MODIFICATIONS OF PT ALUMINA COMBUSTION CATALYSTS BY BARIUM ADDITION .1. PROPERTIES OF FRESH CATALYSTS/

Platinum was deposited onto pure alumina as well as on alumina modifie d by addition of 7 and 15 wt.-% barium. The alumina hydroxyl groups we re neutralized by barium addition and the surface of the modified supp ort had a basic character. The introduction of barium decreased the ac cessible platinum area because of a sintering of the metal particles a ssociated with a partial coverage of the platinum crystallites by bari um containing species. In addition, the platinum surface atoms were el ectron-enriched. As a consequence the catalytic activity of alumina su pported platinum was lowered in the presence of barium. Nevertheless, the turn-over numbers were not strongly modified by the barium additiv e, suggesting that the catalytic properties of accessible platinum ato ms were not sensitive to the electronic effect induced by barium addit ion.