| 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. |