Ammonia formation from nitric oxide over Pd-based catalysts in multicomponent feed gas compositions

Journal article, 2017

Using multicomponent gas feeds, the formation of ammonia from nitric oxide over Pd/Al2O3 and Pd/Ce/Al2O3 model catalysts was compared to that of a commercially-available three-way catalyst. Steady- state oxygen-sweep experiments show that the highest activity for ammonia formation is obtained over the Pd/Ce/Al2O3 catalyst whilst the lowest activity is observed for the three-way catalyst. The latter is consid- ered to be linked to the incorporation of rhodium, a component that promotes the NOx reduction selectivity towards N2. Also, lean/rich cycling experiments were carried out to simulate the cycling conditions that passive-SCR after treatment systems depend upon. High activity is again seen over the Pd/Ce/Al2O3 cata- lyst during short periodic switches. For the three-way catalyst, longer periodic switches are required for the onset of ammonia formation due to the high oxygen storage capacity of this sample as compared to the other two. Hence, a future direction of investigation could be to develop materials with equivalent water- gas shift properties of ceria, but with reduced oxygen storage capacity so as to provide hydrogen for reaction without incurring a significant delay in ammonia formation.