A method for rapidly preparing silicon-modified hierarchical porous nano-gamma-Al2O3

Abstract

The application discloses a method for rapidly preparing silicon-modified multi-level hole nano gamma-Al2O3, and specifically comprises the following steps: dissolving NaAlO2 in water to form a sodium metaaluminate solution; dissolving a precipitant in water to form a solution, and transferring the solution into a reaction kettle; adding a silicon source into the reaction kettle, wherein the adding amount of the silicon source is calculated according to the adding amount of SiO2; slowly adding the sodium metaaluminate solution into the reaction kettle, and adjusting the pH value of the obtained mixed solution to 9-11; adding a pore-expanding aid, and aging for 3-10 hours; after aging, performing solid-liquid separation, recycling the filtrate, sufficiently washing the powder with deionized water, and drying to obtain basic aluminum ammonium carbonate; and calcining the AACH in a muffle furnace at a temperature increasing rate of 2 DEG C / min to 300-500 DEG C to obtain silicon-modified nano gamma-Al2O3 powder. The nano gamma-Al2O3 prepared by the method can directly hydrothermally synthesize a silicon-modified precursor AACH in one step without other complex steps, has less impurities, and has high purity. The prepared nano gamma-Al2O3 has high specific surface area, large pore diameter and high pore volume.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalytic material preparation, and particularly relates to a method for rapidly preparing silicon-modified hierarchical porous nano gamma-Al2O3. BACKGROUND

[0002] Among various forms of alumina, gamma-Al2O3 occupies an extremely important position. Gamma-Al2O3 is widely used as a catalyst, and can be used not only as a catalyst for alcohol dehydration and the like, but also as a catalyst carrier, and is widely applied in automobile exhaust purification and petroleum refining processes. Generally, gamma-Al2O3 is obtained by calcining a precursor at a temperature above 450 DEG C. How to prepare gamma-Al2O3 with a larger specific surface area and a certain pore size distribution and pore volume is a current research hotspot.

[0003] Aluminum ammonium carbonate hydroxide (AACH) is an important precursor for preparing nano-alumina, and the gas generated in the high-temperature calcination process is pollution-free, and the gas generated in the calcination process can further play a pore-expanding role. The preparation methods of AACH include gas-solid method, liquid-liquid method and solid-solid method. Among them, the most common is the liquid-liquid method. The gas-solid method for preparing AACH often has the defects of large quality fluctuation of different batches, and the solid-solid method often has the defects of particle aggregation and impurities, so the liquid-liquid method is mostly selected.

[0004] Alumina powder prepared by thermal decomposition method has the advantages of low raw material cost and industrialization, but the synthesis of the precursor aluminum ammonium carbonate (referred to as AACH) requires strict conditions, otherwise the aluminum ammonium carbonate precursor cannot be obtained, or the obtained precursor is seriously aggregated. Therefore, the preparation of AACH is a key step to determine the properties of the obtained alumina powder. When an aluminum salt solution and an ammonium bicarbonate solution are used to prepare AACH, different precipitates are obtained, as shown in the following two formulas:

[0005] 2Al 3+ +6(NH4)HCO3 = 2AlO(OH) +6NH 4+ +6CO2+2H2O

[0006] Al 3+ +4(NH4)HCO3 = NH4Al(OH)CO3 +3NH4 +3CO2+H2O

[0007] Therefore, how to avoid the generation of impurities and obtain a precursor AACH with good crystallinity and uniform dispersion is a key point of the technology.

[0008] However, when active alumina is applied in some high temperature environment, especially in high temperature water vapor environment, sintering and phase transition will occur, resulting in a substantial reduction of its specific surface area and pore volume. Its high temperature stability and hydrothermal stability often cannot meet the requirements. For example, in the treatment of automobile exhaust and catalytic combustion, the working temperature of alumina is as high as 1000℃ or above. At this time, ordinary alumina is basically changed into a-Al2O3 with no pores, and its specific surface area and pore volume are greatly reduced, losing catalytic and adsorption activity. Therefore, it is of great significance to improve the thermal stability of alumina. At present, the main method to improve the thermal stability of alumina is to introduce other elements to modify alumina. SiO2 is a commonly used modifier for alumina. The surface acidity of alumina is weak, but after modification by SiO2, the surface acidity of alumina is significantly enhanced, and the pore structure and thermal stability of the prepared carrier are also improved. SUMMARY

[0009] The purpose of the present application is to provide a method for rapidly preparing silicon-modified hierarchical pore nanometer γ-Al2O3.

[0010] The technical solution of the present application is as follows:

[0011] A method for rapidly preparing silicon-modified hierarchical pore nanometer γ-Al2O3, the specific preparation process is as follows:

[0012] (1) Dissolve NaAlO2 in water to form a 0.8-1.5 mol / L sodium aluminate solution;

[0013] (2) Dissolve the precipitating agent in water to form a 1.0-1.4 mo / L solution, and transfer it to the reaction kettle;

[0014] (3) Add 0.3-0.6 mol of silicon source to the reaction kettle, wherein the addition amount of silicon source is calculated according to the addition amount of SiO2, and uniformly stir at a speed of 500-800 r / min;

[0015] (4) Raise the temperature of the reaction kettle to 60-75℃, and continue to stir;

[0016] (5) Slowly add the sodium aluminate solution to the reaction kettle, the addition time is 30-60 min, the pH value of the obtained mixed solution is adjusted to 9-11, the stirring speed is 500-800 r / min, and after the addition is completed, stir for 30 min;

[0017] (6) Raise the temperature of the reaction kettle to 90-100℃, add a pore expanding aid, the molar ratio of the pore expanding aid to sodium aluminate is 1:8-1:10, and age for 3-10 h;

[0018] (7) After aging, separate the solid and liquid, recycle the filtrate, wash the powder with deionized water, and dry to obtain basic aluminum ammonium carbonate;

[0019] (8) AACH is calcined in a muffle furnace at 2 ℃ / min to 300-500 ℃ to obtain silicon-modified nano γ-Al2O3 powder.

[0020] Further, the precipitant is selected from one of ammonium carbonate or ammonium bicarbonate.

[0021] Further, the silicon source is selected from one of silica sol, sodium silicate or tetraethyl orthosilicate.

[0022] Further, the reaming aid is selected from one of ammonium carbonate, ammonium bicarbonate or urea.

[0023] The second aspect of the present application provides a silicon-modified nano γ-Al2O3 powder prepared by the above-mentioned method.

[0024] The present application has the following advantages: the nano γ-Al2O3 prepared by the present application directly hydrothermally synthesizes a silicon-modified precursor AACH in one step without other complex steps, has less impurities and high purity; the synthesis raw materials are cheap and easy to obtain, the synthesis process is easy to operate and has low cost; the introduction of the silicon source enhances the thermal stability of the material and can meet higher temperature application requirements; no waste water is generated, energy is saved and emission is reduced, and the process has high recycling. The prepared nano γ-Al2O3 also has high specific surface area, large pore size and high pore volume, and has great application advantages. BRIEF DESCRIPTION OF DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed in the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0026] Figure 1 XRD of AACH before calcination for Example 1;

[0027] Figure 2 XRD of AACH before calcination for Example 2;

[0028] Figure 3 XRD of AACH before calcination for Example 3;

[0029] Figure 4 XRD of AACH before calcination for Example 4;

[0030] Figure 5 XRD of AACH before calcination for Example 5;

[0031] Figure 6 XRD of AACH before calcination for Example 6;

[0032] Figure 7 XRD of AACH before calcination for Example 7;

[0033] Figure 8 XRD patterns of γ-Al2O3 after calcination for Example 1-Example 7;

[0034] Figure 9 N2 adsorption isotherms of γ-Al2O3 after calcination for Example 1-Example 7;

[0035] Figure 10 Pore size distribution curves of γ-Al2O3 after calcination for Example 1-Example 7. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application.

[0037] The first aspect of the present application provides a method for rapidly preparing silicon-modified hierarchical porous nano γ-Al2O3, wherein the method comprises the following steps:

[0038] (1) dissolving NaAlO2 in water to form a 0.8-1.5 mol / L sodium metaaluminate solution;

[0039] (2) dissolving a precipitating agent in water to form a 1.0-1.4 mo / L solution, and transferring it to a reaction kettle;

[0040] (3) adding 0.3-0.6 mol of a silicon source to the reaction kettle, wherein the amount of the silicon source is calculated according to the amount of SiO2 added, and stirring uniformly at a rotation speed of 500-800 r / min;

[0041] (4) raising the temperature of the reaction kettle to 60-75℃, and continuously stirring;

[0042] (5) slowly adding the sodium metaaluminate solution to the reaction kettle, the adding time being 30-60 min, the pH value of the obtained mixed solution being adjusted to 9-11, the stirring rotation speed being 500-800 r / min, and stirring for 30 min after the adding is completed;

[0043] (6) raising the temperature of the reaction kettle to 90-100℃, adding a pore-expanding aid, the molar ratio of the pore-expanding aid to the sodium metaaluminate being 1:8-1:10, and aging for 3-10 h;

[0044] (7) after the aging is completed, performing solid-liquid separation, recycling the filtrate, washing the powder with deionized water, and drying to obtain basic aluminum ammonium carbonate;

[0045] (8) AACH is heated in a muffle furnace at 2 ℃ / min to 300-500 ℃ to obtain silicon modified nano γ-Al2O3 powder.

[0046] According to the present application, the precipitating agent is selected from one of ammonium carbonate or ammonium bicarbonate.

[0047] According to the present application, the silicon source is selected from one of silica sol, sodium silicate or tetraethyl orthosilicate.

[0048] According to the present application, the reaming aid is selected from one of ammonium carbonate, ammonium bicarbonate or urea. Example

[0049] 30 mol of ammonium carbonate is weighed into deionized water to configure a 1.1 mol / L solution, named solution A1 and transferred into a 50 L reaction kettle, and heating is started to 75 ℃; 0.58 mol of silica sol is weighed into the kettle and stirred for 5 min; 23.85 mol of sodium metaaluminate is weighed into deionized water to configure a 1.5 mol / L sodium metaaluminate solution, named solution B1; solution B1 is slowly added into the kettle at 75 ℃ under stirring, the control time is 1 h, and pH = 9.5; after stirring is completed, heating is started, after heating to 90 ℃, 3.75 mol of ammonium bicarbonate is added, stirring is stopped, and aging is performed for 3 h; after aging is completed, solid-liquid separation is performed, the filtrate is recovered for use in the next process, a proper amount of deionized water is used for washing, and drying is performed at 120 ℃ for 12 h to obtain basic aluminum ammonium carbonate, which is calcined in a muffle furnace at 2 ℃ / min to 500 ℃ to obtain silicon modified nano γ-Al2O3 powder. Example

[0050] 30 mol of ammonium bicarbonate is weighed into deionized water to configure a 1.1 mol / L solution, named solution A2 and transferred into a 50 L reaction kettle, and heating is started to 75 ℃; 0.58 mol of silica sol is weighed into the kettle and stirred for 5 min; 23.85 mol of sodium metaaluminate is weighed into deionized water to configure a 1.5 mol / L sodium metaaluminate solution, named solution B2; solution B2 is slowly added into the kettle at 75 ℃ under stirring, the control time is 1 h, and pH = 9.5; after stirring is completed, heating is started, after heating to 90 ℃, 3.75 mol of ammonium bicarbonate is added, stirring is stopped, and aging is performed for 3 h; after aging is completed, solid-liquid separation is performed, the filtrate is recovered for use in the next process, a proper amount of deionized water is used for washing, and drying is performed at 120 ℃ for 12 h to obtain basic aluminum ammonium carbonate, which is calcined in a muffle furnace at 2 ℃ / min to 500 ℃ to obtain silicon modified nano γ-Al2O3 powder. Example

[0051] Take 27 mol of ammonium bicarbonate into deionized water to configure 1.1 mol / L solution, named solution A3 and transferred to 50L reactor, start to heat to 60℃; take 0.52 mol of silica sol into the kettle and stir for 5 min; take 19.07 mol of sodium metaaluminate into deionized water to configure 1.14 mol / L sodium metaaluminate solution, named solution B3; slowly add solution B2 into the kettle at 60℃ under the condition of heat preservation and stirring using peristaltic pump, control time 40 min, pH=10; after stirring, start to heat, after heating to 100℃, add 2.7 mol of ammonium bicarbonate, stop stirring, aging for 6h; after aging, solid-liquid separation, the filtrate is recovered for use in the next process, washed with deionized water, dried at 120℃ for 12h, get basic aluminum ammonium carbonate, calcined in muffle furnace at 2℃ / min to 500℃ to get silicon modified nano γ-Al2O3 powder. Example

[0052] Take 27 mol of ammonium bicarbonate into deionized water to configure 0.8 mol / L solution, named solution A4 and transferred to 50L reactor, start to heat to 60℃; take 0.52 mol of silica sol into the kettle and stir for 5 min; take 19.07 mol of sodium metaaluminate into deionized water to configure 1.14 mol / L sodium metaaluminate solution, named solution B4; slowly add solution B4 into the kettle at 60℃ under the condition of heat preservation and stirring using peristaltic pump, control time 40 min, pH=10.5; after stirring, start to heat, after heating to 90℃, add 3.3 mol of ammonium bicarbonate, stop stirring, aging for 6h; after aging, solid-liquid separation, the filtrate is recovered for use in the next process, washed with deionized water, dried at 120℃ for 12h, get basic aluminum ammonium carbonate, calcined in muffle furnace at 2℃ / min to 500℃ to get silicon modified nano γ-Al2O3 powder. Example

[0053] Take 27 mol of ammonium bicarbonate into deionized water to configure 1.4 mol / L solution, named solution A5 and transferred to 50L reactor, start to heat to 60℃; take 0.52 mol of tetraethyl orthosilicate into the kettle and stir for 5 min; take 19.07 mol of sodium metaaluminate into deionized water to configure 1.14 mol / L sodium metaaluminate solution, named solution B5; slowly add solution B5 into the kettle using peristaltic pump under 60℃ heat and stirring, control time 40 min, pH=10; after stirring, start to heat, after heating to 95℃, add 2.7 mol of urea, stop stirring, aging for 6h; after aging, solid-liquid separation, the filtrate is recovered for use in the next process, washed with deionized water, dried at 120℃ for 12h, get basic aluminum ammonium carbonate, calcined in muffle furnace at 2℃ / min to 450℃ to get silicon modified nano γ-Al2O3 powder. Example

[0054] Take 27 mol of ammonium bicarbonate into deionized water to configure 1 mol / L solution, named solution A6 and transferred to 50L reactor, start to heat to 60℃; take 0.52 mol of silica sol into the kettle and stir for 5 min; take 19.07 mol of sodium metaaluminate into deionized water to configure 1.14 mol / L sodium metaaluminate solution, named solution B6; slowly add solution B6 into the kettle using peristaltic pump under 70℃ heat and stirring, control time 40 min, pH=11; after stirring, start to heat, after heating to 90℃, add 2.7 mol of ammonium carbonate, stop stirring, aging for 6h; after aging, solid-liquid separation, the filtrate is recovered for use in the next process, washed with deionized water, dried at 120℃ for 12h, get basic aluminum ammonium carbonate, calcined in muffle furnace at 2℃ / min to 400℃ to get silicon modified nano γ-Al2O3 powder. Example

[0055] Take 27 mol of ammonium bicarbonate and dissolve it in the reused water in Example 6 to prepare a 1 mol / L solution, name the solution A7 and transfer it to a 50 L reactor, start heating to 60℃; take 0.52 mol of sodium silicate (in terms of SiO2) and add it to the reactor and stir for 5 min; take 19.07 mol of sodium metaaluminate and dissolve it in deionized water to prepare a 1.14 mol / L sodium metaaluminate solution, name the solution B7; slowly add the solution B7 to the reactor at 70℃ under stirring, pH=10.5, the amount is determined according to the pH; after stirring, start heating, after heating to 90℃, add 2.7 mol of ammonium carbonate, stop stirring, and age for 10 h; after aging, separate the solid and the liquid, recover the filtrate for use in the next process, wash with deionized water, and dry at 120℃ for 12 h to obtain basic aluminum ammonium carbonate, and then heat to 500℃ at 2℃ / min in a muffle furnace to obtain silicon-modified nano γ-Al2O3 powder.

[0056] The second aspect of the present application provides a silicon-modified nano γ-Al2O3 powder prepared by the preparation method described above.

[0057] According to Examples 1-7, the specific surface area, pore volume and average pore diameter of the silicon-modified nano γ-Al2O3 powder after calcination are shown in Table 1.

[0058] Table 1

[0059] According to the present application, the average pore diameter of the silicon-modified nano γ-Al2O3 powder is 10.03-14.01 nm, the specific surface area is 382.36-451.69 m2 / g, and the pore volume is 0.986-1.321 ml / g. The prepared silicon-modified nano γ-Al2O3 has high specific surface area, large pore diameter and high pore volume, and has great application advantages.

[0060] The above examples prove that all the preparation methods of Examples 1-7 can prepare silicon-modified nano γ-Al2O3; when ammonium bicarbonate is selected as the precipitant, the optimal concentration of ammonium bicarbonate is 0.8-1.0 mol / L, the optimal reaction temperature is 60℃, and the optimal crystallization temperature is 90℃.

[0061] The above only describes the preferred embodiments of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can make equivalent substitutions or changes to the technical solutions and inventive concepts of the present application within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A method for rapidly preparing silicon-modified hierarchical porous nanosized γ- Al2O3, characterized in that, The specific preparation process is as follows: (1) dissolving NaAlO2 in water to form a 0.8-1.5 mol / L sodium aluminate solution; (2) dissolving a precipitant in water to form a 1.0-1.4 mol / L solution, and transferring the solution into a reaction kettle; (3) adding 0.3-0.6 mol of a silicon source into the reaction kettle, wherein the amount of the silicon source is calculated according to the amount of SiO2, and stirring uniformly at a rotating speed of 500-800 r / min; (4) raising the temperature of the reaction kettle to 60-75 ℃, and continuously stirring; (5) slowly adding the sodium aluminate solution into the reaction kettle, the adding time is 30-60 min, the pH value of the obtained mixed solution is adjusted to 9-11, the stirring rotating speed is 500-800 r / min, and stirring for 30 min after the adding is completed; (6) raising the temperature of the reaction kettle to 90-100 ℃, adding a pore-expanding aid, the molar ratio of the pore-expanding aid to sodium aluminate is 1:8-1:10, and aging for 3-10 h; (7) after the aging is completed, solid-liquid separation is performed, the filtrate is recycled, the powder is washed with deionized water, and drying to obtain an alkali aluminum ammonium carbonate; (8) calcining the AACH in a muffle furnace at a temperature increasing rate of 2 ℃ / min to 300-500 ℃ to obtain a silicon-modified nano γ-Al2O3 powder.

2. The method for rapidly preparing silicon-modified hierarchical porous nano-γ- Al2O3 according to claim 1, characterized in that, The precipitant is selected from one of ammonium carbonate or ammonium bicarbonate.

3. The method for rapidly preparing silicon-modified hierarchical porous nanosized γ- Al2O3 according to claim 1, characterized in that, The silicon source is selected from one of silica sol, sodium silicate or tetraethyl orthosilicate.

4. The method for rapidly preparing silicon-modified hierarchical porous nanosized γ- Al2O3 according to claim 1, characterized in that, The pore-expanding aid is selected from one of ammonium carbonate, ammonium bicarbonate or urea.

5. A silicon-modified nano γ-Al2O3 powder prepared by the method of any one of claims 1-4. The average pore diameter of the silicon modified nano γ-Al2O3 powder is 10.03-14.01 nm, the specific surface area is 382.36-451.69 m 2 / g, and the pore volume is 0.986-1.321 ml / g.

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