Titanium dioxide coated gold-based catalyst as well as preparation method and application thereof

Abstract

The invention relates to preparation of a titanium dioxide coated gold-based catalyst and application of the titanium dioxide coated gold-based catalyst in CO oxidation reaction. The active species gold is dispersed on the titanium dioxide carrier, the loading rate is 0.5-20wt%, and the titanium dioxide carrier is one or more than two of rutile, anatase or composite crystal phase P25. Ascorbic acid is used for modification, and after high-temperature roasting treatment in an inert atmosphere, the titanium dioxide carrier is coated with the gold nanoparticles. The catalyst shows good catalytic activity on CO catalytic oxidation, simulation of automobile exhaust CO elimination and other oxidation reactions. Meanwhile, after the catalyst is recycled for multiple times, the activity of the catalyst is not obviously reduced, the catalyst is not obviously inactivated after being continuously used for 50 hours, and excellent reaction stability is shown. The catalyst is novel in design and preparation method and simple in process, has the advantages of good catalytic activity and high stability, and has a good application prospect.

Description

Technical Field

[0001] The present invention relates to the technical fields of catalytic chemistry and nanoscience technology, and particularly to a preparation method of a supported gold catalyst wrapped with a titanium dioxide support. The preparation method of the catalyst comprises two key steps: firstly, a TiO 2 supported gold catalyst is prepared by a deposition-precipitation method; then the catalyst is put into a solution of ascorbic acid for modification, and then centrifuged, washed, and dried, and the obtained material is subjected to high-temperature calcination treatment in an inert atmosphere to obtain a gold-based catalyst with high activity and good stability. The preparation method is simple, the support is easy to obtain, and the structure is unique, and it has good catalytic activity and excellent stability in the catalytic CO oxidation reaction. The present invention provides a preparation method of a catalyst with high activity and high stability.

[0002] Background Introduction

[0003] Due to their unique electronic structures and excellent low-temperature activities, noble metal nanocatalysts are widely used in fields such as petrochemical industry, environmental catalysis, and organic synthesis. Noble metals are expensive and scarce in reserves. In order to improve their utilization efficiency, they are usually supported on supports with high specific surface areas to prepare supported catalysts. Noble metal catalysts usually use Pt, Pd, Rh, Au, etc. as active components, among which the research on Pt, Pd, Rh, etc. started earlier. For a long time, researchers believed that gold is a relatively inert metal and has almost no application in the field of catalysts. It was not until the 1980s that Haruta, Hutchings, etc. found that when the particle size of gold nanoparticles was controlled below 5 nm and supported on metal oxide supports, it could have ultra-high activity for CO oxidation and acetylene hydrochlorination reactions. Thus, supported gold catalysts have received extensive attention and in-depth research. Nowadays, gold catalysts show attractive prospects in oxidation reactions, hydrogenation reactions, hydrogen energy conversion, and the elimination of atmospheric pollutants. However, under many high-temperature reaction conditions, gold nanoparticles are prone to sintering and deactivation, which greatly limits the practical application of gold nanocatalysts in industrial catalytic processes. Therefore, developing supported metal nanocatalysts with both high activity and high stability is the key to solving this problem and is also an urgent problem to be solved for the industrial application of supported noble metal catalysts.

[0004] Strong metal-support interaction (SMSI) is a key strategy for constructing sinter-resistant nanocatalysts. The key to improving the stability of the SMSI structure lies in the formation of a transition metal oxide coating layer, which can protect noble metal nanoparticles from sintering and leaching. Since the pioneering work of Tauster et al., researchers have further expanded the types of supports and developed different construction strategies. It has been proven that a variety of methods can be used for SMSI construction, such as: high-temperature treatment (>300 °C) of metal nanoparticles supported on phosphates, hydroxyapatite, and zinc oxide in an oxidizing atmosphere (O-SMSI), sacrificial carbon coating strategy (500 - 700 °C), wet chemical method (wc-SMSI), adsorbate-induced SMSI (A-SMSI), reaction-induced SMSI between Ni and hexagonal boron nitride (h-BN) systems (750 - 850 °C), photo-induced SMSI, and mechanical chemical methods such as ultrasound and ball milling to induce SMSI. Despite many advances, each method has its own limitations, such as limitations in the types of supports, high equipment requirements, and unclear driving forces behind them. Therefore, developing new strategies to achieve an efficient and controllable method for constructing the SMSI coating layer is necessary for developing catalysts with both high activity and high stability and understanding the driving mechanism behind the SMSI phenomenon. Summary of the Invention

[0005] The object of the present invention is to provide a preparation method and application of a titanium dioxide-coated gold-based catalyst, which can achieve the complete oxidation of CO at a relatively low temperature. A coating layer is formed on the surface of gold nanoparticles, and it is a catalyst with both high activity and stability.

[0006] For the gold nanocatalyst supported on a titanium dioxide support, after being modified with ascorbic acid and calcined at a high temperature in an inert atmosphere, there is a strong metal-support interaction between the metal particles and the titanium dioxide support, and a stable coating layer structure is formed on the surface of the gold particles, ensuring excellent stability of the catalyst. This is the first time that the coating of titanium dioxide species on gold nanoparticles is achieved by calcination in an inert atmosphere under the induction of ascorbic acid (the thickness range of the coating layer is 0.2 - 2.0 nm). The presence of the coating layer endows the catalyst with good stability, and the activity remains unchanged significantly for 50 h during CO oxidation.

[0007] The specific technical solution of the present invention is described as follows:

[0008] 1) Prepare the gold catalyst supported on titanium dioxide by the deposition-precipitation method: First, prepare a solution with a concentration of 1.0 - 3.0 mg Au mL -1 (preferably 1.0 - 2.0 mg Au mL -1An aqueous solution of chloroauric acid, while stirring, a basic solution with a concentration of 0.1 - 1 mol / L (preferably 0.1 - 0.5 mol / L) is added dropwise thereto to adjust the pH of the solution to be between 8 and 12 (preferably 9 - 10). Subsequently, 1.0 g of a titanium dioxide support is added, and the alkali solution is continuously added dropwise to maintain the pH value for 1 - 3 hours, and then a constant temperature water bath reaction is carried out at 60 - 90 °C (preferably 60 - 70 °C) for 1 - 5 hours (preferably 1 - 3 hours). The product is centrifuged and washed, and dried at 60 - 80 °C for 12 - 24 hours; -1 (preferably 0.1 - 0.5 mol / L -1 ) to adjust the solution pH to be between 8 and 12 (preferably 9 - 10). Subsequently, 1.0 g of a titanium dioxide support is added, and the alkali solution is continuously added dropwise to maintain the pH value for 1 - 3 hours, and then a constant temperature water bath reaction is carried out at 60 - 90 °C (preferably 60 - 70 °C) for 1 - 5 hours (preferably 1 - 3 hours). The product is centrifuged and washed, and dried at 60 - 80 °C for 12 - 24 hours;

[0009] 2) Modification process of ascorbic acid: The catalyst prepared by the above DP method is pretreated by calcination at 200 - 600 °C (preferably 200 - 400 °C) for 2 - 5 hours (preferably 2 - 3 hours) in an air atmosphere. Then, 0.1 - 1 g (preferably 0.1 - 0.5 g) is dispersed in 30 - 60 mL of an ascorbic acid solution with a concentration of 1 - 10 mg / mL (preferably 3 - 5 mg / mL), and stirred at 50 - 90 °C (preferably 60 - 70 °C) in a constant temperature water bath for 12 - 48 hours (preferably 24 - 30 hours), centrifuged and washed, and dried at 60 - 80 °C for 12 - 24 hours; then calcined at 200 - 800 °C (preferably 400 - 600 °C) for 2 - 5 hours (preferably 3 - 4 hours) in an inert atmosphere to finally obtain the gold-based catalyst encapsulated with titanium dioxide.

[0010] The present invention also relates to protecting the application of the above-mentioned gold-based catalyst encapsulated with titanium dioxide in CO oxidation and water gas shift reaction. In the CO oxidation reaction, a fixed-bed reactor is used, the reaction pressure is atmospheric pressure, the raw material gas composition is 1 - 10 vol% CO + 1 - 10 vol% O 2 + 80 - 98 vol% He, the space velocity of the raw material gas is 20 - 50 L g cat -1 h -1 , and the reaction temperature includes - 60 °C to 500 °C. The reaction product is analyzed online by an Agilent 6890 chromatograph equipped with a TCD detector.

[0011] For the water gas shift reaction, a fixed-bed reactor is used, the raw material gas composition is 2 - 10 vol% CO + 8 - 10 vol% H 2 O + 80 - 95 vol% He, the space velocity of the raw material gas is 15 - 30 L g cat -1 h -1 , and the reaction temperature is 400 - 600 °C (preferably 500 - 600 °C). The reaction product is analyzed online by an Agilent 6890 chromatograph equipped with a TCD detector.

[0012] The catalyst of the present invention exhibits good catalytic activity for oxidation reactions such as the catalytic oxidation of CO and the elimination of CO in simulated automobile exhaust. At the same time, after being recycled multiple times, the activity of the catalyst does not decrease significantly. After continuous use for 50 hours, the catalyst does not show obvious deactivation, demonstrating excellent reaction stability. The design and preparation method of the catalyst of the present invention is novel and the process is simple, with the advantages of good catalytic activity and high stability, and has good application prospects.

[0013] The present invention has the following effects:

[0014] 1) The preparation method is simple and novel. For the first time, the means of ascorbic acid modification and calcination in an inert atmosphere are used, and the steps are simple and easy to expand and apply.

[0015] 2) The TiO 2 support encapsulates the gold nanoparticles, thereby inhibiting the sintering of the active metal components of the catalyst and further improving the stability of the catalyst.

[0016] 3) The prepared catalyst can still achieve complete conversion of CO at room temperature after calcination at 600 °C. When the catalyst is reused for the sixth time, its catalytic activity does not decrease significantly, and its microstructure does not change significantly. After continuous reaction for 50 hours, no obvious downward trend is observed, showing good industrial application prospects.

[0017] Description of the drawings

[0018] Figure 1 is the electron microscope picture of the catalyst in Example 1 of the method of the present invention

[0019] Figure 2 is the curve of the conversion rate of CO oxidation with temperature for the catalysts in Example 1 and Comparative Examples 1-3

[0020] Figure 3 is the long-term stability test of the catalyst in Example 1 during CO oxidation

[0021] Figure 4 is the evaluation of the repeated use performance of the catalyst in Example 1 during CO oxidation

[0022] Figure 5 is the stability test of the catalyst in Example 1 during the water-gas shift reaction Detailed implementation manners

[0023] The following is a more specific description of the catalyst preparation in combination with examples. It should be supplemented and explained that: all the reagents used in the present invention are ordinary commercially available products.

[0024] Examples 1-24

[0025] 1. Investigate the influence of various conditions during the deposition-precipitation process on the activity of the catalyst

[0026] 1) Preparation of gold catalyst supported on titanium dioxide by deposition - precipitation (D - P method): First, prepare an aqueous solution of chloroauric acid with a concentration of 1.0 - 3.0 mg Au mL -1 (preferably 1.0 - 2.0 mg Au mL -1 ) in 40 mL of water. While stirring, add an alkaline solution with a concentration of 0.1 - 1 mol / L -1 (preferably 0.1 - 0.5 mol / L -1 ) to adjust the pH of the solution to between 8 and 12 (preferably 9 - 10). Then add 1.0 g of titanium dioxide support, continue to add the alkaline solution to maintain the pH value for 1 hour, and then carry out a constant - temperature water - bath reaction at 60 - 90 °C (preferably 60 - 70 °C) for 1 - 5 hours (preferably 1 - 3 hours). The product is centrifuged, washed, and dried at 60 °C for 12 hours; the specific parameters are shown in Table 1;

[0027] 2) Modification process of ascorbic acid: The catalyst prepared by the above - mentioned DP method is pretreated by calcination at 250 °C for 2 hours in an air atmosphere. Then, take 0.15 g and disperse it in 30 mL of an ascorbic acid solution with a concentration of 3.33 mg / mL, stir at 65 °C in a constant - temperature water - bath for 24 hours, centrifuge, wash, and dry at 60 °C for 12 hours; then calcine at 600 °C for 3 hours in a nitrogen atmosphere to finally obtain the gold - based catalyst encapsulated by titanium dioxide.

[0028] When investigating the influence of various conditions in the deposition - precipitation process on the catalyst activity, the catalytic oxidation of CO to produce CO 2 is selected as a model reaction for evaluation. The reaction is carried out in a micro - fixed - bed quartz reactor under atmospheric pressure. The space velocity of the feed gas is 20 L / gcat -1 h -1 , and the composition is 1 vol% CO + 1 vol% O 2 + 98 vol% He. Before the test, first pass He gas through the catalyst bed at room temperature for 30 min for purging, and then use a liquid - nitrogen ethanol bath and a tube furnace to control the temperature of the catalyst bed under the monitoring of a thermocouple. After the temperature reaches a specific temperature, the feed gas is introduced into the reaction tube. After stabilizing for 10 min, the reaction activity at this temperature is measured. The temperature of the catalyst bed (heating rate 2 °C / min) is increased to the next temperature point. After stabilizing for 10 min, the activity of the catalyst at this temperature is tested, and then continue to heat up to the next temperature point and repeat the above operation to obtain the activity of the catalyst at different temperatures. The activity test temperature range starts from - 60 °C, and a test is carried out every 20 °C until the CO conversion rate reaches 100% and the data collection stops. The reaction products are analyzed online by an Agilent 6890 chromatograph equipped with a TCD detector. The calculation method of the CO conversion rate is as follows:

[0029]

[0030] CO in and CO out represent the concentrations of CO at the inlet and outlet respectively.

[0031] The catalyst activity evaluation selects T 50 as a reference for comparison. The conversion temperature corresponding to a CO conversion rate of 50% is T 50 , T 50 The lower it is, the better the activity of the corresponding catalyst.

[0032] Table 1 Influence of various conditions on the catalyst activity during the DP process

[0033]

[0034]

[0035] Note: The theoretical loading of Au in the catalyst is 5 wt%.

[0036] As can be seen from Table 1, different crystal forms of the carrier have an impact on the catalyst activity. Rutile TiO 2 as the carrier has poorer activity, probably because rutile is more stable at high temperatures, the resulting SMSI effect is relatively weak, and the Au particles show a certain degree of sintering. The concentration of chloroauric acid solution also affects the catalyst activity. In the concentration range of 1.0 - 3.0 mg Au mL -1 , the higher the concentration, the higher the T50 temperature and the lower the activity. Probably because a high concentration results in a relatively small amount of Au actually loaded on the carrier. Therefore, the concentration of chloroauric acid solution is preferably 1.0 - 2.0 mg Au mL -1 , and the more preferred range is 1.0 - 1.5 mg Au mL -1 . Both the type and concentration of the alkali solution will affect the catalytic performance to a certain extent. Too low or too high a concentration of the alkali solution is not good. It is preferably 0.05 - 0.5 mol / L -1 , and more preferably 0.1 - 0.5 mol / L -1 . During the D - P process, the pH range is preferably between 9 and 11, more preferably between 9 and 10, the reaction temperature is between 60 and 70 °C, the reaction time should not be too long, between 1 - 3 h, and the catalyst has better activity. Among them, in Examples 1 - 24, the average particle size distribution range of the active component gold nanoparticles is 2.0 - 5.0 nm, and the thickness range of the Au surface coating layer is 0.2 - 2.0 nm.

[0037] Examples 25 - 49

[0038] 2. Investigate the effects of various conditions during the ascorbic acid modification process on the catalytic performance and activity of the catalyst

[0039] 1) Preparation of titania-supported gold catalyst by deposition-precipitation (D-P method): First, prepare 40 mL of an aqueous solution of chloroauric acid with a concentration of 1.25 mg Au mL -1 . While stirring, add a NaOH solution with a concentration of 0.1 mol / L -1 to adjust the pH of the solution to 9. Subsequently, add 1.0 g of titania (P25) support, continue to add the NaOH solution to maintain the pH value for 1 hour, then carry out a constant-temperature water bath reaction at 65 °C for 1 hour. The product is centrifuged and washed, and dried at 60 °C for 12 hours;

[0040] 2) Modification process of ascorbic acid: The catalyst prepared by the above D-P method is pretreated by calcination at 200 - 600 °C (preferably 200 - 400 °C) for 2 - 5 hours (preferably 2 - 3 hours) in an air atmosphere. After that, take 0.15 g of the catalyst and disperse it in 30 mL of an ascorbic acid solution with a concentration of 1 - 10 mg / mL (preferably 3 - 5 mg / mL), stir at a constant-temperature water bath of 50 - 90 °C (preferably 60 - 70 °C) for 12 - 48 hours (preferably 24 - 30 hours), centrifuge and wash, and dry at 60 °C for 12 hours; then calcine at 200 - 800 °C (preferably 400 - 600 °C) for 2 - 5 hours (preferably 3 - 4 hours) in an inert atmosphere to finally obtain the as-prepared titania-coated gold-based catalyst.

[0041] When investigating the effects of various conditions during the ascorbic acid modification process on the activity of the catalyst, the catalytic oxidation of CO to CO 2 is selected as a model reaction for evaluation. The reaction is carried out in a micro fixed-bed reactor under atmospheric pressure. The space velocity of the feed gas is 20 L / gcat -1 h -1 , and the composition is 1 vol% CO + 1 vol% O 2 + 98 vol% He. Before the test, first pass He gas through the catalyst bed at room temperature for 30 min for purging, and then use a liquid nitrogen-ethanol bath and a tube furnace to control the temperature of the catalyst bed under the monitoring of a thermocouple. After the temperature reaches a specific temperature, introduce the feed gas into the reaction tube. After stabilizing for 10 min, measure the reaction activity at this temperature. Subsequently, the temperature of the catalyst bed (heating rate 2 °C / min) is increased to the next temperature point. After stabilizing for 10 min, test the activity of the catalyst at this temperature, and then continue to heat up to the next temperature point and repeat the above operation to obtain the activity of the catalyst at different temperatures. The activity test temperature range starts from -60 °C, and a test is carried out every 20 °C until the CO conversion rate reaches 100% and the data collection stops. The reaction products are analyzed online by an Agilent 6890 chromatograph equipped with a TCD detector. The calculation method of the CO conversion rate is as follows:

[0042]

[0043] CO in and CO out represent the concentrations of CO at the inlet and outlet respectively.

[0044] T is selected for the evaluation of catalyst activity 50 as a reference for comparison. The conversion temperature corresponding to a CO conversion rate of 50% is T 50 , T 50 The lower T is, the better the activity of the corresponding catalyst.

[0045] Table 2 Influence of various conditions on the activity of the catalyst during the ascorbic acid modification process

[0046]

[0047]

[0048] Note: The theoretical loading of Au in the catalyst is 5 wt%.

[0049] As can be seen from Table 2, the temperature and time of catalyst pretreatment have a significant impact on the catalytic activity. The treatment temperature should not be too high, and the treatment time should not be too long to avoid sintering of Au nanoparticles caused by high temperature. It is preferably treated at 200 - 400 °C, more preferably at 200 - 300 °C for 2 - 4 hours, and even more preferably for 2 - 3 hours to obtain a better catalyst effect. The purpose is to reduce Au and maintain an appropriate particle size. The performance of the catalyst is better when the concentration of ascorbic acid is between 3 - 5 mg / mL. The reaction temperature should not be too high, and the catalyst performance is the best when the reaction time is moderate (24 - 36 h). Different inert atmospheres have an impact on the catalytic performance. In contrast, the activity of the catalyst calcined under N 2 is the best. Too high or too low calcination temperature is not conducive to the catalyst maintaining high activity. The preferred temperature range is 200 - 600 °C, more preferably 300 - 600 °C. This may be because the ascorbic acid adsorbed on the Au surface is not completely decomposed during low-temperature treatment, while high-temperature treatment leads to sintering and growth of Au particles. Among them, the average particle size range of Au particles is 2.0 - 5.0 nm, and the surface coating layer thickness range is 0.2 - 2.0 nm. The calcination time should not be too long either. The treatment time in N 2 should not be too long or too short, preferably 3 - 5 hours, more preferably 3 - 4 hours. Too high temperature or too long time will lead to particle sintering, and the Au particle size range is 3.0 - 7.0 nm. This may be because the interaction between Au and TiO 2 is enhanced, the coating layer thickens, the thickness range is 0.5 - 2.5 nm, blocking some active sites and resulting in a decrease in catalytic activity.

[0050] Example 50

[0051] Investigation of the Au Surface Coating Layer in the Catalyst

[0052] For the Au-based catalysts prepared in each example, 2 mg was taken and ultrasonically dispersed in 2 mL of anhydrous ethanol solution for 10 min, then dropped onto a copper mesh drop by drop and dried with an infrared lamp for TEM testing. As Figure 1 shown, a coating layer was formed on the surface of Au nanoparticles in Example 1. The thickness of the coating layer was between 0.2 - 2.0 nm, and the Au nanoparticles were evenly dispersed on the surface of the support. The average particle size of the statistically counted particles was 3.3 nm. In other Examples 25 - 49, the particle size of most Au particles was in the range of 2.0 - 7.0 nm.

[0053] Example 51

[0054] Evaluation of Catalyst Performance

[0055] 100 mg of the Au / P25-TiO 2 @AA-N600 catalyst prepared in Example 1 was taken and evenly mixed with 130 mg of SiO 2 powder. After that, it was loaded into a quartz tube reactor. The catalyst was first purged in a He atmosphere at room temperature for 30 min, and after the purge, it was used for the evaluation of CO oxidation performance. The evaluation conditions (and process) were the same as in Example 1. As Figure 2 shown, the performance of the catalyst in Example 1 was compared with that of the catalysts in Comparative Examples 1 - 3. Even after high-temperature calcination treatment, the sample in Example 1 could still achieve complete conversion of CO at 20°C, showing good catalytic activity.

[0056] Example 52

[0057] Evaluation of Catalyst Stability

[0058] 3.5 mg of the catalyst prepared in Example 1 was taken and evenly mixed with 230 mg of SiO 2 powder. After that, it was loaded into a quartz tube reactor. The catalyst was first purged in a He atmosphere at room temperature for 30 min, and after the purge, it was used for the evaluation of CO oxidation performance. The evaluation conditions (and process) were the same as in Example 1. As Figure 3 shown, the test results indicated that during the continuous 50-h test of the catalytic CO oxidation reaction at 300°C, the conversion rate did not decrease significantly, indicating that the gold catalyst coated with titanium dioxide had high stability and good industrial application prospects.

[0059] Example 53

[0060] Evaluation of the Catalyst's Performance of Recycling and Reusing

[0061] Take 100 mg of the gold catalyst prepared in Example 1 and mix it evenly with 130 mg of SiO 2 powder. After that, load it into a quartz tube reactor. The catalyst is first purged in a He atmosphere at room temperature for 30 min, and after the purging is completed, it is used for the evaluation of CO oxidation performance. The evaluation conditions (and process) are the same as those in Example 1. The temperature is tested in the range from -40 °C to 600 °C. After each round of testing, wait for the catalyst bed temperature to drop to room temperature and then purge with He for 30 min, and then start the next round of testing. The test results are as Figure 4 , the catalyst shows no obvious decrease in activity during six consecutive cycle tests, proving that this catalyst has good industrial application prospects.

[0062] Example 54

[0063] Stability evaluation of the catalyst in the water-gas shift reaction

[0064] Use the same evaluation device as for CO oxidation. Take 100 mg of the gold catalyst prepared in Example 1 and mix it evenly with 130 mg of SiO 2 powder. After that, load it into a quartz tube reactor. The catalyst is first purged in a He atmosphere at room temperature for 30 min, and after the purging is completed, it is used for the evaluation of the water-gas shift reaction (CO + H 2 O → CO 2 + H 2 ) performance. The composition of the feed gas is 2 vol% CO + 10 vol% H 2 O + 88 vol% He, and the space velocity of the feed gas is 18 L g cat -1 h -1 , and the reaction temperature is 500 °C. The reaction products are analyzed online by an Agilent 6890 chromatograph equipped with a TCD detector. The test results are as Figure 5 shown. The activity of the catalyst does not show an obvious decrease after 50 h, indicating that the coating layer of titanium oxide on the surface of the Au particles can stabilize the catalyst even under high-temperature reaction conditions with water.

[0065] Comparative Example 1

[0066] Preparation of Au / TiO 2 (P25) catalyst and its evaluation of CO oxidation performance

[0067] Compared with Example 1, the difference is that the process of ascorbic acid modification is not carried out, and the gold catalyst prepared by the deposition-precipitation method is directly used for the CO oxidation reaction test. The evaluation conditions (and process) for the performance test of this catalyst are the same as those in Example 51.

[0068] Comparative Example 2

[0069] Au / TiO2 Preparation of -N600(P25) Catalyst and Evaluation of Its CO Oxidation Performance

[0070] Compared with Example 1, the difference is that ascorbic acid modification is not adopted, and the gold catalyst prepared by the deposition - precipitation method is directly calcined at 600 °C for 3 h in N 2 atmosphere to obtain Au / TiO 2 -N600 catalyst for CO oxidation reaction testing. The evaluation conditions (and process) for the performance test of this catalyst are the same as those in Example 51.

[0071] Comparative Example 3

[0072] Au / TiO 2 @AA(P25) Catalyst Preparation and Its CO Oxidation Performance Evaluation

[0073] Compared with Example 1, the difference is that after ascorbic acid modification, the subsequent calcination treatment step is not carried out, and the modified Au / TiO 2 @AA catalyst is directly used for CO oxidation reaction testing. The evaluation conditions (and process) for the performance test of this catalyst are the same as those in Example 51.

[0074] Table 3 Activity Comparison of Catalysts in Example 1 and Comparative Examples 1 - 3

[0075]

[0076] Note: The theoretical loading of Au in the catalyst is 5 wt%.

[0077] It can be seen from the result comparison in Table 4 that the fresh Au catalyst has the best activity. For the catalyst modified by ascorbic acid and calcined in an inert atmosphere, although the Au nanoparticles are wrapped by titanium dioxide, it still retains its good catalytic performance. However, directly calcining without ascorbic acid modification or only modifying without calcination do not have similar effects, and the activity of the catalyst significantly decreases. Similarly, although the fresh catalyst has good activity, due to the lack of protection of the coating layer, the conversion rate decreases by about 10% after continuous operation for 50 h, which may be due to the easy sintering and agglomeration of gold particles during high - temperature reactions, resulting in the gradual inactivation of the catalyst.

Claims

1. A method for preparing a titanium dioxide-coated gold catalyst, characterized in that: The catalyst uses titanium dioxide as a carrier and Au as an active species. The catalyst is further modified in an ascorbic acid solution and then calcined at a high temperature in an inert atmosphere.

2. The method for preparing a highly stable catalyst according to claim 1, characterized in that: The gold species loading amount in the catalyst is 0.5-20.0wt% (preferably 1.0-5.0wt%) of the carrier mass, and the average particle size of the active component gold nanoparticles is 2.0-7.0nm (preferably 2.5-5.0nm).

3. The method for preparing a highly stable catalyst according to claim 1, characterized in that: After ascorbic acid modification and high-temperature calcination, a titanium oxide coating layer is present on the surface of the Au particles, and the thickness of the coating layer ranges from 0.2 to 2.0 nm (preferably 0.3 to 1.5 nm).

4. The preparation method according to claim 1, characterized in that: The crystal form of the carrier titanium dioxide is one or more of P25 type, anatase type and amorphous titanium dioxide.

5. The method for preparing the catalyst according to any one of claims 1, 2, 3 or 4, comprising the following steps: 1) Preparation of Au catalyst by deposition-precipitation method: using a concentration of 0.05-1 mol L -1 (Preferably 0.05 to 0.5 mol L -1 , more preferably 0.1 to 0.5 mol L -1 ) of an alkaline solution with a concentration of 1.0 to 3.0 mg Au mL -1 (Preferably 1.0 to 2.0 mg Au mL -1 , more preferably 1.0 to 1.5 mol L -1 ) is adjusted to a pH value between 8 and 12 (preferably 9 to 11, more preferably 9 to 10), then a titanium dioxide carrier is added according to a desired ratio, and an alkali solution is continuously added dropwise to maintain a pH value between 8 and 12 (preferably 9 to 11, more preferably 9 to 10) for 1 to 3 hours, and then reacted in a constant temperature water bath at 60 to 90° C. (preferably 60 to 70° C.) for 1 to 5 hours (preferably 1 to 3 hours), and the product is centrifuged, washed, and dried; 2) Modification process of ascorbic acid: The catalyst prepared by the DP method is pre-treated by calcining at 200-400°C (preferably 200-300°C, more preferably 200-250°C) in air atmosphere for 2-5 hours (preferably 2-4 hours, more preferably 2-3 hours), and then 0.1-1g (preferably 0.1-0.5g) of the catalyst is dispersed in 30-60mL of ascorbic acid with a concentration of 1-10mg / mL (preferably 3-5mg / mL). The mixture is stirred in a constant temperature water bath at 50-90°C (preferably 60-70°C) for 12-48 hours (preferably 24-30 hours), washed by centrifugation, and dried at 60-80°C for 12-24 hours; then calcined at 300-600°C (preferably 400-600°C, more preferably 500-600°C) in an inert atmosphere for 2-5 hours (preferably 3-5 hours, more preferably 3-4 hours) to finally obtain the titanium dioxide-coated gold-based catalyst.

6. The preparation method according to claim 5, characterized in that: The alkali solution used is one or more of NaOH solution, KOH solution, ammonia water, and sodium carbonate solution, preferably NaOH solution.

7. The preparation method according to claim 6, characterized in that: The inert atmosphere used for calcination is one or more of argon, helium, and nitrogen, preferably nitrogen.

8. A catalyst prepared by the method for preparing the catalyst according to any one of claims 1 to 7.

9. Use of the catalyst according to claim 8 in catalytic oxidation reaction of CO or water gas shift reaction.

10. Use of the catalyst according to claim 9, characterized in that: In the CO oxidation reaction, a fixed bed reactor is used, the reaction pressure is normal pressure, the raw gas composition is 1-10 vol% (preferably 1-5 vol%) CO + 1-10 vol% (preferably 1-5 vol%) O2 + the remaining amount of He, and the raw gas space velocity is 20-50 Lg cat -1 h -1 (Preferably 25 to 35 L g cat -1 h -1 ), the reaction temperature includes -60°C to 500°C (preferably -40 to 300°C); The water gas shift reaction uses a fixed bed reactor, the raw gas composition is 2-10 vol% (preferably 2-5 vol%) CO + 5-10 vol% (preferably 8-10 vol%) H2O + the remaining amount of He, and the raw gas space velocity is 15-30 L g cat -1 h -1 (Preferably 20 to 30 Lg cat -1 h -1 ), reaction temperature 400~600℃ (preferably 500~600℃).

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