AU2014224354A1 - Diesel exhaust gas oxidation catalyst, and method for purifying diesel exhaust gas by using same - Google Patents

Diesel exhaust gas oxidation catalyst, and method for purifying diesel exhaust gas by using same Download PDF

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AU2014224354A1
AU2014224354A1 AU2014224354A AU2014224354A AU2014224354A1 AU 2014224354 A1 AU2014224354 A1 AU 2014224354A1 AU 2014224354 A AU2014224354 A AU 2014224354A AU 2014224354 A AU2014224354 A AU 2014224354A AU 2014224354 A1 AU2014224354 A1 AU 2014224354A1
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exhaust gas
alumina
supported
oxidation catalyst
catalyst
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AU2014224354A8 (en
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Masaoki Iwasaki
Yuichi Sobue
Toshiyuki Tanaka
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Toyota Motor Corp
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Toyota Motor Corp
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    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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    • 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
    • B01D53/944—Simultaneously removing carbon monoxide, hydrocarbons or carbon making use of oxidation catalysts
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  • General Chemical & Material Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Catalysts (AREA)
  • Exhaust Gas After Treatment (AREA)
  • Exhaust Gas Treatment By Means Of Catalyst (AREA)

Abstract

A diesel exhaust gas oxidation catalyst, which is configured to purify exhaust gas from a diesel engine, includes: an alumina-based carrier in which a content of alumina is 40 mass% or higher; Pt supported on the alumina-based carrier; Pd supported on the alumina-based carrier; and at least one type of added element that is selected from the group consisting of alkali metal elements and alkaline earth metal elements and that is supported on the alumina-based carrier. A supported quantity of the Pt is 0.1 to 5 parts by mass relative to 100 parts by mass of the alumina-based carrier. A molar ratio obtained by dividing a supported quantity of the Pd by the supported quantity of the Pt is 0.1 to 1.5. A molar ratio obtained by dividing a supported quantity of the added element by the supported quantity of the Pt is 1 to 12.

Description

WO 2014/135937 PCT/IB2014/000183 1 DIESEL EXHAUST GAS OXIDATION CATALYST, AND METHOD FOR PURIFYING DIESEL EXHAUST GAS BY USING SAME BACKGROUND OF THE INVENTION 5 1. Field of the Invention (00011 The invention relates to a diesel exhaust gas oxidation catalyst and a method for purifying diesel exhaust gas by using same. 10 2. Description of Related Art 100021 Proposals have been made in the past for a variety of catalysts used to purify gases emitted from diesel engines. For example, Japanese Patent Application Publication No. 1-171626 (JP 1-171626A) proposes a diesel exhaust gas catalyst in which a noble metal is supported on a porous inorganic oxide. However, catalysts having 15 similar features to the invention, such as that disclosed in JP 1-171626A, did not necessarily achieve satisfactory performance in terms of oxidizing and purifying, from low temperatures, carbon monoxide and hydrocarbons present in gases emitted from diesel engines. In addition, catalysts having similar features to the invention, such as that disclosed in JP 1-]171626A, involved problems such as insufficient heat resistance and a 20 decrease in exhaust gas purifying performance when exposed to high temperatures. Moreover, regulations relating to gases emitted from diesel engines have become stricter in recent years. Therefore, in the field of oxidation catalysts for diesel exhaust gas, there is a need for a catalyst which can oxidize and purify carbon monoxide and hydrocarbons from lower temperatures and which can maintain this performance sufficiently even under 25 actual usage conditions, in which the catalyst is exposed to high temperatures. 100031 Meanwhile, recent years have seen the development of so-called NO, absorption and reduction type exhaust gas purifying catalysts as catalysts for purifying components such as NO, and CO contained in gases in lean (oxygen-rich) air/fuel (A/F) ratio atmospheres emitted from internal combustion engines of vehicles and the like. As WO 2014/135937 PCT/IB2014/000183 2 an example of this type of catalyst, Japanese Patent Application Publication No. 5-317652 (JP 5-317652A) and Japanese Patent Application Publication No. 8-117602 (JP 8-117602A) each disclose a catalyst in which an alkaline earth metal and platinum are supported on a carrier consisting of alumina. However, exhaust gas purifying catalysts 5 having similar features to the invention, such as those disclosed in JP 5-317652A and JP 8-l17602A, did not necessarily achieve satisfactory performance in terms of oxidizing and purifying carbon monoxide and hydrocarbons after being exposed to high temperatures when used to purify exhaust gases from diesel engines. 10 SUMMARY OF THE INVENTION 100041 The invention provides a diesel exhaust gas oxidation catalyst and a method for purifying diesel exhaust gas by using same. 10005) A first aspect of the invention is a diesel exhaust gas oxidation catalyst that is configured to purify exhaust gas from a diesel engine. The catalyst includes: an 15 alumina-based carrier in which a content of alumina is 40 mass% or higher: Pt supported on the alumina-based carrier; Pd supported on the alumina-based carrier; and at least one type of added element that is selected from the group consisting of alkali metal elements and alkaline earth metal elements and that is supported on the alumina-based carrier. A supported quantity of the Pt is 0.1 to 5 parts by mass relative to 100 parts by mass of the 20 alumina-based carrier. A molar ratio obtained by dividing a supported quantity of the Pd by the supported quantity of the Pt is 0.1 to 1.5. A molar ratio obtained by dividing a supported quantity of the added element by the supported quantity of the Pt is I to 12. [00061 In the first aspect of the invention, the molar ratio obtained by dividing the supported quantity of the added element by the supported quantity of the Pt may be 3 to 12. 25 (00071 In the first aspect of the invention, the content of alumina in the alumina-based carrier may be 50 to 100 mass%. 10008] A second aspect of the invention is a method for purifying diesel exhaust gas. The method for purifying diesel exhaust gas includes bringing lean atmosphere exhaust gas, having an air/fuel ratio of 15 or higher and emitted by a diesel engine, into WO 2014/135937 PCT/IB2014/000183 3 contact \\ith the diesel exhaust gas oxidation catalyst according to the first aspect of the invention. 100091 According to the aspects of the invention, it is possible to sufficiently oxidize and purify carbon monoxide and hydrocarbons from low temperatures and it is 5 possible to achieve excellent high temperature durability and sufficiently high catalytic activity from low temperatures even after the catalyst is exposed to high temperatures. BRIEF DESCRIPTION OF THE DRAWINGS 100101 Features, advantages, and technical and industrial significance of 10 exemplary embodiments of the invention will be described belo\v with reference to the accompanying drawings, in which like numerals denote like elements, and wherein: FIG. I is a conceptual diagram that schematically illustrates the relationship between CO. HC and 0 in cases where an embodiment of the diesel exhaust gas oxidation catalyst of the invention is used; 15 FIG. 2 is a graph that shows the relationship between the CO-T50 and HC-T50 values (temperatures) of the oxidation catalysts obtained in Working Examples I to 4 and Comparative Examples I and 2 and the Ba/Pt molar ratio in these catalysts; FIG. 3 is a graph that shows the CO-T50 and HC-T50 values (temperatures) of the catalysts obtained in Working Example 8 and Comparative Example 7; 20 FIG. 4 is a table that shows the characteristics of the oxidation catalysts obtained in Working Examples I to 7 and Comparative Examples I to 6; FIG. 5 is a table which relates to the oxidation catalysts obtained in Working Examples I to 7 and Comparative Examples I to 6 and which shows results relating to the temperature at which the CO purification rate reaches 50% and the temperature at which 25 the C 3
H
6 purification rate reaches 50%; FIG. 6 is a table that shows the characteristics of the catalysts obtained in. Working Example 8 and Comparative Example 7; FIG. 7 is a table that shows the characteristics of the catalysts obtained in Working Example 8 and Comparative Examples 7 to 9; and WO 2014/135937 PCT/IB2014/000183 4 FIG. 8 is a table which relates to the catalysts obtained in Working Example 8 and Comparative Examples 7 to 9 and which shows results relating to the temperature at which the CO purification rate reaches 50% and the temperature at which the C 3
H
6 purification rate reaches 50%. DETAILED DESCRIPTION OF EMBODIMENTS [0011] First, with regard to the diesel exhaust gas oxidation catalyst of the invention, the thoughts of the inventors of the invention relating to embodiments of the invention will be mentioned. The reasons why it is possible to sufficiently oxidize and 10 purify carbon monoxide and hydrocarbons from lo\\ temperatures and to achieve excellent high temperature durability and sufficiently high catalytic activity from low temperatures even after the catalyst is exposed to high temperatures by using an embodiment of the diesel exhaust gas oxidation catalyst of the invention are not necessarily certain. However, the inventors of the invention surmise the following. First, catalysts that are 15 used to purify exhaust gases emitted from diesel engines are generally used in oxygen-rich atmospheres due to exhaust gases generally being oxygen-rich atmosphere gases. The inventors of the invention carried out diligent research into cases in which catalysts having similar features to the invention (catalysts in vhich Pt is supported on a carrier, and the like), such as that disclosed in JP 1-171626A, are used as diesel exhaust gas oxidation 20 catalysts used in this type of oxygen-rich atmosphere. As a result, the inventors of the invention found that in this type of catalyst having similar features to the invention, carbon monoxide (CO) and hydrocarbons (HC) present in exhaust gas were strongly adsorbed onto the surface of the Pt at low temperatures, meaning that the surface of the Pt, which is an active catalyst site, became significantly poisoned by the adsorption of the CO and HC, 25 thereby causing the catalytic activity to deteriorate and making sufficient CO and HC oxidation from low temperatures impossible. As a result of further diligent research on the basis of these findings, the inventors of the invention found that by supporting at least one type of added element selected from the group consisting of alkali metal elements and alkaline earth metal elements on the alumina-based carrier at a prescribed molar ratio WO 2014/135937 PCT/IB2014/000183 relative to the supported quantity of the Pt, it was possible to sufficiently alleviate this poisoning caused by adsorption. Prescribed molar ratio means that the molar ratio of the supported quantity of the added element to the supported quantity of the Pt ([added element]/{Pt]) falls within the range I to 12. As mentioned above, poisoning caused by 5 adsorption of CO and HC hinders oxidation reactions. Moreover, the inventors of the invention surmise that the reason that this type of added element alleviates poisoning of Pt by adsorption of CO and HC in cases where the added element is used at a quantity whereby the molar ratio of the supported quantity of the added element to the supported quantity of the Pt falls within the range is because the electronic state of the Pt shifts 10 slightly from a metallic state to an oxide state under conditions whereby CO and HC undergo oxidation reactions. Because poisoning of Pt due to adsorption of CO and HC is alleviated by the electronic state of Pt shifting to an appropriate degree when the added element is used at the prescribed molar ratio, as mentioned above, oxygen present in the gas phase is readily adsorbed onto the surface of the Pt on which poisoning has been 15 alleviated and oxidation reactions between CO and HC adsorbed on the Pt and 0) in the gas phase are facilitated. Moreover, the degree by which the reduction of Pt is inhibited by this type of added element (the degree of shifting to an oxide state) can be confirmed by measuring the intensity of absorption from a 2pm orbit to a 5d orbit in an X-Ray absorption spectrum of the L3 absorption end of Pt while increasing the temperature at a 20 constant rate in the reaction atmosphere. By carrying out such measurements, the inventors of the invention confirmed that by using the added element within the above-mentioned range in addition to Pt, the electronic state of the Pt during the reaction shifted from a metallic state to an oxide state. Here. FIG. I shows a conceptual diagram of oxidation reactions between 0 in the gas phase and CO and HC in a case where an 25 embodiment of the diesel exhaust gas oxidation catalyst of the invention is used. In an embodiment of the invention, because the electronic state of platinum 2 shifts slightly to an oxide state in the vicinity of sites at which an added element 3 is supported, as shown in FIG. 1, it is difficult for CO or HC to be adsorbed by the platinum 2 at sites close to positions where the added element 3 is supported. Therefore, the inventors of the WO 2014/135937 PCT/IB2014/000183 6 invention surmise that poisoning by adsorption is alleviated. oxygen is adsorbed at these sites, and reactions bv which CO and HC adsorbed close to these oxygen-adsorbed sites are oxidized are facilitated. In addition, in the embodiments of the invention, Pt and Pd are supported on the alumina-based carrier at quantities whereby the molar ratio of the 5 supported quantity of Pd to the supported quantity of Pt ([Pd]/'.[Pt]) falls within the range 0.1 to 1.5. By using Pt and Pd at such a ratio, Pt grain growth is sufficiently inhibited under high temperature conditions of 700'C or higher. Therefore, in the embodiments of the invention, it is possible to sufficiently inhibit a decrease in the number of active catalyst sites caused by grain growth even after the catalyst is exposed to high 10 temperatures, and it is possible to maintain sufficiently high Pt-derived catalytic activity. In addition, in the embodiments of the diesel exhaust gas oxidation catalyst of the invention, a carrier in which the content of alumina is 40 mass% or higher (an alumina-based carrier) is used as a carrier. The inventors of the invention surmise that it is possible to maintain a sufficient specific surface area even under high temperature 15 conditions of 700'C or higher by setting the content of alumina to be 40 mass% or higher, and that it is possible to satisfactorily achieve the effect of altering the electronic state of the Pt by using the added element. Mainly due to the reasons given above, the inventors of the invention surmise that the embodiments of the diesel exhaust gas oxidation catalyst of the invention, in which Pt, Pd and an added element are supported at prescribed 20 proportions on the alumina-based carrier. can sufficiently oxidize and purify carbon monoxide and hydrocarbons from lo\w temperatures and can achieve excellent high temperature durability and sufficiently high catalytic activity from low temperatures even after the catalyst is exposed to high temperatures. 10012] The invention will now be explained in greater detail through the use of 25 preferred embodiments. [0013] First, an explanation will be given of an embodiment of the diesel exhaust gas oxidation catalyst of the invention. The embodiment of the diesel exhaust gas oxidation catalyst of the invention purifies exhaust gas from a diesel engine. Furthermore, the catalyst includes: an alumina-based carrier in which a content of alumina WO 2014/135937 PCT/IB2014/000183 7 is 40 mass% or higher; Pt supported on the alumina-based carrier; Pd supported on the alumina-based carrier; and at least one type of added element that is selected from the group consisting of alkali metal elements and alkaline earth metal elements and that is supported on the alumina-based carrier. A supported quantity of the Pt is 0.1 to 5 parts by mass relative to 100 parts by mass of the alumina-based carrier. A molar ratio obtained by dividing a supported quantity of the Pd by the supported quantity of the Pt is 0.1 to 1.5. A molar ratio obtained by dividing a supported quantity of the added element by the supported quantity of the Pt is I to 12. 100141 In this alumina-based carrier in the embodiments of the invention, the 10 content of alumina in the carrier is 40 mass% or higher in tens of oxide. If the content of alumina is lower than the lower limit, the proportion of Pt present on the surface of the alumina decreases, and it is therefore not possible to achieve sufficient interaction between the alumina and the Pt. Therefore. catalytic activity from low temperatures decreases and the effect of the embodiments of the invention cannot be satisfactorily achieved, In 15 addition, in the embodiments of the invention, the content of alumina in the carrier is more preferably 50 to 100 mass%., further preferably 60 to 100 mass%, particularly preferably 70 to 100 mass%., and most preferably 80 to 100 mass%,. in order to achieve higher catalytic activity. 10015] Other publicly available components able to be used in catalyst carriers 20 can be used as appropriate as components other than alumina able to be incorporated in this type of alumina-based carrier. Oxides of elements such as titanium (Ti), silicon (Si), phosphorus (P), zirconium (Zr), cerium (Ce), yttrium (Y) and lanthanum (La) can be advantageously used as components other than alumina able to be incorporated in this type Of alumina-based carrier from the perspectives of thermal stability of the carrier and 25 catalytic activity. Moreover, it is possible to use one oxide of these elements, or a combination of two or more types thereof. In addition, examples of such alumina-based carriers that contain components other than alumina include alumina-titania-zirconia, alumina-ceria-zirconia, alumina-silica and alumina-phosphate. [00161 In addition, the form of this type of alumina-based carier is not WO 2014/135937 PCT/IB2014/000183 8 particularly limited, but a particulate or needle-like carrier is preferred from the perspectives of further increasing the specific surface area and achieving even higher catalytic activity. In addition, in cases where this type of alumina-based carrier is a particulate carrier, the average particle diameter of the carrier is preferably 0.05 to 500 pim, S and more preferably 0.1 to 100 pm. If the average particle diameter is lower than the lower limit, obtaining a finely divided carrier becomes costly and handling of such a finely particulate carTier tends to be difficult. Meanwhile, if the average particle diameter exceeds the upper limit, it tends to be difficult to stably fix the alumina-based carrier on a catalyst base material such as that mentioned below (for example. a DPF base material or 10 monolithic base material). Moreover, in the embodiments of the invention, the average particle diameter of the particles can be obtained by measuring 100 or more arbitrarily selected particles with a transmission electron microscope (TENI). determining the diameter of each particle, and then calculating the average value of these particle diameters. In addition. the particle diameter means the maximum diameter through a 15 cross section of the particle, and in cases where the particle cross-section is not circular, the particle diameter is taken to be the diameter of the largest circumscribed circle in the cross section of the particle. 100171 In addition, the specific surface area of this type of alumina-based carrier is preferably 50 m 2g or higher, and more preferably 100 to 300 m 2 g. If the specific 20 surface area is lower than the lower limit, dispersibility of the noble metals (Pt and Pd) tends to deteriorate. Meanwhile, if the specific surface area exceeds the upper limit, there tends to be a greater decrease in specific surface area caused by thermal degradation. Moreover, this specific surface area can be determined by the Brunauer-Emmett-Teller (BET) adsorption isotherm equation from a nitrogen adsorption isotherm obtained using a 25 nitrogen adsorption method. For example, the specific surface area can be determined by carrying out measurements using an automatic gas/vapor adsorption measurement device (Belsorp-18 Plus, manufactured by BEL Japan, Inc.). [00181 Furthermore, the method for preparing this type of alumina-based carrier is not particularly limited, and a publicly available method can be used as appropriate.
WO 2014/135937 PCT/IB2014/000183 9 For example, when preparing a carrier that contains alumina and another component (such as titania or zirconia), it is possible to use a so-called coprecipitation method. In addition, it is possible to use a commercially available product as this type of alumina-based carrier as long as the product satisfies the above-mentioned condition relating to the content of 5 alumina. [0019] In addition. in the embodiments of the diesel exhaust gas oxidation catalyst of the invention, Pt (platinum), Pd (palladium) and the added element are supported on the alumina-based carrier. The supported quantity of Pt, which is one of these supported components, is 0. 1 to 5 parts by mass relative to 100 parts by mass of the 10 alumina-based carrier. If the supported quantity of Pt is lower than the lower limit, the supported quantity becomes too small, and it is not possible to achieve sufficient Pt-derived catalytic activity. Meanwhile, if the supported quantity of Pt exceeds the upper limit, particles of Pt supported on the alumina-based carrier become too large. sufficient catalytic activity for the supported quantity of Pt cannot be achieved, and 15 economy and so on deteriorates. In addition., for the same reasons, the supported quantity of Pt is more preferably 1 to 4 parts by mass relative to 100 parts by mass of the alumina-based carrier. (00201 In addition, in the embodiments of the invention, Pt and Pd are supported on the alumina-based carrier, as mentioned above. The supported quantity of Pd is a 20 quantity whereby the molar ratio of the supported quantity of Pd to the supported quantity of Pt ([Pd]/[Pt]) falls within the range 0.1 to 1.5. If the molar ratio of Pd to Pt is lower than the lower limit, the supported quantity of Pd is too low, it is not possible to sufficiently achieve the effect of inhibiting Pt grain growth under high temperature conditions. and catalytic activity deteriorates when the catalyst is exposed to high 25 temperatures. Meanwhile, if the molar ratio exceeds the upper limit, Pd precipitates on the surface of the Pt, the effect 'achieved by supporting the added element (the effect of appropriately suppressing reduction of Pt to a metallic state) is inhibited, and the effect achieved by using the added element cannot be sufficiently achieved. Therefore, by using Pd at a proportion thereby the molar ratio is satisfied, it is possible to achieve a good WO 2014/135937 PCT/IB2014/000183 10 balance between the effect of inhibiting Pt grain growth under conditions of high temperature and the effect achieved by supporting the added element. In addition, in order to achieve a good balance between the effect achieved by supporting Pd and the effect achieved by using the added element, the molar ratio of the supported quantity of Pd 5 and the supported quantity of Pt ([Pd]/[Pt)) preferably falls within the range 0.5 to 1.2. 100211 In addition, the supported quantity of Pd relative to 100 parts by mass of the alumina-based carrier is preferably 0.005 to 4 parts by mass, and more preferably 0.03 to 3 parts by mass. If the quantity of Pd supported on the alumina-based carrier is lower than the lower limit, it tends to be impossible to satisfactorily achieve the effect of 10 inhibiting Pt grain growth under conditions of high temperature. Meanwhile, if the quantity of Pd supported on the alumina-based carrier exceeds the upper limit, Pd readily precipitates on the surface of the Pt, and the effect achieved by supporting the added element tends to be impaired. [00221 In addition, in the embodiments of the invention, an added element is 15 supported on the alumina-based carrier, as mentioned above. This type of added element is an alkali metal element and/or an alkaline earth metal element. From the perspective of exhibiting strong basicity, this type of added element is preferably Li, Na, K, Cs, Mg, Ca, Sr or Ba. more preferably Na, K, Cs, Sr or Ba, and further preferably K, Cs or Ba. Moreover, it is possible to use one such added element, or a combination of two or more 20 types thereof. 10023] In addition, the supported quantity of the added element is a quantity whereby the molar ratio of the supported quantity of the added element to the supported quantity of the Pt ([added element]/[Pt)) falls within the range I to 12. By supporting the added element in such a way that the above-mentioned molar ratio is satisfied, the exhaust 25 gas purification activity (and especially the CO and HC oxidation activity) is improved under conditions where the catalyst is exposed to exhaust gases such as oxygen-rich atmospheres that are commonly emitted by diesel engines. Moreover, the inventors of the invention surmise that by supporting the added element in such a way that the above-mentioned molar ratio is satisfied, it is possible to appropriately inhibit reduction of WO 2014/135937 PCT/IB2014/000183 11 Pt from an oxide state to a metallic state., strong adsorption of CO and HC to Pt is suppressed. and CO and HC oxidation activity is therefore improved from low temperatures when subjecting CO and HC present in exhaust gas to oxidation reactions. In addition, if the molar ratio of the added element to Pt is lower than the lower limit, the 5 supported quantity of the added element is reduced and the added element has little impact on the activity, and it is therefore not possible to satisfactorily achieve the effect achieved by supporting the added element. Meanwhile, if the molar ratio of the added element to Pt exceeds the upper limit, the Pt, which is an active species in the catalyst, forms an oxide state and becomes overly stabilized due to the effect of the added element, meaning that 10 HC oxidation does not occur and sufficient catalytic activity cannot be achieved. In addition, for the same reasons. the molar ratio of the supported quantity of the added element to the supported quantity of Pt ([added element) [Pt)) preferably falls within the range 3 to 12. [00241 In addition, the supported quantity of the added element relative to the 15 alumina-based carrier is preferably 0.005 to 3 mmol/g, and more preferably 0.015 to 2.5 mmol/g. If the supported quantity of the added element relative to the alumina-based carrier is lower than the lower limit, the effect achieved by supporting the added element tends to be impossible to achieve satisfactorily. Nleanwhile, if the supported quantity of the added element relative to the alumina-based carrier exceeds the upper limit, the Pt. 20 'which is an active species in the catalyst, becomes stabilized and oxidation of HC in the exhaust gas tends not to occur satisfactorily. (00251 In the embodiments of the diesel exhaust gas oxidation catalyst of the invention, it is possible to further support Rh on the alumina-based carrier. In cases Where Rh is supported on the alumina-based carrier, the molar ratio of the supported 25 quantity of Rh to the supported quantity of Pt ((Rh]/[Pt]) is preferably 0.05 or lower (and more preferably 0.01 or lover). If this molar ratio exceeds the upper limit, excess Rh covers the surface of Pt particles, meaning that the catalytic activity of the Pt decreases and it tends to be impossible to achieve sufficient catalytic activity, [0026] In addition, the method for supporting Pt or Pd on the alumina-based WO 2014/135937 PCT/IB2014/000183 12 carrier is not particularly limited, and a publicly available method may be used as appropriate. For example, it is possible to prepare a solution by dissolving a compound that contains Pt (for example, a platinum salt such as a nitrate, chloride or acetate or a platinum complex) in water or a solvent such as an alcohol and a solution by dissolving a 5 compound that contains Pd (for example, a palladium salt such as a nitrate, chloride or acetate or a palladium complex) in water or a solvent such as an alcohol. It is then possible to bring these solutions into contact with the alumina-based carrier, and then subject the carrier to drying and firing. For example, it is possible to add the above-mentioned solutions to a dispersion obtained by dispersing the alumina-based carrier 10 in water or a solvent such as an alcohol, thereby bringing the above-mentioned solutions into contact with the alumina-based carrier. Moreover, the conditions when subjecting the carrier to driving and firing are not particularly limited, and publicly available conditions may be used as appropriate, for example, heating at a temperature of 80 to I 40'C for a period of I to 24 hours as the drying conditions and heating at a temperature of 15 200 to 500'C for a period of 0.5 to 5 hours as the firing conditions. In addition, in cases where Rh is also supported on the carrier, the method for supporting the Rh is not particularly limited, and a publicly available method may be used as appropriate. For example, it is possible to use a method that includes preparing a solution by dissolving a compound that contains Rh (for example, a rhodium salt such as a nitrate, chloride or 20 acetate or a rhodium complex) in water or a solvent such as an alcohol. bringing this solution into contact with the alumina-based carrier and then subjecting the carrier to drying and firing, and it is possible to use publicly available conditions as appropriate when carrying out such a method. 100271 Furthermore, the method for supporting the added element on the 25 alumina-based carrier is not particularly limited, and a publicly available method may be used as appropriate. For example, it is possible to use a method that includes bringing an aqueous solution, which contains a salt of the above-mentioned element that can be advantageously used as the added element (for example, a carbonate, a nitrate, a citrate, a carboxylate. a dicarboxylate or a sulfate) or a complex of the above-mentioned element, WO 2014/135937 PCT/IB2014/000183 13 into contact with the alumina-based cancer, and then firing the carrier, Moreover, the conditions when firing the carrier are not particularly limited, and it is possible to use publicly available conditions as appropriate, for example heating at a temperature of 200 to 500'C for a period of 0.5 to 5 hours. 5 100281 In addition, other publicly available components able to be used in the field of diesel exhaust gas oxidation catalysts can be used as appropriate in the diesel exhaust gas oxidation catalyst of the embodiment of the invention as long as the effect achieved by the invention is not impaired. 10029] In addition, the form of the diesel exhaust gas oxidation catalyst of the 10 embodiment of the invention is not particularly limited, and the catalyst can be a honeycomb monolithic catalyst, a pellet-form catalyst, or the like. The method for producing a diesel exhaust gas oxidation catalyst having such a form is not particularly limited, and a publicly available method may be used as appropriate. For example. it is possible to use a method in which a pellet-form diesel exhaust gas oxidation catalyst is 15 obtained by molding a powdered catalyst (a catalyst powder) into pellets. Alternatively, it is possible to use a method in which a diesel exhaust gas oxidation catalyst fixed on a catalyst base material is obtained by coating a catalyst-based material with a slurry that contains a catalyst powder. Moreover, when obtaining a diesel exhaust gas oxidation catalyst fixed on a catalyst base material, it is possible to use a method that includes 20 coating a catalyst base material with the alumina-based carrier and then supporting Pt, Pd and an added element in an arbitrary order on the alumina-based carrier. Alternatively, it is possible to use a method that includes obtaining a support body for Pt and Pd by supporting Pt and Pd on the alumina-based carrier in advance, coating this support body for Pt and Pd on a base material, and then supporting an added element, The order in 25 which the components are supported on the carrier and the form of the materials used during the coating are not particularly limited as long as the method can eventually form the above-mentioned diesel exhaust gas oxidation catalyst of the embodiment of the invention on a catalyst base material. In addition, this type of catalyst base material is not particularly limited, and is selected as appropriate according to the intended use of the WO 2014/135937 PCT/IB2014/000183 14 obtained exhaust gas purifying catalyst, and so on. For example, a DPF base material, a monolithic base material, a pellet-form base material, a plate-like base material, or the like can be advantageously used. In addition, the material of this type of catalyst base material is not particularly limited, but a base material formed of a ceramic such as 5 cordierite., silicon carbide or mullite, or a base material formed of a metal such as a stainless steel that contains chromium and aluminum can be advantageously used. 100301 Moreover, when obtaining a form in which the catalyst is fixed on the catalyst base material. the supported quantity of the alumina-based carrier per 1 L of volume of the base material is preferably 50 to 300 g L, and more preferably 100 to 250 10 g/L, from the perspectives of obtaining sufficient catalytic activity in the obtained exhaust gas purifying catalyst and suppressing an increase in pressure drop and detachment of coating layers. (0031] In addition, the embodiments of the diesel exhaust gas oxidation catalyst of the invention may be used in combination with other catalysts. Such other catalysts are 15 not particularly limited, and publicly available catalysts (for example. NO, reduction catalysts, NO, storage and reduction catalysts (NSR catalysts) and NO, selective catalytic reduction catalysts (SCR catalysts)) can be used as appropriate. In addition, in cases where this type of other catalyst is used in combination with the catalyst of the invention, it is possible, for example. to form a catalyst having a multilaver structure in which a layer 20 constituted by an embodiment of the diesel exhaust gas oxidation catalyst of the invention is laminated with a layer constituted by the other catalyst. Moreover, the embodiments of the diesel exhaust gas oxidation catalyst of the invention are catalysts that are used to purify exhaust gas from a diesel engine, but this type of diesel engine is not particularly limited, and may be, for example, a publicly available automotive diesel engine. 25 100321 The diesel exhaust gas oxidation catalyst of the embodiment of the invention has been explained above, but the method for purifying diesel exhaust gas of the embodiment of the invention will now be explained. 10033] The embodiment of method for purifying diesel exhaust gas of the invention includes bringing lean atmosphere exhaust gas, having an air/fuel ratio of 15 or WO 2014/135937 PCT/IB2014/000183 15 higher and emitted by a diesel engine, into contact with the diesel exhaust gas oxidation catalyst according to any one of claims 1 to 10 so as to purify the exhaust gas. 10034] In this way, an embodiment of the invention is a method for purifying a lean (oxygen-rich) atmosphere exhaust gas emitted from a diesel engine, in which the 5 air/fuel ratio (the mixing ratio of air and fuel: A/F ratio) is 15 or higher. b\ using the above-mentioned embodiments of the diesel exhaust gas oxidation catalyst of the embodiment of the invention. In general, exhaust gases from diesel engines are lean (ox\gen-rich) atmosphere exhaust gases having air/fuel ratios of 25 or higher. Therefore. by bringing exhaust gas from a diesel engine into contact with the embodiments of the 10 diesel exhaust gas oxidation catalyst of the invention in situ. the method for purifying diesel exhaust gas of the invention can be carried out and the exhaust gas (and especially carbon monoxide and hydrocarbons present in the exhaust gas) can be efficiently purified. Moreover, in cases where the air/fuel ratio (the mixino ratio of air and fuel: A/F ratio) of the exhaust gas is lower than 15 (and especially 14.6 or lower), the quantity of oxygen in 15 the exhaust gas decreases and the proportion of fuel in the exhaust gas increases. Therefore, in the above-mentioned embodiments of the diesel exhaust gas oxidation catalyst of the invention, the impact caused by the fuel reducing the Pt is greater than the impact achieved by supporting the added element (the effect of altering the electronic state of the Pt and suppressing reduction of the Pt by supporting the added element). 20 Therefore, it tends to be difficult to efficiently oxidize and purify components present in the exhaust gas (and especially carbon monoxide and hydrocarbons). In this way, the above-mentioned embodiments of the diesel exhaust gas oxidation catalyst of the invention are catalysts by which it is possible to achieve higher exhaust gas purification activity in lean atmospheres having air/fuel ratios of 15 or higher. Therefore. in cases where the 25 air/fuel ratio (the mixing ratio of and fuel: A/F ratio) of the exhaust gas is lower than 15, the air/fuel ratio in the exhaust gas can be adjusted as appropriate before the exhaust gas is brought into contact with the above-mentioned embodiments of the diesel exhaust gas oxidation catalyst of the invention. For example, air can be added to the exhaust gas as appropriate. Moreover, the air/fuel ratio (the mixing ratio of and fuel: A/F ratio) of the WO 2014/135937 PCT/IB2014/000183 16 exhaust gas is preferably 20 or higher, and more preferably 30 or higher, in order to more efficiently purify the exhaust gas (and especially carbon monoxide and hydrocarbons present in the exhaust gas). In addition, this type of diesel engine is not particularly limited, and a publicly available diesel engine can be used as appropriate. Furthermore, 5 the method for bringing the exhaust gas into contact with the above-mentioned embodiments of the diesel exhaust gas oxidation catalyst of the invention. For example, the above-mentioned embodiments of the diesel exhaust gas oxidation catalyst of the invention should be disposed in the exhaust gas flow path of the diesel engine. 100351 By bringing a lean atmosphere exhaust gas emitted from a diesel engine, 10 in vhich the air fuel ratio (A/F ratio) is 15 or higher, into contact with the above-mentioned embodiments of the diesel exhaust gas oxidation catalyst of the invention in this \\ay. it is possible to purify the exhaust gas more efficiently (and especially to oxidize and purify carbon monoxide and hydrocarbons present in the exhaust gas more efficiently). In addition, the above-mentioned embodiments of the diesel exhaust gas 15 oxidation catalyst of the invention achieve excellent exhaust gas purifying performance from low temperatures in particular, and can therefore efficiently purify exhaust gas even at low temperatures in an extremely short time after a diesel engine is started. [00361 The invention will now be explained in greater detail through the use of working examples and comparative examples, but is not limited to the working examples 20 given below. 100371 An explanation will now be given of the production of Working Example 1. First, a dispersion was obtained by dispersing a powder of y-Al 2
O
3 (product name "MI307", manufactured by Grace, specific surface area 160 m 2 /g, average particle diameter 17 pm) in ion exchanged water. A mixed liquid was then obtained by adding a solution 25 of dinitrodiammine platinum nitrate (manufactured by Tanaka Kikinzoku) and a solution of dinitrodiammine palladium nitrate (manufactured by Tanaka Kikinzoku) to the dispersion and stiring for 2 hours (a mixed liquid preparation step). A support body for Pt and Pd (a Pt-Pd support body) was then obtained by evaporating off the solvent from the mixed liquid, drying the obtained solid component for 12 hours at 120'C and then firing WO 2014/135937 PCT/IB2014/000183 17 for 3 hours at 550'C. Moreover, the quantities of the solution of dinitrodiammine platinum nitrate and the solution of dinitrodiammine palladium nitrate added in the mixed liquid preparation step were adjusted so that the supported quantities of Pt and Pd were 1.8 pails by mass and 0.9 parts by mass respectively relative to 100 parts by mass of the 5 y-Al 2 03 in the obtained Pt-Pd support body. 100381 Next, a coating liquid was obtained by dispersing the obtained Pt-Pd support body in ion exchanged water together with an alumina sol (solid content: 10 wt%), and this coating liquid was provided on a hexagonal cell cordierite monolithic base material (diameter 30 mm, length 50 mm, volume 35 mL (35 cc), cell density 400 10 cells inch') by means of a wash coat method so that the coating quantity was 150 g per I L of the base material. Next, the hexagonal cell cordierite monolithic base material on which the coating liquid was provided \was fired for 3 hours at a temperature of 500'C so as to obtain the base material, in which a coating layer was formed on the Pt-Pd support body. Next, an aqueous solution containing barium acetate was supported on the coating 15 layer by water absorption in such a way that the supported quantity of barium was 0.20 mmol per I g of y-A1 2 0 3 (Ba/Pt molar ratio: 2.2). The coating layer, on which the aqueous solution was supported by water absorption, was then fired for 5 hours at a temperature of 550'C so as to support Ba on the y-Al2O (Ba supporting step). In this way, an oxidation catalyst fixed on a monolithic base material (a catalyst in which Pt, Pd 20 and Ba vere supported on y-A 2 03) was obtained. Moreover, the characteristics of the obtained oxidation catalyst are shown in FIG. 4. 100391 An explanation will now be given of the production of Working Examples 2 to 4. Oxidation catalysts were produced in the same way as Working Example 1. except that the aqueous solution containing barium acetate was supported by water absorption in 25 the Ba supporting step in such a way that the supported quantity of Ba per I g of y-AI20 3 was the proportion shown in FIG. 4. 100401 An explanation will now be given of the production of Working Example 5. An oxidation catalyst was produced in the same way as Working Example 1, except that the firing temperature in the Ba supporting step was changed to 750'C. Moreover, WO 2014/135937 PCT/IB2014/000183 18 the characteristics of the obtained oxidation catalyst are shown in FIG. 4. 100411 An explanation will now be given of the production of Working Examples 6 and 7. Oxidation catalysts were produced in the same way as Working Example 5, except that the aqueous solution containing barium acetate was supported by water 5 absorption in the Ba supporting step in such a way that the supported quantity of Ba per l g of y-All03 was the proportion shown in FIG. 4. Moreover, the characteristics of the obtained oxidation catalysts are shown in FIG. 4. 100421 An explanation will now be given of the production of Comparative Example 1. A comparative oxidation catalyst was produced in the same way as Working 10 Example 1, except that the Ba supporting step was not carried out after forming the coating layer on the Pt-Pd support body and firing was carried out for 5 hours at a temperature of 550'C after forming the coating layer. Moreover, the characteristics of the obtained oxidation catalyst are shown in FIG. 4. [00431 An explanation will now be given of the production of Comparative 15 Example 2. A comparative oxidation catalyst was produced in the same way as Working Example I, except that the aqueous solution containing barium acetate was supported by water absorption in the Ba supporting step in such a way that the supported quantity of Ba per I g of y-A1O 2 was the proportion shown in FIG. 4. Moreover, the characteristics of the obtained oxidation catalyst are shown in FIG. 4. 20 100441 An explanation will now be given of the production of Comparative Example 3. A comparative oxidation catalyst was produced in the same way as Working Example 5. except that the Ba supporting step was not carried out after forming the coating layer on the Pt-Pd support body and firing was carried out for 5 hours at a temperature of 750'C after forming the coating layer. Moreover, the characteristics of the obtained 25 oxidation catalyst are shown in FIG. 4. 100451 An explanation will now be given of the production of Comparative Example 4. In Comparative Example 4. a solution of dinitrodiammine palladium nitrate was not added and only a solution of dinitrodiammine platinum nitrate wxas added in the mixed liquid preparation step. In addition, a support body for Pt (a Pt support body) was WO 2014/135937 PCT/IB2014/000183 19 produced instead of a support body for Pt and Pd (a Pt-Pd support body), In addition. the added quantity of the solution of dinitrodiammine platinum nitrate in the mixed liquid preparation step w as changed so that the supported quantity of Pt was 2 parts by mass relative to 100 pails by mass of the y-A1 2 0s in the Pt support body. Furthermore, in the 5 Ba supporting step. the Pt support body was used instead of the Pt-Pd support body and the aqueous solution containing barium acetate was supported by water absorption in such a way that the supported quantity of Ba per I g of y-Al 2 0, was the proportion shown in FIG. 4. The oxidation catalyst of Comparative Example 4 was produced in the same way as Working Example 5. except for the changes mentioned above. Moreover, the 10 characteristics of the obtained oxidation catalyst are shown in FIG. 4. [0046) An explanation will now be given of the production of Comparative Example 5. In Comparative Example 5. the quantities of the solution of dinitrodiammine platinum nitrate and the solution of dinitrodiammine palladium nitrate added in the mixed liquid preparation step were changed so that the supported quantities of Pt and Pd were 15 0.67 parts by mass and 1.26 parts by mass respectively relative to 100 parts by mass of the y-AlO3 in the obtained Pt-Pd support body. In addition, in the Ba supporting step. the aqueous solution containing barium acetate was supported by water absorption in such a way that the supported quantity of Ba per I g of y-Al 2 03 w\as the proportion shown in FIG. 4. The oxidation catalyst of Comparative Example 5 was produced in the same way as 20 Working Example 5. except for the changes mentioned above. Moreover, the characteristics of the obtained oxidation catalyst are shown in FIG. 4. (00471 An explanation will now be given of the production of Comparative Example 6. In Comparative Example 6, a solution of dinitrodiammine platinum nitrate was not added and only a solution of dinitrodiammine palladium nitrate was added in the 25 mixed liquid preparation step. Ii addition, a support body for Pd (a Pd support body) was produced instead of a support body for Pt and Pd (a Pt-Pd support body). In addition, the added quantity of the solution of dinitrodiammine palladium nitrate in the mixed liquid preparation step was changed so that the supported quantity of Pd was 2 parts by mass relative to 100 pails by mass of the y-AlO- in the Pd support body. Furthermore, in the WO 2014/135937 PCT/IB2014/000183 20 Ba supporting step, the Pd support body was used instead of the Pt-Pd support body and the aqueous solution containing barium acetate was supported by water absorption in such a way that the supported quantity of Ba per I g of y-A 2 0 3 was the proportion shown in FIG. 4. The oxidation catalyst of Comparative Example 6 was produced for comparison 5 in the same way as Working Example 5, except for the changes mentioned above. Moreover. the characteristics of the obtained oxidation catalyst are shown in FIG. 4. 100481 An explanation will now be given of the evaluation of the characteristics of the oxidation catalysts obtained in Working Examples I to 7 and Comparative Examples I to 6. First, an explanation will be given of the evaluation of catalyst activity (i). The 10 oxidation catalysts obtained in Working Examples I to 7 and Comparative Examples 1 to 6 (catalysts supported on monolithic base materials) were placed in an atmospheric pressure fixed bed flow reactor (CATA-5000, manufactured by Best Sokki). and a model gas consisting of CO (800 ppm), C 3
H
6 (400 ppmC). 02 (10 vol%.), CO 2 (10 vol%), H 2 0 (8 vol%) and N 2 (balance) (catalyst input gas. model diesel exhaust gas having an A/F ratio of 15 253) was supplied to each of the oxidation catalysts at a gas flow rate of 30 L/min and was brought into contact with the oxidation catalyst. When supplying this gas. the temperature of the gas brought into contact with the catalyst (the catalyst input gas) was increased from 50'C (the initial temperature) to 350'C at a rate of temperature increase of 10 C min. In addition, the CO concentration and C 3
H
6 concentration in the gas following 20 contact with the catalyst (the catalyst output gas) were measured. In addition, the temperature at \\hich the CO purification rate reached 50% (CO 50% purification temperature: CO-T50) and the temperature at.which the C3H- 6 purification rate reached 50% (HC 50% purification temperature: HC-T50) were determined on the basis of these measured values (CO concentration and C 3
H
6 concentration in the catalyst output gas) and 25 the values of the CO concentration and C 3
H
6 concentration in the catalyst. input gas. The obtained results are shown in FIG. 5. In addition, FIG. 2 is a graph that shows the relationship between the CO-T50 and HC-T50 values of the oxidation catalysts obtained in Working Examples I to 4 and Comparative Examples I and 2 and the Ba/Pt molar ratio in these catalysts.
WO 2014/135937 PCT/IB2014/000183 21 (00491 As is clear from the result sho\n in FIGS. 2 and 5 (and especially the results obtained using the oxidation catalysts obtained in Working Examples 1 to 4 and Comparative Examples I and 2), it was confirmed that the CO-T50 value decreased as the added quantity of Ba in the oxidation catalyst increased, and it was understood that 5 catalytic activity against CO improved as the added quantity of Ba increased. Moreover. the inventors of the invention surmise that such results show that by supporting an added element (Ba). the electronic state of Pt changes and catalyst poisoning due to the strong adsorption of CO is suppressed. meaning that oxidation reactions are facilitated. In addition, as is clear from the results shown in FIG. 2, the HC-T50 value decreased in cases 10 where the BaPt ratio in the oxidation catalyst was up to 8.8 compared to cases where Ba was not supported. Meanwhile, it was confirmed that the HC-T50 value suddenly increased \\hen the Ba Pt ratio reached 15.4 (Comparative Example 2), The inventors of the invention surmise that such results show that in cases where the added quantity of an added element (Ba) is too high (for example, Comparative Example 2), the electronic state 15 of the Pt shifts too far to the oxide side, it is difficult for the Pt to activate HC, and the catalytic activity (oxidation activity) of the oxidation catalyst deteriorates. [00501 In addition, as is clear from the results shown in FIG. 5, by comparing oxidation catalysts obtained by firing at a high temperature such as 750'C after supporting Pt and/or Pd when producing the catalysts (Working Examples 5 to 7 and Comparative 20 Examples 3 to 6), it was confirmed that oxidation catalysts obtained by supporting Pt, Pd and Ba (Working Examples 5 to 7) exhibited improved catalytic activity against CO and HC compared to the oxidation catalyst obtained in Comparative Example 3, in which Pt and Pd were supported but Ba was not supported. As a result, it was understood that oxidation catalysts obtained in working examples of the invention (Working Examples 5 to 25 7) maintained Pt catalytic activity and exhibited sufficiently high catalytic activity and excellent high temperature heat resistance even when exposed to high temperatures of 750'C or higher after Pt and Pd were supported. In addition, by comparing the oxidation catalysts obtained in Working Examples 5 to 7, the oxidation catalyst obtained in Comparative Example 4, in which Pd was not supported by Pt and Ba were supported, and WO 2014/135937 PCT/IB2014/000183 22 the oxidation catalyst obtained in Comparative Example 6, in which Pt and Ba were not supported but Pd was supported, it was understood that oxidation catalysts obtained in working examples of the invention (Working Examples 5 to 7) maintained Pt catalytic activity even when exposed to high temperatures of 750'C or higher after Pt and Pd were 5 supported, whereas cases where a combination of Pt and Pd was not supported and only one of Pt or Pd was supported (Comparative Examples 4 and 6) could not necessarily achieve sufficient catalytic activity when exposed to high temperatures of 750'C or higher after Pt or Pd was supported. Furthermore, by comparing the oxidation catalysts obtained in Working Examples 5 to 7 \with the oxidation catalyst obtained in Comparative Example 10 5, it was confirmed that in a case where the Pd Pt ratio was 3.5 (Comparative Example 5.), it was not possible to maintain sufficient Pt catalytic activity when the catalyst \as exposed to high temperatures even if both Pt and Pd were supported on the catalyst. 100511 From these results, it was understood that sufficient catalytic activity and excellent high temperature heat resistance can be achieved by supporting Pt and Pd at a 15 [Pd]/'[Pt] molar ratio of 0.1 to 1.5 on an alumina-based carrier and supporting an added element (Ba) at an [added element]/[Pt] molar ratio of I to 12 on the alumina-based carrier. 100521 An explanation will now be given of the production of Working Example 8. First, an explanation will be given of the preparation of a Pt-Pd support body (A). A dispersion was obtained by dispersing a powder of y-A] 2
O
3 (product name "M1307", 20 manufactured by Grace. specific surface area 160 m2/g, average particle diameter 17 pm) in ion exchanged water. A mixed liquid was then obtained by adding a solution of dinitrodiammine platinum nitrate (manufactured by Tanaka Kikinzoku) and a solution of dinitrodiammine palladium nitrate (manufactured by Tanaka Kikinzoku) to the dispersion and stirring for 2 hours (a mixed liquid preparation step). A support body for Pt and Pd (a 25 Pt-Pd support body (A)) was then obtained by evaporating off the solvent from the mixed liquid, drying the obtained solid component for 12 hours at 120'C and then firing for 3 hours at 550'C. Moreover, the quantities of the solution of dinitrodiammine platinum nitrate and the solution of dinitrodiammine palladium nitrate added in the mixed liquid preparation step were adjusted so that the supported quantities of Pt and Pd were 2.1 parts WO 2014/135937 PCT/IB2014/000183 23 by mass and 0.5 parts by mass respectively relative to 100 parts by mass of the y-Al20 3 in the obtained Pt-Pd support body (A). 100531 An explanation will now be given of the preparation of a Pd support body. A precipitate was obtained by adding aqueous ammonia. which contained ammonia at 1.2 5 times the neutralization equivalent quantity for the total quantity of metal cations, to a solution containing aluminum nitrate, titanium chloride and zirconium oxynitrate while stirring vigorously. An Al0 2 -TiO 2 -ZrO2 powder (having a specific surface area of 1.20 12/g was then obtained by firing the obtained precipitate for 5 hours at 800 0 C (a coprecipitation method). Moreover, the content of aluminum nitrate, titanium chloride 10 and zirconium oxynitrate in the solution was adjusted so that the AlO /TiO 2 /ZrO2 mass ratio in the obtained AIbO;-TiO-ZrO2 powder was 60/12/28. 100541 A dispersion \\as then obtained by dispersing the AbOr-TiO-ZrO' powder (an alumina-based carrier) in ion exchanged water. A mixed liquid \\as then obtained by adding a solution of dinitrodiammine palladium nitrate (manufactured by Tanaka 15 Kikinzoku) to the dispersion and stirring for 2 hours (a mixed liquid preparation step). A support body for Pd (a Pd support body) was then obtained by evaporating off the solvent from the mixed liquid, drying the obtained solid component for 12 hours at 120 C and then firing for 3 hours at 550'C. Moreover, the quantity of the solution of dinitrodiammine palladium nitrate added in the mixed liquid preparation step was adjusted so that the 20 supported quantity of Pd was 0.8 parts by mass relative to 100 parts by mass of the alumina-based carrier (AlbO 3 -TiO 2 -ZrO2 powder) in the obtained Pd support body. 100551 An explanation will now be given of the preparation of a Pt-Pd support body (B). The quantities of the solution of dinitrodiammine platinum nitrate and the solution of dinitrodiammine palladium nitrate added in the mixed liquid preparation step 25 were adjusted so that the supported quantities of Pt and Pd were 3.1 parts by mass and 1.5 parts by mass respectively relative to 100 parts by mass of the y-A 2 0 3 in the obtained support body for Pt and Pd. Apart from this change, a support body for Pt and Pd (a Pt-Pd support body (B)) was obtained using a method similar to the above-mentioned method for preparing a support body for Pt and Pd (A).
WO 2014/135937 PCT/IB2014/000183 24 100561 An explanation will now be given of the preparation of a catalyst that contains an oxidation catalyst layer fixed on a monolithic base material. First, a coating liquid was obtained by dispersing 45 g of the Pt-Pd support body (A). 30 g of the Pd support body and an alumina sol (solid content: 10 \I%) in ion exchanged water. The 5 obtained coating liquid was provided on a tetragonal cell cordierite monolithic base material (diameter 30 mm, length 50 mm, volume 35 mL 35 cc), cell density 400 cells inchI) by means of a wash coat method so that the coating quantity was 75 g per I L of the base material. A first coating layer was formed by firing the tetragonal cell cordierite monolithic base material coated with a coating liquid for 5 hours at a 10 temperature of 500'C. Next, an aqueous solution containing barium acetate was supported on the first coating layer by water absorption in such a way that the supported quantity of Ba was 0.67 mmol per I g of the carrier (a mixture of the Al 2 0-TiO2-ZrO2 powder and Al 2 0 3 ) (the supported quantity was 0.05 mol per I L of the base material), Ba was then supported on the carrier by firing for 5 hours at a temperature of 550'C (a Ba 15 supporting step). In this way, a coating layer consisting of an oxidation catalyst (an oxidation catalyst coating layer) was fixed to a monolithic base material. This oxidation catalyst is a catalyst in which Pt, Pd and Ba are supported on an alumina-based carrier. Moreover, the total content (proportion) of Al 2 O, relative to the total quantity of the A1 2 0-TiO 2 -ZrO 2 powder derived from the Pt-Pd support body (A) and A1 2 0 3 derived from 20 the Pd support body is 84 mass in terms of oxide. [0057] Next, a coating liquid was obtained by dispersing 15 g of the Pt-Pd support body (B), 40 g of a P type zeolite powder (product name "HSZ940-HOA", manufactured by Tosoh Corporation, Si/Al 2 = 37, specific surface area = 450 m2/g, average particle diameter = 5 pim) and an alumina sol (solid content: 10 wt\%) in ion exchanged 25 water. The obtained coating liquid was provided on the coating layer (lower layer) of the oxidation catalyst at a coating quantity of 55 g per I L of the base material. The oxidation catalyst provided with the coating liquid was fired for 5 hours in air at a temperature of 550'C so as to form a second coating layer on the coating layer (lower layer) of the oxidation catalyst and form a catalyst having a two layer coated structure (lower layer: WO 2014/135937 PCT/IB2014/000183 25 oxidation catalyst, upper layer: Pt-Pd support body (B)'and 0 type zeolite). The catalyst having a two layer coated structure was then fired for 10 hours in air at a temperature of 750'C. Moreover, the characteristics of the catalyst are shown in FIG. 6. 100581 An explanation will now be given of the production of Comparative 5 Example 7. A comparative catalyst was obtained by using a method similar to the method for preparing a catalyst containing an oxidation catalyst layer fixed on a monolithic base material used in Working Example 8, except that the Ba supporting step was not carried out and the first coating layer was formed as the lower layer before Ba w\as supported. MIoreover, this comparative catalyst was formed and then fired for 10 hours in air at a 10 temperature of 750'C. The characteristics of this comparative catalyst are shown in FIG 6. 100591 An explanation will now be given of the production of Comparative Example 8. First, 1.6 L of a mixed aqueous solution was prepared by dissolving I mole of aluminum nitrate. 0.6 moles ,of cerium (III) nitrate. 0.4 moles of zirconium oxynitrate 15 and 0.66 moles of H 2 0 2 . A precipitate was obtained by adding aqueous ammonia, which contained ammonia at 1.2 times the neutralization equivalent quantity for all metal cations. to 1.6 L of the prepared mixed aqueous solution while stining vigorously. An AlO-CeO2-ZrO2 powder (Al 2 0v/CeO 2 /ZrO2 molar ratio = 5/6/4, specific surface area = 89 m 2g) was then obtained by firing this precipitate for 5 hours at temperature of 800'C (a 20 coprecipitation method). 100601 Next, a coating liquid was obtained by dispersing the AI0-CeO 2 -ZrO 2 powder (a carrier having an alumina content of 25 mass%) and an alumina sol (solid content: 10 wt%) in ion exchanged water. The coating liquid was then provided on a hexagonal cell cordierite monolithic base material (diameter 30 mm, length 50 mm, 25 volume 35 mL (35 cc), cell density 400 cells/inch 2 ) by means of a wash coat method so that the coated quantity was 200 g per I L of the base material. A coating layer of the powder was then formed on the base material by firing the hexagonal cell cordierite monolithic base material coated with the coating liquid for 5 hours at a temperature of 500*C. Next, a solution of dinitrodiammine platinum nitrate and a solution of WO 2014/135937 PCT/IB2014/000183 26 dinitrodiammine palladium nitrate were supported on the coating layer by water absorption in such a way that the supported quantities of Pt and Pd were 2.7 g (Pt) and 1.3 g (Pd) per I L of the catalyst base material. Pt and Pd were then supported on the powder by firing the coating layer for 5 hours at a temperature of 550'C. 100611 An aqueous solution containing barium acetate was then supported on the coating layer, on which Pt and Pd had been supported, by water absorption in such a way that the supported quantity of Ba was 0.1 moles per I L of the base material. Ba was then supported by firing the coating layer for 5 hours at a temperature of 500'C (a Ba supporting step). In this vay, a comparative oxidation catalyst fixed on a monolithic base 10 material was obtained. Here, the oxidation catalyst of Comparative Example 8 is a catalyst in which Pt. Pd and Ba are supported on a carrier having an alumina content of 25 mass% (an A1O-CeO-ZrO 2 powder). Moreover, the oxidation catalyst obtained in this way was fired for 10 hours at a temperature of 800C. Moreover, the characteristics of the catalyst are shown in FIG. 7. 15 100621 An explanation will now be given of the method for producing Comparative Example 9. A comparative oxidation catalyst fixed on a monolithic base material was obtained in the same way as Comparative Example 8, except that the Ba supporting step was not carried out. Here. the oxidation catalyst of Comparative Example 9 is a catalyst in which Pt and Pd are supported on a carrier having an alumina content of 20 25 mass% (an Al 2 0 3 -CeO-ZrO2 powder). Moreover, the oxidation catalyst obtained in this way was fired for 10 hours at a temperature of 800'C. Moreover, the characteristics of the catalyst are shown in FIG. 7. 10063] An explanation will now be given of the evaluation of the characteristics of the oxidation catalysts obtained in Working Example 8 and Comparative Examples 7 to 25 9. First, an explanation will be given of the evaluation of catalyst activity (ii). The catalysts obtained in Working Example 8 and Comparative Examples 7 to 9 (catalysts supported on monolithic base materials) were placed in an atmospheric pressure fixed bed flow reactor (CATA-5000, manufactured by Best Sokki), and a model gas consisting of CO (800 ppm), C 3
H
6 (400 ppmC), NO (100 ppm), 02 (10 vol%), CO 2 (10 vol%), H 2 0 (8 WO 2014/135937 PCT/IB2014/000183 27 vol%) and N 2 (balance) (catalyst input gas, model diesel exhaust gas having an A/F ratio of 253) was supplied to each of the catalysts at a gas flow rate of 30 Lmin and was brought into contact with the catalyst. When supplying this gas, the temperature of the gas brought into contact with the catalyst (the catalyst input gas) was increased from 50'C (the 5 initial temperature) to 350'C at a rate of temperature increase of 10 C/min. In addition, the CO concentration and C 3
H
6 concentration in the gas following contact with the catalyst (the catalyst output gas) were measured. In addition, the temperature at which the CO purification rate reached 50% (CO 50O' purification temperature: CO-T50) and the temperature at which the C 3
H
6 purification rate reached 50% (HC 50% purification 10 temperature: HC-T50) were determined on the basis of these measured values (CO concentration and CH 6 concentration in the catalyst output gas) and the values of the CO concentration and C 3
H
6 concentration in the catalyst input gas. The obtained results are shown in FIG. 8. In addition, FIG. 3 is a graph that shows the CO-T50 and HC-T50 values of the catalysts obtained in Working Example 8 and Comparative Example 7. 15 [00641 In the catalyst obtained in Working Example 8, a layer consisting of an oxidation catalyst on which Pt. Pd and Ba are supported is fomed on the lower layer. as mentioned above. In addition, in the catalyst obtained in Comparative Example 7, a layer consisting of an oxidation catalyst on which Ba is not supported is forced on the lower layer. As is clear from the results shown in FIGS. 3 and 8, it was confined that the 20 catalyst obtained in Working Example 8 exhibited lower CO-T50 and HC-T50 values than the catalyst obtained in Comparative Example 7, and exhibited sufficiently high oxidation activity against CO and HC. In this way, it was confirmed that, in a case where another catalyst layer was provided on the upper layer of a monolithic base material having a lower layer coated with a diesel exhaust gas oxidation catalyst of a working example of the 25 invention (Working Example 8), sufficiently high oxidation activity against CO and HC was exhibited, Furthermore, it was confirned that sufficient catalytic activity was achieved even when a working example of the invention was used in combination with another catalyst. 100651 In addition, it was understood that in cases where a carrier having a low WO 2014/135937 PCT/IB2014/000183 28
A]
2
O
3 content of 25 mass% (Comparative Examples 8 and 9), an improvement in activity against CO and HC was not seen even if Ba \was supported as an added element. Furthermore. it was understood that in a case in which Ba was supported (Comparative Example 8), catalytic activity actually decreased. From the results obtained using the 5 catalysts obtained in Working Example 8 and Comparative Examples 8 and 9, it was understood that sufficient catalytic activity against CO and HC could be achieved by using a combination of Pt. Pd and an added element (Ba) while setting the content of A1 2 0 3 in the carrier to be 40 massO' or higher. 100661 As explained above, according to the invention, it is possible to provide a 10 diesel exhaust gas oxidation catalyst which can oxidize and purify carbon monoxide and hydrocarbons from low temperatures, which exhibits excellent durability at high temperatures and which exhibits sufficiently high catalytic activity from low temperatures even after being exposed to high temperatures, and it is also possible to provide a method for purifying diesel exhaust gas by using this diesel exhaust gas oxidation catalyst. 15 Therefore. the diesel exhaust gas oxidation catalyst of the invention is particularly useful as a catalyst for oxidizing and purifying carbon monoxide and hydrocarbons in. for example, gases (exhaust gases) emitted from diesel engines.

Claims (11)

1. A diesel exhaust gas oxidation catalyst that is configured to purify exhaust gas from a diesel engine, the catalyst comprising: an alumina-based carrier in which a content of alumina is 40 mass% or higher; Pt supported on the alumina-based carrier: Pd supported on the alumina-based carrier: and at least one type of added element that is selected from the group consisting of alkali metal elements and alkaline earth metal elements and that is supported on the alumina-based carrier, wherein a supported quantity of the Pt is 0.1 to 5 parts by mass relative to 100 parts by mass of the alumina-based carrier, a molar ratio obtained by dividing a supported quantity of the Pd by the supported quantity of the Pt is 0,1 to 1.5. and a molar ratio obtained by dividing a supported quantity of the added element by the supported quantity of the Pt is I to 12.
2. The diesel exhaust gas oxidation catalyst according to claim 1. wherein the molar ratio obtained by dividing the supported quantity of the added element by the supported quantity of the Pt is 3 to 12.
3. The diesel exhaust gas oxidation catalyst according to claim I or claim 2, wherein the content of alumina in the alumina-based carrier is 50 to 100 mass%.
4. The diesel exhaust gas oxidation catalyst according to claim 3, wherein the content of alumina in the alumina-based carrier is 80 to 100 mass%.
5. The diesel exhaust gas oxidation catalyst according to any one of claims I to 4. wherein WO 2014/135937 PCT/IB2014/000183 30 the supported quantity of the Pt is I to 4 parts by mass relative to 100 parts by mass of the alumina-based carrier.
6. The diesel exhaust gas oxidation catalyst according to any one of claims I to 5, wherein the molar ratio obtained by dividing the supported quantity of the Pd by the supported quantity of the Pt is 0.5 to 1.2.
7. The diesel exhaust gas oxidation catalyst according to any one of claims I to 6, wherein the supported quantity of the Pd is 0.005 to 4 parts by mass relative to 100 parts by mass of the alumina-based carrier.
8. The diesel exhaust gas oxidation catalyst according to claim 7, wherein the supported quantity of the Pd is 0.03 to 3 parts by mass relative to 100 parts by mass of the alumina-based carrier.
9. The diesel exhaust gas oxidation catalyst according to any one of claims I to -8, wherein the supported quantity of the added element is 0.005 to 3 mmol/g relative to the alumina-based carrier.
10. The diesel exhaust gas oxidation catalyst according to claim 9. wherein the supported quantity of the added element is 0.015 to 2.5 mmol/g relative to the alumina-based carrier.
11. A method for purifying diesel exhaust gas, comprising: bringing lean atmosphere exhaust gas, having an air/fuel ratio of 15 or higher and emitted by a diesel engine, into contact with the diesel exhaust gas oxidation catalyst WO 2014/135937 PCT/IB2014/000183 31 according to any one of claims I to 10 so as to purify the exhaust gas.
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CA1025636A (en) * 1972-12-15 1978-02-07 Uop Inc. Exhaust gas conversion catalyst and use thereof
JPS6078640A (en) * 1983-10-04 1985-05-04 Nippon Shokubai Kagaku Kogyo Co Ltd Catalyst for purifying exhaust gas and preparation thereof
JPH01171626A (en) 1987-12-28 1989-07-06 Nippon Shokubai Kagaku Kogyo Co Ltd Method for cleaning exhaust gas from diesel engine
JP3328318B2 (en) 1992-05-22 2002-09-24 トヨタ自動車株式会社 Exhaust gas purification method
JP3378096B2 (en) 1994-10-21 2003-02-17 トヨタ自動車株式会社 Exhaust gas purification catalyst
JP3386621B2 (en) * 1995-03-30 2003-03-17 トヨタ自動車株式会社 Exhaust gas purification catalyst for diesel engines
JP3384255B2 (en) * 1996-07-11 2003-03-10 株式会社日立製作所 Internal combustion engine exhaust gas purification method
JP4012320B2 (en) * 1998-10-15 2007-11-21 株式会社アイシーティー Exhaust gas purification catalyst for lean combustion engine
JP2004188388A (en) * 2002-12-13 2004-07-08 Babcock Hitachi Kk Filter for cleaning diesel exhaust gas and its production method
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JP5323093B2 (en) * 2008-12-19 2013-10-23 株式会社キャタラー Exhaust gas purification catalyst
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