CN105032410A - A kind of Ag/Al2O3 catalyst, preparation method and application thereof - Google Patents

Abstract

The invention provides an Ag/Al ₂ O ₃ catalyst, a preparation method and an application thereof. The catalyst is composed of a carrier and an active component, the carrier is Al ₂ O ₃ , the active component includes a first active component and a second active component, the first active component is Ag ₂ O, the second The precursor of the active component is any one or a mixture of at least two of NbCl ₅ , TiO ₂ , SiO ₂ , AlCl ₃ , AgAlO ₂ , GaN, AlN or InN. The present invention significantly improves the low-temperature HC-SCR catalytic activity of the catalyst by using the second active component to dope and modify the Ag/Al ₂ O ₃ catalyst, which can avoid the poor low-temperature activity of the conventional Ag/Al ₂ O ₃ catalyst And additional online hydrogen supply equipment.

Description

A kind of Ag/Al2O3 catalyst, preparation method and application thereof

technical field

The invention belongs to the technical field of catalysts, and relates to an Ag/Al ₂ O ₃ catalyst, a preparation method and an application thereof.

Background technique

With the continuous growth of energy consumption and the rapid increase of the number of motor vehicles, the pollution of nitrogen oxides (NO _x ) emitted into the atmosphere due to the consumption of a large number of fossil fuels (stationary and mobile sources) is increasing, and the resulting Acid deposition, photochemical smog and haze have become the most prominent environmental problems today. In particular, the severe haze pollution incidents in North China since January 2013 have made us realize that there is still a long way to go to control NO _x emissions from motor vehicle exhaust, represented by diesel vehicles. Up to now, the elimination of NO _x , especially the purification of NO _x under oxygen-enriched conditions is still a big challenge.

Taking the typical working conditions of diesel vehicles as an example, the way of oxygen-enriched combustion leads to a large excess of oxygen in the exhaust of diesel vehicles and insufficient absolute amount of reducing agent. In order to purify diesel vehicle exhaust NO _x , additional reducing agents need to be added. According to different external reducing agents, SCR technology is divided into NH ₃ -SCR and HC-SCR. At present, the NH ₃ -SCR technology that replaces ammonia with urea water solution has been applied on a large scale in the purification of diesel vehicle exhaust, but there are many shortcomings in the process of popularization and application of this technology: the construction of the reductant urea water solution adding station is costly, Especially in countries with a vast territory; the instantaneous leakage of ammonia will be caused by the change of engine operating conditions. The biggest advantage of HC-SCR technology in diesel engine exhaust NO _x purification is that it can use vehicle oil as the final source of reducing agent, that is, to avoid the shortage of NH ₃ -SCR through the dual function of vehicle oil, so HC-SCR technology has been receiving much attention.

Based on the above reasons, in February 2009, GE and Tenneco signed a strategic cooperation agreement, aiming to develop efficient and complete HC-SCR after-treatment technology, and promote this technology in diesel vehicles, ships and stationary source exhaust NOx Purification application.

CN1439455A (lean combustion tail gas nitrogen oxide purification catalyst and purification method) discloses a catalyst for the reduction and catalytic purification of _NOx on Ag/Al ₂ O ₃ catalysts by adding hydrocarbons at a temperature of 150-600°C method.

CN103159242A (a method for preparing gibbsite and its application) uses gibbsite to prepare the carrier of Ag/Al ₂ O ₃ catalyst to expand the operating temperature window, and ethanol is the best reducing agent.

Among many HC-SCR catalytic systems, silver/alumina (Ag/Al ₂ O ₃ ) has excellent catalytic activity for selective reduction of NO _x by HC and especially oxygen-containing HC (such as ethanol), strong anti- The water sulfur tolerance has attracted extensive attention of researchers. However, in order to meet the increasingly stringent emission regulations, the improvement of low-temperature activity matching the exhaust temperature of diesel vehicles or the temperature characteristics of stationary source exhaust still faces major challenges. It is worth mentioning that: HC-SCR also has a typical H ₂ effect, that is, mixing a small amount of H ₂ in the exhaust gas can significantly improve the low-temperature activity of the Ag/Al ₂ O ₃ catalyst. However, considering the technical barriers to online hydrogen supply from mobile sources or stationary sources, the real technological breakthrough is to develop catalysts with excellent low-temperature activity.

Therefore, in order to achieve effective control of NO _x emissions from mobile and stationary sources and protect the atmospheric environment we live on, it is of great practical significance to develop environmentally friendly catalysts that can selectively reduce NO _x with low-temperature catalytic HC.

Contents of the invention

In view of the problems in the prior art, one of the objectives of the present invention is to provide an Ag/Al ₂ O ₃ catalyst, which can effectively improve the catalytic activity of low-temperature HC-SCR, and avoid the need to provide hydrogen online in the flue gas purification tedious steps.

In order to achieve the above object, the present invention adopts following technical scheme:

An Ag/Al ₂ O ₃ catalyst, which consists of a carrier and an active component, the carrier is Al ₂ O ₃ , the active component includes a first active component and a second active component, the first active component Divided into Ag ₂ O, the precursor of the second active component is any one or a mixture of at least two of NbCl ₅ , TiO ₂ , SiO ₂ , AlCl ₃ , AgAlO ₂ , GaN, AlN or InN.

Preferably, the precursor of the second active component is any one or a mixture of at least two of GaN, AlN or InN, preferably GaN or/and InN, more preferably GaN. GaN, especially AlN, will be denitrified and oxidized during the preparation process to form more defect sites, which is conducive to the anchoring of active metal silver. Therefore, when the precursor of the second active component is GaN or/and InN, the low-temperature activity of the catalyst can be improved more effectively. Others are more preferable, wherein, when the precursor of the second active component is GaN, the low-temperature activity improvement effect of the catalyst is the best, and the NOx conversion rate at 250° C. can reach 90%.

Preferably, based on the mass of metal Ag, the first active component Ag ₂ O is 0-10% of the mass of the carrier Al ₂ O ₃ and does not include 0, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9% or 9.5%, preferably 2 ~ 4wt%, at this time The catalytic activity of the catalyst is the best.

Preferably, the mass ratio of the mass of the second active component precursor to the metal Ag is 30:1 to 1:1, such as 28:1, 25:1, 22:1, 20:1, 15:1, 12:1 1, 9:1, 6:1 or 3:1, preferably 5:1 to 1:1, more preferably 2:1, at this time the catalytic activity at low temperature is the best and the cost is the lowest.

The second object of the present invention is to provide a kind of preparation method of Ag/Al ₂ O ₃ catalyst as mentioned above, described method is impregnation method, comprises the following steps:

The aqueous solution of the first active component Ag ₂ O precursor, the water slurry of the carrier Al ₂ O ₃ precursor and the aqueous solution of the second active component precursor are mixed, and the obtained slurry is rotated, dried, roasted and optionally ground to obtain Ag/Al ₂ O ₃ catalyst.

Preferably, the method comprises the steps of:

(1) Mix the aqueous solution of the first active component Ag ₂ O precursor with the water slurry of the carrier Al ₂ O ₃ precursor;

(2) Add the aqueous solution of the precursor of the second active component to the slurry obtained in step (1), rotate the obtained slurry, dry, roast and optionally pulverize to obtain the Ag/Al ₂ O ₃ catalyst.

Preferably, the carrier Al ₂ O ₃ precursor is pseudo-boehmite (AlOOH) or/and activated alumina (γ-Al ₂ O ₃ ).

An exemplary method for preparing the aqueous slurry of the carrier Al ₂ O ₃ precursor is: weighing the carrier Al ₂ O ₃ precursor such as pseudoboehmite (AlOOH) or/and activated alumina (γ-Al ₂ O ₃ ) , then add deionized water to mix and beat and keep stirring.

Preferably, the precursor of the first active component is any one or a mixture of at least two of AgNO ₃ , Ag ₂ SO ₄ , C ₂ H ₃ AgO ₂ or Ag ₂ O.

An exemplary operation method of step (2) is: after dissolving the Ag ₂ O precursor of the first active component in water, it is directly placed in the water slurry of the carrier Al ₂ O ₃ precursor and stirred evenly.

Preferably, after uniform stirring for at least 1 h, the obtained slurry is rotary evaporated.

Preferably, the obtained slurry is transferred to a rotary evaporating bottle, and the rotary evaporating water bath is heated under vacuum and reduced pressure to 30-90°C, preferably 60°C.

Preferably, the drying temperature is 100-180°C, and the drying time is 6-36h;

Preferably, the drying temperature is 120° C., and the drying time is 12 hours.

Preferably, the heating rate during the roasting process is 1°C to 20°C/min, such as 2°C/min, 4°C/min, 6°C/min, 8°C/min, 10°C/min, 12°C/min, 14°C /min, 16°C/min or 18°C/min, the calcination temperature is 600-800°C, such as 620°C, 640°C, 660°C, 680°C, 700°C, 720°C, 740°C, 760°C or 780°C.

Preferably, the firing atmosphere is a mixed gas of any one or a combination of at least two of O ₂ , H ₂ O or NH ₃ and N ₂ .

Preferably, the firing atmosphere is a mixed gas of N ₂ and O ₂ , a mixed gas of N ₂ and H ₂ O, a mixed gas of N ₂ , H ₂ O and O ₂ or a mixed gas of N ₂ , NH ₃ and H ₂ O any of the.

Preferably, in the mixed gas of N ₂ and O ₂ , the volume content of O ₂ is 0-20 vol%, excluding 0.

Preferably, in the mixed gas of N ₂ and H ₂ O, the volume content of H ₂ O is 1-20 vol%.

Preferably, in the mixed gas of N ₂ , H ₂ O and O ₂ , the volume content of H ₂ O is 0-10 vol% and excluding 0, and the volume content of O ₂ is 0-20 vol% and excluding 0.

Preferably, in the mixed gas of N ₂ , NH ₃ and H ₂ O, the volume content of NH ₃ is 0-0.12 vol% and excluding 0, and the volume content of H ₂ O is 0-10 vol% and excluding 0.

In the above mixed gas, _N2 is used as the balance gas.

Preferably, the calcining atmosphere flow ranges from 500 to 1000 mL/min.

Preferably, it is crushed into 20-40 mesh particles.

The third object of the present invention is a kind of preparation method of Ag/Al ₂ O ₃ catalyst as described above, described method is dry method ball milling, comprises the following steps:

(1) Mix the carrier Al ₂ O ₃ precursor, the first active component Ag ₂ O precursor and the second active component precursor, and then add water to wet the mixed sample;

(2) The mixed sample obtained in step (1) is ball milled, calcined and optionally pulverized to obtain an Ag/Al ₂ O ₃ catalyst.

Preferably, the method comprises the steps of:

(1) Add the carrier Al ₂ O ₃ precursor, the first active component Ag ₂ O precursor and the second active component precursor to the ball milling tank in sequence, and then add water to wet the mixed sample;

(2) The mixed sample obtained in step (1) is ball milled, calcined and optionally pulverized to obtain an Ag/Al ₂ O ₃ catalyst.

Preferably, the carrier Al ₂ O ₃ precursor is pseudo-boehmite (AlOOH) or/and activated alumina (γ-Al ₂ O ₃ ).

Preferably, the precursor of the first active component is any one or a mixture of at least two of AgNO ₃ , Ag ₂ SO ₄ , C ₂ H ₃ AgO ₂ or Ag ₂ O.

Preferably, the ball milling is carried out in a ball mill jar.

Preferably, there are 5-30 balls with a diameter of Φ10 mm and 0-20 balls with a diameter of 20 mm in the ball mill jar, for example, 2, 5, 8, 12, 15 or 18 balls.

Preferably, said ball milling is carried out in a planetary ball mill.

Preferably, the ball milling speed is 100-400r/min, such as 130r/min, 160r/min, 190r/min, 220r/min, 250r/min, 280r/min, 310r/min, 340r/min or 370r/min , the ball milling time is 1-9h, such as 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h or 8.5h.

Preferably, the heating rate during the roasting process is 1°C to 20°C/min, such as 2°C/min, 4°C/min, 6°C/min, 8°C/min, 10°C/min, 12°C/min, 14°C /min, 16°C/min or 18°C/min, the calcination temperature is 600-800°C, such as 620°C, 640°C, 660°C, 680°C, 700°C, 720°C, 740°C, 760°C or 780°C.

Preferably, the firing atmosphere is a mixed gas of any one or a combination of at least two of O ₂ , H ₂ O or NH ₃ and N ₂ .

Preferably, the firing atmosphere is a mixed gas of N ₂ and O ₂ , a mixed gas of N ₂ and H ₂ O, a mixed gas of N ₂ , H ₂ O and O ₂ or a mixed gas of N ₂ , NH ₃ and H ₂ O any of the.

Preferably, in the mixed gas of N ₂ and O ₂ , the volume content of O ₂ is 0-20 vol%, excluding 0.

Preferably, in the mixed gas of N ₂ and H ₂ O, the volume content of H ₂ O is 1-20 vol%.

Preferably, in the mixed gas of N ₂ , H ₂ O and O ₂ , the volume content of H ₂ O is 0-10 vol% and excluding 0, and the volume content of O ₂ is 0-20 vol% and excluding 0.

Preferably, in the mixed gas of N ₂ , NH ₃ and H ₂ O, the volume content of NH ₃ is 0-0.12 vol% and excluding 0, and the volume content of H ₂ O is 0-10 vol% and excluding 0.

In the above mixed gas, _N2 is used as the balance gas.

Preferably, the calcining atmosphere flow ranges from 500 to 1000 mL/min.

Preferably, it is crushed into 20-40 mesh particles.

The fourth object of the present invention is to provide an application of the above-mentioned Ag/Al ₂ O ₃ catalyst for HC-SCR reaction.

Considering the environmental friendliness and reactivity of the reducing agent comprehensively, the reducing agent is preferably ethanol.

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

The present invention significantly improves the low-temperature HC-SCR catalytic activity of the catalyst by using the second active component to dope and modify the Ag/Al ₂ O ₃ catalyst, which can avoid the poor low-temperature activity of the conventional Ag/Al ₂ O ₃ catalyst And additional online hydrogen supply equipment.

The Ag/Al ₂ O ₃ catalyst of the present invention can be prepared by wet impregnation or dry ball milling, which is simple and easy to control, and the preparation parameters are convenient to adjust and easy to enlarge the preparation scale.

Description of drawings

Fig. 1 _is the NO conversion rate evaluation figure of embodiment 1 and embodiment 2 catalyst;

Fig. 2 is the evaluation figure of _NOx conversion rate of embodiment 1 and embodiment 3 catalyst;

Fig. 3 _is the NO conversion rate evaluation figure of embodiment 1 and embodiment 4 catalyst;

Fig. 4 is the evaluation figure of _NOx conversion rate of embodiment 1 and embodiment 5 catalyst;

Fig. 5 _is the NO conversion rate evaluation figure of embodiment 1 and embodiment 6 catalyst;

Fig. 6 is embodiment 1,2 and embodiment 5,6 catalytic activity comparative figure;

Figure 7 is a comparison of the activity of Ag/Al ₂ O ₃ catalysts with different silver contents. It can be seen that, based on the mass of metal Ag, the first active component Ag ₂ O is 2 to 4 wt% of the mass of the carrier Al ₂ O ₃ , excellent catalytic activity.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and through specific implementation methods.

Example 1:

Catalyst preparation: Weigh 25 grams of Al ₂ O ₃ and add deionized water to mix and stir evenly, weigh 0.7875 grams of AgNO ₃ solid and add deionized water to dissolve, add the prepared solution into the Al ₂ O ₃ slurry and continue stirring 1h. The obtained solution was placed in a rotary evaporating flask, heated under reduced pressure and rotary evaporated to 60 °C. Remove the dry sample and dry it in a 120-degree oven overnight, then put the sample into the atmosphere furnace for roasting. The roasting condition is: N ₂ +O ₂ (20vol%), the total flow rate is 600mL/min. The heating rate was 10°C/min, and the temperature was raised to 600°C and kept for 3h. Then let it cool down to room temperature naturally. The samples were taken out and crushed into 20-40 meshes by tableting for later use, that is, a 2wt% Ag/Al ₂ O ₃ catalyst prepared by a conventional impregnation method was obtained.

Purification reaction conditions: Example 1 sample, weight: 0.3 g was put into the catalyst activity evaluation device, and the activity evaluation was carried out in a fixed-bed reactor. The composition of simulated flue gas is (1565ppm C ₂ H ₅ OH, 800ppm NO, 10% O ₂ , 10% H ₂ O), N ₂ is the balance gas, the total flow rate is 1000mL/min, and the reaction space velocity is 100000h ^-1 .

Purification effect: within the reaction temperature range of 300-500°C, the catalyst has the ability to convert 100% of NOx. Low temperature effect is not good, at 250°C, NOx conversion is only 50%. The specific results are shown in Figure 1.

Example 2:

Catalyst preparation: The catalyst preparation method is as described in Example 1.

Purification reaction conditions: Example 1 sample, weight: 0.3 g was put into the catalyst activity evaluation device, and the activity evaluation was carried out in a fixed-bed reactor. The simulated flue gas composition is (1565ppmC ₂ H ₅ OH, 800ppmNO, 10%O ₂ , 10%H ₂ O, 1%H ₂ ), N ₂ is the balance gas, the total flow rate is 1000mL/min, and the reaction space velocity is 100000h ^{- 1} .

Purification effect:

The specific results are shown in Figure 1.

Example 3:

Catalyst preparation: Weigh 25 grams of Al ₂ O ₃ and place it in a 125 mL corundum ball mill jar, weigh 0.7875 grams of AgNO ₃ solid and put it directly into the above grinding jar for uniform mixing, then weigh 1.08 grams of NbCl ₅ and put it into the above mixed sample. Using a 10 mL syringe, slowly drop 10 mL of deionized water into the sample while stirring the powder mixture. Then put the grinding jar into the planetary ball mill for grinding. The processing conditions are: the rotation speed is 300r/min, and the grinding time is 1h. The samples ground by a ball mill were sieved through a sieve and then roasted in an atmosphere furnace. The calcination condition is: N ₂ +O ₂ (20vol%)+H ₂ O (10vol%), the total flow rate is 600mL/min. The heating rate was 5°C/min, the temperature was raised to 600°C and kept for 3 hours, and then cooled to room temperature naturally. The samples were taken out and crushed to 20-40 mesh for later use, that is, a 2wt% Ag/Al ₂ O ₃ catalyst with Nb added was obtained by dry ball milling.

Purification reaction conditions: the same as in Example 1.

Purification effect:

The specific results are shown in Figure 2.

Example 4:

Catalyst preparation: Weigh 25 grams of Al ₂ O ₃ and place it in a 125 mL corundum ball mill jar, weigh 0.7875 grams of AgNO ₃ solid and put it directly into the above grinding jar for uniform mixing, then weigh 0.82 grams of AlN and put it into the above mixed sample. Using a 10 mL syringe, slowly drop 10 mL of deionized water into the sample while stirring the powder mixture. Then put the grinding jar into the planetary ball mill for grinding. The processing conditions are: rotating speed 300r/min. Grinding time is 1h. The samples ground by a ball mill were sieved through a sieve and then roasted in an atmosphere furnace. The roasting conditions are: N ₂ +O ₂ (20vol%, total flow rate 600mL/min. The heating rate is 5°C/min, the temperature is raised to 600°C and kept for 3h, and then it is naturally cooled to room temperature. The sample is taken out and crushed to 20-40 It is ready for use, that is, a 2wt% Ag/Al ₂ O ₃ catalyst with an AlN structure is prepared by dry ball milling.

Purification reaction conditions: the same as in Example 1.

Purification effect:

The specific results are shown in Figure 3.

Example 5:

Catalyst preparation: weigh 25 grams of Al ₂ O ₃ and place it in a 125 mL corundum ball mill jar, weigh 0.7875 grams of AgNO ₃ solid and put it directly into the above grinding jar for uniform mixing, then weigh 0.84 grams of GaN and put it into the above mixed sample. Using a 10 mL syringe, slowly drop 10 mL of deionized water into the sample while stirring the powder mixture. Then put the grinding jar into the planetary ball mill for grinding. The processing conditions are: rotating speed 300r/min. Grinding time is 1h. The samples ground by a ball mill were sieved through a sieve and then roasted in an atmosphere furnace. The calcination condition is: N ₂ +O ₂ (20vol%)+H ₂ O (10vol%), the total flow rate is 600mL/min. The heating rate was 5°C/min, the temperature was raised to 600°C and kept for 3 hours, and then cooled to room temperature naturally. The samples were taken out, pressed into tablets and crushed to 20-40 mesh for later use, that is, a 2wt% Ag/Al ₂ O ₃ catalyst added with a GaN structure was obtained by dry ball milling.

Purification reaction conditions: with embodiment 1.

Purification effect:

The specific results are shown in Figure 4.

Embodiment 6:

Catalyst preparation: Weigh 32 grams of AlOOH and add deionized water to mix and beat and stir evenly. Weigh 0.7875 grams of AgNO ₃ solid and add deionized water to dissolve it. The prepared solution is added to the AlOOH slurry. Then weigh AlN solid: 0.84 g and put it into the slurry as above and continue to stir for 1 h. The obtained solution was put into a rotary evaporating flask, heated under reduced pressure and rotary evaporated to 60°C. Remove the dry sample and dry it in a 120-degree oven overnight, then put the sample into the atmosphere furnace for roasting. The roasting condition is: N ₂ +O ₂ (20vol%)+NH3 (0.12vol%), the total flow rate is 600mL/min. The heating rate was 1°C/min, the temperature was raised to 600°C and kept for 3 hours, and then cooled to room temperature naturally. The samples were taken out and crushed into 20-40 meshes by tableting for use, that is, a 2wt% Ag/Al ₂ O ₃ catalyst with an AlN structure added by a conventional impregnation method was obtained.

Purification reaction conditions: with embodiment 1.

Purification effect:

The specific results are shown in Figure 5.

The applicant declares that the present invention illustrates the detailed methods of the present invention through the above-mentioned examples, but the present invention is not limited to the above-mentioned detailed methods, that is, it does not mean that the present invention must rely on the above-mentioned detailed methods to be implemented. Those skilled in the art should understand that any improvement of the present invention, the equivalent replacement of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc., all fall within the scope of protection and disclosure of the present invention.

Claims (10)

1. A Ag/Al ₂ O ₃ catalyst, it is made up of support and active component, and described support is Al ₂ O ₃ , and described active component comprises first active component and second active component, the first The active component is Ag ₂ O, and the precursor of the second active component is any one or a mixture of at least two of NbCl ₅ , TiO ₂ , SiO ₂ , AlCl ₃ , AgAlO ₂ , GaN, AlN or InN. 2. The catalyst according to claim 1, wherein the precursor of the second active component is any one or a mixture of at least two of GaN, AlN or InN, preferably GaN or/and InN, GaN is further preferred; Preferably, based on the mass of metal Ag, the first active component Ag ₂ O is 0-10% of the mass of the carrier Al ₂ O ₃ and does not include 0, preferably 2-4 wt%; Preferably, the mass ratio of the precursor of the second active component to the metal Ag is 30:1˜1:1, preferably 5:1˜1:1, more preferably 2:1. 3. a kind of Ag/Al as claimed in claim 1 or ₂ O _The preparation method of O catalyzer, described method is impregnation method, may further comprise the steps: The aqueous solution of the first active component Ag ₂ O precursor, the water slurry of the carrier Al ₂ O ₃ precursor and the aqueous solution of the second active component precursor are mixed, and the obtained slurry is rotated, dried, roasted and optionally Ground pulverization, obtains Ag/Al ₂ O ₃ catalysts; Preferably, the method comprises the steps of: (1) Mix the aqueous solution of the first active component Ag ₂ O precursor with the water slurry of the carrier Al ₂ O ₃ precursor; (2) Add the aqueous solution of the precursor of the second active component to the slurry obtained in step (1), rotate the obtained slurry, dry, roast and optionally pulverize to obtain the Ag/Al ₂ O ₃ catalyst. 4. The method according to claim 3, wherein the carrier Al ₂ O ₃ precursor is pseudo-boehmite or/and activated alumina; Preferably, the precursor of the first active component is any one or a mixture of at least two of AgNO ₃ , Ag ₂ SO ₄ , C ₂ H ₃ AgO ₂ or Ag ₂ O; Preferably, after being uniformly stirred for at least 1 hour, the obtained slurry is rotary evaporated; Preferably, the resulting slurry is transferred to a rotary evaporator, and the rotary evaporating water bath is heated under vacuum and reduced pressure to 30-90°C, preferably 60°C; Preferably, the drying temperature is 100-180°C, and the drying time is 6-36h; Preferably, the drying temperature is 120° C., and the drying time is 12 hours. 5. The method according to claim 3 or 4, wherein the heating rate during the calcination process is 1°C to 20°C/min, and the calcination temperature is 600 to 800°C; Preferably, the atmosphere for firing is a mixed gas of any one of O ₂ , H ₂ O or NH ₃ or a combination of at least two of them and N ₂ ; Preferably, the firing atmosphere is a mixed gas of N ₂ and O ₂ , a mixed gas of N ₂ and H ₂ O, a mixed gas of N ₂ , H ₂ O and O ₂ or a mixed gas of N ₂ , NH ₃ and H ₂ O any of the Preferably, in the mixed gas of _N2 and _O2 , the volume content of _O2 is 0-20vol%, and 0 is not included; Preferably, in the mixed gas of N ₂ and H ₂ O, the volume content of H ₂ O is 1-20 vol%; Preferably, in the mixed gas of N ₂ , H ₂ O and O ₂ , the volume content of H ₂ O is 0-10 vol% and excluding 0, and the volume content of O ₂ is 0-20 vol% and excluding 0; Preferably, in the mixed gas of N ₂ , NH ₃ and H ₂ O, the volume content of NH ₃ is 0-0.12 vol% and excluding 0, and the volume content of H ₂ O is 0-10 vol% and excluding 0; Preferably, the flow rate range of the roasting atmosphere is 500-1000mL/min; Preferably, it is crushed into 20-40 mesh particles. 6. a kind of Ag/Al as claimed in claim 1 or ₂ O _The preparation method of O catalyzer, described method is dry process ball milling, comprises the following steps: (1) Mix the carrier Al ₂ O ₃ precursor, the first active component Ag ₂ O precursor and the second active component precursor, and then add water to wet the mixed sample; (2) The mixed sample obtained in step (1) is ball milled, roasted and optionally pulverized to obtain Ag/Al ₂ O ₃ catalyst; Preferably, the method comprises the steps of: (1) Add the carrier Al ₂ O ₃ precursor, the first active component Ag ₂ O precursor and the second active component precursor to the ball milling tank in sequence, and then add water to wet the mixed sample; (2) The mixed sample obtained in step (1) is ball milled, calcined and optionally pulverized to obtain an Ag/Al ₂ O ₃ catalyst. 7. The method according to claim 6, characterized in that, the carrier Al ₂ O ₃ precursor is pseudo-boehmite or/and activated alumina; Preferably, the precursor of the first active component is any one or a mixture of at least two of AgNO ₃ , Ag ₂ SO ₄ , C ₂ H ₃ AgO ₂ or Ag ₂ O. 8. The method according to claim 6 or 7, characterized in that, the ball milling is carried out in a ball milling tank; Preferably, there are 5-30 small balls of Ф10mm and 0-20 small balls of Ф20mm in the ball mill jar; Preferably, said ball milling is carried out in a planetary ball mill; Preferably, the ball milling speed is 100-400r/min, and the ball milling time is 1-9h. 9. The method according to any one of claims 6-8, characterized in that the heating rate during the calcination process is 1°C-20°C/min, and the calcination temperature is 600-800°C; Preferably, the atmosphere for firing is a mixed gas of any one of O ₂ , H ₂ O or NH ₃ or a combination of at least two of them and N ₂ ; Preferably, the firing atmosphere is a mixed gas of N ₂ and O ₂ , a mixed gas of N ₂ and H ₂ O, a mixed gas of N ₂ , H ₂ O and O ₂ or a mixed gas of N ₂ , NH ₃ and H ₂ O any of the Preferably, in the mixed gas of _N2 and _O2 , the volume content of _O2 is 0-20vol%, and 0 is not included; Preferably, in the mixed gas of N ₂ and H ₂ O, the volume content of H ₂ O is 1-20 vol%; Preferably, in the mixed gas of N ₂ , H ₂ O and O ₂ , the volume content of H ₂ O is 0-10 vol% and excluding 0, and the volume content of O ₂ is 0-20 vol% and excluding 0; Preferably, in the mixed gas of N ₂ , NH ₃ and H ₂ O, the volume content of NH ₃ is 0-0.12 vol% and excluding 0, and the volume content of H ₂ O is 0-10 vol% and excluding 0; Preferably, the flow rate range of the roasting atmosphere is 500-1000mL/min; Preferably, it is crushed into 20-40 mesh particles. 10. A use of the Ag/Al ₂ O ₃ catalyst as claimed in claim 1 or 2, which is used for HC-SCR reaction.