CN111054424A

CN111054424A - Palladium-containing single-atom monolithic catalyst and preparation method and application thereof

Info

Publication number: CN111054424A
Application number: CN202010027615.9A
Authority: CN
Inventors: 李亚栋; 张泽栋; 王定胜; 冀淑方
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2020-01-10
Filing date: 2020-01-10
Publication date: 2020-04-24
Anticipated expiration: 2040-01-10
Also published as: CN111054424B

Abstract

The invention provides a palladium-containing single-atom monolithic catalyst, a preparation method and application thereof, wherein a nitrogen-containing carbon sponge is used for loading catalytic active components, and then heat treatment is carried out at a certain temperature, so that the monolithic catalyst with a specific solid morphology is directly obtained. In addition, the invention also provides a method for obtaining an aromatic olefin compound by catalyzing selective hydrogenation of aromatic alkyne by using the monoatomic palladium-containing catalyst, and application of the monoatomic palladium-containing catalyst. The obtained catalyst has high activity and good selectivity for preparing olefin by acetylene hydrocarbon hydrogenation, and active components of the catalyst are directly compounded with a nitrogen-carbon carrier in the heat treatment process to form a composite integrated structure of the monatomic catalyst and the carrier, so that the stability of the monatomic catalyst is ensured.

Description

Palladium-containing single-atom monolithic catalyst and preparation method and application thereof

Technical Field

The invention relates to the field of catalysts, in particular to an integral monatomic catalyst which can be used for selective hydrogen addition of aromatic alkyne.

Background

In recent years, monatomic catalysts have become a hotspot of catalytic chemistry research, and homogeneous phase heterogenization is a unique property of the monatomic catalysts. However, most of the traditional monatomic catalyst carriers are powder, and the molding and processing procedures are complex; the integral catalyst is favorable for industrial catalysis due to the characteristics of good mass transfer efficiency, small amplification effect and easy separation by simple operation.

Styrene is a raw material for producing PS, ABS resin and styrene-butadiene rubber, and the industrial preparation of styrene mainly utilizes pyrolysis gasoline for recovery at present, but the physical properties of phenylacetylene are not much different from that of styrene, the traditional distillation method cannot realize effective separation, and the phenylacetylene needs to be selectively hydrogenated to prepare the styrene. However, the conventional hydrogenation catalyst has low efficiency, especially poor selectivity, and can continuously hydrogenate part of styrene or hydrogenate and reduce nitro groups on benzene rings into amino groups. In addition, selective hydrogenation of alkyne into olefin is an important deprotection means for organic synthesis, olefin is also an important reactant required in production, and particularly, a preparation process for selective hydrogenation reduction of aromatic alkyne into aromatic alkene is provided. Therefore, the development of a catalyst system for preparing aromatic alkyne by selective hydrogenation of aromatic alkyne with high efficiency and good selectivity is needed.

Documents in the prior art relating to selective catalytic hydrogenation of alkynes: CN105536851A discloses a method for preparing an acetylene selective hydrogenation catalyst, which comprises performing atomic layer deposition on a carrier of a metal oxide, performing Pd atomic deposition on the carrier after the metal oxide deposition by using a palladium-containing reactant to form Pd nanoparticles dispersed on the surface of a substrate, placing the Pd nanoparticles into a tubular furnace, and performing heating reduction by using a reducing gas to obtain the catalyst. The carrier is Al₂O₃、SiO₂Or a silicon-aluminum mixed mesoporous material. However, the catalyst obtained in the patent is not a monoatomic catalyst, and when the catalyst is used for preparing olefin by selectively hydrogenating alkyne, the conversion rate and the selectivity are both common. CN102886267A discloses a catalyst for selective hydrogenation of phenylacetylene, which uses Al₂O₃-SiO₂、Al₂O₃Or SiO₂As a carrier, Ni is used as an active component, and at least one metal of group IVB of the periodic table, at least one metal of group VIB of the periodic table and at least one alkali metal and/or alkaline earth metal are used as an auxiliary agent. But the main purpose is to remove a small amount of phenylacetylene from a phenylacetylene-containing styrene mixture by a selective hydrogenation method, the catalytic activity of the catalyst is still to be enhanced, and the preparation process is responsible and high in cost, so that the catalyst is not suitable for being used as a catalyst in industrial production. In the prior art, CN1317367A, CN109622000A and CN1317367A all disclose catalyst systems for selective hydrogenation of alkynes, but all have the defects of low catalytic activity and poor selectivity. Patent CN 102649663 a discloses a method for selective hydrogenation of phenylacetylene, which comprises a metal oxide and a carrier, wherein the carrier is alumina, and the catalyst can be used for the selective hydrogenation reaction of phenylacetylene in the presence of styrene, but the catalytic efficiency of the catalyst system is not high, and particularly the selectivity can not meet the requirement.

Joongjai et al (Applied Catalysis A: general.2006,314: 128-133) convert a certain amount of Pd (NO)₃)₂Supported on nano-sized TiO₂In hydrogen²⁺Reduction preparation of Pd/TiO₂The catalyst proves that the obtained catalyst can improve the yield of olefin prepared by selective hydrogenation of acetylene hydrocarbon to a certain extent, particularly the selective hydrogenation of acetylene hydrocarbon to ethylene. However, the method cannot effectively control the size of the catalyst and cannot obtain the monatomic catalyst.

A sponge carrier containing nitrogen carbon is a common carrier, and the prior art also has a document that melamine-formaldehyde resin is used as a carrier to load some catalysts.

CN 108067302A prepares a cross-linked copolymer of a melamine monomer and a diformaldehyde monomer as a carrier, and palladium nanoparticles are used as a catalyst with a catalytic active component loaded on the carrier, and are used for preparing alkynylamine by taking haloacetylene as a raw material. However, the catalyst obtained by the method is not suitable for the selective hydrogenation of alkyne to prepare olefin, in particular for the selective hydrogenation of aromatic alkyne to prepare aromatic alkene. CN 108067302A discloses a composite catalyst which uses melamine-xylene cross-linked copolymer as a carrier and loads divalent palladium ions. CN 107964213 a discloses a graphene-loaded nano-scale melamine foam for removing formaldehyde. CN 110124748A discloses a catalyst system of melamine formaldehyde foam loaded with nano manganese dioxide, which is used for catalyzing formaldehyde decomposition. However, in the prior art, only the porous structure of the melamine-formaldehyde resin is utilized, and a single-atom catalyst system is not prepared and is not used for selective hydrogenation of alkyne.

In conclusion, a catalyst system which is efficient, has good selectivity and is suitable for industrial selective hydrogenation of alkynes, especially aromatic alkynes, is still lacking at present.

Disclosure of Invention

In order to overcome the defects of low selective hydrogenation efficiency and poor selectivity of aromatic alkyne in the prior art, the invention provides a palladium-containing single-atom monolithic catalyst. The invention unexpectedly discovers that the monolithic catalyst with a specific solid morphology is directly obtained by utilizing a nitrogen-containing carbon sponge to load a palladium active ingredient and then carrying out heat treatment at a certain temperature. The obtained catalyst has high activity and good selectivity for preparing olefin by acetylene hydrocarbon hydrogenation, and active components of the catalyst are directly compounded with a nitrogen-carbon carrier in the heat treatment process to form a composite integrated structure of the monatomic catalyst and the carrier, so that the stability of the monatomic catalyst is ensured, and the monatomic catalyst can be conveniently recycled.

The first object of the present invention is to provide a palladium-containing monatomic bulk catalyst in which a palladium active ingredient is supported as a monatomic form on the skeleton of a porous nitrogen-carbon sponge, capable of maintaining the overall shape of the nitrogen-carbon sponge, which is prepared by immersing a nitrogen-carbon sponge in a solution of a palladium-based complex and then subjecting the immersed sponge to a heat treatment at 600-.

In the preferable technical scheme of the invention, the palladium-containing monatomic monolithic catalyst is prepared by soaking a nitrogen-carbon sponge in a solution of a palladium complex and then performing heat treatment at the temperature of 650-800 ℃.

The nitrogen-containing carbon sponge is preferably melamine-formaldehyde sponge. The melamine-formaldehyde sponge provided by the invention is a three-dimensional carbon nitrogen carrier with good structural strength and high specific surface area. The invention utilizes the surface N (sp) of the melamine-formaldehyde sponge²) The functional group coordinates and adsorbs the palladium catalyst, and during the high-temperature calcination process, the formed nitrogen-doped carbon nano foam generates a large number of unsaturated nitrogen sites, so that palladium atoms are stabilized at defect sites, and the integral single-atom palladium catalyst is synthesized in one step.

The palladium complex is an organic palladium complex compound, preferably an organic palladium complex compound coordinated with a carbonyl group, more preferably a combination of one or more of palladium acetylacetonate, (3-allyl) (hexafluoroacetylacetonato) palladium, (3-allyl) (acetylacetonato) palladium, (3-allyl) (cyclopentadienyl) palladium, and dimethylbis (triethylphosphine) palladium.

The solution of the palladium complex is an alcoholic solution of the palladium complex, and the concentration is 60-70 mg/L; the alcohol is not particularly limited, such as methanol, ethanol, propanol, and the like.

The loading capacity of the metal palladium in the palladium-containing single-atom monolithic catalyst is 0.01-0.05 wt%.

The X-ray absorption spectrum of the palladium-containing monatomic monolith catalyst has no absorption peak in the range of 2A to 4A in the R space. Peaks in the range of 2A to 4A indicate the presence of Pd — Pd bonds, i.e. not a monoatomic morphology.

The microstructure of the palladium-containing single-atom monolithic catalyst is Pd-N₃Structure, i.e. one Pd atom coordinates with three nitrogen atoms to form Pd-N₃And (5) structure.

The second purpose of the invention is to provide a preparation method of the palladium-containing single-atom monolithic catalyst, which comprises the following steps:

l1) soaking the nitrogen-containing carbon sponge in the alcoholic solution of the palladium catalyst, and mixing uniformly;

l2) washing and drying the palladium-adsorbed nitrogen-containing carbon sponge obtained in the step L1;

l3) heat-treating the obtained dried sponge to obtain the monatomic palladium-containing catalyst.

In the alcoholic solution of the palladium catalyst in the step L1), the concentration is 60-70 mg/L; the uniform mixing refers to low-speed shaking and adsorption on a shaking table for 6-10 h;

washing with alcohol for 3-5 times in the step L2), and vacuum drying for 20-30min at 60-80 ℃;

step L3) the heat treatment is carried out at 600-900 ℃ for 0.5-2h under a nitrogen atmosphere.

The method takes nitrogen-containing carbon sponge as a carrier and carries out adsorption in an alcoholic solution of a palladium catalyst. The nitrogen-containing carbon sponge is subjected to simple physical washing to remove metal salts adsorbed by physical capillary action, only the amino on the surface of the metal palladium salt is left to be subjected to chemical adsorption, and the metal palladium salt is calcined in a high-temperature inert atmosphere after being dried in vacuum. The inventors have unexpectedly discovered that by controlling the calcination temperature at 600-900 deg.C, the formed polymer structure does not collapse during calcination, and the resulting nitrogen sites trap the high temperature reduced metal atoms, resulting in a stable, structurally strong, monolithic palladium catalyst. The obtained catalyst has high catalytic activity and good selectivity; and metal palladium atoms are stabilized in nitrogen defects in the high-temperature reduction process, the catalyst has a stable support structure and is stable, after the reaction is finished, the catalyst can be recycled only by simple alcohol washing, the activity and the selectivity of the catalyst cannot be reduced after five times of cyclic catalytic reaction, and the catalyst has good popularization prospect and economic value in the application of preparing aromatic alkene by selective hydrogenation of industrial aromatic alkyne.

The third purpose of the invention is to provide the application of the catalyst, which is used for catalyzing the selective hydrogenation of aromatic alkyne to prepare aromatic alkene compound. In particular to the selective hydrogenation of aromatic alkyne under the condition that the palladium-containing single-atom monolithic catalyst and boron-ammonia complex coexist.

Preferably, the method specifically comprises the following steps:

1) adding the palladium-containing single-atom monolithic catalyst, aromatic alkyne and boron-ammonia complex into a reaction vessel according to a certain proportion, and keeping stirring;

2) carrying out catalytic oxidation reaction at 40-70 deg.C for 3-24 hr, preferably at 45-60 deg.C for 8-15 hr;

3) after the reaction is finished, cooling the reaction container to room temperature, and separating the product by a silica gel column or a distillation mode to obtain the corresponding substance of the aromatic olefin.

The aromatic alkyne is an aromatic compound having an alkynyl group, and is not particularly limited, and examples thereof include, but are not limited to, phenylacetylene, p-nitroacetylene, p-methylphenylacetylene, m-methylphenylacetylene, p-methoxyphenylacetylene, p-bromophenylacetylene, p-chlorophenylacetylene, and naphthylacetylene.

The amount of catalyst used is 0.005-0.01 wt.% of the aromatic alkyne, calculated as palladium. The active component palladium of the catalyst is uniformly dispersed on the melamine-formaldehyde sponge in a monoatomic state, so that the catalyst has high catalytic activity, and the selective hydrogenation reaction of the aromatic alkyne can be completed under the condition of lower palladium consumption.

The palladium-containing single-atom monolithic catalyst provided by the invention has good conversion rate and selectivity in the preparation of aromatic alkene by selective hydrogenation of aromatic alkyne. Particularly, when the reactant is p-nitroacetylene, the p-nitroacetylene can be selectively hydrogenated to prepare p-nitroacetylene, and the nitro group can not be reduced into amino under the hydrogenation condition.

In addition, the catalyst provided by the invention is dispersed on the nitrogen defect on the surface of the melamine-formaldehyde sponge in a monatomic form, and due to the specific three-dimensional network structure of the melamine-formaldehyde sponge, the palladium-containing monatomic catalyst is a morphology-controllable monolithic catalyst, the monolithic catalyst has a stable structure and good catalytic activity and selectivity, after the catalytic reaction is finished, the catalyst can be recycled by simply washing with alcohol, and in the circulation reaction within ten times, although the activity and the selectivity of the catalyst are slightly reduced, the performance of the catalyst is still satisfactory.

Compared with the prior art, the invention has the following advantages:

the invention can obtain the integral monatomic catalyst, the structure and the appearance can be randomly regulated and controlled, the preparation method is simple, the consumption of noble metal is small, the metal active sites are dispersed, and further, the catalytic activity is high and the selectivity is good. The catalyst is used for preparing aromatic olefin by selective hydrogenation of aromatic alkyne, not only has high yield, but also has good selectivity, and the selectivity of preparing aromatic olefin by selective hydrogenation of various aromatic alkyne is more than 97%.

The catalyst has good activity and selectivity in the traditional homogeneous catalysis of selective hydrogenation of acetylene functional groups, has good circulation stability, can be used in a large scale, can be recycled for many times by a simple cleaning and recycling process after reaction, still keeps satisfactory catalytic activity and specific selectivity of the recycled catalyst, does not obviously reduce the activity and the selectivity of the catalyst, and shows the advantages of industrial popularization of the catalyst.

The preparation method of the catalyst is simple, only a substrate needs to be added into a reaction container, soaked and calcined at a specific temperature, the operation method is simple, acid-base or toxic substances are not added as additives, strong corrosive solvents are not needed, the environmental pollution is little, the catalyst can be carried out in low pressure even in air, the acid-base resistance and pressure resistance of the reaction container are not required, and the production cost can be reduced, so that the catalyst has an industrial production prospect.

Drawings

FIG. 1 is an image of a high angle annular dark field scanning transmission electron microscope of a monatomic palladium-containing catalyst prepared and synthesized in preparation example 1.

FIG. 2 is an image of a monoatomic catalyst containing palladium prepared in preparation example 1 under a high-resolution scanning electron microscope.

FIG. 3 is an X-ray absorption spectrum (R space) of a monoatomic catalyst containing palladium prepared in preparation example 1.

FIG. 4 is a macroscopic view of the monatomic palladium-containing catalyst prepared in preparation example 1.

FIG. 5 is a photograph of a melamine-formaldehyde sponge soaked with a palladium solution in preparation example 1 before and after heat treatment.

FIG. 6 is a schematic diagram showing a simulated structure in which one palladium atom is bonded and coordinated to three monoatomic atoms in the monoatomic palladium monolith catalyst obtained in preparation example 1.

FIG. 7 is an image of a monoatomic catalyst containing palladium prepared in preparation example 2 under a high-resolution scanning electron microscope.

FIG. 8 is an image of a monoatomic catalyst containing palladium prepared in preparation example 3 under a high-resolution scanning electron microscope.

Fig. 9 is an image under a high-resolution scanning electron microscope of the catalyst after the reaction in example 1.

FIG. 10 is an image of the catalyst after reaction in example 1 under a high angle annular dark field scanning transmission electron microscope.

Fig. 11 is an electron micrograph of the palladium nanoparticles of comparative example 2, which have a particle diameter of about 5 nm.

Fig. 12 is a spherical aberration electron micrograph of the catalyst material obtained in comparative example 2.

FIG. 13 is an electron micrograph of a palladium-carbon nitrogen catalyst prepared in comparative example 3.

FIG. 14 is a dark field spherical aberration electron micrograph of the monoatomic palladium-carbon nitrogen catalyst prepared in comparative example 6.

Detailed Description

The monatomic palladium-containing catalyst of the present invention is further illustrated below with reference to the following examples, which are intended to be merely illustrative of specific embodiments and are not intended to limit the present invention.

The melamine-formaldehyde sponge used in the invention is purchased from Beijing cleaning plants.

The commercial Pd/C catalyst was purchased from alpha and was nano-palladium particles supported on activated carbon at a loading of 10 wt%.

The loading of palladium in the catalyst was tested by inductively coupled plasma emission spectroscopy.

Preparation example 1

A melamine-formaldehyde sponge of 2cm by 2.5cm was soaked in 30mL of a 67mg/L solution of palladium acetylacetonate in methanol. Shaking the shaking table at low speed for 6 h. The obtained palladium ion-adsorbing sponge is washed with methanol for three times and dried for 24 hours at 70 ℃ in vacuum. And carrying out heat treatment on the obtained dried palladium salt loaded sponge at 800 ℃ for 0.5h in a nitrogen atmosphere. Through inductively coupled plasma emission spectroscopy testing, the loading amount of palladium in the obtained catalyst is 0.023 wt%.

The obtained solid is taken out, the obtained black solid is the final monatomic palladium-containing catalyst, fig. 1 is an image of the obtained catalyst under a high-angle annular dark-field scanning transmission electron microscope, and a bright point in the image is the synthesized monatomic Pd, which shows that the metal atoms of the Pd are in a monodisperse state on the carbon nitrogen carrier and no cluster or nano particle is formed. Fig. 2 is an image of the catalyst under a high-resolution scanning electron microscope, and it can be seen that the calcined sponge is flammable and maintains a complete microscopic tertiary pore structure, rather than being powdery, and has a certain structural strength. FIG. 3 is an X-ray absorption spectrum test of the monatomic palladium-containing catalyst prepared in example 1, and the absorption edge energy of Pd element K characterized by the synchrotron radiation X-ray fine structure of FIG. 3 is obtained by Fourier transform, and it can be seen that there is no absorption peak in the region of 2A to 4A, and the metal-metal bond is generally in the length of the second shell (2-4A), so if there is no peak in the second shell, it is indicated that there is no metal-to-metal bond, i.e., that there is no Pd-Pd bond in the catalyst obtained in example 1, and the catalyst is a monatomic catalyst. Through calculation of a fitted absorption spectrum, the coordination number of Pd and N atoms is 3, which indicates that Pd-N₃And (5) structure. The successful preparation of the palladium supported monatomic catalyst of preparation example 1 is illustrated by FIGS. 1 to 3.

Fig. 4 shows, from left to right, melamine-formaldehyde sponge soaked in palladium acetylacetonate-methanol solution, and palladium-loaded melamine-formaldehyde sponge subjected to heat treatment at 800 ℃. It is shown that after the heat treatment, palladium is uniformly loaded on the melamine-formaldehyde surface in a single atom, and the catalyst as a whole is obtained, which is convenient to take out, clean and recycle for reuse. FIG. 5 is a photograph of a melamine-formaldehyde sponge soaked with a palladium solution in preparation example 1 before and after heat treatment. It can be seen that the monatomic palladium catalyst prepared by the invention is a whole due to the supporting effect of the three-dimensional network structure of the melamine-formaldehyde sponge, the shape of the melamine-formaldehyde sponge is still kept after heat treatment, and the monatomic palladium catalyst is convenient to take out, clean and reuse after reaction.

Preparation example 2

The other steps and conditions are the same as those of the preparation example, except that the obtained dried palladium salt supported sponge is subjected to heat treatment for 0.5h at 650 ℃ in the nitrogen atmosphere to prepare the palladium supported monatomic catalyst, and fig. 7 is an image of the catalyst under a high-resolution scanning electron microscope, so that the shape of the melamine-formaldehyde sponge is still maintained after the heat treatment, and a better supporting structure and strength are maintained. The loading of palladium in the resulting catalyst was 0.021 wt%.

Preparation example 3

The other steps and conditions are the same as those of the preparation example, except that the obtained dried palladium salt supported sponge is subjected to heat treatment at 900 ℃ for 0.5h in a nitrogen atmosphere to prepare the palladium supported monatomic catalyst, and fig. 8 is an image of the catalyst under a high-resolution scanning electron microscope, so that the structure of the catalyst is broken, the diameter of a carbon-nitrogen frame is reduced, the frame nodes are damaged, and the structural strength is slightly poor compared with that of the carbon sponge in an optimal temperature region. The loading of palladium in the resulting catalyst was 0.025 wt%.

Comparative preparation example 1

Other steps and conditions are the same as those of the preparation example, except that the obtained dried palladium salt supported sponge is subjected to heat treatment at 500 ℃ for 0.5h in a nitrogen atmosphere to prepare the supported palladium catalyst, and the supported amount of palladium in the catalyst is 0.021 wt%.

Comparative preparation example 2

The other steps and conditions are the same as those of the preparation example, except that the obtained dried palladium salt supported sponge is subjected to heat treatment for 0.5h at 1000 ℃ in a nitrogen atmosphere, and the final product is powdery, so that a blocky monolithic catalyst cannot be obtained.

Examples example 1

The method for producing p-nitroacetylene by catalyzing selective hydrogenation reaction of p-nitroacetylene has the following reaction equation:

0.2mmol of p-nitroacetylene (29.4mg), 1.2mmol of boron-ammonia complex (37.0mg) and 10mg of monatomic palladium monolithic catalyst (the dosage of the catalyst is 0.078 wt% of the p-nitroacetylene in terms of palladium) are mixed and added into 4.9mL of ethanol and 0.1mL of deionized water, the reaction system is carried out in a 25mL pressure-resistant bottle, the reaction temperature is kept at 50 ℃, after 3 hours of reaction, GC analysis is used, the conversion rate of the p-nitroacetylene is 100%, the selectivity of a product for producing the p-nitroacetylene is 99.73%, namely the content of the product 1 is 99.7%.

The product is detected by GC-FID, and the residual catalyst is washed and dried by a simple ethanol solvent to continuously participate in the next reaction. Due to the stable structure of the melamine-formaldehyde sponge, the catalyst of the invention maintains the shape of a complete block after reaction, and fig. 9 is an image of the reacted catalyst under a high-resolution scanning electron microscope, which shows that the three-dimensional network structure of the melamine-formaldehyde sponge is not changed. Taking out the whole catalyst, washing the monoatomic palladium monolithic catalyst with ethanol for more than three times, and drying to obtain the monolithic catalyst again. Fig. 10 is an electron microscope image of the reacted catalyst, and it can be seen that palladium in the catalyst is still distributed on the three-dimensional network of the melamine-formaldehyde sponge in a monatomic state after the reaction, which illustrates that the monatomic palladium catalyst provided by the invention not only has good catalytic activity and selectivity, but also has excellent stability, can be recycled, and obviously has industrial advantages.

The alcohol-washed catalyst is continuously subjected to a reaction of catalytic selective hydrogenation of p-nitroacetylene, wherein the conversion rate of the p-nitroacetylene is 100%, and the selectivity of a product for producing the p-nitroacetylene is 97.4%.

The fifth catalytic cycle was repeated, and the data are shown in table 1 below:

TABLE 1

	1 st time	2 nd time	3 rd time	4 th time	5 th time
						Conversion (%)	100	100	100	100	98
Selectivity (%)	99.7	97.4	97.1	96.6	95.4

The monatomic catalyst obtained in preparation example 1 was also tested for catalytic reaction with other aromatic alkynes, and the aromatic alkynes were selectively hydrogenated under the same conditions using 0.078 wt.% of the aromatic alkynes as reactants, calculated as palladium, with the conversion and selectivity data set forth in table 2 below:

TABLE 2

Example 2

Otherwise as in example 1, the monatomic catalyst obtained in preparation example 2 was used to selectively hydrogenate the various aromatic alkynes described above, wherein the amount of catalyst used was 0.078% by weight, calculated as palladium, of the reactant aromatic alkynes, and the conversion and selectivity data are shown in Table 3 below

TABLE 3

Reactants	Product of	Conversion (%)	Selectivity (%)
				P-nitrophenylacetylene	p-Nitrophenyl ethylene	100	99.3
Phenylacetylene	Styrene (meth) acrylic acid ester	100	99.7
				M-methyl phenylacetylene	M-methylstyrene	100	96.8
P-methyl phenylacetylene	Para-methylstyrene		100					97.5
				P-methoxyphenylacetylene	P-methoxystyrene	100	96.0
Para-bromophenylacetylene	Para-bromostyrene	100	97.2
				P-chlorophenylacetylene	P-chlorostyrene	100	99.3
Naphthalene acetylene	Naphthalene ethylene	100	97.4
				2-ethynylpyridines	2-vinylpyridines	100	99.5

Example 3

The monatomic catalyst obtained in preparation example 3 was used to selectively hydrogenate the various aromatic alkynes described above, wherein the amount of catalyst used was 0.078 wt% of the reactant aromatic alkynes, calculated as palladium, and the conversion and selectivity data are given in table 4 below:

TABLE 4

Reactants	Product of	Conversion (%)	Selectivity (%)
				P-nitrophenylacetylene	p-Nitrophenyl ethylene	73	94.5
Phenylacetylene	Styrene (meth) acrylic acid ester	67	94.0
				M-methyl phenylacetylene	M-methylstyrene	63	93.3
P-methyl phenylacetylene	Para-methylstyrene	62	94.2
				P-methoxyphenylacetylene	P-methoxystyrene	65	91.6
Para-bromophenylacetylene	Para-bromostyrene	71	92.5
				P-chlorophenylacetylene	P-chlorostyrene	73	92.7
Naphthalene acetylene	Naphthalene ethylene	66	93.2
				2-ethynylpyridines	2-vinylpyridines	76	93.4

Comparative example 1

The other steps are the same as example 1, except that different catalysts are used, the dosage of the catalyst is about 0.078 wt% of the aromatic alkyne serving as a reactant calculated by palladium, namely when the same Pd feeding content and the same reaction conditions are kept and the catalyst is palladium acetylacetonate, the products obtained by catalysis are all p-amino-phenylethane and have no hydrogenation selectivity.

The commercial 10% Pd/C catalyst product is 75% p-amino styrene and 25% p-amino styrene, and the nitro group cannot be retained.

Pure carbon nitrogen sponge (without palladium metal) has no catalytic reaction product, i.e. no catalytic activity.

Comparative example 2

Preparing palladium nanoparticles: 50mg of polyvinylpyrrolidone and 17mg of potassium iodide were reacted in 5ml of formamide in an oil bath at 120 ℃ and 29.5mg of sodium chloropalladate powder was added and dissolved in the system with stirring and the temperature of 120 ℃ was maintained for 10 minutes. The prepared product was washed with methanol and dispersed into a 67mg/L palladium nanoparticle-methanol dispersion, and an electron micrograph of the palladium nanoparticles was shown in FIG. 11, which had a particle size of about 5 nm.

The other steps were the same as in example 1 except that the palladium acetylacetonate palladium-methanol solution was replaced with the palladium nanoparticle-methanol dispersion prepared above, and high-temperature calcination was also carried out at 800 ℃ for 30 minutes after adsorption of the palladium nanoparticle-methanol dispersion (0.05mg/ml) using melamine-formaldehyde sponge. The obtained catalyst material is shown in a spherical aberration electron microscope image as shown in fig. 12, the size of the palladium nano-particles is about 5nm, and a large amount of palladium nano-particles with the size of about 5nm are formed at the edge of the material and cannot be dispersed on the carrier in a single atom form. Through inductively coupled plasma emission spectroscopy testing, the loading amount of palladium in the obtained catalyst is 0.013 wt%.

In the catalytic test, 0.2mmol of p-nitroacetylene (29.4mg), 1.2mmol of boron-ammonia complex (37.0mg) and 17.6mg of palladium nanoparticle-carbon-nitrogen sponge monolithic catalyst (the dosage of the catalyst is 0.078 wt% of the p-nitroacetylene in terms of palladium) are mixed and added into 4.9mL of ethanol and 0.1mL of deionized water, the reaction system is carried out in a 25mL pressure-resistant bottle, and the reaction temperature is kept at 50 ℃. The conversion rate of the p-amino phenylethane obtained by the reaction is 100 percent, namely, the hydrogenation selectivity is not existed.

Comparative example 3

To demonstrate the effect of bulk morphology on the formation of the monatomic catalyst, 3g of melamine and 13ml of aqueous formaldehyde solution were sonicated in 14ml of deionized water. Then slowly dropwise adding 2.5ml of sodium hydroxide solution with the concentration of 0.1mol/L, and continuously heating to 60 ℃ for 2h to finally obtain the melamine-formaldehyde resin.

100mg of dried melamine-formaldehyde resin (approximately equal to the sponge mass in the above experiment) was soaked in 67mg/L palladium acetylacetonate in methanol (30 mL). Shaking the shaking table at low speed for 6 h. The obtained palladium ion-melamine-formaldehyde adsorption resin is washed with methanol for three times and dried for 24 hours in vacuum at 70 ℃. The resulting dry mixture resin was heat treated at 800 ℃ for 0.5h under nitrogen atmosphere. According to the inductively coupled plasma emission spectrum test, the loading amount of palladium in the obtained catalyst is about 0.020 wt%. FIG. 13 is a spherical aberration electron micrograph of the synthesized palladium-carbon nitrogen catalyst, which clearly shows that a large number of palladium nanoparticles are formed at the edge of the material and cannot remain monoatomic in the material.

Comparative example 4

The other procedure was the same as in example 1, except that the catalyst used was the catalyst obtained in comparative preparation example 1, and the palladium catalyst obtained in comparative preparation example 1 was subjected to selective hydrogenation catalytic activity and selective test in the same manner as in example 1, and the results are shown in Table 5.

TABLE 5

Example 4

The catalyst of the invention has the recycling performance in the reaction of preparing styrene by selectively hydrogenating phenylacetylene by using the catalyst obtained in the preparation example 1. The specific method is that 0.2mmol of phenylacetylene (20.5mg), 1.2mmol of boron ammonia complex (37.0mg) and 7mg of monoatomic palladium monolithic catalyst (the dosage of the catalyst is 0.078 wt% of phenylacetylene calculated by palladium) are mixed and added into 4.9mL of ethanol and 0.1mL of deionized water, the reaction system is carried out in a 25mL pressure-resistant bottle, the reaction temperature is kept at 50 ℃, and after 3 hours of reaction, GC analysis is used for testing the conversion rate and the selectivity of generated styrene. After the reaction is finished, the whole catalyst is taken out, washed with ethanol for three times, 10mL each time, vacuum-dried and then continuously used as the catalyst, and phenylacetylene is selectively hydrogenated to prepare styrene, the steps are repeated for 5 times, and the conversion rate and the selectivity of each time are tested, and the results are shown in the following table 6.

TABLE 6

	1 st time	2 nd time	3 rd time	4 th time	5 th time
						Conversion (%)	100	100	100	99	98
Selectivity (%)	99.1	98.3	97.6	97.3	96.5

As can be seen from the data in Table 5, the monatomic catalyst obtained in the invention has extremely high stability, is reused for selective hydrogenation reaction after being simply washed with alcohol, has no reduction in catalytic activity and selectivity, and has good prospects for industrial application.

Comparative example 5

The catalyst of the invention has the recycling performance in the reaction of preparing styrene by selectively hydrogenating phenylacetylene by using the catalyst obtained in the comparative preparation example 1. The specific method is that 0.2mmol of phenylacetylene (20.5mg), 1.2mmol of boron ammonia complex (37.0mg) and 7mg of monoatomic palladium monolithic catalyst (the dosage of the catalyst is 0.078 wt% of phenylacetylene calculated by palladium) are mixed and added into 4.9mL of ethanol and 0.1mL of deionized water, the reaction system is carried out in a 25mL pressure-resistant bottle, the reaction temperature is kept at 50 ℃, and after 3 hours of reaction, GC analysis is used for testing the conversion rate and the selectivity of generated styrene. After the reaction is finished, the whole catalyst is taken out, washed with ethanol for three times, 10mL each time, vacuum-dried and then continuously used as the catalyst, and phenylacetylene is selectively hydrogenated to prepare styrene, the steps are repeated for 5 times, and the conversion rate and the selectivity of each time are tested, and the results are shown in the following table 7.

TABLE 7

	1 st time	2 nd time	3 rd time	4 th time	5 th time
						Conversion (%)	33	34	31	28	23
Selectivity (%)	91.2	90.3	89.7	89.4	88.9

As can be seen from the data in table 6, the melamine-sponge impregnated with palladium salt has an effect on catalytic activity and selectivity when the heat treatment temperature is insufficient, and the activity is greatly affected to meet the actual demand.

Comparative example 6

The melamine-formaldehyde resin obtained in the comparative example 3 was directly subjected to high-temperature calcination with nitrogen to obtain a defective carbon-nitrogen material, and after adsorbing 67mg/L of palladium acetylacetonate, it was further subjected to nitrogen calcination at a low temperature of 150 ℃ for 1 hour. The obtained dark field spherical aberration electron micrograph of the monoatomic palladium-carbon nitrogen material (from melamine-formaldehyde resin) is shown in FIG. 14, pd monoatomic is enclosed, and the palladium content of the test material is 0.016%.

The catalytic reaction of the p-nitroacetylene selective hydrogenation reaction in example 1 to produce p-nitroacetylene was carried out, and the obtained product had a conversion rate of 38% for p-nitroacetylene and a composition of 89% for p-nitroacetylene and 11% for p-nitroalethane. The cycle performance test as in example 4 was performed, and the results are shown in table 7 below. It is shown that monatomic palladium favors the selectivity of the catalytic product, but the choice of support influences the catalytic activity of the catalyst.

TABLE 7

	1 st time	2 nd time	3 rd time	4 th time	5 th time
						Conversion (%)	38	33	32	29	17
Selectivity (%)	89.3	87.5	85.6	83.7	79.2

The data of the above examples and comparative examples show that the overall palladium-containing monatomic catalyst with controllable morphology can be obtained by simple impregnation and heat treatment, palladium is uniformly dispersed on melamine-formaldehyde sponge in the form of monatomic, and the palladium-containing monatomic catalyst is used for the reaction of preparing aromatic alkene by selective hydrogenation of aromatic alkyne, has high catalytic activity and good specific selectivity, particularly when p-nitroacetylene is selectively hydrogenated, the nitro group is not affected, and p-nitroacetylene can be efficiently prepared.

In addition, the palladium-containing monatomic catalyst provided by the invention has the advantages that the carrier with the three-dimensional network structure after the carrier melamine-formaldehyde sponge is sintered provides good stability and strength, so that the catalyst is the integral monatomic catalyst with controllable shape, the catalyst is convenient to take out and clean after the reaction is finished, the palladium atom in the catalyst still keeps the monatomic shape after the simple cleaning, the catalyst can be recycled repeatedly, the catalytic activity and the selectivity are not obviously reduced, the catalyst is the integral catalyst which can be recycled conveniently, and the convenience is provided for the selective hydrogenation reaction of the aromatic alkyne.

The above embodiments are merely illustrative of the present disclosure and do not represent a limitation of the present disclosure. Other variations of the specific structure of the invention will occur to those skilled in the art.

Claims

1. A palladium-containing monatomic monolith catalyst in which a palladium active ingredient is supported in the form of a monatomic atom on the framework of a porous nitrogen-carbon sponge, and the overall shape of the nitrogen-carbon sponge can be maintained; the palladium-carbon composite material is prepared by soaking a nitrogen-carbon sponge in a solution of a palladium complex and then performing heat treatment at 600-900 ℃.

2. The catalyst of claim 1, wherein the heat treatment temperature is 650-800 ℃.

3. The catalyst according to claim 1, wherein the palladium complex compound is an organopalladium complex compound, preferably a carbonyl-coordinated organopalladium complex compound.

4. The catalyst of claim 3, wherein the organopalladium complex is selected from the group consisting of palladium acetylacetonate, palladium (3-allyl) (hexafluoroacetylacetonate), palladium (3-allyl) (acetylacetonate), palladium (3-allyl) (cyclopentadienyl), and palladium (dimethylbis (triethylphosphine).

5. The catalyst of claim 1, wherein the solution of the palladium complex is an alcoholic solution of the palladium complex at a concentration of 60 to 70 mg/L.

6. The catalyst of claim 1, wherein the palladium-containing monatomic monolith catalyst has a metallic palladium loading of 0.01 to 0.05 wt%.

7. The catalyst of any one of claims 1-6, wherein the palladium-containing monatomic monolith catalyst has an X-ray absorption spectrum without an absorption peak in the R-space in the range of 2A to 4A.

8. The catalyst of any one of claims 1 to 6, wherein the palladium-containing monatomic monolith catalyst has a microstructure of Pd-N₃Structure, i.e. one Pd atom coordinates with three nitrogen atoms to form Pd-N₃And (5) structure.

9. A process for preparing a catalyst as claimed in any one of claims 1 to 8, comprising the steps of:

10. Use of the catalyst of any one of claims 1 to 7 for catalyzing the selective hydrogenation of aromatic alkynes to aromatic alkene compounds.