Modified alumina, method for producing the same, and use thereof

Abstract

This invention relates to the field of catalyst technology, specifically to a modified alumina, its preparation method and application, and a supported catalyst and its application. The modified alumina comprises silicon and alumina, wherein the silicon is bonded to the surface of the alumina via Si-O-Al chemical bonds, and adjacent silicon atoms on the surface of the alumina are bonded via Si-O-Si chemical bonds; the silicon-to-alumina ratio of the modified alumina is <1; and the Brønsted acid density of the modified alumina is ≤2 μmol / g. This invention effectively reduces the Brønsted acid density of the modified alumina while ensuring that the modified alumina possesses low wear index, high crushing strength, high specific surface area, and low average pore size; simultaneously, when this modified alumina is used as a catalyst support, the resulting supported catalyst exhibits high catalytic activity.

Description

Technical Field

[0001] This invention relates to the field of catalyst technology, specifically to a modified alumina, its preparation method and application, and a supported catalyst containing the modified alumina and its application. Background Technology

[0002] Catalyst supports are a crucial foundation for the synthesis of supported catalysts, and their structure and physicochemical properties significantly influence the properties and applications of these catalysts. Alumina is an important and common industrial catalyst support, and its reactivity, hydrothermal stability, and wear resistance are key indicators for evaluating catalyst supports. Surface modification of alumina can enhance certain properties, which is significant for expanding its application range.

[0003] CN101448565A discloses an alumina with high hydrothermal stability, which improves the hydrothermal stability of a transitional alumina used as an adsorbent and catalyst support by treating it with a soluble silica inorganic compound.

[0004] CN107774248A discloses a silicon-modified Fischer-Tropsch synthesis catalyst and its application. The alumina catalyst support synthesized by the silicon modification method exhibits excellent stability and wear resistance in the Fischer-Tropsch reaction.

[0005] CN106582597A discloses a silicon-modified alumina, its preparation method, and its applications. By adjusting the pH value of the alumina sol and silica sol mixture, it is possible to flexibly switch between focusing on improving pore volume and focusing on improving Brønsted acid content. The material surface Brønsted acid / L ratio is 40-95%, and the pore volume is 0.8-1.2 cm³. 3 / g.

[0006] CN113562751A discloses a modified pseudoboehmite and its preparation method. In the preparation of modified pseudoboehmite, by adding phosphorus-containing compounds, non-metallic auxiliary compounds, grain growth regulators, and segmented pH control during the preparation process, the modified pseudoboehmite has a specific surface hydroxyl distribution after calcination, thereby giving the catalyst excellent heavy oil hydrogenation activity and high stability.

[0007] None of the aforementioned existing technologies address how to modulate the complex acidic sites on the alumina surface; typically, the different types and intensities of acidic sites significantly limit the application of alumina in the fine chemical industry. Therefore, there is an urgent need for a modified alumina with low acidity. Summary of the Invention

[0008] The purpose of this invention is to overcome the problems of existing modified alumina having complex acidic sites, failing to simultaneously possess wear resistance, high stability, and controllable acid content, as well as low activity and short lifespan in the fine chemical industry. This invention provides a modified alumina, its preparation method, and its applications; a supported catalyst containing this modified alumina and its applications; this modified alumina has a low Brønsted acid density, and also possesses a low wear index, high crushing strength, high specific surface area, and low average pore size; furthermore, when used as a catalyst support, this modified alumina exhibits high activity.

[0009] To achieve the above objectives, a first aspect of the present invention provides a modified alumina comprising silicon and alumina, wherein the silicon is bonded to the surface of the alumina by Si-O-Al chemical bonds, and adjacent silicon atoms on the surface of the alumina are bonded by Si-O-Si chemical bonds; the silicon-to-alumina ratio of the modified alumina is <1.

[0010] The modified alumina has a Brønsted acid density ≤ 2 μmol / g.

[0011] Preferably, the Brønsted acid density of the modified alumina is 0-2 μmol / g, more preferably 0-1.4 μmol / g, and even more preferably 0-0.5 μmol / g.

[0012] Preferably, based on the total weight of the modified alumina, the alumina content is 50-90 wt%; with SiO2 as the main component. x The silicon content is calculated to be 10-50 wt%, wherein 1 ≤ x ≤ 2;

[0013] Preferably, the alumina is γ-alumina.

[0014] A second aspect of this invention provides a method for preparing modified alumina, the method comprising the following steps:

[0015] (1) The aluminum source, the acidic compound and water are mixed in a first mixture to obtain a first mixture;

[0016] (2) The first mixture is subjected to molding, first drying and first calcination in sequence to obtain molded alumina;

[0017] (3) Dissolve the shaped alumina in water, first add an alkaline compound to adjust the pH to 7-12, then add a silicon source for a second mixing to obtain a second mixture;

[0018] (4) The second mixture is subjected to solid-liquid separation, and the resulting modified alumina precursor is subjected to a second drying and a second calcination to obtain modified alumina.

[0019] The third aspect of this invention provides the application of the modified alumina provided in the first aspect, or the modified alumina prepared by the method provided in the second aspect, in catalyst supports, gas-liquid adsorption, and solid-phase fillers.

[0020] A fourth aspect of the present invention provides a supported catalyst, the supported catalyst comprising a support and an active component supported on the support;

[0021] The carrier is selected from the modified alumina provided in the first aspect, or the modified alumina prepared by the method provided in the second aspect.

[0022] The fifth aspect of this invention provides the application of the supported catalyst provided in the fourth aspect in the catalytic synthesis of lysine-type antibacterial monomers, the aminoalkylation reaction of aromatic amines, and the preparation of derivatives of amide compounds.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) The modified alumina provided by the present invention, by limiting the silicon in the modified alumina to be connected to the surface of the alumina by Si-O-Al chemical bonds and the adjacent silicon on the surface of the alumina to be connected by Si-O-Si chemical bonds, and combined with the silicon-aluminum ratio <1, achieves the regulation of complex acidic sites on the surface of the alumina. Under the premise of ensuring that the modified alumina has low wear index, high crushing strength, high specific surface area and low average pore size, the Brønsted acid density of the modified alumina is effectively reduced. In particular, by regulating the content of silicon and alumina in the modified alumina, it is more conducive to regulating the Brønsted acid density of the modified alumina.

[0025] (2) The modified alumina preparation method provided by the present invention simplifies the process flow and facilitates industrial production; in particular, by adjusting the amount of silicon source input and the pH range of the mixing system in the second mixture, the Brønsted acid density of the modified alumina can be controlled.

[0026] (3) The modified alumina provided by the present invention has a low acid concentration and can be widely used in fine chemicals, especially as a catalyst support, gas-liquid adsorption or solid phase filler.

[0027] (4) The modified alumina provided by the present invention is used as a catalyst support. The resulting supported catalyst has high catalytic activity, especially in the catalytic synthesis of lysine-type antibacterial monomers, the aminoalkylation reaction of aromatic amines, and the preparation of derivatives of amide compounds, with high conversion rate and selectivity. Attached Figure Description

[0028] Figure 1 (a) is the transmission infrared spectrum of the modified alumina S1 prepared in Example 1; Figure 1(b) Transmission infrared spectrum of the modified alumina DS1 prepared in Comparative Example 1, wherein the wavenumber is 1066 cm⁻¹. -1 and 1160cm -1 The signal peaks at these locations are vibrational absorption peaks of Si-O-Si and Si-O-Al bonds, respectively.

[0029] Figure 2 These are the pyridine infrared characterization spectra of the modified alumina prepared in Example 1 and Comparative Examples 1-2, where the wavenumber is 1540 cm⁻¹. -1 The absorption peak at that location indicates the Brønsted acid sites on the surface of the modified alumina.

[0030] Figure 3 This is a SEM image of the modified alumina obtained in Example 1;

[0031] Figure 4 These are the XRD patterns of the modified alumina prepared in Example 1 and Comparative Example 2. Detailed Implementation

[0032] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0033] In this invention, unless otherwise specified, "first" and "second" do not indicate a sequence or limit the specific materials or steps; they are merely used to distinguish that these are not the same material or step. For example, in "first mixture" and "second mixture," "first" and "second" are used only to indicate that these are not the same mixture.

[0034] The first aspect of the present invention provides a modified alumina comprising silicon and alumina, wherein the silicon is bonded to the surface of the alumina by Si-O-Al chemical bonds, and adjacent silicon atoms on the surface of the alumina are bonded by Si-O-Si chemical bonds; the silicon-to-alumina ratio of the modified alumina is <1; and the Brønsted acid density of the modified alumina is ≤2 μmol / g.

[0035] The inventors of this invention discovered that the surface of alumina contains complex acidic sites, and the different types and intensities of these acidic sites significantly limit the application of alumina in the fine chemical industry. Therefore, by loading silicon onto the surface of alumina, and defining the silicon as connected to the alumina surface via Si-O-Al chemical bonds, and defining adjacent silicon atoms on the alumina surface as connected via Si-O-Si chemical bonds, the acidic sites on the alumina surface can be effectively masked while ensuring that the modified alumina possesses low wear index, high crushing strength, high specific surface area, and low average pore size. This allows for the control of the Brønsted acid (B acid) density on the modified alumina surface, resulting in a B acid density ≤2 μmol / g.

[0036] In this invention, unless otherwise specified, the silicon bonded to the surface of alumina via Si-O-Al chemical bonds refers to the shared O portion between Si and Al in alumina, thereby forming SiO2. x Silicon, in its present form, is anchored to the surface of the alumina.

[0037] In this invention, unless otherwise specified, the density of Brønsted acid refers to... Acid density.

[0038] In this invention, the Brønsted acid density parameter is calculated based on the amount of pyridine desorbed by heating; Brønsted acid density = amount of modified alumina acid used to test the infrared spectrum of pyridine (in μmol) / mass of modified alumina (in g).

[0039] In some embodiments of the present invention, preferably, the Brønsted acid density of the modified alumina is 0-2 μmol / g, for example, 0 μmol / g, 0.1 μmol / g, 0.2 μmol / g, 0.3 μmol / g, 0.5 μmol / g, 0.8 μmol / g, 1 μmol / g, 1.4 μmol / g, 1.5 μmol / g, 2 μmol / g, and any value within the range of any two values, preferably 0-1.4 μmol / g, more preferably 0-0.5 μmol / g.

[0040] In some embodiments of the present invention, preferably, the specific surface area of ​​the modified alumina is 100-220 m². 2 / g, preferably 120-200m 2 / g; average pore size is 10-30nm, preferably 15-25nm; wear index is 1-20%, preferably 1-15%; crushing strength is 50-150N / cm, preferably 70-130N / cm.

[0041] In this invention, unless otherwise specified, the specific surface area parameter is measured using a fully automatic isothermal adsorption instrument; the average pore size parameter is calculated using a fully automatic isothermal adsorption instrument in conjunction with the BJH model; the wear index parameter is measured using a wear index analyzer; and the crushing strength parameter is measured using a particle strength tester.

[0042] In this invention, unless otherwise specified, the modified alumina contains no other components besides silicon and alumina, that is, the sum of the contents of silicon and alumina is 100 wt%.

[0043] In some embodiments of the present invention, the content of the alumina is 50-90 wt%, preferably 70-80 wt%, based on the total weight of the modified alumina; with SiO x The silicon content is calculated to be 10-50 wt%, preferably 20-30 wt%, wherein 1 ≤ x ≤ 2. Using these preferred conditions is more conducive to reducing the Brønsted acid density of the modified alumina.

[0044] In some embodiments of the present invention, preferably, the modified alumina is selected from spherical or strip-shaped, wherein the spherical shape includes, but is not limited to, microspheres or small spheres.

[0045] In some embodiments of the present invention, preferably, the alumina is selected from γ-alumina. Using preferred conditions is more conducive to improving the activity of the modified alumina.

[0046] A second aspect of this invention provides a method for preparing modified alumina, the method comprising the following steps:

[0047] (1) The aluminum source, the acidic compound and water are mixed in a first mixture to obtain a first mixture;

[0048] (2) The first mixture is subjected to molding, first drying and first calcination in sequence to obtain molded alumina;

[0049] (3) Dissolve the shaped alumina in water, first add an alkaline compound to adjust the pH to 7-12, then add a silicon source for a second mixing to obtain a second mixture;

[0050] (4) The second mixture is subjected to solid-liquid separation, and the resulting modified alumina precursor is subjected to a second drying and a second calcination to obtain modified alumina.

[0051] In some embodiments of the present invention, preferably, in step (1), the content of aluminum source in the first mixture is 0.01-10 wt%, preferably 0.05-5 wt%; the content of acidic compound is 0.01-3 wt%, preferably 0.05-1 wt%. In the present invention, the ratio of the amount of aluminum source, acidic compound and water fed / used can satisfy the above-mentioned limitations.

[0052] In this invention, a wide range of aluminum sources can be selected. Preferably, the aluminum source is a soluble aluminum salt, including but not limited to γ-alumina, hydroxyalumina, boehmite, aluminum chloride, aluminum nitrate, etc. When the aluminum source is selected from γ-alumina, steps (1)-(2) are to acidify the surface of the powdered alumina to form a hydrated hydroxyl state, which facilitates the subsequent addition of alkaline compounds and silicon sources for silicon modification.

[0053] In this invention, a wide range of types of acidic compounds can be selected. Preferably, the acidic compound is selected from at least one of hydrochloric acid, nitric acid, sulfuric acid, and phosphoric acid. In this invention, the acidic compound exists in the form of an aqueous solution, and preferably the concentration of the acidic compound in the solution is 1-50 wt%.

[0054] In this invention, the first mixing method has a wide range of options, as long as the aluminum source, acidic compound, and water are mixed. Preferably, the conditions for the first mixing include: a temperature of 15-40°C, preferably 20-30°C; a rotation speed of 100-1000 rpm, preferably 300-1000 rpm; and a time of 0.1-5 h, preferably 0.1-2 h.

[0055] In this invention, there is a wide range of options for the molding method. Preferably, in step (2), the molding method includes, but is not limited to, oil-ammonia droplet molding, spray drying molding, and extrusion molding.

[0056] In this invention, the first drying is intended to remove water from the first mixture. Preferably, in step (2), the conditions for the first drying include: a temperature of 80-120°C and a time of 90-110°C; the time is 1-20 hours, preferably 1-12 hours.

[0057] In this invention, the first drying method has a wide range of options, as long as the conditions for the first drying meet the above-mentioned limitations. Preferably, the first drying method includes, but is not limited to, spray drying, forced-air drying, vacuum drying, etc.

[0058] In some embodiments of the present invention, preferably, in step (2), the conditions for the first calcination include: a temperature of 700-1200℃, preferably 800-1000℃; and a time of 1-10h, preferably 1-5h. In the present invention, the first calcination is carried out in a muffle furnace or a tube furnace, and the calcination atmosphere is a non-reducing gas, preferably at least one of air, nitrogen, and argon.

[0059] In this invention, in step (3), the shaped alumina is first dissolved in water, an alkaline compound is added to adjust the pH, and then a silicon source is added for a second mixing, in order to obtain polyhydroxy silicic acid and / or hydroxy hydrated silicon.

[0060] In some embodiments of the present invention, the pH is preferably adjusted to 8-12, for example, 8, 9, 10, 10.5, 11.5, 12, and any value within the range of any two values, preferably 10.5-11.5.

[0061] In some embodiments of the present invention, preferably, the shaped alumina is calculated as Al2O3 and the alumina is calculated as SiO2. x The weight ratio of the silicon source is 5-9:1-5, preferably 7-8:2-3; wherein 1≤x≤2.

[0062] In this invention, a wide range of silicon sources can be selected. Preferably, the silicon source is a soluble silicon salt, preferably selected from organosilicon salts and / or inorganic silicon salts, including but not limited to at least one of tetramethylsilane, tetramethylsilane, silica aerogel, and silicon tetrachloride.

[0063] In this invention, unless otherwise specified, solubility means being easily soluble in water, or being easily soluble in water with the help of additives.

[0064] In some embodiments of the present invention, preferably, the alkaline compound is selected from at least one of ammonium carbonate, ammonium bicarbonate and ammonia water.

[0065] In some embodiments of the present invention, preferably, the conditions for the second mixing include: a temperature of 20-70°C, preferably 25-60°C; a rotation speed of 100-1000 rpm, preferably 300-1000 rpm; and a time of 1-20 h, preferably 6-12 h.

[0066] In this invention, the solid-liquid separation method has a wide range of options, as long as the second mixture is subjected to solid-liquid separation to obtain the modified alumina precursor; the solid-liquid separation method includes, but is not limited to, filtration, sedimentation, etc.

[0067] In this invention, the second drying is intended to remove residual moisture from the modified alumina precursor. Preferably, in step (4), the conditions for the second drying include: a temperature of 80-120°C and a time of 90-110°C; the time is 1-20 hours, preferably 1-12 hours.

[0068] In this invention, the second drying method has a wide range of options, as long as the conditions for the second drying meet the above-mentioned limitations. Preferably, the second drying method includes, but is not limited to, spray drying, forced-air drying, vacuum drying, etc.

[0069] In some embodiments of the present invention, preferably, in step (4), the conditions for the second calcination include: a temperature of 400-1000℃, preferably 500-900℃; and a time of 1-10h, preferably 1-5h. In the present invention, the second calcination is carried out in a muffle furnace or a tube furnace, and the calcination atmosphere is a non-reducing gas, preferably at least one of air, nitrogen, and argon.

[0070] The third aspect of this invention provides the application of the modified alumina provided in the first aspect, or the modified alumina prepared by the method provided in the second aspect, in catalyst supports, gas-liquid adsorption, and solid-phase fillers.

[0071] A fourth aspect of the present invention provides a supported catalyst, the supported catalyst comprising a support and an active component supported on the support;

[0072] The carrier is selected from the modified alumina provided in the first aspect, or the modified alumina prepared by the method provided in the second aspect.

[0073] In some embodiments provided by the present invention, preferably, the supported catalyst includes modified alumina and an active component, wherein the active component is selected from Pd and Pt.

[0074] In this invention, there is a wide range of options for the preparation method of the supported catalyst, as long as the active component is loaded on the surface of the modified alumina.

[0075] The fifth aspect of this invention provides the application of the supported catalyst provided in the fourth aspect in the catalytic synthesis of lysine-type antibacterial monomers, the aminoalkylation reaction of aromatic amines, and the preparation of derivatives of amide compounds.

[0076] According to the present invention, when the supported catalyst is used in the above-mentioned applications, the conversion rate of the raw materials and the selectivity of the products can be effectively improved, thereby increasing the yield of the target product.

[0077] According to a particularly preferred embodiment of the present invention, the modified alumina comprises silicon and alumina; wherein the silicon is bonded to the surface of the alumina by Si-O-Al chemical bonds, and adjacent silicon atoms on the surface of the alumina are bonded by Si-O-Si chemical bonds; the silicon-to-alumina ratio of the modified alumina is <1; wherein the Brønsted acid density of the modified alumina is 0-0.5 μmol / g.

[0078] The modified alumina is prepared by the following method:

[0079] (1) The aluminum source, the acidic compound and water are mixed in a first mixture to obtain a first mixture;

[0080] (2) The first mixture is subjected to molding, first drying and first calcination in sequence to obtain molded alumina;

[0081] (3) Dissolve the shaped alumina in water, first add an alkaline compound to adjust the pH to 8-12, then add a silicon source for a second mixing to obtain a second mixture;

[0082] (4) The second mixture is subjected to solid-liquid separation, and the resulting modified alumina precursor is subjected to a second drying and a second calcination to obtain the modified alumina.

[0083] The present invention will be described in detail below through embodiments.

[0084] The Brønsted acid density parameter is calculated based on the amount of pyridine desorbed upon heating; that is, Brønsted acid density = amount of modified alumina (in μmol) used to test the infrared spectrum of pyridine / mass of modified alumina (in g).

[0085] Specific surface area parameters were measured using a fully automated isothermal adsorption analyzer.

[0086] The average pore size parameters were obtained using a fully automated isothermal adsorption instrument and in conjunction with the BJH model.

[0087] The wear index parameters were measured using a wear index analyzer.

[0088] The crushing strength parameters were measured using a particle strength tester.

[0089] The physical properties of the modified alumina (S1-S7 and DS1-DS6) prepared in Examples 1-7 and Comparative Examples 1-6 are listed in Table 1.

[0090] Example 1

[0091] (1) 80g of aluminum source (pseudoboehmite), 5g of acidic compound aqueous solution (30wt% dilute nitric acid solution) and 800mL of water were mixed in a 1500mL stirred tank (temperature 25℃, speed 600rpm, time 1h) to obtain the first mixture;

[0092] (2) The first mixture above is spray-dried and shaped (temperature is 100℃, time is 5h), and then calcined in a muffle furnace at static air temperature of 800℃ for 3h to obtain micro-spherical shaped alumina.

[0093] (3) Dissolve the above-mentioned shaped alumina in 800 mL of water, first add an alkaline compound (ammonia) to adjust the pH to 10, then add 60 g of silicon source (tetraethyl orthosilicate) for a second mixing (temperature 25℃, rotation speed 600 rpm, time 12 h) to obtain the second mixture;

[0094] (4) The above second mixture is subjected to solid-liquid separation. The modified alumina precursor is dried in a vacuum drying oven at 100°C for 5 hours and then calcined in a muffle furnace at 600°C under static air for 3 hours to obtain modified alumina S1.

[0095] The transmission infrared spectrum of modified alumina S1 is as follows: Figure 1 As shown in (a); by Figure 1 (a) It can be seen that the wave number is 1066 cm⁻¹ -1 and 1160cm -1 The signal peaks at these locations are vibrational absorption peaks of Si-O-Si and Si-O-Al bonds, respectively, indicating that silicon in the modified alumina S1 is bonded to the alumina through Si-O-Al chemical bonds, and that adjacent silicon on the surface of the alumina is bonded to SiO-Al bonds. x Clusters of (1≤x≤2) exist.

[0096] The pyridine infrared characterization spectrum of modified alumina S1 is shown below. Figure 2 As shown, by Figure 2 It can be seen that modified alumina S1 has extremely low Brønsted acid sites.

[0097] The SEM image of modified alumina S1 is shown below. Figure 3 As shown, by Figure 3 It can be seen that the modified alumina S1 is in the form of microspheres.

[0098] The XRD pattern of modified alumina S1 is shown below. Figure 4 As shown, by Figure 4 It can be seen that the alumina in modified alumina S1 is γ-alumina.

[0099] Example 2

[0100] (1) 80g of aluminum source (aluminum hydroxide), 10g of acidic compound aqueous solution (10wt% dilute nitric acid solution) and 800mL of water were mixed in a 1500mL stirred tank (temperature 20℃, speed 400rpm, time 1h) to obtain the first mixture;

[0101] (2) The first mixture above is spray-dried and shaped (temperature is 100℃, time is 5h), and then calcined in a muffle furnace at static air temperature of 800℃ for 3h to obtain micro-spherical shaped alumina.

[0102] (3) Dissolve the above-mentioned shaped alumina in 800 mL of water, first add an alkaline compound (ammonia) to adjust the pH to 12, then add 60 g of silicon source (tetraethyl orthosilicate) for a second mixing (temperature 25℃, rotation speed 400 rpm, time 8 h) to obtain the second mixture;

[0103] (4) The second mixture was subjected to solid-liquid separation. The modified alumina precursor was dried in a vacuum drying oven at 100°C for 5 hours and then calcined in a muffle furnace at 600°C for 3 hours under static air to obtain modified alumina S2.

[0104] Example 3

[0105] (1) 40g of aluminum source (boehmite), 4g of acidic compound aqueous solution (20wt% dilute nitric acid solution) and 800mL of water were mixed in a 1500mL stirred tank (temperature 30℃, speed 400rpm, time 1h) to obtain the first mixture;

[0106] (2) After the first mixture is extruded and vacuum dried (at 100°C for 5 hours), it is calcined in a muffle furnace at 1000°C for 2 hours to obtain strip-shaped alumina.

[0107] (3) Dissolve the above-mentioned shaped alumina in 800 mL of water, first add an alkaline compound (ammonia) to adjust the pH to 12, then add 10 g of silicon source (tetraethyl orthosilicate) for a second mixing (temperature 40℃, rotation speed 400 rpm, time 6 h) to obtain the second mixture;

[0108] (4) The second mixture was subjected to solid-liquid separation. The modified alumina precursor was dried in a vacuum drying oven at 100°C for 5 hours and then calcined in a muffle furnace at 600°C for 3 hours under static air to obtain strip-shaped modified alumina S3.

[0109] Example 4

[0110] (1) 50g of aluminum source (boehmite), 10g of acidic compound aqueous solution (20wt% dilute nitric acid solution) and 800mL of water were mixed in a 1500mL stirred tank (temperature 30℃, speed 400rpm, time 1h) to obtain the first mixture;

[0111] (2) After the first mixture above is subjected to oil-ammonia drop ball forming and forced air drying (temperature is 100℃, time is 5h), it is calcined in a muffle furnace at static air of 1000℃ for 2h to obtain small spherical alumina.

[0112] (3) Dissolve the above-mentioned shaped alumina in 800 mL of water, first add an alkaline compound (ammonia) to adjust the pH to 10, then add 10 g of silicon source (silicon tetrachloride) for a second mixing (temperature 25℃, speed 400 rpm, time 6 h) to obtain the second mixture;

[0113] (4) The second mixture was subjected to solid-liquid separation. The modified alumina precursor was dried in a blower oven at 100°C for 5 hours and then calcined in a muffle furnace at 800°C for 3 hours to obtain small spherical modified alumina S4.

[0114] Example 5

[0115] (1) 80g of aluminum source (γ-alumina), 5g of acidic compound aqueous solution (30wt% dilute hydrochloric acid solution) and 800mL of water were mixed in a 1500mL stirred tank (temperature 30℃, speed 800rpm, time 1h) to obtain the first mixture;

[0116] (2) The first mixture above is spray-dried and shaped (temperature is 100℃, time is 5h), and then calcined in a muffle furnace at static air temperature of 800℃ for 3h to obtain micro-spherical shaped alumina.

[0117] (3) Dissolve the above-mentioned shaped alumina in 800 mL of water, first add an alkaline compound (ammonia) to adjust the pH to 12, then add 50 g of silicon source (silica aerogel) for a second mixing (temperature 25℃, speed 400 rpm, time 12 h) to obtain the second mixture;

[0118] (4) The second mixture was subjected to solid-liquid separation. The modified alumina precursor was dried in a blower oven at 100°C for 5 hours and then calcined in a muffle furnace at 800°C for 3 hours to obtain microspherical modified alumina S5.

[0119] Example 6

[0120] (1) 80g of aluminum source (boehmite), 20g of acidic compound aqueous solution (10wt% dilute sulfuric acid solution) and 800mL of water were mixed in a 1500mL stirred tank (temperature 30℃, speed 800rpm, time 1h) to obtain the first mixture;

[0121] (2) After the first mixture is extruded and dried by blowing (temperature is 100℃, time is 5h), it is calcined in a muffle furnace at static air temperature of 800℃ for 3h to obtain strip-shaped alumina.

[0122] (3) Dissolve the above-mentioned shaped alumina in 800 mL of water, first add an alkaline compound (ammonia) to adjust the pH to 12, then add 30 g of silicon source (tetraethyl orthosilicate) for a second mixing (temperature 60℃, rotation speed 800 rpm, time 6 h) to obtain the second mixture;

[0123] (4) The second mixture was subjected to solid-liquid separation. The modified alumina precursor was dried in a vacuum drying oven at 100°C for 5 hours and then calcined in a muffle furnace at 800°C for 3 hours to obtain strip-shaped modified alumina S6.

[0124] Example 7

[0125] The method of Example 1 is followed, except that in step (3), the pH is adjusted to 7, while the other conditions are the same, to obtain microspherical modified alumina S7.

[0126] Comparative Example 1

[0127] 800 mL of deionized water, 80 g of boehmite and 10 g of 10 wt% dilute nitric acid aqueous solution were mixed in a 1500 mL stirred tank (temperature 25℃, rotation speed 800 rpm, time 5 h). The resulting mixture was subjected to solid-liquid separation. The solid obtained was spray-dried and then calcined in a muffle furnace under static air at 800℃ for 3 h to obtain microspherical modified alumina DS1.

[0128] The transmission infrared spectrum of modified alumina DS1 is shown in 1(b); Figure 1 (b) It can be seen that the wave number is 1066 cm⁻¹. -1 and 1160cm -1 No signal peaks were observed at any point, indicating that silicon and alumina in modified alumina DS1 are not chemically bonded, and adjacent silicon on the surface of alumina are also not chemically bonded.

[0129] The pyridine infrared characterization spectrum of modified alumina DS1 is shown below. Figure 2 As shown in Figure 2, the modified alumina DS1 has a high number of Brønsted acid sites.

[0130] Comparative Example 2

[0131] 800 mL of deionized water, 80 g of boehmite, and 20 g of 5 wt% dilute nitric acid solution were mixed in a 1500 mL stirred tank (temperature 25℃, speed 800 rpm, time 5 h). Then, 60 g of tetraethyl orthosilicate was added, and ammonia was added to adjust the pH to 12. The mixture was stirred at 25℃ for 12 h. The resulting mixture was spray-dried and calcined in a muffle furnace under static air at 800℃ for 3 h to obtain microspherical modified alumina DS2.

[0132] The pyridine infrared characterization spectrum of modified alumina DS2 is shown below. Figure 2 As shown, by Figure 2 It can be seen that the modified alumina DS2 has a high number of Brønsted acid sites.

[0133] The XRD pattern of modified alumina DS2 is shown below. Figure 4 As shown, by Figure 4 It can be seen that the alumina in modified alumina DS2 is γ-alumina.

[0134] Comparative Example 3

[0135] The method of Example 1 is different except that steps (1)-(2) are omitted, that is, 80g of aluminum source (pseudoboehmite) is directly dissolved in 800mL of water, and the other conditions are the same to obtain modified alumina DS3.

[0136] Comparative Example 4

[0137] The method of Example 1 is the same except that step (2) is omitted. That is, the first mixture obtained in step (1) is directly subjected to step (3) under the same conditions to obtain modified alumina DS4.

[0138] Comparative Example 5

[0139] The method of Example 1 is different except that in step (3), the above-mentioned shaped alumina, 800 mL of water, alkaline compound (ammonia) and 60 g of silicon source (tetraethyl orthosilicate) are directly mixed for the second time (temperature is 25°C, rotation speed is 600 rpm, time is 12 h), and the pH is adjusted to 10. The other conditions are the same, and modified alumina DS5 is obtained.

[0140] Comparative Example 6

[0141] Following the method of Example 1, except that in step (3), ammonia was not added to adjust the pH to 10, while the other conditions remained the same, and modified alumina DS6 was obtained.

[0142] Table 1

[0143]

[0144] Note: *-Silicon content is expressed as SiO₂ x Calculate, where 1≤x≤2.

[0145] Continued from Table 1

[0146]

[0147]

[0148] As can be seen from the results in Table 1, compared with Comparative Examples 1-7, the modified alumina prepared in Examples 1-6 has the characteristics of low Brønsted acid density, low wear index, high crushing strength, high specific surface area and low average pore size. That is, the modified alumina provided by the present invention has low Brønsted acid density, wear resistance, high stability and excellent pore structure.

[0149] Test case

[0150] The modified alumina (S1-S7 and DS1-DS6) prepared in Examples 1-7 and Comparative Examples 1-6 were used as catalyst supports and impregnated in a Pd(NH3)4Cl2 solution prepared with 30wt% ammonia water to load 10wt% Pd on the surface of the catalyst support. The catalysts were dried in a vacuum drying oven and calcined in a muffle furnace at 500°C under static air for 3 hours to obtain supported catalysts (P1-P7 and DP1-DP6).

[0151] Based on the total weight of the supported catalysts (P1-P7 and DP1-DP6), the content of active component Pd is 10 wt%, and the content of modified alumina is 90 wt%.

[0152] The catalytic effect of the above-mentioned supported catalyst was evaluated using an intermittent high-pressure reactor. The specific operation included: in the presence of 50 mL methanol and 0.1 g of supported catalyst (P1-P7 and DP1-DP6), 0.2 g of aminocaprolactam and 0.1 g of paraformaldehyde were subjected to a hydrogenation reaction. The conditions for the hydrogenation reaction were: hydrogen pressure of 0.3 MPa, temperature of 80 °C, and time of 3 h, to obtain the reaction products, which included dimethylaminocaprolactam, methylaminocaprolactam, and other byproducts.

[0153] The catalytic reaction results were analyzed by gas chromatography, and the test results are listed in Table 2.

[0154] Table 2

[0155]

[0156] As can be seen from the results in Table 2, using the modified alumina provided by this invention as a support and loading the active component Pd, the resulting catalyst for the hydrogenation reaction of aminocaprolactam and paraformaldehyde has a high feed conversion rate and product selectivity, that is, the dimethylaminocaprolactam obtained has a high yield.

[0157] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A modified alumina, characterized in that, The modified alumina comprises silicon and alumina; wherein the silicon is bonded to the surface of the alumina by Si-O-Al chemical bonds, and adjacent silicon atoms on the surface of the alumina are bonded by Si-O-Si chemical bonds; the silicon-to-alumina ratio of the modified alumina is <1. The modified alumina has a Brønsted acid density of 0-1.4 μmol / g and a specific surface area of ​​100-220 m². 2 / g, average pore size is 10-30nm, wear index is 1-20%, crushing strength is 50-150N / cm; Wherein, based on the total weight of the modified alumina, the alumina content is 50-90 wt%; with SiO2 as the main component. x The silicon content is calculated to be 10-50 wt%, wherein 1 ≤ x ≤ 2; The modified alumina is prepared by the following method: (1) Aluminum source, acidic compound and water are mixed for the first time to obtain a first mixture; (2) The first mixture is successively shaped, dried and calcined to obtain shaped alumina; (3) The shaped alumina is dissolved in water, an alkaline compound is added to adjust the pH to 7-12, and a silicon source is added for the second mixing to obtain a second mixture; (4) The second mixture is subjected to solid-liquid separation, and the modified alumina precursor obtained is successively dried and calcined to obtain the modified alumina.

2. The modified alumina according to claim 1, wherein, The modified alumina has a Brønsted acid density of 0-0.5 μmol / g.

3. The modified alumina according to claim 1, wherein, The specific surface area of ​​the modified alumina is 120-200 m². 2 / g; average pore size is 15-25nm; wear index is 1-15%; crushing strength is 70-130N / cm.

4. The modified alumina according to claim 1, wherein, Based on the total weight of the modified alumina, the alumina content is 70-80 wt%; with SiO2 as the main component. x The silicon content is calculated to be 20-30 wt%, wherein 1 ≤ x ≤ 2; The alumina is γ-alumina.

5. A method for preparing modified alumina according to any one of claims 1-4, characterized in that, The method includes the following steps: (1) The aluminum source, the acidic compound, and water are mixed in a first mixture to obtain a first mixture; (2) The first mixture is subjected to molding, first drying and first calcination in sequence to obtain shaped alumina; (3) Dissolve the shaped alumina in water, first add an alkaline compound to adjust the pH to 7-12, then add a silicon source for a second mixing to obtain a second mixture; (4) The second mixture is subjected to solid-liquid separation, and the resulting modified alumina precursor is subjected to second drying and second calcination to obtain modified alumina.

6. The method according to claim 5, wherein, In step (1), the content of the aluminum source in the first mixture is 0.01-10 wt%; the content of the acidic compound is 0.01-3 wt%. The conditions for the first mixing include: a temperature of 15-40℃; a rotation speed of 100-1000 rpm; and a time of 0.1-5h.

7. The method according to claim 6, wherein, In step (1), the content of the aluminum source in the first mixture is 0.05-5 wt%; the content of the acidic compound is 0.05-1 wt%. The conditions for the first mixing include: a temperature of 20-30℃; a rotation speed of 300-1000 rpm; and a time of 0.1-2 h.

8. The method according to claim 5, wherein, In step (2), the molding method is selected from oil-ammonia droplet molding, spray drying molding, and extrusion molding; In step (2), the conditions for the first roasting include: a temperature of 700-1200℃ and a time of 1-10h.

9. The method according to claim 8, wherein, In step (2), the conditions for the first roasting include: a temperature of 800-1000℃ and a time of 1-5h.

10. The method according to claim 5, wherein, In step (3), adjust the pH to 8-12; The shaped alumina, calculated as Al2O3, and the alumina calculated as SiO2O3, are present in the form of... x The weight ratio of the silicon source is 5-9:1-5; where 1≤x≤2; The conditions for the second mixing include: a temperature of 20-70℃; a rotation speed of 100-1000 rpm; and a time of 1-20 h.

11. The method according to claim 10, wherein, In step (3), the pH is adjusted to 10.5-11.5; The shaped alumina, calculated as Al2O3, and the alumina calculated as SiO2O3, are present in the form of... x The weight ratio of the silicon source is calculated to be 7-8:2-3; where 1≤x≤2; The conditions for the second mixing include: a temperature of 25-60℃; a rotation speed of 300-1000 rpm; and a time of 6-12 hours.

12. The method according to claim 5, wherein, In step (4), the conditions for the second calcination include: a temperature of 400-1000℃ and a time of 1-10h.

13. The method according to claim 12, wherein, In step (4), the conditions for the second calcination include: a temperature of 500-900℃ and a time of 1-5h.

14. A supported catalyst, characterized in that, The supported catalyst includes a support and an active component supported on the support; The carrier is selected from the modified alumina according to any one of claims 1-4.

15. The application of the supported catalyst according to claim 14 in the hydrogenation reaction of aminocaprolactam and paraformaldehyde to prepare dimethylaminocaprolactam.

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