Transition metal / alkali metal bimetallic monatomic catalyst for catalyzing hydrochlorination reaction of acetylene as well as preparation method and application of transition metal / alkali metal bimetallic monatomic catalyst

Abstract

The invention relates to the technical field of transition metal catalysts, in particular to a transition metal / alkali metal bimetallic monatomic catalyst for catalyzing acetylene hydrochlorination reaction and a preparation method and application of the transition metal / alkali metal bimetallic monatomic catalyst. After dipping in an alkali metal nitrate solution, the alkali metal is firstly converted into a metal oxide through two-stage calcination, and then the metal oxide is converted into a super-strong alkali metal monatomic material containing a high defect site. And dipping the alkali metal monatomic catalyst in a transition metal salt solution to obtain the transition metal / alkali metal bimetallic monatomic catalyst. Transition metal monatomic serves as a main active center, alkali metal monatomic serves as a super alkali auxiliary, the microenvironment of active sites is greatly improved, the adsorption capacity of the transition metal sites to reactants is enhanced, meanwhile, carbon deposition side reaction can be inhibited, and synergistic catalysis between transition metal and alkali metal monatomic is achieved; the catalyst shows high catalytic activity and stability on acetylene hydrochlorination reaction.

Description

Technical Field

[0001] The invention relates to the technical field of transition metal catalysts, and in particular to a transition metal / alkali metal bimetallic single atom catalyst for catalyzing acetylene hydrochlorination reaction, and a preparation method and application thereof. Background Art

[0002] Polyvinyl chloride (PVC) is a polymer material produced by the polymerization of vinyl chloride monomer (VCM) and is widely used in industrial construction and other fields. The industrial production of VCM mainly adopts the calcium carbide acetylene process. In industry, carbon-supported mercuric chloride catalysts are used to catalyze the acetylene hydrochlorination reaction. The active component mercury is easily sublimated and lost into the environmental system above 200°C. Mercury, as a highly toxic metal, causes great damage to the human kidneys, liver and nervous system, namely "Minamata disease". Therefore, the research and development of efficient mercury-free catalysts is urgent, and finding catalysts with high catalytic activity, long service life and low cost is the key goal. In the acetylene hydrochlorination reaction, the precious metals gold, platinum and ruthenium have excellent catalytic activity and stability, and copper has the advantages of high catalytic activity and low price, so it has been widely studied.

[0003] Alkali metals can play a good promoting role in many reactions. Han You and others prepared a new type of solid superbase single-atom catalyst K1 / G through a tandem redox strategy. The strong alkalinity and highly dispersed alkaline sites of the K1 / G catalyst give it excellent catalytic performance in ester exchange reactions. Sun Linbing adopted the sublimation-migration-anchoring strategy to capture magnesium single atoms on defective graphene to prepare the Mg1 / G superbase catalyst. The magnesium single atom and the carbon atom are in a tetracoordinated form and form superalkalinity. The catalyst shows high activity in the ester exchange reaction of ethylene carbonate and methanol to synthesize dimethyl carbonate. Patent 202111406524.7 disperses ruthenium trichloride and alkali metal salts on activated carbon by an impregnation method to obtain an additive-modified catalyst, and then disperses the ionic liquid on the modified catalyst. The catalyst shows high acetylene hydrochlorination activity.

[0004] Single-atom catalysts have attracted extensive attention from researchers due to their high catalytic activity and high atomic utilization. Han You prepared a Ru-N4 coordinated single-atom catalyst through a step-by-step anchoring strategy. -1 The acetylene conversion rate was 95.4%. Xu Haomiao used Ru single atoms wrapped in metal organic frameworks to achieve rapid adsorption and activation of C2H2, so that C2H2 molecules can be quickly transferred to the Ru-N4 active site for activation.

[0005] Existing methods for preparing single-atom catalysts include wet chemical method, atomic layer deposition method, thermal decomposition method and template method. Although single-atom catalysts have high catalytic activity and high atomic utilization rate, the existing methods have problems such as difficulty in controlling the uniform dispersion of metals during the preparation process, easy agglomeration of metal atoms, high preparation cost and unsuitability for large-scale production. In addition, the prepared single-atom catalysts still have problems of carbon deposition and deactivation and insufficient stability during the acetylene hydrochlorination process. Summary of the invention

[0006] In view of the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a transition metal / alkali metal bimetallic single atom catalyst for catalyzing acetylene hydrochlorination reaction and its preparation method and application. The catalyst prepared by the present invention uses transition metal single atoms as the main active center and alkali metal single atoms as super base auxiliary agents, which greatly improves the microenvironment of the active site, enhances the adsorption capacity of the transition metal site for reactants, and can inhibit carbon deposition side reactions. The synergistic catalysis between the transition metal and alkali metal bimetallic single atoms shows high catalytic activity and stability for acetylene hydrochlorination reaction.

[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions: A method for preparing a transition metal / alkali metal bimetallic single atom catalyst for catalyzing acetylene hydrochlorination reaction comprises the following steps: The activated carbon is dispersed in an organic solution containing heteroatoms, dried and calcined in an inert gas to dope nitrogen, phosphorus or sulfur on the activated carbon to obtain an activated carbon carrier with abundant defect sites.

[0008] Alkali metal nitrate is dissolved in a mixed solvent of water and ethanol to obtain an alkali metal nitrate solution, and then the activated carbon carrier containing defect sites is impregnated with the alkali metal nitrate solution. After drying, two-stage calcination is performed. In the nitrate solution, the alkali metal is first converted into a metal oxide and then converted into an alkali metal single-atom catalyst containing high defect sites.

[0009] The alkali metal single atom catalyst is impregnated with a transition metal precursor solution and mixed, the product is collected by centrifugation, and the product is acid-etched to obtain a transition metal / alkali metal bimetallic single atom catalyst.

[0010] The transition metal / alkali metal bimetallic single atom catalyst for catalyzing acetylene hydrochlorination provided by the present invention is an activated carbon carrier rich in defect sites by calcining, containing activated carbon treated with heteroatom organic solution, and then using alkali metal nitrate solution to impregnate the activated carbon carrier containing defect sites, in the nitrate solution, the alkali metal is first converted into a metal oxide by two-stage calcination, and then converted into a super alkali metal single atom material containing high defect sites, and the transition metal single atom can be well anchored by the formation of defect sites. The transition metal salt solution is impregnated on the alkali metal single atom catalyst, and then etching is performed to further ensure that the transition metal is in a single atom state, and the desired transition metal / alkali metal bimetallic single atom catalyst is obtained. The catalyst prepared by the present invention uses transition metal single atoms as the main active center, and alkali metal single atoms as super base additives greatly improve the microenvironment of the active site, enhance the adsorption capacity of the transition metal site to the reactant, and can inhibit the carbon deposition side reaction, and the transition metal and alkali metal bimetallic single atoms are synergistically catalyzed, showing high catalytic activity and stability for acetylene hydrochlorination.

[0011] The reason why the present invention uses organic matter to impregnate activated carbon and calcines it in a tubular furnace is that N, P or S atoms are doped into the activated carbon through high-temperature calcination in an inert atmosphere, thereby expanding the surface defects of the carbon carrier and ensuring that transition metal single atoms and alkali metal single atoms are anchored more stably.

[0012] The purpose of using the two-stage temperature-increasing calcination method is to convert the alkali metal nitrate into alkali metal oxide at 300°C~600°C and into alkali metal single atoms at 700°C~1000°C, so that more abundant defect sites can be generated on the material surface during the calcination process.

[0013] The purpose of centrifugation is that when there is an excess of transition metal components in the solution, centrifugation can wash away the transition metal components that are not anchored by the activated carbon carrier.

[0014] The purpose of acid etching is to disperse and wash away larger clusters and nanoparticles by acid etching, leaving only single atoms with strong anchoring effects.

[0015] In a preferred embodiment of the present invention, the calcination temperature for preparing the activated carbon carrier containing defect sites is 400° C. to 800° C., and the calcination time is 1 h to 5 h.

[0016] In a preferred embodiment of the present invention, the two-stage calcination temperatures are 300° C. to 600° C. and 700° C. to 1000° C., respectively, and the calcination time is 2 h to 5 h.

[0017] In a preferred embodiment of the present invention, in the transition metal / alkali metal bimetallic single atom catalyst, the loading amount of the transition metal element is 1 wt.%~5 wt.%, and the loading amount of the alkali metal element is 0.01 wt.%~0.2 wt.%.

[0018] In a preferred embodiment of the present invention, the mass concentration of the alkali metal nitrate solution is 7.66×10 -4 g / mL~6.05×10 -3 g / mL, and the mass concentration of the transition metal precursor solution was 4.5×10 -3 g / mL~6.6×10 -3 g / mL.

[0019] In a preferred embodiment of the present invention, in the alkali metal salt, the alkali metal is one of Ce, Mg, Ba and K, and in the transition metal precursor solution, the transition metal is one of Au, Pt, Ru and Cu.

[0020] In a preferred embodiment of the present invention, the organic solution containing heteroatoms includes a phosphorus-containing, nitrogen-containing or sulfur-containing organic solution, wherein the phosphorus-containing organic solution is one of hydroxyethylidene diphosphonic acid, chlorodiisopropylphosphine, hexamethylphosphoramide and triphenylphosphine, the nitrogen-containing organic solution is one of urea, pyridine and imidazole, and the sulfur-containing organic solution is one of thiourea, thiophene and thioether.

[0021] In a preferred embodiment of the present invention, the alkali metal salt is one of Ce(NO3)3·6H2O, Mg(NO3)2, Ba(NO3)2 and KNO3.

[0022] In a preferred embodiment of the present invention, the transition metal precursor is one of chloroauric acid, chloroplatinic acid, ruthenium trichloride and cupric chloride.

[0023] In a preferred embodiment of the present invention, the acid solution used for etching is one of dilute nitric acid, dilute hydrochloric acid, and dilute sulfuric acid, and the concentration is 0.5 mol / L to 5 mol / L.

[0024] Another object of the present invention is to provide a transition metal / alkali metal bimetallic single atom catalyst for catalyzing acetylene hydrochlorination reaction, prepared by any of the preparation methods described above.

[0025] The third object of the present invention is to provide an application of the above-mentioned transition metal / alkali metal bimetallic single atom catalyst in catalyzing acetylene hydrochlorination reaction.

[0026] In a preferred embodiment of the present invention, the transition metal / alkali metal bimetallic single atom catalyst is filled in a fixed bed reactor, acetylene and hydrogen chloride reaction gas are introduced, and the temperature is 110° C. to 300° C., and the acetylene space velocity is 30 h 1 ~1500 h 1 , the reaction is carried out under the reaction conditions that the volume ratio of acetylene to hydrogen chloride is 1~1.5:1.

[0027] The main reactions involved in the acetylene hydrochlorination process include: Main reaction: C2H2 + HCl → CH2 = CHCl Non-polymerization side reactions: CH2=CHCl + HCl → CH3CHCl2 CH2=CHCl + HCl → CH2ClCH2Cl Polymerization side reactions: 2CH2=CHCl → CH2ClCH=CCl-CH3 2C2H2→ CH2=CH-C≡CH Existing thermodynamic studies have shown that the above-mentioned main reaction is greatly affected by the polymerization side reaction, and the non-polymerization side reaction has little effect on the main reaction. The above-mentioned main and side reactions are exothermic reactions, but the thermal effect of the polymerization side reaction is greater than that of the main reaction. Higher temperatures are more conducive to inhibiting the polymerization side reaction (polymerization products may be deposited on the catalyst surface to form carbon deposits), improving the selectivity of the main reaction and reducing carbon deposits, but metal catalysts have the problem of valence deactivation at high temperatures. After comprehensively considering the effect of temperature on polymerization side reactions and catalyst reduction deactivation, the reaction temperature is controlled at 110°C~300°C, and more preferably, the reaction temperature is controlled at 140°C~240°C. The volume ratio of acetylene to hydrogen chloride adopts the commonly used volume ratio in the field, specifically 1:1~2, more preferably, the volume ratio of acetylene to hydrogen chloride is 1:1~1.5, and most preferably, the volume ratio of acetylene to hydrogen chloride is 1:1.02~1.2. The gas phase reaction is carried out in a fixed bed reactor, and the metal complex catalyst is loaded in the fixed bed reactor. The acetylene air velocity control range adopts the commonly used control range in this field, specifically within 30 h -1 ~1500 h -1 .

[0028] Although single-atom catalysts have high catalytic activity and high atomic utilization, they still have problems of carbon deposition, deactivation, and insufficient stability in the acetylene hydrochlorination process. Therefore, in the development of single-atom catalysts, the acidity and alkalinity of the catalyst surface are improved by increasing the defect sites on the material surface and introducing a second alkali metal single atom, thereby adjusting the electronic structure of the transition metal and inhibiting carbon deposition in the catalytic reaction process. Therefore, the development of transition metal / alkali metal bimetallic single-atom catalysts is an important way to solve the insufficient stability of single-atom transition metal catalysts.

[0029] Compared with the prior art, the present invention has the following beneficial effects: 1. The transition metal / alkali metal bimetallic single atom catalyst for catalyzing the hydrochlorination reaction of acetylene provided by the present invention is calcined by activated carbon treated with a heteroatom organic solution to dope the heteroatom into the activated carbon, expand the surface defects of the activated carbon carrier, ensure that the transition metal single atom and the alkali metal single atom are more stably anchored, so that the metal single atoms are evenly dispersed and not easy to agglomerate, and obtain an activated carbon carrier with rich defect sites, and then use an alkali metal nitrate solution to impregnate the activated carbon carrier containing defect sites. In the nitrate solution, the alkali metal is first converted into a metal oxide through two-stage calcination, and then converted into a super-strong alkali metal single atom material containing high defect sites. The transition metal salt solution is impregnated on the alkali metal single atom catalyst, and then etching is performed to obtain the desired transition metal / alkali metal bimetallic single atom catalyst. The catalyst prepared by the present invention uses a transition metal single atom as the main active center, and an alkali metal single atom as a super base auxiliary agent, which greatly improves the microenvironment of the active site, enhances the adsorption capacity of the transition metal site for reactants, and can inhibit carbon deposition side reactions. The transition metal and alkali metal bimetallic single atoms synergistically catalyze, and show high catalytic activity and stability for acetylene hydrochlorination reaction. In addition, the preparation method of the present invention has uniform dispersion of metal atoms, is not easy to agglomerate, has low preparation cost, and is suitable for large-scale production.

[0030] 2. Compared with the existing carbon-supported metal catalysts for acetylene hydrochlorination reaction, the transition metal / alkali metal bimetallic single atoms of the present invention will form abundant defect sites during the initial preparation of the superbase catalyst, which can better anchor the alkali metal and transition metal species. The transition metal single atoms serve as the main active sites, and the alkali metal single atoms serve as superbase additives. They can not only adjust the electronic structure of the transition metal and enhance its adsorption capacity, but also inhibit the carbon deposition of the transition metal. The bimetallic single atom catalyst not only has a high atomic utilization rate, but also the synergistic catalytic effect between the transition metal and alkali metal bimetallic single atoms makes the catalyst have good catalytic activity and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1In the figure, a is the acetylene conversion rate-reaction time relationship diagram of the catalyst prepared in Example 1, and b is the vinyl chloride selectivity-reaction time relationship diagram.

[0032] Figure 2 In the figure, a is the acetylene conversion rate-reaction time relationship diagram of the catalyst prepared in Example 2, and b is the vinyl chloride selectivity-reaction time relationship diagram.

[0033] Figure 3 In the figure, a is the relationship diagram of acetylene conversion rate-reaction time of the catalyst prepared in Example 3, and b is the relationship diagram of vinyl chloride selectivity-reaction time.

[0034] Figure 4 In the figure, a is the relationship diagram of acetylene conversion rate-reaction time of the catalyst prepared in Example 4, and b is the relationship diagram of vinyl chloride selectivity-reaction time.

[0035] Figure 5 AC-HAADF-STEM images of Au SAC / PC1 and Au-K DSAC / PC1 catalysts in Example 1.

[0036] Figure 6 AC-HAADF-STEM images of Pt SAC / PC2 and Pt-Ce DSAC / PC2 catalysts in Example 2.

[0037] Figure 7 AC-HAADF-STEM images of Ru SAC / NC and Ru-Mg DSAC / NC catalysts in Example 3.

[0038] Figure 8 AC-HAADF-STEM images of Cu SAC / SC and Cu-Ba DSAC / SC catalysts in Example 4.

[0039] Fig. 9 Raman spectra of carrier AC and NC and Mg SAC / NC catalysts in Example 3.

[0040] Fig.10 This is the CO2-TPD curve of the catalyst in Example 3.

[0041] Fig.11 The CO2-TPD curves of the catalysts prepared in Comparative Examples 3 and 4 are shown. DETAILED DESCRIPTION

[0042] The following is a detailed description of the technical solutions in the embodiments of the present invention in combination with the preferred embodiments and the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0043] It should be noted that all professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, various raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be purchased from the market or prepared by existing methods.

[0044] Example 1 A method for preparing a gold / potassium bimetallic single atom catalyst comprises the following steps: Synthesis of Au-K DSAC / PC1 Step 1, disperse coconut shell activated carbon (AC) in hydroxyethylidene diphosphonic acid solution, put it into a tube furnace after drying, and calcine it in inert gas at 400 ° C for 2 h to obtain a carrier, which is recorded as PC1.

[0045] Step 2, dissolve 0.0268 g of KNO3 in 35 mL of a mixed solvent of water and ethanol, wherein the volume ratio of ethanol to water in the mixed solvent is 1:1, then add 5 g of the PC1 carrier prepared in step 1, evaporate the mixture in a water bath, and after drying, calcine the product by a two-stage heating method, heat treating at 300°C and 700°C in a nitrogen atmosphere for 2 h, respectively. The obtained product is recorded as K SAC / PC1.

[0046] Step 3, dissolve 0.09027 g of HAuCl4 in 20 mL of deionized water, add 5 g of K SAC / PC1, mix it with the gold solution, collect the product by centrifugation, and then etch it with 1 mol / L nitric acid solution. After washing, it is dried to obtain the gold / potassium bimetallic single atom catalyst Au-K DSAC / PC1.

[0047] In addition, Au SAC / PC1 can be obtained by replacing K SAC / PC1 in step 3 with PC1 and treating it according to the same experimental method as step 3.

[0048] According to ICP-OES test, the mass fraction of gold in Au-K DSAC / PC1 was 0.8 wt.%, and the mass fraction of potassium was 0.02 wt.%; at the same time, the mass fraction of gold in Au SAC / PC1 was 0.8 wt.%.

[0049] Comparative Example 1 Synthesis of Benchmark Gold / Potassium Catalyst: 0.0696 g of HAuCl4 and 0.0026 g of KNO3 were dissolved in 35 mL of deionized water and ultrasonicated for 30 min. 5 g of the carrier PC1 in Example 1 was added to the above solution and stirred for 12 h. The mixture was placed in a 70°C water bath and refluxed for 6 h, then the water was continuously evaporated in the water bath and dried in a vacuum oven at 110°C for 16 h to obtain a benchmark gold / potassium catalyst, recorded as Au-K / PC1.

[0050] Example 2 A method for preparing a platinum / cerium bimetallic single-atom catalyst comprises the following steps: Synthesis of Pt-Ce DSAC / PC2 Step 1, disperse coconut shell activated carbon (AC) in diisopropyl phosphine chloride solution, put it into a tube furnace after drying, and calcine it in an inert gas at 500 ° C for 3 h to obtain a carrier, which is recorded as PC2.

[0051] Step 2, dissolve 0.1133 g of Ce(NO3)3·6H2O in 35 mL of a mixed solvent of water and ethanol, wherein the volume ratio of ethanol to water in the mixed solvent is 1:1, then add 5 g of the PC2 carrier prepared in step 1, evaporate the mixture in a water bath, and calcine the product by a two-stage heating method after drying, and heat treat the product in a helium atmosphere at 400°C and 800°C for 3 h, respectively. The obtained product is recorded as CeSAC / PC2.

[0052] Step 3, dissolve 0.1069 g of H2PtCl6 in 20 mL of deionized water, add 5 g of CeSAC / PC1 and mix it with the platinum solution, collect the product by centrifugation, and then etch it with 1 mol / L hydrochloric acid solution. After washing, dry it to obtain the platinum / cerium bimetallic single atom catalyst Pt-Ce DSAC / PC2.

[0053] In addition, Ce SAC / PC2 in step 3 is replaced by PC2, and Pt SAC / PC2 is obtained by treating it according to the same experimental method as step 3.

[0054] According to ICP-OES test, the mass fraction of platinum in Pt-Ce DSAC / PC2 was 0.8 wt.%, and the mass fraction of cerium was 0.02 wt.%; at the same time, the mass fraction of Pt in Pt SAC / PC1 was 0.8 wt.%.

[0055] Comparative Example 2 Synthesis of Benchmark Pt / Ce Catalyst: 0.0847 g H2PtCl6 and 0.00312 g Ce(NO3)3·6H2O were dissolved in 35 mL deionized water and ultrasonicated for 30 min. 5 g of the carrier PC2 in Example 2 was added to the above solution and stirred for 12 h. The mixture was placed in a 70°C water bath and refluxed for 6 h, then the water was continuously evaporated in the water bath and dried in a vacuum oven at 110°C for 16 h to obtain a benchmark platinum / cerium catalyst, recorded as Pt-Ce / PC2.

[0056] Example 3 A method for preparing a ruthenium / magnesium bimetallic single atom catalyst comprises the following steps: Synthesis of Ru-Mg DSAC / NC Step 1: Coconut shell activated carbon (AC) was dispersed in a pyridine solution, dried, and placed in a tube furnace for calcination at 700 °C in an inert gas for 4 h to obtain a carrier, which was recorded as NC.

[0057] Step 2, dissolve 0.1295 g of Mg(NO3)2·6H2O in 35 mL of a mixed solvent of water and ethanol, wherein the volume ratio of ethanol to water in the mixed solvent is 1:1, then add 5 g of the NC support prepared in step 1, evaporate the mixture in a water bath, and after drying, calcine the product by a two-stage heating method, heat treating at 500°C and 900°C in an argon atmosphere for 4 h, respectively, and the obtained product is recorded as MgSAC / NC.

[0058] Step 3, dissolve 0.1321 g of RuCl3·3H2O in 20 mL of deionized water, add 5 g of MgSAC / NC and mix it with the ruthenium solution, collect the product by centrifugation, and then etch it with 1 mol / L sulfuric acid solution, wash it and then dry it to obtain the ruthenium / magnesium double single atom catalyst Ru-Mg DSAC / NC.

[0059] In addition, the Ru SAC / NC can be obtained by replacing the MgSAC / NC in step 3 with NC and treating it according to the same experimental method as step 3.

[0060] According to ICP-OES test, the mass fraction of ruthenium in Ru-Mg DSAC / NC was 0.8 wt.%, and the mass fraction of magnesium was 0.02 wt.%; at the same time, the mass fraction of ruthenium in Ru SAC / NC was 0.8 wt.%.

[0061] Comparative Example 3 Synthesis of Benchmark Ruthenium / Magnesium Catalysts: 0.1044 g of RuCl3·3H2O and 0.0106 g of Mg(NO3)2·6H2O were dissolved in 35 mL of deionized water and ultrasonicated for 30 min. 5 g of the carrier NC in Example 3 was added to the above solution and stirred for 12 h. The mixture was placed in a 70°C water bath and refluxed for 6 h, then the water was continuously evaporated in the water bath and dried in a vacuum oven at 110°C for 16 h to obtain a benchmark ruthenium / magnesium catalyst, recorded as Ru-Mg / NC.

[0062] Comparative Example 4 Synthesis of Ruthenium Single Atom Supported Magnesium Catalyst: 0.0106 g of Mg(NO3)2·6H2O was dissolved in 35 mL of deionized water, ultrasonicated for 30 min, and 5 g of the Ru SAC / NC catalyst prepared in Example 3 was added and stirred for 12 h. The mixture was placed in a 70°C water bath and refluxed for 6 h, then the water was continuously evaporated in the water bath, and then placed in a vacuum oven at 110°C and dried for 16 h, which was recorded as Ru SAC-Mg / NC.

[0063] Example 4 A method for preparing a copper / barium bimetallic single atom catalyst comprises the following steps: Synthesis of Cu-Ba DSAC / SC Step 1: disperse coconut shell activated carbon (AC) in sulfide solution, dry it, put it into a tube furnace, and calcine it in inert gas at 900 °C for 2 h to obtain a carrier, which is recorded as SC.

[0064] Step 2, dissolve 0.212 g of Ba(NO3)2 in 35 mL of a mixed solvent of water and ethanol, wherein the volume ratio of ethanol to water in the mixed solvent is 1:1, then add 5 g of the SC carrier prepared in step 1, evaporate the mixture in a water bath, and after drying, calcine the product using a two-stage heating method, heat-treating it at 600°C and 1000°C in a nitrogen atmosphere for 3 h, respectively. The obtained product is recorded as BaSAC / SC.

[0065] Step 3, dissolve 0.1091 g of CuCl2 in 20 mL of deionized water, add 5 g of BaSAC / SC and mix it with the copper solution, collect the product by centrifugation, and then etch it with 1 mol / L hydrochloric acid solution. After washing, it is dried to obtain the copper / barium double single atom catalyst Cu-Ba DSAC / SC.

[0066] In addition, the BaSAC / SC in step 3 is replaced with SC, and the Cu SAC / SC is obtained by treating it according to the same experimental method as step 3.

[0067] ICP-OES test showed that the mass fraction of copper in the Cu-Ba DSAC / SC was 0.8 wt.%, and the mass fraction of barium was 0.02 wt.%; at the same time, the mass fraction of copper in the Cu SAC / SC was 0.8 wt.%.

[0068] Comparative Example 5 Synthesis of Benchmark Copper / Barium Catalyst: Dissolve 0.0854 g CuCl2 and 0.0019 g Ba(NO3)2 in 35 mL deionized water and perform ultrasonic treatment for 30 min. Add 5 g of the carrier SC prepared in step 1 of Example 2 to the above solution and stir for 12 h. Reflux the mixture in a 70°C water bath for 6 h, then continue to evaporate the water in the water bath and dry in a vacuum oven at 110°C for 16 h to obtain a benchmark copper / barium catalyst, recorded as Cu-Ba / SC.

[0069] Results Analysis 3 mL of the PC1, K SAC / PC1, Au-K DSAC / PC1, Au SAC / PC1 and Au-K / PC1 catalysts described in Example 1 were loaded into a fixed bed reactor, and acetylene and hydrogen chloride reaction gases were passed through at 180 °C and an acetylene space velocity (GHSV) of 1200 h -1 , the volume ratio of acetylene to hydrogen chloride was 1:1.15, the reaction was carried out for 24 h, and the acetylene conversion rate and vinyl chloride selectivity were detected. The test results of the acetylene hydrochlorination reaction catalyzed by each catalyst are shown in Table 1 and Figure 1 .

[0070] 3 mL of the PC2, CeSAC / PC2, Pt-Ce DSAC / PC2, Pt SAC / PC2 and Pt-Ce / PC2 catalysts described in Example 2 and Comparative Example 2 were loaded into a fixed bed reactor, and acetylene and hydrogen chloride reaction gases were passed through at 180 °C and an acetylene space velocity (GHSV) of 1200 h -1 , under the reaction conditions of a volume ratio of acetylene to hydrogen chloride of 1:1.15, the reaction was carried out for 24 h, and the acetylene conversion rate and vinyl chloride selectivity were detected. The test results of the acetylene hydrochlorination reaction catalyzed by each catalyst are shown in Table 1 and Figure 2 .

[0071] 3 mL of the NC, Mg SAC / NC, Ru-Mg DSAC / NC, Ru SAC / NC described in Example 3, the Ru-Mg / NC described in Comparative Example 3, and the Ru SAC-Mg / NC described in Comparative Example 4 were loaded into a fixed bed reactor, and acetylene and hydrogen chloride reaction gases were passed through at 180°C and an acetylene space velocity (GHSV) of 180 h -1, the volume ratio of acetylene to hydrogen chloride was 1:1.15, the reaction was carried out for 24 h, and the acetylene conversion rate and vinyl chloride selectivity were detected. The test results of the acetylene hydrochlorination reaction catalyzed by each catalyst are shown in Table 1 and Figure 3 .

[0072] 3 mL of the SC, BaSAC / SC, Cu-Ba DSAC / SC, Cu SAC / SC in Example 4 and the Cu-Ba / SC in Comparative Example 5 were loaded into a fixed bed reactor, and acetylene and hydrogen chloride reaction gases were passed through at 180 °C and an acetylene space velocity (GHSV) of 90 h -1 , under the reaction conditions of a volume ratio of acetylene to hydrogen chloride of 1:1.15, the reaction was carried out for 24 h, and the acetylene conversion rate and vinyl chloride selectivity were detected. The test results of the acetylene hydrochlorination reaction catalyzed by each catalyst are shown in Table 1 and Figure 1 and Figure 4 .

[0073] Among them, the calculation method of acetylene conversion rate is: .

[0074] The calculation method of vinyl chloride selectivity is: .

[0075] Where: Φ A0 Indicates the volume fraction of acetylene in the reactants; Φ A Indicates the remaining acetylene volume fraction in the reaction; Φ VCM Indicates the volume fraction of vinyl chloride produced.

[0076] Figure 1~Figure 4 1 is a graph showing the relationship between acetylene conversion and reaction time and vinyl chloride selectivity and reaction time of the catalysts prepared in Examples 1 to 4. Table 1 shows the relevant parameters, conversion and selectivity for evaluating the acetylene hydrochlorination reaction catalyzed by different catalysts. Figure 1~Figure 4 It can be seen from the catalytic test results that the activity and stability of transition metal / alkali metal bimetallic single atom catalysts are better than those of transition metal single atom and alkali metal single atom catalysts.

[0077] Figure 5~Figure 8 The AC-HAADF-STEM images are of the transition metal single atom and transition metal / alkali metal bimetallic single atom catalysts prepared in Examples 1 to 4, respectively. The successful preparation of the single atom and bi-single atom catalysts was proved by spherical aberration electron microscopy.

[0078] Table 1 Evaluation of relevant parameters, conversion rate and selectivity of acetylene hydrochlorination reaction catalyzed by different catalysts Fig. 9The Raman spectra of the carrier AC, NC in Example 3, and Mg SAC / NC catalyst show that the I D / I G significantly increased, which is more conducive to anchoring alkali metal and transition metal species; further, the I D / I G The further increase relative to NC indicates that abundant defect sites are formed during the preparation of superalkali metal single atoms, which is more conducive to anchoring transition metal species.

[0079] In order to determine the source of basicity in the catalyst, the catalyst described in Example 3 was characterized by CO2-TPD. The results are as follows Fig.10 As shown, all materials have a CO2 desorption peak at about 100°C~500°C, which is caused by the physical adsorption of CO2 on the carrier. In Mg SAC / NC and Ru-Mg DSAC / NC, a CO2 desorption peak centered at 800°C appeared, indicating that the Mg SAC / NC and Ru-Mg DSAC / NC catalysts prepared by the method of the present invention contain a large number of strong basic sites. However, the CO2-TPD characterization of the benchmark catalyst Ru-Mg / NC prepared by the general room temperature impregnation method and the Ru SAC-Mg / NC obtained by impregnating Mg species on the ruthenium single atom catalyst only showed a CO2 desorption peak at 100°C~500°C. The results are as follows Fig.11 , there is no obvious desorption peak at higher temperatures, indicating that there are no strong basic sites on Ru-Mg / NC and Ru SAC-Mg / NC.

[0080] In summary, compared with single-atom catalysts, transition metal / alkali metal bimetallic single-atom catalysts have excellent catalytic activity and stability. In the process of preparing superbase catalysts, abundant defect sites will be formed, which can better anchor alkali metal and transition metal species. Transition metal single atoms serve as the main active sites, and alkali metal single atoms serve as superbase additives. They can not only adjust the electronic structure of transition metals and enhance their adsorption capacity, but also inhibit the carbon deposition of transition metals. The synergistic catalysis between transition metals and alkali metals enables the catalyst to still have good stability and catalytic activity in long-term reactions.

[0081] It should be noted that when the present invention involves a numerical range, it should be understood that the two endpoints of each numerical range and any value between the two endpoints can be selected. Since the steps and methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes a preferred embodiment. Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the attached claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0082] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the protection scope of the present invention and its equivalent technology, the present invention is also intended to include these changes and variations.

Claims

1. A method for preparing a transition metal / alkali metal bimetallic single atom catalyst for catalyzing acetylene hydrochlorination, characterized in that: The following steps are involved: The activated carbon is dispersed in an organic solution containing heteroatoms, dried, and then calcined in an inert gas to dope the heteroatoms on the activated carbon, thereby obtaining an activated carbon carrier containing defect sites; Dissolving an alkali metal nitrate in a mixed solvent of water and ethanol to obtain an alkali metal nitrate solution, then using the alkali metal nitrate solution to impregnate the activated carbon support containing defect sites, and performing two-stage calcination after drying to convert the alkali metal into a metal oxide first, and then into an alkali metal single atom catalyst having abundant defect sites; A transition metal precursor solution is impregnated on an alkali metal single atom catalyst, a product is collected by centrifugation, and the product is acid-etched to obtain a transition metal / alkali metal bimetallic single atom catalyst.

2. The method for preparing a transition metal / alkali metal bimetallic single atom catalyst for catalyzing acetylene hydrochlorination according to claim 1, characterized in that: The calcination temperature for preparing the activated carbon support containing defect sites is 400℃~800℃, and the calcination time is 1 h~5 h.

3. The method for preparing a transition metal / alkali metal bimetallic single atom catalyst for catalyzing acetylene hydrochlorination according to claim 1, characterized in that: The two-stage calcination temperatures are 300℃~600℃ and 700℃~1000℃ respectively, and the calcination time is 2 h~5 h.

4. The method for preparing a transition metal / alkali metal bimetallic single atom catalyst for catalyzing acetylene hydrochlorination according to claim 1, characterized in that: In the transition metal / alkali metal bimetallic single atom catalyst, the loading amount of the transition metal element is 1 wt.% to 5 wt.%, and the loading amount of the alkali metal element is 0.01 wt.% to 0.2 wt.%.

5. The method for preparing a transition metal / alkali metal bimetallic single atom catalyst for catalyzing acetylene hydrochlorination according to claim 1, characterized in that: The mass concentration of alkali metal nitrate solution is 7.66×10 -4 g / mL~6.05×10 -3 g / mL, and the mass concentration of the transition metal precursor solution was 4.5×10 -3 g / mL~6.6×10 -3 g / mL.

6. The method for preparing a transition metal / alkali metal bimetallic single atom catalyst for catalyzing acetylene hydrochlorination according to claim 1, characterized in that: In the alkali metal salt, the alkali metal is one of Ce, Mg, Ba and K. In the transition metal precursor solution, the transition metal is one of Au, Pt, Ru and Cu.

7. The method for preparing a transition metal / alkali metal bimetallic single atom catalyst for catalyzing acetylene hydrochlorination according to claim 1, characterized in that: Organic solutions containing heteroatoms include phosphorus-containing, nitrogen-containing or sulfur-containing organic solutions.

8. A transition metal / alkali metal bimetallic single atom catalyst for catalyzing acetylene hydrochlorination reaction obtained by the preparation method according to any one of claims 1 to 7.

9. Use of the transition metal / alkali metal bimetallic single atom catalyst according to claim 8 in catalyzing acetylene hydrochlorination reaction.

10. The use according to claim 9, characterized in that: The transition metal / alkali metal bimetallic single atom catalyst is placed in a fixed bed reactor, acetylene and hydrogen chloride reaction gases are introduced, and the temperature is 110°C to 300°C, and the acetylene space velocity is 30 h -1 ~1500 h -1 , the reaction is carried out under the reaction conditions that the volume ratio of acetylene to hydrogen chloride is 1~1.5:1.

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