CN110801832A - Gasoline engine tail gas purification three-effect catalyst meeting national emission standard - Google Patents

Abstract

A gasoline engine tail gas purification three-effect catalyst meeting the national six-emission standard comprises a main catalyst and a pre-catalyst, wherein the main components of the pre-catalyst are modified alumina, cerium/zirconium mixed oxide and precious metal active components, the pre-catalyst comprises a base layer I, a middle layer II and an outer layer III, each layer is provided with a front region and a rear region, the front region is an upstream region with more precious metal active components, the rear region is a downstream region with lower precious metal active components than the front region, the main catalyst comprises a base layer A, a middle layer B and an outer layer C, the precious metal active component content of the middle layer is higher than that of the base layer A and the outer layer C, the precious metal active component content in the main catalyst is lower than that of the pre-catalyst, the effective utilization of the precious metal active components and the remarkable improvement of the thermal stability of the catalyst are realized, and the light-off temperature, the ignition temperature and the ignition temperature of the catalyst are reduced, The durability of the catalyst is improved.

Description

Gasoline engine tail gas purification three-effect catalyst meeting national emission standard

Technical Field

The invention belongs to the technical field of gasoline engine tail gas purification, and particularly relates to a gasoline engine tail gas purification three-way catalyst meeting the national emission standard.

Background

The method is the most effective mode for treating the tail gas of the gasoline engine, namely 12 and 23 days in 2016, GB18352.6-2016 (national ministry of environmental protection) publication GB18352.6-2016 (limit for emission of pollutants in light-duty automobiles) and a measurement method (sixth stage in China), from 7 and 1 days in 2020, all light-duty automobiles sold and registered should meet the standard requirement, wherein a type I test should meet the 6a limit requirement; since 7/1/2023, all light vehicles sold and registered should meet the standards, with the type i test meeting the 6b limit.

In consideration of long development period and high development cost of new vehicles, a plurality of vehicle enterprises select to directly develop vehicle types meeting the emission standard of the national Liu-b; this also means that a matched gasoline engine exhaust purifier must employ a three-way catalyst that meets the emissions standards of the national Liuba.

National emission standards of six allow for a significant reduction in emission values for pollutants relative to national emission standards of five, which means that the matched catalyst needs to have higher conversion efficiency and lower light-off temperature; the national emission standard adopts more transient WLTC circulation, and a matched catalyst has more excellent oxygen storage and release performance; and the regulation of the national six-emission standard on the use aging of the catalyst is 20 kilometers, and higher requirements are put on the thermal stability of the catalyst.

The document with the grant number CN104334255B discloses a three-way catalyst system, which comprises a first three-way catalyst on an inert catalyst support and a second three-way catalyst located upstream of the first three-way catalyst, wherein the first three-way catalyst is a double-layer catalyst comprising a first layer and a second layer, the first layer comprises active alumina, cerium/zirconium mixed oxide and palladium, and the second layer comprises active alumina and rhodium and does not contain cerium and cerium-containing materials.

Disclosure of Invention

The invention aims to provide a gasoline engine tail gas purification three-way catalyst meeting the national emission standard, which realizes high dispersion of noble metal active components according to different types and concentrations of noble metals adsorbed and deposited in different subareas so as to integrally improve the high-temperature thermal stability of the catalyst.

In order to achieve the purpose, the technical scheme of the invention is as follows:

a gasoline engine tail gas purification three-effect catalyst meeting the national emission standard comprises a main catalyst and a pre-catalyst, wherein the main components of the pre-catalyst are modified alumina, cerium/zirconium mixed oxide and precious metal active components, the pre-catalyst comprises a base layer I, a middle layer II and an outer layer III, each layer is provided with a front region and a rear region, the front region is an upstream region with more precious metal active components, and the rear region is a downstream region with lower precious metal active components than the front region.

Further, the main catalyst comprises a base layer A, an intermediate layer B and an outer layer C, the content of the noble metal active component in the intermediate layer is larger than that of the base layer A and the outer layer C, and the content of the noble metal active component in the main catalyst is lower than that in the pre-catalyst.

In the design of the scheme, a double-layer catalyst comprising a main catalyst and a pre-catalyst is arranged, in order to improve the dispersion degree and the effective utilization of the active components of the precious metal in the catalyst, the pre-catalyst which plays the main catalytic action is divided into at least six areas from top to bottom and from upstream to downstream, through the layout mode, the proportion of modified oxides and rare earth composite oxides among different levels and different areas can be adjusted, so that the type and the concentration of the precious metal are adjusted, the content of the active components of the precious metal is lower than that of the pre-catalyst according to the flow direction of tail gas, the content of the active components of the precious metal is gradually reduced from upstream to downstream, and the characteristics that the content of the basic layer, the middle layer and the middle layer of the outer layer is reduced towards two sides are distributed, so that the effective utilization of the active components of the precious metal and the remarkable improvement of the thermal, The durability of the catalyst is improved.

Preferably, the cerium/zirconium mixed oxide comprises: ce₁: the weight ratio of the cerium oxide to the zirconium oxide is 0.8-1.2; ce₂: the weight ratio of the cerium oxide to the zirconium oxide is 0.6-0.8.

Further, Ce₁Or Ce₂The specific surface area of (A) is 70-100 m²Per g, pore volume of 0.5-0.6 cm³The pore diameter is 10-100 nm.

Further preferably, Ce₁Or Ce₂Aging at 1000 deg.C to specific surface area of 40m or more²G, aging at 1100 deg.C, and specific surface area of not less than 20m²/g。

In the design of the scheme, through repeated tests, the cerium/zirconium mixed oxide with the parameters has good high-temperature sintering resistance, excellent oxygen hole concentration and oxygen storage capacity, and can reduce the ignition temperature of the three-way catalyst.

Preferably, the modified alumina is a rare earth modified alumina material, the rare earth elements comprise lanthanum, neodymium and yttrium, and the specific surface area of the rare earth elements is 160-260 m²Per g, pore volume of 0.3-0.8 cm³The pore diameter is 0.5-100 nm.

More preferably, the specific surface area of the modified alumina is 180-200 m²Per g, pore volume of 0.5-0.8 cm³The pore diameter is 4-40 nm, and the specific surface area is more than or equal to 40m after aging at 1200 DEG C²/g。

The stability of the overall catalyst depends to a large extent on the surface area of the coating in which w (gamma-Al) is present and the adhesion of the coating to the support₂O₃) Usually more than 90%, so that gamma-Al₂O₃The stability of the solution is critical, and in the design of the solution, the solution is pure gamma-Al₂O₃For preventing gamma-Al at high temperature₂O₃To α -Al₂O₃Oxides of lanthanum, neodymium, yttrium elements converted as stabilizers and against gamma-Al₂O₃The specific surface area limit value of the catalyst is within a higher standard, the modified alumina with good stability and larger specific surface area under high temperature condition is obtained, the noble metal active component is favorably highly dispersed on a base layer consisting of the modified alumina and the cerium/zirconium mixed oxide, and the utilization rate of the noble metal active component is improved.

Preferably, the noble metal active component comprises one or more of platinum, palladium, rhodium.

Platinum or palladium is selected and mainly used for converting CO and HC, and has the advantages of low price, rich resources, good heat resistance and the like; rh is the main component for controlling the content of nitrogen oxide and can effectively treat NO_xAnd has good durability and is not easy to be poisoned.

Preferably, oxides of lanthanum, neodymium, yttrium and praseodymium are contained in the cerium/zirconium mixed oxide for improving the performance.

The invention has the following beneficial effects:

in the design of the scheme, the catalyst comprises a plurality of catalyst subareas with different precious metal active components and concentrations, each subarea comprises an aluminum oxide material with large surface area and high thermal stability, a rare earth composite oxide material with excellent oxygen storage and storage performance and other auxiliary agents, and the catalyst is coated on a common honeycomb ceramic carrier, so that the high dispersion and thermal stability of the precious metal active components on the subareas can be realized, and the catalyst is applied to an exhaust purifier, has lower ignition temperature, improved oxygen storage and storage performance and high-temperature thermal stability, and enables the automobile exhaust emission to meet the requirements of the emission standard of the national Liub.

Detailed Description

Examples

The three-effect catalyst for purifying the tail gas of the gasoline engine comprises a main catalyst coated on a honeycomb ceramic carrier and a pre-catalyst which is applied to the main catalyst and is in direct contact with the exhaust to be purified, wherein the main catalyst comprises a base layer A, a middle layer B and an outer layer C, and the specific mixture ratio is as follows:

base layer A: the base layer was composed of a catalyst containing 3.5% by weight of lanthanum oxide and having a specific surface area of 180 m²Per g, pore volume 0.5m³Alumina with a pore diameter of 40nm and/gContaining 1.0wt% of yttrium oxide and having a specific surface area of 70 m²Pore volume of 0.5 cm/g³Ce of 100nm pore diameter/g₁Is mixed to prepare, wherein, Ce₁Medium cerium oxide: zirconium oxide is 1:1, palladium nitrate is used as a noble metal precursor and is deposited on the base layer;

the composition of the base layer a is: 80g/L lanthanum oxide stabilized alumina, 60g/L Ce mixed yttria₁0.3g/L palladium (on all ingredients).

An intermediate layer B: the base layer was composed of a catalyst containing 3.0wt% of lanthanum oxide and having a specific surface area of 190 m²Per g, pore volume 0.6m³Alumina with a pore diameter of 20nm and a specific surface area of 80 m containing 1.0 wt.% of praseodymium oxide²Pore volume of 0.6 cm/g³Ce of 50nm pore size/g₁Is mixed to prepare, wherein, Ce₁Medium cerium oxide: zirconium oxide is 4:5, palladium nitrate and rhodium nitrate are used as noble metal precursors and are deposited on the base layer;

the composition of the intermediate layer B is: 70g/L lanthanum oxide stabilized alumina, 35g/L mixed praseodymium oxide Ce₁0.3g/L palladium (on all ingredients), 0.15g/L rhodium (on all ingredients).

An outer layer C: the base layer is composed of a material containing 2.5wt% of lanthanum oxide and having a specific surface area of 200m²Per g, pore volume 0.8m³Alumina with a pore diameter of 4 nm and a specific surface area of 100m containing 1.0 wt.% of neodymium oxide²Per g, pore volume 0.55cm³Ce of 10nm pore diameter/g₁Is mixed to prepare, wherein, Ce₁Medium cerium oxide: zirconium oxide is 6:5, palladium nitrate and rhodium nitrate are used as noble metal precursors and are deposited on the base layer;

the composition of the outer layer C is: 75g/L lanthanum oxide stabilized alumina, 75g/L mixed neodymium oxide Ce₁0.2g/L palladium (on all ingredients), 0.05g/L rhodium (on all ingredients).

The precatalyst comprises: the base layer I front area, the base layer I back area, the middle layer II front area, the middle layer II back area, the outer layer III front area and the outer layer III back area are specifically proportioned as follows:

base layer i front zone: base ofThe layer is composed of a layer containing 3.0wt% of lanthanum oxide and having a specific surface area of 200m²Per g, pore volume 0.6m³Alumina with a pore diameter of 20nm and a specific surface area of 95 m containing 0.5 wt.% of neodymium oxide²Pore volume of 0.5 cm/g³Ce of 20nm pore diameter/g₁Is mixed to prepare, wherein, Ce₁Medium cerium oxide: zirconium oxide is 6:5, palladium nitrate is used as a noble metal precursor and is deposited on the base layer;

the composition of the base layer I front region is: 80g/L lanthanum oxide stabilized alumina, 60g/L mixed neodymium oxide Ce₁0.5g/L palladium (on all ingredients).

Base layer i rear zone: the base layer was composed of a catalyst containing 3.0wt% of lanthanum oxide and having a specific surface area of 200m²Per g, pore volume 0.8m³Alumina with a pore diameter of 20nm and a specific surface area of 100m containing 0.5 wt.% of neodymium oxide²Pore volume of 0.6 cm/g³Ce of 10nm pore diameter/g₁Is mixed to prepare, wherein, Ce₁Medium cerium oxide: zirconium oxide is 4:5, palladium nitrate is used as a noble metal precursor and is deposited on the base layer;

the composition of the base layer I back zone is: 80g/L lanthanum oxide stabilized alumina, 40g/L mixed neodymium oxide Ce₁0.3g/L palladium (on all ingredients).

Front region of middle layer II: the base layer was composed of a catalyst containing 3.0wt% of lanthanum oxide and having a specific surface area of 200m²Per g, pore volume 0.8m³Alumina with a pore diameter of 20nm and a specific surface area of 100m containing 1.5 wt.% of neodymium oxide²Pore volume of 0.6 cm/g³Ce of 10nm pore diameter/g₁Is mixed to prepare, wherein, Ce₁Medium cerium oxide: zirconium oxide is 1:1, palladium nitrate and rhodium nitrate are used as noble metal precursors and are deposited on the base layer;

the composition of the front region of the middle layer II is: 80g/L lanthanum oxide stabilized alumina, 20g/L mixed neodymium oxide Ce₁0.85g/L palladium (on all ingredients), 0.06g/L rhodium (on all ingredients).

Zone after intermediate layer ii: the base layer was composed of a catalyst containing 3.0wt% of lanthanum oxide and having a specific surface area of 200m²Per g, pore volume 0.8m³Alumina with a pore diameter of 20nm and a specific surface area of 100m containing 1.5 wt.% of neodymium oxide²Pore volume of 0.6 cm/g³Ce of 10nm pore diameter/g₁Is mixed to prepare, wherein, Ce₁Medium cerium oxide: zirconium oxide is 1:1, palladium nitrate and rhodium nitrate are used as noble metal precursors and are deposited on the base layer;

the composition of the zone behind the intermediate layer II is: 80g/L lanthanum oxide stabilized alumina, 20g/L mixed neodymium oxide Ce₁0.75g/L palladium (on all ingredients), 0.05g/L rhodium (on all ingredients).

Front region of outer layer III: the base layer is composed of a material containing 2.5wt% of lanthanum oxide and having a specific surface area of 200m²Per g, pore volume 0.8m³Alumina with a pore diameter of 4 nm and a specific surface area of 100m containing 1.0 wt.% of lanthanum oxide²Per g, pore volume 0.55cm³Ce of 10nm pore diameter/g₁And Ce₂Is mixed to prepare, wherein, Ce₁Medium cerium oxide: zirconia is 6:5, Ce₂Medium cerium oxide: zirconium oxide is 4:5, palladium nitrate and rhodium nitrate are used as noble metal precursors and are deposited on the base layer;

the composition of the pro-region of outer layer III was: alumina stabilized by 80g/L lanthana, Ce of 60g/L mixed lanthana₁60g/L of mixed lanthanum oxide Ce₂0.375g/L palladium (on all ingredients), 0.025g/L rhodium (on all ingredients).

Outer zone III rear zone: the base layer is composed of a material containing 2.5wt% of lanthanum oxide and having a specific surface area of 200m²Per g, pore volume 0.8m³Alumina with a pore diameter of 4 nm and containing 1.0 wt.% of yttrium oxide and having a specific surface area of 100m²Per g, pore volume 0.55cm³Ce of 10nm pore diameter/g₁And Ce₂Is mixed to prepare, wherein, Ce₁Medium cerium oxide: zirconia is 6:5, Ce₂Medium cerium oxide: zirconium oxide is 4:5, palladium nitrate and rhodium nitrate are used as noble metal precursors and are deposited on the base layer;

the composition of the outer zone III rear section is: 80g/L lanthanum oxide stabilized alumina, 70g/L Ce mixed yttria₁50g/L of a mixtureCe of yttria₂0.0385g/L palladium (on all ingredients), 0.0125g/L rhodium (on all ingredients).

Coating a pre-catalyst and a main catalyst on a honeycomb ceramic carrier, packaging the honeycomb ceramic carrier into a purifier, and mounting the purifier on an engine bench to test the ignition temperature T50, wherein HC is less than or equal to 280^oC，CO≤270^oC，NO_x≤270^oC. After simulating 20 kilometres of durable aging, the test ignition temperature T50 is that HC is less than or equal to 390^oC，CO≤390^oC，NO_x≤390^oC. After being installed on the whole vehicle (matched with a 1.5L engine), the emission results of the I-type test of the whole vehicle are shown in the following table:

test result of vehicle emission type I and catalyst conversion efficiency

After aging, the finished vehicle type I test emission results are shown in the following table:

from the above data, it can be seen that the system of this example is applicable to THC, NMHC and NO_xThe purification effect of CO is good, and the purification effect after aging also meets the requirement of the emission standard of the national Liu B.

Comparative example

Main catalyst: the difference from the embodiment 1 is that the main catalyst is not layered, and the content of the noble metal is the total amount of the noble metal in the main catalyst in the embodiment 1;

pre-catalyst: the difference from the example 1 is that the precatalyst is not layered and zoned, and the content of the noble metal is the total amount of the noble metal in the precatalyst in the example 1;

repeatedly coating (repeating for at least 3 times) the main catalyst and the pre-catalyst on the honeycomb ceramic carrier, wherein the quality of the coating is the same as that in the embodiment 1, packaging the main catalyst and the pre-catalyst into a purifier, and mounting the purifier on an engine bench to test the ignition temperature T50, wherein HC is less than or equal to 290^oC，CO≤290^oC，NO_x≤280^oC. After simulating 20 kilometres of durable aging, testing the ignition temperature T50 and HC less than or equal to 420^oC，CO≤420^oC，NO_x≤420^oC. After being installed on the whole vehicle (matched with a 1.5L engine), the emission results of the I-type test of the whole vehicle are shown in the following table:

after aging, the finished vehicle type I test emission results are shown in the following table:

as is clear from the results of the examples and comparative examples, the results of the comparative examples were found to be for THC, NMHC and NO_xThe purification effect of CO was not as good as that of the example, and the degradation of the purification effect after aging was significant, which proved that the thermal stability of the catalyst was not good, probably due to the poor dispersion of the noble metal active ingredient caused by the non-zoned precatalyst.

The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.

Claims (10)

1. The three-way catalyst for purifying the tail gas of the gasoline engine as claimed in claim 1, which comprises a pre-catalyst, wherein the pre-catalyst comprises a base layer I containing modified alumina, cerium/zirconium mixed oxide and noble metal active component, and an intermediate layer II and an outer layer III having the same main components as the base layer I, the intermediate layer II and the outer layer III respectively comprise a front region and a rear region, and the content of the noble metal active component in the front region of each layer is greater than that in the rear region.

2. The three-way catalyst for purifying the tail gas of the gasoline engine as claimed in claim 1, which comprises a main catalyst, wherein the main catalyst comprises a base layer A containing modified alumina, cerium/zirconium mixed oxide and precious metal active components, and an intermediate layer B and an outer layer C which have the same main components as the base layer A, and the content of the precious metal active components in the intermediate layer B is greater than that in the base layer A or the outer layer C.

3. The three-way catalyst for purifying the tail gas of the gasoline engine as claimed in any one of claims 1 or 2, wherein the cerium/zirconium mixed oxide comprises:

Ce₁: the mass ratio of the cerium oxide to the zirconium oxide is 0.8-1.2;

Ce₂: the mass ratio of the cerium oxide to the zirconium oxide is 0.6-0.8.

4. The three-way catalyst for purifying tail gas of gasoline engines as claimed in claim 3, wherein the Ce is₁Or Ce₂The specific surface area of (A) is 70-100 m²Per g, pore volume of 0.5-0.6 cm³The pore diameter is 10-100 nm.

5. The three-way catalyst for purifying tail gas of gasoline engines as claimed in claim 4, wherein the Ce is₁Or Ce₂Aging at 1000 deg.C to specific surface area of 40m or more²G, aging at 1100 deg.C, and specific surface area of not less than 20m²/g。

6. The three-way catalyst for purifying the tail gas of the gasoline engine as claimed in any one of claims 1 or 2, wherein the specific surface area of the modified alumina is 160-260 m²Per g, pore volume of 0.3-0.8 cm³The pore diameter is 0.5-100 nm.

7. The three-way catalyst for purifying the tail gas of the gasoline engine as claimed in claim 6, wherein the specific surface area of the modified alumina is 180-200 m²Per g, pore volume of 0.5-0.8 cm³The pore diameter is 4-40 nm, and the specific surface area is more than or equal to 40m after aging at 1200 DEG C²/g。

8. The three-way catalyst for purifying the tail gas of the gasoline engine as claimed in claim 1, wherein the noble metal active component comprises one or more of platinum, palladium and rhodium.

9. The three-way catalyst for purifying the tail gas of the gasoline engine as claimed in claim 1, wherein the modified alumina is a rare earth modified alumina material, and the rare earth elements comprise lanthanum, neodymium and yttrium.

10. The three-way catalyst for purifying the tail gas of the gasoline engine as claimed in claim 1, wherein the cerium/zirconium mixed oxide contains oxides of lanthanum, neodymium, yttrium and praseodymium.