Classifications

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  • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
  • C01G25/00—Compounds of zirconium
  • C01G25/02—Oxides
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  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
  • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
  • B01D53/9404—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
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  • B01D—SEPARATION
  • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
  • B01D53/34—Chemical or biological purification of waste gases
  • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
  • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
  • B01D53/9445—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]
  • B01D53/945—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC] characterised by a specific catalyst
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  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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  • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
  • B01J13/0004—Preparation of sols
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  • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
  • B01J13/0004—Preparation of sols
  • B01J13/0021—Preparation of sols containing a solid organic phase
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  • B01J13/00—Colloid chemistry, e.g. the production of colloidal materials or their solutions, not otherwise provided for; Making microcapsules or microballoons
  • B01J13/0004—Preparation of sols
  • B01J13/0047—Preparation of sols containing a metal oxide
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  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
  • B01J21/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
  • B01J21/066—Zirconium or hafnium; Oxides or hydroxides thereof
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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  • B01J2235/00—Indexing scheme associated with group B01J35/00, related to the analysis techniques used to determine the catalysts form or properties
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/002—Mixed oxides other than spinels, e.g. perovskite
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01J23/10—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of rare earths
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
  • B01J23/14—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of germanium, tin or lead
• • 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
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
  • B01J27/02—Sulfur, selenium or tellurium; Compounds thereof
  • B01J27/053—Sulfates
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  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
  • B01J35/61—Surface area
  • B01J35/613—10-100 m2/g
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  • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
  • B01J35/63—Pore volume
  • B01J35/633—Pore volume less than 0.5 ml/g
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
  • B01J35/63—Pore volume
  • B01J35/635—0.5-1.0 ml/g
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01J35/00—Catalysts, in general, characterised by their form or physical properties
  • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
  • B01J35/64—Pore diameter
  • B01J35/647—2-50 nm
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01J35/60—Catalysts, in general, characterised by their form or physical properties characterised by their surface properties or porosity
  • B01J35/64—Pore diameter
  • B01J35/651—50-500 nm
• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/0009—Use of binding agents; Moulding; Pressing; Powdering; Granulating; Addition of materials ameliorating the mechanical properties of the product catalyst
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• • B—PERFORMING OPERATIONS; TRANSPORTING
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• • B—PERFORMING OPERATIONS; TRANSPORTING
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  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B25/00—Phosphorus; Compounds thereof
  • C01B25/16—Oxyacids of phosphorus; Salts thereof
  • C01B25/26—Phosphates
  • C01B25/37—Phosphates of heavy metals
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  • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
  • C01F17/00—Compounds of rare earth metals
  • C01F17/30—Compounds containing rare earth metals and at least one element other than a rare earth metal, oxygen or hydrogen, e.g. La4S3Br6
  • C01F17/32—Compounds containing rare earth metals and at least one element other than a rare earth metal, oxygen or hydrogen, e.g. La4S3Br6 oxide or hydroxide being the only anion, e.g. NaCeO2 or MgxCayEuO
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  • C01F7/00—Compounds of aluminium
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  • C07F7/00—Compounds containing elements of Groups 4 or 14 of the Periodic Table
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
  • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES
  • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
  • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
  • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
  • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
  • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion
  • F01N3/206—Adding periodically or continuously substances to exhaust gases for promoting purification, e.g. catalytic material in liquid form, NOx reducing agents
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  • C01P2002/80—Crystal-structural characteristics defined by measured data other than those specified in group C01P2002/70
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• • C—CHEMISTRY; METALLURGY
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  • C01P2006/17—Pore diameter distribution
• • 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

• This invention relates to processes for preparing cerium-zirconium based mixed hydroxides and mixed oxides, compositions comprising zirconium hydroxide/oxide and cerium hydroxide/oxide, as well as the use of the mixed oxide in catalysis such as for treating vehicle exhaust gases.
• a catalytic converter is an emissions control device that converts toxic pollutants in exhaust gas to less toxic pollutants by catalysing a redox reaction (oxidation or reduction).
• a three-way catalytic converter has three simultaneous tasks:
• compositions comprising zirconium oxide and cerium oxide (also referred to as cerium-zirconium based mixed oxides) are known for use in TWCs.
• Such TWC materials need to have a minimum level of thermal stability, in addition to good redox properties, in order to meet legislative requirements in various countries.
• Thermal stability is normally tested by known analytical tests which demonstrate the existence and retention of a desired porous structure upon thermal ageing. This aspect is important in the area of TWCs as the retention of good dispersion of PGM on ageing is essential for the durability and activity requirements of a TWC material in an exhaust stream, especially when accelerated ageing in hydrothermal conditions are used.
• compositions for use in TWCs have good oxygen diffusion kinetics.
• a primary role of the composition for use in TWCs is to act as an oxygen storage and release material throughout the lean-rich cycling in a gasoline powered internal combustion engine.
• a composition comprising zirconium oxide and cerium oxide, this is by virtue of the variable oxidation state of the cerium cations in the zirconia lattice.
• catalysts that work more efficiently as well as under more brutal thermal conditions are desired. A large majority of emissions are released prior to the light off of the catalyst, so a catalyst that can operate at lower temperatures is interesting in the field.
• compositions for use as TWCs comprising zirconium oxide and cerium oxide, having improved thermal stability and superior oxygen diffusion characteristics have therefore been sought.
• improved interaction of the oxygen storage function and the PGM could result in maintaining a more effective dispersion of the active metal after ageing. This enhanced PGM coupling allows the potential of efficient operation over a wider range of dynamic conditions.
• Hydrogen TPR Although hydrogen is commonly used as the probe molecule, other gases or other gas mixtures can be used to investigate the Oxygen Storage behaviour of cerium and zirconium based mixed oxides. Hydrogen TPR has the advantage of being quick, cheap and widely available without large capital investment.
• Materials under test can either be as prepared, subjected to a thermal treatment or a hydrothermal treatment, and with or without a PGM (a Platinum Group Metal, ie palladium, platinum, rhodium, ruthenium, iridium and/or osmium). It is useful to know the ability of the solid to retain the OSC function after an appropriate ageing condition with PGM dispersed on the material. This will be most like the conditions in practical use. Retention of the OSC function available for catalysis after ageing being desirable.
• PGM Platinum Group Metal
• a test method such as an H 2 pulsing technique may be used. This involves taking 100mg of a powdered sample (typically 1 %Pd-loaded, but no PGM or other PGM's and loadings could be chosen). This is pre-oxidised initially by pulsing 20%O 2 /He at 100°C followed by flowing 20%O 2 /He at 500°C for 30mins. The temperature is then lowered to the desired experimental conditions (e.g. 70°C in our case) under flowing Ar. A series of 521 microlitre pulses (15 in total) of 70%H 2 /Ar are passed over the sample, and their reaction monitored by TCD.
• a powdered sample typically 1 %Pd-loaded, but no PGM or other PGM's and loadings could be chosen.
• This is pre-oxidised initially by pulsing 20%O 2 /He at 100°C followed by flowing 20%O 2 /He at 500°C for 30mins. The temperature is then lowered to the desired experimental conditions (e.g. 70
• the sample becomes 'saturated' and the amount of reaction in the first pulse is compared against this saturation limit to give a first pulse/'dynamic' OSC value.
• a low temperature and high H 2 concentration are used to stress the system.
• a series of 521 microlitre pulses (14 in total) of 20%O 2 /He are passed over the sample, and their reaction monitored by Thermal Conductivity Detector (TCD).
• TCD Thermal Conductivity Detector
• the sample becomes 'saturated' and the amount of reaction in the first pulse is compared against this saturation limit to give a first pulse/'dynamic' OSC value.
• the total OSC is calculated by summing the results of each pulse up to the point of saturation.
• a low temperature and high 0 2 concentration are used to stress the system.
• Temperature Isothermal Reduction techniques involve determination of the kinetics of reduction of a given solid metal oxide by a probe gas under isothermal conditions. This is a dynamic technique, similar to the TPR technique except the reduction kinetics are a function of time at constant temperature. At any given temperature, the kinetics of reduction of a solid is characterised by a line profile rather than by a single point in the TPR technique. It is therefore suggested that this technique is more advantageous for comparing the reduction kinetics of metal or mixed metal oxides.
• WO2014/122140 and US6171572 describe cerium-zirconium based mixed oxides and methods for preparing such materials. However, the compositions disclosed do not have the pore volume properties after ageing which are achieved with the present invention.
• the one or more complexing agents being an organic compound comprising at least one of the following functional groups: an amine, an organosulphate, a sulphonate, a hydroxyl, an ether or a carboxylic acid group,
• cerium-zirconium based mixed hydroxide (e) adding a base to form a cerium-zirconium based mixed hydroxide.
• cerium-zirconium based mixed hydroxides and oxides produced by this process are aged, especially using hydrothermal ageing conditions at high temperatures, the pore volume in the mesoporous region can be advantageously retained. This can provide two benefits: (i) to retain a pore size that minimises any gas diffusion limitations in the resulting solid; and (ii) to retain sufficient volume of pores of an appropriate size such that reduction of catalytic activity by loss of PGM dispersion is minimised.
• the zirconium salt may be zirconium basic carbonate or zirconium hydroxide.
• zirconium basic carbonate ZBC
• ZBC zirconium basic carbonate
• the aqueous acid may be hydrochloric acid, sulphuric acid, nitric acid or acetic acid, in particular the aqueous acid is nitric acid.
• the molar ratio of zirconium ions to nitrate ions in the solution or sol may be 1 :0.8 to 1 : 1.5, more particularly 1 : 1.0 to 1 :1.3.
• the term complexing agent is used to mean a ligand that bonds to zirconium.
• the complexing agent may be a carboxylic acid, a dicarboxylic acid, an alpha hydroxycarboxylic acid, an amino acid, an organosulphate or a polyol.
• the complexing agent may be a multidentate, more particularly a bidentate, ligand.
• the polyol may be a polysaccharide, for example starch.
• the complexing agent may be an alpha hydroxycarboxylic acid.
• the complexing agent generally has a polar group (ie an amine, an organosulphate, a sulphonate, a hydroxyl, an ether or a carboxylic acid group) which coordinates to zirconium, and one or more hydrocarbon groups.
• the one or more hydrocarbon groups may comprise one or more aromatic substituents, more particularly one or more phenyl substituents.
• multidentate ligands coordinate effectively to metal ions.
• the combination of different functional groups within the same molecule may be advantageous to interact with different coordination environments on the metal ion; providing both steric and electronic effects.
• complexing agents with different hydrocarbon groups may be used.
• the alpha hydroxy carboxylic acid may be an aromatic (for example, phenyl) or non-aromatic alpha hydroxycarboxylic acid, more particularly mandelic or benzillic or lactic acid.
• the solution formed may be heated.
• the solution may be heated to a temperature above 25°C, more particularly to at least 40°C, even more particularly at least 50°C, more particularly to a temperature in the range 50-70°C. More particularly, the solution may be heated to around 60°C.
• step (a) the pH of the solution may be increased (i.e., partially neutralised) by adding a base.
• a base may be sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, ammonium hydroxide, ammonium carbonate, ammonium hydrogen carbonate, potassium hydroxide, potassium carbonate, and/or potassium hydrogen carbonate.
• step (b) may additionally comprise adding water, normally deionised water, to the heated solution.
• the solution has an equivalent zirconium content of 5-25% by weight expressed as Zr0 2 , more particularly 10-20% by weight, even more particularly 12-16% by weight, expressed as Zr0 2 .
• the equivalent zirconium content expressed as Zr0 2 means that, for example, 100g of a 15% by weight solution would have the same zirconium content as 15g of Zr0 2 .
• the heating may comprise heating the solution or sol to a temperature of 60-100°C, more particularly 80-100°C, for 1-15 hours. In particular, the heating may be carried out for 1-5 hours. More particularly, in step (c) the temperature of the solution or sol may be increased at a rate of 0.1-1.5°C/min.
• the solution or sol may be allowed to cool, or cooled, before adding the sulphating agent. More particularly, the solution or sol may be allowed to cool, or cooled, to a temperature less than 40°C, even more particularly less than 30°C.
• Possible sulphating agents are water soluble salts of sulphate, bisulphate, sulphite, bisulphite. In particular, the sulphating agent may be sulphuric acid.
• the sulphating agent may be added such that the molar ratio of zirconium ions to sulphate ions is from 1 :0.05 to 1 :1
• the process may comprise the step of isolating the solid from the solution or sol, for example by filtering.
• step (d) may additionally comprise adding an aqueous electrolyte before the addition of the sulphating agent.
• the aqueous electrolyte may be added before the addition of the cerium salt.
• the aqueous electrolyte may be fully or partially neutralised hydrochloric acid, fully or partially neutralised nitric acid or fully or partially neutralised acetic acid. Partially neutralised nitric acid is also referred to as acidified sodium nitrate.
• the cerium salt may be cerium carbonate, cerium chloride, cerium nitrate (for example, cerous nitrate, eerie nitrate or a mixture thereof) or ammonium cerium nitrate.
• step (d) may additionally comprise adding one or more salts of: silica, aluminium, strontium, a transition metal (more particularly tin, niobium, tungsten, manganese and/or iron), or a rare earth element (more particularly scandium lanthanum, neodymium, praseodymium, yttrium, gadolinium and/or samarium).
• the base may be sodium hydroxide, sodium carbonate, sodium hydrogen carbonate, ammonium hydroxide, ammonium carbonate, ammonium hydrogen carbonate, potassium hydroxide, potassium carbonate and/or potassium hydrogen carbonate. More particularly, in step (e) the addition of the base is to form a cerium-zirconium based mixed hydroxide precipitate. Step (e) may be carried out at any temperature at which the solution or sol is not frozen, ie from -5°C to 95°C, more particularly, 10°C to 80°C.
• the process may comprise after step (e) the step of (f) heat treating the cerium-zirconium based mixed hydroxide.
• the heat treatment may be hydrothermal treatment.
• the hydrothermal treatment may comprise heating the solution or sol to a temperature of 80-250°C, more particularly 100-250°C, for 1-15 hours in an autoclave.
• the process may comprise the steps of isolating, for example by filtering, and/or washing the cerium-zirconium based mixed hydroxide. These steps may be carried out to remove chloride ions, sulphate ions, nitrate ions, acetate ions, sodium ions, potassium ions, ammonium ions and/or organic residue if desired. Levels of sulphate ions may be reduced to 0.3% by weight or less, more particularly 0.1 % by weight or less. Levels of sodium, potassium and chloride ions may be reduced to 0.05% by weight or less each, more particularly 0.01 % by weight or less each.
• the process may comprise after step (f), or after step (e) if step (f) is not carried out, the step of (g) drying the cerium-zirconium mixed hydroxide.
• this may be by oven-drying, spray-drying or vacuum-drying. Drying may be carried out in an oxidising, inert (eg N 2 ) or reducing atmosphere.
• the cerium-zirconium based mixed hydroxide may be dried at a temperature of 50-200°C. If a vacuum is used, the drying temperature can be at the lower end of this range. Without a vacuum, temperatures at the higher end of this range may be required, for example 100-150°C.
• the process may comprise after step (g), or after step (e) or (f) if step (f) and/or (g) is not carried out, the step of (h) calcining the cerium- zirconium mixed hydroxide to form a cerium-zirconium based mixed oxide. More particularly, the calcining step may be carried out at temperature of 500-1300°C, even more particularly 700-1 100°C. The calcining step may be carried out for 1-10 hours, more particularly 2-8hours. The calcining step may be carried out in any gaseous atmosphere. In particular, the calcining step may be carried out in a static or flowing air atmosphere, although a reductive or neutral atmosphere could be used.
• an air atmosphere is generally preferred since this can assist in removing organic species.
• a neutral atmosphere is generally defined as one which neither oxidises nor reduces the composition in that atmosphere. This can be done by removing air or removing oxygen from the atmosphere.
• a further example of a neutral atmosphere is a nitrogen atmosphere.
• the calcination atmosphere could be that of the combustion gases generated from a gas-fired kiln.
• the invention also relates to compositions obtainable by the above process.
• composition comprising zirconium oxide and cerium oxide having:
• composition has a surface area of at least 48m 2 /g after ageing at 950°C in an air atmosphere for 2 hours.
• the composition has a surface area of at least 60m 2 /g after ageing at 950°C in an air atmosphere for 2 hours, optionally at least 70m 2 /g. In some embodiments, the composition has a surface area of less than 120m 2 /g after ageing at 950°C in an air atmosphere for 2 hours.
• composition comprising zirconium oxide and cerium oxide having:
• the composition has a total pore volume as measured by N 2 physisorption of at least 0.29cm 3 /g after ageing at 950°C in an air atmosphere for 2 hours.
• the composition has a total pore volume as measured by N 2 physisorption of at least 0.37cm 3 /g after ageing at 950°C in an air atmosphere for 2 hours, optionally at least 0.41 cm 3 /g.
• the composition has a total pore volume as measured by N 2 physisorption of less than 1.0cm 3 /g after ageing at 950°C in an air atmosphere for 2 hours.
• composition has a crystallite size as measured by applying the Scherrer equation to the relevant peak in its XRD scan of no greater than 12nm after ageing at 950°C in an air atmosphere for 2 hours.
• relevant peak is the diffraction peak for zirconia in either a metastable tetragonal system or in a cubic system in the X-ray diffraction (XRD) scan.
• the composition has a crystallite size as measured by applying the Scherrer equation to the relevant peak in its XRD scan of no greater than 10nm after ageing at 950°C in an air atmosphere for 2 hours, more preferably no greater than 9.5nm.
• the composition has a surface area of at least 42m 2 /g after ageing at 1000°C in an air atmosphere for 4 hours.
• the composition has a surface area of at least 50m 2 /g after ageing at 1000°C in an air atmosphere for 4 hours, optionally at least 60m 2 /g.
• the composition has a surface area of less than 120m 2 /g after ageing at 1000°C in an air atmosphere for 4 hours.
• the composition has a total pore volume as measured by N 2 physisorption of at least 0.31 cm 3 /g after ageing at 1000°C in an air atmosphere for 4 hours.
• the composition has a total pore volume as measured by N 2 physisorption of at least 0.35cm 3 /g after ageing at 1000°C in an air atmosphere for 4 hours, optionally at least 0.40cm 3 /g, and in some embodiments at least 0.45cm 3 /g.
• the composition has a total pore volume as measured by N 2 physisorption of less than 1.0cm 3 /g after ageing at 1000°C in an air atmosphere for 4 hours.
• composition comprising zirconium oxide and cerium oxide having:
• composition has a crystallite size as measured by applying the Scherrer equation to the relevant peak in its XRD scan of no greater than 14nm after ageing at 1000°C in an air atmosphere for 4 hours.
• the composition has a crystallite size as measured by applying the Scherrer equation to the relevant peak in its XRD scan of no greater than 1 1 nm after ageing at 1000°C in an air atmosphere for 4 hours, in some embodiments no greater than 10nm.
• a composition comprising zirconium oxide and cerium oxide having:
• composition has a surface area of at least 33m 2 /g after ageing at 1050°C in an air atmosphere for 2 hours. In some embodiments, the composition has a surface area of less than 120m 2 /g after ageing at 1050°C in an air atmosphere for 2 hours.
• the composition has a surface area of at least 38m 2 /g after ageing at 1050°C in an air atmosphere for 2 hours, optionally at least 40m 2 /g.
• composition comprising zirconium oxide and cerium oxide having:
• composition has a total pore volume as measured by N 2 physisorption of at least 0.20cm 3 /g after ageing at 1050°C in an air atmosphere for 2 hours. In some embodiments, the composition has a total pore volume as measured by N 2 physisorption of less than 1.0cm 3 /g after ageing at 1050°C in an air atmosphere for 2 hours.
• the composition has a total pore volume as measured by N 2 physisorption of at least 0.25cm 3 /g after ageing at 1050°C in an air atmosphere for 2 hours, optionally at least 0.28cm 3 /g.
• composition comprising zirconium oxide and cerium oxide having:
• composition comprising zirconium oxide and cerium oxide having:
• the composition has a surface area of at least 18m 2 /g after ageing at 1 100°C in an air atmosphere for 6 hours. In some embodiments, the composition has a surface area of less than 120m 2 /g after ageing at 1100°C in an air atmosphere for 6 hours. [0057] It is preferred that the composition has a surface area of at least 20m 2 /g after ageing at 1100°C in an air atmosphere for 6 hours, in some embodiments at least 23m 2 /g, optionally at least 25m 2 /g.
• composition comprising zirconium oxide and cerium oxide having:
• composition has a total pore volume as measured by N 2 physisorption of at least 0.1 1 cm 3 /g after ageing at 1 100°C in an air atmosphere for 6 hours. In some embodiments, the composition has a total pore volume as measured by N 2 physisorption of less than 1.0cm 3 /g after ageing at 1 100°C in an air atmosphere for 6 hours. [0059] In some embodiments, the composition has a total pore volume as measured by N 2 physisorption of at least 0.14cm 3 /g after ageing at 1100°C in an air atmosphere for 6 hours, optionally at least 0.17cm 3 /g. [0060] According to a thirteenth aspect of the invention, and/or in combination with the compositional features defined above, there is provided a composition comprising zirconium oxide and cerium oxide having:
• composition has a crystallite size as measured by applying the Scherrer equation to the relevant peak in its XRD scan of no greater than 26nm after ageing at 1100°C in an air atmosphere for 6 hours.
• composition comprising zirconium oxide and cerium oxide having:
• the composition has a surface area of at least 19m 2 /g after hydrothermal ageing at 1 100°C for 12 hours in an air atmosphere comprising 10% by weight of volume, optionally at least 20m 2 /g.
• composition comprising zirconium oxide and cerium oxide having:
• composition has a total pore volume as measured by N 2 physisorption of at least 0.11 cm 3 /g after hydrothermal ageing at 1 100°C for 12 hours in an air atmosphere comprising 10% by volume of water.
• composition has total pore volume as measured by N 2 physisorption of less than 1.0cm 3 /g after ageing at 1100°C for 12 hours in an air atmosphere comprising 10% by volume of water.
• the composition has a total pore volume as measured by N 2 physisorption of at least 0.13cm 3 /g after hydrothermal ageing at 1 100°C for 12 hours in an air atmosphere comprising 10% by volume of water, optionally at least 0.15cm 3 /g.
• composition comprising zirconium oxide and cerium oxide having:
• composition comprising zirconium oxide and cerium oxide having:
• composition has a Dynamic-Oxygen Storage Capacity (D-OSC) value as measured by H 2 -TIR of greater than ⁇ at 600°C after ageing at 800°C in an air atmosphere for 2 hours.
• D-OSC Dynamic-Oxygen Storage Capacity
• the composition has D-OSC value as measured by H 2 -TIR of less than ⁇ / ⁇ at 600°C after ageing at 800°C in an air atmosphere for 2 hours.
• the composition has a D-OSC value as measured by H 2 - TIR of greater than 875 ⁇ at 700°C after ageing at 800°C in an air atmosphere for 2 hours, more preferably greater than ⁇ at 800°C.
• increase in the average pore diameter of the composition as measured by N 2 physisorption after hydrothermal ageing at 1 100°C for 12 hours in an air atmosphere comprising 10% by volume of water is no greater than 30%, more preferably no greater than 10%.
• composition comprising zirconium oxide and cerium oxide having:
• the composition comprises 3-7% by weight, preferably about 5% by weight, of praseodymium oxide and 3-7% by weight, preferably about 5% by weight, of lanthanum oxide.
• the composition may also comprise one or more of tin oxide, niobium oxide, tungsten oxide, silica and iron oxide.
• the total amount of rare earth oxides other than cerium oxide is preferably less than 30% by weight. In some embodiments, the total amount of rare earth oxides other than cerium oxide is less than 20% by weight, optionally less than 15% by weight.
• compositions defined herein, or made by the process defined above comprise 5-50% by weight of cerium oxide, more preferably 10-50% by weight cerium oxide, even more preferably 20-45% by weight, in some embodiments about 40% by weight cerium oxide.
• compositions derived herein, or made by the process defined above comprise at least 20% by weight of zirconium oxide, more preferably at least 30% by weight.
• the total amount of cerium oxide and zirconium oxide is at least 80% by weight, more preferably at least 85% by weight.
• compositions defined herein, or made by the process defined above generally comprise hafnium oxide (hafnia) as an impurity. This is normally derived from the material which is used as the source of zirconium. The amount of hafnia generally depends on the level of zirconium, but is normally less than 2% by weight, and often less than 1 % by weight.
• compositions defined herein, or made by the process defined above comprise less than 0.3% by weight of S0 4 , preferably less than 0.2% by weight, more preferably less than 0.1 % by weight.
• An upper limit of 0.1 % by weight is acceptable for most uses, although the S0 4 content can be further reduced by repeating the relevant washing steps of the preparative method described below.
• the compositions defined herein, or made by the process defined above preferably comprise incidental impurities (ie those not deliberately added) in an amount of up to 0.5% by weight.
• incidental impurities does not include, for example, carbonate, sulphate or nitrate ions since these may be deliberately added.
• compositions defined herein, or made by the process defined above comprise less than 0.10% by weight of CI, preferably less than 0.05% by weight, more preferably less than 0.02% by weight.
• An upper limit of 0.02% by weight is acceptable for most uses, although the CI content can be further reduced by repeating the relevant washing steps of the preparative method described below.
• compositions defined herein, or made by the process defined above comprise less than 250ppm of Na or K, preferably less than 200ppm, more preferably less than 125ppm.
• An upper limit of 125ppm is acceptable for most uses, although the sodium or potassium content can be further reduced by repeating the relevant washing steps of the preparative method described below.
• the compositions defined herein, or made by the process defined above may include up to 5% by weight of a platinum group metal, normally up to 2% by weight, in some embodiments around 1 % by weight of a platinum group metal (PGM).
• PGMs platinum group metal
• the PGMs are palladium, platinum, rhodium, ruthenium, iridium and/or osmium. Palladium, rhodium and platinum and the most commonly used PGMs. These metals are normally added into the composition as an aqueous solution, normally in a formulation with other components, coated onto a monolith and then calcined.
• one type of diffraction peak for zirconia in either a tetragonal system or in a cubic system is observed on an XRD scan.
• step (a) it is preferred that the nitrate to zirconium molar ratio is less than 1.6.
• Step (b) is carried out in order to ensure optimum polymer/oligomer size for mesoporous powder preparation.
• the thermal treatment normally comprises heating the solution to a temperature above room temperature.
• the process may comprise the optional step of adding surfactants or organic templating molecules such as polyols, amino acids, a-hydroxy acids, carbohydrate polymers, and/or sulphate derivatives to the solution.
• step (c) the solution is preferably cooled to below 40°C.
• the bi/polydentate ligand may be phosphate, nitrate or sulphate, or a mixture thereof.
• soluble solutions comprising rare earth metals other than cerium can be added. This is in order to provide a mixed zirconium-rare earth dispersion with intimate mixing of the zirconium and rare earth elements.
• zirconium oxychloride can also be used.
• the base can be either ammonium hydroxide or an alkali metal hydroxide, preferably sodium hydroxide.
• ammonium hydroxide the maximum pH that can be achieved is normally about pH 10.
• alkali metal hydroxides the pH can be adjusted to pH 1 1-13 or higher.
• Hydrogen peroxide may also be added to the precipitate (ie after step (f) or before the addition of base (ie before step (f)).
• the precipitate optionally may be heated to 50°C minimum, for 30 minutes to 24 hours.
• the process may comprise a further step of filtering and/ or washing the precipitate. This is done in order to remove impurity ions such as sodium, potassium, sulphate, phosphate and/or nitrate.
• Alkali metal ions may be removed by an additional step of reslurrying the washed precipitate cake and adding a mineral acid.
• the mineral acid is preferably nitric acid from about 10% to 60% by weight concentration.
• the pH of the solution is generally adjusted to a pH less than 9, preferably adjusted to between pH 7-9.
• the process may comprise the optional step of redispersing the precipitate in an aqueous medium and heating the resulting dispersed slurry or wet cake to between 100°C and 350°C, preferably between 100°C to 200°C. This can be in a sealed reaction vessel such as an autoclave or up to 100°C in an open vessel.
• Calcining is preferably carried out at 800-1000°C for 2-4 hours, more preferably at around 920°C for around 3 hours.
• the solid can be milled.
• the process for treating comprises one of more of (a) reduction of nitrogen oxides to nitrogen, (b) oxidation of carbon monoxide to carbon dioxide, and (c) oxidation of hydrocarbons, in the exhaust gas. In some embodiments, the process for treating comprises (a) reduction of nitrogen oxides to nitrogen, (b) oxidation of carbon monoxide to carbon dioxide, and (c) oxidation of hydrocarbons, in the exhaust gas.
• the invention also relates to a diesel oxidation catalyst, a NO x trap, a passive NO x absorber, a gasoline particulate filter coating or a lean NO x trap comprising the composition as defined herein, or made by the processes defined above.
• Figure 1 shows air aged (1 100°C/6hr) porosity data for the compositions of Preparative Examples6, 9 and 11-14,
• Figure 3 shows air aged (1 100°C/6hr) incremental pore volume data for the compositions of Preparative Examples 6, 9 and 1 1-14,
• Figure 4 shows H 2 pulse data for Preparative Examples 3, 5 and 8 and Comparative Example 1 ,
• Comparative Example 1 - 40Ce/5La/5Pr A sample was prepared according to the composition defined above, i.e. 40% by weight cerium (IV) oxide, 5% by weight lanthanum oxide, 5% by weight praseodymium oxide and the remainder (i.e. -50% by weight) zirconium dioxide. [0097] 1 18.8g of zirconium basic carbonate (ZBC, 42.1 %Zr0 2 ) was dissolved in 126.9g of nitric acid. This solution was then heated to 60°C. 1 19.5g of water was then added. In this example, a complexing agent was not added to the solution. This solution was then heated to boiling and boiled for 2 hours.
• ZBC zirconium basic carbonate
• the resulting slurry was then filtered.
• the filter cake was washed with deionised water at 60°C.
• the cake was then re-dispersed and then adjusted to pH 8.0 with a 30wt% solution of nitric acid.
• the resulting slurry was then filtered.
• the filter cake was washed with deionised water at 60°C.
• the final filter cake was heated in an autoclave to 127°C for 1 hour.
• the resulting suspension was then filtered and the resulting filter cake was calcined in air for 3 hours at 930°C, and milled, to give a cerium-zirconium based mixed oxide.
• Preparative Example 2 - 40Ce/5La/5Pr A sample was prepared according to the composition defined above, i.e. 40% by weight cerium (IV) oxide, 5% by weight lanthanum oxide, 5% by weight praseodymium oxide and the remainder (i.e. -50% by weight) zirconium dioxide. [00104] 1 19.9g of zirconium basic carbonate (ZBC, 41.7%Zr0 2 ) was dissolved in 126.9g of nitric acid. This solution was then heated to 60°C. 3.0g of soluble starch was added to the solution, along with 108.0g of water. This solution was then heated to boiling and boiled for 2 hours.
• ZBC zirconium basic carbonate
• the final filter cake was calcined in air for 2 hours at 850°C and then milled.
• a sample was prepared according to the composition defined above, i.e. 40% by weight cerium (IV) oxide, 5% by weight lanthanum oxide, 5% by weight praseodymium oxide and the remainder (i.e. -50% by weight) zirconium dioxide.
• a sample was prepared according to the composition defined above, i.e. 40% by weight cerium (IV) oxide, 5% by weight lanthanum oxide, 5% by weight praseodymium oxide and the remainder (i.e. -50% by weight) zirconium dioxide.
• a sample was prepared according to the composition defined above, i.e. 40% by weight cerium (IV) oxide, 5% by weight lanthanum oxide, 5% by weight praseodymium oxide and the remainder (i.e. -50% by weight) zirconium dioxide.
• the resulting slurry was then filtered.
• the filter cake was washed with deionised water at 60°C.
• the cake was then re-dispersed and then adjusted to pH 8.0 with a 30wt% solution of nitric acid.
• the resulting slurry was then filtered.
• the filter cake was washed with deionised water at 60°C.
• the precipitate was hydrothermally treated at 127°C for 1 hour.
• the resulting suspension was then dried at 1 10°C in a static air oven and calcined in air for 2 hours at 800°C and milled.
• a sample was prepared according to the composition defined above, i.e. 40% by weight cerium (IV) oxide, 5% by weight lanthanum oxide, 5% by weight praseodymium oxide and the remainder (i.e. -50% by weight) zirconium dioxide.
• the sample was prepared according to patent EP1444036B1 (ie no complexing agent).
• a sample was prepared according to the composition defined above, i.e. 40% by weight cerium (IV) oxide, 5% by weight lanthanum oxide, 5% by weight praseodymium oxide and the remainder (i.e. -50% by weight) zirconium dioxide.
• a zirconium basic sulphate precursor was prepared according to the following reference [S.M. Flask, I. A. Sheka, "Interaction of zirconium oxychloride and sulfuric acid in aqueous solution", Russ. J. Inorg .Chem. 1969, 17 (1), 60-65].
• Preparative Example 11 - 45Ce/5La/5Y A sample was prepared according to the composition defined above, i.e. 45% by weight cerium (IV) oxide, 5% by weight lanthanum oxide, 5% by weight yttrium oxide and the remainder (i.e. -45% by weight) zirconium dioxide.
• 109.0g of zirconium basic carbonate (ZBC, 41.3%Zr0 2 ) was dissolved in 107.4g of nitric acid. This solution was then heated to 60°C. 0.83g of mandelic acid was added to the solution, along with 104.2g of water. This solution was then heated to boiling and boiled for 2 hours.
• a sample was prepared according to the composition defined above, i.e. 35.5% by weight cerium (IV) oxide, 5.5% by weight lanthanum oxide and the remainder (i.e. -59% by weight) zirconium dioxide.
• a sample was prepared according to the composition defined above, i.e. 25% by weight cerium (IV) oxide, 3.5% by weight lanthanum oxide, 4% by weight yttrium oxide and the remainder (i.e. -67.5% by weight) zirconium dioxide.
• a sample was prepared according to the composition defined above, i.e. 20% by weight cerium (IV) oxide, 1.5% by weight lanthanum oxide, 5% by weight neodymium oxide and the remainder (i.e. -73.5% by weight) zirconium dioxide.

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