KR100232464B1 - Oxidative catalyst for reducing particulate matter of diesel engine - Google Patents

Abstract

The present invention relates to an oxidation catalyst for reducing particulate matter of a diesel vehicle, and is conventionally coated with a titania on a cordierite monolith carrier with a support layer, and on the support layer a noble metal catalyst and a nonmetallic promoter. Even though the heat resistance to withstand the oxidation catalyst of 600 ~ 900 degrees Celsius when exposed to heat of exhaust gas for a long time should be large, the phase change of titania (TiO ₂ ) constituting the supporting layer becomes a stable rutile phase by the exhaust heat. There was a problem that the active surface area is reduced to significantly reduce the particulate matter removal performance.

In the present invention, as shown in FIG. 1, the titania carrying layer 2 is supported with a promoter 4 such as ceria, zirconia, vanadium oxite, and the aforementioned promoters are completely composed of anatase titania as rutile titania. By preventing phase transformation, it is possible to improve the heat resistance of the supporting layer and to prevent the sudden deterioration of the oxidation catalyst, thereby improving the life of the oxidation catalyst.

Description

Oxidation catalyst for reducing particulate matter in diesel engines

The present invention relates to an oxidation catalyst for reducing particulate matter in diesel vehicles, and more specifically, ceria (CeO ₂ ) and zirconia (ZrO ₂ ) on a supporting layer of titania (TiO ₂ ) formed on the surface of a monolith carrier made of cordierite. ), At least one promoter of zirconia-doped ceria (ZrO ₂ -doped CeO ₂ ) or seamium oxite (V ₂ O ₂ ) is added to inhibit the phase change of the titania-supported layer of anatase to rutile phase by exhaust heat. The present invention relates to an oxidation catalyst for reducing particulate matter in diesel vehicles, thereby improving heat resistance.

Since combustion of diesel engines is carried out in an oxidizing atmosphere with an average excess air ratio of 1.0 or more (about 1.2 or more in poor engines, or about 1.3 or more in direct injection engines), HC and CO emissions are lower than in gasoline engines. Because it is necessary to finish diffuse spray combustion within a very short time in the inside, there are many emissions of so-called particulate matter such as black smoke and tar material, which is unpleasant to people in terms of poor visibility, dirt and odor. Most of these particulate matter are less than 1 micron in size and can easily float in the air, which is easily inhaled and harmed by the human body when breathing.

Therefore, research and efforts are being made to reduce the emission of particulate matter. Among them, the method of improving combustion by engine modification reduces the insoluble ratio of particulate matter in the dark smoke concentration emitted from the engine. In response, however, the proportion of soluble organic matter (SOF) increases relatively. Therefore, when it is necessary to reduce the particulate matter again, measures focused on reducing the SOF content become important.

The SOF component is composed of unburned fuel, unburned engine oil, and incombustible combustion products. It is composed of hydrocarbons having a relatively high carbon number, so that engine oil consumption is reduced and the engine body is improved. Even if it is, there is a limit to the reduction of the SOF powder. Therefore, when it is desired to reduce the SOF powder, it is necessary to use an oxidation catalyst.

Most of the oxidation catalysts for decomposing SOF components are precious metals such as platinum (Pt), palladium (Pd) and rhodium (Rh). Pt and Pd are known to exhibit high activity in the oxidation reaction of SOF fraction, but when these are used as exhaust post-treatment devices of diesel engines, sulfur dioxide (SO ₂ ), a combustion product of sulfur contained in diesel fuel, is oxidized and sulfur dioxide (SO ₃ ), which reacts with the water vapor in the exhaust gas to form sulfate, resulting in an adverse effect of increasing the discharge weight of particulate matter in reverse. For this reason, in the catalyst apparatus actually used, these metal catalysts are nonmetallic cocatalysts such as oxides such as cobalt (CO), nickel (Ni), manganese (Mn), vanadium (V), chromium (Cr) and titanium (Ti). A method of suppressing the formation of sulfate while promoting the oxidation of the SOF component by adding is taken. However, it is not clear what kind of cocatalyst is mixed to what extent and what kind of treatment is applied to the actual catalytic device because it is hidden by the veil as a secret for each company. Platinum (Pt) and palladium (Pd) are expensive precious metals and must be studied to achieve high performance with as little use as possible. To this end, the surface of the carrier is coated with a material having a large specific surface area such as γ-alumina, and the precious metal is finely dispersed and maintained to promote efficient use of the precious metal.

However, the activated alumina (γ-Al ₂ O ₃₎ writing the current gasoline the catalyst will promote the oxidation ability of the SO ₂ has excellent adsorption of SO _2. Therefore, many oxidation catalysts using titania (TiO ₂ ) as a supporting layer are used. The above-mentioned oxidation catalyst is usually a monolith made of cordierite (2MgO · 2Al ₂ O ₃ · 5SiO ₂ ) as a carrier and supported on the surface of the carrier substrate. The catalyst is supported on the layer. Many monolithic carriers made of cordierite have a honeycomb shape of about 400 cells per square inch, and in the case of automobile catalysts, since the frequency of exposure to sudden changes in the exhaust temperature due to acceleration and deceleration is high, the carrier has a high thermal stress. If it occurs and its thermal stress exceeds the strength limit, the carrier will crack. In order to suppress the stress caused by thermal shock as low as possible, a material having high thermal conductivity and low thermal expansion or Young's modulus should be selected.

By the way, conventional ceramics have a Young's modulus of about 1.0-1.5 × 10 5 kg / cm ² , so that the difference in materials is relatively small, so that cordierite having a low coefficient of thermal expansion is widely used as a catalyst carrier.

However, a conventional oxidation catalyst coated with a titania on a cordierite monolith carrier with a support layer of a noble metal and a catalyst of a noble metal and a nonmetallic promoter is exposed to heat of an exhaust gas of 600 to 900 degrees Celsius for a long time. Even though the heat resistance to withstand this should be large, the titania (TiO ₂ ) constituting the supporting layer has a phase change to a stable rutile phase due to the exhaust heat, and thus the active surface area decreases, so that the particulate matter removal performance is significantly degraded. there was.

Accordingly, the present invention has been made to solve the above-mentioned problem, and the titania supporting layer has a cocatalyst so as not to be transformed from the active anatase phase to the stable rutile phase even if the titania is exposed to exhaust heat for a long time, thereby enhancing the heat resistance of the catalyst. An object of the present invention is to provide an oxidation catalyst for reducing particulate matter in a diesel vehicle.

The present invention for achieving the above object is a catalyst supporting layer mainly composed of a monolith carrier made of cordierite and titania (TiO ₂ ) formed on the surface of the carrier, and platinum (Pt) and palladium ( Pd), rhodium (Rh) and the like, and the catalyst support layer includes ceria (CeO ₂ ), zirconia (ZrO ₂ ), zirconia-doped ceria (ZrO ₂ -doped CeO ₂ ) and vanadium oxite (v At least one component selected from ₂ O ₂ ) is contained as a promoter.

Therefore, the present invention supports a promoter such as ceria, zirconia, vanadium oxite, and the like in the titania supporting layer to prevent the co-catalysts from completely transforming the anatase titania into rutile titania. It can improve and prevent the sudden deactivation of oxidation catalyst.

1 is a schematic diagram showing the configuration of an oxidation catalyst according to the present invention.

* Explanation of symbols for main parts of the drawings

1 carrier 2 support layer

3: catalyst 4: promoter

Referring to the configuration and operation of the present invention in detail based on the accompanying drawings as follows.

The present invention provides a monolith carrier made of cordierite (1), a catalyst support layer (2) mainly composed of titania (TiO ₂ ) formed on the surface of the support, platinum (Pt) supported on the catalyst support layer, Catalyst 3 such as palladium (Pd) and rhodium (Rh), and the catalyst support layer 2 include ceria (CeO ₂ ), zirconia (ZrO ₂ ) and zirconia doped ceria (ZrO ₂ -doped CeO ₂ ) And an oxidizing catalyst for reducing particulate matter in a diesel engine comprising a cocatalyst 4 containing at least one component selected from vanadium oxite (v ₂ O ₂ ).

Exemplary Drawings FIG. 1 is a schematic diagram showing the configuration of an oxidation catalyst according to the present invention.

Here, the present invention is cordierite _{(2MgO · 2Al 2 O 3 ·} SiO 2) the monolith substrate (1), platinum on titania (TiO ₂₎ forming a layer (2) supported on the surface (Pt), palladium (Pd ) And a co-catalyst (4) of a component for supporting a noble metal catalyst (3) such as rhodium (Rh) and suppressing phase change of titania even when the supporting layer is brought into contact with a high temperature exhaust heat for a long time. Is an oxidation catalyst that suppresses the decrease in the active area

In other words, titania (TiO ₂ ) constituting the supporting layer (2) on the surface of the carrier is represented by two phases, an anatase as an active phase and a rutile as a stable phase. The phase has a larger active surface area than the rutile phase, which is a stable phase, to enhance the action of the noble metal catalyst 3 for the removal of particulate matter.

However, if the anatase phase as the active phase causes a complete transition to the rutile phase as a stable phase, that is, when the anatase phase undergoes complete phase transformation into the rutile phase, the active surface area is reduced and the action of the catalyst (4) is significantly reduced, resulting in a drastic removal of particulate matter. .

This is because the anatase phase titania is exposed to high temperature heat for a long time to cause phase change to a rutile phase, which makes it stable. Since the surface of the anatase phase is unstable and rough in contact with particulate matter, it is easy to collect particulate matter. This is because the rutile phase has a smooth surface so that particulate matter entering the catalytic converter side during the exhaust stroke and flying into the fine cell of the monolithic catalyst carrier is not easily caught on the titania surface.

Therefore, the cocatalyst 4 supported together with the noble metal catalyst 3 on the supporting layer has a property of suppressing phase transformation to the rutile phase to the maximum so that titania of the supporting layer 2 can maintain the anatase phase in which the active phase is active. Should be

Promoter materials of the present invention having such properties include ceria (CeO ₂ ), zirconia (ZrO ₂ ), zirconia-doped ceria (ZrO ₂ -doped CeO ₂ ), vanadium oxite (V ₂ O ₂ ), and the like. As used in the table below, platinum (Pt), palladium (Pd), and rhodium (Rh) were formed on a titania (TiO ₂ ) supporting layer on the surface of a monolith carrier made of cordierite (2MgO.2Al ₂ O ₃ .5SiO ₂ ). X-ray diffraction analysis was performed to carry out aging deterioration in an electric furnace for 10 hours in an air atmosphere of 700 degrees Celsius while supporting precious metal catalysts, etc.). The data analyzed are shown.

In the above diagram, the content of Example 1) is that the supporting layer 2 coated on the surface of the cordierite monolith carrier 1 has a titania (TiO ₂ ) supporting layer having 78% anatase and 22% rutile phase. 10 wt% of ceria (CeO ₂ ) was supported as the cocatalyst (4), and the result of the aging in the electric furnace for 10 hours in an air atmosphere of 700 degrees Celsius was 49% for the anatase phase and 51% for the rutile phase. Only 29% are rutile. Interpretation of the above results indicates that the oxidation catalyst containing the ceria (CeO ₂ ) promoter has many active phases with a wide active surface area even after high temperature exhaust heat contacting for a long time, so that the oxidation catalyst has a high effect of removing particulate matter. You can see.

Example 2) of 10wt% zirconia as the support (1) carrying layer (2) coated on the surface of the anatase phase of 78% and rutile tank in day-to-day, 22% of titania (TiO ₂₎ carrying layer catalyst (4) (ZrO ₂ ), the result of the aging experiment was 5% for the anatase phase, 95% for the rutile phase, and 73% for the anatase phase before the experiment occurred with rutile. This decreases the active surface area much more than in Example 1, thereby reducing the effect of removing particulate matter. However, the effect of removing particulate matter is still large compared to the comparative example.

Example 3) has a carrier (1) carrying layer (2) coated on the surface of the anatase phase of 78%, and doubled daily is 22% of titania (TiO ₂₎ as a co-catalyst 4 to the carrying layer of zirconia doping of 10wt% It was loaded with ceria (ZrO ₂ -doped CeO ₂ ), and the result of the aging experiment was 25% for the anatase phase, 75% for the rutile phase, and 53% of the anatase phase before the experiment occurred with rutile.

In summary, the titania constituting the supporting layer includes ceria (CeO ₂ ), zirconia (ZrO ₂ ), zirconia-doped ceria (ZrO ₂ -doped CeO ₂ ), vanadium oxite (V ₂ O ₂ ), and the like. By adding the cocatalyst, the active anatase phase prevents the complete phase transformation from the stable rutile phase to the heat resistance of the supporting layer of the diesel oxidation catalyst, thereby maintaining the removal effect of particulate matter even during long time use of the oxidation catalyst. Will be.

As described above, the present invention supports the promoter 4 such as ceria, zirconia, vanadium oxite and the like in the titania supporting layer 2 so that the promoters are completely transformed into anatase titania into rutile titania. It is possible to improve the heat resistance of the supporting layer and to prevent the sudden deactivation of the oxidation catalyst by preventing it, thereby improving the life of the oxidation catalyst.

Claims (1)

A monolith carrier made of cordierite (1), a catalyst support layer (2) mainly composed of titania (TiO ₂ ) formed on the surface of the support, supported on the catalyst support layer, and platinum (Pt), palladium (Pd) and ZrO ₂ -doped CeO ₂ , comprising one catalyst 3 selected from rhodium (Rd) and zirconia doped in the catalyst support layer _{2 and} co-catalyst 4. Oxidation catalyst for reducing particulate matter in diesel engines.

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