An anti-sintering platinum-based catalyst and its preparation and application

Abstract

The present invention relates to an anti-sintering platinum-based catalyst and its preparation and application. The catalyst is a catalyst with a magnesium aluminate spinel structure loaded with Pt, and the total mass percentage of Pt in the catalyst is 0.1-4 wt%. The preparation steps of the catalyst include the preparation of a PtMg x Al2O y solid solution, and finally Pt particles are in-situ generated on the surface of the PtMg x Al2O y solid solution by adjusting the calcination atmosphere. Compared with the prior art, the present invention controls the number of missing Mg sites in the spinel structure lattice by adjusting the feeding ratio of the Mg source and the Al source, ensures that the noble metal Pt can occupy the Mg sites in the spinel lattice, and at the same time adjusts the calcination atmosphere and temperature to control the number of noble metal Pt nanoparticles. The obtained catalyst has high reactivity for treating common polluting atmospheric substances such as propylene and excellent anti-sintering ability. The preparation method has the advantages of simple and easy synthesis steps, good reproducibility, easy control and adjustment, etc.

Description

Technical Field

[0001] The present invention relates to the fields of catalytic technology and environmental catalysis, and particularly to an anti-sintering platinum-based catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] For the elimination treatment of low-concentration pollutants, noble metal platinum catalysts are often used. Although the mass fraction of platinum in these catalysts is relatively low, they can exhibit good pollutant elimination effects. However, during actual use, due to the possible exposure to high temperatures (greater than or equal to 800 °C), the platinum component may undergo sintering. This sintering phenomenon is more severe when the atmosphere contains reducing gases. During sintering, the purification efficiency often drops significantly, and it is difficult for the sintered catalyst to regenerate and restore its original purification efficiency. Therefore, designing and developing platinum catalysts with excellent anti-sintering properties is of great practical and economic significance.

[0003] The existing patented technologies for synthesizing anti-sintering platinum catalysts (CN104338530B, CN105964274A, and CN108355649A) basically have the disadvantages of inconvenient operation and complex raw materials. Although there are examples in the above technologies where noble metal components can withstand high temperatures greater than or equal to 900 °C, these technologies all have certain problems of poor stability and low activity. For example, in CN104338530B, the particle size of the gold-platinum-palladium alloy particles grew to 9.2 nm after being treated at 900 °C, and when the noble metal catalyst treated at 950 °C in CN108355649A was applied to the actual low-concentration propylene combustion elimination reaction, its ignition temperature was higher than 200 °C, failing to meet the requirements of high purification efficiency at low temperatures.

[0004] In summary, there are still difficulties in simply synthesizing highly active platinum catalysts that are resistant to high-temperature sintering. Therefore, it is urgent to develop anti-sintering Pt catalysts to meet the actual industrial needs. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of the above-mentioned existing technologies and provide an anti-sintering platinum-based catalyst and a preparation method thereof, which have good stability and activity.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] One of the technical solutions of the present invention is to provide an anti-sintering platinum-based catalyst, which is a catalyst with a magnesium aluminate spinel structure loaded with Pt. The total mass percentage of Pt in the catalyst is 0.1-4 wt%, the size is 0.4-2.5 nm, and the ratio of magnesium to aluminum elements in the catalyst is 0.8-0.99:2.

[0008] Furthermore, the Pt component exists in the catalyst in two forms. One is in the form of metal nanoparticles on the surface of magnesium aluminate spinel, and the other exists as a high-valence cation located at the missing magnesium site in the lattice of magnesium aluminate spinel.

[0009] Furthermore, the Pt component in the catalyst resists sintering in an oxidative atmosphere at 800 °C to 1000 °C or a reducing atmosphere at 800 to 1000 °C.

[0010] The second technical solution of the present invention lies in providing a preparation method of an anti-sintering platinum-based catalyst, including the following steps:

[0011] (1) Dissolve the corresponding salts of the Pt source precursor, Mg source and Al source precursors in deionized water, with the Mg / Al molar ratio being 0.8:2 to 0.99:2, and then dropwise add an excessive amount of base to control the pH to 11 to 12;

[0012] (2) Let the resulting suspension stand, filter and wash the obtained precipitate, dry it, and grind it into powder;

[0013] (3) Calcinate the powdered solid at 800 °C to 1000 °C in air for 3 to 9 h to obtain a precursor with platinum ions inside the lattice;

[0014] (4) Calcinate the precursor prepared in step (3) at 800 °C to 1000 °C in a reducing atmosphere for 3 to 9 h to obtain the target catalyst PtMg x Al2O y .

[0015] Furthermore, in step (1), the Pt source precursor includes platinum acetylacetonate, chloroplatinic acid, platinum nitrate or tetraammineplatinum nitrate.

[0016] Furthermore, the Mg source and Al source precursors in step (1) include the corresponding sulfates, halides, nitrates or acetates, and the bases used include NaOH, Na2CO3, KOH or K2CO3.

[0017] Furthermore, the air condition in step (3) includes static and flowing states.

[0018] Furthermore, the reducing atmosphere in step (4) includes CO or H2 and their mixed atmospheres.

[0019] Furthermore, by adjusting the feeding ratio of the Mg source and Al source, controlling the number of missing Mg sites in the spinel structure lattice, making Pt located at the missing magnesium sites, and at the same time by adjusting the calcination temperature and atmosphere in steps (3) and (4), adjusting the number of surface Pt metal nanoparticles, the higher the reduction temperature, the more the number of exposed metallic Pt nanoparticles.

[0020] The third technical solution of the present invention lies in providing an application of an anti-sintering platinum-based catalyst, using the catalyst for propylene catalytic combustion.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention utilizes the compatibility of magnesium aluminate spinel with high-valence platinum ions, and the matching interaction between the

[111] plane of platinum metal particles and the

[111] plane of magnesium aluminate spinel. By adjusting the calcination atmosphere and temperature, highly dispersed platinum metal particles can be generated in situ on the surface of the carrier, and a platinum-based catalyst with excellent anti-sintering performance can be prepared. According to the literature (Acta Crystallographica, 1976, A32: 751-767), it is known that the radius of magnesium ions Mg in the magnesium aluminate spinel structure 2+ is 0.086 nm, and the radius of aluminum ions Al 3+ is 0.053 nm. The radius of high-oxidation-state platinum ions Pt 5+ is (0.071 nm), which is smaller than that of magnesium ions Mg 2 + (0.086 nm). Therefore, platinum ions can occupy the magnesium positions lacking in the lattice of the magnesium aluminate spinel carrier. The high-oxidation-state platinum ions located at the magnesium positions in the lattice of the magnesium aluminate spinel carrier in the catalyst are very stable and need to be reduced at high temperature to obtain small-sized platinum metal nanoparticles in situ on the surface. By adjusting the temperature conditions of high-temperature reduction, the amount of surface metallic platinum can be controlled. The higher the reduction temperature, the more exposed metallic platinum nanoparticles.

[0023] 2. The present invention uses an alkali to co-precipitate Pt, Mg sources and Al sources to form MgAl hydroxide containing noble metal Pt, and forms magnesium aluminate spinel containing noble metal Pt by calcination in air at a high temperature (800 °C - 1000 °C). The radius of magnesium ions (0.086 nm) in the spinel structure is larger than that of high-oxidation-state Pt ions (0.071 nm). Therefore, Pt can stably exist in the magnesium positions of the spinel in the form of high-oxidation-state Pt ions, avoiding the sintering of Pt on the surface of the spinel to form large particles in a high-temperature air environment. There is a lattice match between the

[111] plane of surface metallic platinum and the

[111] plane of the magnesium aluminate spinel carrier structure. Coupled with the interaction of platinum ions inside the carrier, the surface metallic platinum has the ability to resist high-temperature sintering.

[0024] 3. The present invention adopts a high-temperature reduction treatment (800 °C - 1000 °C) to reduce some of the platinum ions originally in the magnesium position, and they precipitate out as metallic Pt nanoparticles on the surface. The size range is 0.4 - 2.5 nm. The number of precipitated nanoparticles is positively correlated with the reduction temperature, and their particle size remains unchanged. The matching effect of the

[111] crystal plane of the spinel and the interaction with the internal platinum ions jointly limit the further growth of the surface Pt particles, improving the thermal stability of the catalyst. Even after being aged in an acrylene combustion reaction atmosphere at 1000 °C for 3 h, the final catalyst still exhibits high activity in the acrylene combustion elimination reaction. Description of the Drawings

[0025] Figure 1 It is a diagram showing the relationship between the catalytic acrylene combustion elimination efficiency and temperature before and after the aging of the catalysts of Examples 1, 2, and 3.

[0026] Figure 2 It is a diagram showing the relationship between the catalytic acrylene combustion elimination efficiency and temperature before and after the aging of the catalysts of Example 3, Comparative Example 1, and Comparative Example 2.

[0027] Figure 3 It is the quantitative result of carbon monoxide adsorption and Pt dispersion of the catalysts of Examples 1, 2, and 3.

[0028] Figure 4 It is the X-ray diffraction pattern of the catalysts of Comparative Example 1 and Comparative Example 2, and Examples 1, 4, and 5.

[0029] Figure 5 It is the X-ray photoelectron spectrum of Example 3 after different Ar purge etching treatment times.

[0030] Figure 6 It is the high-angle annular dark-field scanning transmission electron microscope photograph of Example 3. Detailed Embodiment

[0031] The following details the embodiments of the present invention. These embodiments are implemented on the premise of the technical solution of the present invention, and detailed implementation methods and specific operation processes are given. However, the protection scope of the present invention is not limited to the following embodiments. Example 1

[0032] An anti-sintering platinum-based catalyst is prepared by the following method:

[0033] 1) Dissolve 0.009 mol of magnesium acetate, 0.02 mol of aluminum acetate, and platinum nitrate in 250 mL of deionized water (Pt concentration is 0.06 g / L).

[0034] 2) Prepare a NaOH solution with a concentration of 0.7 mol / L, add the NaOH solution to the mixed solution in 1), control the pH to 11 - 12, after standing for 12 h, filter and wash the obtained precipitate, then transfer it to an oven for drying and grind it into powder.

[0035] 3) Calcinate the powdery solid obtained in step 2) in air at 800 °C for 3 h to obtain a precursor with platinum ions inside the crystal lattice.

[0036] 4) Calcinate the precursor obtained in step 3) in a hydrogen atmosphere at 800 °C for 3 h to obtain PtMg 0.9 Al2O y -1 with a platinum content of 0.8 wt%. Example 2

[0037] An anti-sintering platinum-based catalyst is prepared by the following method:

[0038] 1) Dissolve 0.009 mol of magnesium acetate, 0.02 mol of aluminum acetate and platinum nitrate in 250 mL of deionized water (Pt concentration is 0.06 g / L).

[0039] 2) Prepare a NaOH solution with a concentration of 0.7 mol / L, add the NaOH solution to the mixed solution in 1), control the pH to 11 - 12, after standing for 12 h, filter and wash the obtained precipitate, then transfer it to an oven for drying and grind it into powder.

[0040] 3) Calcinate the powdery solid at 800 °C in air for 3 h to obtain a precursor with platinum ions inside the crystal lattice.

[0041] 4) Calcinate the precursor at 900 °C in a hydrogen atmosphere for 3 h to obtain PtMg 0.9 Al2O y -2 with a platinum content of 0.8 wt%. Example 3

[0042] An anti-sintering platinum-based catalyst is prepared by the following method:

[0043] 1) Dissolve 0.009 mol of magnesium acetate, 0.02 mol of aluminum acetate and platinum nitrate in 250 mL of deionized water (Pt concentration is 0.06 g / L).

[0044] 2) Prepare a NaOH solution with a concentration of 0.7 mol / L, add the NaOH solution to the mixed solution in 1), control the pH to 11 - 12, after standing for 12 h, filter and wash the obtained precipitate, then transfer it to an oven for drying and grind it into powder.

[0045] 3) Calcinate the powdery solid at 800 °C in air for 3 h to obtain a precursor with platinum ions inside the crystal lattice.

[0046] 4) Calcinate the precursor at 1000 °C in a hydrogen atmosphere for 3 h to obtain PtMg 0.9 Al2O y -3 with a platinum content of 0.8 wt%. Example 4

[0047] Control the addition amount of platinum nitrate so that the platinum content in the catalyst PtMg 0.9 Al2O y is 0.1 wt%. The rest is the same as in Example 1. Example 5

[0048] Control the addition amount of platinum nitrate so that the platinum content in the catalyst PtMg 0.9 Al2O y is 4 wt%. The rest is the same as in Example 1.

[0049] Comparative Example 1

[0050] 1) Immerse a certain amount of platinum nitrate solution onto 1 g of commercial alumina, place it in an oven to dry, and grind it into powder.

[0051] 2) Calcinate the powdery solid at 800 °C in air for 3 h, and then switch to calcination at 800 °C in a hydrogen atmosphere for 3 h to obtain Pt / Al2O3 with a platinum content of 0.8 wt%.

[0052] Comparative Example 2

[0053] Immerse a certain amount of platinum nitrate solution onto commercially available magnesium aluminate spinel, place it in an oven to dry, grind it into powder, calcinate it at 800 °C in air for 3 h, and then switch to calcination at 800 °C in a hydrogen atmosphere for 3 h to obtain Pt / Mg1Al2O4 with a platinum content of 0.8 wt%.

[0054] Place the above examples and comparative examples in a tubular furnace and age them for 3 h in a flowing 0.2 vol.% C3H6 / 4 vol.% O2 atmosphere at 1000 °C to obtain the corresponding high-temperature aged samples (Example-aged or Comparative Example-aged).

[0055] Catalyst performance test

[0056] (1) Press and screen the powder catalysts prepared from each example, comparative example, and each high-temperature aged sample to ensure that the particle size of the catalyst is between 40 and 60 mesh, and then evaluate the propylene catalytic combustion on a fixed-bed reactor. The evaluation conditions are: the total gas flow rate is 50 mL·min -1, The gas composition is 0.2 vol.% C3H6 / 4 vol.% O2, with N2 as the balance gas, and the mass space velocity is 30000 mL·g -1 ·h -1 .

[0057] The concentration of propylene in the gas entering and leaving the fixed bed was detected by gas chromatography, and the propylene conversion rate was calculated.

[0058] The calculation method of propylene conversion rate is as follows:

[0059]

[0060] Where: r C3H6 is the propylene conversion rate, [C3H6] inlet is the chromatographic area of C3H6 at the inlet, [C3H6] inlet is the chromatographic area of C3H6 at the outlet.

[0061] The reaction performance of the above catalyst applied to the combustion elimination of propylene is shown in Table 1 and Figure 1 and 2 .

[0062] Table 1

[0063]

[0064] In Table 1, T 10 and T 90 respectively represent the corresponding temperatures at 10% and 90% of the propylene combustion elimination conversion rate.

[0065] From Table 1 and Figure 1 and Figure 2 it can be seen that for the catalyst obtained in the embodiment of the present invention, T 10 is less than 150 °C, T 90 is less than 250 °C, while for Comparative Examples 1 and 2, their T 10 are 191 and 170 °C respectively, and T 90 is 258 and 242 °C, much higher than the catalysts of Examples 1-5 above. It is proved that the platinum-based catalyst prepared by the method of the present invention has high activity. Moreover, the present invention breaks the understanding that conventional Pt catalysts are prone to deactivation at high temperatures. The high-temperature reduction treatment of the catalyst of the present invention can improve the propylene combustion elimination activity of the PtMg1Al2O y catalyst. When the reduction temperature ranges from 800 °C to 1000 °C, good activity or stability is still maintained. In addition, after the catalysts of Examples 1, 2, and 3 are further aged, the activity slightly decreases, and T 10 and T 90 only increase by about 10 °C. While for Comparative Examples 1 and 2 after aging, T 10 and T90 All increased by 30 - 40 °C. Among them, Example 3 had the best activity, T 10 decreased from 137 °C in Example 1 to 117 °C, T 90 decreased from 224 °C in Example 1 to 189 °C. The activity of the comparative example was not as good as that of the catalyst of the present invention, especially the typical Example 3-aged catalyst, which further illustrated the excellent stability of the catalyst of the present invention. For Examples 4 - 5 compared with Example 1, the addition amount of Pt changed. It can be seen that after aging, the catalyst activity only decreased slightly, indicating that the Pt content of the catalyst of the present invention has a wide applicable range.

[0066] (2)Quantitative experiment on Pt species exposed on the catalyst surface

[0067] The quantification of Pt species exposed on the catalyst surface was obtained from carbon monoxide pulse adsorption experiments. The experiments were carried out on a Micromeritic Autochem II 2920 chemisorption instrument. 0.05 g of the catalyst was placed in a sample tube and reduced at 300 °C for 1 h with a 50 mL / min 10 vol.% H2 / N2 gas mixture. After that, the gas was switched to He and purged for 0.5 h, then cooled to room temperature. Then, a pulse adsorption experiment was carried out with 1 vol.% CO + 2 vol.% Ar + 97 vol.% He, and the adsorption signal of CO was detected with a Hiden VII mass spectrometer. Based on CO / Pt = 1, the amount of Pt species exposed on the surface can be calculated. Then, the amount of Pt species exposed on the surface was divided by the total Pt content of the catalyst to calculate the platinum dispersion.

[0068] The results are as Figure 3 shown. It can be seen from the figure that the higher the reduction temperature, the higher the Pt dispersion and the greater the CO adsorption amount. This quantitative result proves that Examples 1, 2, and 3 have high platinum dispersion, and the dispersion of Example 3 exceeds 70%, further illustrating the high thermal stability of the catalyst prepared by this method.

[0069] (3)X-ray photoelectron spectroscopy (XPS) test experiment of the catalyst after different Ar purge etching treatment times

[0070] The Ar purge etching treatment and XPS test were both carried out on a Thermo ESCALAB 250Xi instrument, and the intensity of the Ar purge etching was set to the strong gear.

[0071] Figure 4 For Comparative Examples 1 and 2, and the X-ray diffraction spectra of the catalysts of Examples 1, 4, and 5, from Figure 4It can be seen that obvious diffraction peaks of metallic platinum can be observed for the catalysts of Comparative Examples 1 and 2, while only typical characteristic diffraction peaks of magnesium aluminate spinel (PDF# 77-0435) can be observed for Examples 1, 4, and 5. This shows from another aspect that the platinum-based catalyst prepared by this preparation method has good thermal stability and anti-sintering ability.

[0072] Figure 5 Figure 4 is the X-ray photoelectron spectroscopy of Example 3 after different Ar purge etching treatment times. From Figure 5 the XPS spectra with different Ar etching treatment times, it can be seen that the signal of metallic Pt can be observed without etching, while when the etching time reaches 500 s, the signal of Pt species changes from the metallic state to the oxidized state, indicating that the distribution form of Pt in Example 3 is surface metallic state and exists in the form of oxidized state ions inside. This distribution form ensures the excellent thermal stability of Pt on the catalyst.

[0073] Figure 6 Figure 5 is the high-angle annular dark-field scanning transmission electron microscope photograph of Example 3. It can be seen that the particle size of Pt nanoparticles on the catalyst surface is less than 2.5 nm, which proves the high dispersion of Pt in the example and the existence form of surface Pt is nanoparticles, not single atoms.

[0074] As described above, the above 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, without departing from the spirit and scope of the present invention, the technical solutions recorded in the foregoing embodiments can still be modified, or some of the technical features can be equivalently replaced. These changes and improvements all fall within the scope of the present invention claimed.

Claims

1. A sintering-resistant platinum-based catalyst, characterized in that: The catalyst is a Pt-loaded magnesium-aluminum spinel structure catalyst, the total mass percentage of Pt in the catalyst is 0.1-4wt%, the surface metal Pt exists in the form of nanoparticles with a size of 0.4-2.5nm, and the magnesium-aluminum element ratio in the catalyst is 0.8-0.99:2; The catalyst is prepared by the following method: (1) dissolving the corresponding salts of the Pt source precursor, the Mg source and the Al source precursor in deionized water, wherein the Mg / Al molar ratio is 0.8:2 to 0.99:2, and then adding an excess amount of alkali to control the pH to 11 to 12; (2) allowing the generated suspension to stand, filtering and washing the obtained precipitate, drying it, and grinding it into powder; (3) calcining the powdered solid at 800° C. to 1000° C. in air for 3 to 9 hours to obtain a precursor in which platinum ions are located inside the crystal lattice; (4) The precursor obtained in step (3) is calcined at 800°C to 1000°C in a reducing atmosphere for 3 to 9 hours to obtain the target catalyst PtMg x Al2O y ; The Pt component exists in the catalyst in two forms, one is in the form of metal nanoparticles on the surface of magnesium-aluminum spinel, and the other is in the form of high-valent cations located at the magnesium position in the magnesium-aluminum spinel lattice; the number of surface Pt metal nanoparticles is adjusted by adjusting the calcination temperature and calcination atmosphere of step (3) and step (4); the higher the reduction temperature, the greater the number of exposed metal Pt nanoparticles; There is a Mg deficiency in the lattice of Mg-alumina spinel structure.

2. A method for preparing a sintering-resistant platinum-based catalyst as claimed in claim 1, characterized in that: The following steps are involved: (1) Dissolve the corresponding salts of the Pt source precursor, Mg source and Al source precursor in deionized water, then add excess alkali to control the pH to 11-12; (2) allowing the generated suspension to stand, filtering and washing the obtained precipitate, drying it, and grinding it into powder; (3) calcining the powdered solid at 800° C. to 1000° C. in air for 3 to 9 hours to obtain a precursor in which platinum ions are located inside the crystal lattice; (4) The precursor obtained in step (3) is calcined at 800°C to 1000°C in a reducing atmosphere for 3 to 9 hours to obtain the target catalyst PtMg x Al2O y .

3. The method for preparing a sintering-resistant platinum-based catalyst according to claim 2, characterized in that: The Pt source precursor in step (1) includes platinum acetylacetonate, chloroplatinic acid, platinum nitrate or tetraammineplatinum nitrate.

4. The method for preparing a sintering-resistant platinum-based catalyst according to claim 2, characterized in that: The Mg source and Al source precursors described in step (1) include corresponding sulfates, halides, nitrates or acetates.

5. The method for preparing a sintering-resistant platinum-based catalyst according to claim 2, characterized in that: The air conditions in step (3) include static and flowing states.

6. The method for preparing a sintering-resistant platinum-based catalyst according to claim 2, characterized in that: The reducing atmosphere described in step (4) includes CO or H2 or a mixture of the two.

7. The method for preparing a sintering-resistant platinum-based catalyst according to claim 2, characterized in that: By adjusting the feed ratio of Mg source and Al source, the number of missing magnesium sites in the spinel structure lattice is controlled so that Pt is located at the missing magnesium sites. At the same time, by adjusting the calcination temperature and calcination atmosphere of step (3) and step (4), the number of surface Pt metal nanoparticles is adjusted. The higher the reduction temperature, the greater the number of exposed metallic Pt nanoparticles.

8. A use of the anti-sintering platinum-based catalyst as claimed in claim 1, characterized in that: The catalyst is used for catalytic combustion of propylene.

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