Preparation method of an atomic-level PtFe bimetallic supported catalyst and its application in the selective hydrogenation of halogenated nitrobenzenes

Abstract

The present invention provides a method for preparing an atomic-level PtFe bimetallic supported catalyst and its application in the selective hydrogenation of halogenated nitrobenzenes. x Low-loaded PtFe bimetallic catalysts were used, and Pt and Fe precursors were anchored on MO using strong electrostatic adsorption. x Atomically dispersed PtFe / MO is obtained at surface defects x Catalyst: PtFe / MO x Pt and MO in catalyst x The hydrogen overflow effect between the catalyst and the FeO2 produces a large number of hydroxyl groups (M‑OH and M‑OH‑M) and oxygen defects on the catalyst surface, which is beneficial to the activation and hydrogenation of halogenated nitrobenzenes. x The introduction of the species promotes the adsorption of the NO2 functional group, improving the selectivity of the halogenated aniline. Consequently, the catalyst of the present invention significantly enhances the selective hydrogenation activity of halogenated nitrobenzenes, achieving a halogenated aniline yield exceeding 99%, significantly suppressing the occurrence of dehalogenation side reactions, and achieving efficient utilization of the precious metal Pt.

Description

Technical Field

[0001] The present invention relates to the technical field of metal catalysts, and in particular to a preparation method of an atomic-level PtFe bimetallic supported catalyst and application of the catalyst in the selective hydrogenation of halogenated nitrobenzenes. Background Art

[0002] Substituted aromatic amines, as important chemical intermediates, are crucial raw materials for the synthesis of various fine chemicals and pharmaceuticals. For example, p-chloroaniline is widely used in dyes, rubber, pharmaceuticals, pesticides, and other fine chemicals. Currently, the industrial process for preparing substituted aromatic amines primarily involves reducing substituted nitrobenzenes, including chemical reduction (using Fe powder, alkali sulfide, and hydrogen sulfide) and catalytic hydrogenation. Heterogeneous catalytic hydrogenation using hydrogen as a reducing agent offers advantages such as low waste, low cost, high product purity, and easily separable and regenerable catalysts, making it the primary method for preparing substituted aromatic amines in industry. However, during the catalytic hydrogenation of halogenated nitrobenzenes, the C—X bond is susceptible to hydrogenolysis, resulting in low selectivity for the target haloaniline product. This is particularly true when using noble metals such as Pt and Pd as catalysts, where dehalogenation is more pronounced. Adding dechlorination inhibitors is a common strategy to inhibit C—X bond cleavage, but this can introduce impurities. Therefore, researchers often optimize the type and structure of catalysts to achieve efficient and selective hydrogenation activity, thereby avoiding the formation of dehalogenation byproducts and the introduction of impurities.

[0003] By manipulating the geometric and electronic structures of supported Pt-based catalysts, Wang et al. decoupled the geometric and electronic effects of the Pt center on C-X bond cleavage activity (Chem., 2020, 6, 752-765; Nat. Commun., 2022, 13, 3561). The high coordination number of positive Pt atoms with quasi-planar positions and Pt sites on the surface of larger Pt particles results in severe d-orbital deformation of the Pt sites, preventing them from effectively bonding with the electrons in the non-bonding orbitals of Cl in the C-Cl bond, resulting in excellent selectivity for chloroaniline. CN116651442A reports a surface-confined, atomically dispersed Pt@SiO2-N catalyst prepared using atomic layer deposition (ALD). This catalyst achieved a 99% yield of p-chloroaniline at a reaction temperature of 80°C. However, this ALD method suffers from drawbacks such as slow deposition rate, limited and expensive precursors, complex deposition mechanism, and high equipment costs, which severely restrict its industrial production. Therefore, it is particularly important to develop a universal and efficient method to prepare atomically dispersed Pt-based catalysts on a large scale to improve the selectivity of halogenated nitrobenzenes in hydrogenation to halogenated aromatic amines. Summary of the Invention

[0004] In view of this, the present invention provides a method for preparing an atomic-level PtFe bimetallic supported catalyst and its application in the selective hydrogenation of halogenated nitrobenzenes. The atomic-level PtFe bimetallic supported catalyst with the advantages of low Pt loading, high atomic utilization, high activity, high selectivity and easy recycling is prepared by a strong electrostatic adsorption method. The hydrogen overflow effect between Pt and the defect-rich reducible oxide support and the FeO x The adsorption of -NO2 groups by species enables the efficient preparation of halogenated anilines under mild conditions, effectively solving the problems of complex catalyst preparation process, low activity and selectivity in the existing technology.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] In the first step, the reducible metal oxide support prepared by the hydrothermal method is pretreated in a reducing atmosphere such as H2 or H2 / Ar mixed gas to obtain a defect oxide MO with a surface rich in oxygen vacancies and coordinated unsaturated metal cations. x ;

[0007] In the second step, the MO obtained in the first step x The carrier is dispersed in water, and then the pH regulator is added dropwise to adjust the MO x After dispersion, a precursor solution containing Pt and Fe was added and stirred at room temperature for 0.5-6 h. After centrifugation, overnight drying, calcination at 250-500 °C and reduction at 100-300 °C, atomically dispersed PtFe / MO was obtained. x Bimetallic catalysts.

[0008] In the third step, the prepared PtFe bimetallic supported catalyst was used in the selective hydrogenation reaction of halonitrobenzene. In a high-pressure reactor, using p-chloronitrobenzene as raw material, the selective hydrogenation performance evaluation experiment was carried out at a reaction temperature of 40~60 ℃ and a H2 pressure of 1 MPa.

[0009] Preferably, the reducible oxide carrier in step 1 is one or more of CeO2, WO3, Nb2O5, TiO2, ZrO2 and MoO3.

[0010] Preferably, in step 1, the carrier pretreatment temperature is 200-400° C., and the calcination time is 1-2 h.

[0011] Preferably, the pH adjuster in step 2 is one or more of Na2CO3, K2CO3, Li2CO3, NaHCO3, KHCO3, NH3∙H2O, (NH4)2CO3, NH4HCO3, 3-aminopropyltrimethoxysilane and ethylenediamine solution, and the solution concentration is 0.01~0.2 mol / L.

[0012] The pH regulator in step 2 is one or more of Na2CO3, K2CO3, Li2CO3, NaHCO3, KHCO3, NH3∙H2O, (NH4)2CO3, NH4HCO3, 3-aminopropyltrimethoxysilane (APTMS) and ethylenediamine solution with a concentration of 0.01-0.2 mol / L. For negatively charged metal anion precursors, the pH value is adjusted to be lower than MO x The zero charge point of the surface enriches the positive charge, and for the positively charged metal cation precursor, the pH value is adjusted to be higher than MO x The zero charge point makes its surface negatively charged. x The surface-enriched charged ions with opposite electrical properties can be strongly adsorbed on MO by electrostatic adsorption. x Highly dispersed PtFe / MO is formed on the surface x Supported catalyst.

[0013] Preferably, the Pt precursor in step 2 is one or more of (NH4)2PtCl6, K2PtCl6, Na2PtCl6, H2PtCl6, Pt(NH3)4(NO3)2, Pt(acac)2, K2Pt(NO2)4 and Pt(NH3)4Cl2.

[0014] The Fe precursor is one or more of Fe(NO3)3, FeCl3, Fe(acac)3, FeCl2, FeSO4, and Fe2(SO4)3. The concentrations of the Pt and Fe precursor solutions are 0.5-5 and 3-12 mmol / L, respectively, and the Fe / Pt molar ratio is 2-6.

[0015] Preferably, in the PtFe bimetallic supported catalyst in step 2, the Pt loading amount is 0.02-0.5 wt%, and the Fe loading amount is 0.05-0.5 wt%.

[0016] Preferably, in step 3, the mass ratio of p-chloronitrobenzene to Pt is 100-435%.

[0017] In summary, compared with the prior art, the present invention has the following advantages:

[0018] (1) The present invention relates to an atomic-level PtFe bimetallic supported catalyst, which is prepared by a strong electrostatic adsorption method. The method is simple to operate and does not require complex or expensive equipment;

[0019] (2) The atomic-level PtFe bimetallic supported catalyst can be synthesized through the hydrogen overflow effect between Pt and reducible metal oxides, the defect sites on the surface of reducible oxides and FeOx The adsorption of oxygen-containing groups (NO₂) simultaneously enhances the hydrogenation activity of halonitrobenzenes and the selectivity of halogenated anilines under mild conditions. The catalyst provided by this invention achieves conversion rates and selectivity exceeding 99%, with no significant dehalogenation byproducts generated over an extended period. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 0.2Pt0.2Fe / WO in Example 1 of the present invention x Spherical aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) image of the catalyst.

[0021] Figure 2 0.2Pt0.2Fe / WO in Example 4 of the present invention x High-magnification transmission electron microscopy (HRTEM) image of the -IM catalyst.

[0022] Figure 3 1 is the p-chloronitrobenzene hydrogenation kinetic curve of Application Examples 1, 12 and 13 of the present invention.

[0023] Figure 4 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0024] In order to more clearly illustrate the purpose, technical solutions and corresponding advantages of the present invention, the present invention will provide a series of catalyst preparation examples and application examples using p-chloronitrobenzene as a probe molecule, and explain in detail the specific operation process and actual application effects of the present invention, thereby verifying the effectiveness and practicality of the present invention.

[0025] In this embodiment, the preparation method of the atomic-grade PtFe bimetallic supported catalyst consists of the following steps:

[0026] (1) Disperse ammonium metatungstate and citric acid in aqueous solution and place in a hydrothermal reactor at 180 °C for 12 h. Cool to room temperature and then wash and dry to obtain light blue WO3. Pre-treat WO3 at 400 °C for 1 h in H2 atmosphere to obtain a surface rich in oxygen vacancies and W δ+ (0<δ<6) dark blue powder WO x ;

[0027] (2) The pre-treated WO xThe product was dispersed in water, and then 30 mL of 0.1 mol / L ammonium bicarbonate solution was added dropwise. After stirring evenly, H2PtCl6 and Fe(NO3)3 solutions were added in sequence and stirred at room temperature for 1 h. After centrifugation and drying, it was placed in a muffle furnace and calcined at 300 °C for 2 h, and then reduced at 200 °C in a H2 atmosphere for 2 h to obtain atomically dispersed 0.2Pt0.2Fe / WO with Pt and Fe loadings of 0.2 wt% and 0.2 wt%, respectively. x Bimetallic catalysts (see Figure 1 ), where Fe is in the form of FeO x Form exists.

[0028] Example 2

[0029] Example 2 was prepared by the impregnation method. No pH regulator was added in step (2). x After adding H2PtCl6 and Fe(NO3)3 solution to the suspension, the mixture was stirred and evaporated to dryness at 80℃. The remaining steps were the same as those in Example 1. HRTEM images showed that the 0.2Pt0.2Fe / WO prepared by this method x -IM catalysts Pt and Fe mainly exist in the form of nanoparticles and the particle sizes are not uniform (e.g. Figure 2 ).

[0030] Examples 3 and 4

[0031] The preparation methods of Examples 3 and 4 are the same as those of Example 1, except that the ammonium bicarbonate solution in step (2) is replaced with 3-aminopropyltrimethoxysilane (APTMS) and ethylenediamine solution.

[0032] Examples 5 to 9

[0033] The preparation methods of Examples 5-9 are the same as those of Example 1, except that:

[0034] The loading amount of Pt in step (2) is 0.2 wt%, and 0.2Pt / WO is obtained. x catalyst;

[0035] In step (2), the loading amount of Pt is 0.2 wt%, and the loading amount of Fe is 0.1 wt%, and 0.2Pt0.1Fe / WO is obtained. x catalyst;

[0036] In step (2), the loading amount of Pt is 0.2 wt%, and the loading amount of Fe is 0.3 wt%, and 0.2Pt0.3Fe / WO is obtained. x catalyst;

[0037] In step (2), the loading amount of Pt is 0.1 wt%, and the loading amount of Fe is 0.2 wt%, and 0.1Pt0.2Fe / WO is obtained. x catalyst;

[0038] In step (2), the loading amount of Pt is 0.3 wt%, and the loading amount of Fe is 0.2 wt%, and 0.3Pt0.2Fe / WO is obtained. x catalyst.

[0039] Examples 10-12

[0040] The preparation methods of Examples 10 to 12 are the same as those of Example 1, except that the reducible oxides in step (1) are CeO2, ZrO2 and TiO2, respectively, to obtain 0.2Pt0.2Fe / CeO x 、0.2Pt0.2Fe / ZrO x and 0.2Pt0.2Fe / TiO x Catalysts. CeO2 is prepared by mixing cerium nitrate with a NaOH solution and then heating it to 100°C for 24 hours. ZrO2 is prepared by mixing zirconyl nitrate with urea in a methanol solution and then hydroheating it at 140°C for 12 hours. TiO2 is prepared by dissolving TiCl4 in an ethylene glycol solution containing a small amount of water and then hydroheating it at 150°C for 4 hours.

[0041] Comparative Examples 1 and 2

[0042] The preparation methods of Comparative Examples 1 and 2 are the same as those of Example 1, except that the reducible metal oxide in step (1) is replaced by non-reducible carriers of commercial activated carbon and SiO2 to obtain 0.2Pt0.2Fe / C and 0.2Pt0.2Fe / SiO2 catalysts.

[0043] Application Examples 1 to 14

[0044] The defect-rich reducible metal oxide-supported PtFe-based catalysts prepared in Examples 1 to 12 and the non-reducing carrier-supported PtFe catalysts prepared in Comparative Examples 1 to 2 were respectively subjected to performance evaluation for the selective hydrogenation of p-chloronitrobenzene to obtain Application Examples 1 to 14. The specific reaction conditions were:

[0045] The catalytic hydrogenation of p-chloronitrobenzene was carried out in a 50 mL stainless steel high-pressure batch reactor. Using anhydrous ethanol as the solvent, the mass ratio of p-chloronitrobenzene (p-CNB) to Pt in the PtFe bimetallic supported catalyst was 4:3:5. The selective hydrogenation performance of p-chloronitrobenzene was evaluated at a hydrogen pressure of 1 MPa and a reaction temperature of 40°C. After the reaction, the reaction mixture was centrifuged, and the supernatant was analyzed by gas chromatography. The product composition was confirmed by gas chromatography-mass spectrometry.

[0046] Application Examples 15 and 16

[0047] The atomic-grade 0.2Pt0.2Fe / WO prepared in Example 1 x The selective hydrogenation experiment of p-CNB was carried out under the conditions of p-CNB / Pt mass ratio of 238 and 100, respectively, to obtain the corresponding application examples 15 and 16. The other conditions were the same as those of application examples 1 to 14. The kinetic data obtained from application examples 1, 15 and 16 were plotted as Figure 3 It can be seen that with the increase of p-CNB conversion, the yield of p-chloroaniline gradually increases. When p-CNB is fully converted, the selectivity of p-chloroaniline (p-CAN) can reach more than 99%. More importantly, at a low p-CNB / Pt mass ratio, that is, at an excess of 0.2Pt0.2Fe / WO x Under the catalyst, the selectivity of p-CAN can still be maintained at above 99%. When the reaction time is further extended to 23 h with complete conversion of p-chloronitrobenzene, the selectivity of p-CAN can still reach above 95.6%, indicating that the catalyst significantly inhibits the breakage of the C-Cl bond.

[0048] Table 1. Catalytic performance of a series of PtFe bimetallic supported catalysts for hydrogenation of p-chloronitrobenzene.

[0049]

[0050] The above experiments show that the 0.2Pt0.2Fe / WO with uneven metal particle size prepared by impregnation method x Compared with the IM catalyst, 0.2Pt0.2Fe / WO prepared by strong electrostatic adsorption method x Pt and Fe in the catalyst are highly dispersed and no obvious particles appear. x The introduction of species can increase the adsorption of -NO2 functional groups in p-chloronitrobenzene, thereby improving the hydrogenation activity of p-chloronitrobenzene and the selectivity of p-chloroaniline, and successfully inhibiting the occurrence of dechlorination side reactions. Compared with non-reducing supports activated carbon and SiO2, hydrogen is activated on Pt and overflows to the reducible oxide WO x 、CeO x 、ZrO x , TiO2 surface can significantly improve the hydrogenation activity of 4-chloronitrobenzene. In addition, the surface of the reducible oxide after hydrogen reduction is rich in oxygen vacancies and coordinated unsaturated metal cations, which can promote the adsorption of oxygen-containing groups -NO2 on the catalyst surface, which is beneficial to the hydrogenation of -NO2 and inhibits the breakage of C-Cl bonds. Therefore, this PtFe bimetallic catalyst prepared by strong electrostatic adsorption method has atomically dispersed precious metal Pt, which improves the atomic utilization of Pt, and also improves the atomic utilization of Pt through FeOx The species, active component Pt and reducible oxide defect sites synergistically catalyze the selective hydrogenation of p-chloronitrobenzene, greatly improving the yield of p-chloroaniline.

[0051] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. Application of atomic-scale PtFe bimetallic supported catalysts in the selective hydrogenation of halonitrobenzenes to halogenated anilines; The preparation method of the atomic-level PtFe bimetallic supported catalyst comprises the following steps: (1) Pre-reduction treatment of the carrier: The reducible oxide carrier is calcined in a reducing atmosphere of H2 or H2 / Ar mixed gas to obtain a defect oxide MO with a surface rich in oxygen vacancies and coordinated unsaturated metal cations. x ; (2) Preparation of PtFe / MO by strong electrostatic adsorption method x Catalyst: MO obtained in step (1) x Disperse in water, then add pH regulator drop by drop to adjust MO x The isoelectric point of the surface is obtained by adding a precursor solution containing Pt and Fe after dispersion and stirring at room temperature. After centrifugation, drying, calcination and reduction, atomically dispersed PtFe / MO is obtained. x Bimetallic catalysts.

2. The use according to claim 1, characterized in that The prepared catalyst is placed in a high-pressure reactor with a mass ratio of halonitrobenzene to Pt of 100-435%. The halonitrobenzene is selectively hydrogenated to produce halogenated aniline at a reaction temperature of 40-60°C and a H2 pressure of 1-2 MPa.

3. The use according to claim 1, characterized in that The reducible oxide carrier is selected from one or more of CeO2, WO3, Nb2O5, TiO2, ZrO2 and MoO3, and the defective oxide MO after reduction is x CeO x , WO x 、NbO x 、TiO x 、ZrO x and MoO x One or more of .

4. The use according to claim 1, characterized in that In the step (1), the carrier pre-reduction calcination temperature is 150-500°C, and the calcination time is 0.5-6 h.

5. The use according to claim 4, characterized in that In the step (1), the carrier pre-reduction calcination temperature is 200-400°C, and the calcination time is 1-2 h.

6. The use according to claim 1, characterized in that The pH regulator in step (2) is one or more of Na2CO3, K2CO3, Li2CO3, NaHCO3, KHCO3, NH3∙H2O, (NH4)2CO3, NH4HCO3, 3-aminopropyltrimethoxysilane and ethylenediamine solution, and the solution concentration is 0.01~0.2 mol / L.

7. The use according to claim 1, characterized in that In the step (2), the Pt precursor is one or more of (NH4)2PtCl6, K2PtCl6, Na2PtCl6, H2PtCl6, Pt(NH3)4(NO3)2, Pt(acac)2, K2Pt(NO2)4 and Pt(NH3)4Cl2; the Fe precursor is one or more of Fe(NO3)3, FeCl3, Fe(acac)3, FeCl2, FeSO4 and Fe2(SO4)3.

8. The use according to claim 1, characterized in that In step (2), the concentration of the Pt precursor solution is 0.5-5 mmol / L, the concentration of the Fe precursor solution is 3-12 mmol / L, and the molar ratio of Fe to Pt is 2-6.

9. The use according to claim 1, characterized in that In step (2), the calcination temperature is 250-500°C, and the calcination time is 1-4 h; the reduction temperature is 100-300°C, and the reduction time is 0.5-3.5 h; the Pt loading is 0.02-0.5 wt%, and the Fe loading is 0.05-0.5 wt%.

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