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WO2008150462A2 - Catalyseur pour la réduction sélective d'oxydes d'azote, son procédé de fabrication et d'utilisation - Google Patents

Catalyseur pour la réduction sélective d'oxydes d'azote, son procédé de fabrication et d'utilisation Download PDF

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Publication number
WO2008150462A2
WO2008150462A2 PCT/US2008/006877 US2008006877W WO2008150462A2 WO 2008150462 A2 WO2008150462 A2 WO 2008150462A2 US 2008006877 W US2008006877 W US 2008006877W WO 2008150462 A2 WO2008150462 A2 WO 2008150462A2
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Prior art keywords
component
catalyst
cerium
zirconium
catalyst according
Prior art date
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Ceased
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PCT/US2008/006877
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English (en)
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WO2008150462A3 (fr
Inventor
Hao Cheng
Ye Li
Akira Okada
Shudong Wang
Yuming Xie
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Dalian Institute of Chemical Physics of CAS
Corning Inc
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Dalian Institute of Chemical Physics of CAS
Corning Inc
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Publication of WO2008150462A2 publication Critical patent/WO2008150462A2/fr
Publication of WO2008150462A3 publication Critical patent/WO2008150462A3/fr
Anticipated expiration legal-status Critical
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
    • B01D53/8621—Removing nitrogen compounds
    • B01D53/8625—Nitrogen oxides
    • B01D53/8628—Processes characterised by a specific catalyst
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/9404—Removing only nitrogen compounds
    • B01D53/9409—Nitrogen oxides
    • B01D53/9413—Processes characterised by a specific catalyst
    • B01D53/9418—Processes characterised by a specific catalyst for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • B01J23/20—Vanadium, niobium or tantalum
    • B01J23/22—Vanadium
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    • B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
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    • B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
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    • B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • B01J23/32—Manganese, technetium or rhenium
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    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/83—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with rare earths or actinides
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    • B01J37/0236—Drying, e.g. preparing a suspension, adding a soluble salt and drying
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    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • Y02C20/00—Capture or disposal of greenhouse gases
    • Y02C20/10—Capture or disposal of greenhouse gases of nitrous oxide (N2O)

Definitions

  • the present invention relates to a catalyst for the catalytic reduction of nitrogen oxides, method for making same and use thereof.
  • the present invention relates to an oxide catalyst for the selective catalytic reduction of nitrogen oxides, method for making same and use thereof in reducing NO x emission in stationery and mobile sources.
  • the present invention is useful, e.g., in reducing NO x emission from automobiles and other vehicles.
  • NO x nitrogen oxides
  • NO x is stored in the catalyst during the normal lean operation stage of the engine, while regeneration of the catalyst is carried out by short pulses of engine operation in the rich mode, and during these short periods, the NO x stored is released and reduced over noble metal surfaces
  • This process can bring about a very high NO x removal rate (>85%), but the remaining problem is that the NSR catalyst is extremely sensitive to SO 2 , and SO 2 in the exhaust gas will deactivate the catalyst, thus limiting its use to countries and regions where the content of sulfur in the fuel is very low.
  • many researchers have shifted their attention to vanadium oxide or zeolite catalyst for the selective reduction of NO x using ammonia.
  • a first aspect of the present invention relates to a catalyst for the selective catalytic reduction of nitrogen oxides, characterized in that it comprises a first component and a second component that provides the first component with physical support and synergic or auxiliary catalytic functions, wherein: the first component is selected from oxides of a transitional metal other than the metal contained in the second component, and mixtures and combinations thereof; the amount of the first component, based on the total weight of the first component and the second component, is from 0.1% to 30%; the second component is selected from cerium oxides, oxides of a lanthanide metal other than cerium, cerium-zirconium composite oxides, composite oxides of a lanthanide metal other than cerium and zirconium, cerium-titanium composite oxides, and composite oxides of a lanthanide metal other than cerium and titanium, and mixtures and combinations thereof; the amount, in moles, of lanthanide atoms in the second component is at least 1% of the total amount, in moles,
  • the content of the first component, based on the total weight of the first component and the second component is from 5% to 20%. In certain other embodiments of the catalyst of the present invention, the content of the first component, based on the total weight of the first component and the second component, is from 6% to 15%.
  • the first component is essentially distributed on the surface of the particles of the second component.
  • the first component is selected from Fe 2 O 3 , CrO 3 , MnO 2 , V 2 O 5 , MoO 3 , WO 3 , and mixtures and combinations thereof. In certain other embodiments of the catalyst of the present invention, the first component is selected from MoO 3 , WO 3 , and mixtures and combinations thereof. In still certain other embodiments of the catalyst of the present invention, the first component is WO 3 .
  • the second component is selected from cerium oxides, composite oxides of cerium and zirconium, and composite oxides of cerium and titanium, and mixtures and combinations thereof.
  • the second component is a composite oxide of cerium and zirconium.
  • the second component is a composite oxide of cerium and zirconium, and the molar ratio of cerium atoms to zirconium atoms in said second component is 0.01 : 1 to 10:1.
  • the second component is a composite oxide of cerium and zirconium, and the molar ratio of cerium atoms to zirconium atoms in the second component is 1 :4 to 4: 1.
  • the second component is a composite oxide of cerium and zirconium, with the molar ratio of cerium atoms to zirconium atoms in the second component being 1 :2 to 2:1.
  • the second component is a composite oxide of cerium and zirconium, with the molar ratio of cerium atoms to zirconium atoms in the second component being 1.0:1.1 to 1.1 :10.
  • the second component is a nanocrystalline substance.
  • the mean particle size of the second component is 10-500 nanometers.
  • the mean particle size of the second component is 20-200 nanometers.
  • the mean particle size of the second component is 20- 100 nanometers.
  • the catalyst is in pellet form.
  • said catalyst also contains an inert support, with the support being loaded with the first component and the second component as described above.
  • the first component is distributed on the surface of the particles of the second component, and the composite particles of said first component and second component are loaded on the surface of the inert support.
  • at least part of the first component and at least part of the second component are loaded on the surface of the inert support.
  • said catalyst also contains a porous support; loaded on said support are the first component and the second component as described above.
  • said porous support may be an inert support as described above.
  • a second aspect of the present invention involves a process for making the various above-mentioned catalysts in pellet form, characterized in that it comprises the following steps:
  • Step (1) ( 1 ) forming a precursor of the second component by co-precipitation of an aqueous solution, and calcining the precursor to obtain the second component; (2) loading a precursor of the first component on the second component obtained in Step (1).
  • Step (1) above comprises the following steps: (IA) preparing an aqueous dispersion containing a salt of cerium (such as a nitrate), a salt of zirconium (such as nitrate), and urea;
  • the cerium nitrate may be Ce(NO 3 ) 3 or (NHj) 2 Ce(NOs) 6 ; and the zirconium nitrate may be Zr(NOa) 4 .
  • Step (2) above comprises the following steps:
  • Certain embodiments for making the catalyst in pellet form in the present invention comprises the following steps: (i) preparing an aqueous dispersion comprising a salt of cerium, a salt of zirconium, a salt of tungsten and urea; (ii) heating the dispersion until it decomposes; and (iii) calcining the powder obtained in step (ii) to obtain a catalyst.
  • a third aspect of the present invention involves a first category process for making the various above-mentioned catalysts containing a porous support, characterized in that it includes:
  • Step (I) drying and calcining the object treated in Step (FV).
  • Step (I) mentioned above includes:
  • Step (IB) adding ammonia to the aqueous dispersion obtained in Step (IA) until a gel comprising cerium and zirconium is obtained;
  • Step (IC) adding nitric acid into the gel obtained in Step (IB), to obtain a sol containing cerium and zirconium.
  • Step (I) mentioned above includes: (Ia) preparing the powder of cerium-zirconium composite oxide;
  • Step (I) mentioned above includes:
  • Step (14) drying and calcining the solid particles obtained in Step (14); (16) mixing the solid particles obtained in Step (15), the cerium-zirconium sol, and nitric acid, then grinding the mixture;
  • a fourth aspect of the present invention involves a second category process for making the various above-mentioned catalysts comprising a porous support, characterized in that it includes:
  • a fifth aspect of the present invention involves the use of the various catalysts mentioned above, characterized in that it is used for selective catalytic reduction of nitrogen oxides emitted from a stationery source or mobile source.
  • said catalyst is used for the selective catalytic reduction of nitrogen oxides emitted from an internal combustion engine.
  • ammonia or urea is used as a reducing agent.
  • Catalysts in some of the embodiments of the present invention have a fairly high hydrothermal stability and good thermal stability.
  • catalysts in some of the embodiments of the present invention are not significantly susceptible to adverse effects of substances such as SO 2 , H 2 O, CO 2 , CO, and other hydrocarbon compounds, and they can maintain their catalytic activity in gas emission systems.
  • Catalysts in certain embodiments of the present invention essentially will not emit toxic metals in the process of use, so they are not hazards to human health.
  • FIG. 1 is a diagram showing NO conversion rates as a function of temperature of a series of catalysts according to certain embodiments of the present invention, as well as a series of catalysts not according to the present invention, in pellet form.
  • FIG. 2 is diagram showing NO and NH 3 conversion rates of the pellet-form WO 3 ZCe 0 8 Zr 02 O 2 (1/10) catalyst in certain embodiments of the present invention at 300 0 C, during a 200-hour testing period, and the concentration of N 2 O in the reaction effluent gas;
  • FIGS. 3 A and 3B show NO conversion rates as a function of temperature of the pellet-form WO 3 /Ce x Zr 1-x O 2 catalyst in certain embodiments of the present invention before and after aging.
  • FIG. 4 shows NO conversion rate as a function of temperature of the pellet- form WO 3 ZCe 0 S Zr 02 O 2 catalyst prepared by means of an incipient wet impregnation process in certain embodiments of the present invention.
  • FIG. 5 A and 5B show NO conversion rate as a function of temperature of the pellet-form WO 3 ZCe 0 5 Zr 0 5 O 2 catalyst prepared by means of incipient wet impregnation process in certain embodiments of the present invention in a reaction under programmed temperature control, before and after aging.
  • FIG. 6 shows NO x conversion rate as a function of temperature of the pellet- form WO 3 ZCe x Ti 1-x ⁇ 2 catalyst prepared by means of incipient wet impregnation process in certain embodiments of the present invention.
  • FIG. 7 shows NO conversion rate as a function of temperature of the pellet- form WO 3 ZCe O 5 Zr 0 5 O 2 catalyst prepared by means of impregnation process in certain embodiments of the present invention after aging, when NO 2 is present in the influent gas.
  • FIG. 8 shows NO conversion rate as a function of temperature of the pellet- form W ⁇ 3 /Ceo 5 Zro 5 O 2 catalyst prepared by means of combustion synthesis in certain embodiments of the present invention.
  • FIG. 9 shows NO conversion rate as a function of temperature of the pellet- form MoO 3 ZCe 0 5 Zro 5 O 2 catalyst prepared by means of impregnation process in certain embodiments of the present invention.
  • FIG. 10 shows NO conversion rate as a function of temperature of the pellet- form CrO 3 /Ce 0 5 Zr 0 5 O 2 catalyst prepared by means of impregnation process in certain embodiments of the present invention, before and after aging.
  • FIG. 11 shows NO conversion rate as a function of temperature of the pellet- form Fe 2 0 3 /Ceo 5 Zr o 5 O 2 catalyst prepared by means of impregnation process in certain embodiments of the present invention, before and after aging.
  • FIG. 12 shows NO conversion rate as a function of temperature of the pellet- form MnO x /Ce 0 5 Zr 0 5 O 2 catalyst prepared by means of impregnation process in certain embodiments of the present invention, before and after aging.
  • FIG. 13 shows NO conversion rate as a function of temperature of the pellet- form V 2 O 5 ZCe 05 Zr 0 5 O 2 catalyst prepared by means of impregnation process in certain embodiments of the present invention, before and after aging.
  • FIG. 14 show NO conversion rate as a function of temperature of the structured WO 3 ZCe O sZr 02 O 2 Zcordierite honeycomb ceramic catalysts having differing cell density in certain embodiments of the present invention.
  • FIG. 15 shows NO conversion rate as a function of temperature of a structured WO 3 ZCe 0 3 Zr 02 O 2 Zcordierite honeycomb ceramic catalyst in another embodiment of the present invention.
  • FIG. 16 shows NO conversion rate as a function of temperature of a structured WO 3 ZCe 05 Zr 0 5 O 2 Zcordierite honeycomb ceramic catalyst in another embodiment of the present invention.
  • FIG. 17 shows NO conversion rate as a function of temperature of a structured WO 3 ZCe 05 Zr 05 O 2 Zcordierite honeycomb ceramic catalyst in another embodiment of the present invention.
  • FIG. 18 shows and compares the performances of a series of catalysts of the present invention and those not of the present invention under certain testing conditions.
  • FIG. 19 shows and compares the performances of a series of catalysts of the present invention and those not of the present invention under other certain testing conditions.
  • an alkali metal includes embodiments having two or more such elements, unless the context clearly indicates otherwise.
  • X, Y, Z, .. and combinations thereof means a group consisting of the following elements: X, Y, Z,...., and combinations of any 2, or more than 2 members of X, Y, Z, ..., at any proportion.
  • nano-crystalline material as used herein means a relevant material having a mean crystal size smaller than 500 run.
  • aqueous solution or “aqueous dispersion” as used herein means a material system comprising water and with or without any other solvent.
  • an aqueous solution or an aqueous dispersion may also contain, in addition to water, other solvents such as an alcohol, and the like.
  • a "precursor of the first component" as used herein means a substance capable of dispersing in a material system to act as a source material for one or more oxides in the first component of the catalyst of the present invention.
  • the precursor of the first component is a water-soluble salt of the relevant metal. Examples of such salt include, but are not limited to, ammonium metatungstate; ammonium metamolybdate; ammonium vanadate; ammonium dichromate; iron nitrate; manganese nitrate, and the like.
  • a "precursor of the second component” as used herein means a substance capable of dispersing in a material system to act as a source material for one or more oxides in the second component of the catalyst of the present invention.
  • the precursor of the second component is a water-soluble salt of the relevant metal. Examples of such salt include, but are not limited to: cerium nitrate; zirconium nitrate; ammonium cerium nitrate, and the like.
  • the term "Ce-Zr sol” as used herein means a material system comprising Ce and Zr-containing colloidal particles having a mean particle size of 1-100 nm dispersed therein. The pH of such material is typically acidic.
  • the pH thereof is from 1 to 5. In certain other embodiments, the pH thereof is from 1 to 1.5.
  • composite oxides as used herein means a mixture of oxides of two or more metal elements.
  • Pellet catalyst described in the present invention in general refers to the catalyst packed in an irregular manner in the reactor when being used. The geometric configuration of a pellet catalyst may be, but is not restricted to, spherical, cylindrical, flake-like, or powdery.
  • Structured catalyst as used herein in general refers to a catalyst arranged in a regular manner in the reactor when being used.
  • the geometric configuration of a structured catalyst may be, but is not restricted to, a honeycomb, a foam, a corrugated metal plate, and the like.
  • the catalyst can be prepared in such a way that the active component of the catalyst is loaded in the form of a wash coat onto the surface or the channels of the support; it can also be prepared in such a manner as to extrude the active component of the catalyst as a structured unit.
  • C NO indicates NO conversion rate
  • T indicates the temperature
  • the first component of the catalyst of the present invention provides the active site.
  • ammonia is adsorbed onto the active site of the first component (which may be a Bronsted acid or Lewis acid).
  • the active site of the first component which may be a Bronsted acid or Lewis acid.
  • hydrogen integrated with nitrogen molecules by means of a covalent bond in ammonia is activated.
  • ammonia molecules are activated and dehydrogenated, reacting with NO x in the gas phase, forming non-toxic nitrogen and water via the Rideal mechanism.
  • the metal center in the active site is reduced, and needs to undergo oxidation before entering the next cycle.
  • the first component of the catalyst based on the present invention has two characteristics: acidity and activity associated with oxidation and reduction. Being acidic allows for the adsorption of ammonia at operating temperatures.
  • the oxidation and reduction activity relates to activation of the ammonia molecule adsorbed, while activation of ammonia requires a transfer of hydrogen atoms.
  • the first component of the catalyst may be selected from: Fe 2 O 3 , MnO 2 , CrO 3 , V 2 O 5 , MoO 3 , and WO 3 .
  • the metal elements in the first component are mainly present in the catalyst of the present invention in the form of oxides. The valency of said metal element is not limited to one value only.
  • tungsten may be present in the +6 valency (such as WO 4 2" , WO 3 , etc.), +4 valency (such as WO 3 2" , WO 2 etc.), or another valency.
  • vanadium may be present in the +5, +4, +3, or other valency.
  • part of the first component may also be combined through chemical or physical means, with other components of the catalyst, such as the second component, a support, a small amount of water, etc.
  • the total amount of the first component or the subtotal amount of the various components refer to the total amount of all of the relevant metals in various states, but will be calculated and indicated only in the forms selected above (Fe 2 O 3 , MnO 2 , CrO 3 , V 2 O 5 , MoO 3 , and WO 3 ).
  • the first component contains OH surface groups, which can be combined with molecules of ammonia compounds and derivatives thereof (nitrogen- containing substances with a low nitrogen valency, such as NH 3 , NH 2 NH 2 , urea, etc.) in the waste gas to be treated. Upon oxidation and reduction, ammonia is transformed into the active state in the SCR reaction.
  • the catalyst of the present invention may contain Fe 2 O 3 , MnO 2 , CrO 3 , and/or V 2 O 5 as part or all of the first component.
  • the first component mainly contains WO 3 , MoO 3 , or their combinations in various proportions. In certain other advantageous embodiments of the present invention, the first component mainly contains WO 3 .
  • the content of the first component based on the total weight of the first component and the second component is 0.1%-20%, or is l%-20% in certain embodiments, 2%-20% in certain other embodiments, 5%-18% in certain other embodiments, 8%-18% in certain other embodiments, 10%-18% in certain other embodiments, 10%-17% in certain other embodiments, 5%-20% in certain other embodiments, or 6%-15% in certain other embodiments.
  • Data indicate that when the content of the first component is 10% to 18%, said catalyst has a good nitrogen monoxide conversion rate.
  • part of the first component can be distributed inside the particles of the second component, inside the support material other than the first component and the second component, or on the surface of said support (if said support is present).
  • the first component is essentially distributed (for example, at least 50%, including 60%, 70%, 80%, and even 90%) on the surface of the particles of the second component.
  • the first component is partially distributed on the surface of the particles of the second component, and partially distributed on the surface of the support.
  • the second component of the catalyst of the present invention is selected from: cerium oxides, oxides of a lanthanide metal other than cerium, cerium-zirconium composite oxides, composite oxides of a lanthanide metal other than cerium and zirconium, cerium-titanium composite oxides, composite oxides of a lanthanide metal other than cerium and titanium, and mixtures or combinations thereof.
  • the second component is selected from cerium oxides, cerium-zirconium composite oxides, cerium - titanium composite oxides, and mixtures or combinations thereof. In certain other embodiments of the present invention, the second component is a cerium-zirconium composite oxide.
  • the content of the second component is 70%-99.9%, or is 80%-99% in certain embodiments, 80%-98% in certain other embodiments, 82%-95% in certain other embodiments, 82%— 92% in certain other embodiments, 82%-90% in certain other embodiments, and 83%-90% in certain other embodiments.
  • cerium or some other lanthanide metal provides the required storage function and oxygen-supplying function. If there is a metal oxide other than that of a lanthanide, such as zirconium or titanium oxides, their function is mainly to enhance the stability of the catalyst.
  • the specific surface area of the catalyst has a very important effect on its catalytic activity.
  • the more the first component is distributed at the gas phase-solid phase interface the higher the activity of the catalyst. Therefore, the larger the specific surface area of the support used for the first component, the higher the activity of the catalyst up to a certain level.
  • the stability of the catalytic activity is directly related to the stability of the specific surface area of the support used for the first component. If the catalyst in the process used will be subjected to heat, the thermal stability of the support used for the first component has direct effects on the thermal stability of the catalyst.
  • the second component of the catalyst provides a physical support for the first component. Therefore, for a high catalytic performance, the second component should have a higher specific surface area; also, to maintain the stability of the general performance of the catalyst, the specific surface area of the second component should maintain a certain level of stability.
  • the second component comprises a nanocrystalline material.
  • the mean particle size of the second component is 1-500 nm; in certain other embodiments, the mean crystal particle size of the particles of the second component is 1-200 nm, and in still certain other embodiments, the mean crystal particle size of the nanocrystalline material is 1-100 nm.
  • the specific surface area of the particle of the second component is at least 70 m 2 g ⁇ '; in certain other embodiments the specific surface area of the particle of the second component is at least 100 m 2 -g ⁇ ! .
  • the second component In terms of the thermal stability of the catalyst at an elevated temperature, the second component not only needs to maintain a high specific surface area, but also needs to maintain a certain level of oxidation and reduction capacity upon exposure to an elevated temperature.
  • oxides of lanthanides such as cerium oxide are capable of undergoing a rapid cycle of oxidation and reduction (Ce 4+ ⁇ — > Ce 3+ ), with its oxygen storage and release function being highly associated with its specific surface area — the greater the specific surface area, the better the oxygen storage and release performance will be.
  • the second component contains only fine particles of pure cerium oxide, in certain embodiments it still has a high initial activity for nitrogen oxide conversion.
  • pure cerium oxide particles will be sintered upon heating, the crystal particles will grow rapidly, and the specific surface area will decrease significantly, resulting in a decrease in the oxidation and reduction performance. Therefore, catalysts whose second component contains only cerium oxide are not the most favorable for use under elevated temperatures (such as some exhaust-gas purification devices for a diesel engine, whose operation temperature is as high as 700- 800°C). There is consistently a need to add a heat stabilizer to these catalysts to meet the stability requirement.
  • the second component is a composite oxide of cerium and zirconium, and the mole ratio of cerium atoms to zirconium atoms in the second component is 0.01 : 1 to 10: 1.
  • the second component is a composite oxide of cerium and zirconium, and the mole ratio of cerium atoms to zirconium atoms in the second component is 1 :4 to 4: 1. In certain other embodiments of this type, the second component is a composite oxide of cerium and zirconium, and the mole ratio of cerium atoms to zirconium atoms in the second component is 1 :2 to 2: 1. In still certain other embodiments of this type, the second component is a composite oxide of cerium and zirconium, and the mole ratio of cerium atoms to zirconium atoms in the second component is 1.0: 1.1 to 1.1 : 10.
  • the cerium-zirconium composite oxide consists of a nanocrystalline material as mentioned above.
  • the cerium-zirconium composite oxide with the nano structure provides the required surface area and thermal stability; it also provides the required oxidation and reduction capacity.
  • the second component is essentially a single-phase crystalline material of composite oxides.
  • single-phase is meant that the characteristic peaks of the individual oxides cannot be all observed on an XRD spectrum. Without intending to be bound by a particular theory, it is believed that in single-phase composite oxides, when one oxide forms crystals, the other oxide enters the crystal lattice to form a homogenous mixture.
  • phase separation at the scale of 100 nm cannot be observed in said composite oxide.
  • phase separation at the scale of 10 nm cannot be observed in said composite oxide.
  • Single-phase composite oxides, particularly single-phase cerium- zirconium composite oxides, have a fairly good thermal stability that is better than that of multi-phase mixtures of oxides.
  • the enlargement of the crystal particles does not exceed 20%; it does not exceed 10% in certain other embodiments, it does not exceed 5% in certain other embodiments, it does not exceed 3% in certain other embodiments, it does not exceed 2% in certain other embodiments, and it does not exceed 1% in certain other embodiments.
  • said catalyst is present in the form of pellets.
  • said pellets essentially consist of a first component and a second component.
  • said pellets also contain, in addition to the first component and the second component, an inert support (inorganic glass, inorganic ceramic, metals, refractory materials, etc.), and the first component and the second component are respectively loaded on it.
  • an inert support inorganic glass, inorganic ceramic, metals, refractory materials, etc.
  • the catalyst further comprises a porous support, and the first component and the second component are loaded respectively on the surface of the porous support, hi certain embodiments, said porous support is a structured honeycomb support.
  • Said support may be composed of the following materials: inorganic glass, inorganic ceramic, metals, refractory materials, etc. (such as honeycomb ceramics, foam ceramic, or metal honeycomb, etc.).
  • a coated honeycomb-shaped catalyst may be employed to treat waste gas emitted from a stationery source or a mobile source, such as the waste gas emitted from a diesel engine or direct-injection gas engine.
  • the first component is loaded on the surface of the particles of the second component, while the composite particles of said first component and second component are loaded on the surface of the porous support.
  • part of the first component is loaded on the surface of the particles of the second component, composite particles of said first component and second component are loaded on the surface of the porous support, while another part of the first component is directly loaded on the surface of the porous support.
  • Also provided in the present invention is a process for making the catalyst for the selective catalytic reduction of nitrogen oxides, which includes preparation of the first component from the precursor of said first component, preparation of the second component using chemical synthesis techniques such as the process of precipitation, the process of homogeneous precipitation, and the microemulsion process, etc., then loading the first component onto the second component by impregnation, precipitation, and other techniques.
  • a process for making the catalyst for the selective catalytic reduction of nitrogen oxides wherein through the process of solution combustion synthesis, a catalyst containing the first component and the second component is prepared in one step.
  • Certain embodiments of processes of this type include the following steps: (i) preparation of an aqueous dispersion of a cerium- containing salt (such as cerium nitrate), zirconium nitrate, tungsten-containing salt, and urea; and (ii) heating the aqueous dispersion prepared in Step (i) until it is decomposed.
  • the first component may be loaded onto the surface of the second component by means of the process of equal-volume impregnation or excess impregnation.
  • the particles of the second components are nanocrystalline material.
  • a nanocrystalline material can be prepared through several types of chemical synthesis, including the process of co-precipitation, the process of homogenous precipitation, the process of microemulsion precipitation, and the process of solution combustion synthesis, as long as the material produced is an oxygen storage material capable of high oxygen conductivity at low temperature.
  • the first component may be derived from various precursors, such as oxides or salts.
  • the first component may be coated onto the auxiliary support by means of impregnation, precipitation, or other techniques.
  • the catalyst in pellet form can be prepared by the following processes:
  • the precursor of the second component is prepared; also, through calcining said precursor, the second component is prepared; (2) The precursor of the first component is loaded onto the second component prepared in Step (1) mentioned above.
  • Step (1) mentioned above includes the following steps:
  • Step (IB) Preparing the precursor of the cerium-zirconium composite oxides by means of mixing and co-precipitating the aqueous dispersion obtained in Step (IA);
  • the cerium nitrate may be Ce(NO 3 ) 3 or (NH 4 ) 2 Ce(NO 3 ) 6 ; the zirconium nitrate may be Zr(NO 3 ) 4 .
  • Step (2) above comprises the following steps: (2A) Preparing an aqueous dispersion containing the precursor of the first component and the second component obtained in Step (1);
  • one of the specific processes to prepare the catalyst in pellet form may be: (A) Preparing a stock solution from salts selected from those of titanium, cerium, or zirconium elements or their combination (such as a solution prepared from the mixture of a certain amount of Ce(NOs) 3 solution, Zr(NO 3 ) 4 solution, and urea with its cation concentration of 0.1-0.3 mole/L), stirring and heating to its boiling point, until co- precipitation can be observed; the precipitate obtained is then aged at the boiling point, then stirred at room temperature; said precipitate is filtered and washed, then dried at 50- 80°C for 10-20 hours.
  • the dried precipitate is calcined at 400-600°C for 1-3 hours, and the support material is obtained;
  • (B) Loading the salt made from V, Cr, Nb, Ta, Cr, Mo, W, Mn, and Fe elements to serve as the active component onto the support material obtained from Step (A) mentioned above;
  • (C) The powder obtained from Step (B) is pressed and ground; those powder particles of 20-30 mesh are selected through screening, and can serve as the catalyst that can be used directly.
  • the process using the support described may be such that:
  • the support material obtained in Step (A) mentioned above is prepared into a powder, which is stirred and suspended in deionized water, then the salt made from V, Mo, W, Mn, and Fe elements serves as the active component, or a solution of the salt is added to the mixed suspension mentioned above; the mixture obtained is heated to 80-90°C, being heated and stirred continuously, until most of the moisture evaporates, obtaining a paste.
  • the paste is dried at 100-150 0 C for 5-20 hours, then the dried sample is calcined at 400— 600 0 C for 1—3 hours.
  • the process using the support described may also be such that:
  • the catalyst support particles of 20-30 mesh obtained in Step (A) are impregnated using the salt made from V, Cr, Mo, W, Mn, and Fe elements to serve as the active component, or using a solution of the salt, the particles are dried at room temperature for 3—9 hours, then at 100-150 0 C for 2-8 hours, then calcined at 400-600 0 C for 1-3 hours.
  • the various catalysts mentioned above that contain the porous support may be prepared through a first category process listed below: (I) Preparation of the aqueous dispersion of the second component;
  • Step (I) mentioned above includes: (IA) Preparing the aqueous dispersion containing a salt of cerium (such as a nitrate) or a salt of zirconium (such as a nitrate);
  • Step (IB) Adding ammonia to the aqueous dispersion obtained in Step (IA) until a gel comprising cerium and zirconium is obtained;
  • Step (I) mentioned above includes: (Ia) Preparing the powder of cerium-zirconium composite oxide; (Ib) Preparing the sol containing cerium and zirconium;
  • Step (Ic) Mixing nitric acid, the cerium-zirconium composite oxide powder prepared in Step (Ia), and the sol containing cerium and zirconium prepared in Step (Ib), then grinding the mixture;
  • the slurry prepared from such is the aqueous dispersion of the second component.
  • Step (I) mentioned above includes:
  • Step (14) Drying and calcining the solid particles obtained in Step (14); (16) Mixing the solid particles obtained in Step (15), the cerium-zirconium sol, and nitric acid, then grinding the mixture;
  • the slurry prepared from such is the aqueous dispersion of the second component.
  • the porous support may be a honeycomb-type ceramic, including but not limited to a cordierite honeycomb ceramic.
  • One of the specific examples of the process of the first type used to prepare the catalyst containing a porous support may include: (I) Preparing the Ce-Zr dispersion; (II) Impregnating the honeycomb ceramic using the Ce- Zr dispersion obtained in Step (I), then removing the residual dispersion in the honeycomb passageway using hot air; after the removal is complete, the sample is dried, then calcined at 400-600°C for 1-3 hours, and this step is repeated three to nine times; (III) Impregnating the material obtained in Step (II) using the salt solution of the active component selected from V, Cr, Mo, W, Mn, and Fe elements, then removing the residual solution in the honeycomb passageway using hot air; after the removal is complete, the sample is dried, then calcined at
  • the process used to prepare the Ce-Zr dispersion described in Step (I) may include: Mixing the Ce(NO 3 ) 6 solution and Zr(NO 3 ) 4 solution, then adding aqueous ammonia (ammonium hydroxide) droplets into the Ce-Zr solution, with stirring, obtaining a Ce-Zr gel. Next, with stirring, HNO 3 is added to the gel, and the mixture is stirred for 6-10 hours, obtaining a Ce-Zr sol.
  • the process used to prepare the Ce-Zr dispersion described in Step (I) may also include: The cerium-zirconium composite oxide (such as Ceo .
  • the process used to prepare the Ce-Zr dispersion described in Step (I) may also include: (1) Polyoxyethylene octylphenlyl ether and n-hexanol are added to cyclohexane, until the solution mixture becomes clear, then Ce(NO 3 ) 3 and Zr(NO 3 ) 4 solutions are added to the solution mixture and stirred until the solution becomes clear again; (2) Polyoxyethylene octylphenyl ether and n-hexanol are added at room temperature into cyclohexane, with stirring, to n- hexane, until the solution mixture becomes clear, then an ammonium hydroxide solution is added to the solution mixture and stirred, until the solution becomes clear again; (3) The microemulsions obtained from Step (1)
  • the fourth aspect of the present invention relates to a second category of process for making the various above-mentioned catalysts that contain the porous support, characterized in that it includes:
  • Specific examples of the process of the first type to prepare the catalyst containing a porous support may be: (A) With stirring, the cerium-zirconium composite oxide (such as Ce 0 5 Zr 0 5 O 2 ) powder is mixed and suspended in water, then ammonium metatungstate is added to the mixed suspension; the mixture obtained is heated to 70— 100 0 C, heated continuously and with stirring, until most of the moisture evaporates, obtaining a paste. The paste is dried at 120 0 C for 6—12 hours, then the dried sample is calcined at 400-600 0 C for 1-3 hours.
  • the cerium-zirconium composite oxide such as Ce 0 5 Zr 0 5 O 2
  • the precipitate was filtered, then washed with stirring using deionized water for 15 minutes. This step was repeated three times.
  • the filter cake was then eluted with isopropanol using a Buchner funnel. After excess isopropanol was removed through filtering, the precipitate obtained was placed in a vacuum oven dryer, where it was dried at 60°C for approximately 15 hours. This dried precipitate was then calcined at 500 0 C in a furnace for 2 hours, so that it decomposed to form a Ce x Zr 1-x O 2 oxide.
  • Pure ZrO 2 was prepared using the same process, with pure CeO 2 being prepared by the decomposition Of Ce(NOs) 3 -OH 2 O at 500°C.
  • the concentration of the gas was measured using a Fourier Transform Infrared (FTIR) spectrometer with a 10-m optical path gas cell (Nicolet Nexus 470 model, DTGS detector).
  • FTIR Fourier Transform Infrared
  • An FTIR spectrometer can rapidly determine the concentration of several gases on-line, including NO, NO 2 , N 2 O, and NH 3 . Concentrations of various gases could be quantified using QuantPad software. Said software is based on CLS processing (classical least-squares fitting), and can correct the spectral absorption in the non-linear zone. For test results, see FIG. 1. In FIG.
  • Curve ⁇ -4 shows NO conversion rate as a function of temperature on the WO 3 ZCeO 2 catalyst
  • Curve 1-5 shows NO conversion rate as a function of temperature on the WO 3 ZZrO 2 catalyst.
  • the drawing also shows NO conversion rate on a WO 3 /ZrO 2 sample without containing CeO 2 , wherein at a high temperature (> 400 0 C), said sample shows a certain catalytic activity, as its NO conversion rate at 450 0 C can reach 78%; however, at a low temperature (below 300 0 C), said sample almost has no catalytic activity, and its NO conversion rate is extremely low (approximately 10%).
  • Example 2 [00112] Characterization of the long-term stability of WO 1 ZCe n sZrn ⁇ O? HZlO) pellet catalyst at 300 0 C
  • the stability of the catalyst was examined via the SCR reaction at 300 0 C for 200 hour.
  • the test conditions were the same as in Example 1 mentioned above. See FIG. 2 for test results.
  • Curve 2-1 shows NO conversion rate for a test period of 200 hours
  • Curve 2-2 shows the NH 3 conversion rate for a test period of 200 hours
  • Curve 2—3 shows the concentration of the N 2 O in the reaction effluent gas for a test period of 200 hours.
  • the powder was pressed, then ground, with powder particles of 20-30 mesh being selected through screening.
  • the composition of the feedstock gas was a simulation of the composition of the exhaust gas of a diesel engine, which was: 550 ppm NO; 550 ppm NH 3 , 6% O 2 , 10% CO 2 , 10% H 2 O and balance N 2 (hereinafter "Feedstock Gas B").
  • the gas flow rate was set at 1.5 L/minute (STP), and the space velocity was 90000 IT 1 .
  • SCR activity as a function of temperature of the catalyst was determined. After the test of the activity of the fresh catalyst was completed, the catalyst was treated in an air flow at 800 0 C for 4 hours ("aging" process as used herein), then the SCR activity as a function of temperature of the aged catalyst was tested.
  • FIG. 3 A Shown in FIG. 3 A is NO conversion rate of the relevant catalyst before aging. Shown in FIG. 3B is NO conversion rate of the relevant catalyst after aging.
  • the catalytic activity decreases noticeably; in the range of 300— 400 0 C, the tendency of the decline of the activity tends to slow down, while in the range of 400— 500 0 C, the activity is enhanced instead.
  • the change in the activity of the catalyst before and after aging is related to the redox ability of the catalyst surface.
  • the catalyst with the CeZZr mole ratio of 1 : 1 had the best SCR activity over the entire temperature range. With both the activity and thermal stability of the catalyst taken into comprehensive consideration, it is advantageous that the CeZZr mole ratio in the second component of the catalyst is about 1:1.
  • Curve 4-A shows NO conversion rate as a function of temperature on the Ce 08 Zr 02 O 2 support.
  • Example 4 indicate that the SCR activity of the independent second component cerium-zirconium composite oxides without being loaded with the first component is relatively low, as NO conversion rate reaches the highest level at 350 0 C, which is 70%, and when the temperature is below or higher than 350 0 C, its catalytic activity will drop rapidly in either case. Yet after it is loaded with a certain amount of the first component WO 3 , the functional temperature range is greatly widened, and the activity at both low temperature and high temperature is significantly enhanced. Also, with an increase in the content of the first component WO 3 , the activity of the catalyst at low temperature (200-250 0 C) and its activity at high temperature (400-500 0 C) are further enhanced. [00126] Example 5
  • the process used to prepare the second component Ce 0 5 Zr 0 5 O 2 was the same as in Example 3 mentioned above.
  • the WO 3 /Ce 0 5 Zr 0 5 O 2 catalyst was synthesized using the process of incipient wet impregnation. 4 g of Ce 05 Zr 0 5 O 2 particles of approximately 20-30 mesh were impregnated by ammonium metatungstate (NH 4 WO 3 ) solutions at a series of concentrations, to prepare the WO 3 /Ce 0 5 Zr 0 5 O 2 catalyst with different WO 3 loadings. The particles after impregnation were dried at room temperature for 6 hours, and at 120 0 C for 3 hours, and then calcined at 500 0 C for 2 hours.
  • Example 6 Preparation of WOVCeyTruyO? pellet catalyst using the process of incipient wet impregnation, and its characterization
  • the precursor of WO 3 was ammonium metatungstate (NH 4 WO 3 ).
  • 25 g OfNH 4 WO 3 was dissolved in deionized water to prepare to 100 ml of solution.
  • 6 g of Ce x Ti 1-x O 2 particles of approximately 20-30 mesh were impregnated using the solution mentioned above. The particles after impregnation were dried at room temperature for 6 hours, and at 120 0 C for 3 hours, then calcined at 500°C for 2 hours.
  • the gas flow rate was set at 1.5 LZmin (STP), and the space velocity was set at 90000 tf 1 .
  • the SCR activity as a function of temperature of the catalyst was tested. See FIG. 7 for the test results.
  • Curve 7-1 shows NO conversion rate as a function of temperature, after the WO 3 ZCe 0 5 Zr 0 5 O 2 catalyst is aged, with the concentration ratio between NO and NO 2 in the feedstock gas being 1 :1
  • Curve 7-2 shows NO conversion rate as a function of temperature, after the WO 3 ZCe 05 Zro .5 O 2 catalyst is aged, with the concentration ratio between NO and NO 2 in the feedstock gas being 2:1
  • Curve 7-3 shows NO conversion rate as a function of temperature , after the WO 3 ZCe O 5 Zr 0 5 O 2 catalyst is aged, with the concentration ratio between NO and NO 2 in the feedstock gas being 3:1.
  • the muffle furnace was turned off; when the furnace had cooled to below 200°C, the evaporation dish was taken out and a foam-like catalyst sample was obtained.
  • the sample was calcined, then ground, and passed through a 200-mesh sieve, with the catalyst powder being obtained.
  • the catalyst powder was pressed and shaped, ground, and crushed, and particles of approximately 20—30 mesh were selected through screening for the assessment test.
  • Curve 8-2 shows NO conversion rate as a function of temperature of the catalyst treated by a 600 0 C air stream for 4 hours
  • Curve 8-3 shows NO conversion rate as a function of temperature of the catalyst treated by a 650 0 C air stream for 4 hours
  • Curve 8-4 shows NO conversion rate as a function of temperature of the catalyst treated by a 700 0 C air stream for 4 hours.
  • the catalyst treated at 600 0 C, 650 0 C and 700 0 C had improved activity in the full functional temperature range, particularly in the lower range ( ⁇ 250°C) and higher range (>500°C) where the improvement was appreciable.
  • the one calcined at 700°C showed the best performance in lower temperature range ( ⁇ 250°C) and higher temperature range (>500°C).
  • Curve 9-2 shows NO conversion rate as a function of temperature of the MoO 3 ZCe 05 Zr 0 5 O 2 catalyst after aging.
  • the process used to prepare the second component Ce 0 5 Zr 0 5 O 2 was the same as in Example 3 mentioned above.
  • the CKVCeo 5 Zro 5 O 2 catalyst was synthesized using the process of impregnation. First of all, with stirring, 10 g of Ce 0 5 Zro 5 O 2 powder was mixed and suspended in 50 ml of deionized water. Next, 1.6578 g of ammonium dichromate ((NHt) 2 Cr 2 O 7 ) was added to the suspension mentioned above, then the mixture obtained was heated in an oil bath to 85°C.
  • the curves of FIG. 10 indicate that the fresh CrO 3 /Ce 0 5 Zr 0 5 O 2 catalyst shows good catalytic activity in the temperature range of 175-300 0 C, and at 250 0 C it reaches the highest NO conversion rate, which is 89%.
  • NO conversion rate drops rapidly.
  • the rapid drop in the activity of the catalyst at high temperature is related to a stronger oxidation ability of CrO 3 , as a result of which more NH 3 is oxidized by O 2 instead of participating in the reduction reaction of NO; also, the product of the oxidation of NH 3 contains a certain amount of NO x .
  • Example 11 [00158] impregnation and characterization of its performance before and after aging [00159]
  • the process used to prepare the second component Ce 05 Zr 0 5 O 2 was the same as in Example 3 mentioned above.
  • the Fe 2 O 3 ZCe O 5 Zro 5 O 2 catalyst was synthesized using the process of impregnation. First of all, with stirring, 10 g of Ceo 5 Zro 5 O 2 powder was mixed and suspended in 50 ml of deionized water.
  • the curves of FIG. 12 indicate that the fresh MnO x ZCe 0 5 Zr 0 5 O 2 catalyst shows a certain catalytic activity; at 350 0 C, it reaches the highest NO conversion rate, which is 61%. After aging, the performance of the MnO x ZCe 0 5 Zr 0 5 O 2 catalyst is further attenuated. [00167] Example 13
  • the paste was transferred to a dryer, where it was dried at 120°C for 6 hours.
  • the powder was pressed, then ground, and those particles of 20-30 mesh were selected through screening.
  • the present example relates to the preparation of a structured catalyst.
  • Cordierite honeycomb of 400 cells/square inch (cells per square inch, cpsi) (made in Shanghai) and cordierite honeycomb of 600 cpsi (made by Corning of the United States) were used as the ceramic support.
  • the honeycomb cordierite was cut into small cylinders with a size of 0 16 x 25 (mm).
  • the honeycomb ceramic was then washed at room temperature for 3 hours using a 3.0-wt% nitric acid solution.
  • the ceramic was dried in a dryer at 120°C for 10 hours, then calcined at 900°C for 2 hours.
  • the cerium-zirconium sol sample was prepared as follows: First of all, 434 g of Ce(NO 3 V 6H 2 O was dissolved in a solution of water and 125 ml of a 2 mol/L solution of Zr(NO 3 ) 4 . The solution of the cerium-zirconium mixture was diluted to a volume of
  • the sample was dried using a microwave oven for three minutes, then calcined at 500°C for 2 hours in a programmed temperature furnace.
  • this step was repeated 4 times; approximately 0.7 g of the cerium-zirconium composite oxide was loaded on the honeycomb ceramic.
  • this step was repeated seven times; approximately 0.78 g of the cerium-zirconium composite oxide was loaded on the honeycomb ceramic.
  • cerium-zirconium composite oxide/cordierite honeycomb ceramic was then impregnated using an ammonium metatungstate (NH 4 WO 3 ) solution (100 ml of the solution was prepared from 25 g OfNH 4 WO 3 dissolved in deionized water), then the residual solution in the honeycomb passageway was removed using hot air. After the removal was complete, the sample was dried using a microwave rapid drying machine, then calcined at 500°C for 2 hours in a programmed temperature furnace. [00178] An assessment was made of the SCR activity of the
  • the feedstock gas was that of Feedstock Gas A.
  • the gas flow rate was set at 1.5 L/min (STP), and the space velocity was set at 22500 h "1 . See FIG. 14 for the test results.
  • Curve 14—1 shows NO conversion rate as a function of temperature of the WO 3 /Ce 0.8 Zr 0.2 O 2 /cordierite honeycomb ceramic catalyst with a 400 cpsi cell density
  • Curve 14-2 shows NO conversion rate as a function of temperature of the WO 3 ZCe 0 8 Zr 02 O 2 /cordierite honeycomb ceramic catalyst with a 600 cpsi cell density.
  • the curves in FIG. 14 indicate that the WO 3 ZCe 08 Zr 02 O 2 /cordierite honeycomb ceramic catalyst prepared with cerium-zirconium sol as the cerium- zirconium precursor has a very good SCR catalytic activity. The higher the cell density of the honeycomb ceramic, the better the active component of the catalyst can be utilized, and the higher its catalytic activity will be.
  • Example 15 shows NO conversion rate as a function of temperature of the WO 3 /Ce 0.8 Zr 0.2 O 2 /cordierite honeycomb ceramic catalyst with a 400 cpsi cell
  • the present example relates to the preparation of a structured catalyst.
  • a 400 cpsi honeycomb cordierite made in Shanghai was used as the ceramic support.
  • the process of pre-treatment was the same as described in Example 14.
  • a cerium-zirconium slurry was used in place of the cerium-zirconium sol for preparation of the coating of the ceramic.
  • the mixture was ground by means of the wet ball milling process for 18 hours and the cerium-zirconium slurry was obtained.
  • the honeycomb ceramic after pre-treatment was impregnated using the cerium-zirconium slurry obtained, then the residual sol or slurry in the honeycomb passageway was removed using hot air. After the removal was complete, the sample was dried using a microwave rapid drying machine, then calcined at 500°C for 2 hours in a programmed temperature furnace. This step was repeated six times, so that approximately 0.77 g of the cerium-zirconium composite oxide was loaded onto the honeycomb ceramic.
  • the cerium-zirconium composite oxide/cordierite honeycomb ceramic was then impregnated using an ammonium metatungstate (NH 4 WO 3 ) solution (100 ml of the solution was prepared from 25 g OfNH 4 WO 3 dissolved in deionized water), then the residual solution in the honeycomb passageway was removed using hot air. After the removal was complete, the sample was dried using a microwave rapid drying machine, then calcined at 500 0 C for 2 hours in a programmed temperature furnace. [00185] An assessment was made of the SCR activity of the WO 3 /Ce 0 8 Zr 02 ⁇ 2 /cordierite catalyst using the quartz fixed-bed reactor. The feedstock gas was Feedstock Gas A.
  • NH 4 WO 3 ammonium metatungstate
  • the present example relates to the preparation of a structured catalyst.
  • the cerium-zirconium slurry was used for preparation of the catalytic coating.
  • the cerium-zirconium slurry was prepared from Ce 0.5 Zro .5 0 2 powder prepared using the microemulsion process.
  • the process used to prepare the Ce 0 5 Zr 0 5 O 2 powder was as follows: Step 1—43.42 g of cerium nitrate and 42.92 g of zirconium nitrate were dissolved using deionized water and the concentration was set to 1 mol/L; also, 25 ml of a 25-wt% aqueous ammonia solution was diluted to 50 ml, and a 7.5M aqueous ammonia solution was obtained. Step 2— production of the microemulsion.
  • Step 1 100 ml of polyoxyethlene (10) octylphenyl ether (hereinafter "Np-10") and 120 ml of n-hexanol were added at room temperature and under stirring to 400 ml of n-hexane, until the solution mixture became clear.
  • the Ce(NO 3 ) 3 and Zr(NO 3 ) 4 solution obtained in Step 1 was then added to the solution mixture, and stirred, until the mixture solution became clear again.
  • Another emulsion in which 50 ml of the aqueous ammonia solution obtained in Step 1 was dissolved was prepared using the same technique mentioned above.
  • Step 3 the two kinds of microemulsions with different concentration levels were mixed in a 2000 ml beaker.
  • the mixture was reacted, with stirring, for half an hour, then the microparticles were separated through reflux and vacuum dried at 70°C for 12 hours.
  • the dried sample was calcined at 500°C in a muffle furnace for 2 hours. As a result, approximately 12 g of an extremely fine powder of cerium-zirconium composite oxide was obtained.
  • the sample was dried using a microwave rapid drying machine, then calcined at 500°C for 2 hours in a programmed temperature furnace. This step was repeated for several times, so that approximately 0.6358 g and 0.4165 g of the cerium-zirconium composite oxides were respectively loaded onto the honeycomb ceramic.
  • the cerium-zirconium composite oxide/cordierite honeycomb ceramic was then impregnated using an ammonium metatungstate (NH 4 WO 3 ) solution (100 ml of the solution was prepared from 25 g OfNH 4 WO 3 dissolved in deionized water), then the residual solution in the honeycomb passageway was removed using hot air. After the removal was complete, the sample was dried using a microwave rapid drying machine, then calcined at 500°C for 2 hours in a programmed temperature furnace. [00193] An assessment was made of the SCR activity of the W0 3 /Ceo 5 Zr o 5 O 2 /cordierite catalyst using the quartz fixed-bed reactor.
  • NH 4 WO 3 ammonium metatungstate
  • a reaction under programmed heating was carried out; the heating rate was 2 K/min and the feedstock gas was Feedstock Gas B.
  • the gas flow rate was set at 1.5 L/min (STP), and the space velocity was set at 22500 h "1 . See FIG. 16 for the test results.
  • Curve 16— 1 is NO conversion rate as a function of temperature of the W0 3 /Ceo 5 Zr 0 5 O 2 /cordierite honeycomb ceramic catalyst when the Ceo 5 Zro 5 O 2 loading is 0.6358 g;
  • Curve 16-2 is NO conversion rate as a function of temperature of the WO 3 /Ce 0 5 Zr 0 5 O 2 /cordierite honeycomb ceramic catalyst with a 0.4165 g Ce 0 5 Zr 0 5 O 2 loading.
  • Example 17 [00196] Preparation of the structured W ⁇ yCe(vsZrn_s ⁇ 2/cordierite honeycomb ceramic catalyst, and characterization of its performance
  • the present example relates to the preparation of an structured catalyst.
  • the WO 3 /Ce 0 5 Zr 0 5 O 2 powder was synthesized using the process of impregnation. With stirring, 12 g of Ce 0 5 Zr 0 5 O 2 powder (the process of preparation is the same as in Example 3) was mixed and suspended in 50 ml of deionized water. Next, 1.4117 g of ammonium metatungstate (NH 4 WO 3 ) was added to the suspension mentioned above, and the mixture obtained was heated in an oil bath to 85°C. It was heated continuously with stirring, until most of the moisture evaporated, and a paste was obtained. The paste was transferred to a dryer, where it was dried at 120°C overnight.
  • NH 4 WO 3 ammonium metatungstate
  • WO 3 may be loaded onto the honeycomb ceramic catalysts in different ways.
  • Example 18 (comparative example ' )
  • the filter cake was put into an 85°C oven dryer where it was dried for 12 hours, then transferred to a muffle furnace where it was calcined d at 825°C for 3 hours. After the calcined sample was ground, it was screened with a 200-mesh sieve, and the catalyst powder was obtained. The catalyst powder was pressed and shaped, ground, and crushed, then particles of 20-30 mesh were selected through screening for the assessment tests. The assessment tests were conducted once under the following two conditions (Condition A, Condition B) respectively.
  • Condition A (the following data on the composition are volume percentages and volume fractions):
  • Composition of the feedstock gas 500 ppm NO, 500 ppm NH 3, and 1% O 2, and balance N 2.
  • Space velocity 800000 hr "1 .
  • Curve 18-1 shows the results of assessment of the catalyst of the present example.
  • Condition B (the following data on the composition included the volume percentage and volume fraction):
  • composition of the feedstock gas 550 ppm NO, 550 ppm NH 3> 10% H 2 O,
  • a catalyst with the chemical composition of the present invention was prepared using the process disclosed in Column 9 of U.S. Patent No. 5,552,128 for Catalyst B disclosed therein; its performance was tested and characterized. Compared with Catalyst B disclosed in Column 9 of U.S. Patent No. 5,552,128, the catalyst prepared in the present example had an even higher content of cerium.
  • the specific process of preparation was as follows.
  • Solution BB2 was added drop-wise into the beaker containing Solution AA2, with a controlled addition rate such that the addition process was complete within 30-40 minutes.
  • a certain amount of concentrated aqueous ammonia (mass concentration 25%) was added to the beaker, to adjust the pH value of the mixture to approximately 9.
  • the mixture obtained was then transferred to a three-neck flask to be aged in a 100°C oil bath for 72 hours. After the aging was complete, the mixture was filtered so that the precipitate was separated from the mother liquor, and the precipitate was washed with stirring using 100°C hot water for 20 minutes. It was thoroughly washed 3 times; after each washing, the solid and liquid were separated by filtering.
  • the filter cake was put into an 85°C oven dryer where it was dried for 12 hours, then transferred to a muffle furnace where it was calcined at 825 °C for 3 hours. After the calcined sample was ground, it was screened with a 200-mesh sieve and the catalyst powder was obtained. The catalyst powder was pressed and shaped, ground, and crushed, and particles of 20— 30 mesh were selected through screening for the assessment tests. The assessment tests were conducted once respectively under Condition A and Condition B as described in
  • Example 18 For the results of the assessment under Condition A, see FIG. 18. In the drawing, Curve 18-2 shows the results of the assessment of the catalyst of the present example. For the results of the assessment under Condition B, see FIG. 19. In the drawing, Curve 19-2 shows the results of the assessment of the catalyst of the present example.
  • Example 18 In order to make an effective comparison with Example 18 and Example 19, a catalyst whose chemical composition was the same as that of the catalyst of Example 18 was prepared in the present example using the process of the present invention, and its performance was tested and characterized.
  • the specific method was as follows. [00221 ] 2000 ml of a solution with the cation concentration of 0.1 mol/L was prepared from 54.8 g Of(NIL t ) 2 Ce(NOs) 6 and 50 ml of a 2-mol/L Zr(NO 3 ) 4 solution and deionized water. With stirring, said solution was heated to its boiling point, until the precipitate was observed. The mixture obtained was then aged at the boiling point for 2 hours, then stirred at room temperature for 2 hours.
  • the precipitate was filtered, then washed with stirring using 1500 ml of deionized water for 15 minutes. This step was repeated three times.
  • the filter cake was then eluted with 300 ml of propanol using a Buchner funnel. After excess propanol was removed through filtering, the precipitate obtained was placed in a vacuum oven dryer, where it was dried at 60 0 C for approximately 15 hours.
  • the dried precipitate was then calcined at 500 0 C in a furnace for 2 hours, so that it decomposed to form a Ce 0 5 Zr 0 5 O 2 oxide.
  • the WO 3 /Ce 0 5 Zr 0 5 O 2 catalyst was synthesized using the process of impregnation. With stirring, 15 g of Ce 0 5 Zr 0 5 O 2 powder was mixed and suspended in 50 ml of deionized water. Next, 1.7647 g of ammonium metatungstate (NH -I ) 6 H 2 W 12 O 4O -XH 2 O) was added to the suspension mentioned above, and the mixture obtained was heated to 85°C. It was heated continuously with stirring, until most of the moisture evaporated, and a paste was obtained. The paste was transferred to a dryer, where it was dried at 120 0 C for 6 hours.
  • NH -I ammonium metatungstate
  • the catalyst powder was pressed and shaped, then ground and crushed, and particles of approximately 20-30 mesh were selected through screening for the assessment tests.
  • the assessment tests were conducted once respectively under Condition A and Condition B as described in Example 18. For the results of the assessment under Condition A, see FIG. 18. In the drawing, Curve 18-3 shows the results of the assessment of the catalyst of the present example. For the results of the assessment under Condition B, see FIG. 19. In the drawing, Curve 19-3 shows the results of the assessment of the catalyst of the present example. [00224]
  • Example 21 Example 21
  • the catalyst was synthesized using the process of impregnation. First of all, with stirring, the oxide powder prepared as mentioned above was mixed and suspended in 50 ml of deionized water. Next 4.41 g of ammonium metatungstate (NFLi)OH 2 W 12 O 4O -XH 2 O) was added to the suspension mentioned above, and the mixture obtained was heated to 85°C.
  • NFLi ammonium metatungstate

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Abstract

La présente invention concerne un catalyseur pour la réduction catalytique sélective d'un oxyde d'azote, comportant un premier constituant choisi parmi des oxydes d'un métal de transition autre que le métal contenu dans le second constituant, ou un mélange ou combinaison de ceux-ci, un second constituant choisi parmi des oxydes de cérium, des oxydes composites de cérium-zirconium, et des oxydes composites de cérium-titane, et des combinaisons de ceux-ci. Le catalyseur peut être utilisé sous forme de pastilles, ou revêtu sur une céramique monolithique poreuse pour former un catalyseur en nid d'abeilles. L'invention concerne également un procédé de fabrication dudit catalyseur, comprenant : la préparation du premier constituant à partir du précurseur du premier constituant ; la préparation du second constituant ; et le chargement du premier constituant sur le second constituant.
PCT/US2008/006877 2007-05-31 2008-05-30 Catalyseur pour la réduction sélective d'oxydes d'azote, son procédé de fabrication et d'utilisation Ceased WO2008150462A2 (fr)

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US10343117B2 (en) 2009-02-27 2019-07-09 Corning Incorporated Ceria-zirconia-zeolite catalyst body
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US8529853B2 (en) 2010-03-26 2013-09-10 Umicore Ag & Co. Kg ZrOx, Ce-ZrOx, Ce-Zr-REOx as host matrices for redox active cations for low temperature, hydrothermally durable and poison resistant SCR catalysts
WO2011116907A2 (fr) 2010-03-26 2011-09-29 Umicore Ag & Co. Kg Zrox, ce-zrox, ce-zr-reox au titre de matrices hôtes pour des cations à activité redox pour catalyseurs de réduction sélective à basse température, à durabilité hydrothermique satisfaisante et résistants à l'empoisonnement
CN102008954A (zh) * 2010-10-14 2011-04-13 北京石油化工学院 六铝酸盐金属氧化物催化剂、制备方法及其应用
US8580701B2 (en) 2010-11-19 2013-11-12 Corning Incorporated Method of controlling Ce:Zr ratio in oxide nanoparticles
CN111744490A (zh) * 2019-03-28 2020-10-09 苏州华加星光环保工程技术有限公司 一种铁基脱硝催化剂及其制备方法
CN113318726A (zh) * 2020-02-28 2021-08-31 广东粤能净环保科技有限公司 一种具有释放负氧离子功能的光催化剂及其制法和应用
CN113318726B (zh) * 2020-02-28 2023-08-01 中科粤能净(山东)新材料有限公司 一种具有释放负氧离子功能的光催化剂及其制法和应用
CN115178254A (zh) * 2022-08-26 2022-10-14 天津工业大学 一种无毒性、高活性、高稳定性的稀土基nh3-scr催化剂及其制备技术
CN115178254B (zh) * 2022-08-26 2024-03-19 天津工业大学 一种无毒性、高活性、高稳定性的稀土基nh3-scr催化剂及其制备技术
CN116637613A (zh) * 2023-04-07 2023-08-25 福州大学 一种含复合金属氧化物粒子的Pickering型SCR催化功能乳液制备方法
CN118371274A (zh) * 2024-06-21 2024-07-23 内蒙古京能康巴什热电有限公司 一种多孔陶瓷负载双层氧化物的scr催化剂的制备方法和脱硝方法
CN118371274B (zh) * 2024-06-21 2024-10-18 内蒙古京能康巴什热电有限公司 一种多孔陶瓷负载双层氧化物的scr催化剂的制备方法和脱硝方法

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