Methods of controlling emissions from a diesel engine are provided. The method includes contacting the emissions with a perovskite-type catalyst consisting essentially of a metal oxide composition represented by the general formula A.sub.a-xB.sub.xMO.sub.b, in which A is a mixture originally in the form of single phase mixed lanthanides collected from bastnasite; B is a divalent or monovalent cation; M is at least one element selected from the group consisting of M is at least one element selected from the group consisting of elements of an atomic number of from 22 to 30, 40 to 51, and 73 to 80; a is 1 or 2; b is 3 when a is 1 or b is 4 when a is 2; and x is a number defined by 0