Gamma-alumina octahedral crystal grain material and preparation method thereof
Technical Field
The invention belongs to the field of inorganic material preparation, and particularly relates to a gamma-alumina octahedral crystal grain material and a preparation method thereof.
Background
Activated alumina, as a carrier material widely used in the industrial field, generally has the advantages of high pore volume, high specific surface area, high catalytic activity, and the like. In the heterogeneous catalysis process, key factors influencing the reaction activity and selectivity of the catalyst comprise the properties of the surface and the like of the catalyst. The surface property of the crystal catalyst is closely related to the crystal face of the crystal, the anisotropy of the crystal causes the physicochemical properties of the crystal on different crystal faces to be different, and the catalytic performance of the catalyst has stronger correlation with the exposed crystal face.
For activated alumina (gamma-alumina), research has shown that the (110) crystal plane is most thermodynamically stable and therefore is usually preferentially exposed. Other crystal faces of the activated alumina, such as (111) face and (100) face, have different interface chemical properties from (110) face, and in order to obtain an alumina carrier material with higher performance, the crystal faces of the alumina can be regulated and modified by a series of means to obtain special physicochemical properties. But the intrinsic crystal growth habit of the predominance of the (110) crystal plane of activated alumina is difficult to change easily.
[ fine petrochemical, 2014, 31 (5): 38-43, the relation between the surface properties and the crystal plane characteristics of the single crystal small particle gamma-alumina is studied, and the alumina crystal is found to mainly expose (110) crystal plane family and (111) crystal plane family, wherein the surface of the (110) crystal plane family accounts for 70.4 percent, and the surface of the (111) crystal plane family accounts for 29.6 percent.
[ contemporary chemical industry, 2015, 44 (5): 951-954 ] nanometer gamma-alumina single crystal particles containing a (110) crystal plane and also having high-index surface crystal planes (752), (541) are prepared. However, the high-index crystal face of alumina has high activity and large interface energy, is difficult to exist stably in thermodynamics, and is not suitable for being used as a catalytic material in the field of catalytic reaction.
[ petroleum refining and chemical engineering, 2013, 44 (9): 47-50 the crystal face distribution range of the alumina single crystal particles can be changed to a certain extent by adding sodium nitrate into a hydrothermal system, but the adjustable range is limited due to the inherent habit of alumina crystals, and the crystal face of alumina is still dominated by (110).
The research results show that the space for directly regulating and controlling the crystal face distribution of the aluminum oxide single crystal particles is very limited, and the effect is not very obvious. Other indirect methods of modulating the crystal plane of alumina that may exist are self-assembly. CN200910011627.6, CN200910206229.X and CN200910011626.1 adopt aluminum hydroxide gel prepared by a molten salt super-solubilization micelle self-assembly method as a raw material, and after roasting, regular rod-shaped nano aluminum oxide secondary particles are obtained. [ Chinese science, 2009, 39 (5): 420-431 and [ journal of inorganic chemistry, 2015, 31 (8): 1539-1547, the self-assembly technique and mechanism of alumina super solubilizing micelle are provided. The self-assembly method of the activated alumina secondary particles can greatly affect the pore structure and the aggregation form of the material, but the obvious effect on the regulation and control of the crystal plane distribution and the exposure characteristic of the activated alumina is still difficult to obtain.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a gamma-alumina octahedral crystal grain material and a preparation method thereof.
The gamma-alumina octahedral crystal grain material has the following properties: the material is of a single crystal structure, the shape of the material is a hexagonal prism, the upper hexagonal bottom surface and the lower hexagonal bottom surface are (110) crystal faces, the rectangular side surfaces of the prism are respectively a (111) crystal face and a (100) crystal face, the total area of the exposed crystal faces of the alumina material is taken as a reference, the distribution proportion of the (110) crystal faces is 1% -15%, preferably 5% -10%, the distribution proportion of the (111) crystal faces is 60% -85%, preferably 70% -80%, and the distribution proportion of the (100) crystal faces is 1% -25%, preferably 10% -15%; along the [110] crystal axis direction, the length of the alumina material is 100-5000nm.
The preparation method of the gamma-alumina octahedral crystal grain material comprises the following steps:
(1) Roasting the alumina precursor powder, then doping a certain amount of inorganic sodium salt, then grinding the powder, washing the ground powder with water to remove the sodium salt, drying, preparing a suspension with a certain concentration, adding a certain amount of organic acid, and uniformly mixing;
(2) Adding a certain amount of organic amine and low-carbon alcohol into the material obtained in the step (1) and uniformly stirring;
(3) And (3) carrying out closed hydrothermal treatment on the material obtained in the step (2), and after the treatment is finished, carrying out solid-liquid separation, drying and roasting to obtain a product.
In the method of the present invention, the alumina precursor in step (1) refers to pseudo-boehmite and pseudo-boehmite powder modified by various elements such as silicon, boron, titanium, magnesium, lanthanum, etc.
In the method of the invention, the roasting temperature in the step (1) is 650-900 ℃, preferably 700-800 ℃, and the roasting time is 1-24 hours, preferably 3-12 hours.
In the method, the material in the step (1) is treated by grinding (such as ball milling) to obtain the powder granularity of more than 50 meshes, and the powder granularity is preferably 100-2000 meshes.
In the method, the inorganic sodium salt in the step (1) is one or more of sodium nitrate, sodium chloride or sodium sulfate, and the using amount of the inorganic sodium salt accounts for 0.1-10% of the mass of the calcined alumina precursor powder.
In the method of the present invention, the concentration of the suspension in the step (1) is 1 to 100g/L, preferably 10 to 50g/L.
In the method, the organic acid in the step (1) is one or more of formic acid, acetic acid or citric acid, and the using amount of the organic acid is 0.1-8% of the mass of the calcined alumina precursor, and is preferably 0.5-5%.
In the method of the invention, the organic amine in the step (2) is one or more of aniline, diphenylamine, benzidine or o-phenylenediamine. The concentration of the organic amine in the material system is 1-200g/L, preferably 10-100g/L.
In the method of the present invention, the lower alcohol in step (2) is one or more of methanol, ethanol or propanol, preferably methanol and/or ethanol. The concentration of the lower alcohol in the material system is 1-40g/L, preferably 10-30g/L.
In the method, the closed hydrothermal conditions in the step (3) are as follows: hydrothermal treatment at 100-300 deg.C for 0.5-24 hr, preferably 150-250 deg.C for 2-12 hr.
In the method of the present invention, the drying temperature in the step (3) is not more than 200 ℃, preferably not more than 120 ℃, and the drying degree is that the material reaches a constant weight at the drying temperature.
In the method, the roasting conditions in the step (3) are as follows: roasting at 450-750 deg.c for 1-24 hr, preferably at 500-650 deg.c for 3-12 hr.
The invention also provides a distillate oil hydrofining catalyst, which comprises the gamma-alumina octahedral crystal grain material.
The gamma-alumina octahedral crystal grain material has unique crystal face distribution characteristic, simple preparation process, low cost and excellent application foreground in fraction oil hydrorefining field.
Drawings
Fig. 1 is a scanning electron micrograph of the gamma-alumina material prepared in example 1.
FIG. 2 is an electron diffraction spectrum in the [110] direction of the gamma-alumina material prepared in example 1.
Fig. 3 is an XRD spectrum of the gamma-alumina material prepared in example 1.
Detailed Description
The process of the present invention is described in detail by examples below. The grain size of the gamma-alumina material was measured according to scanning electron microscopy images. Randomly measuring 20 particles, and taking the average axial length value as the height value of the particles; the crystal form is characterized by X-ray diffraction; collecting an electron diffraction spectrum through a transmission electron microscope, and processing a sample through a slicing means before carrying out electron diffraction analysis on a large-particle sample.
Example 1
Calcining 10g of pseudo-boehmite powder at 700 ℃ for 5 hours, adding 0.5 g of sodium chloride, uniformly mixing, grinding into micropowder by using a ball mill, sieving to obtain particles with about 500 meshes, washing with distilled water to remove the sodium chloride, and preparing 20g/L aqueous suspension. Adding acetic acid into the suspension, wherein the dosage of the acetic acid is 0.5 percent of the mass of the calcined alumina precursor. Adding diphenylamine and ethanol into the system, wherein the mass percentage concentrations of diphenylamine and ethanol are 10g/L and 10g/L respectively, uniformly stirring, sealing the system, and heating to 150 ℃ for hydrothermal treatment for 12 hours. And roasting the product dried at the temperature of 120 ℃ for 4 hours at the temperature of 650 ℃ to obtain the product. The observation of a scanning electron microscope shows that the appearance of the product is approximately regular hexagonal prism. The XRD result of the product shows that the phase state is gamma phase. According to the electron diffraction analysis of the cross section, the orientation is [110] along the column height direction, the bottom surface is a (110) crystal plane (in a hexagon shape), and the side surfaces of the hexagonal prism are respectively a (100) plane and a (111) plane according to the included angle relationship. The material is known to have a single crystal structure because electron diffraction of the material is an ordered arrangement of spots. Wherein, 2 (110) surfaces, 2 (100) and 4 (111) surfaces are provided. The length along the [110] direction was 1080nm, the average size of (100) crystal planes was 125nm 1080nm, and the average size of (111) crystal planes was 248 nm 1080nm. The calculation shows that the proportion of the (110) crystal face is 9 percent, the proportion of the (111) crystal face is 67 percent, and the proportion of the (100) crystal face is 24 percent.
Example 2
10g of pseudo-boehmite powder is roasted for 2 hours at 800 ℃, 0.5 g of sodium nitrate is added and mixed evenly, the mixture is ground into micro powder by a ball mill, particles about 1000 meshes are sieved, the sodium nitrate is removed by washing with distilled water, and then 15g/L of aqueous suspension is prepared. Adding acetic acid into the suspension, wherein the dosage of the acetic acid is 0.3 percent of the mass of the pseudo-boehmite powder. Adding diphenylamine and propanol into the system, wherein the mass percentage concentration of the diphenylamine and the propanol is 10g/L and 25g/L respectively, uniformly stirring, sealing the system, and heating to 200 ℃ for hydrothermal treatment for 12 hours. And roasting the product dried at the temperature of 120 ℃ for 4 hours at the temperature of 650 ℃ to obtain the product. The observation of a scanning electron microscope shows that the appearance of the product is approximately regular hexagonal prism. The XRD result of the product shows that the phase state is gamma phase. According to the electron diffraction analysis of the cross section, the orientation is [110] along the column height direction, the bottom surface is a (110) crystal plane (in a hexagon shape), and the side surfaces of the hexagonal prism are respectively a (100) plane and a (111) plane according to the included angle relationship. The material is known to have a single crystal structure because electron diffraction of the material is an ordered arrangement of spots. Wherein, 2 (110) surfaces, 2 (100) and 4 (111) surfaces are provided. The length along the (110) direction is 2032nm, the average size of (100) surfaces is 85nm 2032nm, and the average size of (111) surfaces is 184 x 2032nm. The calculation revealed that the proportion of (110) plane was 7%, the proportion of (111) plane was 76%, and the proportion of (100) plane was 17%.
Example 3
10g of pseudo-boehmite powder is roasted for 7 hours at 650 ℃, 0.8 g of sodium nitrate is added and mixed evenly, the mixture is ground into micro powder by a ball mill, particles about 2000 meshes are sieved, distilled water is used for washing to remove the sodium nitrate, and then 35g/L of aqueous suspension is prepared. Adding part of acetic acid into the suspension, wherein the dosage of the acetic acid is 1.5 percent of the mass of the pseudo-boehmite powder. The treatment was carried out at room temperature for 15 minutes. And (3) adding benzidine and methanol into the system, wherein the mass percentage concentration of the benzidine and the methanol is 5g/L and 25g/L respectively, uniformly stirring, sealing the system, and heating to 200 ℃ for hydrothermal treatment for 7 hours. And roasting the product dried at the temperature of 120 ℃ for 4 hours at the temperature of 650 ℃ to obtain the product. The observation of a scanning electron microscope shows that the appearance of the product is approximately regular hexagonal prism. The XRD result of the product shows that the phase state is gamma phase. According to the electron diffraction analysis of the cross section, the orientation is [110] along the column height direction, the bottom surface is a (110) crystal plane (in a hexagon shape), and the side surfaces of the hexagonal prism are respectively a (100) plane and a (111) plane according to the included angle relationship. The electron diffraction of the material is orderly arranged spots, so that the material is known to have a single crystal structure. Wherein, 2 (110) surfaces, 2 (100) surfaces and 4 (111) surfaces are provided. The length along the [110] direction was 345nm, the average size of (100) planes was 56nm x 345nm, and the average size of (111) planes was 79 x 345nm. The calculation shows that the proportion of (110) plane is 12.5%, the proportion of (111) plane is 64.7% and the proportion of (100) plane is 22.8%.
Comparative example 1
Reference [ petroleum refining and chemical, 2013, 44 (9): 47-50 ] adjusting the crystal plane distribution of the alumina single crystal particles by adding sodium nitrate. The test conditions are shown in the literature. The two groups were divided, the first group without sodium nitrate and the second group with sodium nitrate. The product obtained by the test analysis comprises (110), (111) and (100) low-index crystal faces. The first set of three crystal planes is distributed: (110) % is 72.3%, (111)% is 20.5%, (100)% is 7.2%; the second set of three crystal planes are: (110) % is 64.2%, (111)% is 26.4%, and (100)% is 9.4%. It can be seen that the (110) crystal plane distribution is greater than 50% and still predominates regardless of the addition of sodium nitrate.
Comparative example 2
According to [ chinese science, 2009, 39 (5): 420-431 ] the molten salt supersolubility micelle self-assembly method is used for preparing the aluminum oxide self-assembly particles. The results obtained were tested and found that the self-assembly as a whole has no significant orientation of the crystal planes and that the individual grains remain the (110) -dominated distribution of crystal planes.