PREPARATION METHOD OF NANO ALUMINUM OXIDE (NANO-Al2O3) WITH CONTROLLABLE HYDROXYL CONTENT AND USE THEREOF

Abstract

The present disclosure provides a preparation method of nano-aluminum oxide (nano-Al.sub.2O.sub.3) with a controllable hydroxyl content, belonging to the technical field of nano-alumina. H.sub.2O.sub.2 dissolved in water dissociates a large number of hydroxyl radicals. In the present disclosure, a resulting H.sub.2O.sub.2 solution is used as a solvent for precipitation; during the precipitation, a soluble aluminum salt and a pore-enlarging agent are reacted to generate a precipitate under alkaline conditions, and the hydroxyl radicals are distributed on a surface of the precipitate. During drying, the hydroxyl radicals are converted into bound water and distributed on a surface and in pores of an aluminum hydroxide precursor; during roasting, the bound water is destroyed to form hydroxyl. The hydroxyl content of the nano-Al.sub.2O.sub.3 can be regulated by controlling a concentration of the H.sub.2O.sub.2 solution, and the nano-Al.sub.2O.sub.3 has the hydroxyl content positively correlated with the concentration of the H.sub.2O.sub.2 solution.

Claims

1. A preparation method of nano-aluminum oxide (nano-Al.sub.2O.sub.3) with a controllable hydroxyl content, comprising the following steps: mixing a soluble aluminum salt and a pore-enlarging agent with a H.sub.2O.sub.2 solution, adjusting a pH value of a resulting mixture to 8 to 9 with an alkaline solution, and conducting precipitation to obtain a precipitate; drying the precipitate to obtain an aluminum hydroxide precursor; and conducting roasting on the aluminum hydroxide precursor to obtain the nano-Al.sub.2O.sub.3; wherein the H.sub.2O.sub.2 solution has a concentration of 0 wt % to 36 wt %, and the nano-Al.sub.2O.sub.3 has a hydroxyl content positively correlated with the concentration of the H.sub.2O.sub.2 solution.

2. The preparation method according to claim 1, wherein the alkaline solution comprises H.sub.2O.sub.2 with a concentration of 0 wt % to 36 wt %.

3. The preparation method according to claim 1, wherein the soluble aluminum salt is one or more selected from the group consisting of Al(NO.sub.3).sub.3.Math.9H.sub.2O, Al(NO.sub.3).sub.3.Math.6H.sub.2O, NaAlO.sub.2, AlPO.sub.4, Al.sub.2(SO.sub.4).sub.3, and AlCl.sub.3.

4. The preparation method according to claim 1, wherein the pore-enlarging agent is one or more selected from the group consisting of sodium dodecyl benzene sulfonate (SDBS), trimethylbenzene, urea, and urotropine.

5. The preparation method according to claim 2, wherein the pore-enlarging agent is one or more selected from the group consisting of sodium dodecyl benzene sulfonate (SDBS), trimethylbenzene, urea, and urotropine.

6. The preparation method according to claim 1, wherein the mixture of the soluble aluminum salt, the pore-enlarging agent, and the H.sub.2O.sub.2 solution has 0.1 mol/L to 2 mol/L of the soluble aluminum salt by concentration.

7. The preparation method according to claim 1, wherein the soluble aluminum salt and the pore-enlarging agent have a mass ratio of 1:(0.0001-0.1).

8. The preparation method according to claim 6, wherein the soluble aluminum salt and the pore-enlarging agent have a mass ratio of 1:(0.0001-0.1).

9. The preparation method according to claim 1, wherein the precipitation is conducted for 0.5 d to 5 d.

10. The preparation method according to claim 1, wherein the drying is conducted at 90° C. to 110° C. for 0.5 d to 14 d.

11. The preparation method according to claim 1, wherein the roasting is conducted at 300° C. to 1,100° C. for 3 h to 9 h.

12. The preparation method according to claim 1, further comprising conducting ultrasonic cleaning on a roasted product at 100 kHz to 200 kHz for 10 min to 2 h.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 shows an X-ray diffraction (XRD) pattern of hydroxyl nano-Al.sub.2O.sub.3 obtained in Examples 4 and 5;

[0023] FIG. 2 shows a contrast of a hydroxyl content of the hydroxyl nano-Al.sub.2O.sub.3 obtained in Examples 1 to 3;

[0024] FIG. 3 shows a contrast of a hydroxyl content of the hydroxyl nano-Al.sub.2O.sub.3 obtained in Examples 4 and 5;

[0025] FIG. 4 shows a transmission electron microscopy (TEM) image of the hydroxyl nano-Al.sub.2O.sub.3 load with a 10 wt % Ag catalyst obtained in Example 1;

[0026] FIG. 5 shows a TEM image of the hydroxyl nano-Al.sub.2O.sub.3 load with a 10 wt % Ag catalyst obtained in Example 2;

[0027] FIG. 6 shows a TEM image of the hydroxyl nano-Al.sub.2O.sub.3 load with a 10 wt % Ag catalyst obtained in Example 5;

[0028] FIG. 7 shows a catalytic effect of 0.1 wt % Pt-supported catalysts of Examples 1 and 3;

[0029] FIG. 8 shows a catalytic effect of 10 wt % Ag-supported catalysts of Examples 1 to 3;

[0030] FIG. 9 shows a catalytic effect of 10 wt % Ag-supported catalysts of Examples 1, 3 and 5; and

[0031] FIG. 10 shows a catalytic effect of 1 wt % Rh-supported catalysts of Examples 1 to 3.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] The present disclosure provides a preparation method of nano-Al.sub.2O.sub.3 with a controllable hydroxyl content, including the following steps:

[0033] mixing a soluble aluminum salt and a pore-enlarging agent with a H.sub.2O.sub.2 solution, adjusting a pH value of a resulting mixture to 8 to 9 with an alkaline solution, and conducting precipitation to obtain a precipitate;

[0034] drying the precipitate to obtain an aluminum hydroxide precursor; and

[0035] conducting roasting on the aluminum hydroxide precursor to obtain the nano-Al.sub.2O.sub.3; where

[0036] the H.sub.2O.sub.2 solution has a concentration of 0 wt % to 36 wt %, and the nano-Al.sub.2O.sub.3 has a hydroxyl content positively correlated with the concentration of the H.sub.2O.sub.2 solution.

[0037] In the present disclosure, a soluble aluminum salt and a pore-enlarging agent are mixed with a H.sub.2O.sub.2 solution, a pH value of a resulting mixture is adjusted to 8 to 9 with an alkaline solution, and precipitation is conducted to obtain a precipitate. The soluble aluminum salt is preferably one or more selected from the group consisting of Al(NO.sub.3).sub.3.Math.9H.sub.2O, Al(NO.sub.3).sub.3.Math.6H.sub.2O, NaAlO.sub.2, AlPO.sub.4, Al.sub.2(SO.sub.4).sub.3, and AlCl.sub.3, more preferably the Al(NO.sub.3).sub.3.Math.9H.sub.2O.

[0038] In the present disclosure, the pore-enlarging agent is preferably one or more selected from the group consisting of SDBS, trimethylbenzene, urea, and urotropine, more preferably the SDBS.

[0039] In the present disclosure, the H.sub.2O.sub.2 solution has a concentration of 0 wt % to 36 wt %, preferably 1 wt % to 30 wt %, more preferably 5 wt % to 25 wt %, and even more preferably 10 wt % to 20 wt %. The concentration of the H.sub.2O.sub.2 solution is adjusted according to the required hydroxyl content, and the hydroxyl content of the nano-Al.sub.2O.sub.3 is positively correlated with the concentration of the H.sub.2O.sub.2 solution. When the concentration of the H.sub.2O.sub.2 solution is 0, it means using water.

[0040] In the present disclosure, the mixture includes preferably 0.1 mol/L to 2 mol/L, more preferably 0.5 mol/L to 1.5 mol/L of the soluble aluminum salt by concentration. A higher concentration of the soluble aluminum salt means a greater mass of a precursor of the obtained aluminum hydroxide species, such that the loss of bound water can be reduced during drying, which is beneficial to obtain nano-Al.sub.2O.sub.3 with a high hydroxyl content.

[0041] In the present disclosure, the soluble aluminum salt and the pore-enlarging agent have a mass ratio of preferably 1:(0.0001-0.1), more preferably 1:(0.001-0.01).

[0042] In the present disclosure, there is no special requirement on a mixing method, and mixing methods well known to those skilled in the art can be used, such as mixing by stirring.

[0043] In the present disclosure, a pH value of a resulting mixture is adjusted to 8 to 9 with an alkaline solution, and precipitation is conducted to obtain a precipitate. In the alkaline solution, an alkaline substance is preferably one or more selected from the group consisting of NaOH, NH.sub.3.Math.H.sub.2O, (NH.sub.4).sub.2CO.sub.3, KOH, and Ba(OH).sub.2, more preferably the (NH.sub.4).sub.2CO.sub.3. The alkaline solution has preferably 0.01 mol/L to 0.2 mol/L, more preferably 0.02 mol/L, 0.05 mol/L, 0.1 mol/L, or 0.2 mol/L of the alkaline substance by concentration. The alkaline solution is preferably added dropwise.

[0044] In the present disclosure, the alkaline solution includes preferably H.sub.2O.sub.2 with a concentration of preferably 0 wt % to 36 wt %, more preferably 5 wt % to 30 wt %, and even more preferably 10 wt % to 20 wt %.

[0045] In the present disclosure, the mixture is adjusted to a pH value of 8 to 9, preferably 8.2 to 8.8, more preferably 8.3 to 8.5 with the alkaline solution.

[0046] In the present disclosure, the precipitation is conducted preferably by standing at preferably a room temperature for preferably 0.5 d to 5 d, more preferably 1 d to 4 d, and even more preferably 2 d to 3 d. After the precipitation, solid-liquid separation is preferably conducted on an obtained precipitation reaction solution to obtain the precipitate; a method for the solid-liquid separation is preferably to pour a supernatant. Through the precipitation, a precursor of aluminum hydroxide species is obtained.

[0047] In the present disclosure, the precipitate is dried to obtain an aluminum hydroxide precursor. The drying is conducted at 90° C. to 110° C., more preferably 95° C. to 105° C., and even more preferably 100° C. for preferably 0.5 d to 14 d, more preferably 1 d to 10 d, and even more preferably 3 d to 5 d. The drying is conducted preferably in an oven. Through the drying, the aluminum hydroxide precursor is obtained, denoted as —Al(OH).sub.3; the aluminum hydroxide precursor includes an unshaped aluminum hydroxide structure and an aluminum sol.

[0048] In the present disclosure, roasting is conducted on the aluminum hydroxide precursor to obtain the nano-Al.sub.2O.sub.3. The roasting is conducted preferably in a muffle furnace at preferably 300° C. to 1,100° C., more preferably 500° C. to 1,000° C., and even more preferably 600° C. to 800° C. The roasting is conducted for preferably 3 h to 9 h, more preferably 4 h to 8 h, and even more preferably 5 h to 6 h. The roasting temperature is obtained by heating at preferably 5° C./min.

[0049] In the present disclosure, a crystal phase of the nano-Al.sub.2O.sub.3 is preferably regulated by controlling the roasting temperature. Specifically, when the roasting temperature is 300° C. to 450° C., the obtained nano-Al.sub.2O.sub.3 is in η-Al.sub.2O.sub.3; when the roasting temperature is 450° C. to 800° C., the obtained nano-Al.sub.2O.sub.3 is γ-Al.sub.2O.sub.3; when the roasting temperature is 800° C. to 1,100° C., the obtained nano-Al.sub.2O.sub.3 is θ-Al.sub.2O.sub.3; and when the roasting temperature is above 1,100° C., the obtained nano-Al.sub.2O.sub.3 is α-Al.sub.2O.sub.3.

[0050] In the present disclosure, during the roasting, the aluminum hydroxide precursor is converted into nano-alumina, while the bound water formed by the hydroxyl radicals during the drying is destroyed into hydroxyl groups.

[0051] In the present disclosure, after the roasting, a roasted product is preferably ground. There is no special requirement for a grinding method, and grinding methods well known to those skilled in the art can be used.

[0052] In the present disclosure, after the roasting, ultrasonic cleaning is preferably on the roasted product at 100 kHz to 200 kHz, more preferably 150 kHz for preferably 10 min to 2 h, more preferably 0.5 h to 1.5 h. The impurity ions on a surface of the nano-Al.sub.2O.sub.3 are removed by the ultrasonic cleaning.

[0053] The preparation method of nano-Al.sub.2O.sub.3 with a controllable hydroxyl content provided by the present disclosure are described in detail below with reference to the examples, but these examples may not be understood as a limitation to the protection scope of the present disclosure.

Example 1

[0054] A preparation method of nano-alumina with a controllable hydroxyl content included the following steps:

[0055] 187.565 g of Al(NO.sub.3).sub.3.Math.9H.sub.2O was mixed with 200 mg of SDBS, and dissolved in 1 L of a 35% H.sub.2O.sub.2 to obtain a mixed solution;

[0056] 96 g of (NH.sub.4).sub.2CO.sub.3 was dissolved with 1 L of deionized water;

[0057] an obtained (NH.sub.4).sub.2CO.sub.3 solution was added dropwise to the mixed solution, and titrated to pH of 8.3;

[0058] a resulting suspension was allowed to stand for 1 d, and a supernatant was discarded, and the above process was repeated 3 times;

[0059] a remaining solid was dried in an oven at 90° C. for 3 d to obtain an —Al(OH).sub.3 precursor;

[0060] a dried —Al(OH).sub.3 precursor was directly roasted in a muffle furnace at 500° C. for 6 h without grinding, to obtain nano-γ-Al.sub.2O.sub.3 with multiple hydroxyl groups; and

[0061] the nano-γ-Al.sub.2O.sub.3 with multiple hydroxyl groups was ground, subjected to ultrasonic cleaning with deionized water for 10 min, and filtered; the above process was repeated 3 times to obtain pure nano-γ-Al.sub.2O.sub.3 with multiple hydroxyl groups.

Example 2

[0062] A preparation method of nano-alumina with a controllable hydroxyl content included the following steps:

[0063] 187.565 g of Al(NO.sub.3).sub.3.9H.sub.2O was mixed with 200 mg of SDBS, and dissolved in 1 L of a 17.5 wt % H.sub.2O.sub.2 to obtain a mixed solution;

[0064] 96 g of (NH.sub.4).sub.2CO.sub.3 was dissolved with 1 L of deionized water;

[0065] an obtained (NH.sub.4).sub.2CO.sub.3 solution was added dropwise to the mixed solution, and titrated to pH of 8.3;

[0066] a resulting suspension was allowed to stand for 1 d, and a supernatant was discarded, and the above process was repeated 3 times;

[0067] a remaining solid was dried in an oven at 90° C. for 3 d to obtain an —Al(OH).sub.3 precursor;

[0068] a dried —Al(OH).sub.3 precursor was directly roasted in a muffle furnace at 500° C. for 6 h without grinding, to obtain nano-γ-Al.sub.2O.sub.3 with moderate hydroxyl groups; and

[0069] the nano-γ-Al.sub.2O.sub.3 with moderate hydroxyl groups was ground, subjected to ultrasonic cleaning with deionized water for 10 min, and filtered; the above process was repeated 3 times to obtain pure nano-γ-Al.sub.2O.sub.3 with moderate hydroxyl groups.

Example 3

[0070] A preparation method of nano-alumina with a controllable hydroxyl content included the following steps:

[0071] 187.565 g of Al(NO.sub.3).sub.3.9H.sub.2O was mixed with 200 mg of SDBS, and dissolved in 1 L of deionized water to obtain a mixed solution;

[0072] 96 g of (NH.sub.4).sub.2CO.sub.3 was dissolved with 1 L of deionized water;

[0073] an obtained (NH.sub.4).sub.2CO.sub.3 solution was added dropwise to the mixed solution, and titrated to pH of 8.3;

[0074] a resulting suspension was allowed to stand for 1 d, and a supernatant was discarded, and the above process was repeated 3 times;

[0075] a remaining solid was dried in an oven at 90° C. for 3 d to obtain an —Al(OH).sub.3 precursor;

[0076] a dried —Al(OH).sub.3 precursor was directly roasted in a muffle furnace at 500° C. for 6 h without grinding, to obtain nano-γ-Al.sub.2O.sub.3 with less hydroxyl groups; and

[0077] the nano-γ-Al.sub.2O.sub.3 with less hydroxyl groups was ground, subjected to ultrasonic cleaning with deionized water for 10 min, and filtered; the above process was repeated 3 times to obtain pure nano-γ-Al.sub.2O.sub.3 with less hydroxyl groups.

Example 4

[0078] 18.75 g of Al(NO.sub.3).sub.3.9H.sub.2O was mixed with 20 mg of SDBS, and dissolved in 100 ml of a 35% H.sub.2O.sub.2 solution to obtain a mixed solution;

[0079] 9.6 g of (NH.sub.4).sub.2CO.sub.3 was dissolved with 100 L of deionized water;

[0080] an obtained (NH.sub.4).sub.2CO.sub.3 solution was added dropwise to the mixed solution, and titrated to pH of 8.3;

[0081] a resulting suspension was allowed to stand for 1 d, and a supernatant was discarded, and the above process was repeated 3 times;

[0082] a remaining solid was dried in an oven at 90° C. for 1 d;

[0083] a dried —Al(OH).sub.3 precursor was directly roasted in a muffle furnace at 500° C. for 6 h without grinding, to obtain nano-γ-Al.sub.2O.sub.3; and

[0084] the nano-γ-Al.sub.2O.sub.3 was ground, subjected to ultrasonic cleaning with deionized water for 10 min, and filtered; the above process was repeated 3 times to obtain pure nano-γ-Al.sub.2O.sub.3.

Example 5

[0085] 18.75 g of Al(NO.sub.3).sub.3.9H.sub.2O was mixed with 20 mg of SDBS, and dissolved in 100 ml of deionized water to obtain a mixed solution;

[0086] 9.6 g of (NH.sub.4).sub.2CO.sub.3 was dissolved with 100 L of deionized water;

[0087] an obtained (NH.sub.4).sub.2CO.sub.3 solution was added dropwise to the mixed solution, and titrated to pH of 8.3;

[0088] a resulting suspension was allowed to stand for 1 d, and a supernatant was discarded, and the above process was repeated 3 times;

[0089] a remaining solid was dried in an oven at 90° C. for 1 d;

[0090] a dried —Al(OH).sub.3 precursor was directly roasted in a muffle furnace at 500° C. for 6 h without grinding, to obtain nano-γ-Al.sub.2O.sub.3 with even less hydroxyl groups; and

[0091] the nano-γ-Al.sub.2O.sub.3 with even less hydroxyl groups was ground, subjected to ultrasonic cleaning with deionized water for 10 min, and filtered; the above process was repeated 3 times to obtain pure nano-γ-Al.sub.2O.sub.3 with even less hydroxyl groups.

Example 6

[0092] 40.95 g of NaAlO.sub.2 was mixed with 100 mg of SDBS, and dissolved in 1 L of a 35% H.sub.2O.sub.2 to obtain a mixed solution;

[0093] 40 g of NaOH was dissolved with 1 L of deionized water;

[0094] an obtained NaOH solution was added dropwise to the mixed solution, and titrated to pH of 9;

[0095] a resulting suspension was allowed to stand for 1 d, and a supernatant was discarded, and the above process was repeated 3 times;

[0096] a remaining solid was dried in an oven at 90° C. for 3 d;

[0097] a dried —Al(OH).sub.3 precursor was directly roasted in a muffle furnace at 500° C. for 6 h without grinding, to obtain nano-γ-Al.sub.2O.sub.3 with relatively more hydroxyl groups; and

[0098] the nano-γ-Al.sub.2O.sub.3 with relatively more hydroxyl groups was ground, subjected to ultrasonic cleaning with deionized water for 10 min, and filtered; the above process was repeated 3 times to obtain pure nano-γ-Al.sub.2O.sub.3 with relatively more hydroxyl groups.

[0099] The XRD patterns of nano-Al.sub.2O.sub.3 obtained in Examples 4 and 5 were shown in FIG. 1. It was seen from FIG. 1 that the Al.sub.2O.sub.3 obtained in the present disclosure were all in the same crystal phase, that is, γ-Al.sub.2O.sub.3.

[0100] The hydroxyl contents of the nano-Al.sub.2O.sub.3 obtained in Examples 1 to 3 were tested by in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTs), and the results were shown in FIG. 2. Since hydroxyl groups could effectively combine with NH.sub.3 to form NH.sub.4.sup.+, within the wavelength range of 4,000 cm.sup.−1 to 3,500 cm.sup.−1 in this spectrum, the more NH.sub.3 adsorption led to a greater loss of hydroxyl peaks, indicating a greater hydroxyl content. It was seen from FIG. 2 that with the increase of the concentration of H.sub.2O.sub.2 solution, the hydroxyl content of the nano-Al.sub.2O.sub.3 increased.

[0101] The hydroxyl contents of nano-Al.sub.2O.sub.3 obtained in Examples 4 to 5 were shown in FIG. 3. Due to the small synthesis amount of nano-Al.sub.2O.sub.3, bound water was also easily lost during the drying. However, the content of hydroxyl groups on γ-Al.sub.2O.sub.3 could still be controlled by adjusting the amount of H.sub.2O.sub.2 added. The more H.sub.2O.sub.2 meant the more abundant hydroxyl groups.

[0102] The hydroxyl nano-γ-Al.sub.2O.sub.3 obtained in Examples 1, 2, and 5 were loaded with 10 wt % Ag nanoparticles to obtain an Ag-supported catalyst.

[0103] The TEM image of the Ag-supported catalyst obtained in Example 1 was shown in FIG. 4. It was seen from FIG. 4 that Ag was anchored on γ-Al.sub.2O.sub.3 in the form of a single atom in the figure without large Ag nanoparticles. Since Ag atoms could be anchored on γ-Al.sub.2O.sub.3 through hydroxyl groups, if the hydroxyl groups were abundant enough, Ag was not easy to agglomerate to form nanoparticles. The more hydroxyl groups, the better the dispersion of Ag and the easier it was to exist in the form of single atoms; the fewer hydroxyl groups, the fewer anchor sites that the γ-Al.sub.2O.sub.3 surface could provide to Ag, such that Ag atoms were easy to aggregate to form nanoparticles.

[0104] The TEM image of the Ag-supported catalyst obtained in Example 2 was shown in FIG. 5. It can be seen from FIG. 5 that due to the limited content of hydroxyl groups, the nano-Al.sub.2O.sub.3 could not provide the components with anchoring sites. Therefore, Ag atoms that could not be anchored by hydroxyl groups were aggregated into nanoparticles within a certain particle size (from 1 nm to 22 nm, mainly including Ag nanoparticles of 5 mm).

[0105] The TEM image of the Ag-supported catalyst obtained in Example 5 was shown in FIG. 6. As shown in FIG. 6, due to the less hydroxyl content, the nano-Al.sub.2O.sub.3 obtained in Example 5 was less likely to provide sufficient Ag anchoring sites, such that Ag atoms were agglomerated in large numbers to form nanoparticles with an average particle size of 30 nm.

Use Example 1

[0106] Using 0.1 wt % Pt loaded with each of Example 1 (Al.sub.2O.sub.3 with multiple hydroxyl groups) and Example 3 (Al.sub.2O.sub.3 with less hydroxyl groups), catalytic oxidation was conducted on formaldehyde at a room temperature, and the results were shown in FIG. 7. The Al.sub.2O.sub.3 with multiple hydroxyl groups was beneficial to Pt dispersion due to more hydroxyl groups, and the active center of formaldehyde catalysis was isolated Pt atoms. Therefore, the Al.sub.2O.sub.3 with multiple hydroxyl groups was beneficial to the oxidation of formaldehyde by Pt atoms. However, the Al.sub.2O.sub.3 with less hydroxyl groups was not conducive to the dispersion of Pt, and there was less Pt existing as a single atom on the surface of Al.sub.2O.sub.3, resulting in a poor oxidation effect on formaldehyde. (Reaction conditions were: HCHO=150 ppm, 20% O.sub.2, at a room temperature, GHSV=120,000 h.sup.−1).

Use Example 2

[0107] Using 10 wt % Ag loaded with each of Example 1 (Al.sub.2O.sub.3 with multiple hydroxyl groups), Example 2 (Al.sub.2O.sub.3 with moderate hydroxyl groups), and Example 3 (Al.sub.2O.sub.3 with less hydroxyl groups), catalytic oxidation was conducted at 100° C. to 300° C. on CO. The results were shown in FIG. 8. The active center of CO catalytic oxidation was Ag nanoparticles. Therefore, in the three kinds of Al.sub.2O.sub.3 with different hydroxyl contents, the Al.sub.2O.sub.3 with less hydroxyl groups was not conducive to the dispersion of Ag atoms and made them agglomerate to form nanoparticles; while Ag on the Al.sub.2O.sub.3 with multiple hydroxyl groups was well dispersed and existed on the surface of Al.sub.2O.sub.3 in the form of isolated atoms. Therefore, Example 3 loaded with the same mass of Ag atoms showed a better CO catalytic oxidation activity. (Reaction conditions were: CO=500 ppm, 10% O.sub.2, GHSV=120,000 h.sup.−1).

Use Example 3

[0108] Using 10 wt % Ag loaded with each of Example 1 (Al.sub.2O.sub.3 with multiple hydroxyl groups), Example 3 (Al.sub.2O.sub.3 with less hydroxyl groups), and Example 5 (Al.sub.2O.sub.3 with less hydroxyl groups), selective catalytic oxidation was conducted at 100° C. to 300° C. on NH.sub.3. The results were shown in FIG. 9. The active center of NH.sub.3 catalytic oxidation was Ag nanoparticles. Therefore, in the three kinds of Al.sub.2O.sub.3 with different hydroxyl contents, the Al.sub.2O.sub.3 with less hydroxyl groups was not conducive to the dispersion of Ag atoms and made them agglomerate to form nanoparticles; while Ag on the Al.sub.2O.sub.3 with multiple hydroxyl groups was well dispersed and existed on the surface of Al.sub.2O.sub.3 in the form of isolated atoms. Therefore, Example 5 (the Al.sub.2O.sub.3 synthesized in Example 5 had surface hydroxyl groups less than that of Example 3) loaded with the same mass of Ag atoms shows a better NH.sub.3 catalytic oxidation activity. (Reaction conditions were: NH.sub.3=500 ppm, 10% O.sub.2, GHSV=120,000 h.sup.−1).

Use Example 4

[0109] Using 1 wt % Rh loaded with each of Example 1 (Al.sub.2O.sub.3 with multiple hydroxyl groups), Example 2 (Al.sub.2O.sub.3 with moderate hydroxyl groups), and Example 3 (Al.sub.2O.sub.3 with less hydroxyl groups), catalytic hydrogenation was conducted at 200° C. to 400° C. on CS.sub.2. The results were shown in FIG. 10. The active center of CS.sub.2 catalytic hydrogenation was Rh nanoparticles. Therefore, in the three kinds of Al.sub.2O.sub.3 with different hydroxyl contents, the Al.sub.2O.sub.3 with less hydroxyl groups was not conducive to the dispersion of Rh atoms and made them agglomerate to form nanoparticles; while Rh on the Al.sub.2O.sub.3 with multiple hydroxyl groups was well dispersed and existed on the surface of Al.sub.2O.sub.3 in the form of isolated atoms. Therefore, Example 3 loaded with the same mass of Rh atoms showed a better CS.sub.2 catalytic hydrogenation activity. (Reaction conditions were: CS.sub.2=200 ppm, 10% H.sub.2, GHSV=120,000 h.sup.−1).

[0110] The above descriptions are merely preferred implementations of the present disclosure. It should be noted that a person of ordinary skill in the art may further make several improvements and modifications without departing from the principle of the present disclosure, but such improvements and modifications should be deemed as falling within the protection scope of the present disclosure.