Alumina bismuth catalyst support and method for its production

Abstract

To provide an improved alumina bismuth support applicable in emission control catalysis having improved characteristics.SOLUTION: An alumina bismuth catalyst support comprises (i) 80 wt.% or more of a transitional alumina based material, and (ii) 1 wt.% to 20 wt.% of a bismuth oxide, characterized by a specific crystallinity value CBi of less than 10, preferably a crystallinity value CBi of less than 3.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a method for preparing an alumina-bismuth catalyst support for emission control applications, an alumina-bismuth catalyst support prepared by the method of the present invention, and an alumina-bismuth catalyst support having specific characteristics.

Background Art

[0002] The main untreated emission pollutants in exhaust gas are CO, NOx, unburned hydrocarbons, and soot particles. Catalytic systems for emission control applications, which include various components and noble metals, are known in the art. Usually, so-called diesel oxidation catalysts (DOCs) containing noble metals supported on high oxides such as alumina or silica-alumina with a high surface area and high refractoriness convert CO to CO2 and unburned hydrocarbons to CO2 and water. Due to continuous strict legislative measures regarding exhaust gas, including Real Driving Emissions (RDE) and the Worldwide Harmonized Light Vehicle Test Procedure (WLTP) for passenger cars and the like, and the introduction of more realistic driving cycles, the low-temperature activity of the above-mentioned catalytic systems has become an important field of development.

[0003] The incorporation of activating additives and / or stabilizing additives (e.g., metal oxides) into the materials of catalysts or catalyst supports are each known endeavors. Patent Document 1 and Patent Document 2 disclose beneficial effects regarding the low-temperature conversion of CO and hydrocarbons by the addition of Bi2O3 to a catalyst. In Patent Document 2, it is described that bismuth is added as a promoter by in-situ reduction treatment. In Patent Document 1, bismuth is supported on the support.

[0004] Therefore, the prior art teaches incorporating Bi2O3 as a separate crystal phase. As described above, since the specific surface area of the promoting additive becomes small, the benefit of the interaction with the active noble metal is limited.

Prior Art Documents

Patent Document

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] Therefore, an object of the present disclosure is to provide an improved alumina-bismuth carrier applicable to an exhaust gas control catalyst with improved characteristics, and to provide a novel manufacturing method for the alumina-bismuth carrier.

Means for Solving the Problems

[0007] According to a first aspect of the present disclosure, there is provided a method for preparing an alumina-bismuth catalyst carrier, the method comprising: (i) providing an aluminum-containing composition comprising (a) boehmite or (b) an aluminum-containing composition comprising silica-containing aluminum oxide; (ii) providing an aqueous bismuth solution comprising a bismuth salt and a nitrogen-containing base, preferably ammonia, having a pH value of 4 to 9; (iii) contacting the aluminum-containing composition with the aqueous bismuth solution to form an aluminum-bismuth intermediate, wherein when the aluminum-containing composition in step (i) contains boehmite, the contact is carried out by mixing the aluminum-containing composition in the form of a dry powder or a suspension with the aqueous bismuth solution to form an aluminum-bismuth intermediate, or when the aluminum-containing composition in step (i) contains silica-containing aluminum oxide, the contact is carried out by impregnating the aluminum-containing composition in the form of a dry powder with the aqueous bismuth solution to form an aluminum-bismuth intermediate step; (iv) Calcining the aluminum-bismuth intermediate to form an alumina-bismuth catalyst support; and comprises.

[0008] In step (iii), when the aluminum-containing composition contains boehmite in step (i), the aluminum-bismuth intermediate can further be referred to as a boehmite-bismuth intermediate.

[0009] In step (iii), when the aluminum-containing composition contains silica in step (i), the aluminum-bismuth intermediate can further be referred to as a silica-aluminum oxide-bismuth intermediate.

[0010] Preferably, the aluminum-containing composition consists of boehmite or silica-containing aluminum oxide for the aluminum-containing compound in the composition. The aluminum-containing composition can further contain, for example, one or more dopants (in addition to silica or another component).

[0011] The aluminum oxide in the silica-containing aluminum oxide is preferably transitional alumina or contains transitional alumina. The silica-containing aluminum oxide more preferably contains transitional alumina, silica, and one or more dopants. The transitional alumina is one or more of gamma (γ)-aluminum oxide, delta (δ)-aluminum oxide, or theta (θ)-aluminum oxide, and is preferably gamma alumina or contains gamma alumina.

[0012] According to one embodiment, the aluminum-containing composition preferably contains 50 weight percent or more of silica-containing aluminum oxide.

[0013] According to a further embodiment, the aluminum-containing composition preferably contains 50 weight percent or more of boehmite. Preferably, the aluminum-containing composition contains boehmite (AlOOH) regardless of the presence or absence of one or more dopants, and more preferably, the aluminum-containing composition contains boehmite, silica, and one or more dopants.

[0014] When silica is present in the aluminum-containing composition, the content of SiO2 is 1 weight percent to 40 weight percent, preferably 1 weight percent to 20 weight percent, based on the total dry mass of SiO2, aluminum oxide, aluminum oxide hydroxide, and aluminum trihydroxide. Preferably, the aluminum-containing composition does not contain aluminum trihydroxide and further contains only aluminum oxide or aluminum oxide hydroxide.

[0015] Boehmite includes boehmite itself and pseudo-boehmite. Boehmite can be defined as any alumina having a molecular formula of AlOOH*xH2O, where x is 0 to 0.5. Aluminum oxide hydroxide is the same as boehmite. Alumina is understood to mean aluminum oxide and / or aluminum oxide hydroxide. Aluminum oxide is Al2O3.

[0016] The dopant can be an oxide or a water-soluble salt of an alkaline earth metal, a transition metal such as Zr or Ti, a rare earth element, or a mixture thereof. Preferably, its content is 0 weight percent to 10 weight percent, more preferably 0 weight percent to 5 weight percent, calculated as an oxide based on the total mass of aluminum oxide, aluminum oxide hydroxide, and aluminum trihydroxide. The transition metal is preferably Mn, Fe, Cu, Nb, Zr, Ti, or a mixture thereof, and more preferably Zr, Ti, or a mixture thereof. The dopant can be a carbonate of an alkaline earth metal, particularly barium carbonate.

[0017] The aluminum-containing composition can be provided in the form of a dry powder or in the form of a suspension of aluminum. When the aluminum-containing composition is in the form of a suspension of aluminum, the suspension preferably contains the aluminum-containing composition and at least water in a weight ratio of 2:98 to 20:80. The suspension of aluminum can further contain a pH-adjusting additive such as a carboxylic acid or ammonia, preferably a monocarboxylic acid such as acetic acid.

[0018] The suspension of aluminum is preferably a boehmite suspension, and boehmite is most preferably prepared by hydrolysis of an aluminum alkoxide including a hydrothermal degradation step. The hydrothermal degradation step is carried out at 100°C to 300°C, preferably 120°C to 240°C, for 0.5 hour to 30 hours, preferably 3 hours to 10 hours, and the time and temperature are selected separately.

[0019] The bismuth aqueous solution preferably contains a water-soluble salt of Bi 3+ more preferably bismuth nitrate or bismuth citrate, and most preferably bismuth citrate. The anion of the salt is preferably an organic compound such as an organic acid. The pH value of the bismuth aqueous solution is 4 to 9, preferably 6 to 8.

[0020] Contact means either (a) mixing an aluminum-containing composition, preferably a suspension of aluminum, with a bismuth aqueous solution to form an aluminum-bismuth intermediate, or (b) impregnating a bismuth aqueous solution into an aluminum-containing composition in the form of a dry powder to form an aluminum-bismuth intermediate. When the aluminum-containing composition is silica-containing aluminum oxide or contains silica-containing aluminum oxide, step (iii) involves "impregnation", and when the aluminum-containing composition is boehmite or contains boehmite, step (iii) involves "mixing".

[0021] The impregnation of the aluminum-containing composition can be carried out by any impregnation method known in the art, preferably by incipient wetness impregnation. The method is provided for impregnating an aluminum-containing composition of 80-100% with an aqueous bismuth solution. "%" means the ratio of (volume of the added liquid) / (pore volume).

[0022] When the aluminum suspension is mixed with the aqueous bismuth solution, the method can further include a step of drying, preferably spray-drying, an aluminum-bismuth intermediate to form a dried body of the aluminum-bismuth intermediate which is calcined later.

[0023] The aluminum-bismuth intermediate or the dried body of the aluminum-bismuth intermediate is calcined at a temperature of 500°C to 1000°C, more preferably 600°C to 900°C, still more preferably 500°C to 700°C, independently of the temperature, for 0.5 hours or more, preferably 0.5 hours to 5 hours, preferably 3 hours.

[0024] According to a second aspect of the present disclosure, an aluminabismuth catalyst support prepared by the method of the present disclosure is provided.

[0025] According to a third aspect of the present disclosure, (i) a material of transition alumina system of 80 weight percent or more, and (ii) a value C of crystallinity Bi is less than 10, preferably the value C of crystallinity Bi is less than 3, characterized by 1 weight percent to 20 weight percent of bismuth oxide and containing an aluminabismuth catalyst support is provided.

[0026] The material of transition alumina system is preferably alumina, silica, and / or a dopant, or can contain alumina, silica, and / or a dopant. More preferably, the material of transition alumina system contains alumina, silica, and one or more dopants.

[0027] The transition alumina-based material preferably contains gamma alumina, delta alumina, or theta alumina, or a mixture thereof.

[0028] The transition alumina-based material preferably contains 50 wt% or more of aluminum oxide.

[0029] When silica is present in the aluminum-containing composition, the content of SiO2 is 1 wt% to 40 wt%, preferably 1 wt% to 20 wt%, based on the mass of the oxides of silica and aluminum oxide.

[0030] The dopant can be an alkaline earth metal, an oxide of a transition metal such as Zr or Ti, a rare earth metal, or an oxide of a mixture thereof. Preferably, its content is 0 wt% to 10 wt%, preferably 0 wt% to 5 wt%, calculated as an oxide based on the total mass of aluminum oxide, silica, and dopant. The transition metal is preferably Mn, Fe, Cu, Nb, Zr, Ti, or a mixture thereof, and more preferably Zr, Ti, or a mixture thereof.

[0031] The BET specific surface area of the alumina-bismuth catalyst support is 50 m 2 / g to 300 m 2 / g, preferably 100 m 2 / g to 200 m 2 / g. The pore volume of the alumina-bismuth catalyst support is 0.1 ml / g to 1.5 ml / g, preferably 0.5 ml / g to 1.0 ml / g.

[0032] According to the present disclosure, an improved heterogeneous catalyst with improved contact between the active phase (noble metal) and the promoter is obtained. The above is achieved by the uniform dispersion of bismuth oxide, which is a promoter, in the substrate of the carrier material, resulting in good accessibility of the promoter to the noble metal and uniform arrangement of the promoter and the noble metal throughout the catalyst. Substantially X-ray amorphous bismuth oxide exhibits the above-described uniform dispersion in the substrate of the alumina-based material.

[0033] Bismuth oxide is uniformly dispersed in the matrix of the alumina-based material. Although not linked to theory, the applicant of the present application believes that a complex of beneficial properties is obtained by the uniform dispersion of small crystals of bismuth oxide in a substantially X-ray amorphous state. The X-ray amorphous state can be described by the degree of crystallinity value as described later.

[0034] The degree of crystallinity as used in this specification is determined by the following method. X-ray diffraction (XRD) of Bi2O3 using the Kα line of copper (Cu) includes the strongest reflection at 2θ = approximately 28 degrees (021 reflection in the space group of P4-21c). The XRD pattern of the transition alumina material includes a strong reflection at 2θ = 67 degrees. The normalized intensity ratio of the above two reflections (see Equation 1) is the measure C of the crystallinity of bismuth oxide in the transition alumina-based material. Bi becomes. C Bi = [(I 28 - I 24 ) / (I 67 - I 72 )] / m Bi (Equation 1) I 28 : Intensity of the reflection at approximately 28 degrees I 24 : Intensity of the baseline near the reflection at approximately 24 degrees I 67 : Intensity of the reflection at approximately 67 degrees I 72 : Intensity of the baseline near the reflection at approximately 72 degrees m Bi : Mass of Bi2O3 / (Mass of Bi2O3 + Mass of the transition alumina-based material)

[0035] The uniformity is measured by image processing of the cross-section of a scanning electron microscope (SEM), and is measured selectively together with elemental mapping of energy dispersive X-ray analysis (EDX) that reveals the domain size of the transition alumina-based material, bismuth oxide, and the alumina bismuth catalyst support region.

[0036] The surface area and pore volume are measured at the temperature of liquid nitrogen by N2 physical adsorption using a general volumetric measuring device such as Quadrasorb from Quantachrome. The surface area is determined using the BET theory (DIN ISO9277), and the pore volume is determined according to DIN66131. The range of pore radius is 18 Å to 1000 Å.

[0037] According to a fourth aspect of the present disclosure, there is provided the use of the aforementioned alumina bismuth catalyst support as a support for an oxidation catalyst, preferably a support for an oxidation catalyst containing platinum (Pt) and / or palladium (Pd), particularly as a support for a diesel oxidation catalyst for vehicle emission control applications.

[0038] Next, the present disclosure will be described with reference to the following non-limiting examples and drawings.

Brief Description of the Drawings

[0039]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0040] [Example 1] (Aluminum-containing composition containing boehmite and silica) Silica alumina doped with bismuth oxide with 3 weight percent Bi2O3 was prepared according to the present disclosure.

[0041] A bismuth citrate solution was prepared by adding 516 g of bismuth citrate to 1.7 kg of H2O. 190 g of a 25 weight percent NH3 solution was added to obtain a clear solution with a pH of 7. The bismuth citrate solution was added to an alumina suspension containing boehmite and silica in a weight ratio of 95:5 calculated by the oxide (SIRAL5). The mixture was spray-dried and calcined at 950 °C for 3 hours.

[0042] [Example 2] (Aluminum-containing composition containing silica-containing aluminum oxide) Silica alumina doped with bismuth oxide with 3 weight percent Bi2O3 was prepared according to the present disclosure.

[0043] A bismuth citrate solution was prepared by adding 12.2 g of bismuth citrate to 148 g of H2O. 4.1 g of a 25 weight percent NH3 solution was added to obtain a clear solution with a pH of 7. The bismuth citrate solution was impregnated into 234 g of silica alumina (SIRALOX5) containing 5 weight percent SiO2 (in dry powder form) by incipient wetness impregnation. The product was calcined at 550 °C for 3 hours.

[0044] [Comparative Example 1] Silica alumina doped with bismuth oxide with 3 weight percent Bi2O3 was prepared according to Example 2 of Patent Document 2.

[0045] A solution with a pH value of 2.8 in which 1 g of bismuth citrate was in 7.7 g of water was prepared. The solution was intensively mixed with 19.7 g of silica alumina (SIRAL5) containing 5 weight percent SiO2 for 15 minutes, dried at 120 °C, pulverized into fine powder, and calcined at 500 °C for 2 hours.

[0046] [Comparative Example 2] The lanthanum-doped alumina doped with 4 wt% of Bi2O3 was prepared according to Example 3 of Patent Document 2.

[0047] A solution of 0.111 g of bismuth acetate in 4 ml of H2O and 1 ml of glacial acetic acid was added to 2 g of lanthanum (La)-doped alumina. The resulting paste was mechanically mixed at room temperature for 60 minutes, dried at 130 °C for 2.5 hours, pulverized into fine powder, and calcined at 500 °C for 1 hour. The material contained 3 wt% of La2O3.

[0048] [Comparative Example 3] The silica alumina doped with 3 wt% of Bi2O3 was prepared according to Example 3 of Patent Document 1.

[0049] An aqueous suspension of 40 g of silica alumina containing 5 wt% of SiO2 was wet pulverized to d90 of 19 μm. Then, a dilute nitric acid solution of 2.1 g of bismuth nitrate was added. The mixture was spray dried and calcined at 500 °C.

[0050] [Example 3] (Aluminum-containing composition containing silica-containing aluminum oxide) A bismuth citrate solution was prepared by adding 3.7 g of bismuth citrate to 16.1 g of H2O. 1.2 g of 25 wt% NH3 solution was added to obtain a transparent solution with pH 7.

[0051] The bismuth citrate solution was impregnated into 18 g of dry powder of silica alumina (SIRALOX5) containing 5 wt% of SiO2. The product was calcined at 550 °C for 3 hours.

[0052] [Comparative Example 4] The silica alumina doped with 10 wt% of Bi2O3 was prepared according to Example 15 of Patent Document 1.

[0053] 3.88 g of bismuth nitrate pentahydrate was dissolved in 2 M nitric acid and impregnated onto 18 g of silica alumina containing 5 wt% SiO2. The product was dried at 105 °C and calcined at 500 °C.

[0054] The results are outlined in FIGS. 1 and 2, and Table 1. The compositions prepared according to the present disclosure are characterized by a substantially lower crystallinity for Bi2O3 compared to the compositions prepared according to the prior art.

[0055] [Table 1]

Claims

1. (i) 80 weight percent or more of a transition alumina-based material; (ii) Crystallinity value C Ｂｉ 1 weight percent to 20 weight percent bismuth oxide, characterized in that An alumina bismuth catalyst support comprising: The crystallinity value C Ｂｉ is calculated by comparing the X-ray diffraction pattern of the alumina bismuth catalyst support using copper Kα radiation with the formula 1. C Ｂｉ = [(I ２８ - I ２４ ) / (I ６７ - I ７２ )] / m Ｂｉ (Equation 1) is determined from I ２８ is the intensity of the reflection at about 28 degrees, I ２４ is the intensity of the baseline near the reflection at about 24 degrees, I ６７ is the intensity of the reflection at about 67 degrees, I ７２ is the intensity of the baseline near the reflection at about 72 degrees, m Ｂｉ But, Bi ２ O ３ Mass of / (Bi ２ O ３ + mass of transition alumina-based material) Alumina bismuth catalyst support.

2. The crystallinity value C Bi is less than 3. The alumina bismuth catalyst support according to claim 1.

3. The transition alumina-based material comprises alumina in the gamma, delta, or theta phases, and optionally further comprises silica and / or dopants. The alumina bismuth catalyst carrier according to claim 1 or 2.

4. (a) 50 m ２ / g to 300m ２ / g BET specific surface area, and / or (b) a pore volume of 0.1 ml / g to 1.5 ml / g and further characterized by one or more of the following properties: The pore volume is determined by the N ２ Measured by physical adsorption The alumina bismuth catalyst carrier according to any one of claims 1 to 3.

5. An alumina bismuth catalyst support according to any one of claims 1 to 4, and one or more of platinum (Pt) and palladium (Pd). Oxidation catalyst.

6. A method for preparing the alumina bismuth catalyst support according to any one of claims 1 to 4, comprising: (i) providing an aluminum-containing composition, wherein the aluminum-containing composition is an aluminum-containing composition comprising boehmite or an aluminum-containing composition comprising silica-containing aluminum oxide; (ii) providing an aqueous bismuth solution having a pH value of 6 to 8, the aqueous bismuth solution comprising a bismuth salt having an anion that is an organic acid and a nitrogen-containing base; (iii) contacting the aluminum-containing composition with the aqueous bismuth solution to form an aluminum-bismuth intermediate, When the aluminum-containing composition of step (i) comprises boehmite, the contacting is carried out by mixing the aluminum-containing composition in the form of a dry powder or in the form of a suspension with the aqueous bismuth solution to form an aluminum-bismuth intermediate; or When the aluminum-containing composition of step (i) comprises a silica-containing aluminum oxide, the contacting is carried out by impregnating the aluminum-containing composition in the form of a dry powder with the aqueous bismuth solution to form an aluminum-bismuth intermediate. The process and (iv) calcining the aluminum bismuth intermediate to form an alumina bismuth catalyst support; A method comprising:

7. The bismuth salt is bismuth citrate. The method of claim 6.

8. The nitrogen-containing base is ammonia.

8. The method according to claim 6 or 7.

9. When the aluminum-containing composition includes silica, the silica content is 1 weight percent to 40 weight percent based on the mass of silica and the aluminum oxide, aluminum hydroxide oxide, and / or aluminum trihydroxide oxide. The method according to any one of claims 6 to 8.

10. The suspension contains the aluminum-containing composition and at least water in a weight ratio of 2:98 to 20:

80. The method according to any one of claims 6 to 9.

11. The impregnation of the aluminum-containing composition comprises incipient wetness impregnation. The method according to any one of claims 6 to 9.

12. The aluminum oxide in the silica-containing aluminum oxide composition is or contains one or more transition aluminas. The method according to any one of claims 6 to 9 and 11.

13. When the aluminum-containing composition including boehmite provided in the form of a dry powder or a suspension is mixed with the aqueous bismuth solution, the method further comprises the step of drying the aluminum bismuth intermediate to form a dried aluminum bismuth intermediate that is subsequently calcined. The method according to any one of claims 6 to 10 and 12.

14. The aluminum bismuth intermediate or the dried aluminum bismuth intermediate is calcined at a temperature of 500°C to 1000°C for 0.5 hours or more. The method according to any one of claims 6 to 11.

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