Pt/AlO@Ce/ZrO-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-fueled engine exhaust gas. Herein a novel bifunctional catalyst was synthesized by mechanically mixing sulfated Ce/ZrO (Ce/ZrO-S) with a small fraction of Pt/AlO (Pt 0.1 wt.%) for SCO of NH. As expected, the introduction of a small amount of Pt/AlO significantly improved NH conversion ability of Ce/ZrO-S catalysts toward low-temperature direction. When the mass ratio of Pt/AlO to Ce/ZrO-S was 7.5% (the corresponding mixed catalyst was denoted as P@CZS-7.5), T temperature was 312 °C. More importantly, P@CZS-7.5 catalyst exhibited a much better N selectivity (> 96%) in a wide temperature range (320 ~ 450 °C). H-TPR results revealed that the addition of a trace amount of Pt/AlO 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-TPD and BET results showed that P@CZS-7.5 catalyst exhibited a similar NH adsorption capacity to Ce/ZrO-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 selectivity in high-concentration NH (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-SCO reactions.