阅读说明：本技术 Nox捕集催化剂载体材料组合物 (NOx trapping catalyst support material composition ) 是由 马科斯·舍尼博恩 迪尔克·尼迈尔 托马斯·哈梅宁 桑德拉·菲比卡尔 于 2018-05-03 设计创作，主要内容包括：本发明涉及制备包含Mg/Al氧化物、铈氧化物和至少另一种稀土元素氧化物的载体材料组合物的方法,涉及载体材料组合物以及涉及该载体材料组合物作为用于处理尾气以降低NO<Sub>x</Sub>含量的催化剂中的氮氧化物储存组分的用途。(The invention relates to a method for producing a support material composition comprising an Mg/Al oxide, a cerium oxide and at least one further rare earth oxide, to a support material composition and to the use of the support material composition as a nitrogen oxide storage component in a catalyst for treating exhaust gases in order to reduce the NOx content.)

1. A method of preparing a carrier material composition comprising the steps of:

i) Preparing an aqueous suspension of a Mg/Al mixed oxide precursor;

ii) preparing an aqueous solution of a cerium salt;

iii) preparing an aqueous solution of one or more rare earth oxide salts other than a cerium salt;

iv) combining at least the aqueous suspension in step i) with the aqueous solution in step ii), and the aqueous solution of step iii) in any order to form an aqueous mixture;

v) drying the aqueous mixture to form a dried particulate material; and

vi) calcining the dried particulate material;

Wherein the content of the one or more rare earth element salts other than cerium is 5 to 50 wt%, preferably 10 to 35 wt%, relative to the total of the following;

-a cerium salt of the aqueous solution from step ii), and

-a rare earth salt other than a cerium salt from the aqueous solution of step iii), and

Each of which is calculated as its oxide.

2. The process according to claim 1, wherein the Mg/Al mixed oxide precursor is prepared by hydrolysis of a mixture of corresponding alkoxides of aluminum and magnesium forming a mixture of hydrotalcite, boehmite, and water.

3. The method of claim 1, wherein the cerium salt comprises one or more of cerium nitrate, ammonium cerium nitrate, cerium sulfate, cerium carbonate, and cerium acetate, preferably cerium acetate.

4. The method of claim 1, wherein the rare earth element salt other than a cerium salt comprises a salt of La, Pr, Nd, Y, Sm, or a mixture thereof.

5. The method of claim 4, wherein the rare earth element salt is an acetate salt of La, Pr, Nd, Y, or mixtures thereof.

6. The method according to any one of the preceding claims, wherein the solutions of step ii) and step iii) are first combined and subsequently combined with the suspension of step i).

7. The method according to any one of the preceding claims, wherein the mixture of suspension and solution is spray dried to form a particulate material, preferably a powder.

8. The process according to any one of the preceding claims, wherein the particulate material is calcined at a temperature of 500 to 1100 ℃, preferably 800 to 1000 ℃, for 30 minutes to 5 hours to obtain the support material composition.

9. A carrier material composition prepared according to the process of any one of claims 1 to 8.

10. A carrier material composition comprising two phases:

i) a first phase comprising a Mg/Al mixed oxide; and

ii) a second phase comprising a cerium-based oxide and a rare earth element-based oxide other than the cerium oxide;

The content of the first phase represents at least 50 wt% of the total support material composition, wherein the amount of Mg in the first phase, calculated as MgO, is 1 wt% to 40 wt%, based on the weight of the first phase, calculated as MgO and Al2O 3.

11. Support material composition according to claim 9 or 10, comprising a BET surface area of more than 50m2/g, and more preferably more than 80m 2/g.

12. Support material composition according to any one of claims 9 to 11, comprising a pore volume of 0.1 to 1.5mL/g, more preferably 0.4 to 1.0 mL/g.

13. the carrier material composition of any of claims 9-12 comprising less than 500ppm Na2O, more preferably less than 100ppm Na 2O.

14. The support material composition of any one of claims 10-12 wherein the second phase is a solid solution.

15. support material composition according to any one of claims 10 to 14, wherein the content of rare earth element oxide other than cerium oxide in the second phase calculated as rare earth element oxide other than cerium is between 5 wt% and 50 wt%, preferably between 10 wt% and 35 wt%, relative to the total second phase.

16. Use of a support material composition according to any one of claims 9 to 15 as a nitrogen oxide storage component in a catalyst for treating exhaust gases to reduce the NOx content.

Technical Field

The present invention relates to a method for producing a support material composition, to a support material composition and to the use of the support material composition as nitrogen oxide storage component in catalysts suitable for treating exhaust gases of, for example, lean-burn engines.

Background

In order to reduce the NOx content in the exhaust gas of lean-burn gasoline or diesel engines, a specified NOx aftertreatment system is required. This is because it is not possible to reduce NOx to N2 in a three-way catalyst (three-way catalyst) operating under prevailing oxidation conditions. Accordingly, certain exhaust aftertreatment catalysts have been developed that include materials capable of storing NOx, for example, as nitrates, under lean conditions. By using a small stoichiometry (short stoichiometric) or rich operating conditions (rich operating condition), the stored NOx can be converted to nitrogen and the storage material regenerated. This catalyst is commonly referred to as a NOx-trap catalyst (NOx-trap catalyst) and is described, for example, in EP 1317953B 1.

As described in EP 1317953B 1, NOx-trapping catalysts comprise nitrogen oxide storage components which are deposited in a highly dispersed manner on a suitable support material to produce a large area interaction with the exhaust gas. Materials capable of storing nitrogen oxides in the form of nitrates are, for example, oxides, carbonates or hydroxides of alkaline earth metals, in particular barium.

suitable support materials must provide high specific surface area and high thermal stability over the capacity to effectively store NOx compounds to ensure long term durability of the final catalyst. In addition, the chemical composition and properties of the support material can affect the nitrogen oxide conversion efficiency and the temperature operating window of the NOx-trap catalyst.

Support materials well described in the art that include these properties are homogeneous Mg/Al mixed oxides in which the magnesium oxide concentration is from 1 wt% to 40 wt%, based on the total weight of the oxide.

the term Mg/Al mixed oxide describes a mixture of two oxides on an atomic scale and therefore does not include a physical mixture of two individual oxides, as well as materials prepared by impregnating alumina with a magnesium oxide precursor solution. Mg/Al mixed oxides of this type are preferably obtained by calcining Mg/Al mixed oxide precursors obtained by hydrolysis of alkoxide mixtures described in detail in DE 19503522A 1.

Further improvement of the storage capacity activity of the NOx-trapping catalyst is achieved by the addition of cerium oxide. This is because cerium oxide has the ability to store NOx at low temperatures.

However, ceria is known to be very sensitive to thermal degradation as it tends to undergo severe sintering under high temperature conditions that may occur, for example, during a catalyst or particulate filter regeneration cycle. The thermal sintering is accompanied by an increase in the size of the cerium oxide crystals (as determined from the powder XRD pattern by Scherrer equation), which leads to a reduction in the specific surface area and ultimately to a deterioration in the low-temperature NOx storage capacity. Therefore, the thermal stabilization treatment of the cerium oxide is required.

WO 2015100313 a1 teaches the combined addition of cerium oxide and praseodymium oxide to Mg/Al mixed oxides. However, according to WO 2015/100313 a1, three different phases are formed, and thus the rare earth element (praseodymium) is not sufficiently used for thermal stabilization of cerium oxide, and further, WO 2015100313 a1 utilizes a precipitation reaction, which is different from the present invention.

it is therefore an object of the present invention to provide a novel process for preparing a support material composition and a support material composition suitable for use in a NOx trap catalyst, which support material composition has an increased thermal stability and an increased nitrogen oxide storage capacity, in particular at higher temperatures.

Disclosure of Invention

according to a first aspect of the present invention, there is provided a method of preparing a carrier material composition, the method comprising at least the steps of:

i) Preparing an aqueous suspension of a Mg/Al mixed oxide precursor;

ii) preparing an aqueous solution of a cerium salt;

iii) preparing an aqueous solution of a salt of one or more rare earth elements other than a cerium salt;

iv) combining at least the aqueous suspension of step i) with the aqueous solution of step ii) and the aqueous solution of step iii) in any order to form an aqueous mixture;

v) drying the aqueous mixture to form a dried particulate material such as a powder; and

vi) calcining the dried particulate material,

Wherein the content of the one or more rare earth element salts other than cerium is 5 to 50 wt%, preferably 10 to 35 wt%, with respect to the total of the following.

-a cerium salt of the aqueous solution from step ii), and

-a rare earth salt other than a cerium salt from the aqueous solution of step iii), and

Each of which is calculated as its oxide.

According to a second aspect of the present invention, there is provided a carrier material composition obtainable according to the first aspect of the present invention.

according to a third aspect of the present invention, there is provided a support material composition comprising at least two phases:

i) A first phase comprising a Mg/Al mixed oxide; and

ii) a second phase comprising a cerium-based oxide and at least one rare earth element-based oxide other than cerium oxide;

The first phase is present in an amount of at least 50 wt% of the total support material composition, wherein the amount of Mg in the first phase is from 1 wt% to 40 wt%, calculated as MgO based on the weight of the first phase calculated as MgO and Al2O 3. The second phase is preferably a solid solution. The carrier material composition of the third aspect of the invention can, for example, be obtained according to the first aspect of the invention.

According to a fourth aspect of the invention, there is provided the use of a support material composition according to the second or third aspect of the invention as a nitrogen oxide storage component in a catalyst for the treatment of exhaust gases.

Detailed Description

the Mg/Al mixed oxide precursor may be prepared by methods known in the art of the present invention, for example, by hydrolyzing a mixture of corresponding alkoxides of aluminum and magnesium to produce a mixture of hydrotalcite (hydrotalcite in the context of this specification means Mg/Al layered double hydroxide) and boehmite.

A preferred aqueous suspension of the Mg/Al mixed oxide precursor is prepared by the process described in DE 19503522A 1 (incorporated herein by reference). DE19503522 a1 describes a process for producing high-purity Mg/Al mixed oxide precursors by reacting an alcohol or alcohol mixture with magnesium and aluminium metal and hydrolysing the resulting alkoxide mixture with water. The mixture obtained by this process comprises hydrotalcite, boehmite and water and is preferably used in the present invention as an aqueous suspension of the Mg/Al mixed oxide precursor of step i) of the present invention. In order to promote the co-formation of boehmite in addition to the layered oxide hydrate, aluminum is used in excess with respect to the stoichiometric ratio of the co-formed layered oxide hydrate (for the magnesium/aluminum ratio that can be used see page 3, lines 16-20 of DE19503522 a 1).

The amount of Mg in the aqueous suspension of the Mg/Al mixed oxide precursor is preferably from 1 to 40 wt.%, calculated as MgO, based on the total amount of Mg/Al mixed oxide added, calculated as MgO and Al2O 3.

the cerium salt is soluble in an aqueous solution and includes cerium nitrate, ammonium cerium nitrate, cerium sulfate, cerium carbonate and cerium acetate. Preferably, the cerium salt is cerium acetate. The cerium salt is added to an aqueous solution comprising water to form an aqueous solution of the cerium salt.

The rare earth element salt other than the cerium salt is a salt selected from La, Pr, Nd, Y, Sm salts or mixtures thereof soluble in aqueous solution. Preferably, the rare earth element salt other than the cerium salt is an acetate of La, Pr, Nd, Y, Sm or a mixture thereof. The rare earth element salt other than the cerium salt is added to an aqueous solution containing water to form an aqueous solution of the rare earth element salt other than the cerium salt.

preferably, the aqueous solution of the cerium salt and the aqueous solution of the one or more rare earth elements other than cerium salt are mixed together before being combined with the suspension, i.e. at least the solutions of step ii) and step iii) are first combined to form a mixed aqueous solution of the cerium salt and the salt of the rare earth element other than cerium salt, and then combined with the suspension of step i).

The amount of Mg/Al mixed oxide precursor in the mixture of the suspension and the solution is 50 to 95 wt.%, calculated as the sum of MgO and Al2O3, based on the total weight dry weight of the aqueous mixture calculated as the respective oxide in its common oxidation state. The total amount of cerium salt and rare earth salt other than cerium is in the range of 5 wt% to 50 wt%, calculated as the sum of the oxides (each in its common oxidation state) on a dry weight basis based on the total weight of the aqueous mixture.

The aqueous mixture is then dried by common methods known in the art to form a particulate material, for example, by spray drying to form a powder.

Finally, the particulate material is calcined at a temperature of 500 to 1100 ℃, preferably 800 to 1000 ℃, for 30 minutes to 5 hours to obtain the support material composition.

According to a second aspect of the present invention, there is provided a carrier material composition capable of being made according to the method of the present invention.

According to a third aspect of the present invention, there is provided a support material composition comprising at least two phases:

i) A first phase comprising a Mg/Al mixed oxide; and

ii) a second phase comprising a cerium-based oxide and a rare earth element-based oxide other than cerium oxide.

The content of the first phase represents at least 50 wt% of the total support material composition, wherein the amount of Mg in the first phase is 1 wt% to 40 wt%, calculated as MgO, based on the weight of the first phase calculated as MgO and A2O 3. The Mg/Al mixed oxide may include spinel (MgAl2O4), alumina and MgO, preferably spinel (MgAl2O4) and alumina.

The second phase is preferably a solid solution of at least cerium oxide and one or more rare earth oxides other than cerium oxide.

The second phase is present in an amount of 5 wt% to 50 wt% of the total support material composition. The content of the rare earth element oxide other than the cerium oxide content in the second phase is 5 to 50 wt%.

According to one embodiment, the sum of the two phases is 100 wt%.

The composition comprises two distinct crystalline phases (crystallline phases) homogeneously distributed with each other.

more specifically, the first and second phases can be distinguished by powder XRD. Furthermore, no more than 10 μm, preferably more than 5pm of agglomerated particles containing only one of the phases could be observed by Scanning Electron Microscopy (SEM) combined with an EDX detector.

First phase-magnesium/aluminium mixed oxide

At least 50 wt% of the support material composition is composed of the first phase, which may include spinel MgAl2O4, alumina and MgO, preferably spinel (MgAl2O4) and alumina).

the first phase of the composition can be obtained by calcining a suitable Mg/Al mixed oxide precursor prepared by methods known in the art of the present invention, i.e. by hydrolysis of the corresponding alkoxide mixture of magnesium and aluminum to produce a mixture of hydrotalcite and boehmite. The preferred Mg/Al mixed oxide precursor is prepared by the method described in DE19503522 (incorporated herein by reference).

The amount of magnesium in the first phase is more preferably in the range of 1 to 30 wt%, preferably 5 to 30 wt%, calculated as MgO, based on the weight of the first phase.

the total amount of said compound of cerium and rare earth element other than cerium in the first phase of the support material composition is preferably less than 5 wt%, more preferably less than 2 wt%, most preferably about 0 wt%, calculated as its oxide, relative to the support material (═ 100 wt%). Meaning that all remaining amounts of the oxide/compound of cerium and a rare earth element other than cerium are in the second phase of the support material.

It was found that the metal compound suspended in the aqueous suspension of step i) forms the first phase. The total amount of said compound of cerium and rare earth element other than cerium (calculated as its oxide) in said aqueous suspension of step i) relative to the oxides of magnesium and aluminum in said aqueous mixture (═ 100 wt%), is preferably less than 5 wt%, more preferably less than 2 wt%, most preferably about 0 wt%. In a preferred embodiment, the aqueous suspension of step i) does not comprise any rare earth element compound (excluding cerium compounds).

second phase-cerium-based oxide and at least one oxide of a rare earth element other than cerium oxide

The second phase is preferably a solid solution of a cerium-based oxide and one or more rare earth element-based oxides other than cerium. The rare earth element oxide other than cerium includes La, Pr, Nd, Y, or a combination thereof. The content of the rare earth oxide other than cerium oxide in the second phase is 5 to 50 wt%, preferably 10 to 35 wt%, calculated as the rare earth oxide other than cerium, with respect to the total second phase.

The total amount of compounds of magnesium and aluminum in the second phase of the support material composition, calculated as MgO and Al2O3, is preferably less than 5 wt%, more preferably less than 2 wt%, most preferably about 0 wt%, relative to the support material (═ 100 wt%). Meaning that all remaining amounts of magnesium and aluminum oxides/compounds are in the first phase of the support material.

It was found that the metal salts in the aqueous solutions of step ii) and step iii) form the second phase (in its oxide form). The total amount of magnesium and aluminium compounds in the combined aqueous solutions of step ii) and step iii) is preferably less than 5 wt%, more preferably less than 2 wt%, most preferably about 0 wt%, relative to cerium and rare earth elements other than cerium (═ 100 wt%, each calculated as their oxides, in the aqueous mixture. In a preferred embodiment, the aqueous solution of step ii) and step iii) does not comprise any magnesium or aluminium compound or magnesium or aluminium metal.

therefore, according to the Vigred's law, adjusting the unit cell volume of the second phase compared to the cerium-based oxide results in a shift in the d-value of the CeO2(111) reflection in the XRD pattern. In addition, the solid solution can be identified, for example, by raman spectroscopy or correlation spectroscopy. In other words, in the powder XRD of the support material composition of the present invention, a separate phase containing a rare earth element-based oxide, which is different from the second phase, cannot be detected. This means that all rare earth element-based oxides contained in the second phase form part of the solid solution.

Thus, the stabilizing effect on cerium oxide in the support material composition of the present invention is maximized by combining all rare earth element-based oxides of the second phase to form a solid solution. This stabilization can be revealed, for example, by the reduced crystal size of the second phase, as determined by the Scherrer method using the (111) reflection of the cubic CeO2 structure. In particular, the crystal size of the second phase is preferably less than 10nm after heat treating the composition at 950 ℃ for 3 h.

Furthermore, it was demonstrated that the support material composition of the invention has a higher low temperature NOx storage capacity after heat treatment at 950 ℃ for 3h, measured at 150 ℃ and 200 ℃, compared to prior art materials without the second phase described above. This clearly reflects the enhanced thermal stability of the low temperature NOx storage function of the composition of the present invention.

a fourth aspect of the invention is the use of a support material composition according to the second or third aspect of the invention as a nitrogen oxide storage component in a catalyst for treating exhaust gases to reduce the NOx content.

The support material compositions according to the second, third and fourth aspects of the invention are optionally further characterized by the following parameters:

The support material composition typically has a surface area of greater than 50m2/g, more preferably greater than 80m 2/g.

The pore volume of the support material composition can be 0.1 to 1.5mL/g, more preferably 0.4 to 1.0 mL/g. The pore volume was determined by the N2 adsorption method.

The carrier material composition contains small amounts of sodium and sulfur impurities. In particular, the carrier material composition comprises less than 500ppm of Na2O, more preferably less than 100ppm of Na2O, and preferably less than 100ppm of sulfur (including sulfur-containing compounds).

the invention relies on the following definitions:

By solution is meant a liquid mixture in which the minor component (solute) is uniformly distributed with the major component (solvent). The solvent and the solute form one phase. An aqueous solution is a solution comprising water as solvent, preferably at least 50 wt% of water, relative to all liquid components comprised in the solution.

By suspension is meant a liquid mixture in which the particles are dispersed in a liquid. The liquid and the particles form two phases. An aqueous suspension is a suspension comprising water as liquid phase, preferably at least 50 wt% of water, relative to all liquid components comprised in the liquid phase.

As used herein, the term "particulate material" refers to particles in the form of powders, beads, extrudates, and similarly shaped particles.

Common oxidation states for Mg, Al, Ce, La, Pr, Nd and Y (for calculating the amount of (metal) oxides) used to calculate the wt% values are MgO, Al2O3, CeO2, La2O3, Pr6O11, Nd2O3, Sm2O3 and Y2O 3.

the term "solid solution" refers to a case where a rare earth element other than cerium shares one crystallographic point (4a Wyckoff position) with a cerium atom within the cubic CeO2 crystal structure.

Surface area and pore volume were measured using N2 physisorption using a typical volumetric apparatus such as Quadrasorb from Quantachrome at liquid nitrogen temperature. The surface area is determined using the BET theory (DIN ISO 9277: 2003-05), while the pore volume is determined in accordance with DIN 66131. The pore diameter range is 0-5000 nm in terms of pore radius. The term BET refers to the Brunauer-Emmett-Teller method used to determine the specific surface area.

The invention will now be described with reference to the accompanying drawings and the following non-limiting examples, in which:

FIG. 1 shows a powder X-ray diffraction pattern of the support material composition of example 1 and theoretical plots of MgAl2O4 (dashed line) and CeO2 (straight line), showing distinguishable first and second phases of the support material composition, and without any other components.