Composite oxides or hydroxides comprising alumina and zirconia for automotive catalyst applications and method of manufacturing

Abstract

An improved method for the formation of composite hydroxides or oxides comprising, on an oxide basis, Al 2 O 3 and ZrO 2 , and optionally CeO 2 , La 2 O 3 , Nd 2 O 3 , Pr 6 O 11 , Sm 2 O 3 , Y 2 O 3 , and other rare earth oxides, comprising the steps of preparing an aqueous metal salt solution and forming a hydroxide precipitate slurry by combining the aqueous metal salt solution with an aqueous solution of a caustic alkali at a pH greater than 8.5 to precipitate out all the metal species. The variation in pH during the precipitation reaction is ±1. The invention also relates to composites formed by this method comprising 20-70 wt % Al 2 O 3 , 10-77 wt % ZrO 2 , 0-34 wt % CeO 2 and 0-22 wt % REOs other than CeO 2 , and to composites per se comprising, on an oxide basis, 42-70 wt % Al 2 O 3 , 10-48 wt % ZrO 2 , 2-34 wt % CeO 2 and 0-9 wt % REOs other than CeO 2 and having the following properties after heating to 850° C. over four hours and holding at 850° C. for four hours then allowing to cool to ambient temperature:—a surface area after aging at 950° C. for 2 hours equal to or greater than 60 m 2 /g, and—a surface area after aging at 1100° C. for 2 hours equal to or greater than 30 m 2 /g.

1 . A method for the formation of composite hydroxides or oxides comprising, on an oxide basis, alumina (Al 2 O 3 ) and zirconia (ZrO 2 ), comprising the following steps:
 preparing an aqueous metal salt solution consisting of the water-soluble salts of metals corresponding to those found in said composite oxide, and   forming a hydroxide precipitate slurry by combining the aqueous metal salt solution with an aqueous solution of an alkali selected from the group consisting of sodium hydroxide, potassium hydroxide, caesium hydroxide, and a mixture thereof, in a reaction vessel with agitation at a pH greater than 8.5 to precipitate out all the metal species, wherein the variation in pH during the precipitation reaction is +/−1.   
     
     
         2 . A method as claimed in  claim 1 , wherein the variation in the pH during the precipitation reaction is +/−0.5. 
     
     
         3 . A method as claimed in  claim 1 , wherein the method comprises the additional step of
 treating the hydroxide precipitate slurry at a treatment pH of between 8.0 and 10.5, at a treatment temperature of greater than or equal to 60° C., and at a treatment pressure of greater than or equal to 0.0 barg for treatment time of greater than or equal to one hour to form a treated hydroxide precipitate.   
     
     
         4 . A method as claimed in  claim 1 , wherein said aqueous metal salt solution comprises one or more reagents selected from the group consisting of: aluminum nitrate nonahydrate crystals, aqueous aluminum nitrate solution, aluminum sulfate crystals, aluminum chloride crystals, aqueous zirconyl chloride solution, aqueous zirconyl nitrate solution, aqueous zirconium sulfate solution, aqueous cerium (III) nitrate solution, aqueous praseodymium(III) nitrate solution, aqueous lanthanum nitrate solution, and aqueous samarium nitrate solution. 
     
     
         5 . A method as claimed in  claim 1 , wherein said alkali is sodium hydroxide. 
     
     
         6 . A method as claimed in  claim 1 , wherein said step of forming a hydroxide precipitate slurry comprises the following steps:
 adding said aqueous metal salt solution in a controlled manner to an aqueous solution of said alkali in a reaction vessel with agitation at a specific precipitation pH that is sufficiently basic to cause the formation of the hydroxide precipitate, and   maintaining a substantially constant precipitation pH during the addition of the said aqueous metal salt solution by adding a second stream of said alkali in a controlled manner to the reaction vessel until all the aqueous metal salt solution has been added and the precipitation reaction is complete, resulting in said hydroxide precipitate slurry.   
     
     
         7 . A method as claimed in  claim 6 , wherein said precipitation pH is greater than 8.5 but less than or equal to 10.5. 
     
     
         8 . A method as claimed in  claim 7 , wherein the precipitation pH is 10.0. 
     
     
         9 . A method as claimed in  claim 3 , wherein said step of treating the hydroxide precipitate slurry comprises the following steps:
 adding an aqueous solution of hydrogen peroxide to said hydroxide precipitate slurry,   performing a first pre-treatment wash on the hydroxide precipitate to remove anionic by-products and contaminants,   performing a second pre-treatment wash to further remove cationic by-products and contaminants from the hydroxide precipitate, and   adjusting the pH of the washed hydroxide precipitate slurry to a treatment pH of between 8.0 and 10.5 then treating the slurry at a treatment temperature of greater than or equal to 60° C., and at a treatment pressure of greater than or equal to 0.00 barg for a treatment time of greater than or equal to one hour to form said treated hydroxide precipitate.   
     
     
         10 . A method as claimed in  claim 9 , wherein said treatment pH is greater than 9.5 but less than or equal to 10.5. 
     
     
         11 . A method as claimed in  claim 9 , wherein said treatment temperature is 90° C., said treatment pressure is 0.0 barg, and said treatment time is greater than or equal to 6 hours. 
     
     
         12 . A method as claimed in  claim 9 , wherein said treatment temperature is 120° C., said treatment pressure is 1.0 barg, and said treatment time is 6 hours. 
     
     
         13 . A method as claimed in  claim 9 , wherein said treatment temperature is 143° C., said treatment pressure is 3.0 barg, and said treatment time is 5 hours. 
     
     
         14 . A method as claimed in  claim 9 , wherein said first pre-treatment wash comprises the following steps:
 adjusting the pH of the hydroxide precipitate slurry with a caustic alkali to a specific first pre-treatment wash pH that is sufficiently basic so as to facilitate the removal of sulfate anions, chloride anions, and other anionic contaminants from the hydroxide precipitate,   adjusting the first pre-treatment wash temperature of the pH-adjusted hydroxide precipitate slurry to greater than or equal to ambient temperature but less than its boiling point,   separating the by-product- and contaminant-laden liquid from the hydroxide precipitate,   preparing a rinsing solution that consists of de-ionized water or de-ionized water containing sufficient caustic alkali to bring its pH to that of said first pre-treatment wash pH,   adjusting the temperature of the rinsing solution to greater than or equal to ambient temperature but less than or equal to its boiling point,   rinsing the hydroxide precipitate with said rinsing solution, and   further washing the hydroxide precipitate with pure de-ionized water.   
     
     
         15 . A method as claimed in  claim 14 , wherein said first pre-treatment wash pH is greater than 8.5 but less than or equal to 10.5. 
     
     
         16 . (canceled) 
     
     
         17 . A method as claimed in  claim 14 , wherein said first pre-treatment pH is 10.5. 
     
     
         18 . A method as claimed in  claim 14 , wherein said pH-adjusted hydroxide precipitate slurry is heated to 60° C. 
     
     
         19 . A method as claimed in  claim 14 , wherein said rinsing solution is heated to 60° C. 
     
     
         20 . A method as claimed in  claim 14 , wherein said pure de-ionized water has been heated to a temperature greater than or equal to ambient temperature but less than or equal to its boiling point. 
     
     
         21 . (canceled) 
     
     
         22 . A method as claimed in  claim 9 , wherein said second pre-treatment wash comprises the following steps:
 adjusting the pH of the treated hydroxide precipitate slurry to a specific second pre-treatment wash pH that is sufficiently low in basicity so as to facilitate the removal of sodium cations, alkali metal cations, and other cationic contaminants from the hydroxide precipitate,   adjusting the second pre-treatment wash temperature of the pH-adjusted treated hydroxide precipitate slurry to greater than or equal to ambient temperature but less than its boiling point,   separating the by-product- and contaminant-laden liquid from the hydroxide precipitate, and   rinsing the hydroxide precipitate with de-ionized water that has had its temperature adjusted to greater than or equal to ambient temperature but less than its boiling point.   
     
     
         23 . A method as claimed in  claim 22 , wherein said second pre-treatment wash pH is greater than 5.0 but less than or equal to 8.0. 
     
     
         24 . (canceled) 
     
     
         25 . (canceled) 
     
     
         26 . A method as claimed in  claim 22 , wherein said second pre-treatment pH is 8.0. 
     
     
         27 . A method as claimed in  claim 22 , wherein said pH-adjusted hydroxide precipitate slurry has been heated to 60° C. 
     
     
         28 . A method as claimed in  claim 22 , wherein said de-ionized water has been heated to 60° C. 
     
     
         29 . A method as claimed in  claim 45 , wherein said conversion of the treated hydroxide precipitate to a hydroxide or oxide product is performed by
 drying the treated hydroxide precipitate at temperatures of up to 500° C. to remove water to form a dried composite hydroxide or oxide material, and   calcining the dried composite hydroxide or oxide material by heating it to temperatures greater than or equal to 700° C. to convert the material to a composite oxide.   
     
     
         30 . A method as claimed in  claim 29 , wherein said calcination temperature is 700° C. 
     
     
         31 . A method as claimed in  claim 29 , wherein said calcination temperature is 850° C. 
     
     
         32 . A method as claimed in  claim 46 , wherein said post-treatment of the product achieves said specific particle size distribution such that most of the particles are less than 10 microns in diameter, said post-treatment being performed using jet milling. 
     
     
         33 . A composite formed by the method of  claim 1  comprising, on an oxide basis, 20-70 wt % Al 2 O 3 , 10-77 wt % ZrO 2 , 0-34 wt % CeO 2  and 0-22 wt % REOs other than CeO 2  and having a sulfate ion content less than 0.05 percent by mass, a chloride ion content less than 200 ppm and a sodium ion content of less than 200 ppm, all on a dried oxide weight basis. 
     
     
         34 . A composite as claimed in  claim 33  comprising, on an oxide basis, 29-70 wt % Al 2 O 3  and 30-71 wt % ZrO 2 . 
     
     
         35 . A composite as claimed in  claim 33  comprising, on an oxide basis, 59-66 wt % Al 2 O 3  and 34-41 wt % ZrO 2 . 
     
     
         36 . A composite as claimed in  claim 33  comprising, on an oxide basis, 16-22 wt % La 2 O 3 , 20-27 wt % Al 2 O 3  and 54-61 wt % ZrO 2 , having a sulfate ion content less than 0.05 percent by mass, a chloride ion content less than 200 ppm and a sodium ion content of less than 200 ppm, all on a dried oxide weight basis. 
     
     
         37 . (canceled) 
     
     
         38 . (canceled) 
     
     
         39 . (canceled) 
     
     
         40 . (canceled) 
     
     
         41 . (canceled) 
     
     
         42 . (canceled) 
     
     
         43 . A composite comprising, on an oxide basis, 23-30 wt % Al 2 O 3 , and 70-77 wt % ZrO 2  and having the following properties after heating to 700° C. over four hours and holding at 700° C. for four hours then allowing to cool to ambient temperature:
 a surface area after aging at 950° C. for 2 hours equal to or greater than 59 m 2 /g, and 
 a surface area after aging at 1100° C. for 2 hours equal to or greater than 18 m 2 /g. 
 
     
     
         44 . A method as claimed in  claim 1  further including at least one member selected from the group consisting of: ceria (CeO 2 ), lanthana (La 2 O 3 ), neodymia (Nd 2 O 3 ), praseodymia (Pr 6 O 11 ), samaria (Sm 2 O 3 ), yttria (Y 2 O 3 ), and other rare earth oxides (REO). 
     
     
         45 . A method as claimed in  claim 3 , wherein said treated hydroxide precipitate is converted to a hydroxide or oxide product through a specific thermal treatment cycle or cycles. 
     
     
         46 . A method as claimed in  claim 45  wherein said hydroxide or oxide product is post-treated to achieve a specific particle size distribution. 
     
     
         47 . A method as claimed in  claim 3 , wherein the hydroxide precipitate slurry is washed with de-ionized water prior to said treatment. 
     
     
         48 . A method as claimed in  claim 9 , wherein said treated hydroxide precipitate is given a final wash to remove any remaining cationic by-products and contaminants. 
     
     
         49 . A method as claimed in  claim 3 , wherein said step of treating the hydroxide precipitate slurry comprises the following steps:
 adding an aqueous solution of hydrogen peroxide to said hydroxide precipitate slurry,   performing a first pre-treatment wash on the hydroxide precipitate to remove anionic by-products and contaminants,   adjusting the pH of the washed hydroxide precipitate slurry to a treatment pH of between 8.0 and 10.5 then treating the slurry at a treatment temperature of greater than or equal to 60° C., and at a treatment pressure of greater than or equal to 0.00 barg for a treatment time of greater than or equal to one hour to form said treated hydroxide precipitate, and   performing a final wash to remove any remaining cationic by-products and contaminants from the treated hydroxide precipitate.   
     
     
         50 . A method as claimed in  claim 49 , wherein said treatment pH is greater than 9.5 but less than or equal to 10.5. 
     
     
         51 . A method as claimed in  claim 49 , wherein said treatment temperature is 90° C., said treatment pressure is 0.0 barg, and said treatment time is greater than or equal to 6 hours. 
     
     
         52 . A method as claimed in  claim 49 , wherein said treatment temperature is 120° C., said treatment pressure is 1.0 barg, and said treatment time is 6 hours. 
     
     
         53 . A method as claimed in  claim 49 , wherein said treatment temperature is 143° C., said treatment pressure is 3.0 barg, and said treatment time is 5 hours. 
     
     
         54 . A method as claimed in  claim 3 , wherein said step of treating the hydroxide precipitate slurry comprises the following steps:
 adding an aqueous solution of hydrogen peroxide to said treated hydrogen peroxide precipitate slurry,   adjusting the pH of the hydroxide precipitate slurry to a treatment pH of between 8.0 and 10.5 then treating the slurry at a treatment temperature of greater than or equal to 60° C., and at a treatment pressure of greater than or equal to 0.00 barg for a treatment time of greater than or equal to one hour to form a treated hydroxide precipitate,   performing a post-treatment wash to remove anionic by-products and contaminants from the treated hydroxide precipitate, and   performing a final wash to remove any remaining cationic by-products and contaminants from the treated hydroxide precipitate.   
     
     
         55 . A method as claimed in  claim 54 , wherein said treatment pH is greater than 9.5 but less than or equal to 10.5. 
     
     
         56 . A method as claimed in  claim 54 , wherein said treatment temperature is 90° C., said treatment pressure is 0.0 barg, and said treatment time is greater than or equal to 6 hours. 
     
     
         57 . A method as claimed in  claim 54 , wherein said treatment temperature is 120° C., said treatment pressure is 1.0 barg, and said treatment time is 6 hours. 
     
     
         58 . A method as claimed in  claim 54 , wherein said treatment temperature is 143° C., said treatment pressure is 3.0 barg, and said treatment time is 5 hours. 
     
     
         59 . A method as claimed in  claim 49 , wherein said first pre-treatment wash comprises the following steps:
 adjusting the pH of the hydroxide precipitate slurry with a caustic alkali to a specific first pre-treatment wash pH that is sufficiently basic so as to facilitate the removal of sulfate anions, chloride anions, and other anionic contaminants from the hydroxide precipitate,   adjusting the first pre-treatment wash temperature of the pH-adjusted hydroxide precipitate slurry to greater than or equal to ambient temperature but less than its boiling point,   separating the by-product- and contaminant-laden liquid from the hydroxide precipitate,   preparing a rinsing solution that consists of de-ionized water or de-ionized water containing sufficient caustic alkali to bring its pH to that of said first pre-treatment wash pH,   adjusting the temperature of the rinsing solution to greater than or equal to ambient temperature but less than or equal to its boiling point,   rinsing the hydroxide precipitate with said rinsing solution, and   further washing the hydroxide precipitate with pure de-ionized water.   
     
     
         60 . A method as claimed in  claim 59 , wherein said first pre-treatment wash pH is greater than 8.5 but less than or equal to 10.5. 
     
     
         61 . A method as claimed in  claim 49 , wherein said first pre-treatment wash pH is 10.5. 
     
     
         62 . A method as claimed in  claim 59 , wherein said pure de-ionized water has been heated to a temperature greater than or equal to ambient temperature but less than or equal to its boiling point. 
     
     
         63 . A method as claimed in  claim 54 , wherein said post-treatment wash comprises the following steps:
 adjusting the pH of the hydroxide precipitate slurry with a caustic alkali to a specific first post-treatment wash pH that is sufficiently basic so as to facilitate the removal of sulfate anions, chloride anions, and other anionic contaminants from the hydroxide precipitate,   adjusting the post-treatment wash temperature of the pH-adjusted hydroxide precipitate slurry to greater than or equal to ambient temperature but less than its boiling point,   separating the by-product- and contaminant-laden liquid from the hydroxide precipitate,   preparing a rinsing solution that consists of de-ionized water or de-ionized water containing sufficient caustic alkali to bring its pH to that of said post-treatment wash pH,   adjusting the temperature of the rinsing solution to greater than or equal to ambient temperature but less than or equal to its boiling point,   rinsing the hydroxide precipitate with said rinsing solution, and   further washing the hydroxide precipitate with pure de-ionized water.   
     
     
         64 . A method as claimed in  claim 49 , wherein said final wash comprises the following steps:
 adjusting the pH of the treated hydroxide precipitate slurry to a specific final wash pH that is sufficiently low in basicity so as to facilitate the removal of sodium cations, alkali metal cations, and other cationic contaminants from the hydroxide precipitate,   adjusting the final wash temperature of the pH-adjusted treated hydroxide precipitate slurry to greater than or equal to ambient temperature but less than its boiling point,   separating the by-product and contaminant-laden liquid from the hydroxide precipitate, and   rinsing the hydroxide precipitate with de-ionized water that has had its temperature adjusted to greater than or equal to ambient temperature but less than its boiling point.   
     
     
         65 . A method as claimed in  claim 64 , wherein said final wash pH is greater than 5.0 but less than or equal to 8.0. 
     
     
         66 . A method as claimed in  claim 64 , wherein said final wash pH is 8.0. 
     
     
         67 . A method as claimed in  claim 54 , wherein said final wash comprises the following steps:
 adjusting the pH of the treated hydroxide precipitate slurry to a specific final wash pH that is sufficiently low in basicity so as to facilitate the removal of sodium cations, alkali metal cations, and other cationic contaminants from the hydroxide precipitate,   adjusting the final wash temperature of the pH-adjusted treated hydroxide precipitate slurry to greater than or equal to ambient temperature but less than its boiling point,   separating the by-product and contaminant-laden liquid from the hydroxide precipitate, and   rinsing the hydroxide precipitate with de-ionized water that has had its temperature adjusted to greater than or equal to ambient temperature but less than its boiling point.   
     
     
         68 . A method as claimed in  claim 45 , wherein said conversion of the treated hydroxide precipitate to a hydroxide or oxide product is performed by directly calcining the treated hydroxide precipitate slurry by heating it to temperatures greater than or equal to 700° C. to convert the material to a composite oxide.