Three-way catalyst composition comprising intermetallic compounds

Abstract

A catalyst composition for a three-way catalyst comprising an intermetallic compound is disclosed. The intermetallic compound includes a transition metal selected from the group consisting of Fe, Ce, Y, Nb, and combinations thereof; and a noble metal selected from the group consisting of Pt, Pd, Rh, and combinations thereof. The invention also relates to a washcoat comprising the catalyst composition as well as a catalyst article comprising the catalyst composition, a method of treating an exhaust gas with the catalyst article, a method of making the catalyst article and a system comprising the catalyst article.

Description

Technical Field

[0001] The present invention relates to a composition for manufacturing a three-way catalyst for treating exhaust gas from an internal combustion engine. The present invention extends to a washcoat comprising the catalyst composition and a catalyst article comprising the catalyst composition. The present invention also extends to a method of manufacturing a catalyst article, a method of treating exhaust gas with a catalyst article, and a system comprising the catalyst article. Background Art

[0002] Three-way catalysts (TWCs) are commonly used to convert carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NO x ) found in the exhaust gas of gasoline-fueled internal combustion engines. These pollutants are harmful substances, and their emissions are strictly controlled by environmental regulations worldwide.

[0003] Three-way catalysts treat exhaust gas by simultaneously oxidizing carbon monoxide and hydrocarbons and reducing nitrogen oxides. Conventional three-way catalysts typically comprise a noble metal (such as platinum, rhodium, palladium, iridium, or ruthenium) on a catalyst support. The catalyst support typically comprises a porous refractory oxide, such as alumina, silica, or ceria. The supported catalyst can then be applied to a substrate or extruded to form a catalyst article.

[0004] Like other exhaust gas catalysts, three-way catalysts typically achieve very high efficiency once they reach their operating temperature (usually 200 °C and higher). However, these catalysts can be relatively inefficient below their operating temperature (i.e., during the cold start phase). The activity of a three-way catalyst can be measured according to the "light-off temperature". Improved light-off performance can indicate improved performance during the cold start phase.

[0005] As used herein, the term "light-off temperature" should be understood to mean the temperature at which 50% catalytic conversion is achieved, and is synonymous with "T 50 ". It should be understood that the light-off temperatures of different components in the exhaust gas can be different from each other. For example, the light-off temperature of the catalyst for carbon monoxide can be different from its light-off temperature for nitrogen oxides.

[0006] TWCs can be exposed to extremely high temperatures of 800 °C to 1000 °C during thermal aging. Exposure to these temperatures causes severe sintering phenomena. This can cause many problems affecting the performance of TWCs: loss of surface area, loss of available reactive oxygen within the catalyst support lattice, and further sintering of the noble metal. Therefore, there is a need for TWCs with improved thermal stability. Conventional methods for improving the thermal stability of TWCs include using cerium-zirconium dioxide or adding other "promoter" elements, such as any of the alkaline earth metals or trivalent rare earth metals.

[0007] Due to the increase in the price of PGM products, a TWC with a reduced noble metal loading is required. A TWC with a reduced metal loading is generally associated with poor emission control performance and poor thermal stability.

[0008] Accordingly, an object of the present invention is to provide a catalyst article that achieves improved thermal stability and improved ignition performance. Another object of the present invention is to provide improved CO, HC, and NO x emission control performance at a significantly reduced noble metal loading. SUMMARY OF THE INVENTION

[0009] The inventors have found that the presence of an intermetallic compound comprising at least a transition metal selected from Fe, Ce, Y, Nb, and combinations thereof and a noble metal selected from Pt, Pd, Rh, and combinations thereof in a catalyst composition provides improved thermal stability and improved ignition performance results. When the composition is used to fabricate a catalyst article, the presence of the above intermetallic compound in the catalyst composition also results in improved CO, HC, and NO x emission control performance at a significantly reduced noble metal loading.

[0010] According to a first aspect, there is provided a catalyst composition comprising an intermetallic compound, wherein the intermetallic compound comprises:

[0011] a transition metal selected from Fe, Ce, Y, Nb, and combinations thereof; and

[0012] a noble metal selected from Pt, Pd, Rh, and combinations thereof.

[0013] Preferably, the intermetallic compound has the formula according to Formula I:

[0014] Al a -X b -PGM c

[0015] Formula I

[0016] wherein:

[0017] a = 100 - b - c;

[0018] 25 ≤ a < 80;

[0019] 20 < b < 75;

[0020] 0 < c < 5.0;

[0021] where a, b, and c are atomic weight percentages;

[0022] where X is the transition metal selected from Fe, Ce, Y, Nb, and combinations thereof; and

[0023] wherein PGM is the noble metal selected from Pt, Pd, Rh, and combinations thereof.

[0024] According to a second aspect of the present invention, there is provided a repair basecoat composition comprising the catalyst composition according to the first aspect of the present invention and a liquid medium.

[0025] A third aspect of the present invention provides a catalyst article comprising a substrate and the catalyst composition according to the first aspect of the present invention.

[0026] A fourth aspect of the present invention provides a method of making the catalyst article according to the third aspect of the present invention, the method comprising the step of coating a substrate with the repair basecoat composition according to the second aspect of the present invention.

[0027] A fifth aspect of the present invention provides an emissions treatment system for treating a combustion exhaust gas stream, the emissions treatment system comprising the catalyst article according to the third aspect.

[0028] A sixth aspect of the present invention provides a method of treating exhaust gas from an engine, the method comprising contacting the exhaust gas with the catalyst article according to the third aspect. Detailed Description

[0029] Preferred and / or optional features of the present invention will now be set forth. Unless the context otherwise requires, any aspect of the present invention may be combined with any other aspect of the present invention. Unless the context otherwise requires, any preferred and / or optional feature of any aspect may be combined, singly or in combination, with any aspect of the present invention.

[0030] The present invention relates to the catalytic treatment of combustion exhaust gases (such as those produced by gasoline engines and other engines), and to related catalyst compositions, catalytic articles, and systems. More specifically, the present invention relates to the simultaneous treatment of NO x , CO, and HC in a vehicle exhaust system.

[0031] A first aspect provides a catalyst composition comprising an intermetallic compound, wherein the intermetallic compound comprises:

[0032] a transition metal selected from Fe, Ce, Y, Nb, and combinations thereof; and

[0033] a noble metal selected from Pt, Pd, Rh, and combinations thereof.

[0034] As will be understood by those skilled in the art, the term "intermetallic compound" refers to a compound formed by at least two metals and having at least partially an ordered crystal structure different from the crystal structures of its constituent elements (metals). Without wishing to be bound by a particular theory, it is believed that a particular combination of the electronic and crystal structures of intermetallic compounds results in chemical potentials of elements that are not readily obtained in other compounds. The chemical potential is largely generated by the electron transfer between the constituent elements of the intermetallic compound.

[0035] The intermetallic compound of Al-X is used as a PGM platform, where PGM atoms can be uniformly dispersed.

[0036] Preferably, the intermetallic compound can have the formula of Formula I as defined above.

[0037] In Formula I, a, b, and c represent atomic weight percentages based on the total metal content of the intermetallic compound.

[0038] In Formula I, X represents a transition metal and can be selected from Fe, Ce, Y, Nb, and combinations thereof. Preferably, X is Fe or Y. Most preferably, X can be Y.

[0039] In Formula I, PGM represents a noble metal and can be selected from Pt, Pd, Rh, and combinations thereof. Preferably, PGM is Rh.

[0040] In Formula I, 25 ≤ a < 80, such as 60 < a < 80, for example a = 75. It may be preferred that 74 ≤ a ≤ 76. It may be more preferred that 74.5 ≤ a ≤ 75.5.

[0041] In Formula I, 20 < b < 75, such as 20 < b ≤ 40 or 20 < b ≤ 35. It may be preferred that 20 < b ≤ 25. It may be preferred that b is between 24 and 25.

[0042] In Formula I, 0 < c < 5.0, such as 0.2 ≤ c < 3.0. It may be preferred that c is greater than or equal to 0.5, or greater than or equal to 0.6. It may be preferred that c is less than or equal to 1.0, or less than or equal to 0.7. It may be preferred that c is 0.2 ≤ c ≤ 0.5. It may be preferred that c is about 0.5.

[0043] As demonstrated in the examples, there are provided compounds having formulas such as Al 74.8 Y 25 Rh 0.2 , Al 74.5 Y 25 Rh 0.5 and Al 74.0 Y 25 Rh 1.0Intermetallic compounds produce catalyst articles with improved properties. In particular, the above intermetallic compounds produce improved thermal stability after the catalyst article ages. In addition, it has been found that these catalyst articles exhibit improved performance at significantly reduced noble metal loadings. This is particularly advantageous because conventional TWCs generally do not perform well at reduced noble metal loadings.

[0044] As used herein, the term "noble metal loading" refers to the measurement result in g / ft 3 as a unit based on the metal weight.

[0045] Various techniques can be used to prepare the intermetallic compounds according to the present invention. Powder metallurgy methods can be preferred, such as annealing in an inert crucible and atmosphere for an appropriate time to achieve thermodynamic equilibrium.

[0046] The intermetallic compound can be prepared according to the method described below.

[0047] The intermetallic compound according to the present invention is prepared by melting metal Al, X, and PGM particles in a furnace (such as an electric arc furnace) under an Ar gas atmosphere. The melting of the particles can be repeated several times, for example, 5 times. The molten material can be annealed in a vacuum condition at 800 °C for 48 hours. Then the annealed material can be cooled to room temperature and subsequently ground in a mill to the desired particle size. The type of mill is not particularly limited and can be selected by those skilled in the art. For example, the mill can be appropriately a ball mill.

[0048] Optionally, the intermetallic compound particles (also referred to as un-leached intermetallic compound particles) obtained by the above method can be further subjected to a leaching step to obtain leached intermetallic compound particles. The intermetallic compound particles can be leached in a suitable leaching solution. Preferably, the intermetallic compound particles can be leached in a 10 wt% aqueous NaOH solution or a 10 wt% aqueous Na2CO3 solution at room temperature for 24 hours. The leached intermetallic compound particles can be filtered and washed thoroughly with distilled water until a pH of 7 is measured. Then the washed particles can be dried at 313 K (40 °C) for 12 hours.

[0049] In particular, Al or substantially Al can be leached from the intermetallic compound of formula I. Preferably, at least 40% of the Al present in the un-leached intermetallic compound particles can be leached. More preferably, at least 50% of the Al present in the un-leached intermetallic compound particles can be leached. Even more preferably, at least 60 wt% of the Al present in the un-leached intermetallic compound particles can be leached, such as at least 64 wt% of the Al. Most preferably, all or substantially all of the Al present in the un-leached intermetallic compound particles can be leached, leaving monodisperse PGM supported on X oxide, such as Rh / Fe2O3 or Pt / Fe2O3, Rh / Y2O3, etc.

[0050] Leaching of the intermetallic compound increases the specific surface area of the intermetallic compound. The specific surface area of the intermetallic compound can be determined by the Brunauer-Emmett-Teller (BET) method. Preferably, the BET specific surface area can be about 90 m 2 / g to about 160 m 2 / g, more preferably about 100 m 2 / g to about 160 m 2 / g, even more preferably about 120 m 2 / g to about 150 m 2 / g.

[0051] The amount of the intermetallic compound present in the catalyst composition can be such that the catalyst composition has a noble metal loading between 0.5 g / ft 3 and 5 g / ft 3 , preferably between 0.5 g / ft 3 and 4 g / ft 3 , even more preferably between 0.5 g / ft 3 and 3 g / ft 3 , such as between 0.5 g / ft 3 and 2 g / ft 3 . The noble metal loading of the catalyst composition can be 2.0 g / ft 3 .

[0052] The composition can include an oxygen storage component and / or an inorganic oxide.

[0053] The oxygen storage component can be cerium oxide, zirconium oxide, cerium dioxide - zirconium oxide mixed oxide, alumina - cerium dioxide - zirconium oxide mixed oxide, or a combination thereof. More preferably, the oxygen storage component can comprise cerium dioxide - zirconium oxide mixed oxide, alumina - cerium dioxide - zirconium oxide mixed oxide, or a combination thereof. The cerium dioxide - zirconium oxide mixed oxide can further comprise dopants such as lanthanum oxide, neodymium oxide, praseodymium oxide, yttrium oxide, etc. In some embodiments, the oxygen storage component can comprise cerium dioxide - zirconium oxide mixed oxide and alumina - cerium dioxide - zirconium oxide mixed oxide.

[0054] Relative to the other components in the catalyst composition, the oxygen storage component can be present in the catalyst composition in an amount between 20 wt% and 80 wt%, preferably in an amount between 20 wt% and 60 wt%, more preferably in an amount between 20 wt% and 50 wt%.

[0055] The inorganic oxide can be doped or undoped alumina, doped or undoped silica, doped or undoped cerium dioxide, or doped or undoped cerium dioxide - zirconium. Preferably, the inorganic oxide is lanthanum - doped alumina (e.g., lanthanum - stabilized alumina), wherein lanthanum is at most 10 wt% of the inorganic oxide, preferably 2 wt% to 8 wt%, 3 wt% to 7 wt%, or 4 wt% to 6 wt%. It should be understood that the inorganic oxide is different from the oxygen storage component.

[0056] Relative to the other components in the catalyst composition, the inorganic oxide can be present in the catalyst composition in an amount between 20 wt% and 80 wt%, preferably in an amount between 40 wt% and 80 wt%, more preferably in an amount of 50 wt% to 80 wt%.

[0057] The leached or unleached intermetallic compound particles, oxygen storage component, and inorganic oxide can be combined to obtain the catalyst composition according to the first aspect of the present invention.

[0058] The catalyst composition can optionally comprise a Group 1 or Group 2 metal. In particular, the catalyst composition can comprise one or more metals selected from magnesium, calcium, strontium, and barium. Preferably, the catalyst composition comprises barium. The Group 1 or Group 2 metal can be supported on the oxygen storage component and / or the inorganic oxide.

[0059] The catalyst composition of the present invention can be a catalyst composition for use as a three - way catalyst for treating combustion exhaust gas by simultaneously oxidizing carbon monoxide and hydrocarbons and reducing nitrogen oxides.

[0060] The catalyst composition can be applied to the substrate in the form of a washcoat. Accordingly, another aspect of the present invention provides a washcoat comprising the catalyst composition of the first aspect and a liquid medium.

[0061] The repair base coating typically has a solids content of 20 wt% to 45 wt%, such as 20 wt% to 35 wt% or about 25 wt%.

[0062] The repair base coating can be prepared according to the method described below.

[0063] The method for producing the repair base coating can include the step of forming a slurry of the oxygen storage component. The slurry of the oxygen storage component can be prepared by suspending the oxygen storage component in a liquid medium (such as deionized water).

[0064] The method for producing the repair base coating can include the step of adding a leached or unleached intermetallic compound (also referred to herein as an intermetallic compound precursor) to the slurry of the oxygen storage component. Those skilled in the art will be able to select alternative intermetallic compounds of formula I according to the desired noble metal loading. The method for producing the repair base coating can include the step of adding an inorganic oxide to the slurry.

[0065] Additives known in the art can be used to adjust the viscosity and rheology of the repair base coating.

[0066] The additive can be added in an aging step before the repair base coating is applied to the substrate.

[0067] The formulation of the intermetallic compound and the amount of the intermetallic compound added to form the composition for forming the repair base coating can be selected by those skilled in the art according to the amount of the noble metal loading required in the catalyst article.

[0068] It has been found that the catalyst article according to the present invention exhibits improved thermal stability under aging conditions and improved ignition performance at a significantly reduced noble metal loading in the catalyst. Thus, in another aspect of the present invention, there is provided a catalyst article suitable for treating exhaust gas in an internal combustion engine, which catalyst article includes a substrate to which the catalyst composition of the first aspect has been applied.

[0069] The substrate can be a flow-through monolith. Alternatively, the substrate can be a wall-flow filter.

[0070] The flow-through monolith substrate has a first face and a second face defining a longitudinal direction therebetween. The flow-through monolith substrate has a plurality of channels extending between the first face and the second face. The plurality of channels extend in the longitudinal direction and provide a plurality of inner surfaces (such as the surfaces of the walls defining each channel). Each of the plurality of channels has an opening at the first face and an opening at the second face. For the avoidance of doubt, the flow-through monolith substrate is not a wall-flow filter.

[0071] The first face is generally at the inlet end of the substrate, and the second face is at the outlet end of the substrate.

[0072] The channels can have a constant width, and each of the plurality of channels can have a uniform channel width.

[0073] Preferably, in a plane orthogonal to the longitudinal direction, the monolithic substrate has from 300 channels per square inch to 900 channels per square inch, preferably from 400 channels per square inch to 800 channels per square inch. For example, on the first surface, the density of the open first channels and the closed second channels is from 600 channels per square inch to 700 channels per square inch. The channels can have a cross-section as follows: rectangular, square, circular, elliptical, triangular, hexagonal, or other polygonal shapes.

[0074] The monolithic substrate serves as a carrier for holding the catalytic material. Suitable materials for forming the monolithic substrate include ceramic-like materials such as cordierite, silicon carbide, silicon nitride, zirconia, mullite, spodumene, alumina-silica magnesia, or zirconium silicate, or porous refractory metals. Such materials and their use in manufacturing porous monolithic substrates are well known in the art.

[0075] It should be noted that the flow-through monolithic substrate described herein is a single component (i.e., a single brick-shaped object). Nevertheless, when forming an emission treatment system, the substrate used can be formed by adhering a plurality of channels together or by adhering a plurality of smaller substrates together, as described herein. Such techniques and suitable housings and configurations for emission treatment systems are well known in the art.

[0076] In embodiments in which the catalyst article of the present invention includes a ceramic substrate, the ceramic substrate can be made of any suitable refractory material, such as alumina, silica, ceria, zirconia, magnesia, zeolite, silicon nitride, silicon carbide, zirconium silicate, magnesium silicate, aluminosilicate, and metal aluminosilicate (such as cordierite and spodumene), or a mixture or mixed oxide of any two or more of them. Cordierite, magnesium aluminosilicate, and silicon carbide are particularly preferred.

[0077] In embodiments in which the catalyst article of the present invention includes a metal substrate, the metal substrate can be made of any suitable metal, and specifically made of heat-resistant metals and metal alloys, such as titanium and stainless steel, and ferritic alloys containing iron, nickel, chromium, and / or aluminum in addition to other trace metals.

[0078] In another aspect of the present invention, there is provided a method for producing a catalyst article comprising the catalyst composition of the first aspect, the method comprising the step of applying the washcoat of the second aspect to a substrate.

[0079] A method of producing a catalyst article can include the steps described above regarding the washcoat for the second aspect of the present invention.

[0080] The method can include the step of applying a washcoat to a substrate to form a coated substrate. The washcoat can be applied to the substrate by any method known in the art. The amount of washcoat applied to the substrate can be determined based on the desired noble metal component loading on the catalyst article. The washcoat can be applied to the substrate in one or more coating steps.

[0081] Optionally, the method can include the step of drying the coated substrate to form a dried coated substrate.

[0082] The method can include the step of calcining the coated substrate. The step of calcining the coated substrate can be carried out on the substrate that has been optionally dried or on the coated substrate after coating. Generally, the coated substrate is calcined at a temperature in the range of 450 to 600 °C for a period of up to 2 hours. Suitably, the coated substrate is calcined in a furnace under an air atmosphere.

[0083] It should be understood that the above steps can be carried out in any suitable order and / or some steps can be combined into a single step. For example, the drying and calcining steps can be combined.

[0084] A method for producing a catalyst article according to the present invention can include the following steps:

[0085] (i) forming a washcoat comprising the catalyst composition of Formula I;

[0086] (ii) applying the washcoat formed in step (i) to a substrate to form a coated substrate;

[0087] (iii) optionally, drying the coated substrate to form a dried coated substrate; and

[0088] (iv) calcining the dried coated substrate to form a catalyst article.

[0089] According to another aspect of the present invention, an exhaust system comprising the catalyst article of the third aspect of the present invention is provided.

[0090] In another aspect of the present invention, a method of treating exhaust gas from an engine is provided, the method comprising contacting the exhaust gas with a catalyst article according to the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0091] The present invention will now be further described in conjunction with the following non-limiting figures.

[0092] Figure 1(a) shows the carbon monoxide (CO) conversion rate (%) as a function of the temperature of the catalyst according to the present invention, wherein the catalyst contains Rh, Pt, and Pd, respectively.

[0093] Figure 1(b) shows the nitrogen oxide (NO x ) conversion rate (%) as a function of the temperature of the catalyst of Figure 1(a).

[0094] Figure 1(c) shows the total hydrocarbon (THC) conversion rate (%) as a function of the temperature of the catalyst of Figure 1(a).

[0095] Figure 2(a) shows the total hydrocarbon (THC) conversion rate (%) of catalyst article 4 and comparative catalysts A to C under fresh and aged conditions at 600 °C.

[0096] Figure 2(b) shows the total nitrogen oxide (NO x ) conversion rate (%) of catalyst article 4 and comparative catalysts A to C under fresh and aged conditions at 600 °C.

[0097] Figure 3(a) shows the total hydrocarbon (THC) conversion rate (%) of the leached and unleached catalyst articles of Figure 3(a) under fresh and aged conditions at 600 °C.

[0098] Figure 3(b) shows the total nitrogen oxide (NO x ) conversion rate (%) of the leached and unleached catalyst articles of Figure 3(a) under fresh and aged conditions at 600 °C.

[0099] Figure 4(a) shows the total hydrocarbon (THC) conversion rate (%) of the catalyst article of Figure 4(a) under fresh and aged conditions at 600 °C.

[0100] Figure 4(b) shows the total nitrogen oxide (NO x ) conversion rate (%) under fresh and aged conditions at 600 °C for the catalyst article of Figure 4(a).

[0101] Example

[0102] The present invention will now be further described in connection with the following non-limiting examples.

[0103] Example 1 - PGM Selection for Intermetallic Compounds

[0104] Catalyst articles 1 to 3 were prepared using catalyst compositions containing different intermetallic compounds as shown in Table 1:

[0105] Table 1

[0106] Intermetallic Compound PGM Loading Catalyst Article 1 <![CDATA[Al 74.3 Fe 22.8 Rh 2.9 > <![CDATA[2.6g / ft 3 Rh]]> Catalyst Article 2 <![CDATA[Al 74.3 Fe 22.8 Pt 2.9 > <![CDATA[2.6 g / ft 3 Pt]]> Catalyst Article 3 <![CDATA[Al 74.3 Fe 22.8 Pd 2.9 > <![CDATA[2.6g / ft 3 Pd]]>

[0107] The different intermetallic compounds listed in Table 1 were prepared using a similar method.

[0108] The intermetallic compounds were prepared using an electric arc furnace under an Ar atmosphere. The alloy samples were annealed in vacuo at 1100 K (827 °C) for 48 h and subsequently milled in a ball mill to a particle size of <75 μm.

[0109] The catalyst composition was prepared by the following method:

[0110] The catalyst composition can be applied to a substrate in the form of a sizing coating comprising the catalyst composition of the first aspect and a liquid medium. The sizing coating can be prepared according to the method described below.

[0111] The pre-prepared inorganic oxide of lanthanum-doped alumina was added to deionized water to form a slurry. The intermetallic compound precursor obtained by the above method was added to the slurry. The resulting mixture was homogenized by stirring. An alkali or acid was slowly added to adjust the pH in the range of about 6.0 to 7.0.

[0112] A thickening agent was added to the slurry, which was then aged to produce a sizing coating suitable for coating the substrate.

[0113] The sizing coating was applied to the substrate by pulling the sizing coating through a channel under vacuum. The substrate was a standard cordierite foil having a pore density of 400 pores per square inch (cpsi), an axial length of 5.00 cm, and a width of 2.54 cm.

[0114] The coated substrate was then dried and calcined.

[0115] For catalyst articles 1 to 3, the ignition temperatures of each of carbon monoxide, nitrogen oxides, and hydrocarbons were determined using a synthetic catalyst activity test (SCAT) apparatus using the gas compositions shown in Table 2 under stoichiometric conditions.

[0116] Table 2

[0117]

[0118] Under the above gas composition, the catalyst articles were heated at a rate of 20 °C / min to 400 °C and held at this temperature for 5 min. The temperature was lowered to 100 °C. The ignition temperature of each catalyst article was measured at a gas flow rate of 40 L / min.

[0119] The complete ignition curves of carbon monoxide, hydrocarbons, and nitrogen oxides are shown in FIGS. 1(a), 1(b), and 1(c). As can be seen from these figures, the catalyst article 1 prepared with the intermetallic compound containing Rh achieved significantly higher conversion rates than the catalyst articles 2 and 3 containing Pt and Pd, respectively.

[0120] Example 2: Performance of the catalyst article according to the present invention and a conventional catalyst at a Rh loading of 0.5 g / ft 3 ​ Comparison

[0121] Comparative Catalyst A

[0122] Comparative catalyst A is a single-layer TWC coated on a ceramic substrate (400 cpsi, 4.0 mil wall thickness). The catalyst layer consists of Rh supported on a washcoat of La-stabilized alumina and Nd-stabilized cerium zirconia, where Rh is pre-fixed on the alumina support. The Rh loading of comparative catalyst A is 0.5 g / ft 3 。

[0123] The method for producing the washcoat for comparative catalysts A to D is similar to the method for producing the washcoat according to the present invention as described above. However, this method differs from the method of the present invention in that a noble metal source is added to the slurry of the oxygen storage component instead of the intermetallic compound precursor. Suitably, the noble metal source can be added to the slurry as one or more soluble compounds of the noble metal required in solution. Suitably, the noble metal source can be provided as a nitrate of the noble metal in an aqueous solution. For example, the noble metal source is added as rhodium nitrate in the preparation of comparative catalyst D.

[0124] Comparative Catalyst B

[0125] Comparative catalyst B is a single-layer TWC coated on a ceramic substrate (400 cpsi, 4.0 mil wall thickness). The catalyst layer consists of Rh supported on a washcoat of Y-doped La-stabilized alumina and Nd-stabilized cerium zirconia, where Rh is pre-fixed on the alumina support. The Y-doped La-stabilized alumina is prepared by a wet impregnation method using an aqueous solution of Y nitrate. The Y concentration is the same as that of catalyst article 4 described below. The Rh loading of comparative catalyst B is 0.5 g / ft 3 。

[0126] Comparative Catalyst C

[0127] Comparative catalyst C is a single-layer TWC coated on a ceramic substrate (400 cpsi, 4.0 mil wall thickness). The catalyst layer consists of Rh supported on a washcoat of yttrium oxide, La-stabilized alumina, and Nd-stabilized cerium zirconia, where Rh is pre-fixed on the yttrium oxide support. The Y concentration in the entire washcoat is the same as that of the following catalyst product 4. The Rh loading of comparative catalyst C is 0.5 g / ft 3 .

[0128] Catalyst Article 4

[0129] Intermetallic compounds of the general formula Al 74.5 -Y 25 -Rh 0.5 are prepared by using a method similar to the above.

[0130] Catalyst product 4 with an Rh loading of 0.5 g / ft 3 is prepared according to a method similar to that described above for catalyst products 1 to 3. The Al-Y-Rh intermetallic compound precursor is mixed with La-stabilized alumina and Nd-stabilized cerium zirconia. The Y concentration in the entire washcoat is the same as that of comparative catalyst B and comparative catalyst C.

[0131] After hydrothermal aging at 1000 °C in air with 10% steam for 4 hours, comparative catalysts A to C and catalyst product 4 are respectively tested on the SCAT device as described above.

[0132] The light-off temperature is measured at a heating rate of 30 °C / min under the reaction gas conditions in Table 2.

[0133] The HC, CO, and NO x conversions of the aged comparative catalysts A to C and catalyst product 4 at 600 °C are shown in Table 3. The data show that, surprisingly, when compared with comparative catalysts A to C used for converting THC and NO x , catalyst product 4 of the present invention gives significantly improved light-off performance. It can be seen that at the same temperature, compared with comparative catalysts A to C, catalyst product 4 achieves significantly higher THC and NO x conversions. The present invention can save valuable natural resources because the reduced noble metal loading can be used to provide a cleaner air environment by significantly improving the performance of the TWC to reduce automotive air pollution.

[0134] Table 3

[0135]

[0136] It has also surprisingly been found that, compared to conventional catalyst materials at the same Rh loading, catalyst article 4 has significantly improved thermal stability at a Rh loading of 0.5 g / ft 3 . This effect is shown in FIGS. 2(a) and 2(b), where after severe lean aging at 1000° C., the conversions of THC and NO x achieved by catalyst 4 at 600° C. are higher than those achieved by comparative catalysts A through C.

[0137] FIGS. 2(a) and 2(b) show the THC and NO x conversion results at 600° C. under fresh and aged conditions. Aging included severe lean aging for 4 hours at 1000° C. in air with 10% steam.

[0138] Example 3 - Effect of Leaching on Catalyst Articles, the Catalyst Articles Comprising

[0139] Catalyst Article 5

[0140] Intermetallic compounds of the general formula Al 74.5 -Y 25 -Rh 0.5 are prepared by using a method similar to that described above.

[0141] Catalyst article 5 with a Rh loading of 2.0 g / ft 3 is prepared in a manner similar to that described above for catalyst article 4.

[0142] Catalyst Article 6

[0143] At room temperature, the crushed intermetallic particles formed in the preparation of catalyst article 5 are leached in a 10 wt % aqueous Na2CO3 solution for 24 hours. The leached intermetallic particles are washed with distilled water until a pH of 7 is measured. The particles are then dried at 313 K (40° C.) for 12 hours. Catalyst article 6 with a Rh loading of 2.0 g / ft 3 is prepared using the leached intermetallic compound particles in a manner similar to that described above for catalyst articles 4 and 5.

[0144] The surface areas of catalyst articles 5 and 6 are measured using the BET method. The surface area measurement results are shown in Table 4. Leaching of the intermetallic compound particles significantly increases the surface area of catalyst article 6 compared to catalyst article 5 prepared from the same composition but non-leached intermetallic compound.

[0145] Table 4

[0146]

[0147]

[0148] Ignition test results for total hydrocarbons and nitrogen oxides were obtained after aging for 4 hours at 1000 °C under lean and severe conditions and at a 10% steam-air balance. These results were obtained under the same conditions as listed in Table 2 and by a similar method as described above in Example 2. The ignition test results are shown in Table 5.

[0149] Leaching of the intermetallic compound results in excellent conversion of total hydrocarbons and nitrogen oxides under severe lean aging conditions.

[0150] Table 5

[0151]

[0152] It was also found that catalyst article 6 has significantly improved thermal stability compared to catalyst article 5. This effect is shown in FIGS. 3(a) and 3(b), where after severe lean aging at 1000 °C, the conversions of THC and NO x achieved by catalyst article 6 at 600 °C are higher than those achieved by catalyst article 5. Thus, it was surprisingly found that leaching of the intermetallic compound results in improved thermal stability of the catalyst article.

[0153] Example 4 - Effective Range of Rh Content in Intermetallic Compounds According to the Invention

[0154] A comparative catalyst D was prepared using a Rh precursor and catalyst articles 7 to 9 were prepared using the intermetallic compounds according to the present invention. The formulations of the Rh precursor and the corresponding intermetallic compounds used are shown in Table 6.

[0155] Table 6

[0156] Formulation Rh Loading Comparative Catalyst D <![CDATA[[Y, La-doped alumina. Rh-N+Nd, La-stabilized Ce / ZrO x > <![CDATA[2.0g / ft 3 > Catalyst Article 7 <![CDATA[[Al 74.8 -Y 25 -Rh 0.2 +La-doped alumina + Nd, La-stabilized Ce / ZrO x > <![CDATA[2.0g / ft 3 > Catalyst Article 8 <![CDATA[[Al 74.5 -Y 25.0 -Rh 0.5 +La-doped alumina + Nd, La-stabilized Ce / ZrO x > <![CDATA[2.0g / ft 3 > Catalyst Article 9 <![CDATA[[Al 74.0 -Y 25.0 -Rh 1.0 +La-doped alumina + Nd, La-stabilized Ce / ZrO x > <![CDATA[2.0g / ft 3 >

[0157] Comparative Catalyst D

[0158] Comparative catalyst D is a single-layer TWC coated on a ceramic substrate (400 cpsi, 4.0 mil wall thickness). The catalyst layer consists of Rh supported on a washcoat of Y-doped La-stabilized alumina and Nd, La-stabilized ceria-zirconia, where the Rh is pre-fixed on the alumina support. The Y-doped La-stabilized alumina was prepared by the wet impregnation method using an aqueous solution of Y nitrate. The Y concentration is the same as that of catalyst articles 7 to 9 described below. The Rh loading of comparative catalyst D is 2.0 g / ft 3 .

[0159] Catalyst Article 7

[0160] An intermetallic compound of the general formula Al 74.8 -Y 25 -Rh 0.2 is prepared by using a method similar to the above.

[0161] At room temperature, the crushed intermetallic particles are leached in a 10 wt% aqueous Na2CO3 solution for 24 hours. The leached intermetallic particles are washed with distilled water until a pH of 7 is measured. Then the particles are dried at 313 K (40 °C) for 12 hours. A catalyst article 7 with a Rh loading of 2.0 g / ft 3 is prepared using the leached intermetallic compound particles in a method similar to that for catalyst articles 4 to 6 above.

[0162] Catalyst Article 8

[0163] An intermetallic compound of the general formula Al 74.5 -Y 25.0 -Rh 0.5 is prepared by using a method similar to the above.

[0164] At room temperature, the crushed intermetallic particles are leached in a 10 wt% aqueous Na2CO3 solution for 24 hours. The leached intermetallic particles are washed with distilled water until a pH of 7 is measured. Then the particles are dried at 313 K (40 °C) for 12 hours. A catalyst article 8 with a Rh loading of 2.0 g / ft 3 is prepared using the leached intermetallic compound particles in a method similar to that for catalyst articles 4 to 6 above.

[0165] Catalyst Article 9

[0166] An intermetallic compound of the general formula Al 74.0 -Y 25.0 -Rh 1.0 is prepared by using a method similar to the above.

[0167] At room temperature, the crushed intermetallic particles are leached in a 10 wt% aqueous Na2CO3 solution for 24 hours. The leached intermetallic particles are washed with distilled water until a pH of 7 is measured. Then the particles are dried at 313 K (40 °C) for 12 hours. A catalyst article 9 with a Rh loading of 2.0 g / ft 3 is prepared using the leached intermetallic compound particles in a method similar to that for catalyst articles 4 to 6 above.

[0168] Ignition test results for total hydrocarbons and nitrogen oxides were obtained. These results were obtained under the same conditions as listed in Table 2 and by a similar method as described above. The ignition test results measured after lean aging are shown in Table 7. Aging included severe lean aging at 1000 °C for 4 hours in air with 10% steam.

[0169] Table 7

[0170]

[0171] It can be seen that the catalyst article 8 with 0.5 wt% Rh atoms achieved the best total HC conversion. Both the catalyst article 7 with 0.2 wt% Rh atoms and the catalyst article 8 with 0.5 wt% Rh atoms achieved good NO x conversion. The atomic weight percentage of Rh in the intermetallic compound (i.e., the value of c in Formula I provided above) can thus be selected based on its application requirements. For example, if the application of the catalyst article focuses on HC conversion, the formulation of catalyst article 8 may be preferred. However, if the application of the catalyst article focuses on NO x conversion, the formulation of catalyst article 7 may be preferred.

[0172] Figures 4(a) and 4(b) also show that in the aging temperature range of 500 °C to 1000 °C, the catalyst article 8 with 0.5 wt% Rh atoms achieved the best thermal stability during total HC conversion. In the aging temperature range of 500 °C to 1000 °C, the catalyst article 7 and the catalyst article 8 showed similar thermal stability during NO x conversion.

Claims

1. A catalyst composition comprising an intermetallic compound, wherein the intermetallic compound comprises: a transition metal selected from Fe, Ce, Y, Nb, and combinations thereof; and a noble metal selected from Pt, Pd, Rh, and combinations thereof.

2. The composition according to claim 1, wherein the intermetallic compound has the formula according to Formula I: Al a -X b -PGM c Formula I wherein: a = 100 - b - c; 25≤a<80； 20<b<75； 0<c≤5.0 where a, b, and c are atomic weight percentages; where X is the transition metal selected from Fe, Ce, Y, Nb, and combinations thereof; and where PGM is the noble metal selected from Pt, Pd, Rh, and combinations thereof.

3. The catalyst composition according to claim 1, wherein the intermetallic compound has been leached prior to forming the composition.

4. The catalyst composition according to claim 3, wherein the intermetallic compound has a BET surface area of about 90 m 2 / g to 160 m 2 / g.

5. The catalyst composition according to any one of the preceding claims, wherein the transition metal is Y.

6. The catalyst composition according to any one of the preceding claims, wherein the noble metal is Rh.

7. The catalyst composition according to any one of the preceding claims, wherein the composition further comprises an oxygen storage component in an amount of 20 wt% to 50 wt% based on the total weight of the catalyst composition.

8. The catalyst composition according to any one of the preceding claims, wherein the composition further comprises an inorganic oxide in an amount of 50 wt% to 80 wt% based on the total weight of the catalyst composition.

9. A patch basecoat composition, the patch basecoat composition comprising: the catalyst composition according to any one of the preceding claims; and a liquid medium.

10. A catalyst article, the catalyst article comprising a substrate and the catalyst composition according to any one of claims 1 to 8 coated on the substrate.

11. The catalyst article according to claim 10, wherein the catalyst article comprises a single layer of the catalyst composition applied to the channels of the substrate.

12. The catalyst article according to claim 10 or claim 11, wherein the noble metal loading on the catalyst article is from 0.5 g / ft 3 to 5.0 g / ft 3 .

13. The catalyst article according to any one of claims 10 to 12, wherein the catalyst article is a three-way catalyst for treating a combustion exhaust gas stream by simultaneously oxidizing carbon monoxide and hydrocarbons and reducing nitrogen oxides.

14. A method of preparing the catalyst article according to any one of claims 10 to 13, the method comprising the step of coating a substrate with the patch basecoat composition according to claim 9.

15. An emission treatment system for treating a combustion exhaust gas stream, the emission treatment system comprising the catalyst article according to any one of claims 10 to 13.

16. A method of treating exhaust gas from an internal combustion engine, the method comprising contacting the exhaust gas with the catalyst article according to any one of claims 10 to 13.

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