Preparation and application of supported Pt-based alloy catalyst

Abstract

The invention belongs to the technical field of catalysts, and relates to preparation and application of a supported Pt-based alloy catalyst. The Pt-based alloy is confined in a KIT-6 mesoporous channel through a double-solvent impregnation method, and a metal precursor preferentially enters the channel by utilizing competitive adsorption of a hydrophilic solvent and a hydrophobic solvent, so that uniform distribution of metal particles in the channel is realized, and agglomeration of the metal particles on the outer surface of the carrier is effectively avoided. Rich silicon hydroxyl on the surface of the KIT-6 carrier is used as an anchoring point, so that the interaction between metal and the carrier is enhanced, and the stability of the catalyst is improved. The Pt-based alloy catalyst prepared by the invention shows excellent C = O bond selectivity in the selective hydrogenation reaction of cinnamyl aldehyde, and the preparation process is simple, easy to amplify and good in industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology and relates to the preparation and application of a supported Pt-based alloy catalyst. Background Technology

[0002] Selective hydrogenation of α,β-unsaturated aldehydes is an important catalytic reaction in the fine chemical industry. The hydrogenation products, unsaturated alcohols, are key raw materials for the synthesis of fragrances, pharmaceutical intermediates, food additives, and pesticide chemicals. Typical α,β-unsaturated aldehydes, such as cinnamaldehyde, citral, and furfural, contain both C=C and C=O double bonds in their molecular structures, forming a conjugated system. From a thermodynamic perspective, the bond energy of the C=C double bond (approximately 614 kJ / mol) is lower than that of the C=O double bond (approximately 745 kJ / mol), making the hydrogenation of the C=C double bond thermodynamically more favorable. However, in actual catalytic hydrogenation processes, due to the conjugation effect, there is competition for adsorption and hydrogenation between the C=C and C=O double bonds, leading to a complex product distribution that may result in saturated aldehydes, unsaturated alcohols, or even the completely hydrogenated product, a saturated alcohol. Therefore, developing catalysts that selectively catalyze the hydrogenation of C=O double bonds while retaining the C=C double bonds is of significant industrial application value for improving the yield of unsaturated alcohols and reducing separation costs.

[0003] Currently, catalysts for the selective hydrogenation of α,β-unsaturated aldehydes mainly fall into two categories: homogeneous catalysts and heterogeneous catalysts. Homogeneous catalysts are primarily water-soluble complexes of transition metals such as Ru, Rh, and Pd. While they exhibit high selectivity, their high cost, difficulty in separation and recovery, and inability to be recycled limit their application in industrial production. Heterogeneous catalysts mainly consist of supported noble metal catalysts (such as Pt, Pd, Ru, and Ir) and non-noble metal catalysts (such as Ni, Co, and Cu). Studies have shown that Pd-based catalysts exhibit high selectivity for hydrogenation of C=C double bonds, while Pt-based catalysts tend to selectively hydrogenate C=O double bonds to form unsaturated alcohols. However, the activity and selectivity of single-metal Pt catalysts under mild reaction conditions still need improvement, and the high cost of noble metal Pt also restricts its large-scale application. Therefore, how to achieve selective hydrogenation of C=O bonds through catalyst structure design has long been a research hotspot and challenge in this field. Researchers often introduce a second metal (such as Fe, Co, Ni, Zn, etc.) to form an alloy with Pt. By modulating the electronic structure of Pt through electronic effects, they can effectively enhance the adsorption and activation ability of C=O bonds. Patent application CN115337936A discloses a PtCo / C catalyst, in which the strong interaction between Pt and Co causes charge transfer from Co to Pt. Co carries a partial positive charge, which readily interacts with the O atoms on C=O and activates the C=O bond, thereby improving the selectivity of C=O bond hydrogenation. Patent application CN115920953A discloses a PtCo@Y catalyst for the selective hydrogenation of 3-nitrostyrene. It utilizes metal-support interactions to modulate the catalyst's microstructure, forming a PtCo intermetallic compound, which alters the electron density of Pt and reduces the aggregation of Pt nanoparticles, thus achieving the regulation of catalytic performance. In the preparation of synthetic catalysts, compared to the traditional impregnation method, which relies on capillary action to directly load the active component onto the support surface and is prone to uneven distribution and agglomeration due to migration of the active component to the pores during drying, the dual-solvent impregnation method pre-fills the pores of the support with one solvent and then places it in another immiscible solvent containing the active component. This utilizes a mild liquid-liquid interface diffusion mechanism to replace the violent solvent evaporation and migration process. This strategy not only significantly suppresses the surface enrichment and agglomeration of the active component through spatial confinement effect, achieving highly uniform loading and smaller nanoparticle size from the inside of the pores outward, but also avoids pore blockage to maintain the original specific surface area and mass transfer performance of the support. Furthermore, because the active component is almost quantitatively deposited in the confined solvent within the pores, the theoretical loading utilization rate is close to 100%.

[0004] The mesoporous molecular sieve KIT-6, with its three-dimensional ordered mesoporous structure and abundant surface silanol groups, is an ideal catalyst support. Developing a dual-solvent impregnation method to uniformly confine Pt-based alloys within the pores of KIT-6 is of great significance for improving the dispersibility and stability of the catalyst. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a supported Pt-based alloy catalyst under mild conditions, which improves the dispersibility and catalytic stability of metal particles by uniformly confining the Pt-based alloy within the mesoporous channels of KIT-6.

[0006] The technical solution of the present invention: A method for preparing a supported Pt-based alloy catalyst includes the following steps: (1) Dehydrate the mesoporous molecular sieve KIT-6 under vacuum conditions at a temperature of 100-200℃ for 4-14 hours. (2) Disperse the mesoporous molecular sieve KIT-6, which has undergone dehydration treatment in step (1), in a hydrophobic solvent, and sonicate it for 0.5-1.5 hours to obtain a uniform dispersion system; the hydrophobic solvent is n-hexane or cyclohexane; (3) Using a dual solvent impregnation method, Pt and the precursor of the second metal are dissolved in a hydrophilic solvent to prepare a precursor solution. The precursor solution is added dropwise to the dispersion system in step (2), stirred and impregnated at room temperature for 2-8 hours, and the upper layer solution is removed after standing. The solid product is collected and dried at 15-60℃. The hydrophilic solvent is water, ethanol or ethylene glycol. (4) The solid product of step (3) is reduced at 100-600℃ for 2-10 hours in a hydrogen atmosphere, with a heating rate of 2-5℃ / min and a cooling rate of 1-10℃ / min to obtain a supported Pt-based alloy catalyst.

[0007] The precursor of Pt is chloroplatinic acid, chloroplatinate, or platinum acetylacetonate, the loading of Pt is 0.1-3%, and the molar ratio of Pt to the second metal is 1:(0.5-10).

[0008] The second metal is Co, Mo, Fe, Ni, Zn, Cu, W, Sn, or Ga.

[0009] The precursors of the second metal Co are cobalt nitrate, cobalt acetylacetonate, or cobalt acetate, with a Co loading of 0.1-5%.

[0010] The precursor for the second metal Mo is ammonium molybdate, with a Mo loading of 0.1-5%.

[0011] The precursor of the second metal Fe is ferric nitrate, with a Fe loading of 0.1-5%.

[0012] The precursor for the second metallic Ni is nickel nitrate, with a Ni loading of 0.1-5%.

[0013] The precursor for the second metal Zn is zinc nitrate, with a Zn loading of 0.1-5%.

[0014] The precursor for the second metal Cu is copper nitrate, with a Cu loading of 0.1-5%.

[0015] The precursor of the second metal W is ammonium metatungstate, with a W loading of 0.1-5%.

[0016] The precursor for the second metal Sn is tin tetrachloride, with a Sn loading of 0.1-5%.

[0017] The precursor for the second metal Ga is gallium nitrate, with a Ga loading of 0.1-5%.

[0018] This invention provides an application of the supported Pt-based alloy catalyst obtained by the above preparation method in the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol. The reaction conditions are: reaction temperature 40-100℃, hydrogen pressure 0.5-3 MPa, solvent is isopropanol or toluene, and reaction time 0.5-4 hours.

[0019] The beneficial effects of this invention are: (1) The present invention confines the Pt-based alloy within the KIT-6 mesoporous channels by a dual solvent impregnation method. By utilizing the competitive adsorption of hydrophilic and hydrophobic solvents, the metal precursor preferentially enters the channel, achieving uniform distribution of metal particles within the channel and effectively avoiding the aggregation of metal particles on the outer surface of the carrier.

[0020] (2) The present invention utilizes the abundant silanol groups on the surface of the KIT-6 support as anchoring points, which enhances the interaction between the metal and the support and improves the stability of the catalyst.

[0021] (3) The Pt-based alloy catalyst prepared by the present invention exhibits excellent C=O bond selectivity (>90%) in the selective hydrogenation reaction of cinnamaldehyde, and the preparation process is simple and easy to scale up, with good prospects for industrial application. Attached Figure Description

[0022] Figure 1 The XRD patterns are those of the catalysts prepared in Examples 1 and 10-13 of this invention.

[0023] Figure 2The images shown are HRTEM images of the PtCo2 / KIT-6-200 catalyst prepared in Example 1 of this invention, where (a) is a low-magnification HRTEM image and (b) is a high-magnification HRTEM image.

[0024] Figure 3 The nitrogen physisorption diagrams are for the catalysts prepared in Examples 1 and 10-13 of this invention.

[0025] Figure 4 The pore size distribution diagrams are for the catalysts prepared in Examples 1 and 10-13 of this invention. Detailed Implementation

[0026] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0027] Example 1 Preparation of PtCo2 / KIT-6-200 catalyst: Step 1: Dry 0.5 g of KIT-6 molecular sieve at 150°C under vacuum for 12 hours.

[0028] Step 2: While still hot, weigh 0.1g of KIT-6 molecular sieve into a 100mL volumetric flask and add 20mL of n-hexane. Sonicate for 60min to ensure good dispersion in the solution.

[0029] Step 3: Measure 56 μL of chloroplatinic acid aqueous solution (50 mg / mL) and 10.0 mg of Co(NO3)2·6H2O and dissolve them in the chloroplatinic acid aqueous solution. Disperse them by sonication and record the solution as solution A.

[0030] Step 4: Slowly add the prepared solution A dropwise to the pretreated KIT-6 system, stir at room temperature for 6 hours, remove the upper layer of n-hexane after standing, and dry at room temperature for 8 hours.

[0031] Step 5: The solid was reduced with hydrogen at 200 °C for 4 h under a hydrogen atmosphere at a heating rate of 5 °C / min to obtain the PtCo2 / KIT-6-200 catalyst.

[0032] Example 2 Preparation of PtCo2 / KIT-6-200-2h catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the reduction time at 200°C is changed to 2 hours.

[0033] Example 3 Preparation of PtCo2 / KIT-6-200-6h catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the reduction time at 200°C is changed to 6 hours.

[0034] Example 4 Preparation of PtCo2 / KIT-6-200-8h catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the reduction time at 200°C is changed to 8 hours.

[0035] Example 5 Preparation of PtCo2 / KIT-6-200-10h catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the reduction time at 200°C is changed to 10 hours.

[0036] Example 6 Preparation of PtCo2 / KIT-6-CYH catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the hydrophobic solvent used in step 2 is replaced with cyclohexane instead of n-hexane.

[0037] Example 7 Preparation of PtCo2 / KIT-6-Et catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the hydrophilic solvent used in step 3 is replaced with ethanol instead of water.

[0038] Example 8 Preparation of PtCo2 / KIT-6-EG catalyst: This implementation is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the hydrophobic solvent used in step 3 is replaced with ethylene glycol instead of water.

[0039] Example 9 Preparation of PtCo2 / KIT-6-100 catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the reduction temperature is 100°C.

[0040] Example 10 Preparation of PtCo2 / KIT-6-300 catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the reduction temperature is 300°C.

[0041] Example 11 Preparation of PtCo2 / KIT-6-400 catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the reduction temperature is 400°C.

[0042] Example 12 Preparation of PtCo2 / KIT-6-500 catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the reduction temperature is 500°C.

[0043] Example 13 Preparation of PtCo2 / KIT-6-600 catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the reduction temperature is 600°C.

[0044] Example 14 Preparation of PtCo3 / KIT-6-200 catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that 15.0 mg of Co(NO3)2·6H2O is added in step 3.

[0045] Example 15 Preparation of PtCo4 / KIT-6-200 catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that 20.0 mg of Co(NO3)2·6H2O is added in step 3.

[0046] Example 16 Preparation of PtCo5 / KIT-6-200 catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that 25.0 mg of Co(NO3)2·6H2O is added in step 3.

[0047] Example 17 Preparation of Pt2Co / KIT-6-200 catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that 112 μL of chloroplatinic acid aqueous solution (50 mg / mL) is added in step 3.

[0048] Example 18 Preparation of Pt3Co / KIT-6-200 catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that 168 μL of chloroplatinic acid aqueous solution (50 mg / mL) is added in step 3.

[0049] Example 19 Preparation of Pt4Co / KIT-6-200 catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that 224 μL of chloroplatinic acid aqueous solution (50 mg / mL) is added in step 3.

[0050] Example 20 Preparation of PtNi / KIT-6 catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the second metal added is Ni(NO3)2·6H2O, and the reduction temperature is 600℃.

[0051] Example 21 Preparation of PtFe / KIT-6 catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the second metal added is Fe(NO3)3·9H2O, and the reduction temperature is 400℃.

[0052] Example 22 Preparation of PtZn / KIT-6 catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the second metal added is Zn(NO3)2·6H2O, and the reduction temperature is 600℃.

[0053] Example 23 Preparation of PtCu / KIT-6 catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the second metal added is Cu(NO3)2·5H2O, and the reduction temperature is 600℃.

[0054] Example 24 Preparation of PtSn / KIT-6 catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that the second metal is SnCl4·5H2O and the reduction temperature is 500℃.

[0055] Example 25 Preparation of PtW / KIT-6 catalyst: This embodiment is a variation of Example 1. Other conditions are the same as in Example 1, except that the second metal is (NH4)6(H2W) added. 12 O 40 The reduction temperature is 700℃.

[0056] Application Example 1 Performance evaluation of PtCo2 / KIT-6 catalyst in selective hydrogenation of crotonaldehyde.

[0057] Application Example 2 Performance evaluation of PtCo2 / KIT-6 catalyst in the selective hydrogenation of furfural.

[0058] Comparative Example 1 Preparation and performance evaluation of Pt / KIT-6 catalyst: This embodiment is a variation of Example 1. Other implementation conditions are the same as in Example 1, except that Co(NO3)2·6H2O is not added.

[0059] Comparative Example 2 Preparation and performance evaluation of PtCo2 / KIT-6-IMP catalyst: This embodiment is a variation of Example 1, synthesized using the impregnation method.

[0060] Step 1: First, weigh 0.1 g of KIT-6 and dissolve it in a 100 mL volumetric flask, then add 20 mL of deionized water and sonicate for 3 min to ensure good dispersion in the solution.

[0061] Step 2: Pipette 280 μL of chloroplatinic acid solution (10 mg / mL) into 5 mL of deionized water, and label this as solution A. Weigh 10 mg of Co(NO3)2·6H2O and add 5 mL of deionized water, and label this as solution B.

[0062] Step 3: Add solutions A and B to the KIT-6 carrier solution at a rate of 2 drops per second. Stir at room temperature for 6 hours. After sonicating the solution for 1 hour, evaporate the sample to dryness using a rotary evaporator at 80 °C, and then dry it in an oven at 105 °C for 12 hours.

[0063] Step 4: The solid was reduced with hydrogen at 200 °C for 4 h under a hydrogen atmosphere at a heating rate of 5 °C / min to obtain the PtCo2 / KIT-6-IMP catalyst.

[0064] The XRD patterns of Examples 1 and 10-13 are as follows: Figure 1As shown, the characteristic diffraction peaks of the embodiment correspond to Pt3Co alloy metal, and the characteristic diffraction peak of Pt3Co(100) at 2θ=40.5° proves the successful preparation of Pt3Co alloy metal catalyst.

[0065] The transmission electron microscope image of Example 1 is shown below. Figure 2 As shown, the Pt3Co alloy metal dispersion in PtCo2 / KIT-6 is good, and the measured lattice spacing of the metal nanoparticles is 0.222 nm, which belongs to the lattice fringes of the Pt3Co alloy.

[0066] The specific surface area and pore size distribution of Examples 1 and 10-13 were determined by nitrogen physical adsorption. Figure 3 and Figure 4 As shown, the samples all exhibited typical Type IV isotherms, and a distinct Type IV isotherm hysteresis loop was observed in the relative pressure range of P / P0 = 0.6~0.9, indicating that the synthesized material maintained the inherent mesoporous structure of the KIT-6 carrier, and the metal loading did not disrupt the pore order of the carrier.

[0067] Performance evaluation of Pt-based alloy catalysts in the selective hydrogenation of cinnamaldehyde and crotonaldehyde: 0.6 g of the PtCo2 / KIT-6 catalyst prepared in Examples 1-8, 1 mmol of cinnamaldehyde, and 15 mL of isopropanol were added to a stainless steel high-pressure reactor with a 100 mL polytetrafluoroethylene liner. The air inside the reactor was replaced with H2 3-5 times, and 1 MPa of H2 was introduced. The stirring speed of the reactor was set to 750 rpm. The reactor was heated to 60°C within 25 min. After the reaction was completed for 2 h, the high-pressure reactor was rapidly cooled to room temperature using ice water, centrifuged, and the liquid product was analyzed by gas chromatography.

[0068] Table 1

[0069] The results showed that the PtCo2 / KIT-6-200 catalyst in Example 1 exhibited the best performance, with a selectivity for cinnamyl alcohol as high as 96.0%. In contrast, the Pt / KIT-6 catalyst supported solely on Pt metal in Comparative Example 1 showed severe over-hydrogenation, indicating that the introduction of Co effectively regulated the electronic structure of Pt and enhanced its adsorption and activation ability for C=O bonds. Compared with the sample impregnated by the impregnation method in Comparative Example 2, the activity was poorer, indicating that the PtCo2 / KIT-6-200 synthesized by the dual solvent impregnation method can load the active metal component as much as possible within the support pores, resulting in excellent reaction performance.

[0070] Table 2

[0071] The results showed that the PtCo2 / KIT-6-200 catalyst in Application Example 1 also exhibited excellent reactivity and selectivity for crotonaldehyde.

[0072] Table 3

[0073] The results showed that the PtCo2 / KIT-6-200 catalyst in Application Example 2 also exhibited excellent reactivity and selectivity for furfural.

[0074] The catalyst preparation method provided by this invention is simple and easy to scale up. The dual-solvent synthesis scheme anchors the active component inside the pores, achieving a uniform distribution from the inside out and a high degree of dispersion at the nanoscale. The prepared catalyst can be used for the industrial production of cinnamaldehyde to cinnamyl alcohol by selective hydrogenation, and can also be extended to the selective hydrogenation reaction of other α,β-unsaturated aldehydes.

[0075] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing a supported Pt-based alloy catalyst, characterized in that, Includes the following steps: (1) Dehydrate the mesoporous molecular sieve KIT-6 under vacuum conditions at a temperature of 100-200℃ for 4-14 hours. (2) Disperse the mesoporous molecular sieve KIT-6, which has undergone dehydration treatment in step (1), in a hydrophobic solvent, and sonicate it for 0.5-1.5 hours to obtain a uniform dispersion system; the hydrophobic solvent is n-hexane or cyclohexane; (3) Using a dual solvent impregnation method, Pt and the precursor of the second metal are dissolved in a hydrophilic solvent to prepare a precursor solution. The precursor solution is added dropwise to the dispersion system in step (2), stirred and impregnated at room temperature for 2-8 hours, and the upper layer solution is removed after standing. The solid product is collected and dried at 15-60℃. The hydrophilic solvent is water, ethanol or ethylene glycol. (4) The solid product of step (3) is reduced at 100-600℃ for 2-10 hours in a hydrogen atmosphere, with a heating rate of 2-5℃ / min and a cooling rate of 1-10℃ / min to obtain a supported Pt-based alloy catalyst.

2. The method for preparing the supported Pt-based alloy catalyst according to claim 1, characterized in that, The precursor of Pt is chloroplatinic acid, chloroplatinate, or platinum acetylacetonate, and the loading of Pt is 0.1-3%.

3. The method for preparing the supported Pt-based alloy catalyst according to claim 1, characterized in that, The second metal is Co, Mo, Fe, Ni, Zn, Cu, W, Sn or Ga, and the loading of the second metal is 0.1-5%.

4. The method for preparing the supported Pt-based alloy catalyst according to claim 1, characterized in that, The molar ratio of Pt to the second metal is 1:(0.5-10).

5. The application of a supported Pt-based alloy catalyst obtained by any one of the preparation methods described in claims 1-4 in the selective hydrogenation of cinnamaldehyde to cinnamyl alcohol, characterized in that, The reaction conditions are: reaction temperature 40-100℃, hydrogen pressure 0.5-3 MPa, solvent is isopropanol or toluene, and reaction time 0.5-4 hours.

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