Promotional effect of titanium on the catalytic performance of anodic alumina supported silver catalyst for the selective reduction of NO with propene

A series of anodic alumina supported silver/titanium catalysts (Ag/Ti/Al2O3) were synthesized to in-vestigate the effect of Ti on the selective catalytic reduction of NO with propene. In the low temperature region, the SCR activity was greatly enhanced on Ag/Ti/Al₂O₃ compared to Ag/Al₂O₃, and this promotion became more significant with increasing Ti loading. Adding Ti to an anodic alumina support did not cause obvious improvement of activity, indicating that the presence of Ti acted as a catalytic promoter of Ag, but did not directly participate in the SCR reaction. The result of NOx-TPD in flowing He showed that no obvious difference in the desorption performance of ads-NOx species was found between Ag/Al₂O₃ and Ag/Ti/Al₂O₃. However, in flowing O₂/C₃H₆/He the desorption peak of nitrate species was decreased by about 50°C when Ti was present. The promoted partial oxidation of the reduc-ing agent was believed to be a main reason. The result of H2-TPR suggested that besides Ag+ ion and metallic Ag another type of silver existed in Ag/Ti/Al₂O₃, possibly a moderately agglomerated Agnδ+ cluster. Additionally, in comparison with the SO2-aged Ag/Al₂O₃ catalyst, the SO₂-aged Ag/Ti/Al₂O₃ catalyst provided a favorable tolerance to SO2 poisoning, and led to higher activity. A relatively lower SO₂ ad-sorption amount and a faster reduction rate of sulfate species by propene were considered to be a reason-able interpretation.