DE102015118097A1 - Catalyst Design for a Selective Catalytic Reduction Filter (SCR) - Google Patents

Abstract

An improved selective catalytic reduction (SCRF) filter apparatus is provided which separates a reduction of nitrogen oxides (NOx) from an oxidation of soot, hydrocarbon (HC), and carbon monoxide (CO). The SCRF apparatus includes a diesel oxidation catalyst unit for oxidizing HC and CO and for oxidizing diesel fuel to promote DPF regeneration, and an SCR filter unit having at least one intake port and connected to the diesel oxidation catalyst unit to provide a (soot) catalyst. ) To control emission, purify hatched HC and CO during a DPF regeneration and to reduce nitrogen oxides in the diesel exhaust. At least one inlet channel is coated with an ammonia-neutral oxidation catalyst, and at least one outlet channel is coated with a selective catalytic reduction catalyst.

Description

FIELD OF THE PRESENT TECHNOLOGY

The present technology generally relates to a diesel exhaust emission control. More specifically, the present technology relates to the simultaneous control of nitrogen oxides (NOx), particulate matter (PM), carbon monoxide (CO), and hydrocarbons (HC) using an innovative SCR filter (SCRF).

BACKGROUND OF THE PRESENT TECHNOLOGY

In a diesel engine, the exhaust gas must be treated properly to remove harmful contaminants from release to the atmosphere. The exhaust gas passes through a catalytic converter system comprising a DOC (Diesel Oxidation Catalyst), an SCR filter (SCRF) and a selective catalytic reduction (SCR) catalyst. The DOC oxidizes carbon monoxide (CO) and hydrocarbons (HC) and nitrogen monoxide (NO) to nitrogen dioxide (NO ₂ ). The DOC also behaves like a "diesel burner" to oxidize the injected diesel fuel to produce exothermic energy to support periodic soot oxidation or diesel particulate filter (DPF) regeneration. The SCRF is a combination of SCR and DPF technologies.

A diesel exhaust fluid injection (DEF) system injects a urea solution into the exhaust gas to provide ammonia (NH ₃ ) to reduce nitrogen oxides (NOx) to safe nitrogen and water in the presence of the SCR catalyst. Diesel exhaust contains relatively high levels of particulate matter (PM), also known as soot. The catalytic converter generally can not remove elemental carbon, such as carbon black. Soot is usually cleaned by the DPF. The DPF must be regenerated by burning off the soot that has accumulated in the DPF at temperatures greater than 500 ° C. The SCR is an individual catalytic converter that reduces the residual nitrogen oxides (NOx) from the exhaust gas by ammonia (NH ₃ ).

The catalytic converter system containing the SCRF, although removing harmful emission components, is due to the low DPF regeneration efficiency, poor CO and HC purification activities of the SCRF during a DPF regeneration process, and potential contamination of the SCR catalyst by ash poisoning, HC -Carbage, soot unloading, etc. not optimally efficient. The present technology is primarily directed to an improved exhaust treatment system through an innovative catalyst design of the SCRF.

SUMMARY OF EMBODIMENTS OF TECHNOLOGY

The present technology has a highly efficient diesel exhaust treatment system that includes a SCRF that improves DPF regeneration efficiency, NOx reduction reliability, and CO and HC purification activities during DPF regeneration.

In one embodiment, the present technology includes a diesel exhaust treatment device including a diesel oxidation catalyst unit for receiving diesel exhaust gas and a selective catalytic reduction (SCRF) filter unit having at least one inlet channel and connected to the diesel oxidation catalyst unit to oxidize CO and HC, nitrogen oxides (NOx) and to control PM emission in the diesel exhaust, wherein at least one inlet channel is coated with an ammonia (NH3) neutral oxidation catalyst and at least one outlet channel with a catalyst for selective catalytic reduction (SCR) using ammonia ( NH3) is coated for NOx reduction.

In another embodiment, the present technology comprises a selective catalytic reduction (SCRF) filter including at least one inlet duct for receiving the diesel exhaust gas and at least one outlet duct connected to the plurality of inlet ducts, the at least one inlet duct having one ammonia-neutral oxidation catalyst is coated and the at least one outlet channel with a catalyst for selective catalytic reduction (SCR) is coated.

In yet another embodiment, the present technology includes a method of improving the reduction of nitrogen oxides (NOx) from diesel exhaust, which includes receiving the diesel exhaust, the diesel exhaust with ammonia (NH3) or DEF (urea) solution as one Ammonia source is fed into a selective catalytic reduction (SCRF) filter apparatus having a plurality of inlet channels coated with an ammonia neutral oxidation catalyst and all of the respective outlet channels are coated with a selective catalytic reduction catalyst, ammonia being passed through the inlet channels to the outlet channels and nitrogen oxides (NOx) in the exhaust passages of the SCRF.

In an additional embodiment, the present technology also includes A method of improving DPF regeneration efficiency with an ammonia neutral oxidation catalyst coated on all inlet channels wherein carbon black (or PM) is continuously deposited or accumulated over time prior to performing DPF regeneration. Moreover, with the given oxidation catalyst, residual CO and HC emissions can be oxidized to effectively reduce exhaust CO and HC emissions during DPF regeneration.

Other features and advantages of the technology as well as the construction and operation of various embodiments of the technology are described in detail below with reference to the accompanying drawings. It should be noted that the technology is not limited to the specific embodiments described herein. Thus, the embodiments are shown herein for illustrative purposes only. Additional embodiments will be apparent to those skilled in the art based on the teachings contained herein.

Brief description of the drawings

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate the present technology and, together with the description, further serve to explain the principles of the technology and to enable one skilled in the art to make and use the technology.

1 is a representation of a catalytic converter;

2 FIG. 13 is a schematic of a prior art SCR filter design; FIG.

3 Figure 12 is a schematic of an SCR filter of the present technology; and

4 Figure 3 is a graph showing performance of ammonia (NH3) neutral catalysts that can be used in a SCR filter of the technology.

Detailed description of embodiments of the technology

While the present technology is described herein with illustrative embodiments for particular applications, it should be understood that the technology is not so limited. Those skilled in the art to which the teachings provided herein recognize additional modifications, applications, and embodiments within the scope thereof, as well as additional fields in which the technology is of significant use. Features described in various embodiments described in the present application may be combined.

1 is a representation of an aftertreatment system 100 for treating exhaust gas in a diesel engine. The given system or similar system may also be used to treat a lean-burn gasoline engine. The exhaust 102 gets into the diesel oxidation catalyst (DOC) 110 enters or enters and passes through a tube so that it has a selective catalytic reduction (SCRF) filter (SCRF). 106 reached. The SCRF represents a combination of SCR and DPF technologies and controls both NOx and particulate matter (both PM and soot) emissions simultaneously. After filtering by the SCRF, the exhaust gas reaches the SCR catalyst 104 where more NOx is removed by reduction.

In the system 100 reduces the SCR catalyst 104 NOx using ammonia (NH3). The ammonia gets into the system 100 through a urea solution, eg. B. a solution for diesel exhaust fluid (DEF) introduced into the exhaust gas flow through a DEF injector 108 is injected. The urea solution mixes with the hot exhaust gas and generates ammonia (NH3), which is a means of reducing NOx in the exhaust gas. Both the inlet and outlet ports of the SCRF 106 are coated with SCR catalyst; however, the DPF substrate of the SCRF 106 be coated with excess SCR catalyst, since the excess coating would build up a back pressure for the diesel engine. Thus, it is generally preferred that a downstream SCR converter 104 is installed. The downstream SCR converter also reduces the residual NOx with ammonia.

During DPF regeneration, the DOC is used to oxidize the injected diesel fuel to produce exothermic energy (heat) to burn off soot that builds up in the intake passages of a SCRF 106 has accumulated. However, some residual KW and CO slip out of the DOC 110 upon oxidation of the injected diesel fuel. If the exhaust gas mixed with HC and CO is out of the DOC 110 slips and the NH3 generated from the urea solution moves through the exhaust system and into the SCRF 106 arrives, removes the SCRF 106 NOx from the exhaust. However, the SCRF 106 does not effectively remove KW and CO since the SCRF 106 with no catalyst agent to effectively oxidize HC and CO. For this purpose, a purification catalyst (in 1 not shown) on the exhaust to remove the remaining HC and CO.

When the exhaust gas with the urea solution through the DPF injector 108 ammonia produced from the urea solution reduces NOx in the SCRF 106 , As NOx is reduced, soot is also generated in the intake ports of the SCRF 106 accumulates. Thus, DPF regeneration is periodically performed while the diesel fuel is exhausted 100 is injected and the DOC 110 burns the injected diesel fuel to burn off the soot. However, a typical SCR catalyst is not effective in oxidizing carbon black during DPF regeneration, and this results in incomplete DPF regeneration. The inefficient DPF regeneration, in turn, increases fuel consumption and increases the likelihood of uncontrolled DPF regeneration.

2 is a schematic representation of a conventional SCRF 200 for processing diesel exhaust. exhaust 202 flows into the inlet channels 210 of the SCRF 200 , The inlet channels 210 are with an SCR catalyst 206 coated, such as a zeolite SCR catalyst. The exhaust 202 is mixed with ammonia generated from the urea solution to reduce NOx in the SCRF; In the meantime, exhaust soot is in the intake passages of the SCRF 200 deposited, and the soot filtered exhaust gas 202 enters through the outlet channel 208 out. The SCRF 200 with the urea can simultaneously control NOx and PM emissions in the diesel exhaust; however, a typical urea-SCR catalyst, such as a zeolite based SCR, is inactive in the oxidation of hydrocarbon (HC) and carbon monoxide (CO) at low exhaust gas temperature (<350 ° C). Moreover, an SCR catalyst for catalyzing soot oxidation during DPF regeneration is relatively inactive, resulting in low DPF regeneration efficiency.

Due to soot build-up within the SCRF 200 The efficiency of NOx removal can be enhanced by a urea SCR catalyst attached to the intake ports 210 may be reduced, and the durability of the SCR catalyst may be affected by contamination from HC coking and ash deposits. The soot build-up also requires periodic DPF regeneration. During DPF regeneration, diesel fuel is injected into the exhaust gas and the soot is burned off. If soot accumulation occurs at a higher rate, more frequent DPF regeneration is required and, as a result, uncontrolled DPF regeneration is more likely to be affected by driving conditions.

The shortcomings of the SCRF of 2 are overcome by an improved design of the SCRF catalyst according to the present technology. 3 is a schematic representation of an improved SCRF 300 , The inlet channels 310 this SCRF are compatible with an ammonia-neutral oxidation catalyst (ANOC) 306 coated. The ANOC 306 is basically inactive or non-selective to ammonia oxidation when the temperature is below 400 ° C, but retains below 400 ° C the capability of HC and CO oxidation as a specific type of DOC catalyst. By coating the inlet channels 310 with a washcoat of ANOC catalyst 306 For example, the ammonia generated via an injection of DEF (urea solution) can safely pass through the intake ports 310 without oxidation, if the temperature is lower than 400 ° C, penetrate. The outlet channels 312 of the new SCRF are coated with a washcoat of a urea SCR catalyst, such as a zeolite based SCR.

As in 3 is shown, the exhaust gas flows 302 with ammonia into the inlet channels 304 of the SCRF 300 and the ammonia can pass through the channels with ANOC 306 are coated, flow and the outlet channels 308 to reach. In the outlet channels 308 The ammonia reduces nitrogen oxides (NOx) of the exhaust gas in the presence of the SCR catalyst 106 before the exhaust gas is released. The SCR catalyst is not consumed during the reduction of NOx. When the exhaust gas flows into the inlet connected to ANOC 306 is coated, occurs a HC and CO oxidation as well as soot deposition, HC coking and ash accumulation. The NOx in the exhaust gas flows substantially unaffected by the intake passages 310 and reaches the outlet channels 312 that with the SCR catalyst 106 are coated. The activity of SCR NOx reduction takes place more reliably in the exhaust ducts because NOx reduction takes place separately from soot separation, HC coking and ash accumulation.

Because the reduction of NOx in the exhaust ducts 312 occurs when the exhaust gas flows through the exhaust ports, and soot deposition, HC coking and ash accumulation mostly in the intake ports 310 occur, contamination of the SCR washcoat in the outlet channels 312 prevented by ash as well as a masking by KW coking. As a result, the reliability and durability of the SCRF 300 increased.

In the improved SCRF catalyst design, DPF regeneration efficiency is enhanced by an ammonia neutral oxidation catalyst (ANOC) along with more effective HC and CO slip control. As a result, lower fuel consumption of the vehicle can be realized, and DPF regeneration must be performed less frequently, thereby reducing the chance that DPF regeneration will be affected by vehicle driving conditions such as uncontrolled DPF regeneration in an idle state.

4 is a diagram 400 showing the performance of ammonia-neutral catalysts in conjunction with the present technology. The X-axis indicates an inlet temperature in degrees Celsius (° C) of ammonia-neutral catalysts having a reference DOC catalyst. The left Y axis indicates a percentage of conversion of ammonia (NH3) and the right Y axis indicates a percentage to recreate the nitrogen oxides (NOx) via ammonia oxidation.

The columns 402 represent a performance of a conventional DOC at different temperatures. The columns 404 represent a performance of an improved ammonia-neutral oxidation catalyst (ANOC) at various temperatures. As can be seen, NOx re-formation does not start until the temperature approaches about 400 ° C for a given ANOC. In contrast, ammonia (NH3) conversion and NOx recharge begins for the typical DOC at a much lower temperature of about 250 ° C.

It should be noted that the portions of the detailed description and not the portions of the compilation and summary are intended to be used to interpret the claims. The Summary and Summary sections may represent one or more (but not all of the exemplary embodiments of the present technology as intended by the inventor (s)), and thus are not intended to be construed as limiting the present technology and the appended claims It is within the scope of the technology that various embodiments described in the present specification may be combined.

Claims (10)

Exhaust treatment device, comprising: a diesel oxidation catalyst unit for receiving exhaust gas; and a selective catalytic reduction filter unit having at least one inlet passage and connected to the diesel oxidation catalyst unit for oxidizing hydrocarbon and carbon monoxide, reducing nitrogen oxide, and controlling particulate matter emission in the exhaust gas; wherein the at least one inlet channel is coated with an ammonia-neutral oxidation catalyst. The exhaust treatment device of claim 1, further comprising at least one exhaust passage coated with a selective catalytic reduction catalyst. The exhaust treatment apparatus according to claim 1, further comprising a selective catalytic reduction catalyst connected to the selective catalytic reduction filter unit for reducing nitrogen oxides. The exhaust treatment device according to claim 1, further comprising a diesel exhaust gas injection device for injecting a urea solution into the exhaust gas. The exhaust treatment device according to claim 4, wherein the diesel exhaust fluid injection device is disposed between the diesel oxidation catalyst unit and the selective catalytic reduction filter unit. Filter with selective catalytic reduction, comprising: at least one inlet channel for receiving exhaust gas; and at least one outlet channel connected to the at least one inlet channel, wherein the at least one inlet channel is coated with an ammonia-neutral oxidation catalyst. The selective catalytic reduction filter of claim 6, wherein the at least one exhaust passage is coated with a selective catalytic reduction catalyst. A method of reducing nitrogen oxides from an exhaust gas, comprising: supplying an exhaust gas with ammonia into a selective catalytic reduction filter device comprising at least one inlet channel coated with an ammonia-neutral oxidation catalyst and at least one outlet channel coated with a selective catalytic reduction catalyst; the ammonia is passed through the at least one inlet channel to the at least one outlet channel; and in the at least one outlet channel nitrogen oxides are reduced in the exhaust gas. The method of claim 8, further comprising injecting a urea solution into the exhaust gas to produce the ammonia. The method of claim 8, further comprising that in the at least one inlet channel Hydrocarbon and carbon monoxide are oxidized in the exhaust gas.

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