CN103084161A - Ce-Zr-Al-based composite oxide rare earth oxygen-storage material and preparation method thereof - Google Patents

Abstract

A cerium-zirconium-aluminum-based composite oxide rare-earth oxygen storage material and a preparation method thereof, the cerium-zirconium-aluminum-based composite oxide rare-earth oxygen storage material is composed of cerium oxide, zirconia, aluminum oxide and other rare earth oxides except cerium The composition of the composite oxide, its weight percentage is as follows: cerium oxide: 15-65%, zirconia: 12-55%, aluminum oxide: 5-50%, other rare earth oxides except cerium: 4-10%; Compared with some products, the interaction between alumina and cerium-zirconium-based composite oxides is strengthened by surface treatment of alumina, and the uniformity between alumina and cerium-zirconium-based composite oxides is fully guaranteed; through The selection and compounding of the precipitating agent and the control of the precipitation end point ensure the yield of the product; by adding the surface treatment agent, the pore diameter and pore volume of the precipitate precursor after roasting are ensured, which improves the high temperature anti-aging of the material ability.

Description

Cerium-zirconium-aluminum-based composite oxide rare earth oxygen storage material and preparation method thereof

technical field

The invention relates to a rare earth oxygen storage material and a preparation method thereof, in particular to a cerium-zirconium-aluminum-based composite oxide rare earth oxygen storage material used for exhaust gas purification or catalytic combustion such as automobile exhaust purification, organic waste gas elimination, and natural gas catalytic combustion, and its preparation method.

Background technique

Reducing vehicle exhaust pollution, protecting the quality of the atmospheric environment, and realizing the sustainable development of the ecological environment and society are one of the important issues of my country's environmental protection at present and for a long time to come.

In order to reduce pollution, breakthroughs must be made in three aspects: improving the quality of gasoline, improving the combustion state of the engine, and increasing the catalytic efficiency of exhaust gas purification. So far, the most effective way to use automobile exhaust purification catalysts is to reduce the content of three toxic gases, HC, CO and NOx, in the exhaust gas through a three-way catalytic device.

The three-way catalyst is mainly composed of a noble metal active component that plays a catalytic role, a catalytic promoter (oxygen storage material) containing CeO ₂ and a carrier for supporting the active component. A suitable oxygen storage coating material for automobile exhaust purification plays a key role in the dispersion and stability of precious metals. At the same time, the oxygen storage coating material can improve the oxygen storage capacity of the catalyst under high temperature conditions, expand its air-fuel ratio operating window, and make the catalyst operate at a very high temperature. The activity is significantly improved under harsh operating conditions.

The currently commercially used cerium-containing rare earth oxygen storage materials and γ-Al ₂ O ₃ with high specific surface area and strong thermal aging resistance were prepared separately.

Due to the poor thermal stability of _CeO2 , its use is limited. Therefore, the sintering of _CeO2 must be suppressed when used at high temperature. When the cerium ions in _CeO2 are partially replaced with other cations, structural defects can be generated, which significantly improves its high-temperature thermal stability.

Adding ZrO ₂ to CeO ₂ can form a CeO ₂ -ZrO ₂ solid solution to improve the bulk phase properties of CeO ₂ , facilitate the migration and diffusion of bulk oxygen atoms, make the bulk phase reaction process more active, and improve the storage capacity of CeO ₂ Oxygen capacity and high temperature stability. At the same time, the addition of rare earth and alkaline earth elements such as Pr, Nd, Y, Nb, La, and Ba can further enhance the high temperature aging resistance of the oxygen storage material and increase its oxygen storage capacity. The oxygen storage material can effectively stabilize the dispersion of the active components, so it has a large specific surface area, a large pore volume and a suitable pore size distribution, and has good high-temperature aging resistance and excellent low-temperature catalytic performance. Cerium-zirconium-based oxygen storage Material becomes the key material of the new three-way catalyst.

The thermal stability, specific surface area, pore volume, pore size distribution, surface acidity and NO adsorption capacity of γ-Al ₂ O ₃ largely affect the catalytic performance of the catalyst. Improving the high-temperature thermal stability and surface properties of γ-Al ₂ O ₃ is of great significance for improving the activity and service life of the catalyst. research shows. The high-temperature thermal stability of alumina can be improved by adding rare earth elements, alkaline earth elements, etc., and the transformation of alumina from γ phase to α phase can be inhibited. At present, it is widely used in the industry to modify the surface of pseudo-boehmite with rare earth elements or transition metal elements and then roast it to prepare alumina with strong thermal aging resistance.

Use rare earth materials such as cerium-zirconium-based solid solution and alumina to modify each other to prepare cerium-zirconium-aluminum matrix composite materials, so that it has the common advantages of oxygen storage materials and alumina, and improves the high-temperature anti-aging ability of oxygen storage materials and alumina. It is the key technology of the new generation of catalytic coating.

The invention patent with the patent number of 200510020615.1 discloses a cerium-zirconium-aluminum-based oxygen storage material and its preparation method. Its basic composition is cerium oxide, zirconia, aluminum oxide and a stabilizer. At least one of alkaline earth metal oxides; the preparation process is (1) preparing a mixed solution of nitrate and an alkaline precipitant according to a given material composition; (2) introducing the prepared two solutions into a reaction vessel in parallel Precipitate at 90-100°C for no less than 2 hours after the precipitation; (3) The solid-liquid separation of the aged reaction feed liquid is carried out, and the separated solid-phase precipitate is washed and then mixed with surfactant and water Prepare a slurry; (4) The slurry is dried by evaporation and then fired to obtain a cerium-zirconium-aluminum-based oxygen storage material.

The specific surface agent of the oxygen storage material prepared by the above method can reach a maximum of 110m ² /g or more than 38m ² /g after calcination at 1000°C for 5 hours; however, this method uses aluminum nitrate as a raw material, and the cost is relatively high. At the same time, the pore size of the prepared oxygen storage material is small, and the high temperature anti-aging performance of the oxygen storage material is poor.

The invention patent with the patent publication number CN101940921A discloses a double-layer structure oxygen storage material and its preparation method, which is composed of a cerium-zirconium solid solution and a large specific surface γ-Al ₂ O ₃ . Lanthanum nitrate solution, cerium nitrate solution, yttrium nitrate and zirconium nitrate solution are placed in a container and ammonia water is added to precipitate to obtain a precipitate; (2) industrial hydrogen peroxide of cerium oxide quality is added to the precipitate in step (1) to obtain cerium-zirconium Precursor compound; (3) Mixing the precursor and γ-Al ₂ O ₃ in a mass ratio of 1:1 and stirring to obtain a mixture; (4) Washing, filtering, and adding a surfactant to the mixture in step (3), After drying, roasting, and jet crushing, a powder oxygen storage material with a double-layer structure is obtained.

The above method uses cerium-zirconium precursors and γ-Al ₂ O ₃ to mechanically mix, which leads to poor mixing uniformity of alumina and cerium-zirconium composite oxides and poor adhesion between alumina and cerium-zirconium composite oxides, which affects Catalytic properties of oxygen storage materials and high temperature thermal stabilizers.

Patent No. 98108256.4 discloses an oxygen storage material with high thermal stability and a method for preparing the material. Cerium oxide and at least one stabilizer selected from praseodymium oxide, lanthanum oxide, yttrium oxide, and neodymium oxide It is highly dispersed on the specific surface of large surface area carriers such as alumina, zirconia, titania, silica or other oxides, and then roasted; its preparation method is to dissolve the precursor of the stabilizer and cerium oxide are added to a previously prepared, constantly stirring aqueous dispersion of the selected carrier material, and then slowly increase the pH of the dispersion to 8-10 by adding alkali, so that the stabilizer and Cerium oxide is precipitated on the support material.

The above method does not carry out surface treatment on the carrier, and the particle size and shape of the carrier affect the uniformity of the coating and the adhesion between the coating layer and the carrier, and affect the catalytic activity and high temperature thermal stability of the oxygen storage material.

In summary, there are few studies on cerium-zirconium-aluminum-based rare earth oxygen storage materials, and there is a big contradiction between the binding force between cerium-zirconium and alumina and the high-temperature aging resistance, and the high-temperature aging resistance of the material is poor. .

Therefore, there is a special need for a cerium-zirconium-aluminum-based composite oxide rare earth oxygen storage material and a preparation method thereof, which have solved the above-mentioned existing problems.

Contents of the invention

The purpose of the present invention is to provide a cerium-zirconium-aluminum-based composite oxide rare earth oxygen storage material and its preparation method, which has the characteristics of large specific surface area, good high temperature anti-aging ability, high oxygen storage and release ability, etc., and is suitable for automobile exhaust gas purification, organic waste gas Exhaust gas purification or catalytic combustion such as elimination and catalytic combustion of natural gas. .

In order to achieve the above object, the technical scheme of the present invention is as follows:

On the one hand, the present invention provides a cerium-zirconium-aluminum-based composite oxide rare-earth oxygen storage material, characterized in that the cerium-zirconium-aluminum-based composite oxide rare-earth oxygen storage material is made of cerium oxide, zirconium oxide, aluminum oxide and decerized The composite oxide composed of other rare earth oxides, the weight percentage is as follows:

Cerium oxide: 15-65%

Zirconia: 12-55%

Alumina: 5-50%

Rare earth oxides other than cerium: 4-10%.

In one embodiment of the present invention, the rare earth oxides other than cerium are selected from one or more of lanthanum oxide, yttrium oxide, praseodymium oxide and neodymium oxide.

In another aspect, the present invention provides a method for preparing a cerium-zirconium-aluminum-based composite oxide rare earth oxygen storage material, which is characterized in that it includes the following steps:

(1) Preparation of aluminum sol, mixing alumina raw material with water, adding nitric acid to adjust the pH to 2-3, shearing dispersion, high-energy ball milling, to form transparent aluminum sol A;

(2) the preparation of mixed metal salt solution, according to material composition, determine the content of cerium oxide, zirconium oxide and other rare earth oxides except cerium, convert into the weight content of corresponding nitrate or carbonate, then Cerium nitrate, soluble nitrates of rare earths other than cerium and zirconium nitrate are dissolved in water to obtain mixed metal nitrate solution B;

(3) Preparation of the active component precursor, according to the composition of the material, the aluminum sol A and the mixed metal nitrate solution B are mixed to obtain the active component precursor C;

(4) Precipitation, at a certain temperature, add an alkaline precipitating agent to the above-mentioned active component precursor C until the end of the precipitation, add stoichiometric hydrogen peroxide, keep warm for a certain period of time, and obtain a precipitate D;

(5) Surface treatment of the precipitate, dehydrating and washing the precipitate D; repulping the dehydrated precipitate D and water at a mass ratio of 2:1, adding a certain amount of surface treatment agent, and shearing and dispersing;

(6) Roasting, calcining the surface-treated precipitate D at 450-800° C. for 4-8 hours to obtain the cerium-zirconium-aluminum-based solid solution rare earth oxygen storage material.

In one embodiment of the present invention, in step (1), the alumina raw material is selected from macroporous γ-Al ₂ O ₃ or macroporous pseudo-boehmite with a pore volume ≥ 0.9 ^{cm 3} /g.

In one embodiment of the present invention, the solid content of the mixed turbid liquid of alumina and water is 5-10%.

In one embodiment of the present invention, in step (2), the cerium oxide source is selected from cerium nitrate or cerium carbonate; the zirconia source is selected from zirconium oxycarbonate; the other rare earth soluble nitrates except cerium One or more selected from lanthanum nitrate, yttrium nitrate, praseodymium nitrate and neodymium nitrate or nitric acid reacts with lanthanum oxide, yttrium oxide, praseodymium oxide and neodymium oxide to form a corresponding nitrate solution.

In one embodiment of the present invention, in step (4), the alkaline precipitation agent is selected from one or more of ammonia water and ammonium bicarbonate; the temperature of the precipitation is 60-90°C; the precipitation The end point is: when ammonia water is selected as the precipitant, the pH of the end point of the precipitation is 9, and when the precipitant contains ammonium bicarbonate, the end point of the precipitation is 6-6.5; the holding time is 1-3h.

In one embodiment of the present invention, in step (5), the dehydration is a conventional dehydration method of plate and frame filter press or centrifugal dehydration; the surface treatment agent is selected from lauric acid, stearic acid and alkenyl succinic anhydride One or more of them, the added amount of the surface treatment agent is 30-50% by weight.

Compared with the existing products, the cerium-zirconium-aluminum-based composite oxide rare earth oxygen storage material and the preparation method thereof of the present invention strengthen the interaction between the alumina and the cerium-zirconium-based composite oxide by surface-treating the alumina , and fully ensure the uniformity between alumina and cerium-zirconium-based composite oxides; through the selection and compounding of precipitating agents, the precipitation endpoint is controlled to ensure the product yield; by adding surface treatment agents, the precipitation is guaranteed The pore diameter and pore volume of the precursor after calcination are larger, which improves the high-temperature anti-aging ability of the material, so that the prepared cerium-zirconium-aluminum-based composite oxide oxygen storage material has high oxygen storage capacity and fast oxygen storage and release speed. The invention has the advantages of strong anti-aging ability under high temperature and the like, and realizes the object of the present invention.

The features of the present invention can be clearly understood by referring to the drawings of the present invention and the detailed description of the following preferred embodiments.

Description of drawings

Fig. 1 is an XRD schematic diagram of the nano-cerium-zirconium-based solid solution rare earth oxygen storage material prepared in Example 1 of the present invention.

Detailed ways

In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention will be further described below in conjunction with specific embodiments.

The cerium-zirconium-aluminum-based composite oxide rare earth oxygen storage material of the present invention, the cerium-zirconium-aluminum-based composite oxide rare earth oxygen storage material is a composite composed of cerium oxide, zirconium oxide, aluminum oxide and other rare earth oxides except cerium Oxide, its weight percent is as follows:

Cerium oxide: 15-65%

Zirconia: 12-55%

Alumina: 5-50%

Rare earth oxides other than cerium: 4-10%; the XRD schematic diagram of the cerium-zirconium-aluminum-based composite oxide rare earth oxygen storage material of the present invention is shown in FIG. 1 .

In the present invention, the rare earth oxides other than cerium are selected from one or more of lanthanum oxide, yttrium oxide, praseodymium oxide and neodymium oxide.

The preparation method of the cerium-zirconium-aluminum-based composite oxide rare earth oxygen storage material of the present invention comprises the following steps:

(1) Preparation of aluminum sol, mixing alumina raw material with water, adding nitric acid to adjust the pH to 2-3, shearing dispersion, high-energy ball milling, to form transparent aluminum sol A;

(2) the preparation of mixed metal salt solution, according to material composition, determine the content of cerium oxide, zirconium oxide and other rare earth oxides except cerium, convert into the weight content of corresponding nitrate or carbonate, then Cerium nitrate, soluble nitrates of rare earths other than cerium and zirconium nitrate are dissolved in water to obtain mixed metal nitrate solution B;

(3) Preparation of the active component precursor, according to the composition of the material, the aluminum sol A and the mixed metal nitrate solution B are mixed to obtain the active component precursor C;

(4) Precipitation, at a certain temperature, add an alkaline precipitating agent to the above-mentioned active component precursor C until the end of the precipitation, add stoichiometric hydrogen peroxide, keep warm for a certain period of time, and obtain a precipitate D;

(5) Surface treatment of the precipitate, dehydrating and washing the precipitate D; repulping the dehydrated precipitate D and water at a mass ratio of 2:1, adding a certain amount of surface treatment agent, and shearing and dispersing;

(6) Roasting, calcining the surface-treated precipitate D at 450-800° C. for 4-8 hours to obtain the cerium-zirconium-aluminum-based solid solution rare earth oxygen storage material.

In the present invention, in step (1), the alumina raw material is selected from macroporous γ-Al ₂ O ₃ or macroporous pseudoboehmite with a pore volume ≥ 0.9 ^{cm 3} /g.

In the present invention, the solid content of the mixed turbid liquid of alumina and water is 5-10%.

In the present invention, in step (2), the source of cerium oxide is selected from cerium nitrate or cerium carbonate; the source of zirconia is selected from zirconyl carbonate; the other rare earth soluble nitrates other than cerium are selected from lanthanum nitrate One or more of yttrium nitrate, praseodymium nitrate and neodymium nitrate or nitric acid reacts with lanthanum oxide, yttrium oxide, praseodymium oxide and neodymium oxide to form the corresponding nitrate solution.

In the present invention, in step (4), the alkaline precipitating agent is selected from one or more of ammonia water and ammonium bicarbonate; the temperature of the precipitation is 60-90°C; the end point of the precipitation is: When ammonia water is used as the precipitant, the pH of the end point of the precipitation is 9, and when the precipitant contains ammonium bicarbonate, the pH of the end point of the precipitation is 6-6.5; the holding time is 1-3h.

In the present invention, in step (5), the dehydration is a conventional dehydration method of plate and frame filter press or centrifugal dehydration; the surface treatment agent is selected from one of lauric acid, stearic acid and alkenyl succinic anhydride or Several kinds, the adding amount of the surface treatment agent is 30-50% by weight.

Example 1

Add 5kg of γ-Al ₂ O ₃ into 140kg of water, adjust the pH to 2 with nitric acid, and obtain transparent sol A through shear dispersion and high-energy ball milling; dissolve 57kg of zirconyl carbonate and 3.5kg of yttrium oxide with nitric acid, and add kg of lanthanum nitrate, 172 kg of cerium nitrate, and 2000 kg of water to obtain a clear and transparent solution B. Mix solutions B and A, heat to 60°C, slowly add ammonia water, control the pH at the end point to 9, add 24 kg of hydrogen peroxide, and keep warm for 3 hours. After the sediment was centrifuged and dehydrated, it was mixed with water at a mass ratio of 2:1, and 30 kg of lauric acid was added for shear dispersion. The dispersed turbid liquid was calcined at 450° C. for 8 hours to obtain the cerium-zirconium-aluminum-based rare earth oxygen storage material.

Among them, 63.7% of cerium oxide, 22.8% of zirconia, 5% of aluminum oxide, 3.5% of yttrium oxide, and 5% of lanthanum oxide.

Example 2

Put 70kg of macroporous pseudo-boehmite into 700kg of water, adjust the pH to 3 with nitric acid, and obtain transparent sol A through shear dispersion and high-energy ball milling; mix 7kg of praseodymium oxide, 7kg of neodymium oxide, and 140kg of zirconium oxycarbonate with nitric acid Dissolve, add 81kg of cerium nitrate and 2000kg of water to obtain a clear and transparent solution B; mix solution B and A, heat to 90°C, slowly add a precipitant mixed with ammonia water and saturated ammonium bicarbonate solution in a mass ratio of 1:1, Control the pH at the end point to 6.5, add 11 kg of hydrogen peroxide, and keep warm for 1 hour. After the precipitate is centrifuged and dehydrated, it is mixed with water at a mass ratio of 2:1, and 50 kg of stearic acid is added for shear dispersion. The dispersed turbid liquid was calcined at 800° C. for 4 hours to obtain the cerium-zirconium-aluminum-based rare earth oxygen storage material.

Among them, 15% of cerium oxide, 28% of zirconia, 50% of aluminum oxide, 3.5% of praseodymium oxide, and 3.5% of lanthanum oxide.

Example 3

Add 5 kg of macroporous pseudo-boehmite into 140 kg of water, adjust the pH to 2 with nitric acid, and obtain transparent sol A through shear dispersion and high-energy ball milling; dissolve 2 kg of praseodymium oxide, 2 kg of lanthanum oxide, and 125 kg of zirconium oxycarbonate with nitric acid, Add 110kg of cerium nitrate and 2000kg of water to obtain clear and transparent solution B; mix solution B and A, heat to 80°C, slowly add ammonia water, control the pH at the end point to 9, add 16kg of hydrogen peroxide, and keep warm for 2 hours. After the sediment was centrifuged and dehydrated, it was mixed with water at a mass ratio of 2:1, and 20 kg of lauric acid and 30 kg of alkenyl succinic anhydride were added for shear dispersion. The dispersed turbid liquid was calcined at 600° C. for 6 hours to obtain the cerium-zirconium-aluminum-based rare earth oxygen storage material.

Among them, 41% of cerium oxide, 50% of zirconia, 5% of aluminum oxide, 2% of praseodymium oxide, and 2% of lanthanum oxide.

Example 4

Put 26kg of large-pore pseudo-boehmite into 500kg of water, adjust the pH to 2 with nitric acid, and obtain transparent sol A through shear dispersion and high-energy ball milling; 5kg of praseodymium oxide, 5kg of neodymium oxide, 30kg of zirconium Dissolve cerium carbonate with nitric acid, add 2000kg of water to obtain a clear and transparent solution B; mix solution B and A, heat to 80°C, slowly add saturated ammonium bicarbonate solution, control the pH of the end point to 6, add 22.3kg of hydrogen peroxide, and keep warm 2h. After the precipitate was centrifuged and dehydrated, it was mixed with water at a mass ratio of 2:1, and 35 kg of alkenyl succinic anhydride was added for shear dispersion. The dispersed turbid liquid was calcined at 600° C. for 5 hours to obtain the cerium-zirconium-aluminum-based rare earth oxygen storage material.

Among them, 60% of cerium oxide, 12% of zirconia, 18% of aluminum oxide, 5% of praseodymium oxide, and 5% of lanthanum oxide.

The basic principles, main features and advantages of the present invention have been shown and described above. Those skilled in the art should understand that the present invention is not limited by the above-mentioned embodiments. What are described in the above-mentioned embodiments and the description are only the principles of the present invention. Variations and improvements, which fall within the scope of the claimed invention. The scope of protection required by the present invention is defined by the appended claims and their equivalents.

Claims (8)

1. A cerium-zirconium-aluminum-based composite oxide rare-earth oxygen storage material, characterized in that the cerium-zirconium-aluminum-based composite oxide rare-earth oxygen storage material is made of cerium oxide, zirconia, aluminum oxide and other rare earth materials except cerium The composite oxide of oxide composition, its weight percent is as follows: Cerium oxide: 15-65% Zirconia: 12-55% Alumina: 5-50% Rare earth oxides other than cerium: 4-10%. 2. The cerium-zirconium-aluminum-based composite oxide rare earth oxygen storage material according to claim 1, wherein said rare earth oxides other than cerium are selected from lanthanum oxide, yttrium oxide, praseodymium oxide and neodymium oxide. one or several. 3. A method for preparing a cerium-zirconium-aluminum-based composite oxide rare earth oxygen storage material, characterized in that it comprises the following steps: (1) Preparation of aluminum sol, mixing alumina raw material with water, adding nitric acid to adjust the pH to 2-3, shearing dispersion, high-energy ball milling, to form transparent aluminum sol A; (2) the preparation of mixed metal salt solution, according to material composition, determine the content of cerium oxide, zirconium oxide and other rare earth oxides except cerium, convert into the weight content of corresponding nitrate or carbonate, then Cerium nitrate, soluble nitrates of rare earths other than cerium and zirconium nitrate are dissolved in water to obtain mixed metal nitrate solution B; (3) Preparation of the active component precursor, according to the composition of the material, the aluminum sol A and the mixed metal nitrate solution B are mixed to obtain the active component precursor C; (4) Precipitation, at a certain temperature, add an alkaline precipitating agent to the above-mentioned active component precursor C until the end of the precipitation, add stoichiometric hydrogen peroxide, keep warm for a certain period of time, and obtain a precipitate D; (5) Surface treatment of the precipitate, dehydrating and washing the precipitate D; repulping the dehydrated precipitate D and water at a mass ratio of 2:1, adding a certain amount of surface treatment agent, and shearing and dispersing; (6) Roasting, calcining the surface-treated precipitate D at 450-800° C. for 4-8 hours to obtain the cerium-zirconium-aluminum-based solid solution rare earth oxygen storage material. 4. The preparation method according to claim 3, characterized in that ^, in step (1), the alumina raw material is selected from macroporous γ-Al ₂ O ₃ or macroporous quasi Boehmite. 5. The preparation method according to claim 3, characterized in that the solid content of the mixed turbid liquid of alumina and water is 5-10%. 6. preparation method according to claim 3, is characterized in that, in step (2), described cerium oxide source is selected from cerium nitrate or cerium carbonate; Described zirconia source is selected from zirconium oxycarbonate; Other rare earth soluble nitrates are selected from one or more of lanthanum nitrate, yttrium nitrate, praseodymium nitrate and neodymium nitrate or react nitric acid with lanthanum oxide, yttrium oxide, praseodymium oxide and neodymium oxide to form the corresponding nitrate solution. 7. preparation method according to claim 3 is characterized in that, in step (4), described alkaline precipitation agent is selected from one or more in ammoniacal liquor and ammonium bicarbonate; The temperature of described precipitation is 60 -90°C; the end point of the precipitation is: when ammonia water is selected as the precipitant, the pH of the end point of the precipitation is 9; when the precipitant contains ammonium bicarbonate, the end point of the precipitation is 6-6.5; the holding time is 1-3h . 8. preparation method according to claim 3 is characterized in that, in step (5), described dehydration is the conventional dehydration mode of plate and frame press filtration or centrifugal dehydration; Described surface treatment agent is selected from lauric acid, stearin One or more of acid and alkenyl succinic anhydride, the added amount of the surface treatment agent is 30-50% by weight.