CN113996290A

CN113996290A - Platinum or palladium catalyst with titanium dioxide coated metal nanoparticles, preparation and application thereof

Info

Publication number: CN113996290A
Application number: CN202010730913.4A
Authority: CN
Inventors: 刘少峰; 王军虎
Original assignee: Dalian Institute of Chemical Physics of CAS
Current assignee: Dalian Institute of Chemical Physics of CAS
Priority date: 2020-07-27
Filing date: 2020-07-27
Publication date: 2022-02-01

Abstract

The invention relates to a catalyst prepared by using melamine to induce a titanium dioxide carrier to wrap platinum and palladium nano particles in an oxidizing atmosphere and a preparation method thereof. After the catalyst is roasted at 800 ℃ in the air, the platinum and palladium nano particles are wrapped by the titanium dioxide carrier, so that the catalyst has good activity and stability in a high-temperature oxidation reaction. Wherein the melamine acts to drive the TiO under a high temperature oxidizing atmosphere₂The carrier wraps the platinum and palladium particles so as to inhibit sintering of the metal particles; TiO 2₂It acts to enhance the reactive sites of the platinum and palladium catalysts.The preparation condition of the catalyst is simple and practical, and meanwhile, the product has high activity and stronger anti-sintering performance, and has an industrial application prospect.

Description

Platinum or palladium catalyst with titanium dioxide coated metal nanoparticles, preparation and application thereof

Technical Field

The patent relates to the field of catalyst preparation and technical application, and particularly discloses a platinum and palladium catalyst with high activity and strong anti-sintering performance and a preparation method thereof. Specifically comprises two steps; 1) preparing a supported platinum and palladium catalyst by an isometric wet impregnation method; 2) the catalyst prepared by the method is modified by melamine, then is roasted in a high-temperature nitrogen atmosphere, and is roasted in a high-temperature air atmosphere, so that the platinum and palladium catalyst with high activity and anti-sintering performance is obtained. Compared with the reported platinum and palladium catalysts, the preparation method of the catalyst is simple, the coating layer structure of the catalyst is unique, the activity is higher, the anti-sintering property is stronger, and especially the stability in high-temperature oxidation reaction is excellent. The invention reports a catalyst with high activity and sintering resistance and a preparation method thereof.

Background

Platinum and palladium belong to transition metals, and the prepared supported catalyst is a very important catalyst and plays an irreplaceable role in the modern chemical production process. However, due to their relatively high price, it is often necessary to support metal nanoparticles on a support to maximize the surface area of the metal and the accessible active site distribution. At present, the nano platinum and palladium catalyst shows excellent catalyst performance in a plurality of important chemical reactions, including CO oxidation, CO selective oxidation under a hydrogen-rich system, a water vapor shift reaction, a selective hydrogenation reaction, automobile exhaust treatment and the like. However, the biggest problem in practical use is that the catalyst is easily deactivated due to the reduction of specific surface area caused by sintering of metal particles or carbon deposition, and metal loss, etc. Meanwhile, catalyst regeneration usually requires leaching, purification, and re-deposition of metals, which is a cumbersome and expensive process.

In order to solve the above problems, researchers have proposed a series of strategies to neglect suppression or prevention of sintering of metal particles. Currently, there are several major implementations that can be omitted. For example, a carbon layer is coated on the surface of the metal particles; depositing a layer of porous oxide on the surface of the metal particles by atomic layer vapor deposition (ALD); the metal particles are anchored inside the material having micropores or mesopores. While these strategies inhibit sintering of the metal particles to some extent, several problems remain. For example, the shell layer on the surface of the metal particle can cover many active sites, thereby sacrificing part of the activity of the catalyst and causing the kinetic diffusion problem of reactant molecules. In addition, when synthesizing a material having micropores or mesopores, the size of the pore passage is largeIt is difficult to control and the synthesis requires the addition of organic structure directing agents which also results in difficult control of the size of the metal particles. In contrast, enhancing metal-support interactions is a different strategy. Tauster et al discovered in 1980 that after a platinum group metal catalyst loaded with a reductive transition metal oxide is subjected to a high-temperature reduction treatment at 500 ℃, the catalyst is used for H₂And the adsorption capacity of CO drops sharply, during which the metal particles are not sintered and the support does not collapse, further studies have found that the above phenomenon is reversible after high-temperature oxidation treatment. Researchers have proposed the concept of strong metal-support interaction (SMSI) for explaining the above phenomena. Researchers subsequently found that SMSI contributed to the increase in catalyst activity or selectivity in certain reduction reactions. Then due to the reversibility of SMSI, it does not exert a significant effect in high temperature oxidation reactions. Therefore, it remains a challenge to coat a platinum or palladium surface with a shell layer that is stable in an oxidizing atmosphere.

Disclosure of Invention

The invention aims to provide a platinum and palladium catalyst with higher activity and stronger anti-sintering performance and a preparation method thereof. Platinum and palladium are used as active centers; titanium dioxide is used as a carrier; modifying the catalyst with melamine, and roasting in nitrogen atmosphere and air atmosphere to form one layer of TiO on the surface of metal particle_xA thin layer. Thus, melamine acts to drive titanium oxide to coat the platinum and palladium nanoparticles upon high temperature calcination, and titanium dioxide acts to enhance the activity of the catalyst. At the same time, TiO_xThe shell layer can still exist stably in the high-temperature oxidation reaction.

Researches show that the surface of platinum and palladium nano particles is wrapped by a thin layer after being roasted in a high-temperature oxidizing atmosphere, and further characterization shows that the wrapped components are Ti and O, and Ti is +3, and is different from Ti in a carrier⁺⁴This phenomenon has not been reported before. In the supported catalyst, platinum and palladium are used as active centers, the carrier is titanium dioxide, the platinum and the palladium are positioned on the surface of the titanium dioxide carrier, and meanwhile, TiO is arranged on the surface of the platinum and palladium nano particles_xA shell layer (the thickness of the shell layer is 0.64 +/-0.2 nm). Encapsulated catalystExhibits good activity in CO oxidation and water-vapor shift reactions, and above all, excellent stability.

In the platinum and palladium catalyst with high activity and sintering resistance, the mass ratio of the platinum, the palladium and the titanium dioxide carrier is 0.01-0.1 (preferably 0.02-0.06);

the invention is realized by the following technical scheme:

preparation of platinum catalyst: 1) loading platinum onto a titania support using an equivalent volume wet impregnation method (IWI method); dropwise adding a certain amount of platinum source solution onto a titanium dioxide carrier, so that the mass ratio of platinum to the titanium dioxide carrier is 0.01-0.1; then drying at 50-80 ℃ for 1-3 hours, then drying at 100-150 ℃ for 10-15 hours, then roasting at 200-500 ℃ for 3-4 hours in the air, and finally roasting at 400-600 ℃ for 1-4 hours in a nitrogen atmosphere; 2) the melamine modification process comprises the following steps: dissolving 0.1-0.3 g of melamine in 30-60 mL of water, adding 0.1-0.6 g of the prepared catalyst, reacting at 60-90 ℃ for 12-48 hours, centrifuging, washing, and drying at 50-80 ℃ for 12-18 hours. Roasting the catalyst for 1-6 hours at 400-700 ℃ in a nitrogen atmosphere; then cooling to room temperature and roasting for 2-4 hours at 700-800 ℃ in air.

Preparation of palladium catalyst: 1) loading palladium on a titania carrier by an isometric wet impregnation method (IWI method); dropwise adding a certain amount of palladium source solution onto a titanium dioxide carrier, so that the mass ratio of palladium to the titanium dioxide carrier is 0.01-0.1; then drying for 1-3 hours at 50-80 ℃, then drying for 10-15 hours at 100-150 ℃, and then roasting for 3-4 hours at 200-500 ℃ in air; 2) the melamine modification process comprises the following steps: dissolving 0.1-0.3 g of melamine in 30-60 mL of water, adding 0.2-0.5 g of the prepared catalyst, reacting at 60-90 ℃ for 12-48 hours, centrifuging, washing, and drying at 50-80 ℃ for 12-18 hours. Roasting the catalyst for 2-4 hours at 300-400 ℃ in a nitrogen atmosphere; then cooling to room temperature and roasting for 2-4 hours at 700-800 ℃ in air.

The preparation method of the catalyst is simple and convenient, the product has high activity and sintering resistance, and the catalyst prepared after high-temperature roasting has high activity and excellent stability.

After the catalyst is roasted in the air, the platinum and palladium nano particles are wrapped by the titanium dioxide carrier, so that the catalyst has good activity and stability in a high-temperature oxidation reaction. Wherein the melamine functions to drive the titanium dioxide support to wrap the platinum and palladium particles under the high temperature oxidizing atmosphere and thereby inhibit sintering of the metal particles; the titanium dioxide serves to reinforce the active centers of the platinum and palladium catalysts. The preparation condition of the catalyst is simple and practical, and meanwhile, the product has high activity and stronger anti-sintering performance, and has an industrial application prospect.

Drawings

FIG. 1 TEM and HRTEM images of example 32.

FIG. 2 TEM and HRTEM images of example 34.

FIG. 3.Pt/TiO₂TEM and HRTEM images of 800.

FIG. 4 TEM and HRTEM images of example 37.

FIG. 5 Pd/TiO 2₂TEM and HRTEM images of 800.

Detailed Description

Comparative example 1

Pt/TiO₂

The preparation method comprises the following steps of (1) preparing by an isometric wet impregnation method: 0.5g of a chloroplatinic acid solution having a mass fraction of 7.25% by weight was added dropwise to 1.0g of TiO₂A carrier; then drying for 1 hour at 60 ℃, then drying for 12 hours at 120 ℃, then roasting for 3 hours at 400 ℃ in air, and roasting the sample for 3 hours at 600 ℃, 700 ℃ and 800 ℃ in air atmosphere; are respectively denoted as Pt/TiO₂-600、Pt/TiO₂-700、Pt/TiO₂-800。

Comparative example 2

Pd/TiO₂

The preparation method comprises the following steps of (1) preparing by an isometric wet impregnation method: 0.5g of a palladium chloride solution having a mass fraction of 6.18% by weight was added dropwise to 1.0g of TiO₂A carrier; then dried at 60 ℃ for 1 hour, then dried at 120 ℃ for 12 hours, and then calcined at 400 ℃ for 3 hours in air, and the samples were calcined at 600 ℃, 700 ℃ and 800 ℃ for 3 hours in air atmosphere, and recorded as Pd/TiO₂-600、Pd/TiO₂-700、Pd/TiO₂-800。

Description of T50:

the initial reaction temperature was 25 deg.C, then the reaction temperature was increased at a rate of 5 deg.C/min, and the CO conversion was measured every 25 deg.C until the CO conversion was complete. The temperature at which the CO conversion was 50% was defined as T50.

Examples 1 to 13

1. And (3) investigating the influence of each condition on the activity of the catalyst in the process of the equal-volume wet impregnation method.

Platinum loading by an isometric wet impregnation method (IWI method): dropwise adding a certain amount of platinum source solution with the mass fraction of 1-8.33 wt% onto a titanium dioxide carrier, so that the mass ratio of platinum to the carrier is 0.005-0.04; then drying at 60 ℃ for 2 hours, then drying at 120 ℃ for 12 hours, then roasting at 200-500 ℃ for 4 hours in the air, and then roasting at 400-600 ℃ for 1-4 hours in the nitrogen atmosphere.

Modification of melamine: 0.3g of melamine was dissolved in 60mL of water, and then 0.6g of the above-prepared catalyst was added to react at 75 ℃ for 36 hours, centrifuged, washed with water, dried at 70 ℃ for 12 hours, and the above-prepared catalyst was calcined at 600 ℃ for 3 hours under a nitrogen atmosphere, then cooled to room temperature and calcined at 800 ℃ for 3 hours under an air atmosphere.

When the activity of the catalyst is tested under various conditions in the process of loading platinum by an isometric wet impregnation method, a CO oxidation reaction is used as a probe reaction, and T is used₅₀The activities were compared for reference. The lower the T50, the higher the activity. The reaction device is a miniature fixed bed reactor. The composition (volume ratio) of the raw material gas for reaction is 1 v% CO +1 v% O₂+98 v% He, feed gas space velocity of 20,000mL g_cat ^-1h^-1. Before sample testing, 10 v% H was used₂the/He is reduced at 200 ℃ for 1 h. The surface adsorbed gas was then removed by purging with He for 20 min. The reaction starting materials and products were analyzed on-line by gas chromatography (Agilent 6890N).

TABLE 1 Effect of the conditions on catalyst Activity during IWI

From Table 1 it can be seen that K is used₂PtCl₆The activity is lower, probably due to the presence of K in the product⁺And the residue can affect the generation of a wrapping layer so as to cause Pt aggregation to grow. The activity is better when the Pt loading is higher. At lower air firing temperatures, the activity is poor, probably H₂PtCl₆·6H₂The O precursor is not completely decomposed, so that a part of Cl remains^-And further affect the catalyst reactivity. And when the roasting temperature is higher, the Pt particles are easy to sinter. The lower the nitrogen calcination temperature, the shorter the calcination time, the higher the catalyst activity. Wherein the thickness range of the wrapping layer is 0.49-0.83 nm.

Examples 14 to 31

2. Investigating the influence of each condition on the catalyst activity in the melamine modification process

Platinum loading by an isometric wet impregnation method (IWI method): 0.5g of a chloroplatinic acid solution having a mass fraction of 7.25% by weight was added dropwise to 1.0g of a titanium dioxide carrier; then dried at 60 ℃ for 2 hours, then dried at 120 ℃ for 12 hours, and then calcined at 400 ℃ for 4 hours in an air atmosphere, and then calcined at 600 ℃ for 4 hours in a nitrogen atmosphere.

Modification of melamine: weighing 0.1-0.3 g of melamine, dissolving in 60mL of water, adding 0.1-0.6 g of the prepared catalyst, reacting at 60-90 ℃ for 12-48 hours, centrifuging, washing with water, drying at 80 ℃ for 12 hours, roasting the catalyst at 400-700 ℃ for 1-6 hours in a nitrogen atmosphere, cooling to room temperature, and roasting at 800 ℃ for 3 hours in an air atmosphere.

When the activity test of the catalyst is investigated, the CO oxidation reaction is taken as a probe reaction, and T is taken as₅₀For reference to activity comparison, the lower the T50, the higher the activity. The reaction device is a miniature fixed bed reactor. The composition (volume ratio) of the raw material gas for reaction is 1 v% CO +1 v% O₂+98 v% He, feed gas space velocity of 20,000mL g_cat ^-1h^-1. Before sample testing, 10 v% H was used₂the/He is reduced at 200 ℃ for 1 h. The surface adsorbed gas was then removed by purging with He for 20 min. The reaction starting materials and products were analyzed on-line by gas chromatography (Agilent 6890N).

TABLE 2 influence of the conditions on the catalyst activity during the modification of Melamine

Note: the mass ratio of platinum to the carrier in the catalyst was 0.035.

As can be seen from Table 2, the catalyst activity was highest at a 1:2 ratio of melamine to catalyst. The catalyst activity increases as the reaction temperature increases, probably because increasing the reaction temperature favors more melamine being adsorbed to the catalyst surface. Meanwhile, the reaction time is optimal to 36h, and the improvement of the catalyst activity is not favored by too short or too long time. Increasing the nitrogen firing temperature and suitably extending the firing time favours an increase in reactivity, possibly associated with the carbonisation of the melamine and the interaction of the metal with the support. Wherein the thickness range of the wrapping layer is 0.46-0.87 nm.

Examples 32 to 36

3. Investigating the calcination temperature and TiO_xEffect of the Shell layer on the Activity and stability of the catalyst

Modification of melamine: dissolving 0.3g of melamine in 60mL of water, adding 0.6g of the prepared catalyst, reacting at 75 ℃ for 36 hours, centrifuging, washing with water, drying at 70 ℃ for 12 hours, roasting the catalyst at 600 ℃ for 3 hours under a nitrogen atmosphere, cooling to room temperature, and roasting at 600-800 ℃ for 3 hours under an air atmosphere.

Investigating the calcination temperature and TiO_xWhen the shell layer influences the activity and stability of the catalyst, CO oxidation and simulated automobile exhaust CO elimination reaction are respectively used as probe reactions. By T₅₀For reference to activity comparison, the lower the T50, the higher the activity. The reaction device is a miniature fixed bed reactor. Oxygen of COThe composition (volume ratio) of raw material gas for the gasification reaction is 1 v% CO +1 v% O₂+98 v% He, feed gas space velocity of 20,000mL g_cat ^-1h^-1. The composition (volume ratio) of the simulated automobile exhaust CO elimination reaction raw material gas is 1.6 v% CO +1 v% O₂+0.01 v% propylene +0.0087 v% toluene +10 v% H₂The balance of O and He and the space velocity of the raw material gas are 500L g_cat ^-1h^-1The reaction temperature was 420 ℃. Before sample testing, 10 v% H was used₂the/He is reduced at 200 ℃ for 1 h. The surface adsorbed gas was then removed by purging with He for 20 min. The reaction starting materials and products were analyzed on-line by gas chromatography (Agilent 6890N).

Table 3 explores the calcination temperature and TiO_xEffect of Shell on catalyst Activity and stability

Note: the mass ratio of platinum to the carrier in the catalyst was 0.035.

As can be seen from Table 3, the activity of the catalyst after calcination at 800 ℃ is higher than that of the catalyst after calcination at 600 ℃ and may be TiO_xAfter the shell layer is generated, Pt and TiO_xThe number of active sites at the interface is increased, thereby being beneficial to the improvement of the reaction activity. The electron microscope results of FIG. 1 show that the Pt particles of example 32 have a size distribution of 9.3. + -. 4.6nm, and the platinum particles are bare. The particle size distribution of the platinum particles of example 34 was 5.6. + -. 1.9nm, and it was found that there was a layer of TiO on the surface of the Pt particles_xThin layer with shell thickness of 0.62 + -0.20 nm (FIG. 2). Unmodified Pt/TiO₂The activity of the catalyst gradually decreases with increasing calcination temperature due to the gradual sintering of the platinum particles with increasing calcination temperature. FIG. 3 shows example Pt/TiO₂The Pt particle size of-800 is 62.6 +/-10.2 nm. In the CO oxidation reaction at 500 ℃ for 100h, Pt/TiO₂The initial CO conversion of 93% is higher, however, as the reaction time progresses, the CO conversion gradually decreases and finally the CO conversion decreases to 71%. However, there is TiO on the surface of Pt particles_xIn the case of the shell layer of example 35, the initial conversion of CO was 78% lower, the conversion of CO did not decrease but increased to 92% after 100 hours of reaction,as can be seen, TiO_xThe shell layer plays an important role in stabilizing Pt particles. Also, in simulating the automobile exhaust CO elimination reaction, Pt/TiO₂The CO conversion of (C) was reduced from 92% to 53% in 120h, whereas in example 36 the CO conversion increased from 86% to 91% in 360h of the reaction. From this it can be seen that TiO_xThe shell layer contributes to the enhancement of the catalyst stability.

Examples 37 to 42

4. Investigation of conditions and TiO during the impregnation Process_xEffect of Shell on the Activity and stability of Palladium catalysts

Palladium loading by the isopyknic wet impregnation method (IWI method): 0.5g of a palladium source solution having a mass fraction of 6.18 wt% was added dropwise to 1.0g of a titania carrier; then dried at 60 ℃ for 2 hours, then dried at 120 ℃ for 12 hours, and then calcined at 400 ℃ for 4 hours in an air atmosphere.

Modification of melamine: 0.3g of melamine was dissolved in 60mL of water, and then 0.6g of the above-prepared catalyst was added to react at 70 ℃ for 36 hours, centrifuged, washed with water, dried at 70 ℃ for 12 hours, and the above-mentioned catalyst was calcined at 400 ℃ for 3 hours under a nitrogen atmosphere, then cooled to room temperature and calcined at 800 ℃ for 3 hours under an air atmosphere.

Investigating the conditions and TiO in the process of the isometric immersion method_xWhen the shell layer influences the activity and the stability of the palladium catalyst, a water vapor shift reaction is respectively used as a probe reaction. By T₅₀For reference to activity comparison, the lower the T50, the higher the activity. The reaction device is a miniature fixed bed reactor. The composition (volume ratio) of raw material gas for water-gas shift reaction is 2 v% CO +10 v% H₂O +88 v% He, feed gas space velocity of 18,000mL g_cat ^-1h^-1The reaction temperature was 600 ℃. Before sample testing, 10 v% H was used₂the/He is reduced at 200 ℃ for 1 h. The surface adsorbed gas was then removed by purging with He for 20 min. The reaction starting materials and products were analyzed on-line by gas chromatography (Agilent 6890N).

Table 4 explores the conditions during the impregnation process and the TiO_xEffect of Shell on the Activity and stability of Palladium catalysts

Note: the mass ratio of palladium to the carrier in the catalyst was 0.03.

As can be seen from Table 4, PdCl was used₂And Pd (NH)₃)₄·(NO₃)₂The Pd source is the catalyst with higher activity, while NaPdCl₄In the case of a Pd source, the catalyst activity is slightly low, and the Pd particles are easy to aggregate and grow due to the residual Na probably. The activity of the 800 ℃ calcined catalyst is higher than 600 ℃ due to Pd and TiO_xThe number of active sites at the interface is increased, thereby promoting the improvement of the reactivity. The palladium particles of example 37 had a particle size distribution of 5.8. + -. 2.1nm and a layer of TiO on the surface of the Pd particles_xThe thickness of the shell layer is 0.62 +/-0.23 nm. Pd/TiO in water-gas shift reaction at 600 deg.C₂The initial conversion of CO of-400 was 58% higher, whereas after only 17h of reaction the conversion of CO dropped to 22%. Whereas the initial conversion of CO in example 42 was only 30%, the conversion of CO increased to 53% after 100h of reaction, so that TiO_xThe shell layer has unique effect on improving the stability of the catalyst.

Claims

1. The platinum or palladium catalyst with metal nano particles wrapped by titanium dioxide carrier is characterized in that:

the catalyst is a supported catalyst taking platinum or palladium as an active center, the carrier is titanium dioxide, and a titanium oxide layer is arranged on the surface of platinum or palladium nano particles loaded on the titanium oxide; the mass ratio of the noble metal platinum or palladium to the carrier in the catalyst is 0.01-0.1 (preferably 0.02-0.06).

2. The platinum or palladium catalyst of claim 1 wherein:

the particle size distribution of the platinum nanoparticles is 2.1-8.8 nm (preferably 3.5-6.2 nm), and the thickness range of the coating layer is 0.38-0.89 nm (preferably 0.48-0.82 nm);

the particle size distribution of the palladium nano-particles is 2.5-5.6 nm (preferably 2.1-4.3 nm), and the thickness range of the coating layer is 0.45-0.88 nm (preferably 0.56-0.91 nm).

3. A method for preparing the catalyst of claim 1 or 2, characterized in that:

a, preparation of a platinum catalyst:

1) loading platinum onto a titania support using an equivalent volume wet impregnation method (IWI method); dropwise adding a certain amount of platinum source solution onto a titanium dioxide carrier to ensure that the mass ratio of platinum to the titanium dioxide carrier is 0.01-0.1 (preferably 0.02-0.06); then drying at 50-80 ℃ for 1-3 hours, then drying at 100-150 ℃ (preferably 120-130 ℃) for 10-15 hours (preferably 12-13 hours), then roasting at 200-500 ℃ (preferably 350-400 ℃) for 3-4 hours (preferably 3.5-4 hours) in the air, and finally roasting at 400-600 ℃ (preferably 550-600 ℃) for 1-4 hours (preferably 3-4 hours) in the nitrogen atmosphere;

2) the melamine modification process comprises the following steps: dissolving 0.1-0.3 g (preferably 0.25-0.3 g) of melamine in 30-60 mL of water, adding 0.1-0.6 g (preferably 0.5-0.6 g) of the prepared catalyst, reacting at 60-90 ℃ (preferably 65-75 ℃) for 12-48 hours (preferably 24-30 hours), centrifuging, washing, and drying at 50-80 ℃ for 12-18 hours; roasting the catalyst for 1 to 6 hours (preferably 3 to 3.5 hours) in a nitrogen atmosphere at 400 to 700 ℃ (preferably 550 to 600 ℃); then cooling to room temperature, and roasting for 2-4 hours (preferably 2.8-3 hours) in an oxidizing atmosphere (oxygen-containing atmosphere, such as oxygen and/or air, preferably air) at 700-800 ℃ (preferably 750-800 ℃);

b, preparation of a palladium catalyst:

1) loading palladium on a titania carrier by an isometric wet impregnation method (IWI method); dropwise adding a certain amount of palladium source solution onto a titanium dioxide carrier, so that the mass ratio of palladium to the titanium dioxide carrier is 0.01-0.1 (preferably 0.02-0.06). Then drying the mixture for 1 to 3 hours at 50 to 80 ℃, then drying the mixture for 10 to 15 hours (preferably 12 to 13 hours) at 100 to 150 ℃ (preferably 120 to 130 ℃), and then roasting the mixture for 3 to 4 hours (preferably 3.5 to 4 hours) in an air atmosphere at 200 to 500 ℃ (preferably 350 to 400 ℃);

2) the melamine modification process comprises the following steps: dissolving 0.1-0.3 g (preferably 0.25-0.3 g) of melamine in 30-60 mL of water, adding 0.2-0.5 g (preferably 0.3-0.4 g) of the prepared catalyst, reacting at 60-90 ℃ (preferably 65-70 ℃) for 12-48 hours (preferably 24-30 hours), centrifuging, washing, and drying at 50-80 ℃ for 12-18 hours; roasting the catalyst for 2-4 hours (preferably 3-3.5 hours) in a nitrogen atmosphere at 300-400 ℃ (preferably 350-400 ℃); then cooling to room temperature, and roasting in an oxidizing atmosphere (oxygen-containing atmosphere, such as oxygen and/or air, preferably air) at 700-800 ℃ (preferably 750-800 ℃) (preferably 2.8-3 hours).

4. The method of claim 3, wherein:

the platinum source can be one or more than two of chloroplatinic acid, potassium chloroplatinate and platinum nitrate; the palladium source can be one or more than two of palladium chloride, sodium tetrachloropalladate and tetraammine palladium nitrate.

5. Use of a platinum catalyst according to claim 1 or 2, characterized in that: the platinum catalyst of any one of claims 1 or 2 can be used in a CO oxidation reaction or a simulated automotive exhaust CO elimination reaction.

6. Use of a platinum catalyst according to claim 5. The method is characterized in that:

the CO oxidation reaction device is a fixed bed reactor, and the reactor consists of 1-10 v% of CO and 1-10 v% of O₂+ 80-98 v% He, and the space velocity of the feed gas is 20-60L g_cat ^-1h^-1The reaction temperature is 25-300 ℃ (preferably 50-250 ℃);

the raw material gas for simulating the CO elimination reaction of the automobile exhaust consists of (by volume ratio) 1.6-2.0 v% of CO + 1-1.5 v% of O₂+ 0.01-0.05 v% propylene + 0.0087-0.0099 v% toluene + 10-15 v% H₂The balance of O and He, and the space velocity of the feed gas is 500-550L g_cat ^-1h^-1The reaction temperature is 350-450 ℃ (preferably 390-420 ℃).

7. Use of a palladium catalyst according to claim 1 or 2, characterized in that: the palladium catalyst of any one of claims 1 or 2 may be used in a water vapor shift reaction.

8. Use of a palladium catalyst according to claim 7, characterized in that: the composition (volume ratio) of the raw material gas for the water-vapor shift reaction is 2-5 v% of CO + 8-10 v% of H₂He of O + 85-90 v%, and the space velocity of the feed gas is 18-20L g_cat ^-1h^-1The reaction temperature is 500-600 ℃ (preferably 530-600 ℃).