 16 to 24 hours, the mixture is dried in an oven at 25 to 80°C to obtain a YMgAl-LDHs support;

[0009] Step B: dissolving the M salt solution and the stabilizer in 30-100 mL of deionized water, stirring at 60-80° C. for 0.5-1 h, adding a reducing agent for liquid phase reduction, and continuing to stir for 0.5-1 h to obtain a nanosol; adding the prepared YMgAl-LDHs support, stirring for 2-4 h, washing and centrifuging, and drying at 25-80° C. to obtain a uniformly dispersed M / YMgAl-LDHs precursor with a small particle size (2-8 nm);

[0010] Step C: Place the above M / YMgAl-LDHs in a tube furnace and introduce a reducing atmosphere to activate them to form abundant oxygen vacancies (YO x), which promotes the redispersion of M nanoparticles to form atomically dispersed M1-YO x -MgAlO catalyst, the active metal M loading amount is 0.01~1.00wt.%.

[0011] The reducible Y salt is one of Ga(NO3)3·xH2O, Ce(NO3)3·6H2O, Zr(NO3)4·5H2O, Co(NO3)2·6H2O, Fe(NO3)3·9H2O, and Mn(NO3)2·4H2O, preferably one of Ga(NO3)3·xH2O, Ce(NO3)3·6H2O, and Zr(NO3)4·5H2O.

[0012] The active metal M salt is one of Na2PdCl4, H2PtCl6, RhCl3·3H2O, RuCl3·3H2O, H2IrCl6, AgNO3, HAuCl4, Ni(NO3)2·6H2O, Cu(NO3)2·3H2O, Co(NO3)2·6H2O, and Fe(NO3)3·9H2O, preferably one of Na2PdCl4 and H2PtCl6.

[0013] The stabilizer is one of polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol (PEG), and sodium dodecyl sulfate (SDS), preferably one of PVP and PVA.

[0014] The reducing agent is NaBH4, KBH4, Na2B 12 H 12 、K2B 12 H 12 、CsB 12 H 12 , NaH2PO2, ascorbic acid, sodium citrate, and hydrazine hydrate, preferably one of NaBH4, ascorbic acid, and sodium citrate.

[0015] The mass ratio of the stabilizer to Pd is 10-30:1, and the molar ratio of the reducing agent to Pd is 5-10:1.

[0016] The reducing atmosphere is one of H2, CO, and NH3, and the balance gas is one of inert gases N2, Ar, and He, wherein the volume fraction of the reducing gas in the atmosphere is 1-50%, and the gas flow rate is 5-100 mL / min.

[0017] The activation temperature is 400-800°C, the heating rate is 1-600°C / min, and the heat preservation time is 0.5-2h.

[0018] Beneficial effects of the present invention:

[0019] Using LDHs as an innovative platform, a topological transformation under a high-temperature reducing atmosphere forms uniformly distributed and abundant oxygen vacancies, which can promote the redispersion of M nanoparticles formed during the sol fixation process and anchor them in situ, thereby obtaining M1-YO x -MgAlO catalyst. The active metal M of the catalyst is dispersed at the atomic level and anchored by the oxygen vacancies adjacent to the unsaturated coordinated Y atoms, which triggers the electronic interaction between M and Y and forms an electron-deficient and stable M1 δ+ -YO x Synergistic active centers. The prepared atomically dispersed transition metal M-based catalyst can be used in selective hydrogenation reactions, showing excellent hydrogenation activity and selectivity, outstanding catalytic performance, easy recovery and reuse, and good stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Atomic-level dispersed Pd1-GaO prepared in Example 1 x -AC-STEM and mapping images of MgAlO catalyst;

[0021] Figure 2 Atomic-level dispersed Pd1-GaO prepared in Example 1 x -XPS spectrum of MgAlO catalyst;

[0022] Figure 3 Atomic-level dispersed Pd1-GaO prepared in Example 1 x -EXAFS spectrum of MgAlO catalyst;

[0023] Figure 4 Atomic-level dispersed Pd1-GaO prepared in Example 1 x Histogram of conversion and selectivity in the selective hydrogenation of 1,4-butynediol over MgAlO catalyst. DETAILED DESCRIPTION

[0024] The above technical solutions of the present invention are described in detail below with reference to specific embodiments.

[0025] Example 1

[0026] Step A: Dissolve Mg(NO3)2·6H2O, Al(NO3)3·9H2O and reducible Ga(NO3)3·xH2O in 100 mL of deionized water to prepare a mixed salt solution with a concentration of 0.3 mol L -1 , where the molar ratio of Mg:Al:Ga is 2:0.8:0.2; NaOH and Na2CO3 are dissolved in 100 mL of deionized water to prepare an alkaline solution with a concentration of 0.64 mol L-1 , where OH - The molar ratio of CO3 to total metal ions is 1.6:1. 2- With Al 3+ The molar ratio of the salt solution and the alkali solution is 2:1; the salt solution and the alkali solution are mixed dropwise, and the pH of the mixed solution is maintained at about 9.5 by controlling the dropwise acceleration rate, and then a crystallization reaction is carried out at 50°C. After crystallization for 20 hours, the mixture is dried in an oven at 60°C to obtain a GaMgAl-LDHs support;

[0027] Step B: Add 50.7 μL Na2PdCl4 solution (55.66 mmol L -1 ) and 0.0045 g PVP were added to 40 mL deionized water, stirred at 70°C for 30 min, and then 0.0006 g NaBH4 was added for liquid phase reduction, and stirring was continued for 30 min to obtain a nanosol; 1 g of the prepared GaMgAl-LDHs support was added, stirred for 2 h, washed, centrifuged, and dried at 60°C to obtain a uniformly dispersed Pd / GaMgAl-LDHs precursor with an average particle size of 5.81 nm;

[0028] Step C: The Pd / GaMgAl-LDHs were placed in a tube furnace for activation treatment. A 10% H2 / N2 reducing atmosphere was introduced at a flow rate of 40 mL / min, and the temperature was raised to 700°C at a heating rate of 5°C / min. The temperature was kept at this temperature for 1 h to obtain atomically dispersed Pd1-GaO x -MgAlO catalyst with a Pd loading of 0.05 wt%.

[0029] like Figure 1 As shown, the atomically dispersed Pd1-GaO prepared in Example 1 x AC-STEM and Mapping images of the -MgAlO catalyst showed that Pd was dispersed at the atomic level without obvious aggregated particles, and Pd atoms were adjacent to Ga atoms.

[0030] like Figure 2 As shown, Pd1-GaO was observed from the O1s XPS spectrum. x The oxygen vacancy concentration of -MgAlO is significantly lower than that of GaMgAlO, and the coordination unsaturated Ga δ+ The binding energy of Pd is negatively shifted, indicating that the Pd atoms are successfully anchored on GaO x The Pd atoms are placed in the oxygen vacancies and interact with the neighboring Ga atoms, resulting in an electron-deficient state.

[0031] like Figure 3As shown in the figure, no obvious Pd-Pd coordination bond was observed in the EXAFS spectrum of Pd, but there was a Pd-Ga scattering peak, which further confirmed that Pd was atomically dispersed and anchored by oxygen vacancies to form a Pd-Ga coordination.

[0032] The catalyst prepared in Example 1 was used in the selective hydrogenation reaction of 1,4-butynediol:

[0033] Weigh 0.2g of the above catalyst and 1g of substrate 1,4-butynediol into a reactor, add 30mL of deionized water to dissolve, and introduce 1MPa of hydrogen. The performance test was carried out at 50℃, and the reaction liquid was detected by gas chromatography. The results are shown in Figure 4 When 1,4-butynediol is fully converted, the selectivity of 1,4-butenediol can reach 97.3%. Compared with the catalysts obtained in the following comparative examples 1-3, the catalyst can carry out directionally selective hydrogenation and has significantly improved catalytic performance.

[0034] Example 2

[0035] Step A: Dissolve Mg(NO3)2·6H2O, Al(NO3)3·9H2O and reducible Ga(NO3)3·xH2O in 100 mL of deionized water to prepare a mixed salt solution with a concentration of 0.3 mol L -1 , where the molar ratio of Mg:Al:Ga is 2:0.9:0.1; NaOH and Na2CO3 are dissolved in 100 mL of deionized water to prepare an alkaline solution with a concentration of 0.66 mol L -1 , where OH - The molar ratio of CO3 to total metal ions is 1.6:1. 2- With Al 3+ The molar ratio of the salt solution and the alkali solution is 2:1; the salt solution and the alkali solution are mixed dropwise, and the pH of the mixed solution is maintained at about 9.5 by controlling the dropwise acceleration rate, and then a crystallization reaction is carried out at 50°C. After crystallization for 20 hours, the mixture is dried in an oven at 60°C to obtain a GaMgAl-LDHs support;

[0036] Step B: 30.4 μL Na2PdCl4 solution (55.66 mmol L -1 ) and 0.0027 g PVP were added to 40 mL deionized water, stirred at 70°C for 30 min, and then 0.0004 g NaBH4 was added for liquid phase reduction, and stirring was continued for 30 min to obtain a nanosol; 1 g of the prepared GaMgAl-LDHs support was added, stirred for 2 h, washed, centrifuged, and dried at 60°C to obtain a uniformly dispersed Pd / GaMgAl-LDHs precursor with an average particle size of 5.26 nm;

[0037] Step C: The Pd / GaMgAl-LDHs were placed in a tube furnace for activation treatment. A 10% H2 / N2 reducing atmosphere was introduced at a flow rate of 40 mL / min, and the temperature was raised to 700°C at a heating rate of 5°C / min. The temperature was kept at this temperature for 1 h to obtain atomically dispersed Pd1-GaO x -MgAlO catalyst with a Pd loading of 0.03 wt%.

[0038] The catalyst prepared in Example 2 was used in the selective hydrogenation reaction of 1,4-butynediol:

[0039] 0.33g of the above catalyst and 1g of the substrate 1,4-butynediol were weighed into a reactor, dissolved in 30mL of deionized water, and introduced with 1MPa of hydrogen. Performance testing was performed at 50°C, and the reaction liquid was analyzed by gas chromatography. The catalyst achieved a 97.7% selectivity for 1,4-butenediol when 1,4-butynediol was fully converted.

[0040] Example 3

[0041] Step A: Dissolve Mg(NO3)2·6H2O, Al(NO3)3·9H2O and reducible Ga(NO3)3·xH2O in 100 mL of deionized water to prepare a mixed salt solution with a concentration of 0.3 mol L -1 , where the molar ratio of Mg:Al:Ga is 2:0.7:0.3; NaOH and Na2CO3 are dissolved in 100 mL of deionized water to prepare an alkaline solution with a concentration of 0.62 mol L -1 , where OH - The molar ratio of CO3 to total metal ions is 1.6:1. 2- With Al 3+ The molar ratio of the salt solution and the alkali solution is 2:1; the salt solution and the alkali solution are mixed dropwise, and the pH of the mixed solution is maintained at about 9.5 by controlling the dropwise acceleration rate, and then a crystallization reaction is carried out at 50°C. After crystallization for 20 hours, the mixture is dried in an oven at 60°C to obtain a GaMgAl-LDHs support;

[0042] Step B: 101.4 μL Na2PdCl4 solution (55.66 mmol L -1 ) and 0.009 g PVP were added to 40 mL deionized water, stirred at 70°C for 30 min, and then 0.0012 g NaBH4 was added for liquid phase reduction, and stirring was continued for 30 min to obtain a nanosol; 1 g of the prepared GaMgAl-LDHs support was added, stirred for 2 h, washed, centrifuged, and dried at 60°C to obtain a uniformly dispersed Pd / GaMgAl-LDHs precursor with an average particle size of 6.12 nm;

[0043] Step C: The Pd / GaMgAl-LDHs were placed in a tube furnace for activation treatment. A 10% H2 / N2 reducing atmosphere was introduced at a flow rate of 40 mL / min, and the temperature was raised to 700°C at a heating rate of 5°C / min. The temperature was kept at this temperature for 1 h to obtain atomically dispersed Pd1-GaO x -MgAlO catalyst with a Pd loading of 0.1 wt%.

[0044] The catalyst prepared in Example 3 was used in the selective hydrogenation reaction of 1,4-butynediol:

[0045] 0.1g of the above catalyst and 1g of the substrate 1,4-butynediol were weighed into a reactor, dissolved in 30mL of deionized water, and introduced with 1MPa of hydrogen. Performance testing was performed at 50°C, and the reaction liquid was analyzed by gas chromatography. When the 1,4-butynediol was fully converted, the catalyst achieved a 1,4-butenediol selectivity of 96.8%.

[0046] Example 4

[0047] Step A: Dissolve Mg(NO3)2·6H2O, Al(NO3)3·9H2O and reducible Ga(NO3)3·xH2O in 100 mL of deionized water to prepare a mixed salt solution with a concentration of 0.3 mol L -1 , where the molar ratio of Mg:Al:Ga is 2:0.4:0.6; NaOH and Na2CO3 are dissolved in 100 mL of deionized water to prepare an alkaline solution with a concentration of 0.56 mol L -1 , where OH - The molar ratio of CO3 to total metal ions is 1.6:1. 2- With Al 3+ The molar ratio of the salt solution and the alkali solution is 2:1; the salt solution and the alkali solution are mixed dropwise, and the pH of the mixed solution is maintained at about 9.5 by controlling the dropwise acceleration rate, and then a crystallization reaction is carried out at 50°C. After crystallization for 20 hours, the mixture is dried in an oven at 60°C to obtain a GaMgAl-LDHs support;

[0048] Step B: 304.2 μL Na2PdCl4 solution (55.66 mmol L -1 ) and 0.027 g PVP were added to 40 mL deionized water, stirred at 70°C for 30 min, and then 0.0036 g NaBH4 was added for liquid phase reduction, and stirring was continued for 30 min to obtain a nanosol; 1 g of the prepared GaMgAl-LDHs support was added, stirred for 2 h, washed, centrifuged, and dried at 60°C to obtain a uniformly dispersed Pd / GaMgAl-LDHs precursor with an average particle size of 6.54 nm;

[0049] Step C: The Pd / GaMgAl-LDHs were placed in a tube furnace for activation treatment. A 10% H2 / N2 reducing atmosphere was introduced at a flow rate of 40 mL / min, and the temperature was raised to 700°C at a heating rate of 5°C / min. The temperature was kept at this temperature for 1 h to obtain atomically dispersed Pd1-GaO x -MgAlO catalyst with a Pd loading of 0.3 wt%.

[0050] The catalyst prepared in Example 4 was used in the selective hydrogenation reaction of 1,4-butynediol:

[0051] 0.03g of the above catalyst and 1g of the substrate 1,4-butynediol were weighed into a reactor, dissolved in 30mL of deionized water, and introduced with 1MPa of hydrogen. Performance testing was performed at 50°C, and the reaction liquid was analyzed by gas chromatography. When the 1,4-butynediol was fully converted, the catalyst achieved a 1,4-butenediol selectivity of 96.5%.

[0052] Example 5

[0053] Step A: Dissolve Mg(NO3)2·6H2O, Al(NO3)3·9H2O and reducible Ga(NO3)3·xH2O in 100 mL of deionized water to prepare a mixed salt solution with a concentration of 0.3 mol L -1 , where the molar ratio of Mg:Al:Ga is 2:0.2:0.8; NaOH and Na2CO3 are dissolved in 100 mL of deionized water to prepare an alkaline solution with a concentration of 0.52 mol L -1 , where OH - The molar ratio of CO3 to total metal ions is 1.6:1. 2- With Al 3+ The molar ratio of the salt solution and the alkali solution is 2:1; the salt solution and the alkali solution are mixed dropwise, and the pH of the mixed solution is maintained at about 9.5 by controlling the dropwise acceleration rate, and then a crystallization reaction is carried out at 50°C. After crystallization for 20 hours, the mixture is dried in an oven at 60°C to obtain a GaMgAl-LDHs support;

[0054] Step B: 507 μL Na2PdCl4 solution (55.66 mmol L -1 ) and 0.045 g PVP were added to 40 mL deionized water, stirred at 70°C for 30 min, and then 0.0060 g NaBH4 was added for liquid phase reduction, and stirring was continued for 30 min to obtain a nanosol; 1 g of the prepared GaMgAl-LDHs support was added, stirred for 2 h, washed, centrifuged, and dried at 60°C to obtain a uniformly dispersed Pd / GaMgAl-LDHs precursor with an average particle size of 6.83 nm;

[0055] Step C: The Pd / GaMgAl-LDHs were placed in a tube furnace for activation treatment. A 10% H2 / N2 reducing atmosphere was introduced at a flow rate of 40 mL / min, and the temperature was raised to 700°C at a heating rate of 5°C / min. The temperature was kept at this temperature for 1 h to obtain atomically dispersed Pd1-GaO x -MgAlO catalyst with a Pd loading of 0.5 wt%.

[0056] The catalyst prepared in Example 5 was used in the selective hydrogenation reaction of 1,4-butynediol:

[0057] 0.02g of the above catalyst and 1g of the substrate 1,4-butynediol were weighed into a reactor, dissolved in 30mL of deionized water, and introduced with 1MPa of hydrogen. Performance testing was performed at 50°C, and the reaction liquid was analyzed by gas chromatography. When the 1,4-butynediol was fully converted, the catalyst achieved a 1,4-butenediol selectivity of 95.9%.

[0058] Comparative Example 1

[0059] Step A: Dissolve Mg(NO3)2·6H2O, Al(NO3)3·9H2O and reducible Ga(NO3)3·xH2O in 100 mL of deionized water to prepare a mixed salt solution with a concentration of 0.3 mol L -1 , where the molar ratio of Mg:Al:Ga is 2:0.8:0.2; NaOH and Na2CO3 are dissolved in 100 mL of deionized water to prepare an alkaline solution with a concentration of 0.64 mol L -1 , where OH - The molar ratio of CO3 to total metal ions is 1.6:1. 2- With Al 3+ The molar ratio of the salt solution and the alkali solution is 2:1; the salt solution and the alkali solution are mixed dropwise, and the pH of the mixed solution is maintained at about 9.5 by controlling the dropwise acceleration rate, and then a crystallization reaction is carried out at 50°C. After crystallization for 20 hours, the mixture is dried in an oven at 60°C to obtain a GaMgAl-LDHs support;

[0060] Step B: Add 50.7 μL Na2PdCl4 solution (55.66 mmol L -1 ) was dissolved in 10 mL of deionized water, and 1 g of the prepared GaMgAl-LDHs support was added. After ultrasonic dispersion for 5 min, the mixture was immersed in a 60 ° C water bath. After the solution was evaporated to dryness, Pd was obtained by drying at 60 ° C. 2+ / GaMgAl-LDHs precursor.

[0061] Step C: Add the above Pd 2+ / GaMgAl-LDHs were placed in a tube furnace for activation treatment, and a 10% H2 / N2 reducing atmosphere was introduced at a flow rate of 40 mL / min. The temperature was raised to 700°C at a heating rate of 5°C / min and kept at this temperature for 1 h to obtain Pd n -GaMgAlO catalyst, Pd loading amount is 0.05wt%, wherein Pd exists in the form of nanoparticles with an average particle size of 3.66nm and is x There were no significant interactions.

[0062] The catalyst prepared in Comparative Example 1 was used in the selective hydrogenation reaction of 1,4-butynediol:

[0063] Weigh 0.2g of the above catalyst and 1g of substrate 1,4-butynediol into a reactor, add 30mL of deionized water to dissolve, and introduce 1MPa of hydrogen. The performance test was carried out at 50℃. The reaction liquid was detected by gas chromatography. The results are shown in Figure 4 Since the nanoparticles of Pd n Not with GaO x Effective synergy, at the same temperature, compared with Example 1, the conversion rate and selectivity are greatly reduced to 79.5% and 74.8%.

[0064] Comparative Example 2

[0065] Step A: Dissolve Mg(NO3)2·6H2O and Al(NO3)3·9H2O in 100 mL of deionized water to prepare a mixed salt solution with a concentration of 0.3 mol L -1 , where the molar ratio of Mg:Al is 2:1; NaOH and Na2CO3 are dissolved in 100 mL of deionized water to prepare an alkaline solution with a concentration of 0.68 mol L -1 , where OH - The molar ratio of CO3 to total metal ions is 1.6:1. 2- With Al 3+ The molar ratio of the salt solution and the alkali solution is 2:1; the salt solution and the alkali solution are mixed dropwise, and the pH of the mixed solution is maintained at about 9.5 by controlling the dropwise acceleration rate, and then a crystallization reaction is carried out at 60°C. After crystallization for 10 hours, the mixture is dried in an oven at 60°C to obtain the MgAl-LDHs support;

[0066] Step B: 0.1016 g of Ga(NO3)3·xH2O was dissolved in 10 mL of deionized water, and 1 g of the prepared MgAl-LDHs carrier was added. After ultrasonic dispersion for 5 min, the mixture was immersed in a 60°C water bath. After the solution was evaporated to dryness, it was dried at 60°C to obtain Ga 3+ / MgAl-LDHs; 50.7 μL Na2PdCl4 solution (55.66 mmol L-1 ) and 0.0045g PVP were added to 40mL deionized water, stirred at 70°C for 30min, and then 0.0006g NaBH4 was added for liquid phase reduction, and stirring was continued for 30min to obtain nanosol; Ga was added 3+ / MgAl-LDHs were stirred for 2 h, washed, centrifuged, and dried at 60 °C to obtain Pd / Ga 3+ / MgAl-LDHs precursor;

[0067] Step C: Pd / Ga 3+ / MgAl-LDHs were placed in a tube furnace for activation treatment, and a 10% H2 / N2 reducing atmosphere was introduced at a flow rate of 40 mL / min. The temperature was raised to 700°C at a heating rate of 5°C / min and kept at this temperature for 1 h to obtain Pd n -Ga-MgAlO catalyst, characterized in that Pd exists in the form of nanoparticles with an average particle size of 5.46nm and is x There were no significant interactions.

[0068] The catalyst prepared in Comparative Example 2 was used in the selective hydrogenation reaction of 1,4-butynediol:

[0069] Weigh 0.2g of the above catalyst and 1g of substrate 1,4-butynediol into a reactor, add 30mL of deionized water to dissolve, and introduce 1MPa of hydrogen. The performance test was carried out at 50℃. The reaction liquid was detected by gas chromatography. The results are shown in Figure 4 Since the nanoparticles of Pd n Not with GaO x The conversion rate and selectivity of the reaction mixture decreased significantly to 84.3% and 90.6% compared with those in Example 1 at the same temperature.

[0070] Comparative Example 3

[0071] 84.7 μL Na2PdCl4 solution (55.66 mmol L -1 ) and 0.0075g PVP were added to 40mL deionized water, stirred at 70℃ for 30min, and then 0.0010g NaBH4 was added for liquid phase reduction, and stirring was continued for 30min to obtain nanosol; 1g commercial γ-Al2O3 was added and stirred for 2h, washed and centrifuged, and dried at 60℃ and placed in a tube furnace for activation treatment, 10% H2 / N2 reducing atmosphere was introduced at a flow rate of 40mL / min, and the temperature was increased to 700℃ at a heating rate of 5℃ / min and kept warm for 1h to obtain Pd n / Al2O3 catalyst, with a Pd loading of 0.05wt%, is characterized in that the Pd exists in the form of nanoparticles with an average particle size of 7.50nm.

[0072] The catalyst prepared in Comparative Example 3 was used in the selective hydrogenation reaction of 1,4-butynediol:

[0073] Weigh 0.2g of the above catalyst and 1g of substrate 1,4-butynediol into a reactor, add 30mL of deionized water to dissolve, and introduce 1MPa high-purity hydrogen. The performance test was carried out at 50℃, and the reaction liquid was detected by gas chromatography. The results are shown in Figure 4 Since the second component Ga element is not introduced and the active component is nano-particle Pd n , at the same temperature, compared with Example 1, its conversion rate dropped to 95.7%, and the selectivity was only 20.5%.

Claims

1. A method for preparing an atomically dispersed transition metal M-based catalyst, characterized in that: Including steps: Step A: Dissolve Mg(NO3)2·6H2O, Al(NO3)3·9H2O and reducible Y salt in deionized water to prepare a mixed salt solution with a concentration of 0.2-0.4 mol L -1 , where Mg: The molar ratio of Al:Y is 2-5:0.1-0.9:0.9-0.1; NaOH and Na2CO3 are dissolved in deionized water to prepare an alkaline solution with a concentration of 0.4-1.0 mol L-1, wherein OH - The molar ratio of CO3 to total metal ions is 1 to 2:

1. 2- With Al 3+ The molar ratio of the salt solution and the alkali solution is 1.5 to 3:1; the salt solution and the alkali solution are mixed dropwise, and the pH of the mixed solution is maintained between 9 and 10 by controlling the dropwise acceleration rate, followed by crystallization reaction at 25 to 80°C. After crystallization for 16 to 24 hours, the mixture is dried in an oven at 25 to 80°C to obtain a YMgAl-LDHs support; Step B: dissolving the M salt solution and the stabilizer in 30-100 mL of deionized water, stirring at 60-80° C. for 0.5-1 h, adding a reducing agent for liquid phase reduction, and continuing to stir for 0.5-1 h to obtain a nanosol; adding the prepared YMgAl-LDHs support, stirring for 2-4 h, washing, centrifuging, and drying at 25-80° C. to obtain a uniformly dispersed M / YMgAl-LDHs precursor with a particle size of 2-8 nm; Step C: Place the above M / YMgAl-LDHs in a tube furnace and introduce a reducing atmosphere to activate them to form abundant oxygen vacancies (YO x ), which promotes the redispersion of M nanoparticles to form atomically dispersed M1-YO x -MgAlO catalyst, the active metal M loading amount is 0.01~1.00wt.%.

2. The method for preparing an atomically dispersed transition metal M-based catalyst according to claim 1, wherein the reducible Y salt described in step A is one of Ga(NO3)3·xH2O, Ce(NO3)3·6H2O, Zr(NO3)4·5H2O, Co(NO3)2·6H2O, Fe(NO3)3·9H2O, and Mn(NO3)2·4H2O, preferably one of Ga(NO3)3·xH2O, Ce(NO3)3·6H2O, and Zr(NO3)4·5H2O.

3. The method for preparing an atomically dispersed transition metal M-based catalyst according to claim 1, wherein the active metal M salt described in step B is one of Na2PdCl4, H2PtCl6, RhCl3·3H2O, RuCl3·3H2O, H2IrCl6, AgNO3, HAuCl4, Ni(NO3)2·6H2O, Cu(NO3)2·3H2O, Co(NO3)2·6H2O, and Fe(NO3)3·9H2O, preferably one of Na2PdCl4 and H2PtCl6; and the stabilizer described in step B is one of polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), polyethylene glycol (PEG), and sodium lauryl sulfate (SDS).

4. The method for preparing an atomically dispersed transition metal M-based catalyst according to claim 1, wherein the reducing agent in step B is NaBH4, KBH4, Na2B 12 H 12 、K2B 12 H 12 、CsB 12 H 12 , NaH2PO2, ascorbic acid, sodium citrate, and hydrazine hydrate.

5. The method for preparing an atomically dispersed transition metal M-based catalyst according to claim 1, wherein the mass ratio of the stabilizer to Pd in ​​step B is 10-30:1, and the molar ratio of the reducing agent to Pd is 5-10:

1.

6. The method for preparing an atomically dispersed transition metal M-based catalyst according to claim 1, wherein the reducing atmosphere in step C is one of H2, CO, and NH3, and the balance gas is one of inert gases N2, Ar, and He, wherein the volume fraction of the reducing gas in the atmosphere is 1 to 50%, the gas flow rate is 5 to 100 mL / min, the activation temperature is 400 to 800°C, the heating rate is 1 to 600°C / min, and the holding time is 0.5 to 2 h.

7. An atomically dispersed transition metal M-based catalyst prepared by the method of claim 1, characterized in that: The catalyst is denoted as M1-YO x -MgAlO, wherein M is an active metal, which is one of Pd, Pt, Rh, Ru, Ir, Ag, Au, Ni, Cu, Co, and Fe, and the mass fraction of the active metal M in the catalyst is 0.01 to 1.00 wt%; the metal oxide of Y is reducible, which is one of Ga, Ce, Zr, Co, Fe, and Mn, YO x -MgAlO represents a mixed metal oxide with oxygen vacancies. The structural characteristics of this catalyst are: the oxygen vacancies adjacent to the Y atoms promote the redispersion and anchoring of the M nanoparticles formed during the sol fixation process, generating electronic interactions to form atomically dispersed and electron-deficient M1 δ+ -YO x Synergistic active center.

8. The catalyst according to claim 7, characterized in that The active metal M is one of Pd and Pt, and its loading amount is 0.01-0.30 wt%.

9. The catalyst according to claim 7, characterized in that YO x The -MgAlO support is rich in oxygen vacancies, and the active metal M is confined by the vacancies on the support surface, presenting an atomic-level dispersion and electron-deficient state.

10. Use of the catalyst according to claim 7 in the selective hydrogenation reaction of reactants containing unsaturated functional groups such as alkynes, alkynols, and conjugated dienes.

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