450 u00b0 c the engine speed was then reduced to allow the engine temperature to stabilize at about 300 u00b0 c after the temperature stabilized fuel was injected into the exhaust system before the scr catalyst to raise the temperature after the csf to about 450 u00b0 c after maintaining the temperature after the csf constant for about 15 minutes the addition of fuel into the exhaust system was stopped and the temperature was allow to return to about 300 u00b0 c the temperatures at the inlet to the scr and the outlets from the asc doc and csf were measured these temperature are shown in fig1 18 for the reference contain pt only the catalyst with 18 g ft 3 of pgm with a 1 5 pt pd loading and the catalyst with 18 g ft 3 of pgm with a 2 1 pt pd loading respectively fig1 shows that the use of a catalyst containing only pt as the pgm resulted in the outlet temperature at the asc reaching a maximum of about 350 u00b0 c at about 1250 sec then dropping to about 300 u00b0 c by about 1600 sec however in both systems using a combination of pt and pd the outlet temperature at the asc reached a maximum of about 390 u00b0 c at about 1250 sec and the temperature remained at about 390 u00b0 c until about 2200 sec indicating that both of these catalysts generated an exotherm this stable exotherm was not observed in the reference catalyst containing only pt as the pgm this demonstrates that when using an scr before an asc the scr did not generate.