KR20100016947A - Novel scr catalysts and after-treatment devices for diesel engine exhaust gas - Google Patents

Abstract

PURPOSE: An SCR catalyst composition and an exhaust gas ejecting device using the same is provided to reach desired NOx conversion rate without oxidation catalyst and improve low-temperature activity. CONSTITUTION: An exhaust gas ejecting device using SCR catalyst composition comprises an SCR(Selective Catalytic Reduction) catalytic module, an oxidation catalyst module, and a CSF(Catalyzed Soot Filter) module. The SCR catalytic module comprises an injection unit positioned on the lower part of the diesel engine. The oxidation catalyst module is positioned on the lower part of the catalytic module. The CSF module is successively and serially positioned.

Description

Noc SCR catalysts and after-treatment devices for diesel engine exhaust gas with improved NOC conversion

The present invention relates to an SCR catalyst composition having improved NOx conversion rate and a diesel engine exhaust gas after-treatment apparatus using the same, and more particularly, to an SCR catalyst composition having an ability to effectively convert NOx generated from an engine into a harmless component. And it relates to an exhaust gas discharge device with improved diesel engine exhaust gas purification capacity, in particular nitrogen oxide purification capacity using the same.

Diesel engines have excellent utility as vehicle powertrains due to their inherent high thermal efficiency (i.e. good fuel economy) and high torque at low speeds, and diesel engines have high A under very fuel-lean conditions. / F (air to fuel) drive in rain For this reason, diesel engines have good hydrocarbon and carbon monoxide conversion rates, but diesel emissions have high emissions of nitrogen oxides (NOx) and particulates. Both nitrogen oxides (NOx) and particulates are diesel exhaust components that are difficult to convert to harmless components, but these emission standards have recently been very high in relation to environmental issues. In particular, various methods for removing nitrogen oxides have been sought. Selective Catalytic Reduction (SCR) or Lean NOx Trap (LNT) catalyst systems may be mentioned, but the present invention relates to SCR technology.

1 schematically illustrates an SCR system. SCR reduces NOx to N2 and H2O using ammonia or urea as reducing agents.

     4NO + 4NH3 + O2 ⇒ 4N2 + 6H2O

     2NO2 + 4NH3 + O2 ⇒ 3N2 + 6H2O

     NO + NO2 + 2NH3 ⇒ 2N2 + 3H2O

In general, as the SCR catalyst in the SCR system, the V2O5 / TiO2 catalyst is applied, and the operating temperature range of the V2O5 / TiO2 catalyst is 250-450 ° C, but especially when only NO is present, performance is not secured at low temperatures. However, if there are many NO2 components in the exhaust gas, the performance is improved and the low-temperature operation section is extended. Therefore, an oxidation catalyst is installed upstream of the SCR system to oxidize NO to NO2 to increase the NO2 concentration. On the other hand, if the NO2 / NO ratio is too high, it is known that it is best to keep the NO2 / NO = 1 at the level. Representative patents embodying this principle (hereinafter referred to as JMI patents) may refer to patents for NOx reduction systems (PCT / GB / 00292, WO 99/29809) in exhaust gas, and FIG. It is shown schematically, which consists of an oxidation catalyst, a particulate filter, a reducing agent injection unit and an SCR catalyst sequentially converting NO components of the NOx generated from the engine to NO2. SCR systems of this arrangement are described as having an effect such as achieving an NOx conversion rate of 80% or more. In the JMI patent, a V2O5 / WO3 / TiO2 SCR catalyst was applied.

On the other hand, a particulate filter for reducing particulates mentioned in the JMI patent is a Catalyzed Diesel Particulate Filter (CDPF), also called a Catalyzed Soot Filter (CSF). Schematically, these filters are configured for capturing and regenerating exhaust particulates, including honeycomb wall-flow filters primarily for particulate capture, to collect particulates from diesel exhaust. There are a number of known filter structures that can be used, and particulates collected and accumulated in the filter must be burned (regenerated) from the filter continuously or periodically, so that a catalyst is provided as a means to lower the combustion temperature required for this catalyzed diesel. By constructing a particulate filter, the CDPF or CSF can benefit from at least 90% particulate reduction with passive combustion of the accumulating particulates and thus filter regeneration.

The inventors of the present invention have found that the SCR catalyst mentioned in the JMI patent has the following considerations: 1) NOx conversion rate depends on the NO2 / NO ratio, so that the oxidation catalyst capacity disposed upstream of the SCR catalyst should be considered at the same time. Paying attention to this inconvenient problem, the SCR catalyst has been newly designed to solve this problem. The present inventors have developed a new SCR catalyst based on various catalyst design methods, and the SCR catalyst according to the present invention has excellent low temperature activity and can be effectively reacted even at the temperature of the exhaust gas discharged from an engine, without the aid of an oxidation catalyst. It was found that the desired NOx conversion could be achieved. Therefore, applying the SCR catalyst according to the present invention can achieve a configuration that is remarkably different from the batch implemented in the conventional JMI patent, and thus without considering the association with the conventional SCR catalyst and the oxidation catalyst disposed upstream Also, a diesel engine exhaust gas discharge device having a high NOx conversion rate can be realized. Figure 3 schematically shows a diesel engine exhaust gas discharge apparatus that can be achieved by the present invention.

An object of the present invention is to provide an SCR catalyst composition having excellent low temperature activity and NOx conversion rate. The improved NOx conversion of the SCR catalysts according to the present invention can preclude the placement of oxidation catalysts which must be inevitably disposed upstream of the conventional SCR catalyst.

Another object of the present invention is to propose a diesel engine exhaust gas exhauster using an SCR catalyst having excellent low temperature activity and excellent NOx conversion rate.

In order to achieve the above object, the present invention provides a diesel engine exhaust gas exhaust system comprising an SCR catalyst module including an injection means disposed downstream of a diesel engine, an oxidation catalyst module disposed downstream of the catalyst module, and a CSF module serially arranged. I would suggest.

The SCR catalyst composition of the present invention comprises Cu or Fe inclusion-zeolite, in which platinum, palladium and rhodium are impregnated alone or in combination of two components; It is characterized by consisting of Cu, Fe or Si inclusion alumina impregnated with platinum, palladium, rhodium alone or in combination of two components.

The SCR catalyst according to the present invention can achieve high NOx conversion at low temperature without being bound to the NO2 / NOx ratio, which had to be arbitrarily controlled by the conventional diesel oxidation catalyst, and by applying such SCR catalyst, fluidity in diesel engine exhaust system design There is an effect that can be given.

Exhaust exhaust apparatus according to the present invention is as shown in FIG. That is, the SCR catalyst module-DOC (diesel oxidation catalyst) module-CSF (catalyzed diesel particulate filter) module array is characterized by the arrangement.

Exhaust gas 'downstream' herein refers to the exhaust gas flow direction relative to the engine. 'Module' refers to a unit of the minimum unit for performing a function, for example, 'catalyzed diesel particulate filter module' means to collect the particles discharged from the diesel engine It means a filter device, 'DOC module' refers to a carrier coated with a so-called diesel oxidation catalyst for oxidizing hydrocarbon (HC) or CO emitted from the diesel engine into a harmless component.

According to an embodiment of the present invention, the exhaust device according to the present invention, the SCR catalyst module for inducing NOx conversion by the reducing agent introduced from the exhaust gas discharged from the diesel engine, the side, downstream of the SCR catalyst module A diesel oxidation catalyst module arranged to induce hydrocarbon and CO oxidation, and a diesel engine exhaust exhaust device in which a catalytic diesel particulate module for continuously collecting particulates is arranged in series.

Each element is described in detail below.

1) SCR Catalyst Module

The improved SCR catalysts according to the invention include Cu or Fe inclusion-zeolites in which platinum, palladium, rhodium are impregnated alone or in combination of two components; Or Cu, Fe or Si inclusion alumina impregnated with platinum, palladium, rhodium alone or in combination of two components, such catalysts are coated on a refractory metal carrier such as ceramic or stainless steel such as cordierite Configure the catalyst module. Typical carriers are 'flow-through' type carriers having a front side and a rear side and having a plurality of microchannels extending the carrier to connect the front side and the back side. The SCR catalyst module includes known injection means for spraying a reducing agent mounted at the front end. For example, such injection means may comprise a pump and an injection nozzle for spraying urea or ammonia acting as a reducing agent.

SCR catalyst composition production method applied to the SCR catalyst module of the present invention is as follows. SCR catalyst composition to be applied in the present invention, after the slurry is prepared so that 5 to 10% by weight of platinum impregnated in copper containing 5 to 10% by weight of copper and coated on a cordierite and a metal carrier to be dried and produced by a sintering process Can be. In the same way it can be prepared by impregnating 5-10 wt% iron-containing zeolite with the same weight of platinum. Alumina may be prepared as a carrier in place of the zeolite, and the alumina selected herein is preferably alumina containing Cu, Fe, or Si.

In order to test the NOx conversion performance of the SCR catalyst according to the present invention, the conventional conventional SCR catalyst (V2O5 / TiO2) alone, a combination of the conventional SCR catalyst and DOC catalyst (Pt / Al2O3), and the novel SCR catalyst according to the present invention The NH3 / NOx ratio was set to 1, and the NOx conversion rate was examined as shown in FIG. 4. According to this, it can be seen that the SCR catalyst according to the present invention can effectively convert NOx in the range of 250 to 280 ° C. substantially corresponding to the temperature of the doubling gas from the diesel engine.

Specifically, in the range of 250 ° C. to 280 ° C. corresponding to the diesel engine exhaust gas temperature, as a result of applying the SCR catalyst according to the present invention, NOx conversion of about 90% or more was achieved. This contrasts with the 60-80% NOx conversion rate that would have been achieved with the application. In addition, the novel SCR catalysts according to the present invention exhibit significant conversion in contrast to the 80% efficiency achieved with DOC combinations, which were essential for SCR shearing in order to optimally set the NO2 / NO ratio in the JMI patent. It is showing effect.

2) Diesel Oxidation Catalyst (DOC)

DOC oxidizes HC and CO in diesel exhaust gas and converts it into harmless components, removes 50-80% of soluble organic fraction (SOF), which is a soluble organic substance of particulate matter (PM), and also diesel odor. Also, black smoke is reduced and platinum (Pt) or palladium (Pd) is used as the catalyst. For example, Pt / AlsO3 catalyst is known as a representative DOC catalyst. DOC catalyst to be applied in the present invention is to apply a known module.

3) Catalyzed Diesel Particulate Filter, CDPF, or CSF

In general, the diesel particulate module is a filter for collecting particulate matter (PM) discharged from the diesel engine, a number of ceramic monolith filter (Ceramic Monolith Filter), ceramic fiber filter (Seramic Fiber Filter), metal filter (Sintered Metal Filter) Although there are known filter structures, the most preferred module is a ceramic monolith filter, also called a ceramic wall-flow filter, composed of porous cordierite ceramic, the channel inlet and outlet of the module are alternately blocked, and the exhaust gas flowing from the inlet is Since the outlet is blocked, it passes through the porous wall and exits to the neighboring channel outlet, where particulate matter is collected in the inlet channel. 4 is a front view of the ceramic monolith inlet and a cross sectional view of the exhaust gas flow direction. Since the porous size of the wall directly affects the trapped particle size and the engine back pressure, it is an important factor in the module selection, which is approximately 10 μm. In such a porous structure, the porous size can be collected from the 0.01 μm PM particle size and the PM reduction rate is 85% or more. do. PM collected in such a filter is required to be regenerated in a short time if possible so that the filter can collect PM again. In particular, to lower the collected PM ignition temperature 550-600 ° C to about 250 ° C. Depending on how the catalyst is applied to the channel, the Continuous Regeneration Trap (CRT) and DPX modules may be applied. The proposed module may be illustrated as 250 g / ft3 ZrO2, 500g / ft3 CeO2, Pt 75g / ft3 CSF 12 catalyzed diesel particulate module available from Engelhard. DOC catalyst to be applied in the present invention is to apply a known module.

1 is a schematic diagram of an SCR system,

Figure 2 schematically shows a diesel engine exhaust system in the conventional JMI patent,

Figure 3 shows a diesel engine exhaust system according to the present invention,

Figure 4 is a graph measuring the NOx conversion rate for the comparative catalysts and the novel catalyst composition according to the present invention.

Claims (5)

An SCR catalyst module including an injection means disposed downstream of a diesel engine, an oxidation catalyst module disposed downstream of the catalyst module, and a CSF module serially arranged in series, thereby improving a NOx conversion rate. The SCR catalyst according to claim 1, wherein the SCR catalyst applied to the SCR catalyst module comprises: Cu or Fe inclusion-zeolite impregnated with platinum, palladium or rhodium alone or in combination of two components; Or diesel, exhaust gas improving apparatus for NOx conversion, characterized in that it is composed of Cu, Fe or Si-containing alumina impregnated with platinum, palladium, rhodium alone or in combination of two components. 3. The diesel engine exhaust gas exhaust system according to claim 2, wherein the catalyst is coated on a refractory metal carrier of ceramic type or stainless steel. The method of claim 2, wherein the SCR catalyst, 5-10 wt% copper or iron impregnated with a zeolite containing platinum, palladium or rhodium alone or a plurality of components impregnated 0.5x% by weight, improving the NOx conversion rate Diesel engine exhaust gas discharge device. According to claim 2, The SCR catalyst, NOx, characterized in that 5 to 10% by weight of alumina containing copper or iron or silicon impregnated with platinum, palladium or rhodium alone or a plurality of components 0.5% by weight or less, NOx Diesel engine exhaust emissions improve conversion.

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