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  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
  • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
  • B01D53/9445—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]
  • B01D53/945—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC] characterised by a specific catalyst
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  • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
  • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
  • B01J21/066—Zirconium or hafnium; Oxides or hydroxides thereof
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/0009—Use of binding agents; Moulding; Pressing; Powdering; Granulating; Addition of materials ameliorating the mechanical properties of the product catalyst
  • B01J37/0027—Powdering
  • B01J37/0036—Grinding
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/0201—Impregnation
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/03—Precipitation; Co-precipitation
  • B01J37/031—Precipitation
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  • B01D2255/1025—Rhodium
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  • B01D2255/2065—Cerium
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01D2255/2092—Aluminium
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01D2255/90—Physical characteristics of catalysts
  • B01D2255/908—O2-storage component incorporated in the catalyst
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/10—Internal combustion engine [ICE] based vehicles
  • Y02T10/12—Improving ICE efficiencies

Definitions

• the invention relates to an exhaust gas purification catalyst including a composite oxide support and a precious metal catalyst supported on a surface thereof.
• the exhaust gas purification catalyst includes an oxide catalyst, a ternary catalyst, and a NOx storage and reduction catalyst.
• a catalyst of a precious metal such as platinum, rhodium, or palladium develops catalyst activity.
• the precious metal catalyst is generally used in a state supported on a support composed of porous oxide such as alumina.
• the exhaust gas purification catalyst is generally used under a high temperature atmosphere. Accordingly, it is desirable that a catalyst has high heat resistance that allows to maintain high catalyst activity even after long term use under a high temperature atmosphere .
• a particulate inorganic mixed oxide that contains aluminum, zirconium, cerium and first and second additive elements is disclosed.
• the first and second additive elements are selected from the group consisting of rare earth elements excluding cerium and alkali earth elements. More specifically, the inorganic mixed oxide is composed as shown below.
• a rate of content of aluminum in the inorganic mixed oxide is 60 to 90% by atom as an element with respect to a total amount of elements that become a positive ion in the inorganic mixed oxide; a rate of content of cerium in the inorganic mixed oxide is 0.4 to 50% by atom as an element with respect to a total amount of zirconium and cerium in the inorganic mixed oxide; a rate of content of a total amount of the first and second additive elements is 1 to 12% by atom as elements with respect to a total amount of elements that become positive ions in the inorganic mixed oxide; 80% or more of primary particles of the inorganic mixed oxide has a particle size of 100 nm or less; and in at least a part of superficial portion of the primary particles, a surface concentration region where a rate of content of the second additive element is locally enhanced is formed.
• the first additive element is lanthanum and the second additive element is neodymium.
• An inorganic mixed oxide where neodymium oxide is concentrated on a surface of oxides of aluminum, zirconium and cerium, that is, alumina, zirconia and ceria is a raw material excellent in the heat resistance. Further, the inorganic mixed oxide exerts oxygen storage capacity (OSC capacity), HC modification capacity and NOx purification performance with good balance.
• OSC capacity oxygen storage capacity
• HC modification capacity HC modification capacity
• NOx purification performance with good balance.
• the invention provides an exhaust gas purification catalyst that has high heat resistance, excellent oxygen storage capacity, HC modification capacity and NOx purification capacity, further high oxygen release capacity and endurance, and high pressure loss reduction effect as a catalyst.
• An exhaust gas purification catalyst includes a composite oxide support, and a precious metal catalyst supported on the composite oxide support.
• the composite oxide support includes alumina (A1 2 0 3 ), zirconia (Zr0 2 ) and ceria (Ce0 2 ), a first additive element oxide and a second additive element oxide.
• the first additive element oxide contains an additive element selected from the group consisting of rare earth elements excluding cerium (Ce) and alkali earth elements.
• the second additive element oxide contains an additive element selected from the group consisting of rare earth elements excluding cerium and alkali earth elements.
• alumina is contained in a range of 30 to 40% by mass and zirconia is contained in a range of 36 to 46% by mass.
• a rate of content of alumina is set to a range such low as 30 to 40% by mass
• a rate of content of zirconia can be set to a relatively high range such as 36 to 46% by mass.
• the exhaust gas purification catalyst of the aspect of the invention has high heat resistance, excellent oxygen storage capacity and HC modification capacity and NOx purification capacity. Further, as the exhaust gas purification catalyst of the aspect of the invention, an exhaust gas purification catalyst that has high oxygen release capacity and endurance, and has, as a catalyst, a high pressure loss reduction effect can be obtained.
• FIG. 1 is a diagram showing results of experiments that verified the oxygen storage capacity (OSC capacity) and the oxygen release capacity of each of exhaust gas purification catalysts (Examples 1 and 2, Comparative Examples 1 and 2) when contents of alumina and zirconia were changed;
• FIG. 2 is a diagram showing results of experiments that verified the endurance of each of exhaust gas purification catalysts (Examples 2 to 5, Comparative Example 3) when a content of yttrium oxide was changed;
• FIG. 3 is a diagram showing results of experiments that identified a bulk density of each of exhaust gas purification catalysts (Examples 1 and 2, Comparative Examples 1 and 2) when a content of alumina was changed;
• FIG. 4 is a diagram showing results of experiments that measured pressure loss of each of Example 2 and Comparative Example 1.
• the exhaust gas purification catalyst of the embodiment of the invention includes a composite oxide support and a precious metal catalyst supported on the composite oxide support.
• the composite oxide support includes alumina, zirconia, ceria, a first additive element oxide and a second additive element oxide.
• the first additive element oxide contains an additive element selected from the group consisting of rare earth elements excluding cerium and alkali earth elements.
• the second additive element oxide contains an additive element selected from the group consisting of rare earth elements excluding cerium and alkali earth elements.
• each of the above elements is yttrium (Y), lanthanum (La) and neodymium (Nd), and so on.
• the additive element contained in the first additive element oxide may be different from the additive element included in the second additive element oxide.
• the combination of the first additive element oxide and the second additive element oxide may contain two kinds of additive elements.
• oxides of the two kinds of additive elements may be constituent elements of the composite oxide support.
• alumina and zirconia are respectively contained in the range of 30 to 40% by mass and 36 to 46% by mass.
• the alumina may be amorphous alumina such as activated alumina, or crystalline alumina.
• a surface concentration region where a rate of content of the second additive element oxide is high is formed on at least a part of a superficial layer (of respective primary particles, or secondary particles in which the primary particles are flocculated) of alumina, zirconia and ceria.
• a range of each of rates of content of alumina and zirconia is a range where both oxygen storage capacity and deterioration preventive capacity of a supported precious metal catalyst are efficient.
• the range of each of rates of content is based on results verified. For example, in the range where a content of alumina is less than 30% by mass, an area for supporting the precious metal catalyst reduces. As a result, the deterioration of the precious metal catalyst after endurance test increases.
• two additive elements selected from the group consisting of rare earth elements and alkali earth elements are two elements selected from the group consisting of yttrium (Y), lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Rd).
• the additive element contained in the first additive element oxide may be referred as a first additive element.
• the additive element contained in the second additive element oxide may be referred as a second additive element.
• a precious metal catalyst supported on a surface of the composite oxide support for example, platinum (Pt), palladium (Pd) and rhodium (Rh) may be used singularly or in a combination thereof.
• Pt platinum
• Pd palladium
• Rh rhodium
• a bond represented by Rh-O-M M represents the second additive element
• the second additive element it is preferable to use Y, La, Pr, Nd, Yb, Mg, Ca or Ba. Among those, Nd is more preferable.
• the first additive element is an element for stabilizing a structure.
• the second additive element is an element for surface concentration.
• the same element may be used.
• La may be used as the first additive element (structure stabilization element)
• Nd may be used as the second additive element (surface concentrating element). That is, lanthanum oxide may be bonded to alumina, zirconia and ceria, and then, on at least a part of a surface of each of alumina, zirconia and ceria, a neodymium oxide may form a high concentration region thereof to constitute a composite oxide support.
• an exhaust gas purification catalyst where rhodium is supported on the composite oxide support may be formed.
• a rate of content of alumina may be defined in the range of 30 to 40% by mass and a rate of content of zirconia may be defined in the range of 36 to 46% by mass.
• ceria may be contained by 20% by mass
• each of lanthanum oxide and neodymium oxide may be contained by 2% by mass.
• lanthanum oxide and neodymium oxide may be respectively regarded as the first additive element oxide and the second additive element oxide.
• rates of content of alumina and zirconia may be adjusted in the ranges so that a sum total of rates of content of all compositions may be 100%) by mass.
• an exhaust gas purification catalyst where rhodium is supported on such fabricated composite oxide support may be used.
• a performance of an exhaust gas purification catalyst fabricated as follows is sufficient: a rate of content of alumina is defined in the range of 30 to 40% by mass; a rate of content of zirconia is defined in the range of 36 to 46% by mass; ceria is contained by 20% by mass; and a sum total of rates of content of alumina, zirconia and ceria is less than 100% by mass.
• each of lanthanum oxide and neodymium oxide is contained by 2% by mass.
• a range of the rate of content of alumina of the embodiment of the invention is less than that of a composite oxide support disclosed in JP 2009-107901 A.
• a mass ratio of alumina here, aluminum oxide
• JP 2009-107901 A it is disclosed that a mass ratio of alumina (here, aluminum oxide) is set to at least more than a half of the entire mass ratio.
• a material bulk of the exhaust gas purification catalyst as a constituent element thereof can be reduced when the exhaust gas purification catalyst is formed into a catalyst having definite dimension and shape. As a result thereof, the pressure loss of a catalyst body can be reduced.
• oxygen storage capacity, HC modification capacity and NOx purification capacity can be exerted with good balance.
• the rate of content of alumina is defined to such a low range as 30 to 40% by mass
• the rate of content of zirconia can be set to a relatively high range such as 36 to 46% by mass.
• An Example of an exhaust gas purification catalyst may include a composite oxide support where: lanthanum oxide is bonded to each of alumina, zirconia and ceria; at least a part of a surface of each of alumina, zirconia and ceria is covered with a region where neodymium oxide is concentrated to form a composite oxide; yttrium oxide is bonded in the range of 9% by mass or less to the above composite oxide; and a sum total of each of the rates of content of alumina, zirconia, ceria, lanthanum oxide, neodymium oxide and yttrium oxide is defined as 100% by mass in the composite oxide support.
• a range where yttrium oxide is contained less than 9% by mass means a range where yttrium oxide is contained more than 0% by mass and 9% by mass or less.
• exhaust gas purification catalysts are fabricated respectively by varying the content of yttrium oxide, and these are subjected to XRD measurement after L endurance test (detailed below).
• the RL endurance test is a test where, in an atmosphere where a rich gas and a lean gas are alternately repeated in a period of several minutes, a sample is held under a temperature atmosphere of about 1000°C for several hours.
• a method for manufacturing an exhaust gas purification catalyst will be described. Firstly, a coprecipitate containing aluminum, zirconium, cerium and a first additive element is generated and the resulted coprecipitate is fired. The firing is performed under an oxidizing atmosphere such as an air atmosphere, at a temperature of about 600 to 1200°C for about 1 to 10 hrs. After obtaining a mixture of oxides of the respective elements, the resulted mixture of oxides is, with the second additive element attached thereto, fired to generate a composite oxide support to which the second additive element oxide is further bonded.
• an oxidizing atmosphere such as an air atmosphere
• a solution obtained by dissolving salts of aluminum, zirconium, cerium, and the first additive element in water or alcohol may be used.
• the salts include a sulphate, a nitrate, a chloride, and an acetate.
• the solution for obtaining the coprecipitate is mixed with an alkaline solution to control pH of the solution to a range where hydroxides of the respective metal elements precipitate.
• a coprecipitate as a precursor of the mixture of oxides is generated.
• the alkaline solution from the viewpoint of capable of readily volatilizing to remove during firing, a solution of ammonia or ammonium carbonate is preferred.
• the (oxide of) first additive element is present in a state dissolved and dispersed in only alumina.
• the oxide of the first additive element is present in a state dissolved and dispersed in all of alumina, zirconia and ceria.
• the second additive element is attached to a mixed oxide composed of alumina, zirconia, ceria and the first additive element oxide.
• the mixed oxide is suspended in a solution where a salt (nitrate or the like) of the second additive element is dissolved to allow the mixed oxide to support the second additive element.
• a particulate composite oxide support is obtained.
• a majority of attached second additive element oxide is made to exist in a superficial layer of alumina, zirconia or ceria.
• a composite oxide support having a concentration region where a rate of content of the second additive element oxide is high is obtained.
• the concentration region where a rate of content of the second additive element oxide is high means a region where the second additive element oxide is locally attached to the first additive element Oxide.
• the second additive element oxide is coated on an entirety or a part of a surface of a primary particle of each of alumina, zirconia and ceria.
• the second additive element oxide is coated on an entirety or a part of a surface of a secondary particle constituted by flocculated alumina, flocculated zirconia or flocculated ceria.
• a concentration region where the rate of content of the second additive element oxide is high is formed on a surface of the primary particle or a surface of the secondary particle.
• a degree of the surface concentration of the second additive element oxide can be detected according to a method where the surface is dissolved and measured by ICP (inductively-coupled plasma) or a method where a surface is measured by XPS (X-ray Photoelectron Spectroscopy).
• ICP inductively-coupled plasma
• XPS X-ray Photoelectron Spectroscopy
• the resulted composite oxide support is added into an aqueous solution of nitrate of rhodium and stirred, and water is evaporated. After water is evaporated and a residual solid material is dried, by further heating at about 500°C for several hours, an exhaust gas purification catalyst where rhodium is supported on a composite oxide support is obtained.
• each of exhaust gas purification catalyst supports was fabricated so as to have a rate of content shown in the Table 1. Specifically, after aluminum nitrate nonahydrate was dissolved in ion-exchanged water, each of zirconium oxynitrate dihydrate, cerium nitrate hexahydrate, lanthanum nitrate hexahydrate and yttrium nitrate hexaliydrate was mixed so as to be a predetermined value.
• the resulted oxide precursor was, after subjecting to centrifugation enough to cleanse, dried for 7 hrs in air, under a temperature atmosphere of 150°C.
• the dried matter was calcined at 330°C for 5 hrs to obtain a compact.
• the firing was conducted in air under a temperature atmosphere of 700°C for 5 hrs. Further, by conducting the firing in air under a temperature atmosphere of 900°C for 5 hrs, oxide was obtained.
• the resulted oxide was suspended in an aqueous solution of neodymium nitrate and stirred for 3 hrs. Then, under further stirring, the suspension was overheated to evaporate water content, and a residual solid matter was heated in air under a temperature atmosphere of 110°C for 40 hrs. After the heating, the firing was further conducted under a temperature atmosphere of 900°C for 5 hrs, and particulate composite oxide supports related to the respective Examples and Comparative Examples were obtained.
• each of the composite oxide supports was added in an aqueous solution of rhodium nitrate and stirred, and, under further stirring, the solution was overheated to evaporate water content. After evaporation of water content, a residual solid matter was dried in air under a temperature atmosphere of 1 10°C for 7 hrs. Then, the firing was conducted in air under a temperature atmosphere of 500°C for 3 hrs and a rhodium catalyst was supported by 0.2% by mass with respect to the composite oxide support. As described above, each of test materials of exhaust gas purification catalysts according to Examples and Comparative Examples was fabricated.
• the oxygen storage capacity was measured in such a manner that 2% CO and 1% 0 2 were introduced in an interval of 2 mins, an amount of C0 2 generated after 30 sees of introduction of CO was measured, and based on the amount of generated C0 2 , the oxygen storage capacity was calculated.
• the endurance was measured according to the RL endurance test, and the RL endurance test was conducted in such a manner that each of 1% CO N 2 + 10% H 2 0 and 5% 0 2 N 2 + 10% H 2 0 was fed for 5 mins and the material was held under a temperature atmosphere of about 1000°C for 5 hrs.
• the pressure loss was measured as the pressure loss under 5 m 3 /min. After coating a test material on an 875 cc ceramic honeycomb ( ⁇ 103 mm x LI 05 mm, 600 cell/3 mil, manufactured by Denso Coiporation), an experiment was conducted.
• FIG. 1 is a diagram showing results of experiments that verified the oxygen storage capacity (OSC capacity) and oxygen release capacity of exhaust gas purification catalysts (Examples 1 and 2, Comparative Examples 1 and 2) when contents of alumina and zirconia were varied.
• FIG. 2 is a diagram showing results of experiments that verified the endurance of exhaust gas purification catalysts (Examples 2 to 5, Comparative Example 3) when a content of yttrium oxide was varied.
• FIG. 1 is a diagram showing results of experiments that verified the oxygen storage capacity (OSC capacity) and oxygen release capacity of exhaust gas purification catalysts (Examples 1 and 2, Comparative Examples 1 and 2) when contents of alumina and zirconia were varied.
• FIG. 2 is a diagram showing results of experiments that verified the endurance of exhaust gas purification catalysts (Examples 2 to 5, Comparative Example 3) when a content of yttrium oxide was varied.
• FIG. 1 is a diagram showing results of experiments that verified the oxygen storage capacity (OSC capacity) and oxygen release capacity
• FIG. 3 is a diagram showing results of experiments that identified the bulk density of exhaust gas purification catalysts (Examples 1 and 2, Comparative Examples 1 and 2) when a content of alumina was varied.
• FIG. 4 is a diagram showing results of experiments that measured the pressure losses of Example 2 and Comparative Example 1.
• a content of Y 2 0 3 at an intersection of an approximate curve based on plot points of the respective test materials and a threshold value line is 9% by mass. Based on the tendency of a graph of the endurance, the content of Y 2 0 3 can be defined in the range of 9% by mass or less.
• an exhaust gas purification catalyst includes a composite oxide support that: contains at least alumina, zirconia and ceria; and has a concentration region where a rate of content of the second additive element oxide is high in at least a part of a superficial layer thereof, an exhaust gas purification catalyst where HC modification performance and NOx purification performance are sufficient can be obtained.
• the second additive element oxide for example, may be neodymium oxide, and the above superficial layer is a superficial layer of each of primary particles or a superficial layer of flocculated secondary particle.
• an exhaust gas purification catalyst is efficient in the oxygen storage capacity (OSC capacity), oxygen release capacity and the pressure loss reduction effect. Further, when an exhaust gas purification catalyst contains yttrium oxide in the range of 9% by mass or less, an exhaust gas purification catalyst further improved in the endurance can be obtained.
• a concentration region where a rate of content of the second additive element oxide is high may be formed.
• the additive element contained in the first additive element oxide may be different from the additive element contained in the second additive element oxide.
• the additive element contained in the first additive element oxide may be same as the additive element contained in the second additive element oxide.
• ceria may be contained by 20% by mass in the composite oxide support. Furthermore, a rate of content of alumina and a rate of content of zirconia may be defined so that a sum total of rates of content of alumina and zirconia is less than 100% by mass in the composite oxide support.
• the first additive element oxide may be lanthanum oxide and the second additive element oxide may be neodymium oxide.
• the composite oxide support may further contain yttrium oxide. More specifically, yttrium oxide may be contained in the range of 9% by mass or less. Furthermore, each of rates of content of alumina, zirconia, ceria, the first additive element oxide, the second additive element oxide and yttrium oxide may be defined so that a sum total of rates of content of alumina, zirconia, ceria, the first additive element oxide, the second additive element oxide and yttrium oxide is 100% by mass in the composite oxide support.

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• 2012
  • 2012-03-21 JP JP2012063774A patent/JP5576420B2/ja active Active
• 2013
  • 2013-02-27 CN CN201380010733.7A patent/CN104185505A/zh active Pending
  • 2013-02-27 EP EP13714995.1A patent/EP2827983A1/en not_active Withdrawn
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