Impact of PtO x formation in diesel oxidation catalyst on NO 2 yield during driving cycles

Insight into the Nature of Active Species of Pt/Al2O3 Catalysts for low Temperature NH3 Oxidation

“…The presented operando XANES data demonstrate that in the case of highly dispersed Pt particles the stabilization of PtO x species on the platinum surface takes place in the whole temperature range of interest up to 400 °C (Figure ). Similar behavior was established during mathematical simulations of Pt‐based diesel oxidation catalysts under lean conditions . The surface coverage of PtO x was found to vary from 0.3 to 0.8 depending on the reaction temperature.…”

“…Furthermore, we can observe that the steady‐state value of the average Pt oxidation state is close to +0.9±0.2. In the case of Pt‐N‐400 catalyst, this value was not reached during the first and the second heating‐cooling cycles due to the low rate of Pt oxidation/reduction …”

“…It was claimed that deactivation of Pt/Al 2 O 3 in the catalytic NH 3 oxidation occurs at temperatures below 130°C due to the accumulation of NH x species on the Pt surface while adsorbed oxygen species cause deactivation at higher temperatures. [57,66] The surface coverage of PtO x was found to vary from 0.3 to 0.8 depending on the reaction temperature. Similar behavior was established during mathematical simulations of Pt-based diesel oxidation catalysts under lean conditions.…”

“…[20] The presented operando XANES data demonstrate that in the case of highly dispersed Pt particles the stabilization of PtO x species on the platinum surface takes place in the whole temperature range of interest up to 400°C (Figure 11). [57] In the case of NH 3 oxidation the best catalytic performance is attributed to metallic Pt species providing sites for NH 3 and O 2 adsorption followed by ammonia activation. [57,66] The surface coverage of PtO x was found to vary from 0.3 to 0.8 depending on the reaction temperature.…”

“…A similar but less pronounced trend is observed for the second heating of the Pt-N-400 sample in the reaction mixture (Figure 11b). [57,58] During the operando XANES study the N 2 , N 2 O, and NO x formation trends were similar for the Pt-N-400 and Pt-400-250H catalysts and, hence, independent on the average oxidation state of Pt. Due to the high NH 3 conversion at high temperature, the NH 3 concentration in the gas phase is not sufficient to remove surface oxygen causing Pt oxidation.…”