Single atom catalysts dispersed on ordered intermetallic compound clusters and applications thereof

Abstract

The present application relates to a kind of single-atom catalyst dispersed in ordered intermetallic compound cluster and its application, the catalyst has Pt1-MaMb / support structure, active metal Pt in catalyst exists in single-atom site state, and form ordered intermetallic compound cluster with Ma, Mb, wherein Ma, Mb are independently selected from V, Mn, Fe, Co, Ni, Co, Zn, Sn or Sb, carrier is selected from molecular sieve, alumina or activated carbon.Based on its unique geometric structure and electronic structure, the catalyst has wide application prospect in alkane dehydrogenation to olefin reaction, wherein propylene selectivity in propane dehydrogenation reaction is close to 100%, and carbon deposition resistance is strong.

Description

TECHNICAL FIELD

[0001] The application relates to application of a single-atom catalyst dispersed in ordered intermetallic compound clusters to a propane dehydrogenation reaction to prepare propylene, and belongs to the technical field of petroleum chemical industry. BACKGROUND

[0002] Propylene is a cornerstone of the chemical industry and is widely used to produce polypropylene, propylene oxide, and propylene cyanide and other downstream basic chemical products. According to the raw material source, the current propylene production process mainly includes three routes of petroleum, coal and natural gas. The petroleum route produces low-carbon olefins such as ethylene and propylene through petroleum steam cracking or catalytic cracking; the coal route first produces synthetic gas (CO and H2) through coal-to-synthetic gas, and then produces low-carbon olefins through MTP, MTO or Fischer-Tropsch synthesis process; the natural gas route uses the abundant low-carbon alkanes in natural gas to produce corresponding olefins through dehydrogenation reaction. In recent years, with the large-scale exploitation of shale gas, the cost of propane has been greatly reduced, and the propane dehydrogenation to propylene technology route shows great economic advantages and development prospects.

[0003] In the field of propane dehydrogenation to propylene, improving the propylene selectivity and stability of the catalyst is a core problem. Based on high atom utilization and unique electronic structure, single-atom alloy catalysts have broad application prospects in C-H bond cleavage reactions. The propylene selectivity of Pt / Cu single-atom alloy catalysts in propane dehydrogenation reactions can reach 90%. However, existing single-atom alloy catalysts disperse active metals on disordered solid solutions, and the particle size is often large (> 3 nm). Under harsh reaction conditions, the structure of the disordered solid solution is prone to dislocation, and the catalytic selectivity is poor. Ordered intermetallic compounds have uniform active sites, strong controllability of structure, and high thermal stability. Dispersing single-atom catalysts on ordered intermetallic compound clusters can significantly improve the olefin selectivity and stability of the material. SUMMARY

[0004] The application discloses a single-atom catalyst with a Pt1-MaMb / support structure, wherein the active metal Pt exists in a single-atom site state and forms an ordered intermetallic compound cluster with Ma and Mb, Ma and Mb are independently selected from V, Mn, Fe, Co, Ni, Co, Zn, Sn or Sb, and the support is selected from a molecular sieve, alumina or activated carbon.

[0005] In the catalyst, the content of Pt is 0.5-5 wt%, Ma is preferably Sn, Fe or Zn, Mb is preferably Zn, Co or Mn, the content of Ma and Mb is 0.3-10 wt%, and the rest is the support.

[0006] More preferably, the catalyst is selected from Pt1-SnZn / Al2O3, Pt1-FeCo / Al2O3 or Pt1-ZnMn / ZMS-5.

[0007] The application also discloses a preparation method of a single-atom catalyst with a Pt1-MaMb / support structure, comprising the following steps:

[0008] S1: loading a solution containing metal salt of Ma and Mb onto an alumina, a molecular sieve or an activated carbon support by impregnation, and calcining to obtain metal oxides dispersed on the support;

[0009] S2: adding an acidic substance into a solution of a soluble platinum salt or a platinum complex, and mixing the obtained solution into the metal oxides obtained in S1, and calcining the obtained product;

[0010] S3: reducing the product of S2 to obtain the catalyst;

[0011] wherein Ma and Mb are independently selected from V, Mn, Fe, Co, Ni, Co, Zn, Sn or Sb, and the support is selected from a molecular sieve, alumina or activated carbon;

[0012] In S1, the solvent in the solution of the metal salt is selected from water, C 1-6 alkyl alcohol and C 3-6 alkyl ketone, preferably methanol, ethanol and isopropyl ketone; the impregnation is preferably an equal-volume impregnation; the calcination temperature is 200-600 DEG C; and the metal salt is selected from soluble salts of metals, especially organic solvent-soluble salts, including but not limited to nitrate, hydrochloride, sulfate, organic acid salt and complex of the metals of Ma and Mb, such as zinc chloride, zinc sulfate, zinc phosphate, zinc nitrate, zinc oxalate, zinc citrate, iron chloride, ferrous chloride, iron sulfate, ferrous sulfate, iron phosphate, ferrous sulfate, iron nitrate, ferrous nitrate, iron oxalate, tin chloride, stannous chloride, tin sulfate, tin nitrate, tin oxalate, tin citrate and the like, and the application is implemented by using the chloride of the metal.

[0013] In S2, the platinum salt or platinum complex includes platinum nitrate, platinum chloride, platinum acetate, platinum acetylacetone or a chlorine complex, preferably chloroplatinic acid, platinum nitrate and platinum acetate; the acidic substance is hydrochloric acid, sulfuric acid or nitric acid; the mixing is a conventional mixing method, such as simply adding the solution into the metal oxides, or by other conventional methods; and the calcination temperature is 200-600 DEG C.

[0014] In S3, the reduction is hydrogen reduction, and the reduction is preferably performed in programmed temperature rising; the programmed temperature rising at least includes: maintaining at 100-250 DEG C for 10 min-10 h, preferably 10 min-40 min, to reduce platinum oxide into metal platinum, and maintaining at 250-650 DEG C for 10 min-10 h, preferably 10 min-1 h, to further reduce the metal around Pt, so as to obtain a single-atom catalyst dispersed in ordered intermetallic compound clusters.

[0015] The present application further discloses a use of a single-atom catalyst dispersed in ordered intermetallic compound clusters for preparing C 2-6 alkane compound to prepare C 2-6 olefin compound.

[0016] Meanwhile, the present application discloses a method for preparing olefin by dehydrogenation of alkane, which comprises removing hydrogen from alkane compound in the presence of the catalyst to form olefin compound, wherein the alkane compound is C 2-6 alkane compound, preferably propane, butane, isobutane, pentane, and the olefin compound is C 2-6 alkene compound, preferably propylene, butene, isobutene, pentene.

[0017] Term explanation:

[0018] In the catalyst Pt1-MaMb / support of the present application, the subscript 1 of Pt1 indicates that Pt exists in a single atom site state. The single atom site state, single atom state, single atom distribution, single atom form or single atom level of separation state refers to the state in which the active metal elements are independently separated from each other between metal atoms (ions), and the active metal atoms (Pt atoms in the present application) do not form direct metal-metal bonds or metal-O-metal bonds with each other, in an atomic dispersion state or a single atom site dispersion state. The metal dispersed in a single atom site state can exist in an atomic state or an ionic state, and more likely exists between the atomic and ionic states (the bond length is between the two bond lengths). The single atom site state of the metal protected by the present application is theoretically completely independent of each other. However, due to the random deviation of the control of the preparation operation conditions of different batches, a small amount of agglomerated metal species may exist in the obtained product, for example, clusters containing a certain number of atoms or ions. In other words, in the catalyst of the present application, the active metal may exist in a single atom site dispersion state, at the same time, part of it exists in a cluster state containing metal atom aggregation, and / or part of the metal even presents a nanocrystalline state. And with the change of the external environment, the single atom state changes to the cluster and / or nanometer state. The single atom state protected by the present application requires that the single atom noble metal in the different existence forms of single atom noble metal, noble metal cluster and noble metal nanocrystal in the catalyst has a certain proportion, for example, higher than 10%, preferably higher than 20%, and particularly preferably higher than 50%. But limited to the current technical means, only by relatively rough statistical means, the random large amount of selected different local areas of the catalyst test sample can be analyzed and characterized by high-resolution spherical aberration electron microscopy, and the existence state of the noble metal in various forms can be randomly selected for statistical analysis, or the catalyst sample can be analyzed by X-ray absorption fine structure spectrum (EXAFS) which can characterize the overall information of the sample to obtain the ratio of metal and other atom bonding signal to metal-metal bonding signal, to determine the approximate proportion of the single atom state.

[0019] Intermetallic compound: refers to the combination of different elements in the metal according to the corresponding proportion, and then the combination of different compounds with various element types. Unlike traditional disordered solid solution alloy, intermetallic compound has ordered structure. The intermetallic compound of the present application has uniform active site, strong controllability of structure and high thermal stability.

[0020] Hydrogenation reduction refers to reduction in the presence of hydrogen, which can be carried out in a pure hydrogen atmosphere or a mixed atmosphere of hydrogen and inert gas.

[0021] Equal-volume impregnation: In this invention, noble metal salts are loaded onto a carrier. When the mass of the solution is equal to the adsorption capacity of the carrier, the carrier is impregnated in the solution, and the solution is adsorbed onto the carrier by an equal volume, which is called equal-volume impregnation. When the mass of the solution exceeds the adsorption capacity of the carrier, the carrier is impregnated in excess solution, which is called over-volume impregnation. In practice, the adsorption capacity of the carrier is often measured beforehand, the ratio of adsorption capacity to carrier weight is calculated, and then the amount of solution to be added is calculated according to the ratio of solution to carrier weight.

[0022] Complexes, also known as coordination compounds, include complexes formed by noble metals or transition metals and ligands. Common ligands include halogens (fluorine, chlorine, bromine, iodine), nitro groups, nitroso groups, cyanide groups, ammonia, water molecules, or organic groups. Common complexes include chloride complexes, ammonia complexes, cyanide complexes, etc., including chloroplatinic acid, chloroplatinate, and chloroplatinic acid hydrate. See "Handbook of Synthesis of Noble Metal Compounds and Coordination Compounds (Deluxe Edition)" (Yu Jianmin, 2009, Chemical Industry Press).

[0023] Beneficial effects

[0024] The catalyst of the present invention has the following effects:

[0025] 1. Catalysts with ordered intermetallic compound structures were prepared. The ordered intermetallic compounds exhibit strong structural controllability and high thermal stability. Furthermore, the intermetallic compound particles are extremely small (<1 nm), resulting in high atom utilization of the catalyst.

[0026] 2. The Pt atoms in the catalyst are isolated by neighboring metals, and there are no adjacent Pt-Pt bonds in the catalyst. This is beneficial for suppressing the occurrence of deep dehydrogenation reaction and improving the catalyst's resistance to carbon deposition in alkane dehydrogenation reaction.

[0027] 3. The catalyst exhibits high selectivity and stability in the propane dehydrogenation reaction, with propylene selectivity approaching 100%, and strong resistance to carbon deposition. Attached Figure Description

[0028] Figure 1 The image shows a STEM image of PtSnZn clusters loaded on Al2O3, with an average particle size of 0.9 nm.

[0029] Figure 2 The image shows the synchrotron radiation EXAFS image of the Pt1-SnZn / Al2O3 catalyst. There are no adjacent Pt-Pt bonds in the sample.

[0030] Figure 3 The images show synchrotron radiation EXAFS images of the Pt1-SnZn / Al2O3 catalyst before and after the reaction. The sample structure did not change significantly before and after the reaction.

[0031] Figure 4For the thermogravimetric analysis of the Pt / Al2O3and Pt1-SnZn / Al2O3catalysts after the reaction, the Pt1-SnZn / Al2O3catalyst exhibited high carbon deposition resistance.

[0032] Figure 5 For the XRD pattern of the Pt1-SnZn / Al2O3sample, according to the XRD simulation result, the structure thereof was a ternary ordered intermetallic compound. DETAILED DESCRIPTION

[0033] Terms used in the examples and explanations:

[0034] min: minute

[0035] h: hour

[0036] wt%: mass percentage

[0037] Example 1

[0038] (1) 0.014 g of ZnCl2and 0.023 g of SnCl2.2H2O were dissolved in 0.4 ml of methanol, and the solution was impregnated into 1 g of an Al2O3support in an equal volume, dried at 100°C for 12 hours, and then the precursor was calcined at 550°C for 3 h to form SnZnO x / Al2O3.

[0039] (2) 0.053 g of H2PtCl6.6H2O was dissolved in 0.37 ml of water, and 0.03 ml of concentrated hydrochloric acid (37% HCl) was added dropwise to the solution.

[0040] (3) The solution in step 2 was added dropwise to the SnZnO x / Al2O3precursor in step 1, dried at 100°C for 12 hours, and then the precursor was calcined at 225°C for 3 h.

[0041] (4) The catalyst precursor in step 3 was subjected to hydrogen temperature programmed reduction, reduced at 150°C for 10 minutes, at 200°C for 30 minutes, at 250°C for 10 minutes, and at 550°C for 30 minutes, to obtain a Pt1-SnZn / Al2O3catalyst.

[0042] Example 2

[0043] (1) 0.021 g of FeCl3.6H2O and 0.056 g of CoCl2.6H2O were dissolved in 0.4 ml of ethanol, and the solution was impregnated into 1 g of an Al2O3support in an equal volume, dried at 100°C for 12 hours, and then the precursor was calcined at 450°C for 3 h to form FeCoO x / Al2O3.

[0044] (2) 0.053 g H2PtCl6.6H2O was dissolved in 0.37 ml water and 0.021 ml concentrated nitric acid (68%) was added dropwise to the solution.

[0045] (3) The solution in step 2 was added dropwise to the FeCoO x / Al2O3 precursor in step 1, which was dried at 100°C for 12 hours, and then the precursor was calcined at 350°C for 3h.

[0046] (4) The catalyst precursor in step 3 was subjected to hydrogen temperature programmed reduction, reduced at 100°C for 10 minutes, 200°C for 20 minutes, 250°C for 20 minutes, and 650°C for 30 minutes, to obtain the Pt1-FeCo / Al2O3 catalyst.

[0047] Example 3

[0048] (1) 0.051 g ZnCl2and 0.033 g MnCl2.6H2O were dissolved in 0.4 ml isopropanol, and the solution was impregnated into 1 g ZMS-5 molecular sieve carrier in equal volume, which was dried at 100°C for 12 hours, and then the precursor was calcined at 400°C for 3h to form ZnMnO x / ZMS-5.

[0049] (2) 0.053 g H2PtCl6.6H2O was dissolved in 0.37 ml water and 0.021 ml concentrated nitric acid (68%) was added dropwise to the solution.

[0050] (3) The solution in step 2 was added dropwise to the ZnMnO x / ZMS-5 precursor in step 1, which was dried at 100°C for 12 hours, and then the precursor was calcined at 400°C for 3h.

[0051] (4) The catalyst precursor in step 3 was subjected to hydrogen temperature programmed reduction, reduced at 100°C for 20 minutes, 200°C for 20 minutes, 250°C for 20 minutes, and 500°C for 30 minutes, to obtain the Pt1-ZnMn / ZMS-5 catalyst.

[0052] Comparative Example 1

[0053] (1) 0.053 g H2PtCl6.6H2O was dissolved in 0.4 ml methanol, and the solution was impregnated into 1 g Al2O3 carrier in equal volume.

[0054] (2) The catalyst in step 1 was dried at 100°C for 12 hours, calcined at 350°C for 3h, and reduced at 550°C for 0.5h to form the Pt / Al2O3 nanocatalyst.

[0055] Comparative Example 2

[0056] (1) 0.023g SnCl2.2H2O and 0.053g H2PtCl6.6H2O were dissolved in 0.4ml methanol, and the solution was impregnated into 1g Al2O3 carrier with equal volume.

[0057] (2) The catalyst in step 1 was dried at 100℃ for 12h, calcined at 350℃ for 3h, and reduced at 550℃ for 0.5h to form PtSn / Al2O3 nanocatalyst.

[0058] Application test experiment and data

[0059] The above catalysts were tested for propane dehydrogenation activity in a fixed bed reactor, the reaction tube was a quartz tube, the catalyst dosage was 0.4g, the reaction gas was 5% propane + 95% N2, the gas flow rate was 20ml / min, and the reaction temperature was 500℃. Before the catalytic reaction started, the catalyst was activated, and the activation condition was H2 reduction at 550℃ for half an hour. The catalytic reaction products were analyzed by gas chromatography, and the detector type of the chromatograph was FID.

[0060] The evaluation results of the catalysts are as follows:

[0061]

[0062]

[0063] Conclusion:

[0064] Compared with the nanocatalyst, the single-atom catalyst dispersed on the ordered intermetallic compound cluster has better catalytic performance for propane dehydrogenation to propylene, the catalyst has high propane conversion rate, high propylene selectivity, and good stability, and has high industrial application prospect.

[0065] The above embodiments of the present application are only examples for clearly illustrating the present application, and are not limitations on the embodiments of the present application. For ordinary skilled in the art, other different forms of changes or variations can be made on the basis of the above description, and all the embodiments cannot be exhausted here. Any obvious changes or variations derived from the technical solutions of the present application still fall within the protection scope of the present application.

Claims

1. A single atom catalyst having a Pt1-M a M b support structure, characterized in that, In this catalyst, the active metal Pt exists in a single-atom site state and interacts with M. a M b The formation of ordered intermetallic compound clusters, in which M a For Sn, Fe or Zn, M b The material is Zn, Co, or Mn, and the support is selected from molecular sieves, alumina, or activated carbon. The Pt content in the catalyst is 0.5-5wt%, M a b The Pt content in the catalyst is 0.5-5wt%, MThe Pt content in the catalyst is 0.5-5wt%, M The Pt atoms in the catalyst are isolated by adjacent metals, and there are no adjacent Pt-Pt bonds in the catalyst.

2. The catalyst of claim 1, wherein The catalyst is Pt1-SnZn / Al2O3, Pt1-FeCo / Al2O3, or Pt1-ZnMn / ZMS-5.

3. A process for the preparation of the catalyst according to claim 1 or 2, characterized in that, Comprising: S1: impregnation of a solution containing M a and M b metal salts onto an alumina, molecular sieve or activated carbon support, calcination to obtain metal oxides dispersed on the support; S2: dropping an acidic substance into a soluble platinum salt or platinum complex solution, mixing the obtained solution into the metal oxide obtained in S1, and calcining the obtained product; S3: reducing the product of S2 to obtain the catalyst; wherein M a is selected from Sn, Fe or Zn, M b is Zn, Co or Mn, and the support is selected from a molecular sieve, alumina or activated carbon; The M a and M b The solvent in the solution of the metal salt is selected from water, C 1-6 alkyl alcohol or C 3-6 alkyl ketone; the metal salt is selected from soluble salts of metals which are organic solvent soluble salts.

4. The production method according to claim 3, wherein The solvent is methanol, ethanol, or isopropyl ketone; In step S1, the impregnation method is an equal volume impregnation method; the calcination temperature is 200-600°C; the metal salt is selected from the group consisting of M a , M b nitrates, chlorides, sulfates, organic acid salts, or complexes of metals.

5. The production method according to claim 4, wherein The metal salt is selected from zinc chloride, zinc sulfate, zinc phosphate, zinc nitrate, zinc oxalate, zinc citrate, iron chloride, ferrous chloride, iron sulfate, ferrous sulfate, iron phosphate, ferrous sulfate, iron nitrate, ferrous nitrate, iron oxalate, tin chloride, stannous chloride, tin sulfate, tin nitrate, tin oxalate, or tin citrate.

6. The preparation method of claim 3 or 4, wherein, In the S2 step, the platinum salt or platinum complex includes: platinum nitrate, platinum chloride, platinum acetate, platinum acetylacetone, or a chloro complex; the acidic substance is hydrochloric acid, sulfuric acid, or nitric acid; the mixing is a conventional mixing method; and the calcination temperature is 200-600°C.

7. The production method according to claim 6, wherein The platinum salt or platinum complex is chloroplatinic acid, platinum nitrate, or platinum acetate; and the mixing is dropping the solution into the metal oxide obtained in S1.

8. The production method according to any one of claims 3 to 5, 7, wherein In the S3 step, the reduction is hydrogen reduction.

9. The production method according to claim 8, wherein The reduction is performed in a programmed temperature increase.

10. The production method according to claim 9, wherein The programmed temperature increase at least includes: reduction at 100-250°C for 10 min-10 h, and reduction at 250-650°C for 10 min-10 h.

11. The production method according to claim 10, wherein The programmed temperature increase at least includes: reduction at 100-250°C for 10 min-40 min, and reduction at 250-650°C for 10 min-1 h.

12. Use of a catalyst as claimed in claim 1 or 2, or of a catalyst obtained by a process as claimed in any one of claims 3 to 11, characterized in that, The catalyst is used for C 2-6 alkane compound dehydrogenation to C 2-6 reaction of olefin compound.

13. A process for the dehydrogenation of an alkane to produce an alkene, characterized in that, an alkane compound is removed to form an olefin compound in the presence of a catalyst as claimed in claim 1 or 2, or a catalyst prepared by the process of any one of claims 3 to 11, said alkane compound being C 2-6 an alkane compound, said olefin compound being C 2-6 an olefin compound.

14. The method of claim 13, wherein, The alkane compound is propane, butane, isobutane, or pentane, and the olefin compound is propylene, butene, isobutene, or pentene.

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