CN110075832B

CN110075832B - NOx storage reduction catalyst, preparation method and application thereof

Info

Publication number: CN110075832B
Application number: CN201910294249.0A
Authority: CN
Inventors: 张昭良; 韩增艳; 郑德超; 辛颖; 李倩; 张娜娜
Original assignee: University of Jinan
Current assignee: University of Jinan
Priority date: 2019-04-12
Filing date: 2019-04-12
Publication date: 2022-02-15
Anticipated expiration: 2039-04-12
Also published as: CN110075832A

Abstract

The invention discloses a _NOx storage reduction catalyst and a preparation method and application thereof. The catalyst uses precious metal as an active component, and the precious metal is evenly supported on a carrier, and the carrier is BaTiO ₃ pretreated with alkali. In the present invention, the surface _of the BaTiO3 _perovskite is treated with alkali washing, and then the precious metal is loaded _on the BaTiO3 after the alkali washing to obtain an NSR catalyst with high NSR activity and high temperature resistance. Compared with the catalyst, the _NOx conversion rate of the present invention is increased by more than 10% as a whole, more than 80% at 200-400 ° C, the N ₂ selectivity is slightly improved, and reaches more than 90% after 250 ^° C, and the catalyst preparation process is simple and easy to operate. , which is convenient for industrial production.

Description

NOx storage reduction catalyst and preparation method and application thereof

Technical Field

The invention discloses a NO_xA storage reduction (NSR) catalyst, in particular to a catalyst with NO_xStorage Reduction (NSR) catalytically active Pt/BaTiO₃Perovskite catalyst and preparation method and application thereof.

Background

Aiming at the severity of environmental problems in China, motor vehicle state five emission regulations are comprehensively implemented in 1/2018 in China, and emission limit values and measurement methods of light automobile pollutants (sixth stage of China) (GB 18352.6-2016) are implemented in 7/1/2020 in China, and five pairs of NO in six countries are compared with five pairs of NO in China _xThe emission requirements are more stringent.

NO_xStorage Reduction (NSR) technology is believed to address NO in light-duty diesel vehicles and lean burn gasoline engines_xOne of the most promising post-treatment technologies, the traditional NSR catalyst consisting of Pt/BaO/AlO₃Composition in which Pt is the active component, oxidation of NO to NO in the lean burn stage₂BaO as a storage component, NO to be generated₂And NO is stored in the form of nitrate or nitrite, and when the atmosphere is switched to a rich state, the stored nitrate is decomposed to release NO_xIs reduced into N by a reducing agent under the action of noble metal Pt₂Thereby achieving the purpose of eliminating the nitrogen oxide.

ABO₃Perovskites have high thermal stability and are easy to prepare, with the A site usually being an alkali or alkaline earth metal, which can act as NO_xThe storage location of (2). Li et al report La_x1-Sr_xCoO₃Has NSR activity (Energy environ. Sci., 2011, 4, 3351), and the sulfur resistance of the catalyst can be improved by adding noble metal Pd (ACS Catal. 2013, 3, 1071-. BaTiO 2₃Is ABO₃One of the perovskites, Rajanikanth B S et al (Fuel Processing Technology, 2001, 74:177-_xWas investigated in an experiment in which BaTiO was used ₃As catalyst, when in NO, O₂、N₂Or NO, N₂The removal efficiency is higher when the atmosphere is in the atmosphere, and the concentration of NO is 265 mg/m³When the removal efficiency is as high as 99%, BaTiO is not used under the plasma discharge condition or when the gas composition is changed₃The removal effect on NOx is poor.

Disclosure of Invention

To overcome BaTiO₃Problem of Low NSR catalytic Performance, the present invention provides a NO_xStorage reduction catalyst consisting of a noble metal and BaTiO pretreated with alkaline washing₃Composition, has higher NSR activity.

The present invention also provides the above NO_xMethod for preparing storage reduction catalyst, operation of the methodSimple and convenient to implement, by mixing BaTiO₃Alkali washing pretreatment is carried out to improve the NSR activity, and then the pretreated BaTiO₃And noble metal is loaded on the catalyst, and the obtained catalyst integrally shows higher NSR activity.

The specific technical scheme of the invention is as follows:

NO (nitric oxide)_xThe storage reduction catalyst takes noble metal as an active component, the noble metal is uniformly loaded on a carrier, and the carrier is alkali pretreated BaTiO₃。

NO as defined above_xIn the storage reduction catalyst, the alkali used for pretreatment is an aqueous solution of sodium hydroxide or an aqueous solution of potassium hydroxide, and preferably, the concentration of the aqueous solution of sodium hydroxide or the aqueous solution of potassium hydroxide is 3-8 mol/L. Base on BaTiO ₃The surface is pretreated to remove part of titanium and improve BaTiO₃The NSR activity of (1).

Further, BaTiO is treated with alkali₃When carrying out pretreatment, BaTiO₃Treating with sodium hydroxide or potassium hydroxide aqueous solution at 50-100 ℃ for 1-12 h. The aqueous solution of sodium hydroxide or potassium hydroxide is generally added in excess to make BaTiO₃Completely immersed therein.

Further, the noble metal is at least one of Pt, Pd and Rh.

Further, the loading amount of the noble metal is 0.5-1 wt%. The loading refers to the percentage of the noble metal by mass of the support.

Further, the present invention provides the above NO_xA method of preparing a storage reduction catalyst, the method comprising the steps of:

(1) mixing BaTiO₃Pretreating with sodium hydroxide aqueous solution or potassium hydroxide aqueous solution, and mixing the pretreated BaTiO₃Washing to be neutral;

(2) loading noble metal precursor solution to the pretreated BaTiO₃To obtain NO by roasting_xThe reduction catalyst is stored.

Further, in the step (1), the BaTiO₃Can adoptPrepared by the method disclosed in the prior art, and in one specific embodiment of the invention, a preferred BaTiO is disclosed₃The preparation method comprises the following steps:

a. Uniformly mixing barium nitrate, citric acid and water to obtain a solution A;

b. uniformly mixing tetra-n-butyl titanate and ethylene glycol to obtain a solution B;

c. pouring the solution B into the solution A, heating and stirring at 40-80 ℃ until the solution is clear, then adjusting the pH value to 7-10, heating to 60-100 ℃ and carrying out heat preservation treatment until gel is obtained;

d. drying the obtained gel, heating the obtained precursor to 300-400 ℃ in a muffle furnace (in static air) for roasting for 1h, and then heating to 700-900 ℃ for roasting for 5-8 h to obtain BaTiO₃。

Further, the above-mentioned BaTiO₃In the preparation method, barium nitrate: the molar ratio of tetra-n-butyl titanate is 1.0:0.5 to 1.5, preferably 1.0: 1.0.

Further, the above-mentioned BaTiO₃In the preparation method, the ratio of the total molar amount of titanium and barium to the molar amount of citric acid is 1: 1-3, preferably 1: 1.5.

Further, the above-mentioned BaTiO₃In the preparation method, the weight ratio of ethylene glycol: the molar ratio of Ti is 1: 0.5-5, preferably 2: 3.

Further, the above-mentioned BaTiO₃In the preparation method, the concentration of barium nitrate in the solution A is 0.25-1 mol/L.

Further, the above-mentioned BaTiO₃In the preparation method, the gel is dried at 100-160 ℃.

Further, the above-mentioned BaTiO₃In the preparation method, in the roasting process of the step d, the temperature is increased to the specified temperature according to the temperature rise speed of 5 ℃/min.

Further, in the step (1), BaTiO is treated₃The pretreatment of (a) is as described above.

Further, in the step (2), the noble metal precursor is a salt of a noble metal, for example, a nitrate of a noble metal.

Further, in the above step (2), it is expensiveLoading the pretreated BaTiO with metal precursor solution by an equal volume impregnation method₃The above.

Further, in the step (2), the roasting is carried out in an air atmosphere, the roasting temperature is 400-550 ℃, and the roasting time is 2-4 hours.

Further, the present invention provides the above NO_xUse of a storage reduction catalyst in the treatment of motor vehicle exhaust gases. NO of the invention_xThe storage reduction catalyst has good NO_xStorage and removal capability, and can be used for treating tail gas in motor vehicles, treating NO in tail gas of motor vehicles_x。

Further, the present invention provides a catalyst for motor vehicle exhaust gas, the catalyst effective component comprising the above NO_xThe reduction catalyst is stored. The catalyst may be in the form of NO_xElimination of nitrogen oxides, NO, in motor vehicle exhaust gases by means of storage reduction (NSR)_xThe conversion rate is more than 80 percent at the temperature of 200 ℃ and 400 ℃, and N₂The selectivity of (A) is more than 90% at the temperature of 250-400 ℃.

The invention uses alkali washing to process BaTiO ₃BaTiO on the surface of perovskite and then washed with alkali₃Noble metal is loaded on the catalyst to obtain the high NSR activity and high temperature resistant NSR catalyst and BaTiO which is not subjected to alkali washing treatment₃Compared with the catalyst formed by loading noble metal, NO of the invention_xThe conversion rate is improved by more than 10 percent in whole, the temperature is more than 80 percent at 200 ℃ and 400 ℃, and N is₂The selectivity is slightly increased at 250^oThe content of C is more than 90%, and the catalyst has simple preparation process, easy operation and convenient industrial production.

Drawings

FIG. 1 is an XRD spectrum of the catalyst prepared in example 3 and comparative example 1;

FIG. 2 is a graph of NOx conversion for the catalysts prepared in example 3, comparative example 1;

FIG. 3 is N for the catalysts prepared in example 3 and comparative example 1₂And (4) a selectivity graph.

Detailed Description

The present invention will now be further described with reference to the accompanying drawings, which are given by way of illustration only and are not intended to be limiting of the present invention.

Example 1

1. Preparation of BaTiO₃: 0.01 mol of Ba (NO) is weighed₃)₃And 0.015 mol of citric acid monohydrate are put into a beaker, 10 ml of deionized water is added, and the solution is heated, stirred and dissolved at the temperature of 60 ℃ to obtain solution A; taking 0.005 mol of tetrabutyl titanate and 0.01 mol of ethylene glycol to be uniformly mixed, and marking as a solution B; pouring the solution B into the solution A, and stirring at 60 ℃ until the solution is clear; dropwise adding ammonia water into the clear solution, adjusting the pH value to 8-10, and evaporating water in a water bath kettle at 80 ℃ until colloidal gel is obtained; the obtained gel-like gel was dried at 130 ℃ and the obtained sample precursor was calcined in a muffle furnace in two stages: heating to 300 ℃ at a heating rate of 5 ℃/min, roasting for 1 h, heating to 750 ℃ at the same heating rate, and roasting for 5 h to obtain BaTiO ₃。

2、BaTiO₃The pretreatment of (1): putting 1 g of BaTiO3 into a polytetrafluoroethylene kettle, adding 40ml of 6 mol/L sodium hydroxide aqueous solution, stirring for 1h at 60 ℃, and then filtering or centrifugally washing until the filtrate or washing liquid is neutral to obtain an alkali washing sample BaTiO₃-1；

3. Preparing a catalyst: weighing platinum nitrate according to the loading amount of 0.5wt%, preparing a solution by using water, and loading the noble metal to an alkali washing sample BaTiO by adopting an isovolumetric immersion method₃And (4) heating to 400 ℃ in the air atmosphere, roasting for 4 hours, grinding and screening the obtained sample, and taking a 40-60-mesh sample, namely the 0.5Pt/BaTiO3-1 catalyst.

Example 2

1. Preparation of BaTiO₃: 0.01 mol of Ba (NO) is weighed₃)₃And 0.075 mol of citric acid monohydrate are placed in a beaker, 40ml of deionized water is added, and the mixture is heated and stirred at the temperature of 60 ℃ to be dissolved, so that solution A is obtained; taking 0.015 mol of tetrabutyl titanate and 0.003 mol of ethylene glycol, and uniformly mixing the tetrabutyl titanate and the ethylene glycol to obtain a solution B; pouring the solution B into the solution A, and stirring at 60 ℃ until the solution is clear; dropwise adding ammonia water into the clear solution, adjusting the pH to 9-10, and evaporating water in a water bath kettle at 80 DEG CUntil a gelatinous gel is obtained; the obtained gel-like gel was dried at 130 ℃ and the obtained sample precursor was calcined in a muffle furnace in two stages: heating to 400 deg.C at a rate of 5 deg.C/min, calcining for 1h, heating to 850 deg.C at the same rate, and calcining for 5 h to obtain BaTiO ₃。

2、BaTiO₃The pretreatment of (1): 1 g of BaTiO₃Placing in a polytetrafluoroethylene kettle, adding 40ml of 6 mol/L sodium hydroxide aqueous solution, stirring for 3 h at 80 ℃, then filtering or centrifugally washing until the filtrate or washing liquid is neutral to obtain an alkali washing sample BaTiO₃-2；

3. Preparing a catalyst: weighing platinum nitrate according to the loading amount of 1wt%, preparing the platinum nitrate into a solution by using water, and loading the noble metal to an alkali washing sample BaTiO by adopting an isovolumetric immersion method ₃2, heating to 550 ℃ in air atmosphere, roasting for 2 hours, grinding and screening the obtained sample, and taking a sample of 40-60 meshes, namely 1Pt/BaTiO₃-2 catalyst.

Example 3

1. Preparation of BaTiO₃: 0.01 mol of Ba (NO) is weighed₃)₃Adding 0.03 mol of citric acid monohydrate into a beaker, adding 40ml of deionized water, heating and stirring at 60 ℃ to dissolve to obtain a solution A; taking 0.01 mol of tetrabutyl titanate and 0.0067 mol of ethylene glycol to be uniformly mixed, and marking as a solution B; pouring the solution B into the solution A, and stirring at 60 ℃ until the solution is clear; dropwise adding ammonia water into the clear solution, adjusting the pH value to 7-9, and evaporating water in a water bath kettle at 80 ℃ until colloidal gel is obtained; the obtained gel-like gel was dried at 130 ℃ and the obtained sample precursor was calcined in a muffle furnace in two stages: heating to 300 ℃ at a heating rate of 5 ℃/min, roasting for 1h, heating to 750 ℃ at the same heating rate, and roasting for 5 h to obtain BaTiO ₃。

2、BaTiO₃The pretreatment of (1): 1 g of BaTiO₃Placing in a polytetrafluoroethylene kettle, adding 40ml of 6 mol/L sodium hydroxide aqueous solution, stirring for 2h at 80 ℃, then filtering or centrifugally washing until the filtrate or washing liquid is neutral to obtain an alkali washing sample BaTiO₃-3；

3. Preparing a catalyst: weighing platinum nitrate according to the loading amount of 1wt%, preparing the platinum nitrate into a solution by using water, and loading the noble metal to an alkali washing sample BaTiO by adopting an isovolumetric immersion method ₃3, heating to 500 ℃ in air atmosphere, roasting for 2 hours, grinding and screening the obtained sample, and taking a sample of 40-60 meshes, namely 1Pt/BaTiO₃-3 catalyst.

Example 4

1. Preparation of BaTiO 3: the same as in example 3;

2. pretreatment of BaTiO 3: 1 g of BaTiO₃Placing in a polytetrafluoroethylene kettle, adding 40ml of 8 mol/L sodium hydroxide aqueous solution, stirring for 12 h at 50 ℃, then filtering or centrifugally washing until the filtrate or washing liquid is neutral to obtain an alkali washing sample BaTiO₃-4；

3. Preparing a catalyst: the catalyst obtained in the same manner as in example 3 was 1Pt/BaTiO₃-4 catalyst.

Example 5

1. Preparation of BaTiO 3: the same as in example 3;

2. pretreatment of BaTiO 3: 1 g of BaTiO₃Placing in a polytetrafluoroethylene kettle, adding 40ml of 3mol/L sodium hydroxide aqueous solution, stirring for 1h at 100 ℃, then filtering or centrifugally washing until the filtrate or washing liquid is neutral to obtain an alkali washing sample BaTiO ₃-5；

3. Preparing a catalyst: the catalyst obtained in the same manner as in example 3 was 1Pt/BaTiO₃-5 catalyst.

Comparative example 1

1. Preparation of BaTiO₃: the same as in example 3.

2. Preparing a catalyst: weighing platinum nitrate according to the loading amount of 1wt%, preparing the platinum nitrate into a solution by using water, and loading the noble metal to the BaTiO sample by adopting an isovolumetric impregnation method₃Then, the temperature is raised to 500 ℃ in the air atmosphere for roasting for 2 hours, the obtained sample is ground and sieved, and a 40-60-mesh sample is taken, namely 1Pt/BaTiO₃。

Comparative example 2

1. Preparation of BaTiO₃: the same as in example 3.

2、BaTiO₃The pretreatment of (1): 1 g of BaTiO₃Placing in a polytetrafluoroethylene kettle, adding 40ml of 2 mol/L sodium hydroxide aqueous solution, stirring for 2h at 80 ℃, then filtering or centrifugally washing until the filtrate or washing liquid is neutral to obtain an alkali washing sample BaTiO₃-A；

2. Preparing a catalyst: weighing platinum nitrate according to the loading amount of 1wt%, preparing a solution by using water, and completely loading the solution to an alkali washing sample BaTiO by adopting an isovolumetric immersion method₃And (E) on the substrate A, raising the temperature to 500 ℃ in the air atmosphere, roasting for 2 hours, grinding and screening the obtained sample, and taking a sample of 40-60 meshes, namely 1Pt/BaTiO₃-A。

Comparative example 3

1. Preparation of BaTiO₃: the same as in example 3.

2、BaTiO₃The pretreatment of (1): 1 g of BaTiO₃Placing in a polytetrafluoroethylene kettle, adding 40ml of 6 mol/L sodium hydroxide aqueous solution, stirring for 12h at 35 ℃, then filtering or centrifugally washing until the filtrate or washing liquid is neutral to obtain an alkali washing sample BaTiO ₃-B；

2. Preparing a catalyst: weighing platinum nitrate according to the loading amount of 1wt%, preparing a solution by using water, and completely loading the solution to an alkali washing sample BaTiO by adopting an isovolumetric immersion method₃And (B) heating to 500 ℃ in air atmosphere, roasting for 2 hours, grinding and screening the obtained sample, and taking a 40-60-mesh sample, namely 1Pt/BaTiO₃-B。

Comparative example 4

1. Preparation of BaTiO₃: the same as in example 3.

2、BaTiO₃The pretreatment of (1): 1 g of BaTiO₃Placing in a polytetrafluoroethylene kettle, adding 40ml of 25wt% ammonia water, stirring at 80 ℃ for 2h, filtering or centrifugally washing until the filtrate or washing liquid is neutral to obtain an alkali washing sample BaTiO₃-C；

2. Preparing a catalyst: weighing platinum nitrate according to the loading amount of 1wt%, preparing a solution by using water, and completely loading the solution to an alkali washing sample BaTiO by adopting an isovolumetric immersion method₃Heating to 500 ℃ in air atmosphere, roasting for 2h, grinding and screening the obtained sample, and taking a sample of 40-60 meshesThe product is 1Pt/BaTiO₃-C。

BaTiO after alkaline cleaning pretreatment of example 3₃-3 sample, 1Pt/BaTiO after loading Pt₃-3 samples and comparative example 1 non-pretreated BaTiO₃Sample, 1Pt/BaTiO after loading Pt₃The XRD detection of the sample is shown in figure 1, and the following can be seen: pt-loaded catalyst and BaTiO ₃The perovskite standard card has good correspondence, the structure of the catalyst after alkaline washing pretreatment is not damaged, and no related diffraction peak of Pt appears after noble metal Pt is loaded, which indicates that the Pt has high dispersion degree on the surface of the catalyst.

NO treatment of the catalysts obtained in the above examples and comparative examples_xThe storage reduction (NSR) performance test method comprises the following steps:

the reaction is carried out on a seven-path automatic instantaneous reaction platform, lean combustion is carried out for 60s, rich combustion is carried out for 10s, 50 mg of catalyst with granularity of 40-60 meshes in each embodiment or comparative example is used, each catalyst is placed in a reaction furnace (the inner diameter is 6 mm), and 10 mm of catalyst is placed in pure He atmosphere^oC·min^-1Rise to 400^oC pretreatment for 30 min, then 200-^oTesting NO of each catalyst in C temperature interval under the condition of alternating lean-burn and rich-burn atmospheres_xStoring the reduction activity;

gas composition: a lean burn stage: 300 ppm NO and 7.5% O₂He is used as balance gas; and (3) a rich combustion stage: 1% of H₂He is used as balance gas; the gas flow rate during the reaction was 400 mL/min. Gas NO of each component of the effluent gas of the reactor_x(NO and NO)₂)，N₂O，NH₃And H₂O gas concentration changes were detected on-line by a MultiGas 2030 type fourier transform infrared spectrometer.

FIGS. 2 and 3 are NO for the catalysts of example 3 and comparative example 1 _xConversion and N₂The selectivity results, as can be seen from the figure, for the catalyst NO of example 3_xThe conversion rate is 200-400-^oC greater than 80%, N₂Selectivity at 250-^oC reaches more than 90 percent; catalyst NO of comparative example 1_xThe conversion rate is 200-400- ^oC is greater than 70%, N₂Selectivity at 250-^oC also reaches more than 90 percent. It can be seen from this that the catalyst of example 3 has NO after a caustic wash pretreatment_xThe conversion rate is improved by more than 10 percent compared with the whole proportion, N₂The selectivity is slightly improved, and the catalyst has better NSR catalytic activity.

NO of catalysts of other examples and comparative examples_xConversion and N₂The selectivity pattern was similar to that of example 3 and comparative example 1, with each example having NO at 250 deg.C, 300 deg.C, 350 deg.C_xConversion and N₂The selectivities are shown in table 1 below:

Claims

1. NO (nitric oxide)_xA storage reduction catalyst characterized by: noble metal is used as an active component and is uniformly loaded on a carrier, and the carrier is alkali pretreated BaTiO₃(ii) a The mode of alkali pretreatment is as follows: mixing BaTiO₃Treating with sodium hydroxide or potassium hydroxide aqueous solution at 50-100 deg.C for 1-12 h, wherein the concentration of the sodium hydroxide aqueous solution or potassium hydroxide aqueous solution is 3-8 mol/L.

2. NO according to claim 1_xA storage reduction catalyst characterized by: the noble metal is at least one of Pt, Pd and Rh.

3. NO according to claim 1_xA storage reduction catalyst characterized by: the loading of the noble metal is 0.5-1 wt%.

4. An NO according to any one of claims 1 to 3_xThe preparation method of the storage reduction catalyst is characterized by comprising the following steps of:

(1) mixing BaTiO₃Pretreating with aqueous solution of sodium hydroxide or potassium hydroxideAfter pretreatment, BaTiO is added₃Washing to be neutral;

5. The method according to claim 4, wherein: in the step (1), the BaTiO₃The preparation method comprises the following steps:

d. drying the obtained gel, heating the obtained precursor to 300-400 ℃ in a muffle furnace, roasting for 1h, heating to 700-900 ℃ and roasting for 5-8 h to obtain BaTiO₃。

6. The method according to claim 5, wherein: preparation of BaTiO ₃When the ratio of the barium nitrate to the tetra-n-butyl titanate is 1.0: 0.5-1.5; the ratio of the total molar amount of titanium and barium to the molar amount of citric acid is 1: 1-3; the molar ratio of the ethylene glycol to the Ti is 1: 0.5-5; the concentration of barium nitrate in the solution A is 0.25-1 mol/L.

7. The method of claim 6, wherein: preparation of BaTiO₃When the ratio of the barium nitrate to the tetra-n-butyl titanate is 1.0: 1.0; the ratio of the total molar amount of titanium and barium to the molar amount of citric acid is 1: 1.5; the molar ratio of ethylene glycol to Ti was 2: 3.

8. The method according to claim 4, wherein: in the step (2), the noble metal precursor is a noble metal salt; in the step (2), a noble metal precursor solution is loaded on the pretreated BaTiO by adopting an isometric impregnation method₃The above step (1); in the step (2), roasting is carried out at 400-550 ℃, and the roasting time is 2-4 h.

9. The method of claim 8, wherein: in the step (2), the noble metal precursor is nitrate.

10. NO according to any one of claims 1 to 3_xUse of a storage reduction catalyst in the treatment of motor vehicle exhaust gases.

11. Use according to claim 10, characterized in that: said NO _xStorage reduction catalyst for treating NO in motor vehicle exhaust_x。

12. A catalyst for motor vehicle exhaust, which is characterized in that: the active ingredient comprises NO according to any one of claims 1 to 3_xThe reduction catalyst is stored.