JP2014018768A - Exhaust gas purifying system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust gas purifying system excellent in heat-resistance reliability.SOLUTION: There is provided an exhaust gas purifying system which comprises: a honeycomb filter for collecting particulate substances in exhaust gas; and a honeycomb catalyst body for purifying NOin the exhaust gas. The honeycomb filter has a partition wall for forming a plurality of channels, and the plurality of channels have a plurality of first channels in which an end part on one end surface side of the honeycomb filter is sealed and a plurality of second channels in which an end part on the other end surface side is sealed. The honeycomb catalyst body comprises a honeycomb structure having a partition wall for forming a plurality of channels and a catalyst layer including zeolite formed on the partition wall surface in the plurality of channels, and both partition walls of the honeycomb filter and the honeycomb catalyst body contains aluminum titanate-based ceramics containing at least one kind of elements selected from Mg, Ca, Sr, Y, Ba, lanthanoid and Bi.

Description

  The present invention relates to an exhaust gas purification system.

  The honeycomb filter is used to remove the collected material from the fluid containing the collected material. For example, particulate matter (PM) contained in exhaust gas discharged from an internal combustion engine such as a diesel engine (PM) : Particulate Matter) is used as a ceramic filter (diesel particulate filter). The honeycomb filter has a plurality of parallel flow paths partitioned by partition walls, and one end of a part of the plurality of flow paths and the other end of the remaining part of the plurality of flow paths are sealed. . As a honeycomb structure constituting such a honeycomb filter, for example, structures described in Patent Documents 1 and 2 below are known.

Further, as a method of decomposing the NO _X contained in the exhaust gas, the method of decomposing the NO _X by reaction such as the following formulas (2) to (4) are known from the ammonia. This method is called SCR (Selective Catalytic Reduction) because NO _x is selectively reduced by ammonia. As shown in the following formula (1), ammonia can be generated by hydrolyzing urea water at a high temperature. A method of decomposing NO _X in exhaust gas using ammonia generated from urea is called urea SCR.
CO (NH ₂ ) ₂ + H ₂ O → 2NH ₃ + CO ₂ (1)
4NH ₃ + 4NO + O ₂ → 4N ₂ + 6H ₂ O (2)
2NH ₃ + NO + NO ₂ → 2N ₂ + 3H ₂ O (3)
8NH ₃ + 6NO ₂ → 7N ₂ + 12H ₂ O (4)

In a diesel vehicle, in order to efficiently reduce NO _x by SCR, for example, a honeycomb catalyst body in which a catalyst containing zeolite that easily adsorbs ammonia is supported on a honeycomb structure is used. A honeycomb structure similar to that used for the honeycomb filter is also used for this honeycomb catalyst body. The honeycomb catalyst body and the diesel particulate filter are arranged in series to construct an exhaust gas purification system.

JP 2006-239603 A Japanese Patent Laid-Open No. 2001-46886

  As shown in Patent Documents 1 and 2, cordierite is widely used in the honeycomb structure constituting the diesel particulate filter and the honeycomb catalyst body. However, the diesel particulate filter and honeycomb catalyst body using cordierite may cause melting damage, cracks, and the like when exposed to high temperatures, and there is a problem that the heat resistance reliability is not sufficient.

  An object of this invention is to provide the exhaust gas purification system excellent in heat resistance reliability.

In order to achieve the above object, the present invention is an exhaust gas purification system comprising a honeycomb filter that collects particulate matter contained in exhaust gas, and a honeycomb catalyst body that purifies NO _x contained in the exhaust gas, The honeycomb filter includes partition walls that form a plurality of channels that are parallel to each other, and the plurality of channels are a plurality of first channels that are sealed at one end face side of the honeycomb filter; A plurality of second flow paths whose end portions on the other end face side are sealed,
The honeycomb catalyst body includes a honeycomb structure including partition walls that form a plurality of flow paths parallel to each other, and a catalyst layer containing zeolite formed on the partition wall surfaces in the plurality of flow paths,
Both the partition walls of the honeycomb filter and the partition walls of the honeycomb catalyst body contain at least one element selected from the group consisting of magnesium, calcium, strontium, yttrium, barium, lanthanoid and bismuth, and the aluminum titanate-based ceramics An exhaust gas purification system is provided.

  In the exhaust gas purification system, the partition walls of both the honeycomb filter and the honeycomb catalyst body contain at least one element selected from the group consisting of magnesium, calcium, strontium, yttrium, barium, lanthanoid, and bismuth, and the aluminum titanate ceramics Thus, even when the honeycomb filter and the honeycomb catalyst body are exposed to a high temperature, the occurrence of melting damage, cracks and the like is suppressed, and excellent heat resistance reliability can be obtained.

  In the exhaust gas purification system, it is preferable that one or both of the partition walls of the honeycomb filter and the partition walls of the honeycomb catalyst body further contain silicon dioxide. When the partition wall contains silicon dioxide, a glass phase is formed between the aluminum titanate crystals. Due to the presence of the glass phase, the mechanical strength of the honeycomb filter and the honeycomb catalyst body can be greatly improved.

In the exhaust gas purification system, the catalyst layer further contains at least one metal element selected from the group consisting of titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, rhodium, palladium, silver, and platinum. Is preferred. By the catalyst layer containing these metal elements, it is possible to perform the reduction of the NO _X more effectively. When these metal elements are contained in the catalyst layer, the ceramic in the honeycomb structure carrying the catalyst layer is likely to be thermally decomposed. This is because the metal element in the catalyst layer promotes the movement of aluminum atoms and titanium atoms in the aluminum titanate ceramic, and causes thermal decomposition of the aluminum titanate crystal into alumina and titania. However, because the aluminum titanate ceramics contain the specific element, the contained elements are present at the lattice positions or interstitial positions of the aluminum titanate crystal, and the elements inhibit the movement of aluminum atoms and titanium atoms. In addition, thermal decomposition of the aluminum titanate crystal can be suppressed. Therefore, while maintaining the heat resistance reliability of the honeycomb catalyst body, it is possible to improve the reducibility of NO _X.

  ADVANTAGE OF THE INVENTION According to this invention, the exhaust gas purification system excellent in heat resistance reliability can be provided.

It is a figure which shows typically the honey-comb filter which concerns on 1st Embodiment. It is an II-II arrow line view of FIG. It is a figure which shows typically the honey-comb filter which concerns on 2nd Embodiment. It is the IV-IV arrow line view of FIG. It is a figure which shows typically one Embodiment of a honeycomb catalyst body. It is the schematic of the exhaust gas purification system which concerns on one Embodiment of this invention.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings as the case may be. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and redundant description is omitted. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios.

<Honeycomb filter>
FIG. 1 is a diagram schematically showing the honeycomb filter according to the first embodiment, and FIG. 1B is an enlarged view of a region R1 in FIG. 2 is a view taken in the direction of arrows II-II in FIG. The honeycomb filter 100 has one end face (first end face) 100a and the other end face (second end face) 100b located on the opposite side of the end face 100a.

  The honeycomb filter 100 is a cylindrical body having a plurality of flow paths 110 extending in parallel to each other. The plurality of flow paths 110 are partitioned by partition walls 120 extending in parallel to the central axis of the honeycomb filter 100. The plurality of channels 110 have a plurality of channels (first channels) 110a and a plurality of channels (second channels) 110b adjacent to the channels 110a. The flow path 110a and the flow path 110b extend from the end face 100a to the end face 100b perpendicular to the end faces 100a and 100b.

  One end of the flow path 110a constituting a part of the flow path 110 is open at the end face 100a, and the other end of the flow path 110a is sealed by the sealing portion 130 at the end face 100b. One end of the flow path 110b constituting the remaining part of the plurality of flow paths 110 is sealed by the sealing portion 130 at the end face 100a, and the other end of the flow path 110b is opened at the end face 100b. In the honeycomb filter 100, for example, an end portion on the end surface 100a side of the flow path 110a is opened as a gas inlet, and an end portion on the end face 100b side of the flow path 110b is opened as a gas outlet.

  Cross sections perpendicular to the axial direction of the flow paths 110a and 110b are hexagonal. The cross section of the flow path 110b is, for example, a regular hexagonal shape in which the lengths of the sides 140 forming the cross section are substantially equal to each other, but may be a flat hexagonal shape. The cross section of the flow path 110a has, for example, a flat hexagonal shape, but may have a regular hexagonal shape. The lengths of the sides facing each other in the cross section of the channel 110a are substantially equal to each other. The cross section of the flow path 110a includes two long sides 150a having substantially the same length as the sides 150 forming the cross section, and four (two pairs) short sides 150b having substantially the same length. ,have. The short side 150b is disposed on each side of the long side 150a. The long sides 150a face each other in parallel, and the short sides 150b face each other in parallel.

  The partition 120 has the partition 120a as a part which partitions off the flow path 110a and the flow path 110b. That is, the channel 110a and the channel 110b are adjacent to each other through the partition wall 120a. By disposing one channel 110a between adjacent channels 110b, the channels 110b are alternately arranged with the channels 110a in the arrangement direction of the channels 110b (a direction substantially perpendicular to the side 140). Yes.

  Each of the sides 140 of the channel 110b is opposed to the long side 150a of any one of the plurality of channels 110a in parallel. That is, each of the wall surfaces forming the flow channel 110b faces the one wall surface forming the flow channel 110a in parallel in the partition wall 120a located between the flow channel 110a and the flow channel 110b. Further, the flow path 110 has a structural unit including one flow path 110b and six flow paths 110a surrounding the flow path 110b. In the structural unit, all the sides 140 of the flow path 110b are included. Opposite the long side 150a of the channel 110a. In the honeycomb filter 100, at least one length of the side 140 of the flow path 110b may be substantially equal to the length of the opposed long side 150a, and each length of the side 140 is equal to the length of the opposed long side 150a. It may be substantially equal.

  The partition 120 has the partition 120b as a part which partitions the mutually adjacent flow paths 110a. That is, the flow paths 110a surrounding the flow path 110b are adjacent to each other via the partition wall 120b.

  Each of the short sides 150b of the channel 110a is opposed to the short side 150b of the adjacent channel 110a in parallel. That is, the wall surfaces forming the flow path 110a face each other in parallel in the partition wall 120b located between the adjacent flow paths 110a. In the honey-comb filter 100, between the adjacent flow paths 110a, at least one length of the short side 150b of the flow path 110a may be substantially equal to the length of the opposing short side 150b. May be substantially equal to the length of the opposing short side 150b.

  FIG. 3 is a diagram schematically showing a honeycomb filter according to the second embodiment, and FIG. 3B is an enlarged view of a region R2 in FIG. 4 is a view taken in the direction of arrows IV-IV in FIG. The honeycomb filter 200 has one end face (first end face) 200a and the other end face (second end face) 200b located on the opposite side of the end face 200a.

  The honeycomb filter 200 is a cylindrical body having a plurality of flow paths 210 extending in parallel to each other. The plurality of flow paths 210 are partitioned by partition walls 220 extending in parallel with the central axis of the honeycomb filter 200. The plurality of flow paths 210 include a plurality of flow paths (first flow paths) 210a and a plurality of flow paths (second flow paths) 210b adjacent to the flow paths 210a. The channel 210a and the channel 210b extend from the end surface 200a to the end surface 200b perpendicular to the end surfaces 200a and 200b.

  One end of the flow path 210a forming a part of the flow path 210 is open at the end face 200a, and the other end of the flow path 210a is sealed by the sealing portion 230 at the end face 200b. One end of the flow path 210b forming the remaining part of the plurality of flow paths 210 is sealed by the sealing portion 230 at the end face 200a, and the other end of the flow path 210b is opened at the end face 200b. In the honeycomb filter 200, for example, an end portion on the end surface 200a side of the flow path 210a is opened as a gas inlet, and an end portion of the flow path 210b on the end surface 200b side is opened as a gas outlet.

  Cross sections perpendicular to the axial direction of the flow paths 210a and 210b are hexagonal. The cross section of the flow path 210b is, for example, a regular hexagonal shape in which the lengths of the sides 240 forming the cross section are substantially equal to each other, but may be a flat hexagonal shape. The cross section of the flow path 210a is, for example, a flat hexagonal shape, but may be a regular hexagonal shape. The lengths of the sides facing each other in the cross section of the flow path 210a are different from each other. The cross section of the channel 210a has three long sides 250a having substantially the same length and three short sides 250b having substantially the same length as the sides 250 forming the cross section. The long side 250a and the short side 250b face each other in parallel, and the short side 250b is disposed on each side of the long side 250a.

  The partition 220 has the partition 220a as a part which partitions off the flow path 210a and the flow path 210b. That is, the flow path 210a and the flow path 210b are adjacent to each other through the partition wall 220a. Between the adjacent flow paths 210b, two flow paths 210a adjacent to each other in a direction substantially orthogonal to the arrangement direction of the flow paths 210b are arranged, and the two adjacent flow paths 210a are adjacent to each other. They are arranged symmetrically across a line connecting the centers of the sections of 210b.

  Each of the sides 240 of the flow path 210b faces the long side 250a of any one of the plurality of flow paths 210a in parallel. That is, each of the wall surfaces forming the flow path 210b faces the one wall surface forming the flow path 210a in parallel in the partition wall 220a positioned between the flow path 210a and the flow path 210b. The flow path 210 includes a structural unit including one flow path 210b and six flow paths 210a surrounding the flow path 210b. In the structural unit, all the sides 240 of the flow path 210b are included. It faces the long side 250a of the flow path 210a. Each vertex of the cross section of the flow path 210b is opposed to the apex of the adjacent flow path 210b in the arrangement direction of the flow paths 210b. In the honeycomb filter 200, at least one length of the side 240 of the flow path 210b may be substantially equal to the length of the opposed long side 250a, and each length of the side 240 is equal to the length of the opposed long side 250a. It may be substantially equal.

  The partition 220 has the partition 220b as a part which partitions off the mutually adjacent flow paths 210a. That is, the flow paths 210a surrounding the flow path 210b are adjacent to each other through the partition 220b.

  Each of the short sides 250b of the flow path 210a faces the short side 250b of the adjacent flow path 210a in parallel. That is, the wall surfaces forming the flow path 210a face each other in parallel in the partition 220b located between the adjacent flow paths 210a. One flow path 210a is surrounded by three flow paths 210b. In the honey-comb filter 200, between the adjacent flow paths 210a, at least one length of the short side 250b of the flow path 210a may be substantially equal to the length of the opposing short side 250b. May be substantially equal to the length of the opposing short side 250b.

  The lengths of the honeycomb filters 100 and 200 in the axial direction of the flow path are, for example, 50 to 300 mm. The outer diameter of the honeycomb filters 100 and 200 is, for example, 50 to 250 mm. In the honeycomb filter 100, the length of the side 140 is, for example, 0.4 to 2.0 mm. The length of the long side 150a is, for example, 0.4 to 2.0 mm, and the length of the short side 150b is, for example, 0.3 to 2.0 mm. In the honeycomb filter 200, the length of the side 240 is, for example, 0.4 to 2.0 mm. The length of the long side 250a is, for example, 0.4 to 2.0 mm, and the length of the short side 250b is, for example, 0.3 to 2.0 mm. The thickness (cell wall thickness) of the partition walls 120 and 220 is, for example, 0.1 to 0.8 mm. The cell density in the honeycomb filters 100 and 200 (for example, the total density of the flow path 110a and the flow path 110b in the end face 100a in the honeycomb filter 100) is preferably 50 to 600 cpsi, and more preferably 100 to 500 cpsi.

  In the honey-comb filter 100, it is preferable that the sum total of the opening area of the some flow path 110a in the end surface 100a is larger than the sum total of the opening area of the flow path 110b in the end surface 100b. In the honey-comb filter 200, it is preferable that the sum total of the opening area of the some flow path 210a in the end surface 200a is larger than the sum total of the opening area of the flow path 210b in the end surface 200b.

  The hydraulic diameters of the flow paths 110a and 210a on the end faces 100a and 200a are preferably 1.4 mm or less from the viewpoint that pressure loss is likely to change according to the amount of collected matter. The hydraulic diameters of the flow paths 110a and 210a are preferably 0.5 mm or more, and more preferably 0.7 mm or more, from the viewpoint of further suppressing accumulation of collected substances in the region on the end face side in the flow path.

  The hydraulic diameter of the flow paths 110b and 210b at the end faces 100b and 200b is preferably larger than the hydraulic diameter of the flow paths 110a and 210a at the end faces 100a and 200a. The hydraulic diameters of the flow paths 110b and 210b in the end faces 100b and 200b are preferably 1.7 mm or less, and more preferably 1.6 mm or less, from the viewpoint that the pressure loss is more likely to change depending on the amount of collected matter. . The hydraulic diameters of the flow paths 110b and 210b are preferably 0.5 mm or more, more preferably 0.7 mm or more, from the viewpoint of further suppressing the accumulation of collected substances in the region on the end face side in the flow path. More preferably, it is 9 mm or more.

  The shape of the honeycomb filter is such that the cross section of the first channel perpendicular to the axial direction of the first channel (channels 110a and 210a) is the first side as in the honeycomb filters 100 and 200 described above. (Long sides 150a, 250a) and second sides (short sides 150b, 250b) respectively disposed on both sides of the first side, and a second channel (channels 110b, 210b). ) Each of the sides (sides 140 and 240) forming a cross section of the second flow path perpendicular to the axial direction of the first flow path are opposed to the first side of the first flow path. Each of the second sides may be in a form facing the second side of the adjacent first flow path, but is not necessarily limited to the shape described above.

  Further, the cross section of the channel perpendicular to the axial direction of the channel in the honeycomb filter is not limited to the hexagonal shape, and may be a triangular shape, a rectangular shape, an octagonal shape, a circular shape, an elliptical shape, or the like. . Moreover, in the flow path, those having different diameters may be mixed, or those having different cross-sectional shapes may be mixed. In addition, the arrangement of the flow paths is not particularly limited, and the arrangement of the central axes of the flow paths may be an equilateral triangle arrangement, a staggered arrangement, or the like arranged at the apex of the equilateral triangle. Furthermore, the honeycomb filter is not limited to a cylindrical body, and may be an elliptical column, a triangular column, a quadrangular column, a hexagonal column, an octagonal column, or the like.

  In the honeycomb filters 100 and 200, the partition walls 120 and 220 are porous, and include, for example, a porous ceramic sintered body. The partition walls 120 and 220 have a structure that allows fluid to pass therethrough. Specifically, a large number of communication holes (flow channels) through which fluid can pass are formed in the partition wall.

  The porosity of the partition walls 120 and 220 is preferably 20% by volume or more, and more preferably 30% by volume or more, from the viewpoint of further improving the collection efficiency and pressure loss of the honeycomb filter. The porosity of the partition walls 120 and 220 is preferably 70% by volume or less, and more preferably 60% by volume or less. The average pore diameter of the partition walls 120 and 220 is preferably 5 μm or more, and more preferably 10 μm or more, from the viewpoint of further improving the collection efficiency and pressure loss of the honeycomb filter. The average pore diameter of the partition walls 120 and 220 is preferably 35 μm or less, and more preferably 30 μm or less. The porosity and average pore diameter of the partition walls 120 and 220 can be adjusted by the particle diameter of the raw material, the amount of pore-forming agent added, the type of pore-forming agent, and the firing conditions, and can be measured by mercury porosimetry.

  The partition walls 120 and 220 include aluminum titanate ceramics containing at least one element selected from the group consisting of magnesium, calcium, strontium, yttrium, barium, lanthanoid, and bismuth. The aluminum titanate-based ceramics preferably contains at least one element selected from the group consisting of magnesium, calcium, strontium, barium and lanthanum from the viewpoint of further improving the heat resistance reliability of the honeycomb filter. It is particularly preferable to contain it. When the honeycomb filter is exposed to a high temperature, the movement of aluminum atoms and titanium atoms in the aluminum titanate-based ceramics may be promoted to cause thermal decomposition. For example, in magnesium magnesium titanate, magnesia is a lattice having a crystal structure. Since it exists in a position, the movement of an aluminum atom and a titanium atom can be inhibited and thermal decomposition can be suppressed. Similarly, when the specific element other than magnesium is included, the movement of aluminum atoms and titanium atoms can be similarly inhibited to suppress thermal decomposition.

The oxide content of at least one element selected from the group consisting of magnesium, calcium, strontium, yttrium, barium, lanthanoid and bismuth in the partition walls 120 and 220 is Al in which aluminum and titanium are converted into oxides. The total amount of ₂ O ₃ and TiO ₂ is preferably 0.1 to 20 parts by mass, more preferably 1.0 to 15 parts by mass, and 4.0 to 10 parts by mass with respect to 100 parts by mass. It is particularly preferred. When the content of the specific element is equal to or higher than the lower limit value, the heat resistance reliability of the honeycomb filter tends to be further improved, and when it is equal to or lower than the upper limit value, the mechanical strength can be sufficiently maintained. Tend.

In the aluminum titanate-based ceramics, the molar ratio (aluminum: titanium) of aluminum converted to Al ₂ O ₃ and titanium converted to TiO ₂ is preferably 35:65 to 45:55, and 40:60 to 45: 55 is more preferred. When the partition walls 120 and 220 contain aluminum magnesium titanate, the composition formula of aluminum magnesium titanate is, for example, Al _{2 (1-x)} Mg _x Ti _{(1 + x)} O ₅ , and the value of x is 0.03. The above is preferable, 0.03 to 0.20 is more preferable, and 0.03 to 0.18 is still more preferable.

  The partition walls 120 and 220 containing aluminum titanate ceramics are made of porous ceramics mainly made of aluminum titanate crystals, for example. “Mainly composed of an aluminum titanate crystal” means that the main crystal phase constituting the ceramic fired body is an aluminum titanate crystal phase. The aluminum titanate-based crystal phase contains at least one element selected from the group consisting of magnesium, calcium, strontium, yttrium, barium, lanthanoid and bismuth.

The partition walls 120 and 220 containing the aluminum titanate ceramic may contain a glass phase derived from silicon source powder. The glass phase refers to an amorphous phase in which SiO ₂ is the main component. Moreover, the partition 120,220 containing an aluminum titanate ceramic may contain a crystal phase other than an aluminum titanate crystal phase or a glass phase. Examples of such a crystal phase include a phase derived from a raw material used for producing a ceramic fired body. The phase derived from the raw material is, for example, a phase derived from an aluminum source powder, a titanium source powder, a magnesium source powder, or the like remaining without forming an aluminum titanate-based crystal phase during the manufacture of the honeycomb filter, such as alumina, titania, magnesia. And the like. The crystal phase forming the partition walls 120 and 220 can be confirmed by an X-ray diffraction spectrum.

When the partition walls 120 and 220 contain SiO ₂ , the content is preferably 0.5 to 30% by mass, more preferably 1.0 to 25% by mass, based on the total amount of the partition walls. It is especially preferable that it is 0.0-20 mass%. When the content of SiO ₂ is less than the above lower limit value, the mechanical strength after sintering tends to be low and easily collapses. When the content exceeds the above upper limit value, the thermal expansion coefficient of the sintered honeycomb tends to increase. There is.

  The honey-comb filters 100 and 200 are suitable as a particulate filter which collects particulate substances (collected matter), such as soot, contained in the exhaust gas from internal combustion engines, such as a diesel engine and a gasoline engine, for example. For example, in the honeycomb filter 100, as shown in FIG. 2, the gas G supplied from the end face 100a to the flow path 110a passes through the communication hole in the partition wall 120 and reaches the adjacent flow path 110b, and from the end face 100b. Discharged. At this time, the collected matter in the gas G is collected on the surface of the partition wall 120 or in the communication hole and removed from the gas G, whereby the honeycomb filter 100 functions as a filter. Similarly, the honeycomb filter 200 functions as a filter.

<Honeycomb catalyst body>
FIG. 5 is a diagram schematically showing one embodiment of a honeycomb catalyst body. The honeycomb catalyst body 300 includes a honeycomb structure 330 that includes partition walls 320 that form a plurality of flow paths 310 that are parallel to each other, and a catalyst layer 360 that includes zeolite formed on the surfaces of the partition walls in the plurality of flow paths 310. It is a cylinder. The plurality of flow paths 310 are partitioned by partition walls 320 extending parallel to the central axis of the honeycomb catalyst body 300. The plurality of flow paths 310 extend from one end face to the other end face perpendicular to both end faces of the honeycomb catalyst body 300. The plurality of flow paths 310 are through holes without a sealing portion.

  The cross section of the flow path 310 perpendicular to the axial direction of the flow path has a regular hexagonal shape in which the sides 340 forming the cross section have substantially the same length.

  The length of the honeycomb catalyst body 300 in the axial direction of the flow path is, for example, 50 to 300 mm. The outer diameter of the honeycomb catalyst body 300 is, for example, 30 to 270 mm. In the honeycomb catalyst body 300, the length of the side 340 is, for example, 0.4 to 2.0 mm. The partition 320 has a thickness (cell wall thickness) of, for example, 0.1 to 0.8 mm. The cell density in the honeycomb catalyst body 300 is preferably 50 to 600 cpsi, and more preferably 100 to 500 cpsi.

Loading amount of the catalyst layer 360 per unit volume of the honeycomb catalyst body 300, while suppressing the pressure loss during an exhaust gas passage, from the viewpoint of obtaining excellent NO _X resolution, is preferably 20 to 300 mg / cm ^3, More preferably, it is 50-200 mg / cm ³ .

Hydraulic diameter of the channel 310, while suppressing the pressure loss during an exhaust gas passage, from the viewpoint of obtaining excellent NO _X resolution, is preferably not more than 1.7 mm, more preferably 1.6mm or less, More preferably, it is 1.4 mm or less. The hydraulic diameter of the flow path 310 is preferably 0.5 mm or more, and more preferably 0.7 mm or more from the viewpoint of suppressing pressure loss when the exhaust gas passes.

  In addition, the cross section of the flow path perpendicular to the axial direction of the flow path in the honeycomb catalyst body is not limited to a regular hexagonal shape, and is a flat hexagonal shape or a flat hexagonal shape as shown in FIGS. 1 and 3. And a combination of a regular hexagon and the like. The cross section of the flow path is not limited to a hexagonal shape, and may be a triangular shape, a rectangular shape, an octagonal shape, a circular shape, an elliptical shape, or the like. Moreover, in the flow path, those having different diameters may be mixed, or those having different cross-sectional shapes may be mixed. In addition, the arrangement of the flow paths is not particularly limited, and the arrangement of the central axes of the flow paths may be an equilateral triangle arrangement, a staggered arrangement, or the like arranged at the apex of the equilateral triangle. Furthermore, the honeycomb catalyst body is not limited to a cylindrical body, and may be an elliptical column, a triangular column, a quadrangular column, a hexagonal column, an octagonal column, or the like.

  In the honeycomb catalyst body 300, the partition walls 320 are made of the same material as the partition walls 120 and 220 of the honeycomb filters 100 and 200 described above. The porosity of the partition 320 may be smaller than the porosity of the partition 120, 220 of the honeycomb filter 100, 200 described above from the viewpoint of improving mechanical strength, and the light-off temperature ( From the viewpoint of early arrival at the temperature at which the catalyst becomes active, the same porosity may be used. The partition 320 includes an aluminum titanate ceramic containing at least one element selected from the group consisting of magnesium, calcium, strontium, yttrium, barium, lanthanoid and bismuth. The aluminum titanate-based ceramics preferably contains at least one element selected from the group consisting of magnesium, calcium, strontium, barium and lanthanum from the viewpoint of further improving the heat resistance reliability of the honeycomb catalyst body. It is particularly preferable to contain When the honeycomb catalyst body is exposed to a high temperature, the movement of aluminum atoms and titanium atoms in the aluminum titanate-based ceramics may be promoted and thermal decomposition may occur.For example, in magnesium magnesium titanate, magnesia has a crystal structure. Since it exists in a lattice position, the movement of an aluminum atom and a titanium atom can be inhibited and thermal decomposition can be suppressed. Similarly, when the specific element other than magnesium is included, the movement of aluminum atoms and titanium atoms can be similarly inhibited to suppress thermal decomposition.

The oxide content of at least one element selected from the group consisting of magnesium, calcium, strontium, yttrium, barium, lanthanoid and bismuth in the partition 320 is Al ₂ O in which aluminum and titanium are converted into oxides. ₃ and 100 parts by mass of TiO ₂ are preferably 0.1 to 20 parts by mass, more preferably 1.0 to 15 parts by mass, and 4.0 to 10 parts by mass. Is particularly preferred. When the content of the specific element is equal to or higher than the lower limit value, the heat resistance reliability of the honeycomb catalyst body tends to be further improved, and when the content is equal to or lower than the upper limit value, sufficient mechanical strength can be maintained. There is a tendency to be able to.

In the aluminum titanate-based ceramics, the molar ratio (aluminum: titanium) of aluminum converted to Al ₂ O ₃ and titanium converted to TiO ₂ is preferably 35:65 to 45:55, and 40:60 to 45: 55 is more preferred. When the partition 320 contains aluminum magnesium titanate, the composition formula of aluminum magnesium titanate is, for example, Al _{2 (1-x)} Mg _x Ti _{(1 + x)} O ₅ , and the value of x is 0.03 or more. Preferably, 0.03 to 0.20 is more preferable, and 0.03 to 0.18 is still more preferable.

  The partition 320 containing an aluminum titanate-based ceramic is made of, for example, a porous ceramic mainly made of an aluminum titanate-based crystal. “Mainly composed of an aluminum titanate crystal” means that the main crystal phase constituting the ceramic fired body is an aluminum titanate crystal phase. The aluminum titanate-based crystal phase contains at least one element selected from the group consisting of magnesium, calcium, strontium, yttrium, barium, lanthanoid and bismuth.

The partition 320 containing the aluminum titanate-based ceramics may include a glass phase derived from silicon source powder. The glass phase refers to an amorphous phase in which SiO ₂ is the main component. Moreover, the partition 320 containing an aluminum titanate ceramic may contain a crystal phase other than an aluminum titanate crystal phase or a glass phase. Examples of such a crystal phase include a phase derived from a raw material used for producing a ceramic fired body. The phase derived from the raw material is a phase derived from, for example, an aluminum source powder, a titanium source powder, a magnesium source powder, etc. that remain without forming an aluminum titanate-based crystal phase in the production of the honeycomb catalyst body, such as alumina, titania, Examples include magnesia. The crystal phase forming the partition 320 can be confirmed by an X-ray diffraction spectrum.

If the partition wall 320 contains SiO _2, the content thereof is preferably from 0.5 to 30 wt% of the partition wall based on the total, more preferably from 1.0 to 25 wt%, 2.0 It is especially preferable that it is -20 mass%. When the content of SiO ₂ is less than the above lower limit value, the mechanical strength after sintering tends to be low and easily collapses. When the content exceeds the above upper limit value, the thermal expansion coefficient of the sintered honeycomb tends to increase. There is.

The catalyst layer 360 is a layer mainly composed of porous zeolite. The catalyst layer 360 preferably further contains at least one metal element selected from the group consisting of titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, rhodium, palladium, silver, and platinum. Since the zeolite is a metal ion-exchanged zeolite ion-exchanged with the ions of the above metal elements, the NO _X reducing property is improved. In the metal ion exchanged zeolite, cations such as sodium ions contained in the zeolite are replaced with other metal ions. Since the effect of improving NO _X reduction is great, the metal element is preferably at least one selected from the group consisting of copper, iron, vanadium, cobalt, nickel and silver, and particularly preferably copper. . Examples of the zeolite include ZSM-5, β zeolite, mordenite, ferrierite, chabazite, A-type, X-type, Y-type zeolite, and MCM-22. Among these, zeolite is preferably one containing a ZSM-5 or chabazite since it is excellent in the NO _X reducing.

  The catalyst layer 360 has a structure that allows fluid to permeate. Specifically, a large number of communication holes (flow paths) through which fluid can pass are formed in the catalyst layer. The catalyst layer 360 is provided so as not to block the communication hole (flow path) of the partition wall 320 so that the fluid can pass through both the catalyst layer 360 and the partition wall 320.

The porosity of the catalyst layer 360 is preferably 20% by volume or more, and more preferably 30% by volume or more, from the viewpoint of obtaining excellent NO _X reduction ability. The porosity of the catalyst layer is preferably 70% by volume or less, and more preferably 60% by volume or less, from the viewpoint of obtaining an excellent ammonia adsorption amount and NO _X reduction ability. The average pore diameter of the catalyst layer is preferably 5 μm or more, and more preferably 8 μm or more from the viewpoint of obtaining excellent NO _X reduction ability. The average pore diameter of the catalyst layer is preferably 30 μm or less, and more preferably 25 μm or less, from the viewpoint of obtaining excellent NO _X reducing ability. The porosity and average pore diameter of the catalyst layer can be adjusted by the type of zeolite used and the granulation of the zeolite powder, and can be measured by mercury porosimetry.

The content of at least one metal element selected from the group consisting of titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, rhodium, palladium, silver and platinum in the catalyst layer 360 is an aluminum titanate ceramic. while the degradation of thermal inhibition, from the viewpoint of obtaining excellent NO _X reducing ability is preferably 0.01 to 1.0 wt% of the catalyst layer based on the total at 0.05 to 0.5 mass% More preferably.

The molar ratio of the zeolite of silica in the catalyst layer 360 (SiO ₂₎ and alumina _(Al 2 _{O 3)} (silica / alumina), while suppressing the thermal decomposition of aluminum titanate-based ceramics, excellent NO _X reduction ability Is preferably 10 to 10,000, and more preferably 20 to 5,000.

The honeycomb catalyst body 300 is suitable as a NO _X purification catalyst that purifies NO _X contained in exhaust gas from an internal combustion engine such as a diesel engine or a gasoline engine. In particular, the honeycomb catalyst body 300 is suitable as a catalyst for urea SCR. For example, in the honeycomb catalyst body 300, the exhaust gas is supplied from one end face of the honeycomb catalyst body 300 into the flow path 310 and discharged from the other end face until NO _X in the exhaust gas is N ₂ and H _2. Decomposed into O.

<Exhaust gas purification system>
FIG. 6 is a schematic view showing an embodiment of the exhaust gas purification system. The exhaust gas purification system of the present embodiment includes the above-described honeycomb filter 100 and the honeycomb catalyst body 300. The exhaust gas purification system may include a honeycomb filter 200 instead of the honeycomb filter 100.

In the exhaust gas purification system shown in FIG. 6, the gas G discharged from the internal combustion engine 500 such as a diesel engine or a gasoline engine is first supplied to an oxidation catalyst (DOC: Diesel Oxidation Catalyst) 510. For the oxidation catalyst 510, for example, a noble metal catalyst such as platinum or palladium is used. These noble metal catalysts are used, for example, supported on a honeycomb structure. The oxidation catalyst 510 removes hydrocarbons, carbon monoxide and the like contained in the gas G. Further, the oxidation catalyst 510, also occurs conversion to NO ₂ in the NO. Since NO ₂ functions as a strong oxidant, soot can be oxidized (combusted) efficiently due to the presence of NO ₂ when soot accumulated in the subsequent honeycomb filter 100 is combusted.

Next, the gas G is supplied to the honeycomb filter 100, and particulate matter (collected matter) such as soot is removed. Subsequently, the gas G is supplied to the honeycomb catalyst body 300, and NO _X purification is performed. Ammonia as a reducing agent for purifying NO _X is produced by ejecting from the urea water supply device 520 urea water U in the gas G. Thereby, as shown in the above formulas (1) to (4), NO _X in the gas G is decomposed into N ₂ and H ₂ O.

  The exhaust gas purification system may further include an oxidation catalyst (DOC) at the subsequent stage of the honeycomb catalyst body 300. The oxidation catalyst provided in the subsequent stage of the honeycomb catalyst body 300 is effective for removing the remaining ammonia.

In the exhaust gas purification system shown in FIG. 6, the arrangement of the honeycomb filter 100 and the honeycomb catalyst body 300 may be reversed. That is, the honeycomb catalyst body 300 may be disposed on the upstream side, and the honeycomb filter 100 may be disposed on the downstream side. In this case, after the purification of the NO _X in the presence of ammonia it has been performed by the honeycomb catalyst body 300, particulate matter such as soot in the gas G by a honeycomb filter 100 (to be collected matter) is removed. At this time, the urea water U is supplied upstream of the honeycomb catalyst body 300.

  In the exhaust gas purification system, both the honeycomb filter 100 and the honeycomb catalyst body 300 are required to have high heat resistance. For example, in the exhaust gas purification system shown in FIG. 6, since a high-temperature gas G of 800 ° C. or higher may flow into the honeycomb filter 100 close to the internal combustion engine 500, no melting damage or cracking occurs at the above temperature. High heat resistance is required. Even in the vicinity of the outlet of the honeycomb filter 100, the temperature of the gas G may be as high as 800 ° C. or higher. Therefore, the honeycomb catalyst body 300 is also required to have high heat resistance that does not cause melting or cracking at the above temperature. According to the exhaust gas purification system of the present invention, the partition walls of both the honeycomb filter 100 and the honeycomb catalyst body 300 contain at least one element selected from the group consisting of magnesium, calcium, strontium, yttrium, barium, lanthanoid and bismuth. By including the aluminum titanate-based ceramics, the occurrence of melting damage, cracks, and the like is suppressed, and excellent heat resistance reliability can be obtained.

<Honeycomb filter manufacturing method>
Next, a method for manufacturing a honeycomb filter will be described. The honeycomb filter manufacturing method includes, for example, a raw material preparation step of preparing a raw material mixture containing inorganic compound powder and additives, a forming step of forming the raw material mixture to obtain a formed body having a flow path, and firing the formed body A sealing step of sealing one end of each flow path between the molding step and the baking step or after the baking step. Hereinafter, each step will be described.

[Raw material preparation process]
In the raw material preparation step, the inorganic compound powder and the additive are mixed and then kneaded to prepare a raw material mixture. Inorganic compound powders include, for example, aluminum source powders such as α-alumina powders, titanium source powders (titanium source powders) such as anatase type and rutile type titania powders, and magnesium, calcium, strontium, yttrium, barium, lanthanoids, and the like A raw material powder of at least one element selected from the group consisting of bismuth is included, and a silicon source powder such as silicon oxide powder or glass frit can be further included as necessary. Examples of the magnesium source powder include magnesia powder and magnesia spinel powder. Examples of the calcium source powder include calcia powder, calcium carbonate powder, anorthite, and the like. Examples of the strontium source powder include strontium oxide powder and strontium carbonate powder. Examples of the yttrium source powder include yttrium oxide powder. Examples of the barium source powder include barium oxide powder, barium carbonate powder, and feldspar. Examples of the bismuth source powder include bismuth oxide powder. Each raw material powder may be one type or two or more types. Each raw material powder may contain a trace component derived from the raw material or inevitably contained in the production process.

  For each raw material powder, the volume-based cumulative particle size equivalent to 50% (center particle size, D50) measured by a laser diffraction method is preferably in the following range. D50 of the aluminum source powder is, for example, 20 to 60 μm. D50 of the titanium source powder is, for example, 0.1 to 25 μm. D50 of the magnesium source powder is, for example, 0.5 to 30 μm. D50 of the silicon source powder is, for example, 0.5 to 30 μm.

  The raw material mixture may contain aluminum titanate or aluminum magnesium titanate. For example, when aluminum magnesium titanate is used as a constituent of the raw material mixture, the aluminum magnesium titanate corresponds to a raw material mixture having an aluminum source, a titanium source, and a magnesium source.

  Examples of the additive include a pore-forming agent (pore-forming agent), a binder, a plasticizer, a dispersant, and a solvent.

  As the pore-forming agent, one formed by a material that disappears at a temperature lower than the temperature at which the molded body is degreased and fired in the firing step can be used. In degreasing and firing, when the molded body containing the pore forming agent is heated, the pore forming agent disappears due to combustion or the like. As a result, a space is created at the location where the pore-forming agent was present, and the communication hole through which the fluid can flow is formed in the partition wall by shrinking the inorganic compound powder located between the spaces during firing. Can be formed.

  Examples of the pore-forming agent include corn starch, barley starch, wheat starch, tapioca starch, bean starch, rice starch, pea starch, coral starch, canna starch, and potato starch (potato starch). In the pore-forming agent, the volume-based cumulative particle size (D50) corresponding to a volume-based cumulative percentage measured by a laser diffraction method (D50) is, for example, 5 to 50 μm. When the raw material mixture contains a pore-forming agent, the content of the pore-forming agent is, for example, 1 to 25 parts by mass with respect to 100 parts by mass of the inorganic compound powder.

  The binder is, for example, celluloses such as methyl cellulose, hydroxypropyl methyl cellulose, carboxymethyl cellulose, sodium carboxymethyl cellulose; alcohols such as polyvinyl alcohol; salts such as lignin sulfonate; waxes such as paraffin wax and microcrystalline wax. Content of the binder in a raw material mixture is 20 mass parts or less with respect to 100 mass parts of inorganic compound powder, for example.

  Plasticizers include, for example, alcohols such as glycerin; higher fatty acids such as caprylic acid, lauric acid, palmitic acid, alginic acid, oleic acid, stearic acid; stearic acid metal salts such as Al stearate, polyoxyalkylene alkyl ethers (eg Polyoxyethylene polyoxypropylene butyl ether). Content of the plasticizer in a raw material mixture is 10 mass parts or less with respect to 100 mass parts of inorganic compound powder, for example.

  Examples of the dispersant include inorganic acids such as nitric acid, hydrochloric acid, and sulfuric acid; organic acids such as oxalic acid, citric acid, acetic acid, malic acid, and lactic acid; alcohols such as methanol, ethanol, and propanol; and ammonium polycarboxylate. Content of the dispersing agent in a raw material mixture is 20 mass parts or less with respect to 100 mass parts of inorganic compound powder, for example.

  The solvent is, for example, water, and ion-exchanged water is preferable in terms of few impurities. When a raw material mixture contains a solvent, content of a solvent is 10-100 mass parts with respect to 100 mass parts of inorganic compound powder, for example.

[Molding process]
In the forming step, a green honeycomb formed body having a honeycomb structure is obtained. In the molding step, for example, a so-called extrusion molding method in which the raw material mixture is extruded from a die while being kneaded by a single screw extruder can be employed.

[Baking process]
In the firing step, the honeycomb structured green honeycomb formed body obtained in the forming step is fired to obtain a honeycomb fired body. In the firing step, calcination (degreasing) for removing a binder or the like contained in the molded body (in the raw material mixture) may be performed before the molded body is fired. In the firing of the molded body, the firing temperature is usually 1300 ° C. or higher, preferably 1400 ° C. or higher. Moreover, a calcination temperature is 1650 degrees C or less normally, Preferably it is 1550 degrees C or less. The temperature raising rate is not particularly limited, but is usually 1 to 500 ° C./hour. The firing time may be a time sufficient for the inorganic compound powder to transition to the aluminum titanate-based crystal, and varies depending on the amount of raw material, type of firing furnace, firing temperature, firing atmosphere, etc., but usually 10 minutes to 24 hours.

[Sealing process]
The sealing step is performed between the molding step and the firing step or after the firing step. When a sealing step is performed between the forming step and the firing step, one end of each flow path of the green honeycomb molded body obtained in the forming step is sealed with a sealing material, and then green honeycomb forming is performed in the firing step. By firing the sealing material together with the body, a honeycomb structure including a sealing portion that seals one end of the flow path is obtained. When performing the sealing step after the firing step, after sealing one end of each flow path of the honeycomb fired body obtained in the firing step with the sealing material, the flow path is obtained by firing the sealing material together with the honeycomb fired body. A honeycomb structure provided with a sealing portion that seals one end of the above is obtained. As the sealing material, a mixture similar to the raw material mixture for obtaining the green honeycomb molded body can be used.

<Method for manufacturing honeycomb catalyst body>
Next, a method for manufacturing a honeycomb catalyst body will be described. The method for manufacturing a honeycomb catalyst body includes, for example, a raw material preparation step of preparing a raw material mixture containing inorganic compound powder and additives, a forming step of forming the raw material mixture to obtain a formed body having a flow path, and a formed body. A firing step for firing, and a catalyst layer forming step for forming a catalyst layer. Among these, the steps after firing until obtaining an unsealed honeycomb structure can be performed by the same method as the above-described honeycomb filter manufacturing method.

[Catalyst layer forming step]
The catalyst layer forming step is performed after the firing step. First, zeolite is wet-mixed with at least one metal element selected from the group consisting of titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, rhodium, palladium, silver and platinum, and dried and crushed. After that, this is mixed with silica sol, alumina sol, and water to produce a slurry. For example, among the above metal elements, copper can be exchanged into the pores of the zeolite by using copper acetate and iron as an ammine complex. Next, the prepared slurry is sucked into the flow path of the honeycomb structure and applied to the partition wall surfaces. After application, the film is dried at 600 ° C. to 700 ° C. for about 4 hours to remove moisture. In this way, a catalyst layer containing zeolite and the specific metal element is produced. The catalyst layer does not enter the communication hole of the partition wall, but is formed on the surface of the partition wall. As described above, a honeycomb catalyst body having a catalyst layer on the partition wall surface of the flow path can be obtained.

<Manufacturing method of exhaust gas purification system>
As shown in FIG. 6, the exhaust gas purification system is constructed by arranging the honeycomb filter 100 and the honeycomb catalyst body 300 in series in the middle of the exhaust gas passage through which the gas G discharged from the internal combustion engine 500 flows. be able to. Further, the oxidation catalyst 510 is arranged on the upstream side of the honeycomb filter 100 and the honeycomb catalyst body 300, or on both the upstream side and the downstream side, so that urea water can be injected upstream of the honeycomb catalyst body 300. By disposing the supply device 520, an exhaust gas purification system can be constructed.

  DESCRIPTION OF SYMBOLS 100,200 ... Honeycomb filter, 100a, 200a ... One end surface (1st end surface), 100b, 200b ... The other end surface (2nd end surface), 110, 210 ... Channel, 110a, 210a ... Channel (first) 1 channel), 110b, 210b ... channel (second channel), 120, 220 ... partition wall, 300 ... honeycomb catalyst body, 310 ... channel, 320 ... partition wall, 330 ... honeycomb structure, 360 ... catalyst Layer: 500 ... Internal combustion engine, 510 ... Oxidation catalyst (DOC), 520 ... Urea water supply device.

Claims (3)

An exhaust gas purification system comprising: a honeycomb filter that collects particulate matter contained in exhaust gas; and a honeycomb catalyst body that purifies NO _x contained in exhaust gas,
The honeycomb filter includes partition walls that form a plurality of channels that are parallel to each other, and the plurality of channels are a plurality of first channels that are sealed at one end face side of the honeycomb filter; A plurality of second flow paths whose end portions on the other end face side are sealed,
The honeycomb catalyst body includes a honeycomb structure including partition walls forming a plurality of flow paths parallel to each other, and a catalyst layer including zeolite formed on the partition wall surfaces in the plurality of flow paths,
Both the partition walls of the honeycomb filter and the partition walls of the honeycomb catalyst body contain at least one element selected from the group consisting of magnesium, calcium, strontium, yttrium, barium, lanthanoid and bismuth. Including exhaust gas purification system.   The exhaust gas purification system according to claim 1, wherein one or both of the partition walls of the honeycomb filter and the partition walls of the honeycomb catalyst body further contain silicon dioxide.   The said catalyst layer further contains at least 1 type of metal element selected from the group which consists of titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, rhodium, palladium, silver, and platinum. Exhaust gas purification system.

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