JP5954134B2 - Particulate filter with catalyst - Google Patents

Description

  The present invention relates to a particulate filter with a catalyst provided with a catalyst used for collecting particulates discharged from an engine and burning and removing the collected particulates.

  A filter for collecting particulates (PM: Particulate matter) in exhaust gas is provided in an exhaust gas passage of an automobile equipped with a lean combustion engine such as a diesel engine. When the amount of PM deposited on the filter increases, the filter is clogged. Therefore, the PM accumulation amount is estimated based on the pressure difference of the pressure sensors provided before and after the filter, and when the accumulation amount reaches a predetermined value, engine fuel injection control (fuel increase, post-injection, etc.) Thus, the temperature of the exhaust gas reaching the filter is increased, and PM is burned and removed. In order to promote the combustion of PM, a catalyst is supported on the exhaust gas passage wall of the filter, and in particular, platinum (Pt) is supported as a catalyst metal.

  For example, Patent Document 1 contains zirconium (Zr), neodymium (Nd), and rare earth elements other than cerium (Ce) and Nd in the exhaust gas passage wall of the filter in order to improve the PM combustion rate. It is disclosed to provide a catalyst material in which Pt is supported or doped on the composite oxide particles.

  Patent Document 2 discloses Pt as a three-way catalyst, a selective catalytic reduction (SCR) catalyst, or a diesel oxidation catalyst disposed upstream or downstream of a filter, not for combustion of PM. Instead, it is disclosed that a catalyst material in which palladium (Pd) is supported on a Ce-containing composite oxide is used.

JP 2008-221204 A Special table 2012-518531 gazette

  By the way, in the conventional particulate filter with catalyst, when the amount of PM deposited on the surface of the catalyst layer is small, the PM is combusted and removed relatively efficiently. However, when the amount of PM deposited is large, it takes time for the PM to be removed by combustion. This tendency is seen. The reason is as follows according to findings based on experiments and research by the present inventors.

  That is, the graph of FIG. 1 shows the change over time in the PM remaining ratio when PM deposited on the catalyst layer (PM is described as “煤” in FIGS. 1, 3, and 5) burns. This is shown schematically. Initially, the combustion of PM proceeds rapidly, but after passing through the rapid combustion region (for example, the first combustion period until the PM remaining ratio becomes 100% to 50%), the combustion of PM becomes slow (PM) It shifts to the combustion late stage until the remaining ratio becomes 50% to 0%. This point will be described in detail below.

  As shown in the photograph of FIG. 2, at the beginning of combustion, PM is in contact with the catalyst layer supported on the surface of the filter. For this reason, for example, when the catalyst layer contains Ce-containing oxide particles and Zr-containing oxide particles, as schematically shown in FIG. 3, active internal oxygen released from these oxide particles is generated in the catalyst layer. It is supplied in a highly active state to the contacting PM. As a result, the PM on the catalyst layer surface burns rapidly.

  However, as described above, the PM on the surface of the catalyst layer is burned and removed. As a result, a gap of about several tens of μm is partially formed between the catalyst layer and the PM deposit layer as shown in the photograph of FIG. Therefore, as schematically shown in FIG. 5, the active oxygen released from the inside of the oxide particles maintains the activity for a very short time, but the activity decreases before most of the active oxygen reaches the PM. For example, it becomes the same normal oxygen as oxygen in the gas phase. As a result, the combustion of PM becomes slow. Of course, as shown in the upper left and lower left of FIG. 5, the oxygen in the exhaust gas also contributes to the combustion of PM, but the combustion is slower than the combustion by the active oxygen described above.

  The present invention has been made in view of the above problems, and an object of the present invention is to allow the combustion to proceed efficiently in both the rapid combustion region and the slow combustion region of PM deposited on the filter.

  As a result of further experiments and researches to achieve the above object, the present inventors have used palladium (Pd) as a catalytic metal for burning PM, and this Pd is used in addition to Zr and Ce. Compared with the case where platinum (Pt) is supported, the Pd-supported Zr-containing composite oxide supported on a Zr-containing composite oxide containing rare earth elements is used as a catalyst material. It was found that can be improved. Further, by using a catalyst material including a Pt-supported Zr-containing composite oxide in which Pt is supported on the Zr-containing composite oxide together with a Pd-supported Zr-containing composite oxide, PM in the slow combustion region as well as the rapid combustion region is used. The present invention has been completed by finding that the flammability of can be improved.

That is, in the particulate filter with catalyst according to the present invention, a catalyst layer is provided on the exhaust gas passage wall of the filter that collects particulates in the exhaust gas, and the catalyst layer includes zirconium (Zr) and neodymium (Nd ) and, praseodymium (Pr) and Pd on Zr-containing composite oxide of palladium (Pd) as a catalytic metal Zr-containing composite oxide containing no unrealized and cerium (Ce) is carrying, and Zr-containing composite oxide And a Pt-supported Zr-containing composite oxide in which platinum (Pt) is supported as a catalyst metal.

  According to the particulate filter with catalyst according to the present invention, as described above, the Pd-supported Zr-containing composite oxide improves the PM combustion rate particularly in the rapid combustion region, and the Pt-supported Zr-containing composite oxide particularly in the slow combustion region PM. As a result, the total PM burning rate can be improved. The fact that the total PM combustion speed can be improved means that the engine injection control described above takes a short time, in other words, the fuel consumption is reduced, and the fuel efficiency is improved. Further, since a part of Pd is used instead of Pt as the catalyst metal, the amount of Pt to be used can be reduced and the cost can be reduced.

  In the particulate filter with catalyst according to the present invention, as described above, the Pd-supported Zr-containing composite oxide can improve the PM combustion performance in the rapid combustion region. PM combustion performance can be further improved. However, in consideration of PM combustion performance in the slow combustion region, a predetermined amount of Pt-supported Zr-containing composite oxide may be included without excessively increasing the ratio of the Pd-supported Zr-containing composite oxide contained in the catalyst layer. preferable. As a ratio thereof, the mass ratio Pd / Pt is preferably 1/3 or more and 6/1 or less.

  According to the particulate filter according to the present invention, the PM combustion performance in the rapid combustion region and the slow combustion region can be improved, so that the PM combustion can be advanced efficiently and the fuel efficiency can be improved. Furthermore, since the amount of Pt used as the catalyst metal can be reduced, the cost can also be reduced.

It is a graph which shows typically a time-dependent change of PM residual ratio when PM (soot) deposited on the catalyst layer burns. It is an electron micrograph which shows the state (state in the rapid combustion area | region of FIG. 1) which PM deposit layer is contacting the catalyst layer. It is a schematic diagram which shows the combustion mechanism of PM (soot) in a rapid combustion area | region. It is an electron micrograph which shows the state (state in the slow combustion area | region of FIG. 1) with which the clearance gap was made between the catalyst layer and the deposition layer of PM (soot). It is a schematic diagram which shows the combustion mechanism of PM (soot) in a slow combustion area | region. It is a figure which shows the state which has arrange | positioned the particulate filter in the exhaust gas path of an engine. It is a front view which shows the same filter typically. It is a longitudinal cross-sectional view which shows the same filter typically. It is an expanded sectional view showing typically the exhaust gas passage wall of the filter. It is a graph which compares the carbon combustion performance of Pd carrying | support Zr containing complex oxide and Pt carrying | support Zr containing complex oxide. It is a figure which shows typically the catalyst layer of embodiment of this invention. It is a graph which shows the carbon burning rate of the particulate filter with a catalyst which concerns on the Example and comparative example of this invention.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the invention, its application, or its application.

<Particulate filter structure>
Hereinafter, the structure of the particulate filter for collecting PM will be described.

FIG. 6 shows a particulate filter (hereinafter simply referred to as “filter”) 10 arranged in the exhaust gas passage 11 of the diesel engine. In the exhaust gas passage 11 on the upstream side of the exhaust gas flow from the filter 10, an oxidation catalyst (not shown) in which a catalyst metal typified by Pt, Pd or the like is supported on an oxide or the like support material can be disposed. The exhaust gas component purification catalyst material according to the present embodiment can be used for the oxidation catalyst to be disposed. When such an oxidation catalyst is arranged on the upstream side of the filter 10, HC and CO in the exhaust gas are oxidized by the oxidation catalyst, and the temperature of the exhaust gas flowing into the filter 10 is increased by the oxidation combustion heat to heat the filter 10. This is advantageous for PM removal by combustion. Further, NO is oxidized to NO ₂ by the oxidation catalyst, and the NO ₂ is supplied to the filter 10 as an oxidant for burning PM.

  As schematically shown in FIGS. 7 and 8, the filter 10 has a honeycomb structure and includes a large number of exhaust gas passages 12 and 13 extending in parallel to each other. That is, in the filter 10, the exhaust gas inflow path 12 whose downstream end is blocked by the plug 14 and the exhaust gas outflow path 13 whose upstream end is blocked by the plug 14 are alternately provided. Is separated by a thin wall 15. In FIG. 7, hatched portions indicate the plugs 14 at the upstream end of the exhaust gas outflow passage 13.

In the filter 10, the filter main body including the partition wall 15 is formed of an inorganic porous material such as cordierite, SiC, Si ₃ N ₄ , sialon, or AlTiO ₃ . The exhaust gas flowing into the exhaust gas inflow passage 12 flows out into the adjacent exhaust gas outflow passage 13 through the surrounding partition 15 as shown by the arrows in FIG. That is, as shown in FIG. 9, the partition wall 15 has minute pores (exhaust gas passages) 16 that connect the exhaust gas inflow passage 12 and the exhaust gas outflow passage 13, and the exhaust gas passes through the pores 16. PM is trapped and accumulated mainly in the exhaust gas inlet 12 and the walls of the pores 16.

  A catalyst layer 17 is formed on the wall surface forming the exhaust gas passage (exhaust gas inflow passage 12, exhaust gas outflow passage 13 and pore 16) of the filter body. It is not always necessary to form a catalyst layer on the wall surface on the exhaust gas outflow passage 13 side.

<About catalyst material>
Next, the configuration of the catalyst layer provided in the particulate filter according to the embodiment of the present invention will be described.

The present inventors have for the PM combustion performance is good catalytic material in place of Pt-supporting composite oxide, a result of our experiments and research, the Pd, does not contain a Zr, and Nd, the unrealized and Ce and Pr It has been found that a Pd-supported Zr-containing composite oxide supported on a Zr-containing composite oxide is used as a catalyst material. Here, the carbon combustion test conducted using the Pd-supported Zr-containing composite oxide and the Pt-supported Zr-containing composite oxide in which Pt is supported on the Zr-containing composite oxide will be described below.

In the carbon combustion test, sample filters each carrying a Pd-supported Zr-containing composite oxide or a Pt-supported Zr-containing composite oxide as a catalyst material are prepared, and carbon (carbon black) is deposited on each sample filter to increase the carbon combustion rate. It was measured. As a sample filter, a cylindrical SiC honeycomb having a cell wall thickness of 16 mil (4.064 × 10 ⁻¹ mm), 178 cells per square inch (645.16 mm ² ), a diameter of 17 mm, and a length of 50 mm. (Capacity 11.3 cc) was used, and a filter plugged so as to alternate between the upstream side and the downstream side was adopted.

The carbon was deposited so that 5 g / L of carbon was deposited per 1 L of the carrier volume. After carbon equivalent to 5 g / L was stirred in ion-exchanged water using a stirrer, the inlet side of the sample filter was immersed and sucked from the outlet side using an aspirator. After removing excess water by placing on a water-absorbent sheet, a drying treatment was performed at 150 ° C. for 1 hour. Each of the obtained sample filters was attached to a simulated gas flow reactor, and the gas temperature was raised while flowing N ₂ gas. After the filter inlet temperature was stabilized at 540 ° C., the simulated exhaust gas was switched from N ₂ gas to simulated exhaust gas (O ₂ ; 7.5%, NO; 300 ppm, remaining N ₂ ), and flowed at a space velocity of 45000 / h. The concentration of CO _{2 in} the gas generated by the combustion of carbon was measured in real time at the filter outlet.

As a result, as shown in FIG. 10, the Pd-supported Zr-containing composite oxide (Pd-supported ZrNdPrO _x ) has an extremely high combustion performance at the initial stage of combustion than the Pt-supported Zr-containing composite oxide (Pt-supported ZrNdPrO _x ). Admitted. That is, it was suggested that when a Pd-supported Zr-containing composite oxide is used as a catalyst material, PM combustion performance can be improved particularly in the rapid combustion region. Further, as shown in FIG. 10, in the later stage of combustion, the Pt-supported Zr-containing composite oxide has better combustion performance, so that the Pd-supported Zr-containing composite oxide and the Pt-supported Zr-containing composite oxide It is thought that PM combustion performance can be improved by combining.

  Therefore, as shown in FIG. 11, in this embodiment, the catalyst layer 22 is formed on the surface of the wall surface (filter carrier 21) of the exhaust gas passage wall of the filter, and the catalyst layer 22 has other than Zr and Ce. A Zr-containing composite oxide 23 containing a rare earth element is included. The Zr-containing composite oxide 23 includes those carrying Pd24 and those carrying Pt25. The Zr-containing composite oxide 23 does not contain Ce.

  The ratio of those contained in the catalyst layer is not particularly limited, but if the ratio of the Pd-supported Zr-containing composite oxide is increased, the PM combustion rate in the rapid combustion region can be improved. Increasing the ratio can improve the PM combustion rate in the slow combustion region. For this reason, the user can adjust those ratios contained in a catalyst layer suitably according to the objective.

<Method for preparing catalyst material>
Next, a method for preparing a catalyst material provided in the particulate filter according to the embodiment of the present invention will be described. Here, a method for preparing a ZrNdPr composite oxide as a Zr-containing composite oxide containing Zr and a rare earth element other than Ce will be described.

  First, a zirconyl oxynitrate solution, neodymium nitrate hexahydrate, and praseodymium nitrate are dissolved in ion-exchanged water. This nitrate solution is mixed with an 8-fold diluted solution of 28% by mass ammonia water for neutralization to obtain a ZrNdPr composite oxide precursor (coprecipitate). This coprecipitate is centrifuged, and the dehydration operation for removing the supernatant and the water washing operation for adding ion-exchanged water and stirring are repeated alternately as many times as necessary. The coprecipitate after the final dehydration was dried in the atmosphere at 150 ° C. for a whole day and night, and then pulverized to a mean particle diameter of about 100 nm by a ball mill. Then, a ZrNdPr composite oxide particle material can be obtained by firing at 500 ° C. for 2 hours in the air.

  Next, a method for supporting Pd or Pt on the obtained ZrNdPr composite oxide particle material will be described.

  First, ion-exchanged water is added to the ZrNdPr composite oxide particle material to form a slurry, which is sufficiently stirred with a stirrer or the like. Subsequently, a predetermined amount of dinitrodiamine Pd nitric acid solution or dinitrodiamine Pt nitric acid solution is dropped into the slurry while stirring, and sufficiently stirred. Thereafter, stirring is continued while heating to completely evaporate water. After evaporation, the Pd-supported ZrNdPr composite oxide particle material or the Pt-supported ZrNdPr composite oxide particle material is obtained by firing at 500 ° C. for 2 hours in the atmosphere.

  Ion exchange water and a binder are added to the composite oxide particle material obtained as described above and mixed to form a slurry. The slurry is coated on a filter, dried, and then calcined at 500 ° C. for 2 hours to obtain a particulate filter with catalyst.

The particulate filter with catalyst according to the present invention includes a Pd-supported ZrNdPr composite oxide particle material and a Pt-supported ZrNdPr composite oxide particle material, but may include a third component in addition to these. In the present invention, the Pd-supported ZrNdPr composite oxide particle material improves the PM combustion performance particularly in the rapid combustion region, so that a third component for supplementing the PM combustion performance in the slow combustion region can be further added. As such a catalyst material, for example, a Ce-containing composite oxide containing rhodium (Rh) (for example, CeZrNdO _x ) can be used.

  Below, the Example for demonstrating in detail the particulate filter with a catalyst which concerns on this invention is shown.

  In this example, the Pd-supported ZrNdPr composite oxide particle material and the Pt-supported ZrNdPr composite oxide particle material were used as the catalyst material, and the ratio of those contained in the catalyst material was changed to examine the carbon combustion rate. Further, as comparative examples, a case where only a Pt-supported ZrNdPr composite oxide particle material was used and a case where a Ce-containing composite oxide supporting Pd or Pt was used were examined. The composition of the catalyst material of each example and comparative example is shown in Table 1 below.

The Pd-supported ZrNdPr composite oxide particle material and the Pt-supported ZrNdPr composite oxide particle material included in the catalyst materials of Examples 1 to 5 and Comparative Example 1 were prepared as described above, and in each example, they were mixed. A sample filter (particulate filter with catalyst) was obtained by coating the filter. Note that the composition of the ZrNdPr composite oxide was ZrO ₂ : Nd ₂ O ₃ : Pr ₂ O ₃ = 70: 12: 18 (molar ratio). Here, the total amount of the support material (Zr-containing composite oxide excluding noble metals) was 20 g / L, and the total noble metal amount of Pd and Pt was 0.1 g / L. The ratio between Pd and Pt is as shown in Table 1 above.

The Ce-containing composite oxide (CeZrNdO _x ) contained in the catalyst materials of Comparative Examples 2 and 3 is composed of cerium nitrate hexahydrate, a zirconyl oxynitrate solution, and neodymium nitrate hexahydrate as materials. It was prepared by the same method as the method for preparing the particulate material. The composition of the CeZrNd composite oxide was CeO ₂ : ZrO ₂ : Nd ₂ O ₃ = 24: 72: 4 (molar ratio). A method of supporting Pd and Pt on CeZrNdO _x was also performed using the same method as described above. In addition, in the catalyst material of Comparative Example 2, Pt contained in the first component and the second component is contained, but each contains an equal amount of Pt, and the total mass ratio of Pt and Pd. Is adjusted to 1: 1.

  The carbon was deposited so that 5 g / L of carbon was deposited per liter of the carrier volume. After carbon equivalent to 5 g / L was stirred in ion-exchanged water using a stirrer, the inlet side of the sample filter was immersed and sucked from the outlet side using an aspirator. After removing excess water by placing on a water-absorbent sheet, a drying treatment was performed at 150 ° C. for 1 hour.

Each of the obtained sample filters was attached to a simulated gas flow reactor, and the gas temperature was raised while flowing N ₂ gas. After the filter inlet temperature was stabilized at 540 ° C., the simulated exhaust gas was switched from N ₂ gas to simulated exhaust gas (O ₂ ; 7.5%, NO; 300 ppm, remaining N ₂ ), and flowed at a space velocity of 45000 / h. Then, the CO and CO ₂ gas concentrations produced by the combustion of carbon are measured in real time at the filter outlet, and from these concentrations, the carbon combustion rate (unit time) is determined at predetermined intervals using the following formula. Per PM combustion amount) was calculated.

Carbon burning rate (g / h)
= {Gas flow rate (L / h) x [(CO + CO ₂ ) concentration (ppm) / (1 x 10 ⁶ )]} x 12 (g / mol) /22.4 (L / mol)
The time required for the carbon combustion rate to reach 0% to 50%, 50% to 90%, and 0% to 90% is obtained based on the carbon combustion rate for each predetermined time. The carbon combustion rate (PM combustion amount per minute (1 mg / min-L) in the filter 1 L) was obtained from the integrated value of the carbon combustion amount in the meantime. The result is shown in FIG.

  As shown in FIG. 12, when Examples 1 to 5 and Comparative Examples 1 to 3 are compared, Pd-supported Zr-containing composite oxide is included rather than Comparative Examples 1 to 3 not including Pd-supported Zr-containing composite oxide. Examples 1 to 5 clearly have better PM combustion performance. Further, when Examples 1 to 5 were compared with each other, the combustion rate in the rapid combustion region (carbon combustion rate was 0% to 50%) was improved as the ratio of the Pd-supported Zr-containing composite oxide was increased. Conversely, when the ratio of the Pd-supported Zr-containing composite oxide was decreased to increase the ratio of the Pt-supported Zr-containing composite oxide, the combustion rate in the slow combustion region (carbon combustion rate was 50% to 90%) was improved. As a result, no significant difference was observed in the total carbon burning rate until the carbon burning rate in Examples 1 to 5 reached 0% to 90%.

  On the other hand, since Comparative Example 1 does not include the Pd-supported Zr-containing composite oxide but includes only the Pt-supported Zr-containing composite oxide, the PM combustion performance in the slow combustion region is the same as in Examples 1-5. However, the PM combustion performance in the rapid combustion region was low, and as a result, the total carbon combustion rate until the carbon combustion rate reached 0% to 90% was lower than in Examples 1-5.

In Comparative Examples 2 and 3, Pd and Pt were used as catalyst metals. In particular, in Comparative Example 2, a catalyst material in which both Pd and Pt are supported on Ce-containing composite oxide (CeZrNdO _x ) is used, and in Comparative Example 3, Pd and Pt are each independently Ce-containing composite oxide (CeZrNdO _x ). The catalyst material supported on was used. Although these comparative examples 2 and 3 contained Pd as a catalyst metal, the results of the PM combustion performance were clearly lower than those of Examples 1 to 5. That is, the catalyst material obtained by supporting Pd on the Ce-containing composite oxide could not improve the PM combustion performance in the rapid combustion region. That is, it was recognized that Pd acts as a catalyst material that can improve PM combustion performance in the rapid combustion region by being supported on a Zr-containing composite oxide not containing Ce.

  As described above, by using the Zr-containing composite oxide supporting Pd as the catalyst material, it is possible to significantly improve the PM combustion performance particularly in the rapid combustion region. Further, the Zr-containing composite oxide supporting Pt can be used as a catalyst material. By adding as the second component, it was suggested that the PM combustion performance can be improved particularly in the slow combustion region, and as a result, the total PM combustion performance can be improved.

10 Filter 11 Exhaust gas passage 12 Exhaust gas inflow passage (exhaust gas passage)
13 Exhaust gas outflow passage (exhaust gas passage)
14 plug 15 partition 16 pore (exhaust gas passage)
17 Catalyst layer 21 Filter carrier 22 Catalyst layer 23 Zr-containing composite oxide 24 Palladium (Pd)
25 Platinum (Pt)

Claims (2)

A particulate filter with a catalyst in which a catalyst layer is provided on an exhaust gas passage wall of a filter that collects particulates in exhaust gas,
The catalyst layer includes a zirconium (Zr), and neodymium (Nd), palladium (Pd) is supported as a catalytic metal Zr-containing composite oxide containing no praseodymium (Pr) and unrealized and cerium (Ce) and A particulate filter with catalyst, comprising: a Pd-supported Zr-containing composite oxide; and a Pt-supported Zr-containing composite oxide in which platinum (Pt) is supported as a catalyst metal on the Zr-containing composite oxide.   The particulate filter with catalyst according to claim 1, wherein a mass ratio Pd / Pt of Pd and Pt in the catalyst layer is 1/3 or more and 6/1 or less.