WO2018114245A1

WO2018114245A1 - NOx STORAGE AND REDUCTION CATALYST AND METHOD FOR PREPARING THE SAME

Info

Publication number: WO2018114245A1
Application number: PCT/EP2017/080698
Authority: WO
Inventors: Qiang Wang; Ruoyan YANG
Original assignee: Scg Chemicals Co., Ltd.
Priority date: 2016-12-19
Filing date: 2017-11-28
Publication date: 2018-06-28
Also published as: CN110087771A

Abstract

The present invention relates to NO_x storage and reduction catalyst comprising a material having the genera! formula G/AO/L_xM_yQO_z, wherein L_xM_yQO_z is a substrate and G and A₂O are deposited on the surface of the L_xM_yQO_z substrate; wherein G is a noble metal, A is an element from Group I or II of the Periodic Table of Elements, L and M are independently selected from divalent cations and L and M are not selected as the same divalent cation, Q is at least one trivalent cation, O is oxygen, x is from 0 to 6, y is from 0 to 6, x+y is from 1 to 6 and z is selected to balance the values of x and y stochiometrically, wherein the amount of G is from 0.5 to 6 wt%, preferably from 0.5 to 4 wt%, the amount of A20 is from 5 to 30 wt% and the amount of L_xM_yQO_z balances the amount of G and A₂O to result in 100 wt%, a process for preparing the same and the use thereof.

Description

Oy storage and reduction catalyst and method for preparing the same

The present invention relates to a NO_x storage and reduction catalyst. The invention further relates to a process for preparing such a catalyst.

NO_x emitted from vehicle exhausts and flue gases is a big problem for both the environmental protection and human health.

NO_x storage-reduction catalysts (NSR) work under cyclic conditions of fuel lean and fuel rich environments, Toyota laboratories brought up this concept of NSR in the mid-1990s. Alternating lean/rich conditions are employed during normal driving. Under lean conditions of engines, when oxygen is in excess, NO_x is adsorbed on the catalyst, and under rich conditions, when the reductants evolve, NO_x reduction takes place. Consequently, in principle, an NSR catalyst should have sites for NO_x sorption (alkali metal or alkaline earth metal compounds) and sites for NO_x oxidation/reduction (noble metals). Conventional NSR catalyst is Pt- BaO/Al₂03, which operates at is 250-400°C, which is suitable for vehicle emissions. Table 1 summarized all the NSR.

Table 1. NSR catalysts reported in literature.

Support Catalysts

A1₂0₃ Pt-BaO/Al₂0_3; Pt-CaO/Al₂0₃, Pt-MgO/Al₂0₃, Pt-K₂0/Al₂0_3/

Pt-Rh-BaO/Al₂0₃, Pt-Rh-Ti0₂/Al₂0_¾ Co₃0₄-K₂0/Al₂0_3/ CuO-K₂0/AI,O₅, Pt-BaO-Fe₂0₃/AI₂0₃, Pt-BaO-Co₃(VAI₂0₃

Ce0₂ Co₃0₄-BaO-K₂0/Ce0_2; Pt-BaO/Ce0₂

Ce.Zri _x0₂ Pt-BaO/Ce_xZri _x0₂

KJi₂0₅ Pt/K₂Ti₂0₅, CuO/ ₂Ti₂0_5> CuO Rh/K₂Ti₂O_s

Zi0₂ Pt-BaO/Zr0₂

TiO_rZr0₂ Pt/Ti0₂-Zr0₂

Al₂0₃-Ce0₂ Pt-K₂0-Mn0₂/Al₂0₃-Ce0₂

Ti0₂ Pt BaO/Ti0₂

hydrotalcite Pt/hydrotalcite, Cu/hydrotalcite and Pt-Cu/h yd rota late

perovsklte BaSn0₃, SrSn0_3< CaSn0₃, BaZr0₃, etc. Although great effort has been made during the past several decades to the synthesis of NSR catalysts, currently each catalyst stil! has its own drawbacks and limitations, which hinder the wide application of such NO_x storage and reduction catalysts. LDHs derived NSR catalyst has attracted great attention due to its unique chemical and structural properties. For instance, the mixed metal oxides which are produced from high-temperature calcination of LDHs have the features of large surface areas, basic properties, high metal dispersions and stability against sintering. However, for the LDHs-derived catalysts, one main problem is their NO_x storage capacity is still relatively low. In addition, the NO_x storage temperature is also too high (250- 400°C), which cannot be used for flue gases. For instance, the temperature of the flue gas from naphatha crackers is normally at around 110°C.

Therefore, it is the object of the present invention to provide NO_x storage and reduction catalysts overcoming drawbacks of the prior art, in particular new NO* storage and reduction catalysts which not only have higher NO_x storage capacity but also have a wider NO_x storage temperature range.

This object is achieved by a NO_x storage and reduction catalyst comprising a material having the general formula (1) G/A₂0/L_xM_yQO_z (1), wherein LxM_yQO_z is a substrate and G and A₂0 are deposited on the surface of the L_xM_yQ0₂ substrate; wherein G is a noble metal, A is an element from Group I or II of the Periodic Table of Elements, L and M are independently selected from divalent cations and L and M are not selected as the same divalent cation, Q is at least one trivalent cation, 0 is oxygen, x is from 0 to 6, y is from 0 to 6, x+y is from 1 to 6 and z is selected to balance the values of x and y stochiometrically, wherein the amount of G is from 0.5 to 6 wt%, preferably from 0.5 to 4 wt%, the amount of A₂0 is from 5 to 30 wt% and the amount of L_xM_yQO_z balances the amount of G and A₂0 to result in 100 wt%,.

With respect to the inventive catalyst, it is preferred that the NO_x storage and reduction catalyst consists of the material having the general formula (1) as defined above.

In this regard, the expression "NO_x" refers to nitrogen oxides, in particular NO and N0₂. These gases are produced during combustion, especially at high temperatures. The term "noble metal" as used herein refers to metals that arc resistant to corrosion and oxidation in moist air. Preferably, G is selected from Ag, Pt, Pd, Ir, In, Rh, Ga or mixtures thereof, preferably from Ag and/or Pt.

The elements from Group I and II of the Periodic Table which are a possible selection for A are also known as alkali metals and alkaline earth metals. In this regard, it is preferred that A is selected from , Li, Na, Ba or mixtures thereof, preferably is K, Ba, or mixtures thereof.

It is preferred that L and M are indepeedently selected from Co, Cu, Mg, Ni, Zn, Ca or mixtures thereof, preferably is Mg, Ca, or mixtures thereof.

It is further preferred that Q is selected from Al, n, Fc, Ga, Cr or mixtures thereof, preferably Al.

The object is further achieved by a process for preparing an inventive NO_x storage and reduction catalyst, the process comprising the steps:

a) providing a material comprising water and a layered double-hydroxide of the general formula (2)

wherein L and M are independently selected from divalent cations, Q is a trivalent cation, x is from 0 to 6, y is from 0 to 6, x+y is from 1 to 6, X is an anion, n is 1 to 3 and a is selected to balance the charge of cations and anions dependent from the values of x and y; and b is from 0 to 10;

b) washin the material with a solvent, wherein the solvent is miscible with water and preferably has a solvent polarity (Ρ') in the range from 3.8 to 9; c) drying and calcinating at 200 to 600°C the material obtained in step b);

d) impregnating the material obtained in step c) with a solution of a precursor of an alkali metal oxide and/or an alkaline earth metal oxide A₂0; and

e) impregnating the material obtained in step d) with a solution of a precursor of a noble metal G.

The solvent polarity (Ρ') in this regard is the polarity as defined in Snyder and Kirkland, Introduction to modem liquid chromatography, 2^nd ed.; John Wiley and Sons: ^"New York, 1979; pp 248-250.

Preferably, the steps of the process are performed in the chronological order a), b), c) and d) or a), b), d) and c).

By washing the layered double-hydroxide of formula (1) with the solvent which is miscible with water, a so-called aqueous miscible organic-layered double-hydroxide (A O-LDH) is prepared which has, in comparison with the layered double-hydroxide of formula (1), a reduction in aggregation of particles/crystallines.

By impregnating the AMO-LDH with the alkali metal oxide, NO_x storage capacity is enhanced.

By impregnating the material with the noble metal, the catalytic activity for NO oxidation during lean-burn conditions is increased. Likewise, the catalytic activity for the adsorbed NO_x reduction during rich conditions is enhance.

In a preferred embodiment, the trivalent cation Q is selected from Al, Mn, Fe, Ga, Cr or mixtures thereof, preferably Al. Preferably, X is selected from inorganic anions, carboxylic anions, dicarboxylic anions, anionic surfactants or mixtures thereof, preferably X is carbonate, carboxylate, dicarboxylate or mixtures thereof.

It is also preferred that the solvent which is misciWe with water is selected from acetone, ace- tonitrile, dimethylformamide, dimethylsulfcxide, dioxane, ethanol, methanol, n-propanol, 2- propanol, tetrahydrofuran or mixtures thereof, preferably is acetone.

Most preferred, the alkali metal and/or alkaline earth metal is selected from K, Li, Na, Ba or mixtures thereof, preferably is , Ba, or mixtures thereof.

In a further embodiment of the invention, the noble metal G is selected from Ag, Pt, Pd, Ir, In, Rh, Ga and mixtures thereof, preferably is Ag and/or Pt.

It is preferred that a solvent used during the impregnation with the precursor of the alkali metal oxide and/or the noble metal is selected from water, methanol, ethanol, acetone, ethylene glycol, 2-propanone, dimethylformamide, ucetonitrile, glycerol or mixtures thereof.

The impregnating step d) may be performed as follows. A solution of a precursor of an alkali metal oxide and/or alkaline earth metal oxide A₂0 was added drop-wise to the calcinated LDH. Afterwards, the wet sample was dried at elevated temperatures, preferably at temperatures around 50°C. These steps are repeated until formation of a material A₂0/L_xM_yQO is obtained. As a respective precursor, any compound which is suitable to convert into the alkali metal oxide and/or alkaline earth metal oxide under the above conditions may be used. For example, in case of the alkali metal being potassium ( ), K2CO3 can be used as the precursor of an alkali metal oxide and/or alkaline earth metal oxide.

Furthermore, the impregnating according to step e) encompasses drop-wise addition of a precursor of a noble metal to the material obtained in step d). Just as in case of step d), a drying step at a temperature suitable to evaporate the solvent, preferably around 50°C, is conducted after dropwise addition. These steps are repeated until formation of a material having the gen- eral formula G-A₂0/L_xM_yQO_z, A suitable precursor of the noble metal G in this regard is any compound which converts under the conditions referred to above to the noble metal. For example, if the noble metal is Pt, H₂PtCl_& may be used.

In different embodiments, the order of the steps e) may be switched. That is, in the inventive process step d) can be performed before step e); step e) can be performed before step d); or steps d) and e) can be performed at the same time.

It is also preferred that the process comprises a further step after step d) (or step c) depending on which step is later) of calcinating the material obtained in the last step step c) or d), preferably at a temperature from 300 to 500°C.

Finally, the object is achieved by use of a catalyst according to the invention for adsorbing and/or storing and/or reducing NO_x-gas.

Surprisingly, it was found by the inventors that the inventive catalyst which may be prepared by the inventive process is suitable to achieve the above object. In detail, it was found that the inventive NO_x storage and reduction catalyst can adsorb NO_x in a very wide temperature range of 90 to 500°C with a NO_x storage capacity of as high as 1.5 mmol/g. These inventive effects have been found to be more pronounced when constituting the catalyst i accordance with the preferred embodiments. Best results were achieved when combining two or more of the preferred embodiments.

The current invention provides a ne process for the preparation of NO_x storage and reduction catalyst can adsorb NO_x in very wide temperature range of 90-500°C with a NO_x storage capacity of as high as 1.5 mmol/g. This NO_x storage and reduction catalyst can be used for the treatment of NO_x from vehicle exhausts and flue gases. With proper selected reducing agents, the emitted NO_x can be consequently converted into N₂.

The unique inventive features and results achieved therewith may be summarized as follows: 1. A novel NO_x storage and reduction catalyst consisting of noble metal, alkali metal (and/or alkaline eart metal), and ternary AMO-LDO derived from ternary AMO- LDHs.

2. A novel process for making the above mentioned NO_x storage and reduction catalyst.

3. By washing with certain solvents, the aggregation of LDIIs particles/crystallites could be reduced.

4. By utilizing proper divalent and trivalent cations, both the NO oxidation activity, NO_x storage capacity, and the thermal stability of adsorbed NO_x can be tuned, which enables the NO_x storage and reduction catalysts can work in a very wide temperature range ( 0-500°C).

5. By introducing noble metals, both the NO oxidation during lean-bum conditions and the reduction of adsorbed NO_x could be enhanced.

6. By introducing alkali metals and/or alkaline earth metal, the NO_x storage capacity could be further increased.

7. The NO* storage capacity of this new catalyst is higher than previous reported layered double hydroxides based catalysts.

8. The NO* storage temperature range of this catalyst is very wide (90-500°C) due to proper combination of different divalent and trivalent cations.

Additional features and advantages of the present invention will become apparent in the following detailed description on basis of examples, which are, however, merely to exemplify the invention without limiting the scope thereof. Synthesis of binary AMO-LDHs

The binary AMO-LDHs were synthesized via a conventional coprecipitation method. In brief, a salt solution (100 niL) containing a mixture of 0.075 mol M(N0₃)2"zH₂0 (M= Co, Cu, Mg,

Ni, Zn, or Ca, etc) and 0.025 mol N(N0₃)3'wH₂0 (Al, Mn, Fe, Ga, Cr) was added drop- wise to a basic solution (100 ml.) containing 0.05 mol Na₂C03. The pH value of the precipitation solution was kept constant at 10 by addition of a solution containing 4 M NaOH. The resulting mixture solution was aged at room temperature for 12 h with continuous stirring. The LDH product was first filtered and washed with water to a "wet cake". Then the "wet cake" was redispersed in acetone solution again. After stirring for about 1-2 h, the sample was filtered and washed with acetone. The final LDH product was dried at 60°C.

Synthesis of ternary AMO-LDHs

The ternary AMO-LDHs were synthesized via a conventional coprecipitation method. In brief, a salt solution (100 mL) containing a mixture of 0.075 mol M(N0₃)2._Z¾0 (M is a mixture of two metals selected from Co, Cu, Mg, Ni, Zn or Ca), and 0.025 mol N(N0₃)3.yH₂0 (N = Al, Mn, Fc, Ga, Cr or a mixture of two of them) were added drop- wise to a basic solution (100 mL) containing 0.05 mol Na₂C0₃. The pll value of the precipitation solution was kept constant at 10 by addition of a solution containing 4 M NaOH. The resulting mixture solution was aged at room temperature for 12 h with continuous stirring. The LDH product was first filtered and washed with water to a "wet cake". Then the "wet cake" was redispersed. in acetone solution again. After stirring for about 1-2 h, the sample was filtered and washed with acetone. The final LDH product was dried at 60°C.

Synthesis of Ag/M₃A10*

Ag/M₃A10_X (M= Mg²⁺, Cu²⁺, Co²⁺ and Ni²') catalysts were prepared via the incipient wetness impregnation was prepared via the incipient wetness impregnation (IWI) method. LDH was first pretreated at 400° C for 5 h. Then Ag Oa aqueous solution was added drop-wise to the calcined LDH until it appeared wet. The wet sample was dried at 50°C. These steps were repeated until the Ag/TVb A10_x was obtained. The Ag loading was 2-6 wt%. Synthesis of Ag Co_IMg₃.₎₍A10y

Ag Co_xMg3_-x Al Oy was prepared via the incipient wetness impregnation was prepared via the .incipient wetness impregnation (IWI) method. LDH was first pretreated at 400°C for 5 h. Then AgNQ₃ aqueous solution was added drop- wise to the calcined LDH until it appeared wet. The wet sample was dried at 50°C. These steps were repeated until the Ag/Co_xMg₃__xA10_y was obtained. The Ag loading was 2-6 wt%.

Synthesis of Pt/

Pt/Co_xMg3_-xAlO_y was prepared via the incipient wetness impregnation was prepared via the incipient wetness impregnation (IWI) method. LDH was first pretreated at 400°C for 5 h. Then H₂PtCl_fi ethanol solution was added drop- wise to the calcined LDH until it appeared wet. The wet sample was dried at 50°C. These steps were repeated until the Pt/Co_xMg3_-xA10_y was obtained. The Pt loading was 1-6 wt%.

Synthesis of K₂0/CoMgA10_I

KiO/CoxM j._xAlO_y was prepared via the incipient wetness impregnation method. LDH was first pretreated at 400°C for 5 h. The K₂C0₃ ethylene glycol solution was added drop-wise to the calcined LDH until it appeared wet. The wet sample was dried at 50°C. These steps were repeated until the K.₂0/Co_xMg₃._xA10_y was obtained.

Synthesis of Ag-K₂0/Co_xMg3-xA10_y

Ag-K₂0/Co_xMg3._xA10_y was prepared via the incipient wetness impregnation method. LDH was first pretreated at 400°C for 5 h. The K C0₃ ethylene glycol solution was added drop- wise to the calcined LDH until it appeared wet. The wet sample was dried at 50°C. These steps were repeated until the K 0 Co_xMg3-xA10_y was obtained. The K₂C0₃ loading was 5-25 wt%. The K.₂0/Co_xMg3._xA10_y was pretreated at 400°C for 5 h, and then AgN0₃ aqueous solution was added drop- wise to the calcined ₂0/ Co_xMg₃-_xA10_y until it appeared wet. The wet sample was dried at 50°C. These steps were repeated until the Ag-K₂0/Co_xMg₃-._xA10_y was obtained. The Ag loading was 2-6 wt%.

Synthesis of Pt-K₂0/Co_x g₃._xA10_y

Pt-K₂0/CoxMg₃-_xAlO_y was prepared via the incipient wetness impregnation method. I.DH was first pretreated at 400°C for 5 h. The K₂C0₃ ethylene glycol solution was added drop- wise to the calcined LDH until it appeared wet. The wet sample was dried at 50°C. These steps were repeated until the K₂0 Co_xMg3-._xA10_y was obtained. The K₂C0₃ loading was 5-25 wt%. The K₂0/Co_xMg₃„_xA10_y was pretreated at 400°C for 5 h, and then H₂PtCl₆ ethanol solution was added drop-wise to the calcined K₂0/Cox!Vlg3-xA10_y until it appeared wet. The wet sample was dried at 50°C. These steps were repeated until the Pt- 20/Co_xMg₃-_xA10_y was obtained. The Pt loading was 1-6 wt%.

NO_s storage on binar AMO-LDHs derived mixed oxide

The NO_s storage capacity of LDH-derived catalysts was evaluated using a fixed-bed flow reactor at atmospheric pressure. The catalysts were first calcined in a furnace at 400°C for 5 h under air atmosphere before being transferred to fixed-bed flow reactor. The NO_x concentrations in the inlet and outlet gases were measured with a NO* analyzer (Themio-Scientific- 42i), ΝΟχ storage capacity (in. units of mmol/g) was defined as the total amount of adsorbed NO_x until outlet NO_x levels reached the inlet concentration or two hours later. In our experiments, 0.3 g catalyst was placed in the reactor. After the reactor was heated up to the desired adsorption temperature, the gas mixture (100 ppra NO_x, 10% 02, and the balance Ar) was fed to the reactor. All gases were controlled independently by mass flow controllers (Brooks Instruments) and the total flow rate was 200-300 mL/min.

Example 1 : Ni₃AlO_x

Isothermal NO_x storage on Ni₃A10_x catalyst at different adsorption temperatures was tested. Testing condition: 0.3 g catalyst (calcined at 400°C, 5 h), 300 mL/min (Ar: 270 mL/min, 0₂: 30 mL/min, NO_x: 100 ppm). Adsorption time: 2 h. When the adsorption temperatures were controlled at 120, 150, 180, 250 and 300°C, the NO* storage capacity was 0.24, 0.22, 0.21, 0.23, and 0.10 mmol/g, respectively.

Example 2: CujAlOx

Isothermal NO_x storage on Cu₃A10_x catalyst at different adsorption temperatures was tested. Testing condition: 0.3 g catalyst (calcined at 400°C, 5 h), 300 mL/min (Ar: 270 mL/min, <¾: 30 mL/min, NO_x: 100 ppm). Adsorption time: 2 h. When the adsorption temperatures were controlled at 90, 120, 150, 180 and 250°C, the NO_x storage capacity was 0.14, 0.14, 0.09, 0.03 and 0.03 mmol/g, respectively.

Example 3: Co₃AlQ

Isothermal NO_x storage on Co₃A10_x catalyst at different adsorption temperatures was tested. Testing condition: 0.3 g catalyst (calcined at 400°C, 5 h), 300 mL/min (Ar: 270 mL/min, 0₂: 30 mL/min, NO_x: 100 ppm). Adsorption time: 2 h. When the adsorption temperatures were controlled at 90, 120, 150, 180, 250 and 300°C, the NO storage capacity was 0.11, 0.15, 0.21, 0.21 , 0.15 and 0.10 mmol/g, respectively.

Example 4: MgaA10_x

Isothermal NO* storage on Mg₃A10_x catalyst at different adsorption temperatures was tested. Testing condition: 0.3 g catalyst (calcined at 400°C, 5 h), 200 mL/min (Ar: 180 mL/min, 0₂: 20 mL/min, NO_x: 100 ppm). Adsorption time: 2 h. When the adsorption temperatures were controlled at 90, 150, 200, 300 and 400°C, the NO_x storage capacity was 0.10, 0.13, 0.16 and 0.14 mmol/g, respectively. Example 5: Mg₃MnO_x

Isothermal NO_x storage on Mg₃MnO_x catalyst at different adsorption temperatures was tested. Testing condition: 0.2 g catalyst (calcined at 4Q0°C, 5 h), 300 mL/min (Ar: 270 mL/min, 0₂: 30 mL/min, NO_x: 100 ppm). Adsorption time: 2 h. When the adsorption temperatures were controlled at 150 and 250°C, the NO_x storage capacity was 0.37 and 0.32 mmol/g, respectively. Oj storage of ternary AMO-LDHs derived mixed oxide

The NO_x storage capacity of ternary LDH-derived catalysts was evaluated on a fixed-bed flow reactor at atmospheric pressure. The catalysts were first calcined in a furnace at 400°C for 5 h under air atmosphere before being transferred to fixed-bed flow reactor. NO_x concentrations in the inlet and outlet gases were measured with a NO_x analyzer (Thermo-Scientific-42i), NO_x storage capacity (in units of mmol/g) was defined as the total amount of adsorbed NO_x until outlet NO_x levels reached the Met concentration or two hours later, in our experiments, 0.2- 0.3 g catalyst was placed in the reactor. After the reactor was heated up to the desired adsorption temperature, the gas mixture (100 ppm NO_x, 10% 0₂, and the balance Ar) was fed to the reactor. All gases were controlled independently by mass flow controllers (Brooks Instruments) and the total flow rate was 200-300 mL/min.

Example 1 : Coo^ &_.^AlO_x

Isothermal NO„ storage on Coo ₂₅Mg275AKX catalyst at different adsorption temperatures was tested. Testing condition: 0.2 g catalyst (calcined at 400°C, 5 h), 300 mL min (Ar: 270 mL/min, 0₂: 30 mL/min, NO_x: 100 ppm). Adsorption time: 2 h. When the adsorption temperatures were controlled at 90, 150, 180 and 250°C, the NO_x storage capacity were 0.41, 0.35, 0.36 and 0.55 mmol/g, respectively. Example 2: Coo.5Mg2.sA10_x

Isothermal NO_x storage on Coo 5Mg₂.₅A10_x catalyst at different adsorption temperatures was tested. Testing condition: 0.2 g catalyst (calcined at 400°C, 5 h), 300 mL/min (Ar: 270 mL/min, 0₂: 30 mL/min, NO_x: 100 ppm). Adsorption time: 2 h. When the adsorption temperatures were controlled at 90, 150, 180, 250 and 300°C, the NO_x storage capacity were 0.43, 0.57, 0.49, 0.37 and 0.63 mmol/g, respectively.

Example 3 : CoiMg₂A10_x

Isothermal NO_x storage on CoiMg₂A10_x catalyst at different adsorption temperatures. Testing condition: 0.2 g catalyst (calcined at 400°C, 5 h), 300 mL/min (Ar: 270 mL/min, 0₂: 30 mL/min, ^"NO_x: 100 ppm). Adsorption time: 2 h. When the adsorption temperatures were controlled at 90, 150, 250 and 300°C, the NO_x storage capacity were 0.49, 0.34, 0.57 and 0.63 mmol/g, respectively.

Example 4: Coj 5Mgj.₅AlO_x

Isothermal NO_x storage on Coi sMgi $A10_X catalyst at different adsorption temperatures was tested. Testing condition: 0.2 g catalyst (calcined at 400°C, 5 h), 300 mL/min (Ar: 270 mL/min, 0₂: 30 mL min, NO_x: 100 ppm). Adsorption time: 2 h. When the adsorption temperatures were controlled at 90, 150, 250 and 300°C, the NO_x storage capacity were 0.59, 0.46, 0.51 and 0.55 mmol g, respectively.

Example 5: Cui sMgi ₅Α10χ

isothermal NO_x storage on Cui ₅Mgi ₅A10_X catalyst at different adsorption temperatures was tested. Testing condition: 0.2 g catalyst (calcined at 400°C, 5 h), 300 mL/min (Ar: 270 mL/min, <¼: 30 mL/min, NO_x: 100 ppm). Adsorption time: 2 h. When the adsorption temperature was controlled at 150°C, the NQ_X storage capacity was 0.51 mmol/g. Example 6: Ni₂MgiA10_x

Isothermal NO_x storage on. Ni₂MgiA10_x catalyst at different adsorption temperatures was tested. Testing condition: 0.2 g catalyst (calcined at 400°C, 5 h), 300 mL/min (Ar: 270 mL/min, 0₂: 30 mL/min, NO_x: 100 ppm). Adsorption time: 2 h. When the adsorption temperatures were controlled at 150 and 250°C, the NO_x storage capacity were 0.39 aod 0.42 mmol/g, respectively.

NO, storage of Ag/M₃A10_¾

The NO_x storage capacity of Ag/M₃A10_X ( = Mg²⁺, Cu²⁺, Co²⁺ and Ni²⁺) was evaluated on a fixed bed flow reactor at atmospheric pressure. Catalysts were first calcined in a tube furnace at 400° C for 5 h under air atmosphere before being transferred to fixed-bed flow reactor. O_x concentrations in the inlet and outlet gases were measured with a NO_x analyzer (Thermo- Scientific-42i), NO_x storage capacity (in units of mmol/g) was defined as the total amount of adsorbed NO* until outlet NO_x levels reached the inlet concentration or two hours later. In our experiments, 0,3 g catalyst was placed in the reactor. After the reactor was heated up to the desired adsorption temperature, the gas mixture (100 ppm NO_x, 10% 0₂, and the balance Ar) was fed to the reactor. All gases were controlled independently by mass flow controllers (Brooks Instruments) and the total flow rate was 200-300 mL/min.

Example 1 : Ag CosAlO_x

Isothermal NO_x storage on Ag/CosAlO,, catalyst with different Ag loading was tested. Testing condition: 0.3 g catalyst (calcined at 400°C, 5 h), 300 mL/min (Ar: 270 mL/min, 0₂: 30 mL/min, NO_x: 100 ppm). Adsorption temperature was 150°C, and the adsorption time was 2 h. When the Ag loading was controlled at 2, 4 and 6 wt%, the NO_x storage capacity was 0.21, 0.21 and 0,1.2 mmol/g, respectively. Example 2: 2 wt% Ag/Co₃A10_x

Isothermal NO_x storage on 4 wt% Ag/Mg3AlO_x catalyst at different adsorption temperatures was tested. Testing coedition: 0.3 g catalyst (calcined at 400°C, 5 h), 300 mL/min (AT: 270 mL/min, 0₂: 30 mL/min, NO_x: 100 ppm). Adsorption time: 2 h. When the adsorption temperatures were controlled at 150, 250 and 300°C, the NO* storage capacity were 0.21 , 0.17 and 0.14 mmol/g, respectively.

Example 3: Ag/Mg₃AIO_x

Isothermal NO_x storage on Ag/Mg₃A10_x catalyst with different Ag loading was tested. Testing condition: 0.3 g catalyst (calcined at 400°C, 5 h), 300 mL/min (Ar: 270 mL/min, 0₂: 30 mL min, NO*: 100 ppm). Adsorption temperature was 150°C, and the adsorption time was 2 h. When the Ag loading was controlled at 2, 4 and 6 wt%, the NO_x storage capacity was 0.28, 0.31 and 0.24 mmol/g, respectively.

Example 4: 4 wt% Ag/Mg₃A10_x

Isothermal NO_x storage on 4 wt% Ag/MgaA10_x catalyst at different adsorption temperatures was tested. Testing condition: 0.2 g catalyst (calcined at 400°C, 5 h), 300 mL/min (Ar: 270 mL/min, 0₂: 30 mL/min, NO_x: 100 ppm). Adsorption time: 2 h. When the adsorption temperatures were controlled at 150, 250 and 400°C, the NO_x storage capacity was 0.37, 0.46 and 0.28 mmol/g, respectively.

NO, storage on Pt/Co_sMg₃,_xA10_y

The NQ_X storage capacity of Pt/Co_x g3._xA10_y was evaluated on a fixed-bed flow reactor at atmospheric pressure. Catalysts were first calcined in a tube furnace at 400°C lor 5 h under air atmosphere before ^"being transferred to fixed-bed flow reactor. NO_x concentrations in the inlet and outlet gases were measured wit a NO_x analyzer (Thermo- Scientific-42i), NO_X storage capacity (in units of mmol/g) was defined as the total amount of adsorbed NO_x until outlet NO_x levels reached the inlet concentration or two hours later, In our experiments, 0.1 g catalyst was placed in the reactor. After the reactor was heated up to the desired adsorption temperature, the gas mixture (100 ppm NO_x, 10% 02, and the balance Ax) was fed to the reactor. All gases were controlled independently by mass flow controllers (Brooks Instruments) and the total flow rate was 200-300 mL/min.

Example 1: Pt/Co₁Mg₂A10_x

Isothermal NO_x storage on Pt CoiMg₂A10_x catalyst with different Pt loading was tested. Testing condition: 0.1 g catalyst (calcined at 400°C, 5 h), 300 mL/min (Ar: 270 mL/min, 0₂: 30 mL min, NO_x: 100 ppm). Adsorption temperature was 300°C, and the adsorption time was 2 h. When the Pt loading was controlled at 1, 2 and 4 wt%, the NO_x storage capacity was 0.75, 0.33 and 0.23 mmol/g, respectively.

Example 2: Pt/Co Mgi ₅AlO_x

Isothermal NO_x storage on Pt/Co 1 ₅Mg i .sA10_x catalyst with different Pt loading was tested. Testing condition: 0.1 g catalyst (calcined at 400°C, 5 h), 300 mL/min (Ar: 270 mL/min, 0₂: 30 mL/min, NO_x: 100 ppm). Adsorption temperature was 90°C, and the adsorption time was 2 h. When the Pt loading was controlled at 1, 2 and 4 wt%, the NO_x storage capacity was 0.34, 0.21 and 0.14 mmol/g, respectively.

NO, storage on Pt-K₂0/CoMg3-_xAlO_y and Pt-BaO/Co_xMg₃._xAIO_y

The NO_x storage capacities of Pt-K₂0/Co_xMg3_-xA10_y and Pt-BaO/Co_xMg₃._xAlO_y were evaluated on a fixed-bed flow reactor at atmospheric pressure. Catalysts were first calcined in a tube furnace at 400 °C for 5 h under air atmosphere before being transferred to fixcd-bcd flow reactor. NO_x concentrations in the inlet and outlet gases were measured with a NO_x analyzer (Thermo-Scientific-42i), NO_x storage capacity (in units of mmol/g) was defined as the total amount of adsorbed NO_x until outlet NO_x levels reached the inlet concentration or two hours later. In our experiments, 0.05 g catalyst was placed in the reactor. After the reactor was heat- ed up to the desired adsorption temperature, the gas mixture (100 ppm NO_x, 10% 0₂, and the balance Ar) was fed to the reactor. All gases were controlled independently by mass flow controllers (Brooks Instruments) and the total flow rate was 200-300 mL/min.

Example 1: Pt-K₂0/CoiMg₂A10_x

Isothermal NO_x storage on Pt-K₂0/CoiMg₂A10_x catalyst with 1 wt% Pt/15 wt% K₂0 loading was tested. Testing condition: 0.05 g catalyst (calcined at 400°C, 5 h), 300 mL/min (Ar: 270 mL/min, 0₂: 30 mL/min, NOx: 100 ppm). Adsorption temperature was 300°C, and the adsorption time was 2 h, the NO_x storage capacity was 1.20 mmol/g, respectively,

Example 2: Pt-BaO/CoiMg₂A10_Y

Isothermal NO_x storage on Pt-BaO/CoiMg₂A10_x catalyst with 1 wt% Pt/20 wt% BaO loading was tested. Testing condition: 0.05 g catalyst (calcined at 400°C, 5 h), 300 mL/min (Ar; 270 mL/min,€¾: 30 mL/min, NOx: 100 ppm), and the adsorption time was 2 h. The NO_x storage capacity was 1.20 and 1.30 mmol/g, respectively at adsorption temperature of 250 and 300°C,

The features disclosed in the foregoing description and in the claims may both separately and in any combination be material for realizing the invention in diverse forms thereof.

Claims

1. ΝΟχ storage and reduction catalyst comprising a material having the general formula

(1)

G/A₂0/LxM_yQO_z (1),

wherein LxM_yQO_z is a substrate and G and A₂0 are deposited on the surface of the

L_xM_yQO_z substrate;

wherein G is a noble metal, A is an element from Group I or II of the Periodic Table of

Elements, L and M are independently selected from divalent cations and L and M axe not selected as the same divalent cation,

Q is at least one trivalent cation, O is oxygen, x is from 0 to 6, y is from 0 to 6, x+y is from 1 to 6 and z is selected to balance the values of x and y slochiometrically,

wherein the amount of G is from 0.5 to 6 wt%, preferably from 0.5 to 4 wt%, the amount of A₂0 is from. 5 to 30 wt%, and the amount of L_xM_yQO_z balances the amount of G and A₂0 to result in 100 wt%.

2. ΝΟχ storage and reduction catalyst according to claim 1, wherein G is selected from Ag, Pt, Pd, Ir, In, Rh, Ga or mixtures thereof, preferably from Ag and/or Pt.

3. NO_x storage and reduction catalyst according to claim 1 or 2, wherein A is selected from K, Li, Na, Ba, or mixtures thereof, preferably is K, Ba, or mixtures thereof.

4. ΝΟχ storage and reduction catalyst according to any of the preceding claims, wherein

L and M are independently selected from Co, Cu, Mg, Ni, Zn, Ca or mixtures thereof, NO_x storage and reduction catalyst according to any of the preceding claims, wherein Q is selected from Al, Mn, Fe, Ga, Cr or mixtures thereof.

Process for preparing a NO_x storage and reduction catalyst according to any of the preceding claims, the process comprising the steps:

wherein L and M are independently selected from divalent cations, Q is a triva- lent cation, is from 0 to 6, y is from 0 to 6, x+y is from 1 to 6,

X is an anion, n is 1 to 3 and a is selected to balance the charge of cations and anions dependent from the values of x and y; and b is from 0 to 10;

b) washing the material with a solvent, wherein the solvent is miscible with water and preferably has a solvent polarity (Ρ') in the range from 3.8 to 9;

c) drying and calcinating at 200 to 600°C the material obtained in step b);

d) impregnating the material obtained in step c) with a solution of a precursor of the alkali metal oxide and/or alkaline earth metal oxide A₂0; and

e) impregnating the material obtained in step d) with a solution of a precursor of a noble metal G. 7,. Process according to claim 6, wherein L and M are independently selected from Co, Cu, Mg, Ni, Zn, Ca and mixtures thereof,

8. Process according to claim 6 or 7, wherein the trivalcnt cation Q is selected from Al, n, Fe, Ga, Cr or mixtures thereof.

9. Process according to any of the claims 6 to 8, wherein X is selected from inorganic anions, carboxylic anions, dicarboxylic anions, anionic surfactants or mixtures thereof, preferably X is carbonate, carboxylate, dicarboxylate or mixtures thereof.

10. Process according to any of the claims 6 to 9, wherein the solvent which is miscible with water is selected from acetone, acetonitrile, dimethylformamide, dimethylsulfox- ide, dioxane, ethanol, methanol, n-propanol, 2-propanol, tetrahydrofuran or mixtures thereof, preferably is acetone.

11. Process according to any of the claims 6 to 10, wherein the alkali metal and/or alkaline earth metal oxide A is selected from K, Li, Na, Ba, or mixtures thereof, preferably is K, Ba, or mixtures thereof.

12. Process according to any of the claims 6 to 1 1, wherein the noble metal G is selected from Ag. Pt, Pd, Ir, In, Rh, Ga and mixtures thereof, preferably is Ag and/or Pt.

13. Process according to any of the claims 6 to 12, wherein a solvent used during the impregnation with the precursor of the alkali metal oxide and/or alkaline earth metal oxide and/or the noble metal is selected fro water, methanol, ethanol, acetone, ethylene glycol, 2-propanone, dimethylformamide, acetonitrile, glycerol or mixtures thereof.

14. Process according to any of the claims 6 to 13, wherein the process comprises a further step after step c) or d) of calcinating the material obtained in the last step, preferably at a temperature in a range from 300 to 500°C. Use of a catalyst according to any of the claims 1 to 5 for adsorbing and/or storing and/or reducing NO_x-gas,