Water-gas-shift assisted ammonia formation over Pd/Ce/alumina

We report experimental results for the water-gas-shift assisted formation of ammonia from nitric oxide over alumina supported palladium, modified with various amounts (0-38 wt.%) of cerium. Static and transient flow reactor experiments were performed in order to identify the effects of temperature and the presence of oxygen on the activity for ammonia formation over the catalysts. The water-gas-shift reaction is enhanced with increasing cerium content, thus providing more hydrogen for ammonia formation. During transient operation at temperatures above 350 degrees C, a slight delay in ammonia formation is observed over the sample containing the highest cerium loading due to its (relatively) high dynamic oxygen storage capacity. At temperatures below 175 degrees C, N2O formation is preferred over NH3 formation. This work highlights the importance of balancing the effects that ceria influences when choosing the ceria loading for ammonia formation in passive-SCR applications.