NOx trap catalyst support material composition

A method of preparing a support material composition, the composition comprising two phases:

• a first phase comprising a Mg/Al mixed oxide;
• and
• a second phase comprising a cerium based oxide, and rare-earth element(s) based oxide other than cerium oxide, wherein the second phase is a solid-solution;
• the method comprising the following steps:
• i) preparing an aqueous suspension of a Mg/Al mixed oxide precursor;
• ii) preparing an aqueous solution of a cerium salt;
• iii) preparing an aqueous solution of one or more rare-earth element salt(s) other than cerium salt;
• iv) combining, in any order, at least the aqueous suspension in step i), with the aqueous solution in step ii), and the aqueous solution of step iii) to form an aqueous mixture;
• v) dying the aqueous mixture to form a dried particulate material;
• and
• vi) calcining the dried particulate material;
• wherein the content of the one or more rare-earth element salt(s) other than cerium salt is between 5 and 50 wt. %, relative to the sum of
• the cerium salt from the aqueous solution of step ii) and
• the one or more rare earth element salt(s) other than cerium salt from the aqueous solution of step iii) and,
• wherein each of the salts are calculated as their oxides.