Patent Application
20230001384
The invention relates to a method to prepare an alumina bismuth catalyst support for emission control applications, to an alumina bismuth catalyst support prepared according to the method of the invention and to an alumina bismuth catalyst support having specific characteristics.
The main raw emission pollutants in exhaust gases are CO, NOx, unburned hydrocarbons and soot particles. Catalyst systems, including various components and precious metals, for application in emission control are known in the art. Usually a so-called Diesel Oxidation Catalyst (DOC) containing precious metals supported on high-surface area refractory oxides such as alumina or silica-alumina converts CO into CO2 and the unburned hydrocarbons into CO2 and water. Due to continuously stricter legislation regarding tailpipe emissions and the introduction of more realistic driving cycles, including RDE (Real Driving Emissions) and WLTP (Worldwide Harmonized Light Vehicle Test Procedure), the low temperature activity of such catalyst systems has become an important field of development.
The incorporation of activating and/or stabilizing additives (for example metal oxides) to the catalyst or catalyst support materials respectively is a well-known approach. WO 2017/064498 A1 and U.S. Pat. No. 7,611,680 B2 disclose the beneficial effect of low temperature conversion for CO and hydrocarbons by the addition of Bi2O3 to a catalyst. In U.S. Pat. No. 7,611,680 it is described that the bismuth is added as a promoter by an in situ reduction process. In WO 2017/064498 A1 the bismuth is supported on a support.
The prior art therefore teaches the incorporation of the Bi2O3 as a separate crystalline phase. This leads to low specific surface area of the promoting additive and therefore to limited beneficial interaction with the active precious metal.
The object of the present invention is therefore to provide an improved alumina bismuth support applicable in emission control catalysis having improved characteristics and a novel method for preparation of same.
According to a first aspect of the invention there is provided a method to prepare an alumina bismuth catalyst support, the method comprising the steps of:
In step iii) the aluminum bismuth intermediate may also be called a boehmite bismuth intermediate in case in step i) the aluminum containing composition comprised boehmite.
In step iii) the aluminum bismuth intermediate may also be called a silica aluminum oxide bismuth intermediate in case in step i) the aluminum containing composition comprised silica.
Preferably the aluminum containing composition consists of boehmite or consists of silica containing aluminum oxide with respect to the aluminum containing compounds in the composition. The aluminum containing composition may for example (beside silica or other components) additionally comprise one or more dopants.
The aluminum oxide in the silica containing aluminum oxide preferably is or comprises transitional alumina. The silica containing aluminum oxide more preferably comprises transitional alumina, silica and one or more dopant. The transitional alumina is one or more of gamma (γ), delta (δ) or theta (θ) aluminum oxide, and preferably is or comprises gamma alumina.
According to one embodiment, the aluminum containing composition preferably comprises at least 50 wt.-% silica containing aluminum oxide.
According to a further embodiment, the aluminum containing composition preferably comprises at least 50 wt. % boehmite. Preferably the aluminum containing composition contains boehmite (AlOOH) with or without one or more dopants and even more preferably the aluminum containing composition contains boehmite, silica and one or more dopants.
When silica is present in the aluminum containing composition the SiO2 content is between 1 and 40 wt.-%, preferably between 1 and 20 wt.-%, based on the total dry mass of SiO2, aluminum oxide, aluminum oxide hydroxide and aluminum trihydroxide. Preferably the aluminum containing composition does not additionally comprise aluminum trihydroxide, but only aluminum oxide or aluminum oxide hydroxide.
Boehmite includes boehmite as such and pseudo-boehmite. The boehmite may be defined as any alumina having the molecular formula AlOOH*xH2O, where x is between 0 and 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.
The dopants may be oxides of or water-soluble salts of alkaline earth metals, transition metals, for example Zr, Ti, rare-earth elements or mixtures thereof. Preferably their content is between 0 and 10 wt.-%, more preferably between 0 and 5 wt.-%, calculated as oxides based on the total mass of the aluminum oxide, aluminum oxide hydroxide and aluminum trihydroxide. The transitional metals are preferably Mn, Fe, Cu, Nb, Zr, Ti or mixtures thereof and more preferably Zr, Ti or mixtures thereof. The dopants may also be alkaline earth metal carbonates, in particular barium carbonate.
The aluminum containing composition may be provided in dried powder form or in the form of an aluminum suspension. If the aluminum containing composition is in the form of an aluminum suspension, the suspension comprises the aluminum containing composition and at least water, preferably in a weight ratio of 2:98 to 20:80. The aluminum suspension may further include pH modifying additives for example carboxylic acid or ammonia, preferably mono-carboxylic acids such as acetic acid.
The aluminum suspension is preferably a boehmite suspension wherein the boehmite is prepared by hydrolysis of an Al-alkoxide, most preferably involving hydrothermal aging. Hydrothermal ageing is carried out between 100 and 300° C., preferably between 120 and 240° C. for 0.5 hours to 30 hours, preferably between 3 hours and 10 hours; time and temperature are independently selected.
The bismuth aqueous solution preferably comprises a water-soluble Bi3+ salt, more preferably a Bi nitrate or a Bi citrate and most preferably a Bi Citrate. The anion of such salts are preferably organic compounds such as an organic acid. The pH value of the bismuth aqueous solution is between 4 and 9, preferably between 6 and 8.
Contacting means either a) mixing the aluminum containing composition, preferably the aluminum suspension, with the bismuth aqueous solution to form the aluminum bismuth intermediate or b) impregnating the aluminum containing composition in dried powder form with the bismuth aqueous solution to form the aluminum bismuth intermediate. In the case the aluminum containing composition is or comprises a silica containing aluminum oxide step iii) is with “impregnation” and in case the aluminum containing composition is or comprises boehmite step iii) is with “mixing”.
Impregnation of the aluminum containing composition may be carried out by any impregnation method known in the art, preferably by incipient wetness impregnation. Such a method provides for impregnating between 80 and 100% of the aluminum containing composition with the bismuth aqueous solution. By % is meant the ratio of (volume of liquid added)/(pore volume).
When the aluminum suspension is mixed with the bismuth aqueous solution the method may include the further step of drying, preferably spray drying, the aluminum bismuth intermediate to form a dried aluminum bismuth intermediate that will then be calcined.
The aluminum bismuth intermediate or the dried aluminum bismuth intermediate is calcined at a temperature of between 500 and 1000° C., more preferably between 600 and 900° C., even more preferably at a temperature of between 500 and 700° C., and independent thereof for a period of at least 0.5 hours, preferably between 0.5 and 5 hours, preferably 3 hours.
According to a second aspect of the invention there is provided an alumina bismuth catalyst support prepared according to the method of the invention.
According to a third aspect of the invention, there is provided an alumina bismuth catalyst support comprising:
The transition alumina based material preferably is or may comprise aluminum oxide, silica and/or dopants. More preferably the transition alumina based material comprises aluminum oxide, silica and one or more dopants.
The transition alumina based material preferably comprises Gamma, Delta or Theta aluminum oxides, or mixtures thereof.
The transition alumina based material preferably comprises at least 50 wt.-% of aluminum oxides
When silica is present in the aluminum containing composition the SiO2 content is between 1 and 40 wt.-%, preferably between 1 and 20 wt.-%, based on the oxide mass of silica and the aluminum oxide
The dopants may be oxides of or alkaline earth metals of transition metals, for example Zr, Ti, rare-earth metals or mixtures thereof. Preferably their content is between 0 and 10 wt.-%, preferably between 0 and 5 wt.-%, calculated as oxides based on the total mass of the aluminum oxide, silica and the dopant. The transitional metals are preferably Mn, Fe, Cu, Nb, Zr, Ti or mixtures thereof and more preferably Zr, Ti or mixtures thereof.
The alumina bismuth catalyst support comprises a BET specific surface area between 50 and 300 m2/g, preferably between 100 and 200 m2/g. The alumina bismuth catalyst support comprises a pore volume of between 0.1 and 1.5 ml/g, preferably between 0.5 and 1.0 ml/g.
According to the invention an improved heterogeneous catalysts is obtained with improved contact between the active phase (noble metals) and the promotor. This is achieved by a homogeneous dispersion of the promotor bismuth oxide in the support material matrix leading to good accessibility of the promotor by the noble metals and uniform promotor-noble metal arrangements throughout the entire catalyst. The virtually X-ray amorphous state of the bismuth oxide is indicative for such a homogeneous dispersion in the matrix of the alumina based material.
The bismuth oxide is homogenously dispersed in the matrix of the alumina based material. Without being bound by theory the Applicant believes that a homogenous dispersion of the bismuth oxide small crystals in a virtually X-ray amorphous state leads to the beneficial properties of the composite. The X-ray amorphous state may be described by the crystallinity value as given below.
The crystallinity value as used herein is determined in accordance with the following method. The X-ray diffraction (XRD) pattern of Bi2O3 using Cu K alpha radiation comprises the strongest reflex around 2θ=28° (021 reflex in space group P4-21c). The XRD pattern of a transition based alumina material comprises a strong reflex around 2θ=67°. The normalized intensity ratio of these two reflections (see equation 1) is a measure for the crystallinity of bismuth oxide CBi on the transition alumina based material
C
Bi=[(I28−I24)/(I67−I72)]/mBi (equation 1)
Homogeneity is measured by scanning-electron-microscope (SEM) cross-section imaging, optionally together with EDX (Energy Dispersive X-ray Analysis) element mapping revealing the domain sizes of the transition alumina based material, the bismuth oxide and the alumina bismuth catalyst support.
Surface area and pore volume are measured with N2 physisorption using typical volumetric devices like the Quadrasorb from Quantachrome at the temperature of liquid nitrogen. The surface area is determined using BET theory (DIN ISO 9277) while the pore volume is determined according to DIN 66131. The pore radius range is between 18 and 1000 Å.
According to a fourth aspect of the invention there is provided use of the alumina bismuth catalyst support as hereinbefore described as a support for an oxidation catalyst, preferably comprising platinum (Pt) and/or palladium (Pd), in particular a diesel oxidation catalyst for vehicle emission control applications.
The invention will now be described with reference to the following non-limiting examples and Figures in which:
A bismuth oxide doped silica-alumina with 3 wt.-% Bi2O3 was prepared according to the present invention.
A Bi-Citrate solution was prepared by adding 516 g Bi-Citrate to 1.7 kg H2O. 190 g of a 25 wt.-% NH3 solution was added to obtain a clear solution with pH 7. The Bi-Citrate solution was added to an alumina suspension containing boehmite and silica in a 95:5 weight ratio calculated as per the oxides (SIRAL 5). The mixture was spray dried and calcined at 950° C. for 3 h.
A bismuth oxide doped silica-alumina with 3 wt.-% Bi2O3 was prepared according to the present invention.
A Bi-Citrate solution was prepared by adding 12.2 g Bi-Citrate to 148 g H2O. 4.1 g of a 25 wt.-% NH3 solution was added to obtain a clear solution with pH 7. The Bi-Citrate solution was impregnated by incipient wetness impregnation on 234 g of a silica-alumina, SIRALOX 5, containing 5 wt.-% SiO2 (in dried powder form). The product was calcined at 550° C. for 3 h.
A bismuth oxide doped silica-alumina with 3 wt.-% Bi2O3 was prepared according to U.S. Pat. No. 7,611,680 B2 Example 2.
A solution of 1 g Bi-Citrate in 7.7 g water with a pH value of 2.8 was prepared. This solution was intensively mixed for 15 minutes with 19.7 g of a silica-alumina, SIRAL 5, containing 5 wt.-% SiO2, dried at 120° C., ground into a fine powder and calcined at 500° C. for 2 h.
A bismuth oxide doped lanthanum doped alumina with 4 wt.-% Bi2O3 was prepared according to U.S. Pat. No. 7,611,680 B2 Example 3.
To 2 g of a La doped alumina was added a solution of 0.111 g Bi-acetate in 4 ml H2O and 1 ml glacial acetic acid. The resulting paste was mechanically mixed at room temperature for 60 minutes, dried at 130° C. for 2.5 h, ground into a fine powder, and calcined at 500° C. for 1 h. The material contained 3 wt. % La2O3.
A bismuth oxide doped silica-alumina with 3 wt.-% Bi2O3 was prepared according to WO 2017/064498 Example 3.
An aqueous suspension of 40 g silica-alumina containing 5 wt.-% SiO2 was wet-milled to a d90 of 19 μm. Then a solution of 2.1 g bismuth-nitrate in diluted nitric acid was added. The mixture was spray dried and calcined at 500° C.
A Bi-Citrate solution was prepared by adding 3.7 g Bi-Citrate to 16, 1 g H2O. 1.2 g of a 25 wt.-% NH3 solution was added to obtain a clear solution with pH 7.
The Bi-Citrate solution was impregnated on 18 g of a dried powder of silica-alumina, SIRALOX 5, containing 5 wt.-% SiO2. The product was calcined at 550° C. for 3 h.
A bismuth oxide doped silica-alumina with 10 wt.-% Bi2O3 was prepared according to WO 2017/064498 Example 15.
3.88 g Bi-nitrate pentahydrate were dissolved in 2M nitric acid and impregnated on 18 g of a silica-alumina containing 5 wt.-% SiO2. The product was dried at 105° C. and calcined at 500° C.
The results are summarized in
| Number | Date | Country | Kind |
|---|---|---|---|
| 19212712.4 | Nov 2019 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2020/083968 | 11/30/2020 | WO |
