CN108465472B

CN108465472B - Hydrotalcite-loaded palladium-based alloy catalyst and preparation method thereof

Info

Publication number: CN108465472B
Application number: CN201810257336.4A
Authority: CN
Inventors: 张慧; 王亚娟; 宋颖
Original assignee: Beijing University of Chemical Technology
Current assignee: Beijing University of Chemical Technology
Priority date: 2018-03-26
Filing date: 2018-03-26
Publication date: 2020-09-04
Anticipated expiration: 2038-03-26
Also published as: CN108465472A

Abstract

A hydrotalcite loaded palladium-based alloy catalyst and a preparation method thereof, belonging to the technical field of catalysts. The expression of the catalyst is PdT_x/MAL-LDH, wherein PdT_xIs a palladium-based bimetallic alloy nano particle, T represents cheap transition metal Co, Ni, Fe or Cu, x represents the molar ratio of the transition metal T to Pd and is 0.1-2.2, the mass percentage content of Pd is 0.01-1.0 wt%, MAL-LDH is hydrotalcite, M is Mg²⁺、Ni²⁺、Co²⁺And Cu²⁺Any one or two of the divalent metal ions. The catalyst is obtained by immobilizing palladium-based alloy nano particles prepared by a polyol reduction method on a multi-level structure hydrotalcite carrier, and PdT with the size of about 1.48 nm-2.22 nm_xThe alloy nano particles are highly dispersed on the desert rose-shaped hydrotalcite. The high-dispersion small-size palladium-based alloy nano catalyst has excellent Heck reaction activity, wide substrate applicability, stable catalyst structure and simple preparation process.

Description

Hydrotalcite-loaded palladium-based alloy catalyst and preparation method thereof

Technical Field

The invention belongs to the technical field of catalysts, and particularly relates to a hydrotalcite-loaded palladium-based alloy catalyst and a preparation method thereof.

Background

The Heck coupling reaction of palladium-catalyzed halogenated aromatic hydrocarbon and olefin has become one of the important organic synthesis methods for synthesizing carbon-carbon bonds, and is widely applied to the industrial synthesis fields of natural products, luminescent materials, medicines and fine chemicals. However, homogeneous Pd-based catalysts, e.g. Pd (PPh)₃)₄And PdCl₂(PPh₃)₂The problems of difficult separation and recovery, easy inactivation, high price, environmental pollution and the like exist in Pd-carbene complex compounds, cyclic Pd compounds and the like, and the wide application of the compounds in the industry is greatly limited. Therefore, the preparation of heterogeneous palladium catalysts with easy recovery by loading Pd nanoparticles on various carriers such as polymers, carbon-based and silica-based materials, metal oxides and hydrotalcite is a preferred solution to the above problems (liuhongfei, jia shibo, jishenfu catalytic bulletin, 2012, 757-.

Research shows that the addition of the second metal to the bimetallic palladium-based alloy catalyst can adjust and change the electronic and geometric structure of the metallic palladium, thereby improving the activity of the catalyst, compared with the single metallic palladium catalyst. In 2015, the subject group supported gold-palladium alloy nanoparticles on a hydrotalcite-coated ferroferric oxide carrier to prepare a high-dispersion magnetic supported gold-palladium alloy catalyst, which was applied to Heck coupling reaction of iodobenzene and styrene in a mixed solution of N, N-dimethylformamide and water, and subjected to K coupling reaction₂CO₃The reaction is carried out at 120 ℃ for 3h under the condition of adding alkali, and the conversion rate of iodobenzene is 100 percent (Chinese invention patent No. ZL 201510145564.9). More importantly, bimetallic palladium-based alloy catalysts formed from palladium and inexpensive transition metals have received much attention because the incorporation of non-noble metals (e.g., cobalt, nickel, iron, and copper) reduces the amount of noble metal palladium and thus the cost. Singh et al are K₂PdCl₄And NiCl₂·6H₂O is used as a metal source, PVP is used as a protective agent, and NaBH is adopted₄Reduction method for preparing the catalyst with high Ni/Pd atomic ratio (9)9:1 and 95:5) bimetallic Ni-Pd alloy nanoparticles with average size of about 10nm applied in Suzuki-Miyaura reaction of 4-iodoanisole with 2-methylphenylboronic acid in water-ethanol solution with K₂CO₃TOF of 5h reaction at room temperature for additional base was about 250 and 200h^-1The catalytic activity of the catalyst is obviously superior to that of single metal Ni (TOF of 5h is 0 h)^-1) And Pd catalyst (5h TOF of about 13 h)^-1) (R.K.Rai, K.Gupta, D.Tyagi, A.Mahata, S.Behrens, X.C.Yang, Q.Xu, B.Pathak, S.K.Singh.Catal.Sci.Technol.,2016,6, 5567-5579.). Shaabani et al uses a polypropylene imine branched graphene hybrid as a carrier and PdCl₂And CoCl₂·6H₂O is a metal source, and a co-complexation method and subsequent NaBH are adopted₄The PdCo alloy nanoparticle (2-3 nm) catalyst loaded with the polypropylene imine branched graphene is prepared by a reduction method, and is applied to a Sonogashira coupling reaction of iodobenzene and phenylacetylene under the solvent-free condition, and K is used₂CO₃The yield of diphenylacetylene is 99% in 1h of ultrasonic reaction at room temperature for adding alkali, the catalytic activity of the catalyst is obviously superior to that of a single metal Pd catalyst (the yield of 17h of diphenylacetylene is 99%) and that of a single metal Co catalyst (the yield of 30h of diphenylacetylene is 10%), and the strong synergistic effect between metal Pd and Co in the catalyst is attributed. It is noteworthy that the catalyst still achieves relatively high activity (1h, 70%) under the alkali-free condition, probably due to the fact that the polypropyleneimine-branched graphene hybrid provides an alkaline environment for the alkali-requiring reaction (a. shaabani, m.mahyari.j.mater.chem.a,2013,1, 9303-. However, the preparation of the polypropylene imine branched graphene hybrid is tedious and time-consuming, which greatly limits the practical application thereof. The typical inorganic layered hydrotalcite material is a preferred carrier due to the characteristics of adjustable laminate composition, intrinsic alkalinity, simple and convenient preparation and the like. And so far, no reports on hydrotalcite-supported palladium-inexpensive transition metal alloy (PdCo, PdNi, PdFe, and PdCu) catalysts have been reported.

Therefore, the invention aims to prepare palladium-based alloy (PdCo, PdNi, PdFe and PdCu) nanoparticles by adopting a polyol reduction method and load the palladium-based alloy nanoparticles on a multilevel structure hydrotalcite carrier so as to prepare a supported palladium-based alloy (PdCo, PdNi, PdFe and PdCu) catalyst. Wherein, the palladium-based alloy nano particles with the particle size of 1.48 nm-2.22 nm are highly dispersed on the hydrotalcite carrier. The catalyst shows excellent catalytic activity in Heck coupling reaction.

Disclosure of Invention

The invention aims to provide a hydrotalcite-loaded palladium-based alloy catalyst and a preparation method thereof, which solves the problem of adopting the traditional NaBH₄The problem that the palladium-cheap transition metal alloy nano particles prepared by a reduction method or an impregnation method have larger particle size. The palladium-based alloy nano particles of the catalyst are highly dispersed on a hydrotalcite carrier and have the characteristics of small particle size and narrow particle size distribution. The catalyst shows excellent catalytic activity in Heck reaction, and has the advantages of wide substrate applicability, stable catalyst structure and simple preparation process.

The catalyst is prepared by loading small-sized palladium-based alloy (PdCo, PdNi, PdFe and PdCu) nano particles prepared by a polyol reduction method on a multi-level structure hydrotalcite carrier to obtain a high-dispersion small-sized supported palladium-based alloy catalyst. The expression of the catalyst is PdT_x/MAL-LDH, wherein PdT_xIs palladium-based bimetallic alloy nano-particles, T represents cheap transition metal Co, Ni, Fe or Cu, x represents the molar ratio of the transition metal T to Pd and is 0.1-2.2, the mass percentage content of Pd is 0.01-1.0 wt%, and the particle size is about 1.48-2.22 nm; MAL-LDH as hydrotalcite carrier, M as Mg²⁺、Ni²⁺、Co² ⁺And Cu²⁺One or two of divalent metal ions, the hydrotalcite carrier presents a desert rose-shaped multi-stage structure and is formed by self-assembling nanosheets 100-240 nm in size and 10.0-20.0 nm in thickness.

The hydrotalcite-loaded palladium-based alloy catalyst shows excellent catalytic performance in Heck coupling reaction of aryl iodide and olefin, and the reaction conditions are as follows: 1mmol of iodo aromatic hydrocarbon, 1.5mmol of olefin, a certain amount of catalyst active species Pd accounting for 0.30mol percent of the substrate iodo aromatic hydrocarbon, 3mmol of potassium carbonate, a solvent of a mixed solution of 12mL of N, N-dimethylformamide and 4mL of water, the conversion rate of the iodo aromatic hydrocarbon reaches 99.1-100% after reaction for 1h at 120 ℃, and the yield of a target product, namely the trans-styrene derivative reaches 97.4-99.4%.

The process steps of the invention are as follows:

(1) preparation of hydrotalcite support

Weighing 0.009-0.015 mol of M nitrate and 0.003-0.005 mol of aluminum nitrate nonahydrate, and dissolving in 100mL of deionized water to prepare a mixed salt solution; weighing 0.02-0.04 mol of NaOH and 0.006-0.012 mol of Na₂CO₃Dissolving in 100mL of deionized water to prepare a mixed alkali solution; adding 100mL of deionized water into a 500mL four-neck flask, slowly dropwise adding the mixed alkali solution until the pH value is 10 +/-0.1, stabilizing for 5min, simultaneously dropwise adding the mixed salt solution and the mixed alkali solution until the pH value is kept at 10 +/-0.1, crystallizing the obtained slurry in a 65 ℃ water bath for 4h, cooling to room temperature, centrifugally washing by using deionized water until the pH value of the supernatant is about 7, drying the obtained precipitate at 60 ℃ for 24h to obtain a hydrotalcite carrier MAL-LDH, wherein M is Mg²⁺、Ni²⁺、Co²⁺And Cu²⁺Any one or two of divalent metal ions;

(2)PdT_xpreparation of PVP nanoparticles

Weighing 5.64mmol of PdCl₂And 11.3mmol KCl are dissolved in deionized water to prepare 100mL potassium tetrachloropalladate solution with the molar concentration of 0.056 mol/L; weighing 5.00mmol of T chloride, and dissolving in deionized water to prepare 100mL of T chloride solution with the molar concentration of 0.050 mol/L; dissolving 0.82 g-2.46 g of polyvinylpyrrolidone (PVP) in 150mL of deionized water, adding 2.5mL of the potassium tetrachloropalladate solution and 0.85-8.5 mL of T chloride solution, adding 50mL of ethylene glycol, dropwise adding 1mol/L of NaOH solution to make the pH of the system be 12-13, refluxing for 2h in an oil bath at 140 ℃, and naturally cooling to room temperature to obtain dark brown sol, namely PdT_x-PVP nanoparticle sol, T being any one of Co, Ni, Fe and Cu elements;

(3) hydrotalcite-loaded palladium-based alloy catalyst PdT_xPreparation of/MAL-LDH

Taking the PdT_x100mL of PVP nano particle sol, adding 0.5 g-7.5 g of MAL-LDH carrier, mechanically stirring for 2h at room temperature, alternately washing twice with acetone and deionized water, centrifugally separating, and drying in vacuum at 60 ℃ for 24h to obtain the catalystPdT agents_x/MAl-LDH。

The nitrate of M used in the step (1) is Mg (NO)₃)₂·6H₂O、Ni(NO₃)₂·6H₂O、Co(NO₃)₂·6H₂O and Cu (NO)₃)₂·3H₂Either or both of O.

The chloride salt of T used in the step (2) is CoCl₂·6H₂O、NiCl₂·6H₂O、FeCl₃·6H₂O and CuCl₂·2H₂Any one of O.

The invention has the advantages that:

(1) provides a novel hydrotalcite-loaded palladium-based alloy catalyst with high dispersion and small size and a preparation method thereof. In particular to a method for preparing a palladium-based alloy catalyst PdT by loading small-sized palladium-based bimetallic alloy nano particles prepared from cheap and mild reducing agent ethylene glycol and stabilizer polyvinylpyrrolidone on desert rose pattern multi-level structure hydrotalcite_x/MAL-LDH. The active component palladium-based alloy nano particles have narrow particle size distribution (0.70-4.50 nm), the average particle size (1.48-2.22 nm) is obviously lower than that of most Pd-cheap transition metal alloy particles reported in literature, and the preparation process of the catalyst is simple and convenient.

(2) The prepared catalyst comprises an intrinsic basic hydrotalcite carrier and small-sized cheap transition metal doped palladium-based alloy nano particles. Palladium-based alloy catalyst PdT loaded on hydrotalcite_xIn the/MAL-LDH, a cheap transition metal Co (or Ni, Fe, Cu) is adopted to modify a noble metal Pd catalytic active component, so that the catalytic activity of a Pd center is improved, the using amount of the noble metal Pd active component is reduced, and the cost of a Heck reaction catalyst can be greatly reduced.

(3) The prepared catalyst has stable structure, the catalyst is separated by a centrifugal method after Heck reaction of iodobenzene and styrene is finished, the cycle is 12 times, and the iodobenzene conversion rate is only reduced from 100% to 94.7%. The circulation stability of the catalyst improves the service efficiency of the catalyst for Heck liquid phase catalytic reaction and reduces the separation cost of the liquid phase catalytic reaction. The catalyst shows excellent activity in Heck reaction of various iodo-aromatic hydrocarbons and olefins, and has important industrial application value.

Drawings

FIG. 1 is a scanning electron micrograph of MgAl-LDH supports of the sample of example 1.

FIG. 2 is PdCo of the sample in example 1_0.28-X-ray diffraction pattern of PVP.

FIG. 3 is PdCo of the sample of example 1_0.28High-resolution transmission electron microscope picture of/MgAl-LDH.

FIG. 4 is PdCo of the sample of example 1_0.28Particle size distribution of/MgAl-LDH.

FIG. 5 shows PdNi of the sample of example 2_0.10-X-ray diffraction pattern of PVP.

FIG. 6 is PdCu of example 4_2.2-X-ray diffraction pattern of PVP.

FIG. 7 shows PdCu of example 4_2.2High resolution transmission electron microscopy images of/CoAl-LDH.

FIG. 8 shows PdCu of example 4_2.2Particle size distribution of/CoAl-LDH.

Detailed Description

The invention will be further described with reference to specific examples, but the invention is not limited thereto.

Example 1

(1) Preparation of MgAl-LDH Carrier

Weighing 0.009mol Mg (NO)₃)₂·6H₂O and 0.003mol Al (NO)₃)₃·9H₂Dissolving O in 100mL of deionized water to prepare a mixed salt solution; weighing 0.02mol of NaOH and 0.006mol of Na₂CO₃Dissolving in 100mL of deionized water to prepare a mixed alkali solution; adding 100mL of deionized water into a 500mL four-neck flask, slowly dropwise adding the mixed alkali solution until the pH value is 10 +/-0.1, stabilizing for 5min, simultaneously dropwise adding the mixed salt solution and the alkali solution to keep the pH value of 10 +/-0.1 all the time until the dropwise adding of the mixed salt solution is finished, crystallizing the obtained slurry in a 65 ℃ water bath for 4h, cooling to room temperature, centrifugally washing by using deionized water until the pH value of a supernatant is about 7, and drying the obtained precipitate at 60 ℃ for 24h to obtain white powder, which is recorded as MgAl-LDH. From SEM picture (see figure 1) of sampleThe MgAl-LDH carrier is in a desert rose-shaped multi-level structure and is formed by self-assembling nanosheets with the sizes ranging from 190 nm to 200nm and the thicknesses ranging from 15.0nm to 20.0 nm.

(2)PdCo_0.28Preparation of PVP nanoparticle sols

Weighing 5.64mmol of PdCl₂And 11.3mmol KCl are dissolved in deionized water to prepare 100mL potassium tetrachloropalladate solution with the molar concentration of 0.056 mol/L; 5.00mmol of CoCl was weighed₂·6H₂Dissolving O in deionized water to prepare 100mL of cobalt chloride solution with the molar concentration of 0.050 mol/L; 1.23g of polyvinylpyrrolidone (PVP) was dissolved in 150mL of deionized water, to which was added 2.5mL of potassium tetrachloropalladate solution and 1.4mL of cobalt chloride solution, followed by 50mL of ethylene glycol. Dripping 1mol/L NaOH solution to ensure that the pH value of the system is 13, then refluxing for 2h in oil bath at 140 ℃, and naturally cooling to room temperature to obtain dark brown sol, namely PdCo_0.28-a PVP nanoparticle sol.

100mL of PdCo was taken_0.28Vacuum drying the-PVP nano particle sol at 90 ℃ for 24h to obtain black PdCo_0.28-PVP nanoparticles, XRD spectrum of this sample (see figure 2) at 41.04^oA sharp diffraction peak appears, and the peak is between the diffraction peaks of the characteristic crystal plane of the metal Pd (111) (JCPDS 46-1043, 40.12)^o) And characteristic crystal plane diffraction peaks of Co (111) metal (JCPDS15-0806, 44.22)^o) In between, indicating PdCo_0.28-PVP nano particles are alloy phase.

(3) Catalyst PdCo_0.28Preparation of/MgAl-LDH

Taking the PdCo prepared above_0.28100mL of PVP nano particle sol, 0.75g of MgAl-LDH carrier is added, and mechanical stirring is carried out for 2h at room temperature. Washing with acetone and deionized water by alternate centrifugation twice, vacuum drying the obtained precipitate at 60 deg.C for 12h to obtain light gray powder, as PdCo_0.28The molar ratio of Co to Pd in the catalyst obtained by ICP elemental analysis of the catalyst/MgAl-LDH is 0.28, and the mass content of Pd is 0.86 wt%. The high-resolution electron microscope image of the catalyst shows PdCo thereof_0.28The alloy nano-particles are highly dispersed on a multilevel structure hydrotalcite carrier (shown in figure 3), and the average particle diameter is 2.22 +/-0.42 nm (shown in figure 4).

In iodobenzene and styreneIn the Heck reaction of (3), the reaction conditions are as follows: 1mmol of iodobenzene, 1.5mmol of styrene, 37mg of PdCo as catalyst_0.28CoAl-LDH (active species Pd is 0.30mol percent of substrate iodobenzene), 3mmol of potassium carbonate, and a mixed solution of 12mL of N, N-dimethylformamide and 4mL of water as a solvent at 120 ℃; after 1 hour of reaction, the conversion rate of iodobenzene reaches 100%, and the yield of a target product, namely trans-stilbene reaches 98.0%; the catalyst is centrifugally recovered and reused, the conversion rate of iodobenzene in 12 times of reactions still reaches 95.6%, and the yield of the target product trans-stilbene reaches 94.7%. In the reaction of iodobenzene and ethyl acrylate under the same reaction conditions, the conversion rate of the iodobenzene reaches 99.8 percent after the reaction is carried out for 1 hour, and the yield of a target product, namely trans-ethyl cinnamate reaches 99.2 percent; in the reaction of 4-nitroiodobenzene and styrene under the same reaction conditions, the conversion rate of iodobenzene reaches 100% after 1.0h of reaction, and the yield of a target product, namely trans-4-nitrostilbene reaches 99.0%; in the reaction of 4-acetyl iodobenzene and styrene under the same reaction conditions, after 1.0h of reaction, the conversion rate of iodobenzene reaches 100%, and the yield of the target product trans-4-acetyl stilbene reaches 98.9%.

Example 2

(1) Preparation of CoAl-LDH vector

0.009mol Co (NO) was weighed out₃)₂·6H₂O and 0.003mol Al (NO)₃)₃·9H₂Dissolving O in 100mL of deionized water to prepare a mixed salt solution; weighing 0.02mol of NaOH and 0.006mol of Na₂CO₃Dissolving in 100mL of deionized water to prepare a mixed alkali solution; adding 100mL of deionized water into a 500mL four-neck flask, slowly dropwise adding the mixed alkali solution until the pH value is 10 +/-0.1, stabilizing for 5min, simultaneously dropwise adding the mixed salt solution and the alkali solution to keep the pH value at 10 +/-0.1 all the time until the dropwise adding of the mixed salt solution is finished, crystallizing the obtained suspension in a water bath at 65 ℃ for 4h, cooling to room temperature, centrifugally washing by using deionized water until the pH value of a supernatant is about 7, and drying the obtained precipitate at 60 ℃ for 24h to obtain pink powder which is marked as CoAl-LDH. The CoAl-LDH carrier is in a desert rose-shaped multi-level structure and is formed by self-assembling nanosheets with the sizes of 200-240 nm and the thicknesses of 13.0-15.0 nm.

(2)PdNi_0.10Preparation of PVP Sol

Weighing 5.64mmol of PdCl₂And 11.3mmol KCl are dissolved in deionized water to prepare 100mL potassium tetrachloropalladate solution with the molar concentration of 0.056 mol/L; weighing 5.00mmol NiCl₂·6H₂Dissolving O in deionized water to prepare 100mL of nickel chloride solution with the molar concentration of 0.050 mol/L; 0.82g of polyvinylpyrrolidone (PVP) was weighed out and dissolved in 150mL of deionized water, and 2.5mL of the above potassium tetrachloropalladate solution and 0.85mL of nickel chloride solution were added thereto, followed by 50mL of ethylene glycol. Dripping 1mol/L NaOH solution to make the pH value of the system about 12, then refluxing in oil bath at 140 ℃ for 2h, naturally cooling to room temperature to obtain dark brown sol, namely PdNi_0.10-a PVP nanoparticle sol.

100mL of PdNi was taken_0.10Vacuum drying PVP nanoparticle sol at 90 deg.C for 24h to obtain black solid, XRD spectrum (see figure 5) of the sample at 40.57^oA sharp diffraction peak appears, and the peak is between the diffraction peaks of the characteristic crystal plane of the metal Pd (111) (JCPDS 46-1043, 40.12)^o) And the characteristic crystal plane diffraction peak of metal Ni (111) (JCPDS04-0580, 44.51)^o) And the PdNi-PVP nano particles are shown as an alloy phase.

(3) Catalyst PdNi_0.10Preparation of/CoAl-LDH

Taking the PdNi prepared above_0.10100mL of PVP nanoparticle sol, 0.75g of CoAl-LDH carrier was added, and mechanical stirring was carried out at room temperature for 2 h. Washing twice with acetone and deionized water alternately, vacuum drying the precipitate at 60 deg.c overnight to obtain yellowish powder, named PdNi_0.10The molar ratio of Ni to Pd in the obtained catalyst is 0.10 and the mass content of Pd is 0.83 wt% through ICP elemental analysis.

In the Heck reaction of iodobenzene and styrene, the reaction conditions are as follows: 1mmol of iodobenzene, 1.5mmol of styrene, 38mg of PdNi catalyst_0.10CoAl-LDH (active species Pd is 0.30mol percent of substrate iodo aromatic hydrocarbon), 3mmol of potassium carbonate, and a mixed solution of 12mL of N, N-dimethylformamide and 4mL of water as a solvent at 120 ℃; the conversion rate of iodobenzene after 1 hour of reaction reaches 99.1 percent, and the yield of the target product trans-stilbene reaches 97.4 percent。

Example 3

(1)Cu₁Ni₂Preparation of Al-LDH Carrier

Weighing 0.003mol of Cu (NO)₃)₂·3H₂O、0.006mol Ni(NO₃)₂·6H₂O and 0.003mol Al (NO)₃)₃·9H₂Dissolving O in 100mL of deionized water to prepare a mixed salt solution; weighing 0.02mol of NaOH and 0.006mol of Na₂CO₃Dissolving in 100mL deionized water to prepare a mixed alkali solution. Adding 100mL of deionized water into a 500mL four-neck flask, slowly dropwise adding the mixed alkali solution until the pH value is 10 +/-0.1, stabilizing for 5min, simultaneously dropwise adding the mixed salt solution and the mixed alkali solution until the pH value is kept at 10 +/-0.1, crystallizing the obtained slurry in a 65 ℃ water bath for 4h, cooling to room temperature, centrifugally washing by using deionized water until the pH value of the supernatant is about 7, and drying the obtained precipitate at 60 ℃ for 24h to obtain the hydrotalcite carrier Cu₁Ni₂Al-LDH。Cu₁Ni₂The Al-LDH hydrotalcite carrier presents a desert rose-shaped multi-level structure and is formed by self-assembling nanosheets with the size of 110-150 nm and the thickness of 10.0-14.0 nm.

(2)PdFe_0.30Preparation of PVP

Weighing 5.64mmol of PdCl₂And 11.3mmol KCl are dissolved in deionized water to prepare 100mL potassium tetrachloropalladate solution with the molar concentration of 0.056 mol/L; weighing 5.00mmol FeCl₃·6H₂Dissolving O in deionized water to prepare 100mL of ferric chloride solution with the molar concentration of 0.050 mol/L; 0.82g of polyvinylpyrrolidone (PVP) was dissolved in 150mL of deionized water, and 2.5mL of the above potassium tetrachloropalladate solution and 1.4mL of ferric chloride solution were added thereto, followed by 50mL of ethylene glycol. Dropwise adding 1mol/L NaOH solution to make the pH value of the system about 12, then refluxing in oil bath at 140 ℃ for 2h, naturally cooling to room temperature to obtain dark brown sol, and marking as PdFe_0.30-a PVP nanoparticle sol.

(3) Catalyst PdFe_0.30/Cu₁Ni₂Preparation of Al-LDH

Taking the PdFe prepared above_0.30-PVP nanoparticle sol100mL, 0.75g Cu was added₁Ni₂The Al-LDH carrier is mechanically stirred for 2 hours at room temperature. Washing with acetone and deionized water alternately twice, centrifuging, vacuum drying at 60 deg.C for 24 hr to obtain light green powder, and recording as PdFe_0.30/Cu₁Ni₂And performing ICP elemental analysis on the Al-LDH to obtain the catalyst, wherein the molar ratio of Fe to Pd is 0.30, and the mass percentage of Pd is 1.0 wt%.

In the Heck reaction of iodobenzene and styrene, the reaction conditions are as follows: 1mmol iodobenzene, 1.5mmol olefin, 32mg catalyst PdFe_0.30/Cu₁Ni₂Al-LDH (active species Pd accounts for 0.30mol percent of the substrate iodobenzene), 3mmol of potassium carbonate, and a mixed solution of 12mL of N, N-dimethylformamide and 4mL of water as a solvent at 120 ℃; the conversion rate of iodobenzene after 1 hour of reaction reaches 99.4 percent, and the yield of the target product trans-stilbene reaches 97.6 percent.

Example 4

(1) Preparation of CoAl-LDH vector

(2)PdCu_2.2Preparation of PVP

Weighing 5.64mmol of PdCl₂And 11.3mmol KCl are dissolved in deionized water to prepare 100mL potassium tetrachloropalladate solution with the molar concentration of 0.056 mol/L; weighing 5.00mmolCuCl₂·2H₂Dissolving O in deionized water to prepare 100mL of copper chloride solution with the molar concentration of 0.050 mol/L; 2.45g of polyvinylpyrrolidone (PVP) was dissolved in 150mL of deionized water, and 2.5mL of the above potassium tetrachloropalladate solution and 5.6mL of copper chloride solution were added thereto, followed by addition of 50mL of ethylene glycol. Dripping 1mol/L NaOH solution to make the pH value of the system about 13, then refluxing in oil bath at 140 ℃ for 2h, naturally cooling to room temperature to obtain dark brown sol, namely PdCu_2.2-a PVP nanoparticle sol.

Taking 100mL of the PdCu_2.2Vacuum drying PVP nanoparticle sol at 90 deg.C for 24 hr to obtain black solid, XRD spectrum (see figure 6) of the sample at 42.30^oA sharp diffraction peak appears, and the peak is between the diffraction peaks of the characteristic crystal plane of the metal Pd (111) (JCPDS 46-1043, 40.12)^o) And a characteristic crystal plane diffraction peak of Cu (111) metal (JCPDS 04-0836, 43.30)^o) In between, indicating PdCu_2.2-PVP nano particles are alloy phase.

(3) Catalyst PdCu_2.2Preparation of/CoAl-LDH

Taking the PdCu prepared above_2.2100mL of PVP nanoparticle sol, 0.75g of CoAl-LDH carrier was added, and mechanical stirring was carried out at room temperature for 2 h. Washing with acetone and deionized water alternately twice, centrifuging, and drying at 60 deg.C overnight to obtain powder as PdCu_2.2The molar ratio of Cu to Pd in the obtained catalyst is 2.2 and the mass content of Pd is 0.96 wt% through ICP elemental analysis. Catalyst PdCu_2.2High-resolution electron microscope image of/CoAl-LDH shows PdCu thereof_2.2The alloy nano-particles are highly dispersed on a multilevel structure hydrotalcite carrier (shown in figure 7), and the average particle diameter is 1.48 +/-0.30 nm (shown in figure 8).

In the Heck reaction of iodobenzene and styrene, the reaction conditions are as follows: 1mmol of iodobenzene, 1.5mmol of styrene, 33mg of PdCu catalyst_2.2CoAl-LDH (active species Pd is 0.30mol percent of substrate iodobenzene), 3mmol of potassium carbonate, and a mixed solution of 12mL of N, N-dimethylformamide and 4mL of water as a solvent at 120 ℃; the conversion rate of iodobenzene after 1 hour of reaction reaches 100 percent, and the yield of the target product trans-stilbene reaches 99.4 percent.

Example 5

(1) Preparation of CoAl-LDH vector

0.015mol of Co (NO) was weighed out₃)₂·6H₂O and 0.005mol Al (NO)₃)₃·9H₂Dissolving O in 100mL of deionized water to prepare a mixed salt solution; 0.04mol of NaOH and 0.012mol of Na are weighed₂CO₃Dissolving in 100mL of deionized water to prepare a mixed alkali solution; adding 100mL of deionized water into a 500mL four-neck flask, slowly dropwise adding the mixed alkali solution until the pH value is 10 +/-0.1, stabilizing for 5min, simultaneously dropwise adding the mixed salt solution and the alkali solution to keep the pH value at 10 +/-0.1 all the time until the dropwise adding of the mixed salt solution is finished, crystallizing the obtained slurry in a 65 ℃ water bath for 4h, cooling to room temperature, centrifugally washing by using deionized water until the pH value of a supernatant is about 7, and drying the obtained precipitate at 60 ℃ for 24h to obtain pink powder which is marked as CoAl-LDH. The CoAl-LDH carrier is in a desert rose-shaped multi-level structure and is formed by self-assembling nanosheets with the sizes of 200-240 nm and the thicknesses of 13.0-15.0 nm.

(2)PdCo_0.28Preparation of PVP Sol

Weighing 5.64mmol of PdCl₂And 11.3mmol KCl are dissolved in deionized water to prepare 100mL potassium tetrachloropalladate solution with the molar concentration of 0.056 mol/L; 5.00mmol of CoCl was weighed₂·6H₂Dissolving O in deionized water to prepare 100mL of cobalt chloride solution with the molar concentration of 0.050 mol/L; 1.23g of polyvinylpyrrolidone (PVP) was dissolved in 150mL of deionized water, and 2.5mL of the above potassium tetrachloropalladate solution and 1.4mL of cobalt chloride solution were added thereto, followed by 50mL of ethylene glycol. Dripping 1mol/L NaOH solution to make the pH value of the system about 13, then refluxing in oil bath at 140 ℃ for 2h, naturally cooling to room temperature to obtain dark brown sol, namely PdCo_0.28-a PVP nanoparticle sol.

(3) Catalyst PdCo_0.28Preparation of/CoAl-LDH

Taking 100mL of the PdCo_0.28PVP nano particle sol, adding 7.5g CoAl-LDH carrier, and mechanically stirring for 2h at room temperature. Washing with acetone and deionized water by alternate centrifugation twice, vacuum drying the obtained precipitate at 60 deg.C for 24 hr to obtain yellowish powder, which is recorded as PdCo_0.28/CoAl-LDH. Obtained by ICP elemental analysisThe mass content of Pd in the obtained catalyst was 0.01 wt%.

In the Heck reaction of iodobenzene and styrene, the reaction conditions are as follows: 1mmol of iodobenzene, 1.5mmol of styrene, 3.1g of catalyst PdCo_0.28CoAl-LDH (active species Pd is 0.30mol percent of substrate iodobenzene), 3mmol of potassium carbonate, and a mixed solution of 12mL of N, N-dimethylformamide and 4mL of water as a solvent at 120 ℃; the conversion rate of iodobenzene after 1 hour of reaction reaches 100 percent, and the yield of the target product trans-stilbene reaches 97.9 percent.

Example 6

(1) Preparation of NiAl-LDH vector

0.009mol Ni (NO) was weighed₃)₂·6H₂O and 0.003mol Al (NO)₃)₃·9H₂Dissolving O in 100mL of deionized water, and mixing with a salt solution; weighing 0.02mol of NaOH and 0.006mol of Na₂CO₃Dissolving in 100mL of deionized water to prepare a mixed alkali solution; adding 100mL of deionized water into a 500mL four-neck flask, slowly dropwise adding the mixed alkali solution until the pH value is 10 +/-0.1, stabilizing for 5min, simultaneously dropwise adding the mixed salt solution and the alkali solution to keep the pH value of 10 +/-0.1 all the time until the dropwise adding of the mixed salt solution is finished, crystallizing the obtained slurry in a 65 ℃ water bath for 4h, cooling to room temperature, centrifugally washing by using deionized water until the pH value of a supernatant is about 7, and drying the obtained precipitate at 60 ℃ for 24h to obtain green powder, wherein the green powder is marked as NiAl-LDH. The NiAl-LDH hydrotalcite carrier presents a desert rose-shaped multi-level structure and is formed by self-assembling nano sheets with the size of 100-120 nm and the thickness of 10.0-13.0 nm

(2)PdCo_0.28Preparation of PVP Sol

Weighing 5.64mmol of PdCl₂And 11.3mmol KCl are dissolved in deionized water to prepare 100mL potassium tetrachloropalladate solution with the molar concentration of 0.056 mol/L; 5.00mmol of CoCl was weighed₂·6H₂Dissolving O in deionized water to prepare 100mL of cobalt chloride solution with the molar concentration of 0.050 mol/L; 1.23g of polyvinylpyrrolidone (PVP) was dissolved in 150mL of deionized water, and 2.5mL of the above potassium tetrachloropalladate solution and 1.4mL of cobalt chloride solution were added thereto, followed by 50mL of ethylene glycol. Adding 1mol/L NaOH solution dropwise to make the pH of the system about 13, and then performing oil treatment at 140 DEG CRefluxing in bath for 2h, naturally cooling to room temperature to obtain dark brown sol, namely PdCo_0.28-a PVP nanoparticle sol.

(3) Catalyst PdCo_0.28Preparation of NiAl-LDH

Taking 100mL of the PdCo_0.28-PVP nanoparticle sol, adding 0.75g NiAl-LDH carrier, and mechanically stirring for 2h at room temperature. Washing with acetone and deionized water alternately twice, centrifuging, vacuum drying at 60 deg.C for 24 hr to obtain powder sample, and recording as PdCo_0.28The molar ratio of Co to Pd in the obtained catalyst is 0.28 and the mass content of Pd is 0.64 wt% by ICP elemental analysis for NiAl-LDH.

In the Heck reaction of iodobenzene and styrene, the reaction conditions are as follows: 1mmol iodobenzene, 1.5mmol styrene, 50mg catalyst PdCo_0.28NiAl-LDH (active species Pd accounting for 0.30mol percent of the substrate iodobenzene), 3mmol of potassium carbonate, a mixed solution of 12mL of N, N-dimethylformamide and 4mL of water as a solvent, and the temperature of 120 ℃; the conversion rate of iodobenzene after 1 hour of reaction reaches 99.1 percent, and the yield of the target product trans-stilbene reaches 97.9 percent.

Claims

1. The hydrotalcite-loaded palladium-based alloy catalyst is characterized in that the expression is PdT_x/MAL-LDH, wherein PdT_xThe Pd-based bimetallic alloy nano-particles are prepared by the following steps of preparing Pd-based bimetallic alloy nano-particles, wherein T represents cheap transition metals Co, Ni, Fe or Cu, x represents the molar ratio of the transition metals T to Pd and is 0.1-2.2, the mass percentage content of Pd is 0.01-1.0 wt%, and the particle size is 1.48-2.22 nm; MAL-LDH as hydrotalcite carrier, M as Mg²⁺、Ni²⁺、Co²⁺And Cu²⁺One or two of divalent metal ions, wherein the hydrotalcite carrier has a desert rose-shaped multi-stage structure and is formed by self-assembling nanosheets 100-240 nm in size and 10.0-20.0 nm in thickness;

2. The preparation method of the hydrotalcite-supported palladium-based alloy catalyst according to claim 1, characterized by comprising the following steps:

(1) preparation of hydrotalcite support

Weighing 0.009-0.015 mol of nitrate and 0.003-0.005 mol of aluminum nitrate nonahydrate, dissolving in 100mL of deionized water, and preparing into a mixed salt solution; weighing 0.02-0.04 mol of NaOH and 0.006-0.012 mol of Na₂CO₃Dissolving in 100mL of deionized water to prepare a mixed alkali solution; adding 100mL of deionized water into a 500mL four-neck flask, slowly dropwise adding the mixed alkali solution until the pH value is 10 +/-0.1, stabilizing for 5min, simultaneously dropwise adding the mixed salt solution and the mixed alkali solution until the pH value is kept at 10 +/-0.1, crystallizing the obtained slurry in a 65 ℃ water bath for 4h, cooling to room temperature, centrifugally washing by using deionized water until the pH value of the supernatant is 7, drying the obtained precipitate at 60 ℃ for 24h to obtain a hydrotalcite carrier MAL-LDH, wherein M is Mg²⁺、Ni²⁺、Co²⁺And Cu²⁺Any one or two of divalent metal ions;

(2)PdT_xpreparation of PVP nanoparticle sols

Weighing 5.64mmol of PdCl₂And 11.3mmol KCl are dissolved in deionized water to prepare 100mL potassium tetrachloropalladate solution with the molar concentration of 0.056 mol/L; weighing 5.00mmol of T chloride, dissolving in deionized water, and preparing into 100mL of T chloride solution with a molar concentration of 0.050 mol/L; dissolving 0.82 g-2.46 g of polyvinylpyrrolidone PVP (polyvinylpyrrolidone) in 150mL of deionized water, adding 2.5mL of the potassium tetrachloropalladate solution and 0.85-8.5 mL of a chloride solution, adding 50mL of ethylene glycol, dropwise adding 1mol/L of NaOH solution to adjust the pH value of the system to 12-13, refluxing for 2 hours in an oil bath at 140 ℃, and naturally cooling to room temperature to obtain dark brown sol, namely PdT_x-PVP nanoparticle sol, T being any one of Co, Ni, Fe and Cu elements;

Taking 100mL of the PdT_xAdding 0.5g to 7.5g of MAl-LDH carrier into PVP nano particle sol, mechanically stirring for 2h at room temperature, alternately centrifuging and washing twice by using acetone and deionized water, and drying the obtained precipitate for 24h at 60 ℃ in vacuum to obtain a catalyst PdT_x/MAl-LDH；

The nitrate of M used in the step (1) is Mg (NO)₃)₂·6H₂O、Ni(NO₃)₂·6H₂O、Co(NO₃)₂·6H₂O and Cu (NO)₃)₂·3H₂Any one or two of O;

the chloride salt of T used in the step (2) is CoCl₂·6H₂O、NiCl₂·6H₂O、FeCl₃·6H₂O and CuCl₂·2H₂And O is any one of the above.