Preparation method and application of bimetallic catalyst resistant to CO poisoning

Abstract

The invention relates to a preparation method and application of a bimetallic catalyst resistant to CO poisoning. The catalyst comprises the following components in percentage by weight: 0.5% of Pt, 0.5% of Ru and 99% of TiO2. The bimetallic PtRu / TiO2 catalyst resistant to CO poisoning is developed by using an isovolumetric-co-impregnation method through a lattice matching induced epitaxial growth strategy, the electronic structure of the catalyst can be adjusted, the CO poisoning resistance of the catalyst can be effectively enhanced, and the bimetallic PtRu / TiO2 catalyst still shows excellent nitrobenzene hydrogenation performance under the conditions that the temperature is 35 DEG C and the CO content is 5000 ppm. The catalyst has the advantages of simple and easy synthesis process, mild preparation conditions, easy industrial amplification production, and wide application prospects.

Description

Technical Field

[0001] This application relates to a CO-poison-resistant bimetallic catalyst, its preparation method, and its application, belonging to the field of catalysts. Background Technology

[0002] Aniline is a core chemical raw material for the production of diphenylmethane diisocyanate (MDI), and it is widely used in industries such as dyes, pesticides, pharmaceuticals, and fine chemicals. Currently, the mainstream industrial process for producing aniline is the liquid-phase catalytic hydrogenation of nitrobenzene using hydrogen as a reducing agent. Compared to gas-phase hydrogenation and the gradually phased-out iron powder reduction method, the liquid-phase hydrogenation process using supported noble metals (such as Pt and Pd) has significant advantages, including milder reaction conditions and higher equipment capacity, and has enormous development potential.

[0003] Although supported noble metal catalysts exhibit excellent performance in hydrogenation, their extremely high hydrogenation activity often leads to over-hydrogenation side reactions, reducing the selectivity of the target product. From an economic perspective, directly using inexpensive industrial crude hydrogen (especially crude hydrogen containing CO) instead of expensive high-purity hydrogen in the hydrogenation process offers a significant cost advantage. However, conventional Pt-based catalysts are extremely sensitive to CO; CO molecules readily undergo strong coordination adsorption with noble metal surfaces, occupying catalytic active sites. Even trace amounts of CO impurities in the crude hydrogen can cause Pt-based catalysts to rapidly and severely poison with CO, resulting in complete loss of activity.

[0004] Therefore, to address the shortcomings and defects of existing Pt-based catalysts in stable operation under CO-containing crude hydrogen conditions, a bimetallic catalysis strategy is introduced. By regulating the chemical properties of the catalyst through a second component promoter, a novel catalyst is developed that can control the appropriate hydrogenation and has excellent resistance to CO poisoning. This aims to overcome the technical bottleneck of directly hydrogenating nitrobenzene to aniline using crude hydrogen, thereby significantly reducing industrial production costs. Summary of the Invention

[0005] This invention provides a catalyst that is resistant to CO poisoning and has high catalytic activity for the liquid-phase hydrogenation synthesis of aniline from nitrobenzene under crude hydrogen conditions.

[0006] A CO-poison-resistant bimetallic PtRu / TiO2 catalyst is composed of an active component and a support: the active component is Pt and Ru, wherein the mass percentage content of the active component Pt is 0.5%; the mass percentage content of the active component Ru is 0.5%; and the support is TiO2, which has a mass percentage content of 99%.

[0007] Preferably, the support is rutile TiO2; the bimetallic active components are Pt and Ru. Both the rutile TiO2 support and platinum group metal oxides (including PtO2 and RuO2) belong to the tetragonal crystal system and have similar cell parameters, enabling good lattice matching to induce epitaxial growth on the support surface. When the two platinum group metal oxides are co-supported on the rutile TiO2 support, it promotes tight bonding between the bimetallic oxides, effectively regulating the electronic state of the noble metals to improve the catalyst's resistance to CO poisoning.

[0008] Preferably, the precursors of the active components Pt and Ru are platinum nitrate and ruthenium nitrate solutions.

[0009] The preparation method of the CO-poison-resistant bimetallic PtRu / TiO2 catalyst, using an equal-volume co-impregnation method, includes the following steps:

[0010] (1) Take a certain amount of rutile TiO2 support and dry it in an oven until constant weight. Then add deionized water until the TiO2 support is completely wetted. Weigh the mass of the added deionized water to obtain and calculate the water absorption rate of the rutile TiO2 support.

[0011] (2) The dried TiO2 support from step (1) is added to a mixed solution of platinum nitrate and ruthenium nitrate, and deionized water is added according to the measured water absorption rate until the TiO2 support is completely wetted.

[0012] (3) The mixture obtained in step (2) was ultrasonically stirred for 0.5 hours at room temperature, and then the mixture was placed in a cool, dark place to stand and age for 6 hours to obtain the impregnated catalyst precursor.

[0013] (4) The catalyst precursor obtained in step (3) was dried in an oven at 110 °C for 12 hours and calcined in air at 400 °C for 2 hours to obtain the double noble metal oxide PtRuO. x / TiO2 catalyst;

[0014] (5) The double noble metal oxide PtRuO obtained in step (4) x The CO-poison-resistant bimetallic PtRu / TiO2 catalyst was prepared by reducing the TiO2 catalyst at 300 °C in a 10 vol% H2 / Ar atmosphere for 2 hours.

[0015] In step (1), the determination of the water absorption rate of the carrier can accurately control the solution volume in the subsequent co-impregnation process, meet the requirements of equal volume impregnation, and ensure that the active components are uniformly dispersed on the carrier surface.

[0016] In step (2), the platinum nitrate and ruthenium nitrate, as precursors of the active components, have a good co-impregnation effect on the support, which is beneficial for subsequent calcination to form a tightly coupled double noble metal oxide.

[0017] In step (3), the ultrasonic stirring and light-protected static aging can promote the full and uniform dispersion of the active metal precursor on the surface of the TiO2 support.

[0018] In step (4), the calcination in the air atmosphere causes the two noble metals to grow epitaxially on the surface of the TiO2 support based on lattice matching, forming a unique atomic layer of the two noble metal oxides.

[0019] The PtRu / TiO2 catalyst was applied to the hydrogenation of nitrobenzene to aniline under crude hydrogen conditions. The test conditions were: 10 mg catalyst, 4 mL cyclohexane, 50 mg nitrobenzene, 2 MPa hydrogen gas (pure hydrogen or crude hydrogen), and reaction at 35 °C for 1.5 h.

[0020] Compared with the prior art, the present invention has the following characteristics:

[0021] This invention addresses the shortcomings of existing technologies that use conventional noble metal catalysts to reduce nitrobenzene to aniline, where rapid catalyst deactivation is caused by the susceptibility to poisoning from trace amounts of CO impurities in crude hydrogen. It provides a novel bimetallic catalyst with a simple preparation process and strong resistance to CO poisoning. Even under crude hydrogen conditions at 35 °C containing 5000 ppm CO, this catalyst exhibits excellent hydrogenation activity and selectivity, and offers advantages such as simple operation, effective utilization of inexpensive crude hydrogen, and reduced production costs. Attached Figure Description

[0022] Figure 1 This is a scanning transmission electron microscope image of the PtRu / TiO2 catalyst after reduction treatment in Example 1.

[0023] Figure 2 The following are X-ray photoelectron spectra of the catalysts prepared in Example 1 and Comparative Examples 1 and 2. (a) XPS diagram of the Pt 4f orbitals of the catalysts prepared in Example 1 and Comparative Example 1; (b) XPS diagram of the Ru 3d orbitals of the catalysts prepared in Example 1 and Comparative Example 2.

[0024] Figure 3 The graph shows the hydrogenation performance of nitrobenzene under pure hydrogen conditions for the catalysts prepared in Examples 1, 2 and Comparative Examples 1, 2.

[0025] Figure 4 The graph shows the performance of the catalysts prepared in Examples 1, 2 and Comparative Examples 1, 2 under crude hydrogen conditions for the hydrogenation of nitrobenzene.

[0026] Figure 5 The graph shows the hydrogenation rate of nitrobenzene under crude hydrogen conditions for the catalysts prepared in Examples 1, 2 and Comparative Examples 1, 2.

[0027] Figure 6 The images show HD exchange mass spectra of the catalysts prepared in Example 1 and Comparative Examples 1 and 2 in the presence of CO. Detailed Implementation

[0028] The present invention will now be described in detail with reference to specific embodiments.

[0029] Comparative Example 1:

[0030] Preparation of Pt / TiO2 catalyst:

[0031] (1) 1.000 g of commercial rutile TiO2 was dried in a vacuum oven at 80 ℃ for 12 h, and then ground into powder in a mortar to obtain TiO2 support. Another 1.000 g of the above rutile TiO2 support was placed in a 10 mL beaker, and deionized water was added dropwise while stirring until TiO2 reached saturation adsorption (i.e., completely wetted). The mass of deionized water added was weighed, and the water absorption rate of the commercial rutile TiO2 support was measured to be 0.88 mL.

[0032] (2) Weigh 0.033 g of platinum nitrate aqueous solution (Pt content is 15.13 wt.%) into a 10 mL beaker, add 854 μL of deionized water to dilute and form a homogeneous noble metal precursor solution;

[0033] (3) Weigh 0.995 g of the powdered TiO2 support obtained in step (1) and add it to the beaker obtained in step (2). Stir it ultrasonically at room temperature for 0.5 h, and then let it stand for 6 h to age, and obtain the impregnated sample.

[0034] (4) The sample obtained in step (3) was dried in a 110 °C oven for 12 h, then calcined in a muffle furnace at 400 °C for 2 h; finally, it was reduced in a 10 vol.% H2 / Ar mixed gas at 300 °C for 2 h to obtain the catalyst Pt / TiO2.

[0035] Comparative Example 2:

[0036] Preparation of Ru / TiO2 catalyst:

[0037] (1) 1.000 g of commercial rutile TiO2 was dried in a vacuum oven at 80 ℃ for 12 h, and then ground into powder in a mortar to obtain TiO2 support. Another 1.000 g of the above rutile TiO2 support was placed in a 10 mL beaker, and deionized water was added dropwise while stirring until TiO2 reached saturation adsorption (i.e., completely wetted). The mass of deionized water added was weighed, and the water absorption rate of the commercial rutile TiO2 support was measured to be 0.88 mL.

[0038] (2) Weigh 0.047 g of ruthenium nitrate aqueous solution (Ru content is 10.64 wt.%) into a 10 mL beaker, add 854 μL of deionized water to dilute and form a homogeneous noble metal precursor solution;

[0039] (3) Weigh 0.995 g of the powdered TiO2 support obtained in step (1) and add it to the beaker obtained in step (2). Stir it ultrasonically at room temperature for 0.5 h, and then let it stand for 6 h to age, and obtain the impregnated sample.

[0040] (4) The sample obtained in step (3) was dried in a 110 °C oven for 12 h, then calcined in a muffle furnace at 400 °C for 2 h; finally, it was reduced in a 10 vol.% H2 / Ar mixed gas at 300 °C for 2 h to obtain the catalyst Ru / TiO2.

[0041] Example 1:

[0042] Preparation of PtRu / TiO2 catalyst:

[0043] (1) 1.000 g of commercial rutile TiO2 was dried in a vacuum oven at 80 ℃ for 12 h, and then ground into powder in a mortar to obtain TiO2 support. Another 1.000 g of the above rutile TiO2 support was placed in a 10 mL beaker, and deionized water was added dropwise while stirring until TiO2 reached saturation adsorption (i.e., completely wetted). The mass of deionized water added was weighed, and the water absorption rate of the commercial rutile TiO2 support was measured to be 0.88 mL.

[0044] (2) Weigh 0.033 g of platinum nitrate aqueous solution (Pt content is 15.13 wt.%) and 0.047 g of ruthenium nitrate aqueous solution (Ru content is 10.64 wt.%) into a 10 mL beaker, add 814 μL of deionized water to dilute and form a homogeneous noble metal precursor solution;

[0045] (3) Weigh 0.990 g of the powdered TiO2 support obtained in step (1) and add it to the beaker obtained in step (2). Stir it ultrasonically at room temperature for 0.5 h, and then let it stand for 6 h to age, and obtain the impregnated sample.

[0046] (4) The sample obtained in step (3) was dried in a 110 °C oven for 12 h, then calcined in a muffle furnace at 400 °C for 2 h; finally, it was reduced in a 10 vol.% H2 / Ar mixed gas at 300 °C for 2 h to obtain the catalyst PtRu / TiO2.

[0047] Example 2:

[0048] Preparation of Pt-Ru-Mix catalyst:

[0049] The catalysts prepared in Comparative Example 1 and Comparative Example 2 were physically mixed at a mass ratio of 1:1 to obtain the catalyst Pt-Ru-Mix.

[0050] Figure 1 This is a scanning transmission electron microscope (STEM) image of the PtRu / TiO2 catalyst after reduction treatment in Example 1. It can be seen that after reduction treatment, PtRuO2 epitaxially grows on the rutile TiO2 surface. x The atomic layers remain tightly bound together, distributed in the form of co-location of bimetallic components.

[0051] Figure 2 The X-ray photoelectron spectra of the catalysts prepared in Example 1 and Comparative Examples 1 and 2 show that, after H2 treatment, compared with the single metal catalyst, the strong interaction between Pt and Ru at the interface in the PtRu / TiO2 bimetallic system enables it to retain a large number of high oxidation state noble metal species, effectively regulating the electronic structure of the active components.

[0052] Performance Evaluation

[0053] Evaluation of the catalytic performance of nitrobenzene hydrogenation under pure hydrogen conditions: 10 mg of the catalyst prepared in Examples 1 and 2 and Comparative Examples 1 and 2, 4 mL of cyclohexane, and 50 mg of nitrobenzene were used. Hydrogen gas (pure hydrogen) was introduced at 2 MPa, the reaction temperature was 35 °C, the stirring speed was 600 rpm, and the reaction time was 1.5 hours. The reaction was carried out in a closed high-pressure reactor. After filtering off the catalyst, the liquid organic phase was collected. The liquid product was analyzed using an Agilent 7820 gas chromatograph equipped with a flame ionization detector (FID). The conversion rate of nitrobenzene was quantified by normalization.

[0054] The results are as follows Figure 3 As shown, under pure hydrogen conditions, all catalysts, including bimetallic PtRu / TiO2, monometallic Pt / TiO2, Ru / TiO2, and physically mixed Pt-Ru-Mix, achieved nitrobenzene conversion rates of over 90% within 1.5 h at a low temperature of 35 °C, with aniline selectivity of 99.9%.

[0055] Evaluation of the catalytic performance of nitrobenzene hydrogenation under crude hydrogen conditions: The effect of CO introduction on catalyst activity was investigated. Other operations were the same as above, except that the composition of hydrogen was adjusted to hydrogen containing 5000 ppm CO.

[0056] The results are as follows Figure 4 As shown, after the introduction of 5000 ppm CO, the single-metal Pt / TiO2, Ru / TiO2, and physically mixed Pt-Ru-Mix catalysts were almost completely deactivated at 35 °C, while the bimetallic PtRu / TiO2 catalyst still maintained a 19.6% nitrobenzene conversion rate and an aniline selectivity of 99.9% within 1.5 h. The synergistic effect of the bimetallic components effectively enhanced the catalyst's resistance to CO poisoning.

[0057] Figure 5 The graph shows the hydrogenation rate of nitrobenzene under crude hydrogen conditions for the catalysts prepared in Examples 1 and 2 and Comparative Examples 1 and 2. After introducing 5000 ppm CO, the intrinsic hydrogenation rate of PtRu / TiO2 is 96.4 mol / L. nitrobenzene mol metal -1 s -1 The activity was 7.4 times, 33.2 times, and 16.1 times that of single-metal Pt / TiO2, Ru / TiO2, and physically mixed Pt-Ru-mix, respectively. The results indicate that the PtRu / TiO2 catalyst exhibits significantly higher intrinsic activity in the CO-resistant hydrogenation of nitrobenzene.

[0058] The catalysts prepared in Examples 1 and Comparative Examples 1 and 2 were subjected to HD exchange tests in the presence of CO: 50 mg of catalyst was loaded into a reaction tube. After reduction pretreatment at 300 °C for 30 min, the catalyst was cooled to room temperature. The gas was switched to a mixture of CO / H2 / Ar = 0.5 / 10 / 89.5 (10 mL / min) and D2 (1 mL / min), and the temperature was increased to 200 °C at a rate of 10 °C / min under programmed temperature rise. The signals at m / z = 2 (H2), 3 (HD), and 4 (D2) were analyzed using a mass spectrometer (OMNI Star™ Gas Analysis System). The mass spectrometry signals were normalized to the equilibrium gas signal of Ar (m / z = 40).

[0059] Depend on Figure 6 It can be seen that the onset temperature of H2-D2 exchange in the presence of CO for the PtRu / TiO2 catalyst is 35 °C, which is significantly lower than the onset temperatures of single-metal Pt / TiO2 (103 °C) and Ru / TiO2 (58 °C). This demonstrates that the bimetallic catalyst has superior hydrogen activation ability resistant to CO poisoning.

[0060] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features, without departing from the spirit and scope of the present invention. All such changes and improvements fall within the scope of the present invention as claimed.

Claims

1. A bimetallic catalyst resistant to CO poisoning, characterized in that, Includes the following components and their weight percentages: Pt: 0.5%, Ru: 0.5%, TiO2: 99%.

2. The method for preparing a CO-poison-resistant bimetallic catalyst according to claim 1, characterized in that, Includes the following steps: A measured amount of TiO2 support was dried to constant weight in an oven. Deionized water was added until the TiO2 support was completely wetted. The mass of deionized water added was weighed to obtain the water absorption rate of the TiO2 support. Subsequently, the TiO2 support was added to a mixed solution of platinum and ruthenium precursors, and deionized water was added until the TiO2 support was completely wetted. The mixture was ultrasonically stirred at room temperature for 0.5 hours. Then, the mixture was aged in a cool, dark place for 6 hours, dried in an oven at 110 °C for 12 hours, calcined in air at 400 °C for 2 hours, and finally reduced in H2 atmosphere at 300 °C for 2 hours to obtain the catalyst product.

3. The CO-poison-resistant bimetallic catalyst according to claim 2, characterized in that, The platinum precursor and ruthenium precursor are platinum nitrate and ruthenium nitrate, respectively.

4. The bimetallic catalyst resistant to CO poisoning according to claim 2, characterized in that, The TiO2 support is a rutile crystal phase.

5. The application of a CO-poison-resistant bimetallic catalyst as described in claims 1-4, characterized in that, The catalyst is used for the hydrogenation of nitrobenzene to aniline under crude hydrogen conditions.

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