Intercalated hydrotalcite-like nano-pd-cu pillared catalysts, their preparation and use

Abstract

The application discloses an intercalated hydrotalcite-like nano-palladium-copper pillared catalyst and a preparation and application thereof, and belongs to the technical field of catalysts. The expression of the catalyst is A@M x Al-B@L, wherein A and B represent Pd or Cu elements, A and B are different elements, M x Al represents a hydrotalcite-like layer plate, M is a divalent metal ion, L is an interlayer anion ligand, the pillared catalyst is efficiently synthesized through a simple co-precipitation-liquid phase reduction two-step method, the structure and composition of the pillared catalyst can be adjusted by regulating the types and dosages of metal elements and ligands, and then the synergistic catalysis between the layer plate and the interlayer nano-palladium-copper particles is enhanced. The intercalated hydrotalcite-like nano-palladium-copper pillared catalyst has a catalytic activity in a visible light catalytic Suzuki coupling reaction which is 1 order of magnitude higher than a hot catalytic activity, the catalyst preparation process is simple, the substrate application range is wide, and the catalyst can be recycled.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and relates to a nano-palladium-copper layered column catalyst of intercalated hydrotalcite and its preparation and application. Background Technology

[0002] Catalysts based on the precious metal palladium have a wide range of applications in petrochemicals, fine chemicals, pharmaceuticals, and environmental protection. Among them, Pd-catalyzed C-C coupling reactions (such as the Suzuki, Sonogashira, Heck, Stille, and Ullmann reactions) play an important role in the pharmaceutical, dye, and electronics industries. Compared to homogeneous Pd catalysts, supported heterogeneous Pd catalysts are easier to separate, recover, and recycle, thus heterogeneous Pd-catalyzed C-C coupling reactions are becoming a research hotspot. Among the many supports used for heterogeneous Pd catalysts, layered double hydroxides (also known as layered double hydroxides) have become a promising new type of catalytic material with great research potential and application prospects due to their unique properties such as the compatibility of cations in the layers, the exchangeability of anions between layers, the memory effect of the layered structure, and surface basicity. CN102008957B, CN106187657B, and CN109621949B disclose methods for introducing palladium into the layers or surface of MgAl layered double hydroxides (LDHs), resulting in LDH-supported palladium catalysts that can be used for thermocatalytic Suzuki coupling reactions. CN106391126B discloses a Schiff base palladium anion-intercalated LDH catalyst synthesized under inert gas protection, which can be used for the catalytic oxidation of the Heck reaction. CN108465472B discloses a palladium-based bimetallic alloy catalyst supported on the surface of LDH, which can be used for thermocatalytic Heck reactions. However, the structural characterization results of the above-disclosed catalysts indicate that Pd species are only distributed on the surface or layers of LDHs, and there are no reports of catalysts with nano-Pd particles successfully intercalated into LDHs for use in CC coupling reactions.

[0003] In recent years, the field of photocatalytic green organic synthesis has flourished. Utilizing clean solar energy for photocatalytic CC coupling reactions not only solves the energy and environmental problems faced by traditional thermocatalysis, but also allows for the high-yield acquisition of coupling products under mild conditions. WS2 nanosheets loaded with nano-Pd (~26.6 wt% Pd) can achieve visible-light-catalyzed Suzuki coupling reactions (J. Am. Chem. Soc. 2017, 139, 14767), with a time-to-frequency (TOF) of 915 h⁻¹ in the coupling reaction of iodobenzene and phenylboronic acid. -1 The formation of nanoalloy particles from copper and palladium can reduce the amount of Pd used in photocatalysts. For example, encapsulating nano-PdCu alloys (~0.33 wt% Pd) within MOF (Metal-Oxide-Film) cages for the visible-light photocatalytic coupling reaction of iodobenzene and phenylboronic acid under inert gas protection resulted in a maximum TOF of 158 h⁻¹.-1 (Small Methods 2018, 2, 1800164); PdCu nanoalloy particles loaded on nitrogen-doped carbon nanosheets (~1.2 wt% Pd) were used for the visible-light photocatalytic coupling reaction of iodobenzene and phenylboronic acid under inert gas protection, and the time-of-flight (TOF) of the catalyst reached 418 h⁻¹. -1 (Appl. Catal. B 2022, 300, 120756). However, the reported supported nano-Pd and PdCu alloy catalysts only exhibit high catalytic activity for iodobenzene substrates in the visible-light catalytic Suzuki coupling reaction, while showing very low catalytic activity for bromobenzene and chlorobenzene substrates that are more difficult to activate; in addition, these catalysts are unstable in air and require an inert atmosphere for the reaction.

[0004] Based on the above analysis, developing a more stable and efficient novel supported nano-PdCu catalyst is urgently needed in this field. Summary of the Invention

[0005] In view of the above shortcomings, the purpose of this invention is to provide a nano-palladium-copper intercalation column catalyst with intercalated layered double hydroxides (LDHs) and its preparation and application, which solves the problems of high Pd loading, high cost, poor oxidation stability and low catalytic activity of traditional supported nano-Pd or PdCu alloy catalysts. In this catalyst, nano-Pd / Cu are located in the LDH-like layers and interlayers, forming a special nano-palladium-copper or copper-palladium intercalation column structure, rather than the traditional surface-supported nano-PdCu alloy catalyst. The interlayer spacing of the intercalated LDH can reach 1-2 nm. This catalyst exhibits significant layer-column synergistic catalytic enhancement and excellent catalytic activity in the room-temperature visible light-catalyzed Suzuki coupling reaction under air atmosphere. It has broad substrate adaptability, stable catalyst structure and simple preparation process.

[0006] This invention is achieved through the following technical means:

[0007] This invention first discloses a nano-palladium-copper layered column catalyst with intercalated hydrotalcite-like structure, the formula of which is A@M x Al-B@L, where A and B are Pd or Cu elements, and A and B are different elements; A@M x Al represents A nanoparticles anchored to M in a hydrotalcite-like structure. x Al layer, M is a divalent metal ion, x represents the reaction between divalent metal M and Al. 3+ The molar ratio; B@L represents the complex of B nanoparticles and ligand L intercalated between the hydrotalcite-like layers, where L is an anionic ligand containing amino or hydroxyl groups.

[0008] Preferably, the mass percentage of A or B when it is Pd is 0.2% to 2.0%; and the mass percentage of A or B when it is Cu is 0.5% to 5.0%.

[0009] Preferably, the metal element corresponding to M is one or two of Mg, Co, Ni or Zn; x = 1.5 to 3.9; and L is one of citric acid, tartaric acid, ethylenediaminetetraacetic acid, propylenediaminetetraacetic acid, aspartic acid, and 2-aminoterephthalic acid.

[0010] Preferably, the intercalated hydrotalcite nano-palladium-copper layered column catalyst has a nano-palladium or nano-copper intercalated hydrotalcite structure, and the interlayer spacing of the intercalated hydrotalcite is 1-2 nm.

[0011] This invention also discloses a method for preparing a nano-palladium-copper layered column catalyst with intercalated hydrotalcite, comprising the following steps:

[0012] (1) Dissolve metal nitrates of A, M and Al in water according to the molar ratio to obtain a mixed salt solution, dissolve B and L in water according to the molar ratio to obtain a complex solution, dissolve NaOH in water according to the molar ratio to obtain an alkaline solution, add the mixed salt solution and alkaline solution dropwise to the complex solution under the conditions of water bath and stirring at 30-70℃, keep the pH of the slurry at 8-11, stir and react for 1-48h, filter, wash until the filtrate is neutral, dry the filter cake at 80-120℃ to obtain the intercalated hydrotalcite precursor;

[0013] (2) The intercalated hydrotalcite precursor was dispersed in an aqueous solution, and NaBH4 aqueous solution was added dropwise under stirring. After the reduction reaction was carried out for 0.5 to 5 hours, the mixture was filtered. The solid obtained was thoroughly washed and then dried under vacuum at 40 to 80 °C to obtain the intercalated hydrotalcite nano-palladium-copper layer column catalyst.

[0014] Preferably, the total metal concentration of the metal nitrate solution in step (1) is 0.3–1.5 mol / L, the concentration of the complex solution is 0.1–0.5 mol / L, and the concentration of the NaOH solution is 0.5–2.0 mol / L.

[0015] Preferably, in step (1), the molar ratio of A to M is 0.005 to 0.2, the molar ratio of B to L is 0.01 to 0.3, and the molar ratio of A to B is 0.02 to 2.0.

[0016] Preferably, the concentration of the intercalated hydrotalcite precursor in step (2) in the aqueous solution is 10-50 g / L, and the concentration of the NaBH4 aqueous solution is 0.1-0.5 mol / L.

[0017] Preferably, the molar ratio of NaBH4 to (A+B) in step (2) is 2 to 20.

[0018] The present invention also discloses a nano-palladium-copper layered column catalyst of intercalated hydrotalcite prepared according to any of the above preparation methods.

[0019] The present invention also discloses the application of a nano-palladium-copper layered column catalyst based on any of the above-mentioned intercalated hydrotalcites in the visible light-catalyzed Suzuki coupling reaction.

[0020] Preferably, the visible light catalytic Suzuki coupling reaction conditions are as follows: a halobenzene / phenylboronic acid molar ratio of 1:1 to 1.5, a catalyst Pd content to halobenzene molar ratio of 0.01 to 0.1 mol%, an alkali promoter to halobenzene molar ratio of 0.5 to 1.5, a solvent ethanol / water volume ratio of 1 to 3:1, and stirring at room temperature and pressure under air atmosphere for 5 to 60 min; the visible light source is an LED lamp with a light intensity of 0.1 to 1.0 W / cm². 2 .

[0021] In summary, the technical solutions conceived by this invention have the following beneficial effects compared with the prior art:

[0022] (1) This invention provides a nano-palladium-copper layered column catalyst with intercalated hydrotalcite structure, comprising M x The Al-L type hydrotalcite support also includes nano-Pd or nano-Cu active components in the layers and interlayers of the hydrotalcite support. Intercalation of nano-Pd or Cu particles into the hydrotalcite not only provides reaction channels with interlayer spacing of 1–2 nm, which are not available on the surface of hydrotalcite loaded with nano-metal catalysts, but also helps improve the dispersion and stability of the nano-metals. This confined nano-Pd-Cu columnar structure in the layers and interlayers of the hydrotalcite differs from the traditional nano-Pd-Cu alloy structure, facilitating a more effective synergistic catalytic effect between nano-Pd and nano-Cu. Ultimately, this allows the intercalated hydrotalcite nano-palladium-copper columnar catalyst to serve as a more stable and efficient visible-light photocatalytic Suzuki coupling reaction catalyst.

[0023] (2) The present invention uses a complex of nano-Pd or Cu particles and anionic ligand L intercalated hydrotalcite. The organic groups of ligand L and their coordination effects are beneficial to the mass transfer and diffusion of substrate molecules in the interlayer channel and to the stabilization of nanoparticles. The two-dimensional nano-reaction space between the layers is beneficial to improving the contact efficiency between the substrate and the catalytic active site.

[0024] (3) The catalyst described in this invention is prepared efficiently by a simple two-step co-precipitation-liquid phase reduction method. By controlling the type and amount of metal elements and ligands, the structure and composition of the column catalyst can be modified, thereby enhancing the synergistic catalytic effect between the hydrotalcite-like layer and the interlayer nano-palladium-copper particles. The preparation method is simple, highly controllable, and has good reproducibility.

[0025] (4) This invention provides a green and energy-saving visible light catalytic Suzuki coupling reaction process. The Suzuki coupling reaction can be carried out efficiently under normal temperature and pressure, visible light and air atmosphere. The catalytic efficiency is improved by one order of magnitude compared with the thermal catalytic reaction efficiency.

[0026] (5) The TOF value of the nano-Pd-Cu layered column catalyst used in this invention is much higher than that of the hydrotalcite-supported nano-palladium or palladium-copper alloy catalyst in the photocatalytic Suzuki coupling reaction. Attached Figure Description

[0027] Figure 1 Typical Sample 1 # and 5 # XRD pattern of the catalyst.

[0028] Figure 2 This is a typical sample XRD pattern, where A is 4. # 6 # 7 # 9 # 11 # Catalyst, B is A # B # C # D # Comparative catalysts.

[0029] Figure 3 These are typical SEM images of a sample, where A is 1. # Catalyst, B is 5 # Catalyst, C is A # Comparative catalysts.

[0030] Figure 4 These are typical TEM images of a sample, where A is 1. # Catalyst, B is 5 # Catalyst, C is A # Comparative catalysts.

[0031] Figure 5 Typical Sample 1 # 5 # Catalyst and A # Compare the XPS patterns of the catalysts, where A is the Pd 3d XPS pattern and B is the Cu 2p XPS pattern. 3 / 2 XPS diagram. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0033] This invention provides a nano-palladium-copper layered column catalyst with intercalated hydrotalcite-like structure, the formula of which is A@M x Al-B@L, wherein A and B are Pd or Cu elements, and A and B are different elements; the mass percentage of A or B as Pd is 0.2-2.0%; the mass percentage of A or B as Cu is 0.5-5.0%; and A@M x Al represents A nanoparticles anchored to M in a hydrotalcite-like structure. x Al layer; M is a divalent metal ion, and the corresponding metal element is one or two of Mg, Co, Ni or Zn; x represents the divalent metal M and Al. 3+ The molar ratio is x = 1.5 to 3.9; B@L represents the complex of B nanoparticles and ligand L intercalated between hydrotalcite-like layers; L is an anionic ligand containing amino or hydroxyl groups, and the corresponding ligands are one of citric acid (CA), tartaric acid (TA), ethylenediaminetetraacetic acid (EDTA), propylenediaminetetraacetic acid (PDTA), aspartic acid (ASP), and 2-aminoterephthalic acid (ATA); the nano-palladium-copper layered column catalyst has a nano-palladium or nano-copper intercalated hydrotalcite-like structure, and the intercalation spacing of the hydrotalcite-like layers is 1 to 2 nm.

[0034] This invention also provides a method for preparing the aforementioned intercalated hydrotalcite-like nano-palladium-copper layered column catalyst, comprising two steps: co-precipitation and liquid-phase reduction. The specific steps of this preparation method are as follows:

[0035] (1) Dissolve metal nitrates of A, M and Al in water according to the molar ratio to obtain a mixed salt solution, dissolve B and L in water according to the molar ratio to obtain a complex solution, dissolve NaOH in water according to the molar ratio to obtain an alkaline solution, add the mixed salt solution and alkaline solution dropwise to the complex solution under the conditions of water bath and stirring at 30-70℃, keep the pH of the slurry at 8-11, stir and react for 1-48h, filter, wash until the filtrate is neutral, dry the filter cake at 80-120℃ to obtain the intercalated hydrotalcite precursor;

[0036] (2) The precursor obtained in step (1) was dispersed in an aqueous solution, and NaBH4 aqueous solution was added dropwise under stirring. After the reduction reaction was carried out for 0.5 to 5 hours, the mixture was filtered, and after thorough washing, the solid was dried under vacuum at 40 to 80 °C to obtain A@M. xAl-B@L nano-palladium-copper column catalyst.

[0037] In the above preparation method, the total metal concentration of the metal nitrate solution is 0.3–1.5 mol / L, the concentration of the complex solution is 0.1–0.5 mol / L, and the concentration of the NaOH solution is 0.5–2.0 mol / L. The molar ratio of A to M is 0.005–0.2, the molar ratio of B to L is 0.01–0.3, and the molar ratio of A to B is 0.02–2.0. The concentration of the intercalated hydrotalcite precursor in the aqueous solution is 10–50 g / L, and the concentration of the NaBH4 aqueous solution is 0.1–0.5 mol / L. The molar ratio of NaBH4 to (A+B) is 2–20.

[0038] The intercalated hydrotalcite-like nano-palladium-copper column catalyst described in this invention can be used for visible-light catalytic Suzuki coupling reactions. In some embodiments, the visible light source is an LED lamp with a light intensity of 0.1–1.0 W / cm². 2 The visible light catalytic Suzuki coupling reaction conditions are as follows: the molar ratio of halobenzene / phenylboronic acid is 1:1 to 1.5, the molar ratio of catalyst Pd content to halobenzene is 0.01 to 0.1 mol%, the molar ratio of alkali promoter to halobenzene is 0.5 to 1.5, the volume ratio of solvent ethanol / water is 1 to 3:1, and stirring is carried out at room temperature and pressure under air atmosphere for 5 to 60 min.

[0039] Example 1

[0040] Preparation of intercalated hydrotalcite-based nano-palladium-copper column catalysts:

[0041] Taking item 1 in Table 1 as an example, copper nitrate / magnesium nitrate / aluminum nitrate were dissolved in deionized water to prepare a mixed salt solution with a total concentration of 1.0 mol / L. Palladium nitrate / ethylenediaminetetraacetic acid (EDTA) were dissolved in deionized water to prepare a complex solution with a total concentration of 0.25 mol / L. NaOH was dissolved in deionized water to prepare an alkaline solution with a concentration of 1.0 mol / L. The molar ratio of Cu / Mg / Al / Pd / EDTA / NaOH in the three solutions was 7:193:100:3:50:800. The mixed salt solution was prepared under the conditions of a 30℃ water bath and stirring. Liquid and alkaline solutions were added dropwise to the complex solution, maintaining the pH of the slurry at ~10.0. After stirring for 24 hours, the mixture was filtered and washed until the filtrate was neutral. The filter cake was dried at 80°C to obtain the intercalated hydrotalcite precursor. The precursor was dispersed in deionized water to form a suspension with a concentration of 30 g / L. A 0.2 mol / L NaBH4 solution was added dropwise to the suspension, with a molar ratio of NaBH4 to (Cu+Pd) in the precursor of 5. After a reduction reaction of 1 hour, the mixture was filtered, thoroughly washed, and the solid was vacuum dried at 50°C overnight to obtain the intercalated hydrotalcite nano-palladium-copper layered column catalyst 1.# Its chemical formula is denoted as Cu. 0.07 @Mg 1.93 Al-Pd 0.03 @EDTA 0.5 -30-10.0, where the subscript values ​​represent the metal ion or ligand and Al. 3+ The molar ratio, "30" indicates a water bath temperature of 30℃, and "10.0" indicates that the coprecipitation is maintained at pH ~10.0.

[0042] Following the above steps, adjust the composition and concentration of the mixed salt solution, complex solution, and alkaline solution, as well as the water bath temperature, pH value, and NaBH4 dosage, to obtain a series of catalysts numbered 2 to 12, denoted as catalyst 2. # ~12 # As shown in Table 1, its chemical formula A a @M x Al-B b @L c -T-pH, where a, b, c, x represent the metal ion or ligand and Al 3+ The molar ratio, "T" represents the water bath temperature, and "pH" represents the pH value maintained during coprecipitation.

[0043] Catalyst characterization:

[0044] For number 1 # ~12 # The catalyst was subjected to AAS elemental analysis, as shown in Table 1. The contents of Pd and Cu were in the range of 0.4-0.7 wt% and 0.5-5.0 wt%, respectively, and the mass ratio of Cu to Pd in ​​the sample was in the range of 1-10.

[0045] For number 1 # 4 # 5 # 6 # 7 # 9 # 11 # Seven catalysts were characterized by XRD, of which 1 # and 5 # The XRD results of the two catalysts are as follows Figure 1 As shown, the XRD results of the other five samples are as follows: Figure 2 As shown in A. From Figure 1 and Figure 2As shown in Figure A, all seven catalysts exhibit typical intercalated layered double hydroxide (TLH) structures. Due to the different molecular sizes of the anionic ligand L, the interlayer spacing d(003) ranges from 1.2 to 1.5 nm. When L is CA, EDTA, or PDTA, the interlayer spacings are 1.22, 1.42, and 1.49 nm, respectively. Furthermore, no obvious palladium or copper diffraction peaks were observed in any of the seven samples, indicating that the nano-palladium and nano-copper are highly dispersed in the LDH support.

[0046] For number 1 # and 5 # The two catalysts were characterized by SEM, such as Figure 3 As shown in A and 3B, both samples have a hydrotalcite-like flaky morphology. Due to the intercalation of organic anionic ligands, a large number of small flaky layers appear on the surface of the hydrotalcite-like material, resembling curled leaves, with an average thickness of ~20-30 nm and a major axis dimension of 100-300 nm.

[0047] For number 1 # and 5 # The two catalysts were characterized by TEM, such as Figure 4 As shown in A and 4B, TEM images of both samples show nanoparticles with diameters of 0.3–3.0 nm uniformly dispersed on the support, with an average particle size of ~1.0 nm. Many of the smaller particles have indistinct shapes, likely due to their intercalation between the hydrotalcite-like layers rather than on the surface. Fewer, more clearly defined spherical particles, ranging in size from 1.5–3.0 nm, are anchored to the outer surface layers of the hydrotalcite-like structure. Based on the contrast between Pd and Cu elements, it can be roughly determined that the darker, more clearly defined particles on the surface are Pd nanoparticles, while the lighter-colored particles are Cu nanoparticles. Regardless of whether the Pd nanoparticles are located between the layers... # Samples and 5 located on the surface of the laminate # In the samples, the average size of Pd particles is smaller than that of Cu particles. Based on the combined TEM, SEM, and XRD characterization results, it can be confirmed that the above samples are nano-palladium-copper intercalated layered double hydroxides with a special layer-pillar structure.

[0048] For number 1 # and 5 # The two catalysts were also characterized by XPS, such as Figure 5 As shown in A and 5B, both samples contain Pd. 0 / Pd 2+ and Cu 0 / Cu 2+ Species, this is due to the reduced nano-Pd 0 and Cu 0 The particles are easily oxidized in air, but intercalated in the nano-Pd between the layers (1 #) of Pd 0 and nano Cu (5 # Cu 0 The high content of all these components indicates that the confinement effect between the hydrotalcite-like layers is beneficial to improving the nano-Pd content. 0 and Cu 0 Oxidative stability.

[0049] Table 1

[0050]

[0051] Example 2

[0052] Catalysts used for visible light-catalyzed Suzuki coupling reactions:

[0053] Catalysts 1-12 prepared in Example 1 # ~Catalyst 12 # For visible light catalytic Suzuki coupling reaction, 10 mg of catalyst, 0.5 mmol of bromobenzene, 0.6 mmol of phenylboronic acid, 1.0 mmol of potassium carbonate, 0.25 mmol of dodecane (internal standard), 2 mL of ethanol, and 2 mL of H₂O were sequentially added to a quartz reaction tube. The reaction was carried out under ambient temperature, atmospheric pressure, and air atmosphere using a white LED (0.2 W / cm²). 2 After irradiation and magnetic stirring for 20 min, the light source was turned off, and 4 mL of ethyl acetate was added to extract the product. The conversion rate of bromobenzene, the selectivity of biphenyl, and the TOF based on the Pd content of the catalyst were all calculated by quantitative analysis using gas chromatography.

[0054] The reaction results are shown in Table 2. Adjusting the catalyst composition and preparation conditions does indeed modulate the photocatalytic activity of the catalyst. After 20 min of reaction, the conversion rate of bromobenzene reached 50-100%, the selectivity of biphenyl was greater than 99%, and the TOF was within the range of 2000-4000 h⁻¹. -1 Within the range.

[0055] It should be noted that in the catalytic conversion process, the contribution of photocatalysis is far greater than that of thermocatalysis, because 5 # When the catalyst reacts for 60 minutes under light-free conditions, the conversion rate of bromobenzene is only 30%, and the TOF is only 300 h⁻¹. -1 And the 5 # The photocatalytic activity of the catalyst increases with increasing light intensity (0.1-1.0 W / cm²). 2 (And it increases linearly.)

[0056] Table 2

[0057] catalyst Conversion rate (%) Biphenyl selectivity (%) <![CDATA[TOF(h -1 ) <!-- 6 -->]]> <![CDATA[1 # ]]> 97 >99 2978 <![CDATA[2 # ]]> 92 >99 2880 <![CDATA[3 # ]]> 80 >99 2027 <![CDATA[4 # ]]> 57 >99 2275 <![CDATA[5 # ]]> 99 >99 2982 <![CDATA[6 # ]]> 90 >99 2477 <![CDATA[7 # ]]> 99 >99 2549 <![CDATA[8 # ]]> 93 >99 3452 <![CDATA[9 # ]]> 98 >99 3911 <![CDATA[10 # ]]> 85 >99 2713 <![CDATA[11 # ]]> 72 >99 2554 <![CDATA[12 # ]]> 81 >99 2810

[0058] Comparative Example 1

[0059] Comparative catalyst preparation:

[0060] A mixed salt solution with a total concentration of 1.0 mol / L was prepared by dissolving palladium nitrate, copper nitrate, magnesium nitrate, and aluminum nitrate in deionized water. A solution with a total concentration of 0.5 mol / L was prepared by dissolving Na₂CO₃ in deionized water. A 1.0 mol / L alkaline solution was prepared by dissolving NaOH in deionized water. The molar ratio of Pd / Cu / Mg / Al / Na₂CO₃ / NaOH in the three solutions was 3:7:190:100:100:800. The mixed salt solution and the alkaline solution were then added dropwise under stirring in a 70°C water bath. Add Na₂CO₃ solution, maintain the pH of the slurry at ~10.5, react for 24 h, filter, wash until the filtrate is neutral, and dry the filter cake at 100℃ to obtain a hydrotalcite-like precursor. Disperse the precursor in deionized water to form a suspension with a concentration of 30 g / L, add a 0.2 mol / L NaBH₄ solution to it, with a molar ratio of NaBH₄ to (Cu+Pd) in the precursor of 5, reduce the mixture for 1 h, filter, wash thoroughly, and vacuum dry at 50℃ overnight to obtain hydrotalcite-like layered anchored nano-palladium-copper catalyst A. # Its chemical formula is denoted as Pd. 0.03 Cu 0.07 @Mg 1.9 Al-CO3.

[0061] A similar process was used to first prepare a Mg2Al-CO3 hydrotalcite support, then impregnate it with a mixed solution of palladium nitrate and copper nitrate, followed by reduction with NaBH4 to obtain a nano-palladium-copper catalyst B supported on the hydrotalcite surface. # Its chemical formula is denoted as Pd. 0.03 Cu 0.07 / Mg2Al-CO3.

[0062] Magnesium nitrate and aluminum nitrate were dissolved in deionized water to prepare a mixed salt solution with a total concentration of 1.0 mol / L. Palladium nitrate and EDTA were prepared to prepare a complex solution with a total concentration of 0.3 mol / L. NaOH was prepared to prepare an alkaline solution with a concentration of 1.0 mol / L. The molar ratio of Mg / Al / Pd / EDTA / NaOH in the three solutions was 200:100:3:50:800. The mixed salt solution and the alkaline solution were added dropwise to the complex solution separately under stirring in a 70°C water bath. The slurry pH was maintained at ~10.0, and the reaction was carried out for 24 hours. After filtration, the filtrate was washed until neutral. The filter cake was dried at 100℃ to obtain an intercalated layered double hydroxide precursor. This precursor was dispersed in deionized water to form a suspension with a concentration of 30 g / L. A 0.2 mol / L NaBH4 solution was added dropwise to the suspension, with a molar ratio of NaBH4 to Pd in ​​the precursor of 5. After a reduction reaction of 1 hour, the suspension was filtered, and after thorough washing, the solid was vacuum dried overnight at 50℃ to obtain the nano-palladium intercalated layered double hydroxide catalyst C. # Its chemical formula is Mg2Al-Pd 0.03 @EDTA 0.5 .

[0063] Using and preparing catalyst C # Similar steps were used to prepare nano-palladium-copper intercalated hydrotalcite catalyst D. # Its chemical formula is Mg2Al-Pd 0.03 Cu 0.07 @EDTA 0.5 .

[0064] Using and preparing catalyst C # Similar steps were used to prepare nano-copper intercalated hydrotalcite catalyst E. # Its chemical formula is Mg2Al-Cu 0.07 @EDTA 0.5 .

[0065] Comparative catalyst characterization:

[0066] For number A # ~E # AAS elemental analysis was performed on the comparative catalysts, as shown in Table 3. The contents of Pd and Cu were both in the range of 0-1.0 wt%. For the catalyst designated A... # ~D # Four comparative catalysts were characterized by XRD, such as Figure 2 As shown in B, A # and B # It has a typical carbonate-type hydrotalcite structure with an interlayer spacing d(003) = 0.78 nm; C # and D # Compared with 1 in Example 1 # and 5# Similar to each other, all four samples exhibit an EDTA-intercalated hydrotalcite-like structure with an interlayer spacing d(003) = 1.42 nm. No obvious palladium or copper diffraction peaks were observed in any of the four samples, indicating that the nano-palladium and nano-copper are well dispersed in the hydrotalcite-like support. For A... # SEM characterization was performed, such as Figure 3 As shown in C, it has an uncurled, hydrotalcite-like flake morphology, with the size of the small flakes being greater than 1. # and 5 # The catalyst is relatively small, with an average thickness of 10-20 nm and a major axis dimension of 100-200 nm. (Regarding A) # TEM characterization was performed, such as Figure 4 As shown in Figure C, nanoparticles with a diameter of 3.0–7.0 nm can be observed dispersed on the support, with an average particle size of ~5.0 nm, compared to 1 # and 5 # The average particle size of the catalyst is significantly larger than that of the ~1.0 nm catalyst, indicating that the intercalated hydrotalcite-like nano-palladium-copper column catalyst prepared in Example 1 can effectively improve the dispersion of nano-metals. (Regarding A) # XPS characterization was also performed, such as Figure 5 As shown in A and 5B, Pd in ​​the sample 0 More than Pd 2+ Cu 2+ More than Cu 0 / Cu + This suggests that a core-shell structure may have formed between nano-Pd and Cu, with the outer CuO layer... x For the inner layer Pd 0 The particles provide some protection.

[0067] Comparative catalysts for visible-light catalytic Suzuki coupling reactions:

[0068] The visible light-catalyzed Suzuki coupling reaction was carried out under the same reaction conditions as in Example 2, and the results are shown in Table 3. Catalyst A is a nano-palladium copper supported on a hydrotalcite layer and its surface. # and B # The TOF values ​​were all less than 400 h. -1 Individual nano-Cu intercalated layered hydrotalcite E # Catalysts with no catalytic activity and single nano-Pd intercalation: C # The TOF is 253h -1 Meanwhile, the catalyst D, which is simultaneously intercalated with nano-PdCu, # The TOF is 688h -1This indicates that the nano-PdCu intercalated between the layered hydrotalcite-like layers exhibits a certain degree of Pd-Cu synergistic catalytic effect in the visible-light-catalyzed Suzuki coupling reaction. However, in Example 1, the nano-Pd / Cu were located in the intercalated hydrotalcite-like layer plates and the interlayer column catalyst 1, respectively. # ~12 # Catalyst A, which forms a nano-alloy structure between PdCu, # B # and D # The TOF value is at least 2 to 10 times higher, which fully demonstrates that the intercalated hydrotalcite-like nano-palladium-copper column catalyst of the present invention exhibits a more significant synergistic catalytic enhancement effect of nano-palladium-copper column in visible light-catalyzed Suzuki coupling reaction.

[0069] Table 3

[0070]

[0071] Example 3

[0072] Using 5 in Example 1 # Taking the catalyst as an example, the substrate versatility, light source influence, alkaline additive influence, and recycling performance of the catalyst were investigated by changing the reaction conditions in Example 2.

[0073] The reaction was carried out with iodobenzene as the substrate for 5 min, and other conditions were the same as in Example 2. GC analysis showed that the iodobenzene conversion rate was 55%, the biphenyl selectivity was >99%, and the TOF was 6626 h. -1 .

[0074] Using chlorobenzene as a substrate at 0.5 W / cm 2 The reaction was carried out under white LED irradiation for 30 minutes, with other conditions consistent with Example 2. GC analysis showed that the chlorobenzene conversion rate was 13%, the biphenyl selectivity was >99%, and the TOF was 261 h. -1 .

[0075] Using bromobenzene as a substrate, the reaction was carried out under sunlight for 60 min, with other conditions consistent with Example 2. GC analysis showed that the bromobenzene conversion rate was 88%, the biphenyl selectivity was >99%, and the TOF was 883 h. -1 .

[0076] The reaction was carried out for 30 min with 0.6 mmol potassium tert-butoxide as the base auxiliary agent, and other conditions were the same as in Example 2. GC analysis showed that the bromobenzene conversion rate was 74%, the biphenyl selectivity was >99%, and the TOF was 1486 h. -1 .

[0077] After reacting with 0.6 mmol potassium tert-butoxide as a base for 30 min, the catalyst was centrifuged, washed with ethyl acetate, and dried before being added to the next reaction. Other conditions remained the same as in Example 2. After the catalyst was recycled three times, the bromobenzene conversion was 71%, the biphenyl selectivity was >99%, and the TOF was 1426 h. -1 .

[0078] As can be seen from the above results, the intercalated hydrotalcite nano-palladium-copper layer column catalyst of the present invention has high catalytic activity not only for the more reactive iodobenzene substrate in the visible light catalytic Suzuki coupling reaction, but also for the less reactive bromobenzene and chlorobenzene substrates. Furthermore, the reaction can be carried out under more energy-efficient sunlight, and the catalyst can be easily recycled without significant reduction in catalytic activity.

[0079] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A nano-palladium-copper layered column catalyst with intercalated hydrotalcite structure, expressed as A@MxAl-B@L, wherein: A and B are either Pd or Cu elements. A and B are different elements. When A or B is Pd, the mass percentage of Pd is 0.2% to 2.0%. When A or B is Cu, the mass percentage of Cu is 0.5% to 5.0%. A@M χ Al represents A nanoparticles anchored to M in a hydrotalcite-like structure. χ Al layer; M corresponds to one or two of the metallic elements Mg, Co, Ni, or Zn, and χ represents the divalent metal M and Al. 3+ The molar ratio, χ = 1.5-3.9; B@L represents the intercalation of a complex of B nanoparticles and ligand L between layers of hydrotalcite-like material. L is one of citric acid, tartaric acid, ethylenediaminetetraacetic acid, propylenediaminetetraacetic acid, aspartic acid, and 2-aminoterephthalic acid; This intercalated hydrotalcite-like nano-palladium-copper layered column catalyst has a nano-palladium or nano-copper intercalated hydrotalcite structure, and the interlayer spacing of the intercalated hydrotalcite-like structure is 1-2 nm.

2. A method for preparing the intercalated hydrotalcite nanoparticle palladium-copper layered column catalyst as described in claim 1, comprising the following steps: (1) Dissolve metal nitrates of A, M and Al in water according to the molar ratio to obtain a mixed salt solution; dissolve B and L in water according to the molar ratio to obtain a complex solution; dissolve NaOH in deionized water according to the molar ratio to obtain an alkaline solution; add the mixed salt solution and alkaline solution dropwise to the complex solution under the conditions of water bath and stirring at 30-70℃, keep the pH of the slurry at 8-11, stir and react for 1-48h, filter, wash until the filtrate is neutral, and dry the filter cake at 80-120℃ to obtain the intercalated hydrotalcite precursor; (2) The intercalated hydrotalcite precursor was dispersed in an aqueous solution, and NaBH4 aqueous solution was added dropwise under stirring. After the reduction reaction was carried out for 0.5-5 hours, the mixture was filtered, the solid was thoroughly washed, and then vacuum dried at 40-80℃ to obtain the intercalated hydrotalcite nano-palladium-copper layer column catalyst.

3. The preparation method according to claim 2, wherein: The total metal concentration in the mixed salt solution described in step (1) is 0.3~1.5 mol / L, the concentration of the complex solution is 0.1~0.5 mol / L, and the concentration of the NaOH solution is 0.5~2.0 mol / L.

4. The preparation method according to claim 2, wherein: In step (1), the molar ratio of A to M is 0.005~0.2, the molar ratio of B to L is 0.01~0.3, and the molar ratio of A to B is 0.02~2.

0.

5. The preparation method according to claim 2, wherein: The mass-volume concentration of the intercalated hydrotalcite precursor in step (2) in the aqueous solution is 10~50 g / L, and the concentration of the NaBH4 aqueous solution is 0.1~0.5 mol / L.

6. The preparation method according to claim 2, wherein: The molar ratio of NaBH4 to (A+B) in step (2) is 2~20.

7. A nano-palladium-copper layered column catalyst of intercalated hydrotalcite prepared by any of the preparation methods described in claims 2-6.

8. The application of a nano-palladium-copper layered column catalyst of intercalated hydrotalcite as described in claim 1 or 7 in visible light-catalyzed Suzuki coupling reaction.

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