Diesel engine tail gas treatment system based on low noble metal oxidation catalysis

Abstract

The utility model relates to the technical field of tail gas treatment, in particular to a diesel engine tail gas treatment system based on low noble metal oxidation catalysis, which comprises a catalytic oxidation unit, a particle trap and a selective catalytic reduction unit which are sequentially mounted on an exhaust pipeline according to the exhaust direction, a honeycomb carrier is arranged in the catalytic oxidation unit, and a plating layer coated on the surface of the honeycomb carrier is arranged in a pore channel of the honeycomb carrier; wherein the plating layer comprises an oxidation layer, a transition layer and a reduction layer which are sequentially distributed in the tail gas flow direction. An oxidation layer and a reduction layer which are partitioned are arranged in a honeycomb carrier in a catalytic oxidation unit, in the low-temperature stage, CO / HC is rapidly oxidized through nano-particles of the oxidation layer, the temperature is increased to the ignition temperature of the reduction layer, in the medium-high-temperature stage, airflow is stabilized through a transition section, NOx and intermediate products are cooperatively treated through an adsorption layer and a reaction layer of the reduction layer, the conversion rate of NOx is increased, and the catalytic oxidation efficiency is improved. And the comprehensive conversion efficiency of CO, HC and NOx at low temperature is improved while the usage amount of precious metal is reduced.

Description

Technical Field

[0001] This utility model relates to the field of exhaust gas treatment technology, and more specifically to a diesel engine exhaust gas treatment system based on low-precious metal oxidation catalysis. Background Technology

[0002] The diesel engine exhaust treatment system with low precious metal oxidation catalysis mainly consists of a diesel oxidation catalyst (DOC), a diesel particulate filter (DPF), a selective catalytic reduction system (SCR), and an ammonia leak catalyst (ASC).

[0003] Diesel oxidation catalysts (DOCs) accelerate the oxidation of carbon monoxide and hydrocarbons to produce carbon dioxide and water by using an internal oxidation catalyst (typically coated with precious metals such as platinum, palladium, and rhodium). This process also promotes the reaction of nitric oxide and oxygen in nitrogen oxides to produce nitrogen dioxide, releasing heat to accelerate the reactions in downstream diesel particulate filters (DPFs) and selective catalytic reduction (SCRs). The rare metals in the diesel particulate filter (DPF) react with particulate matter in the exhaust gas, decomposing and adsorbing the particles, thus reducing the amount of particulate matter emitted. Selective catalytic reduction (SCR) involves injecting urea into the catalyst, causing it to decompose into ammonia. The ammonia then reacts with nitrogen oxides in the catalyst to produce nitrogen and water.

[0004] Precious metal oxidation catalysts play an important role in diesel engine exhaust gas treatment. They can convert harmful substances in exhaust gas into harmless substances, thereby reducing exhaust gas pollution.

[0005] However, precious metal oxidation catalysts are expensive, which increases the cost of exhaust gas treatment. Therefore, people hope to develop a diesel engine exhaust gas treatment system with low precious metal oxidation catalysis. However, the reduction of precious metals may lead to insufficient low-temperature activity. How to overcome the insufficient low-temperature activity is an urgent problem to be solved. Utility Model Content

[0006] To address the technical problems existing in the exhaust gas treatment system of the prior art, this utility model proposes a diesel engine exhaust gas treatment system based on low precious metal oxidation catalysis, including a catalytic oxidation unit, a particulate filter and a selective catalytic reduction unit installed in sequence in the exhaust pipe according to the exhaust direction;

[0007] The catalytic oxidation unit is provided with a honeycomb carrier, and the channels of the honeycomb carrier are provided with a coating on its surface.

[0008] The coating includes an oxide layer, a transition layer, and a reduction layer distributed sequentially along the exhaust gas flow direction. The oxide layer is used to oxidize carbon monoxide, hydrocarbons, and nitric oxide in the exhaust gas, and the reduction layer is used to convert nitric oxide and nitrogen dioxide into nitrogen and water.

[0009] Preferably, the oxide layer includes a carrier layer and an active layer, wherein the carrier layer has a porous structure and the active layer includes nanoparticles uniformly dispersed in the carrier layer.

[0010] Preferably, the support layer comprises an Al2O3 or TiO2 mesoporous structure layer, and the nanoparticles comprise supported nanocatalytic nanoparticles.

[0011] Preferably, the reduction layer includes a reaction layer and an adsorption layer, the reaction layer includes a multi-channel three-dimensional network structure, and the adsorption layer includes a microporous-mesoporous hierarchical pore structure.

[0012] Preferably, the adsorption layer comprises Cu-SSZ-13 molecular sieve or Fe-ZSM-5 molecular sieve.

[0013] Preferably, the oxide layer accounts for 25% of the total length of the cellular carrier, the transition layer accounts for 5% of the total length of the cellular carrier, and the reduction layer accounts for 70% of the total length of the cellular carrier.

[0014] Preferably, the thickness ratio of the oxide layer to the reduction layer is 1:2 to 1:3.

[0015] Preferably, the transition layer has a stepped gradient pore structure, with its porosity gradually decreasing from the oxide layer to the reduction layer, and the porosity variation range being 70% to 30%.

[0016] Compared with the prior art, the advantages of this utility model are:

[0017] This application sets up partitioned oxide and reduction layers within a honeycomb carrier in a catalytic oxidation unit. In the low-temperature stage, the nanoparticles of the oxide layer rapidly oxidize CO / HC, raising the temperature to the ignition temperature of the reduction layer. In the medium- and high-temperature stages, the airflow is stabilized through a transition section. The adsorption layer and reaction layer of the reduction layer synergistically process NOx and intermediate products, improving the NOx conversion rate. This reduces the amount of precious metals used while improving the overall conversion efficiency of CO, HC, and NOx at low temperatures. Attached Figure Description

[0018] The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component shown in the various figures may be denoted by the same reference numeral. For clarity, not every component is labeled in each figure. Embodiments of various aspects of the present invention will now be described by way of example and with reference to the accompanying drawings, wherein:

[0019] Figure 1 This is a schematic diagram of the structure of the diesel engine exhaust gas treatment system based on low precious metal oxidation catalysis shown in this utility model;

[0020] Figure 2This is a schematic diagram of the structure of the catalytic oxidation unit shown in this utility model;

[0021] Figure 3 This is a schematic diagram of the structure of the oxide layer shown in this utility model;

[0022] Figure 4 This is a schematic diagram of the structure of the reduction layer shown in this utility model. Detailed Implementation

[0023] To better understand the technical content of this utility model, specific embodiments are provided below in conjunction with the accompanying drawings.

[0024] Combination Figure 1 As shown, this utility model proposes a diesel engine exhaust gas treatment system based on low precious metal oxidation catalysis, including a catalytic oxidation unit 10, a particulate filter 20 and a selective catalytic reduction unit 30 installed sequentially in the exhaust pipe 100 in the exhaust direction.

[0025] It should be understood that diesel combustion produces exhaust gases, the main pollutants of which include CO, HC, NOx, and particulate matter (PM). Due to the reduction of precious metal catalysts, the low-temperature activity is insufficient. In this application, by improving the overall conversion efficiency of CO, HC, and NOx at low temperatures in the catalytic oxidation unit 10, and by providing heat for DPF regeneration through the exothermic reaction of DOC, it is beneficial to burn off the particulate matter captured by the particulate trap 20, and also beneficial to improve the low-temperature efficiency of the selective catalytic reduction unit 30 through the NO2 generated by the catalytic oxidation unit 10.

[0026] Furthermore, a honeycomb carrier 11 is provided in the catalytic oxidation unit 10, and a coating is provided on the surface of the honeycomb carrier 11 through the channels 111.

[0027] Optionally, the honeycomb carrier 11 includes cordierite honeycomb ceramic, which has pores of 400 to 600 mesh.

[0028] The coating includes an oxide layer 12, a transition layer 13, and a reduction layer 14 distributed sequentially along the exhaust gas flow direction. The oxide layer 12 is used to oxidize carbon monoxide, hydrocarbons, and nitric oxide in the exhaust gas, and the reduction layer 14 is used to convert nitric oxide and nitrogen dioxide into nitrogen and water.

[0029] Thus, by utilizing the layered design of oxide layer 12 and reduction layer 14, a synergistic oxidation-reduction pathway is formed, which reduces the reaction energy barrier in stages and improves the overall conversion efficiency of CO, HC and NOx at low temperatures.

[0030] at the same time,

[0031] Specifically, at low temperatures (<200℃), CO and HC are first partially oxidized in the oxide layer 12, and intermediate products (such as aldehydes) are further reacted in the reduction layer, reducing the overall activation energy.

[0032] In an optional embodiment, the oxide layer 12 includes a carrier layer 121 and an active layer 122. The carrier layer 121 has a porous structure, the active layer includes nanoparticles uniformly dispersed in the carrier layer 121, and the active layer 122 is located on the outer layer of the carrier layer 121.

[0033] Among them, nanoparticles include supported nanocatalytic nanoparticles.

[0034] Specifically, low-noble metals (such as 0.5–1.0 wt% Pt or Pd) are loaded onto oxygen storage materials (e.g., CeO2-ZrO2 composite oxides), wherein Pt or Pd is dispersed in nanoparticles of 2–3 nm or in single-atom form to improve atom utilization and facilitate the transfer of oxygen through CeO2. 3+ / Ce 4+ It cyclically releases lattice oxygen, enhancing low-temperature oxidation activity.

[0035] The carrier layer 121 comprises an Al2O3 or TiO2 mesoporous structure layer with a pore size of 10–20 nm. Thus, by employing a high specific surface area mesoporous material to provide three-dimensional diffusion channels, the contact efficiency of the reactants is enhanced.

[0036] In this way, the low-temperature reaction can be quickly initiated through the oxide layer to complete the initial oxidation of CO / HC and generate some NO2 for downstream use.

[0037] Furthermore, the reduction layer 14 includes a reaction layer 141 and an adsorption layer 142. The reaction layer 141 includes a multi-channel three-dimensional network structure, and the adsorption layer 142 includes a microporous-mesoporous hierarchical pore structure, wherein the adsorption layer 142 is located on the outer layer of the reaction layer 141.

[0038] In an optional embodiment, the adsorption layer 142 comprises Cu-SSZ-13 molecular sieve or Fe-ZSM-5 molecular sieve, and the pore size of the adsorption layer 142 is 0.5 to 20 nm.

[0039] In this process, Cu-SSZ-13 or Fe-ZSM-5 molecular sieves activate intermediate products through acidic sites and transfer them to reaction layer 141 for deep reduction, converting NOx into N2. The multi-channel three-dimensional network structure provided by reaction layer 141 can form a circuitous path to prolong residence and reaction time.

[0040] As described above, the oxide layer 12 is located upstream, where low-temperature oxidation is achieved through low-noble metal nanoparticles and mesoporous carriers. The reduction layer 14 is located downstream, where intermediate products are adsorbed and pre-activated through molecular sieve catalysis, and then deeply reduced by the reaction layer 141 to convert NOx into N2.

[0041] In the above embodiments, the oxide layer 12 accounts for 25% of the total length of the cellular carrier 11, the transition layer 13 accounts for 5% of the total length of the cellular carrier 11, and the reduction layer 14 accounts for 70% of the total length of the cellular carrier 11.

[0042] In this way, the low-temperature ignition is completed in a short distance through the oxide layer 12 at the front, and the reduction layer 14 at the rear allows NOx to have a longer residence time, thereby improving the NOx conversion rate.

[0043] Optionally, the thickness ratio of oxide layer 12 to reduction layer 14 is 1:2 to 1:3.

[0044] Preferably, the transition layer 13 has a stepped gradient pore structure, and its porosity gradually decreases from the oxide layer 3 to the reduction layer 4, with a porosity range of 70% to 30%.

[0045] Thus, the stepped, gradually changing pore structure buffers the differences in physical / chemical properties between the oxide layer 12 and the pre-reduction layer 14, preventing interlayer peeling, and guides the airflow to transition smoothly through the gradual change in porosity, reducing reaction interference.

[0046] In conjunction with the above embodiments, this application provides partitioned oxide and reduction layers within the honeycomb carrier in the catalytic oxidation unit. In the low-temperature stage, the nanoparticles of the oxide layer rapidly oxidize CO / HC, raising the temperature to the ignition temperature of the reduction layer. In the medium- and high-temperature stages, the airflow is stabilized through a transition section. The adsorption layer and reaction layer of the reduction layer synergistically process NOx and intermediate products, improving the NOx conversion rate. This reduces the amount of precious metals used while enhancing the overall conversion efficiency of CO, HC, and NOx at low temperatures.

[0047] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Those skilled in the art to which this invention pertains can make various modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of this invention shall be determined by the claims.

Claims

1. A diesel engine exhaust treatment system based on low noble metal oxidation catalysis, characterized in that, The catalytic oxidation unit (10), the particle trap (20) and the selective catalytic reduction unit (30) are sequentially arranged in the exhaust pipe (100) in the exhaust direction; The honeycomb carrier (11) is arranged in the catalytic oxidation unit (10), and a plating layer coated on the surface of the honeycomb carrier (11) is arranged in the channel of the honeycomb carrier (11); The plating layer includes an oxidation layer (12), a transition layer (13) and a reduction layer (14) arranged in the exhaust gas flow direction in sequence, the oxidation layer (12) is used for oxidizing carbon monoxide, hydrocarbons and nitrogen monoxide in the exhaust gas, and the reduction layer (14) is used for converting nitrogen monoxide and nitrogen dioxide into nitrogen and water.

2. The low noble metal oxidation catalysis-based diesel engine exhaust treatment system according to claim 1, characterized by, The oxidation layer (12) includes a carrier layer (121) and an active layer (122), the carrier layer (121) is a porous structure, and the active layer includes nanoparticles uniformly dispersed in the carrier layer (121).

3. The low noble metal oxidation catalytic based diesel engine exhaust treatment system of claim 2, wherein, The carrier layer (121) includes an Al2O3 or TiO2 mesoporous structure layer, and the nanoparticles include supported nanocatalyst particles.

4. The low noble metal oxidation catalysis-based diesel engine exhaust treatment system according to claim 1, characterized by, The reduction layer (14) includes a reaction layer (141) and an adsorption layer (142), the reaction layer (141) includes a multi-channel three-dimensional network structure, and the adsorption layer (142) includes a microporous-mesoporous hierarchical pore structure.

5. The low noble metal oxidation catalytic based diesel engine exhaust treatment system of claim 4, wherein, The adsorption layer (142) includes Cu-SSZ-13 molecular sieve or Fe-ZSM-5 molecular sieve.

6. The low noble metal oxidation catalysis-based diesel engine exhaust treatment system according to claim 1, characterized in that, The oxidation layer (12) accounts for 25% of the total length of the honeycomb carrier (11), the transition layer (13) accounts for 5% of the total length of the honeycomb carrier (11), and the reduction layer (14) accounts for 70% of the total length of the honeycomb carrier (11).

7. The low noble metal oxidation catalysis based diesel engine exhaust treatment system according to claim 1, wherein, The thickness ratio of the oxidation layer (12) to the reduction layer (14) is 1:2-1:

3.

8. The low noble metal oxidation catalysis based diesel engine exhaust treatment system according to claim 1, characterized in that, The transition layer (13) is a stepped gradient pore structure, the porosity gradually decreases from the oxidation layer (12) to the reduction layer (14), and the porosity change range is 70%-30%.

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