Method for making high surface area bismuth-containing pyrochlores

Claim 1

A process for making a pyrochlore corresponding to the formula Bi 2-x M x B 2 O 7-z , wherein M is selected from the group consisting of cadmium, copper, lead, indium, gadolinium, silver and mixtures thereof, B is selected from the group consisting of ruthenium, iridium and mixtures thereof, x is from 0 to 0.5, and z is from 0 to 1, comprising the sequential steps of: (a) firing an intimate admixture of finely divided particles of BO 2 , Bi 2 O 2 CO 3 and carbonate(s) of M when x is greater than zero at a temperature between the thermal decomposition temperature of Bi 2 O 2 CO 3 and 650° C. in an oxidizing atmosphere to form a reaction product comprising Bi 2 O 3 , Bi 2-x M x B 2 O 7-z and oxide(s) of M, the mole ratio of Bi to B being at least 1.4 to 1; (b) forming a dispersion of the fired reaction product of step (a) in dilute aqueous mineral acid in an amount and for a time sufficient to dissolve substantially all the Bi 2 O 3 and, if present, oxides of M in the reaction product; and (c) separating the acid-treated reaction product of step (b) from the dispersion medium.