Pt/Al2O3@Ce/ZrO2-S bifunctional catalysts prepared by mechanically milling for selective catalytic oxidation of high-concentration ammonia
The selective catalytic oxidation (SCO) is an effective method for removing slipped high-concentration ammonia from NH 3 -fueled engine exhaust gas. Herein a novel bifunctional catalyst was synthesized by mechanically mixing sulfated Ce/ZrO 2 (Ce/ZrO 2 -S) with a small fraction of Pt/Al 2 O 3 (Pt 0.1 wt.%) for SCO of NH 3 . As expected, the introduction of a small amount of Pt/Al 2 O 3 significantly improved NH 3 conversion ability of Ce/ZrO 2 -S catalysts toward low-temperature direction. When the mass ratio of Pt/Al 2 O 3 to Ce/ZrO 2 -S was 7.5% (the corresponding mixed catalyst was denoted as P@CZS-7.5), T 90 temperature was 312 °C. More importantly, P@CZS-7.5 catalyst exhibited a much better N 2 selectivity (> 96%) in a wide temperature range (320 ~ 450 °C). H 2 -TPR results revealed that the addition of a trace amount of Pt/Al 2 O 3 significantly led to a distinct shift of reduction temperature peak toward low-temperature direction, thereby greatly improved the low-temperature redox performance of mixed catalysts. Furthermore, NH 3 -TPD and BET results showed that P@CZS-7.5 catalyst exhibited a similar NH 3 adsorption capacity to Ce/ZrO 2 -S catalyst, while the former had a relatively higher specific surface area than the latter. It was considered as a crucial factor for P@CZS-7.5 catalyst maintaining superior N 2 selectivity in high-concentration NH 3 (5000 ppm) removal processes. In situ DRIFTS results indicated that P@CZS-7.5 catalyst followed the internal selective catalytic reduction (i-SCR) mechanism in NH 3 -SCO reactions.
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