WO2004022225A2 - Method for converting nitrogen oxides (nox) in exhaust gases and catalyst useful for it - Google Patents

Method for converting nitrogen oxides (nox) in exhaust gases and catalyst useful for it Download PDF

Info

Publication number
WO2004022225A2
WO2004022225A2 PCT/IB2003/004244 IB0304244W WO2004022225A2 WO 2004022225 A2 WO2004022225 A2 WO 2004022225A2 IB 0304244 W IB0304244 W IB 0304244W WO 2004022225 A2 WO2004022225 A2 WO 2004022225A2
Authority
WO
WIPO (PCT)
Prior art keywords
catalytic material
metal oxide
catalytic
meq
rhodium
Prior art date
Application number
PCT/IB2003/004244
Other languages
French (fr)
Other versions
WO2004022225B1 (en
WO2004022225A3 (en
Inventor
Jorge Flores Moreno
François Figueras
Gérard DELAHAY
Bernard Coq
Corinne Lehaut-Burnouf
Original Assignee
Millennium Chemicals Thann Sas
Centre National De La Recherche Scientifique
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Millennium Chemicals Thann Sas, Centre National De La Recherche Scientifique filed Critical Millennium Chemicals Thann Sas
Priority to AU2003264331A priority Critical patent/AU2003264331A1/en
Publication of WO2004022225A2 publication Critical patent/WO2004022225A2/en
Publication of WO2004022225A3 publication Critical patent/WO2004022225A3/en
Publication of WO2004022225B1 publication Critical patent/WO2004022225B1/en

Links

Classifications

    • 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
    • B01D53/9445—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]
    • B01D53/945—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC] characterised by a specific catalyst
    • 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
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
    • B01J23/46—Ruthenium, rhodium, osmium or iridium
    • B01J23/464—Rhodium
    • B01J35/30—
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/20—Sulfiding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/20—Reductants
    • B01D2251/208—Hydrocarbons
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/10—Noble metals or compounds thereof
    • B01D2255/102—Platinum group metals
    • B01D2255/1025—Rhodium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/204—Alkaline earth metals
    • B01D2255/2042—Barium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/206—Rare earth metals
    • B01D2255/2065—Cerium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/207—Transition metals
    • B01D2255/20707—Titanium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/207—Transition metals
    • B01D2255/20715—Zirconium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/207—Transition metals
    • B01D2255/20776—Tungsten
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/90—Physical characteristics of catalysts
    • B01D2255/911—NH3-storage component incorporated in the catalyst
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/90—Physical characteristics of catalysts
    • B01D2255/92—Dimensions
    • B01D2255/9207—Specific surface
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2258/00—Sources of waste gases
    • B01D2258/01—Engine exhaust gases
    • B01D2258/012—Diesel engines and lean burn gasoline engines
    • B01J35/613—
    • B01J35/615—
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

Definitions

  • the instant invention relates to a catalyst useful for converting nitrogen oxides (NO x ) to N 2 , in particular for use in diesel applications to treat the exhaust gases.
  • Selective catalytic reduction (SCR) is an attractive method to convert nitrogen oxides
  • Three-way catalysts useful for operation with gasoline are often not equivalently suitable for diesel operation because diesel exhaust gas contains oxygen and is lower in temperature generally 200 °C to 600 °C as compared to gasoline exhaust gas.
  • the lean-burn or diesel catalyst must be able to convert NO x at lower temperature than would be suitable for a three-way catalyst and, furthermore, be active in the presence of oxygen.
  • the conventional catalytic converter systems reach maximum efficiency at temperatures between 400 and 800 °C, above the operating temperature range of these engines.
  • Another special property required for present diesel catalysts is that they be sulphur resistant since diesel fuel generally contains higher amounts of sulphur than gasoline fuel.
  • Sulphur compounds like SO 2 and SO 3 (SO x ) present in the fuel can react chemically with the catalyst and/or the support thereof so that the catalyst is less effective for converting exhaust gases.
  • SO x sulfur compounds
  • sulphur reacts with conventional alumina to form sulfate compounds which reduce the surface area of the support. Accordingly, such catalysts have to be periodically regenerated by treatment at higher temperature with some loss of surface area and catalytic properties.
  • the purpose of the instant invention is precisely to propose a new catalytic material which overcomes the deficiencies of prior lean-NO x catalysts and is suited for use in diesel applications to treat the exhaust gases.
  • the wording "Lean-NO x catalyst” includes gasoline lean-burn catalysts and diesel catalysts for NO x conversion.
  • the invention further provides a catalytic substrate including the claimed catalytic material that catalyzes the conversion of emission gases in oxidising exhaust streams fro a combustion process.
  • the material and corresponding catalytic substrate of the invention are particularly useful for NO x conversion under oxidising conditions.
  • the invention is firstly directed to a method for treating exhaust gases generated by a diesel or lean-burn engine containing sulphur oxides and NO x , and comprising the steps of:
  • the invention concerns also a method of reducing NO x in an oxidising and sulphated atmosphere comprising the steps of: (a) providing an acidic catalytic material comprising a noble metal-doped metal oxide material wherein the noble metal is present in the form of at least one oxidised species of rhodium,
  • the claimed methods involve a catalytic material having an acid density greater than 0.2 meq.g "1 , preferably greater than 0.25 meq.g "1 said value of acid density being determined by adsorption of ammonia measured by gravimetry coupled with mass spectrometry at 100°C.
  • the claimed methods involve a catalytic material having an acid density greater than 0.5 meq.g "1 , said value of acid density being determined by temperature programmed desorption of ammonia which desorption is measured by a catharometer cell TPD-TPR Micrometics ® 2910 and corresponds to the integrated area below the curve of desorption of ammonia, translated in meq.g "1 by calibration of the system.
  • so- expressed acid site density is greater than 1.5 meq.g "1 , more particularly greater than 3 meq.g "1 and preferably greater than 5 meq.g "1 .
  • the invention is also directed to a catalytic material comprising a noble metal - doped titania material wherein the noble metal is present in the form of at least an oxidised species of rhodium optionally generated in situ starting from rhodium or mixtures thereof, said catalytic material having an acid site density as defined previously.
  • the inventors found that the efficiency of lean-NO x catalysts could be significantly improved with atmospheres including water and SO 2 and at a temperature lower than 400 °C preferably lower than 385 °C, and more preferably at a temperature about 375 °C with the proviso that their acid site density be greater than 0.2 meq.g "1 determined by adsorption of ammonia measured by gravimetry, and/or greater than 0.5 meq.g -1 ,said value being determined by temperature programmed desorption of ammonia which desorption is measured by a catharometer cell TPD-TPR Micromeritics ® 2910 and corresponding to the integrated area below the curve of desorption of ammonia converted in meq.g " by calibration.
  • such an acid site density is particularly advantageous for increasing the selective NO ⁇ conversion in N 2 compared to NO ⁇ conversion in NO 2 or N 2 O.
  • the NO ⁇ conversion in NO 2 is delayed until higher temperatures, and for example is only of 5 % or lower at a temperature of 400 °C.
  • N 2 O is formed marginally at low temperature, and the selectivity to dinitrogen is >90%.
  • the acid site density also called Acidity, is defined as being representative of the number of acid sites per gram of catalytic material. It is noticed that the values proposed for the acid site density may vary significantly with respect to the method used for determining them. In both cases, the procedure involves the same standardisation of the sample i.e. the catalytic material (about 0.03 g) is first calcined at 500°C in dry air for 1 hour, treated in pure helium at the same temperature for 1 hour, then cooled under helium to 100°C. The method used according to the invention is specifically disclosed hereafter.
  • the amount of ammonia adsorbed may be measured by different methods, for instance by gravimetry using a microbalance or by thermal desorption integrating the signal of the catharometer.
  • the value of 0.2 meq.g "1 is determined by gravimetry, measuring directly the increase of weight upon adsorption of ammonia at 100°C from a flow of helium containing 1 % NH 3 in a SETARAM microbalance operated in controlled atmosphere.
  • the sample is saturated by ammonia introduced in helium (1 % NH 3 ).
  • the increase of weight is then transformed in milli-equivalents per gram (meq/g). At the low temperature used here only adsorption is involved and any reduction of the sample is avoided.
  • the value of 0.5 meq.g "1 is determined by thermal desorption induced by a linear raise of temperature up to 500°C using a chromatographic detection (TPD).
  • TPD chromatographic detection
  • the sample is first saturated by ammonia using pulses of NH 3 in helium (5 % NH 3 ).
  • the desorption produces a peak which is integrated, and the surface of this peak is converted to meq/g assuming that the signal is due to NH 3 only.
  • the desorption of ammonia at high temperature for strongly acidic samples can however provoke a reduction of the sample, which converts NH 3 into N 2 + H 2 O, counted as ammonia in the integration.
  • This technique gives reproducible results which represent acidity if the sample is not reducible (zeolites, silico-aluminates..), or low acidity in which case the two steps of desorption and reduction are well separated.
  • the acidity may be controlled by the presence of some acidic moieties per unit area on the catalytic material and/or by the surface area of the catalytic material.
  • the surface area of the catalytic material is greater than 40 m 2 .g _1 , particularly greater than 50 m .g _1 and more particularly greater than 75 m 2 .g _1 , or better greater than 95 m 2 .g _1 .
  • the surface area is determined after a standard treatment at 280 °C for 5 hours in vacuum (10 "5 torr). The area of commercial supports is measured without any other previous treatment, but the solids which have been modified by acid treatment suffer a calcination for 10 hours at 500°C before the measurement of their surface area.
  • acidic moieties can be naturally present in the metal oxide material or incorporated therein by post-treatment of it with an acid agent.
  • acidic moieties included in the catalytic material can be selected in the group consisting of sulphate, phosphate, tungstate, molybdate, mixtures and derivatives thereof. These are preferably sulphate and/or phosphate moieties or derivatives thereof.
  • sulphate ions they may be supplied to the catalytic material according to the invention by treatment of the solid metal oxide material with sulphuric acid, for example 0.01 -ION sulphuric acid and, preferably 0.1 -5N sulphuric acid.
  • sulphuric acid for example 0.01 -ION sulphuric acid and, preferably 0.1 -5N sulphuric acid.
  • Other compounds such as ammonium sulphate capable of providing sulfate ions can be also employed.
  • Compounds such as hydrogen sulphide or sulphur dioxide or mercaptans, are also capable of forming sulphate ions upon calcination.
  • Preferred catalysts for use according to the invention are those which have been sulphated with persulphate.
  • the metal oxide material includes an amount of sulphate moieties effective for allowing said catalytic material to exhibit, after calcination for 10 hours at 500 °C, a I.R band or shoulder at a wavelength > 1380 cm "1 .
  • the sulphate moieties may be present in the metal oxide material in an amount of about 0.05 to about 5 and preferably from about 0.1 to about 2 weight percent expressed in weight of sulphur based on the weight of the sulphated metal oxide material, evaluated after calcination for 10 hours at 500 °C.
  • the rhodium species may be present on the metal oxide material in an amount of about 0.05 to about 3 weight percent and preferably from about 0.1 to about 2 weight percent based on the weight of the acid metal oxide material.
  • the rhodium species may be loaded onto the metal oxide material from a solution of at least one soluble cationic salt of rhodium.
  • the claimed catalytic material comprises at least some oxidised species of rhodium carried on the surface of the metal oxide material.
  • the active rhodium species may be isolated cations or corresponding oxides.
  • the active phase is oxidised species.
  • the rhodium active form is a mixture of Rh 1 , Rh m and optionally oxychloride RhOCl x resulting from the choice of a chloride derivative of Rhodium as precursor compound. Cations are considered to be acid sites. It is noticed that the optional presence of chlorine at the surface most probably reinforces this acidity.
  • this oxidised species can be generated in situ, starting from the corresponding metal zero i.e. during the carrying out of the claimed catalyst in diesel application.
  • the noble metal catalytic material may be prepared by incorporating the noble metal cationic species by impregnation or cationic exchange.
  • at least one soluble cationic salt of noble metal i.e. rhodium or mixtures thereof could be dissolved in an aqueous or organic solvent to form a solution, which is then impregnated onto the metal oxide material.
  • soluble precursors include for example rhodium chloride, rhodium nitrate and rhodium acetylacetonate.
  • Other noble metal precursor compounds useful in this invention in addition to those listed above will be apparent to those skilled in the art. They include metal zero.
  • the catalyst prepared by impregnation of the metal oxide material from a solution of a precursor of the noble metal oxidised species does not need subsequent reduction to be active.
  • the metal oxide material may be selected from the group consisting of zirconia, titania, tungsten oxide, mixtures and derivatives thereof like for example tungsten oxides-zirconia and tungsten oxides-titania. In particular, it is based on titania, mixtures or derivatives thereof, like mixte oxides.
  • metal oxide materials according to the invention may comprise small amounts i.e. up to about 30 % based on their total weight of at least one other inorganic material like oxide material and for example cerium oxide, barium oxide, lanthanum oxide, silica and/or alumina like alpha-alumina. Such a supplemental inorganic material may be advantageous for modifying or conferring some properties of the corresponding metal oxide material like for example greater thermal or chemical stability. Techniques for making a metal oxide material according to the instant invention will be apparent to those skilled in the art.
  • the acid site density of the catalytic material can also be controlled with the dopping of the metal oxide material.
  • cations of higher or lower valence than that of host cations are particularly convenient.
  • the metal oxide material can be TiO 2 doped with W 6+ cations.
  • Metal oxide materials convenient for the instant invention are for example, materials commercialized under the trademarks G5 ® , GP350 ® , DT51 ® and DT51-D ® by Millennium Chemicals.
  • the catalytic materials according to the invention are calcined at a temperature which may be comprised in the range from about 450 °C to about 700 °C, more preferably from about 550 °C to about 650 °C, and for a period of time in the range from about 2 to 30 hours.
  • this temperature of calcination will be adjusted to ensure no significant changes to the acid site density of the claimed catalysts.
  • the catalytic material will preferably be carried on a high thermal stability carrier which is generally electrically insulating material.
  • a high thermal stability carrier which is generally electrically insulating material.
  • carrier materials are cordierite, mullite, etc.
  • the carrier may be in any suitable configuration, often being employed as a monolithic honeycomb structure, spun fibers, corrugated foils or layered materials.
  • honeycomb monolith is preferably a ceramic honeycomb monolith of the type widely used for automotive catalytic converters. These monoliths are well-known in the art. Such monoliths are extruded from synthetic cordierite materials (ideally Mg Al 4 Si 5 O 18 ) according to well-known ceramic processes.
  • the effective amount of the activated noble metal-doped hydrous metal oxide depends upon the particular application, i.e., the engine operating conditions and the geometry of the coated carrier.
  • the instant invention is also directed to a catalytic substrate more particularly useful for emissions conversion in an oxidising exhaust stream from a combustion process including a catalytic material according to the invention.
  • the catalytic material may be coated on such a carrier.
  • the selective catalytic reductions using the claimed catalytic material generally use saturated hydrocarbons as reductants. Olefins and/or paraffins are also suitable as reductants. Propene is particularly convenient.
  • the inventors have found that by using a catalytic material and/or a catalytic substrate according to the instant invention for treating diesel exhaust gases, selective NO x conversion in N 2 can be efficiently achieved with a yield of conversion of at least 30 %, preferably at least 35 % and better of at least 40 % in an oxidising and/or sulphur containing atmosphere at a temperature lower than 400 °C more particularly lower than 375 °C and in particular from about 350 °C.
  • the reductant used is propene.
  • the catalytic material is provided under the form of a catalytic substrate as previously defined.
  • the claimed catalytic material operates efficiently to reduce the NO x concentration at lower temperatures than conventional lean-burn catalysts.
  • the claimed catalytic material exhibits appreciable effective NO x conversion over a large temperature range (or “window") greater than 50 °C more particularly greater than 60 °C, in particular greater than 70 °C.
  • the temperature window of "appreciable NO x conversion” means the temperature range at which the conversion of NO x to nitrogen is at least 30 %.
  • the width of temperature window of a Rh doped TiO 2 according to the invention ranges from 65 to 120 °C.
  • Corresponding catalytic materials are efficient for converting at least 30 % of NO x to nitrogen from 260 °C to 450 °C, in particular from 275 °C to 430 °C, more particularly from 275 °C to 400 °C.
  • Fig. 1 is a spectrum, which shows the acidity of metal oxide materials according to the invention, after calcination at 500 °C, as an infrared spectrum of pyridine adsorption after desorption at 150 °C.
  • the 1450 cm “1 band is related to the adsorption on Lewis acid sites and the 1545 cm “1 to the adsorption on Bronsted acid sites.
  • Fig. 2 is a spectrum showing the infrared band of sulfates on a material according to the invention after calcination at 500 °C.
  • Fig. 3 is a graph showing the activity of a claimed catalytic material as a function of time at 360 °C.
  • the oxide materials used for preparing the claimed catalysts are the following ones:
  • DT51 ® , DT51D ® , G5 ® , and GP350 ® based on titanium oxide and commercially available from Millennium Chemicals.
  • the acidity of titania can be increased by additive sulphation.
  • a treatment by sulphate was performed by using a 0.1 M solution of sulphuric acid.
  • the so-obtained sulphated catalytic material is calcinated by successively increasing the temperature from 25 °C to 280 °C with a rate of 1 °C/min, maintaining the temperature at 280 °C for 3 hours, increasing the temperature from 280 °C to 550 °C with a rate of 1 °C/min, maintaining the temperature at 550 °C for 4h30 and then cooling at room temperature.
  • the so-obtained sulphated oxide material is called G5-SO 4 .
  • Another method of sulphation consists in an exchange of OH " present on the catalyst with persulphate ions, and is realised as follows: 10 g of solid were introduced in 25 ml of a solution containing 0.5 M of ammonium persulphate. The so-obtained suspension was stirred at room temperature for 2 hours, filtered and dried in a convection oven at 110 °C for 12 hours. This method induces a very high acidity on zirconia with retention of pyridinium ions up to 450 °C.
  • the acidity level is determined by temperature programmed desorption of ammonia.
  • the sample is first standardised by calcinations, flushed with helium.
  • the surface is saturated by NH 3 , introduced in a flow of helium containing 5 % of NH 3) treated under pure helium for 2h at 100 °C to remove weakly adsorbed ammonia, then the temperature is increased under helium with a ramp of 10°/min up to 500 °C.
  • the NH 3 desorbed from the solid is measured by a catharometer cell TPD-TPR Micromeritics ® 2910.
  • the integrated area below the curve is proportional to the amount of ammonia desorbed, and the exact amount is determined by calibration of the system with an error estimated to 15 %.
  • the so-obtained acidity is expressed in meq g "1 or mmol.g "1 .
  • - Evaluation of the acidity level by gravimetry This measure of the ammonia adsorption is performed by measuring directly the increase of weight upon adsorption of ammonia at 100°C using a SETARAM microbalance in controlled atmosphere. The sample (about 0.03 g) is first calcined at 500°C in dry air for 1 hour, then treated in pure helium at the same temperature for 1 h, cooled under helium to 100°C then contacted with a flow of He containing 1% NH 3 . The weight increase is then transformed in milli- equivalents per gram (meq/g). At the low temperature used here only adsorption is involved and any reduction of the sample is avoided.
  • the surface of area for DT51, DT51D was measured by the BET equation as previously disclosed and the surface of area of sulphated G5 and GP350 according to the same method but after a pre-calcination of said material, for 10 hours at 500 °C.
  • the type of acidity for some metal oxide materials was characterized by FTIR and is represented in Figure 1.
  • the spectra show the adsorption of pyridine at Lewis (band at 1450 cm “1 ) and Br ⁇ nsted (band at 1550 cm “1 ) sites and illustrates the increase of acidity upon sulfation.
  • the Figure 2 is a spectrum showing the IR absorbance of catalysts GP350 before and after sulphation, calcination then vacuum treatment at 500 °C.
  • GP350-SO 4 (IN) shows a higher intensity of the infrared bands of sulphate but also a shift of this band towards higher wavenumbers. This shift corresponds to the formation of highly acidic disulphates which exist only on high surface area materials.
  • RhCl 3 x H 2 O Rh 2 (NO 3 ) 2 or Rh (acac) 3 .
  • 0.104 g of the catalytic material was introduced in the reactor.
  • gas containing 9% oxygen, 0 or 2% water, 0 or 20 part per million (ppm) by volume sulphur dioxide, 1000 ppm by volume propylene and 1000 ppm by volume nitrogen oxide was introduced at a rate of 120 cm 3 , min "1 .
  • the procedure was that of reaction in programmed temperature, increasing the temperature from room temperature to 500 °C at 5 °C/minute, to produce a % NOx conversion curve. The conversion was measured decreasing the temperature, after conditioning the catalyst in the reaction mixture at least for 1 hour at 500°C.
  • the catalysts were then calcinated by placing them in a flow reactor with flowing dried air at a rate of 8L.li "1 .
  • ⁇ the temperature is increased from 25 °C to 500 °C according to the following process.
  • the temperature is increased from 25 °C to 500 °C according to the following process:
  • the acidities of the so-obtained catalysts are equivalent to that of the support material.
  • AP means Phosphoric Acid.
  • This example describes the temperature window for a conversion of 30 % of NO x to nitrogen, as defined above.
  • the width of the temperature window is evaluated from the experimental graph representing the NO ⁇ conversion in function of the temperature. Both temperatures for which a NO ⁇ conversion at the considered yield, 30 % for example, is achieved, are detected and their difference represents the width of the temperature window which characterizes the activity of the tested catalytic material.
  • Second cycle (25-500 °C) with the mixture: 1000 ppm NO, 1000 ppm C 3 H 6 , 20 ppm SO 2 and 9% O 2 , WH - 35000 h "1 .

Abstract

The present invention concerns a method for treating exhaust gases containing sulphur dioxides and NOx generated by a diesel or lean-burn engine comprising the steps of:(a) providing an acidic catalytic material comprising a noble metal-doped metal oxide material wherein the noble metal is present in the form of at least an oxidised species of rhodium in the exhaust gas system of said vehicle, and(b) exposing said exhaust gases to said catalytic material.

Description

Method for converting nitrogen oxides (NOv) in exhaust gases and catalyst useful for it.
The instant invention relates to a catalyst useful for converting nitrogen oxides (NOx) to N2, in particular for use in diesel applications to treat the exhaust gases. Selective catalytic reduction (SCR) is an attractive method to convert nitrogen oxides
NOx to N2. It has many practical applications for the purification of the exhaust gas of Diesel engines and stationary power sources.
Numerous catalysts have been developed specifically to operate in "lean burn" (excess- oxygen) situations and effectively converting hydrocarbons, carbon monoxide as well as the NOx. However, in spite of efforts over the last decade to develop a catalytic system effective for reducing NOx to nitrogen under oxidising conditions in a gasoline lean-burn engine or in a diesel engine, the need for improved conversion effectiveness has remained unsatisfied.
Three-way catalysts useful for operation with gasoline are often not equivalently suitable for diesel operation because diesel exhaust gas contains oxygen and is lower in temperature generally 200 °C to 600 °C as compared to gasoline exhaust gas. The lean-burn or diesel catalyst must be able to convert NOx at lower temperature than would be suitable for a three-way catalyst and, furthermore, be active in the presence of oxygen. The conventional catalytic converter systems reach maximum efficiency at temperatures between 400 and 800 °C, above the operating temperature range of these engines. Another special property required for present diesel catalysts is that they be sulphur resistant since diesel fuel generally contains higher amounts of sulphur than gasoline fuel. Sulphur compounds like SO2 and SO3 (SOx) present in the fuel can react chemically with the catalyst and/or the support thereof so that the catalyst is less effective for converting exhaust gases. For example, sulphur reacts with conventional alumina to form sulfate compounds which reduce the surface area of the support. Accordingly, such catalysts have to be periodically regenerated by treatment at higher temperature with some loss of surface area and catalytic properties. Hence, it is desirable that a diesel NOx catalyst be highly resistant to sulphur poisoning.
It is known that the loading of an activated noble metal like Pt or Pd on an oxide metal material such as ZrO2 leads to catalysts which exhibits high stability towards SO2 and water - (Ohtsuka H et al. ; Applied Catalysis B.; vol. 33 (2001) 325-333). However, selective NOx conversion to N2 of 50 % was only obtained at 450 °C with a GHSV (Gas Hourly Space Velocity of volume of gas per hour passing onto the solid divided by the volume of solid) of 15 000 h"1. Moreover, in these conditions, significant NOx conversions is only obtained at a temperature greater than 350 °C. Toubeli et al. (Catal. Lett., (2000), 69, 157) also propose a similar catalytic system like Rh/TiO2 with TiO2 having a low surface area, in particular lower than 25m2/g. They show that the sulphation of such a catalytic system allows maintaining the SCR conversion at the same level in presence of SO2 as in absence thereof. However, NOx conversion is only observed at a yield of 20 % and only at high temperatures. It is noticed that the present requirement of the car industry is a catalyst active from about 200 °C with a maximum of conversion at about 375 °C.
The purpose of the instant invention is precisely to propose a new catalytic material which overcomes the deficiencies of prior lean-NOx catalysts and is suited for use in diesel applications to treat the exhaust gases. According to the instant invention, the wording "Lean-NOx catalyst" includes gasoline lean-burn catalysts and diesel catalysts for NOx conversion.The invention further provides a catalytic substrate including the claimed catalytic material that catalyzes the conversion of emission gases in oxidising exhaust streams fro a combustion process.
The material and corresponding catalytic substrate of the invention are particularly useful for NOx conversion under oxidising conditions.
Accordingly, the invention is firstly directed to a method for treating exhaust gases generated by a diesel or lean-burn engine containing sulphur oxides and NOx, and comprising the steps of:
(a) providing an acidic catalytic material comprising a noble metal-doped metal oxide material wherein the noble metal is present in the form of at least one oxidised species of rhodium and
(b) exposing said exhaust gases to said catalytic material.
The invention concerns also a method of reducing NOx in an oxidising and sulphated atmosphere comprising the steps of: (a) providing an acidic catalytic material comprising a noble metal-doped metal oxide material wherein the noble metal is present in the form of at least one oxidised species of rhodium,
(b) providing an exhaust gas stream having an oxidising atmosphere and,
(c) contacting said catalytic material with said stream to allow the catalytic material to reduce NOx in said stream. According to particular embodiment, the claimed methods involve a catalytic material having an acid density greater than 0.2 meq.g"1, preferably greater than 0.25 meq.g"1 said value of acid density being determined by adsorption of ammonia measured by gravimetry coupled with mass spectrometry at 100°C.
According to another particular embodiment, the claimed methods involve a catalytic material having an acid density greater than 0.5 meq.g"1, said value of acid density being determined by temperature programmed desorption of ammonia which desorption is measured by a catharometer cell TPD-TPR Micrometics® 2910 and corresponds to the integrated area below the curve of desorption of ammonia, translated in meq.g"1 by calibration of the system. In particular, so- expressed acid site density is greater than 1.5 meq.g"1, more particularly greater than 3 meq.g"1 and preferably greater than 5 meq.g"1.
Both methods are disclosed in more details hereafter. The invention is also directed to a catalytic material comprising a noble metal - doped titania material wherein the noble metal is present in the form of at least an oxidised species of rhodium optionally generated in situ starting from rhodium or mixtures thereof, said catalytic material having an acid site density as defined previously.
Advantageously, the inventors found that the efficiency of lean-NOx catalysts could be significantly improved with atmospheres including water and SO2 and at a temperature lower than 400 °C preferably lower than 385 °C, and more preferably at a temperature about 375 °C with the proviso that their acid site density be greater than 0.2 meq.g"1 determined by adsorption of ammonia measured by gravimetry, and/or greater than 0.5 meq.g-1,said value being determined by temperature programmed desorption of ammonia which desorption is measured by a catharometer cell TPD-TPR Micromeritics® 2910 and corresponding to the integrated area below the curve of desorption of ammonia converted in meq.g" by calibration.
Unexpectedly, such an acid site density is particularly advantageous for increasing the selective NOχ conversion in N2 compared to NOχ conversion in NO2 or N2O. As disclosed in the following examples, the NOχ conversion in NO2 is delayed until higher temperatures, and for example is only of 5 % or lower at a temperature of 400 °C. N2O is formed marginally at low temperature, and the selectivity to dinitrogen is >90%.
The acid site density, also called Acidity, is defined as being representative of the number of acid sites per gram of catalytic material. It is noticed that the values proposed for the acid site density may vary significantly with respect to the method used for determining them. In both cases, the procedure involves the same standardisation of the sample i.e. the catalytic material (about 0.03 g) is first calcined at 500°C in dry air for 1 hour, treated in pure helium at the same temperature for 1 hour, then cooled under helium to 100°C. The method used according to the invention is specifically disclosed hereafter.
However, the amount of ammonia adsorbed may be measured by different methods, for instance by gravimetry using a microbalance or by thermal desorption integrating the signal of the catharometer. The value of 0.2 meq.g"1 is determined by gravimetry, measuring directly the increase of weight upon adsorption of ammonia at 100°C from a flow of helium containing 1 % NH3 in a SETARAM microbalance operated in controlled atmosphere. The sample is saturated by ammonia introduced in helium (1 % NH3).The increase of weight is then transformed in milli-equivalents per gram (meq/g). At the low temperature used here only adsorption is involved and any reduction of the sample is avoided.
In contrast the value of 0.5 meq.g"1 is determined by thermal desorption induced by a linear raise of temperature up to 500°C using a chromatographic detection (TPD). The sample is first saturated by ammonia using pulses of NH3 in helium (5 % NH3). The desorption produces a peak which is integrated, and the surface of this peak is converted to meq/g assuming that the signal is due to NH3 only. The desorption of ammonia at high temperature for strongly acidic samples can however provoke a reduction of the sample, which converts NH3 into N2 + H2O, counted as ammonia in the integration. This technique gives reproducible results which represent acidity if the sample is not reducible (zeolites, silico-aluminates..), or low acidity in which case the two steps of desorption and reduction are well separated. The acidity may be controlled by the presence of some acidic moieties per unit area on the catalytic material and/or by the surface area of the catalytic material.
In accordance with a specific embodiment of the claimed process, the surface area of the catalytic material is greater than 40 m2.g_1, particularly greater than 50 m .g_1 and more particularly greater than 75 m2.g_1, or better greater than 95 m2.g_1. The surface area is determined after a standard treatment at 280 °C for 5 hours in vacuum (10"5 torr). The area of commercial supports is measured without any other previous treatment, but the solids which have been modified by acid treatment suffer a calcination for 10 hours at 500°C before the measurement of their surface area.
With respect to the acidic moieties, they can be naturally present in the metal oxide material or incorporated therein by post-treatment of it with an acid agent. These acidic moieties included in the catalytic material can be selected in the group consisting of sulphate, phosphate, tungstate, molybdate, mixtures and derivatives thereof. These are preferably sulphate and/or phosphate moieties or derivatives thereof.
With respect to sulphate ions, they may be supplied to the catalytic material according to the invention by treatment of the solid metal oxide material with sulphuric acid, for example 0.01 -ION sulphuric acid and, preferably 0.1 -5N sulphuric acid. Other compounds such as ammonium sulphate capable of providing sulfate ions can be also employed. Compounds such as hydrogen sulphide or sulphur dioxide or mercaptans, are also capable of forming sulphate ions upon calcination. Preferred catalysts for use according to the invention are those which have been sulphated with persulphate.
According to this specific embodiment, the metal oxide material includes an amount of sulphate moieties effective for allowing said catalytic material to exhibit, after calcination for 10 hours at 500 °C, a I.R band or shoulder at a wavelength > 1380 cm"1.
The sulphate moieties may be present in the metal oxide material in an amount of about 0.05 to about 5 and preferably from about 0.1 to about 2 weight percent expressed in weight of sulphur based on the weight of the sulphated metal oxide material, evaluated after calcination for 10 hours at 500 °C.
The rhodium species may be present on the metal oxide material in an amount of about 0.05 to about 3 weight percent and preferably from about 0.1 to about 2 weight percent based on the weight of the acid metal oxide material.
While it is particularly interesting to use at least rhodium species and optionally only rhodium species as the noble metal, a mixture of any of platinum, palladium and rhodium may be used. It is particularly advantageous to use only oxidised species of rhodium because the selectivity for converting the nitrogen oxides in N2 is increased. In manufacturing the claimed catalytic material, the rhodium species may be loaded onto the metal oxide material from a solution of at least one soluble cationic salt of rhodium. Thus, the claimed catalytic material comprises at least some oxidised species of rhodium carried on the surface of the metal oxide material. The active rhodium species may be isolated cations or corresponding oxides.
While not wishing to be bound by theory, it seems that the active phase is oxidised species. According to a characterization performed by temperature programmed reduction (TPR) the rhodium active form is a mixture of Rh1, Rhm and optionally oxychloride RhOClx resulting from the choice of a chloride derivative of Rhodium as precursor compound. Cations are considered to be acid sites. It is noticed that the optional presence of chlorine at the surface most probably reinforces this acidity. According to a specific embodiment, this oxidised species can be generated in situ, starting from the corresponding metal zero i.e. during the carrying out of the claimed catalyst in diesel application.
The noble metal catalytic material may be prepared by incorporating the noble metal cationic species by impregnation or cationic exchange. According to first technique, at least one soluble cationic salt of noble metal i.e. rhodium or mixtures thereof could be dissolved in an aqueous or organic solvent to form a solution, which is then impregnated onto the metal oxide material. For rhodium, soluble precursors include for example rhodium chloride, rhodium nitrate and rhodium acetylacetonate. Other noble metal precursor compounds useful in this invention in addition to those listed above will be apparent to those skilled in the art. They include metal zero.
Advantageously, the catalyst prepared by impregnation of the metal oxide material from a solution of a precursor of the noble metal oxidised species does not need subsequent reduction to be active.
The metal oxide material may be selected from the group consisting of zirconia, titania, tungsten oxide, mixtures and derivatives thereof like for example tungsten oxides-zirconia and tungsten oxides-titania. In particular, it is based on titania, mixtures or derivatives thereof, like mixte oxides. In particular, metal oxide materials according to the invention may comprise small amounts i.e. up to about 30 % based on their total weight of at least one other inorganic material like oxide material and for example cerium oxide, barium oxide, lanthanum oxide, silica and/or alumina like alpha-alumina. Such a supplemental inorganic material may be advantageous for modifying or conferring some properties of the corresponding metal oxide material like for example greater thermal or chemical stability. Techniques for making a metal oxide material according to the instant invention will be apparent to those skilled in the art.
It is noticed that the acid site density of the catalytic material can also be controlled with the dopping of the metal oxide material. In this respect, cations of higher or lower valence than that of host cations are particularly convenient. For example, the metal oxide material can be TiO2 doped with W6+ cations.
Metal oxide materials convenient for the instant invention are for example, materials commercialized under the trademarks G5®, GP350®, DT51® and DT51-D® by Millennium Chemicals.
The catalytic materials according to the invention are calcined at a temperature which may be comprised in the range from about 450 °C to about 700 °C, more preferably from about 550 °C to about 650 °C, and for a period of time in the range from about 2 to 30 hours. Of course, this temperature of calcination will be adjusted to ensure no significant changes to the acid site density of the claimed catalysts.
For useful application, as a lean-NOx catalyst, in the diesel exhaust gas system the catalytic material will preferably be carried on a high thermal stability carrier which is generally electrically insulating material. Typical of such carrier materials are cordierite, mullite, etc. The carrier may be in any suitable configuration, often being employed as a monolithic honeycomb structure, spun fibers, corrugated foils or layered materials.
One preferred carrier is a honeycomb monolith. The honeycomb monolith is preferably a ceramic honeycomb monolith of the type widely used for automotive catalytic converters. These monoliths are well-known in the art. Such monoliths are extruded from synthetic cordierite materials (ideally Mg Al4Si5O18) according to well-known ceramic processes.
The effective amount of the activated noble metal-doped hydrous metal oxide depends upon the particular application, i.e., the engine operating conditions and the geometry of the coated carrier.
The instant invention is also directed to a catalytic substrate more particularly useful for emissions conversion in an oxidising exhaust stream from a combustion process including a catalytic material according to the invention. The catalytic material may be coated on such a carrier.
The selective catalytic reductions using the claimed catalytic material generally use saturated hydrocarbons as reductants. Olefins and/or paraffins are also suitable as reductants. Propene is particularly convenient.
Advantageously, the inventors have found that by using a catalytic material and/or a catalytic substrate according to the instant invention for treating diesel exhaust gases, selective NOx conversion in N2 can be efficiently achieved with a yield of conversion of at least 30 %, preferably at least 35 % and better of at least 40 % in an oxidising and/or sulphur containing atmosphere at a temperature lower than 400 °C more particularly lower than 375 °C and in particular from about 350 °C. The reductant used is propene.
According to a specific embodiment, the catalytic material is provided under the form of a catalytic substrate as previously defined. As disclosed from the following examples, the claimed catalytic material operates efficiently to reduce the NOx concentration at lower temperatures than conventional lean-burn catalysts. Unexpectedly, the claimed catalytic material exhibits appreciable effective NOx conversion over a large temperature range (or "window") greater than 50 °C more particularly greater than 60 °C, in particular greater than 70 °C. The temperature window of "appreciable NOx conversion" means the temperature range at which the conversion of NOx to nitrogen is at least 30 %. For example, the width of temperature window of a Rh doped TiO2 according to the invention ranges from 65 to 120 °C. Corresponding catalytic materials are efficient for converting at least 30 % of NOx to nitrogen from 260 °C to 450 °C, in particular from 275 °C to 430 °C, more particularly from 275 °C to 400 °C.
The following examples and drawing sheets illustrate the instant invention.
Fig. 1 is a spectrum, which shows the acidity of metal oxide materials according to the invention, after calcination at 500 °C, as an infrared spectrum of pyridine adsorption after desorption at 150 °C. The 1450 cm"1 band is related to the adsorption on Lewis acid sites and the 1545 cm"1 to the adsorption on Bronsted acid sites.
Fig. 2 is a spectrum showing the infrared band of sulfates on a material according to the invention after calcination at 500 °C. Fig. 3 is a graph showing the activity of a claimed catalytic material as a function of time at 360 °C.
MATERIAL AND METHODS
- Materials The oxide materials used for preparing the claimed catalysts are the following ones:
DT51®, DT51D®, G5®, and GP350® based on titanium oxide and commercially available from Millennium Chemicals.
Their surface area was determined by applying the BET equation to the isotherms of nitrogen adsorption at liquid nitrogen temperature. The isotherms were determined on catalytic materials first treated in vacuum (10"5 torr) at 280 °C for 5h. The BET theory gives a measure of surface area affected by an error commonly estimated from 10 % to 15 %.
The acidity of titania can be increased by additive sulphation. For instance, in the case of G5, a treatment by sulphate was performed by using a 0.1 M solution of sulphuric acid. Then, the so-obtained sulphated catalytic material is calcinated by successively increasing the temperature from 25 °C to 280 °C with a rate of 1 °C/min, maintaining the temperature at 280 °C for 3 hours, increasing the temperature from 280 °C to 550 °C with a rate of 1 °C/min, maintaining the temperature at 550 °C for 4h30 and then cooling at room temperature. The so-obtained sulphated oxide material is called G5-SO4.
Another method of sulphation consists in an exchange of OH" present on the catalyst with persulphate ions, and is realised as follows: 10 g of solid were introduced in 25 ml of a solution containing 0.5 M of ammonium persulphate. The so-obtained suspension was stirred at room temperature for 2 hours, filtered and dried in a convection oven at 110 °C for 12 hours. This method induces a very high acidity on zirconia with retention of pyridinium ions up to 450 °C.
The acidities of metal oxide material were evaluated by TPD-NH3 and/or gravimetry according to the methods described hereafter. - Evaluation of the acidity level by TPD-NH3:
The acidity level is determined by temperature programmed desorption of ammonia. The sample is first standardised by calcinations, flushed with helium. The surface is saturated by NH3, introduced in a flow of helium containing 5 % of NH3) treated under pure helium for 2h at 100 °C to remove weakly adsorbed ammonia, then the temperature is increased under helium with a ramp of 10°/min up to 500 °C. The NH3 desorbed from the solid is measured by a catharometer cell TPD-TPR Micromeritics® 2910. The integrated area below the curve is proportional to the amount of ammonia desorbed, and the exact amount is determined by calibration of the system with an error estimated to 15 %. The so-obtained acidity is expressed in meq g"1 or mmol.g"1. - Evaluation of the acidity level by gravimetry This measure of the ammonia adsorption is performed by measuring directly the increase of weight upon adsorption of ammonia at 100°C using a SETARAM microbalance in controlled atmosphere. The sample (about 0.03 g) is first calcined at 500°C in dry air for 1 hour, then treated in pure helium at the same temperature for 1 h, cooled under helium to 100°C then contacted with a flow of He containing 1% NH3. The weight increase is then transformed in milli- equivalents per gram (meq/g). At the low temperature used here only adsorption is involved and any reduction of the sample is avoided.
The amounts adsorbed expressed in mmol of NH3/g of catalytic material (equivalent to meq.g"1), are reported in Table I. Table I
Figure imgf000011_0001
The surface of area for DT51, DT51D was measured by the BET equation as previously disclosed and the surface of area of sulphated G5 and GP350 according to the same method but after a pre-calcination of said material, for 10 hours at 500 °C.
The type of acidity for some metal oxide materials was characterized by FTIR and is represented in Figure 1. The spectra show the adsorption of pyridine at Lewis (band at 1450 cm"1) and Brδnsted (band at 1550 cm"1) sites and illustrates the increase of acidity upon sulfation.
The Figure 2 is a spectrum showing the IR absorbance of catalysts GP350 before and after sulphation, calcination then vacuum treatment at 500 °C. GP350-SO4 (IN) shows a higher intensity of the infrared bands of sulphate but also a shift of this band towards higher wavenumbers. This shift corresponds to the formation of highly acidic disulphates which exist only on high surface area materials.
- The doping of previous oxide material with rhodium species.
It is loaded by the impregnating method by using as starting salts, RhCl3 x H2O, Rh2(NO3)2 or Rh (acac)3.
- Evaluation of the NOy conversion capability.
The materials prepared in the following examples were evaluated for NOx conversion capabilities according to the following method:
0.104 g of the catalytic material was introduced in the reactor. In the reaction mixture, gas containing 9% oxygen, 0 or 2% water, 0 or 20 part per million (ppm) by volume sulphur dioxide, 1000 ppm by volume propylene and 1000 ppm by volume nitrogen oxide was introduced at a rate of 120 cm3, min"1. The procedure was that of reaction in programmed temperature, increasing the temperature from room temperature to 500 °C at 5 °C/minute, to produce a % NOx conversion curve. The conversion was measured decreasing the temperature, after conditioning the catalyst in the reaction mixture at least for 1 hour at 500°C.
EXAMPLE 1
Preparation of lean - catalysts according to the invention.
50 cm3 of a solution containing the salt of rhodium were obtained by dissolving RhCl3 x H2O or Rh (acac)3 either in toluene or distillated water. This solution was then added to 10 g of a metal oxide material to obtain a suspension, which was stirred and heated at 70 °C for three hours. At the end, the temperature is increased until 90 °C to remove the solvent. This last step was stopped after twelve hours. The so-obtained powder was dried in a convection oven at 120 °C for twelve hours.
The catalysts were then calcinated by placing them in a flow reactor with flowing dried air at a rate of 8L.li"1. According to a first embodiment, termed ©, the temperature is increased from 25 °C to 500 °C according to the following process.
- Increasing the temperature from 25 °C to 280 °C at a rate of 2 °C min"1,
- Maintaining the temperature at 280 °C for 3 hours,
- Increasing the temperature from 280 °C to 500 °C at a rate of 2 °C min'1, Maintaining the temperature at 500 °C for 10 hours and then cooling. According to a second embodiment, termed ©, the temperature is increased from 25 °C to 500 °C according to the following process:
Increasing the temperature from 25 °C to 280 °C at a rate of 5 °C min"1, Maintaining the temperature at 280 °C for 2 hours,
- Increasing the temperature from 280 °C to 500 °C at a rate of 5 °C min"1, - Maintaining the temperature at 500 °C for 10 hours and then cooling.
The acidities of the so-obtained catalysts are equivalent to that of the support material.
EXAMPLE 2
This example describes the performances of the catalysts according to the instant invention with respect to the conversion of NOx. Propene is used as reductant. The results are shown in Table II. Table II
Figure imgf000013_0001
AP: means Phosphoric Acid.
SN2 means the selectivity for converting NOx in N .
These results correspond to the maximum of conversion observed for the temperature specified in the column No. 3 of Table II.
They show that selective conversions are observed for all tested catalytic materials with a yield at least equal to 30 % at a temperature lower than 375 °C. Moreover, seven of them lead to a yield at least equal to 40 % at a temperature lower or equal to 385 °C.
EXAMPLE 3
This example describes the temperature window for a conversion of 30 % of NOx to nitrogen, as defined above. The width of the temperature window is evaluated from the experimental graph representing the NOχ conversion in function of the temperature. Both temperatures for which a NOχ conversion at the considered yield, 30 % for example, is achieved, are detected and their difference represents the width of the temperature window which characterizes the activity of the tested catalytic material. Table III
Figure imgf000014_0001
These results show that the claimed catalytic materials exhibit a large window of activity for NOx conversion.
EXAMPLE 4
The activity of the lRh/G5-SO4 has been tested in function of time at 360 °C. The results submitted in Figure 3 show that this activity is maintained.
The stability of its catalytic activity in presence of water and sulphur dioxide has also been tested.
To assess this stability, the following experiments were performed:
• First cycle (25-500 °C) realised with the mixture: 1000 ppm NO, 1000 ppm C3H6, 20 ppm SO2 and 9% O2, WH = 35000 h"1.
• Cooling to 25 °C with the reaction mixture.
• Second cycle (25-500 °C) with the mixture: 1000 ppm NO, 1000 ppm C3H6, 20 ppm SO2 and 9% O2, WH - 35000 h"1.
• Cooling to 360 °C with the mixture and incorporation of 2% of H2O, WH = 35000 h"1.
The result show that the NOx conversion to N2 after 1 hour, then after 72 hours is maintained at 41 %.

Claims

1. A method for treating exhaust gases containing sulphur dioxides and NOx generated by a diesel or lean-burn engine comprising the steps of: (a) providing an acidic catalytic material comprising a noble metal-doped metal oxide material wherein the noble metal is present in the form of at least an oxidised species of rhodium in the exhaust gas system of said vehicle, and
(b) exposing said exhaust gases to said catalytic material.
2. A method of reducing NOx in an oxidising and sulphated atmosphere comprising the steps of:
(a) providing an acidic catalytic material comprising a noble metal-doped metal oxide material wherein the noble metal is present in the form of at least an oxidised species of Rhodium,
(b) providing an exhaust gas stream having an oxidising atmosphere and,
(c) contacting said catalytic material with said stream to allow the catalytic material to reduce MX in said stream.
3. A method according to claim 1 or 2, wherein the catalytic material has an acid density greater than 0.2 meq.g"1, said value being determined by temperature programmed adsorption by ammonia which adsorption is measured by gravimetry.
4. A method according to claim 1, 2 or 3, wherein the catalytic material has an acid density greater than 0.5 meq.g"1, said value being determined by temperature programmed desorption of ammonia which desorption is measured by a catharometer cell TPD-TPR Micromeritics® 2910 and corresponding to the integrated area below the curve of desorption of ammonia converted in meq.g"1 by calibration.
5. The method according to claim 4, wherein the catalytic material has an acid site density greater than 1.5 meq.g"1 and more particularly greater than 3 meq.g"1.
6. The method according to claims 1 to 5, wherein the catalytic material exhibits a surface area greater than 40 m2.g_1 and particularly greater than 50 m2.g_1.
7. The method according to claims 1 to 6, wherein the metal oxide material includes an effective amount of acidic moieties.
8. The method according to claim 7, wherein the acidic moieties are selected in the group consisting of sulphate, phosphate, tungstate, molybdate, mixtures and derivatives thereof.
9. The method according to claim 7 or 8, wherein the acidic moieties are phosphate, sulphate and derivatives thereof.
10. The method according to claims 1 to 9, wherein the metal oxide material includes an amount of sulphate effective to allow said catalytic material to exhibit after calcination for 10 hours at 500 °C, I.R band or shoulder at a wavelength > 1.380 cm"1.
11. The method according to claim 8 or 10, wherein sulphate moieties are included in the metal oxide material in an amount from 0.05 to 5 weight percent and preferably from 0.1 to 2 weight percent expressed in weight of sulphur based on the weight of the sulphated metal oxide material, evaluated after calcination for 10 hours at 500 °C.
12. The method according to claim 1 to 11, wherein the oxidised species of rhodium are present on said metal oxide material in an amount of about 0.05 to about 3 and preferably from about 0.1 to about 2 weight percent of metal based on the weight of the acid metal oxide material.
13. The method according to claim 1 to 12, wherein the oxidised species of rhodium are issued from doping of the metal oxide material with RhCl2 or rhodium acetylacetonate.
14. The method according to claims 1 to 13, wherein the metal oxide material is selected from the group consisting of zirconia, titania and tungsten oxides, mixtures and derivatives thereof.
15. The method according to claims 1 to 14, wherein the metal oxide material is based on titania, mixtures or derivatives thereof.
16. The method according to claims 1 to 15, wherein the metal oxide material further includes a metal oxide selected from the group consisting of cerium oxide, barium oxide, silica and/or alumina.
17. The method according to claims 1 to 16 wherein the catalytic material is effective to catalyze selective conversion of at least 30 % and preferably 35 % of NOx in N2 in an oxidising and sulphur containing atmosphere at a temperature lower than 400 °C.
18. A catalytic material comprising a noble metal - doped titania material, wherein the noble metal is present in the form of at least an oxidised species of rhodium and with said catalytic material having an acid site density greater than 0.2 meq.g"1 determined by temperature programmed desorption by ammonia which adsorption is measured by gravimetry.
19. A catalytic material comprising a noble metal - doped titania material, wherein the noble metal is present in the form of at least an oxidised species of rhodium with said catalytic material having an acid site density greater than 0.5 meq.g"1, particularly greater than 1.5 meq.g"1, more particularly greater than 3 meq.g"1 and preferably greater than 5 meq.g"1, with said value being determined by temperature programmed desorption of ammonia which desorption is measured by a catharometer cell TPD-TPR Micromeritics® 2910 and corresponding to the integrated area below the curve of desorption of ammonia converted in meq.g"1 by calibration.
20. A catalytic material according to claim 18 or 19 as defined in anyone of the claims 5 to 13.
21. A catalytic substrate including a catalytic material according to claims 18 to 20, for emissions conversion in an oxidising exhaust stream from a combustion process.
22. The catalytic substrate according to claim 21, wherein a catalytic material according to claims 18 to 20 is coated on a substrate.
23. The catalytic substrate according to claim 21 or 22, wherein the substrate is a ceramic honeycomb monolith.
PCT/IB2003/004244 2002-09-09 2003-09-09 Method for converting nitrogen oxides (nox) in exhaust gases and catalyst useful for it WO2004022225A2 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2003264331A AU2003264331A1 (en) 2002-09-09 2003-09-09 Method for converting nitrogen oxides (nox) in exhaust gases and catalyst useful for it

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
IB0203612 2002-09-09
IBPCT/IB02/03612 2002-09-09
US44035803P 2003-01-16 2003-01-16
US60/440,358 2003-01-16

Publications (3)

Publication Number Publication Date
WO2004022225A2 true WO2004022225A2 (en) 2004-03-18
WO2004022225A3 WO2004022225A3 (en) 2005-03-24
WO2004022225B1 WO2004022225B1 (en) 2005-04-28

Family

ID=31980343

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/IB2003/004244 WO2004022225A2 (en) 2002-09-09 2003-09-09 Method for converting nitrogen oxides (nox) in exhaust gases and catalyst useful for it

Country Status (1)

Country Link
WO (1) WO2004022225A2 (en)

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0864354A1 (en) * 1997-03-10 1998-09-16 Ford Global Technologies, Inc. Sulphur resistant lean-NOx catalyst for treating diesel emissions
US20020033015A1 (en) * 2000-07-28 2002-03-21 Guido Schaffner Process for denitrification of exhaust gasses, particularly for lean operated internal combustion engines
EP1323470A1 (en) * 2000-09-08 2003-07-02 Toyota Jidosha Kabushiki Kaisha Absorption/reduction type catalyst for no x? removal

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0864354A1 (en) * 1997-03-10 1998-09-16 Ford Global Technologies, Inc. Sulphur resistant lean-NOx catalyst for treating diesel emissions
US20020033015A1 (en) * 2000-07-28 2002-03-21 Guido Schaffner Process for denitrification of exhaust gasses, particularly for lean operated internal combustion engines
EP1323470A1 (en) * 2000-09-08 2003-07-02 Toyota Jidosha Kabushiki Kaisha Absorption/reduction type catalyst for no x? removal

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
A.TOUBELI ET AL.: "NO reduction by C3H6 in excess oxygen over fresh and sulfated Pt- and Rh-based catalysts" CATALYSIS LETTERS, vol. 69, 2002, pages 157-164, XP002228706 cited in the application *
H.OHTSUKA: "The selective catalytic reduction of nitrogen oxides by methane on noble metal-loaded sulfated zirconia" APPLIED CATALYSIS B: ENVIRONMENTAL, vol. 33, 2001, pages 325-333, XP002228705 cited in the application *

Also Published As

Publication number Publication date
WO2004022225B1 (en) 2005-04-28
WO2004022225A3 (en) 2005-03-24

Similar Documents

Publication Publication Date Title
EP2069052B1 (en) Catalysts to reduce nox in an exhaust gas stream and methods of preparation
CA2534806A1 (en) Catalyst arrangement and method of purifying the exhaust gas of internal combustion engines operated under lean conditions
EP1199096A1 (en) Catalyst for destruction of CO, VOC, and halogenated organic emissions
KR20190052715A (en) Catalyzed substrate and exhaust system for internal combustion engines
EP0714693A1 (en) Exhaust gas cleaner and method for cleaning exhaust gas
US5328672A (en) Method for purification of lean-burn engine exhaust gas
CN112041051B (en) Hydrocarbon trapping catalyst
EP0980707B1 (en) NOx trap catalyst for lean burn engines
WO2011117047A1 (en) Catalyst for a denox-application and a process for selective catalytic reduction of nitrogen oxides
AU2007302446A1 (en) Alkali resistant catalyst
IE63828B1 (en) New catalyst capable of being used in a process for the selective reduction of oxides of nitrogen
US6296822B1 (en) Process for manufacturing nox traps with improved sulfur tolerance
Petrov et al. Cu exchanged microporous titanium silicalite (TS-1) coated on polycrystalline mullite fibres as catalyst for the CO and NO conversion
JPH07829A (en) Non-metal catalyst system for lean-burn engine
Martin et al. Influence of support acid pretreatment on the behaviour of CoOx/γ-alumina monolithic catalysts in the CH4-SCR reaction
JPH1199319A (en) Waste gas purifying method
WO2004022225A2 (en) Method for converting nitrogen oxides (nox) in exhaust gases and catalyst useful for it
KR102073307B1 (en) NOx Adsorbent in Which Copper Oxide And Barium Oxide Are Co-Impregnated And Method of Removing NOx Using the Same
WO2023020579A1 (en) Metal oxide catalyst for selective catalytic reduction
JPH11253759A (en) Cleaning method for exhaust gas
EP0864354A1 (en) Sulphur resistant lean-NOx catalyst for treating diesel emissions
RU2784964C2 (en) Catalytic product for use in system for exhaust gas processing
KR0166465B1 (en) Preparation of catalyst for cleaning exhaust gases
JPH11114420A (en) Catalyst for cleaning exhaust gas and method
JPH1157411A (en) Cleaning method for exhaust gas

Legal Events

Date Code Title Description
AK Designated states

Kind code of ref document: A2

Designated state(s): AE AG AL AM AT AU AZ BA BB BG BR BY BZ CA CH CN CO CR CU CZ DE DK DM DZ EC EE ES FI GB GD GE GH GM HR HU ID IL IN IS JP KE KG KP KR KZ LC LK LR LS LT LU LV MA MD MG MK MN MW MX MZ NI NO NZ OM PG PH PL PT RO RU SC SD SE SG SK SL SY TJ TM TN TR TT TZ UA UG US UZ VC VN YU ZA ZM ZW

AL Designated countries for regional patents

Kind code of ref document: A2

Designated state(s): GH GM KE LS MW MZ SD SL SZ TZ UG ZM ZW AM AZ BY KG KZ MD RU TJ TM AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HU IE IT LU MC NL PT RO SE SI SK TR BF BJ CF CG CI CM GA GN GQ GW ML MR NE SN TD TG

121 Ep: the epo has been informed by wipo that ep was designated in this application
B Later publication of amended claims

Effective date: 20050127

122 Ep: pct application non-entry in european phase
NENP Non-entry into the national phase

Ref country code: JP

WWW Wipo information: withdrawn in national office

Country of ref document: JP