Boosting Ag/Al₂O₃ Catalytic Activity for NOx Removal via C₃H₆-SCR through Functional TiO₂ Support Engineering

Alumina supported silver (Ag/Al2O3) is considered as a promising catalyst for the selective catalytic reduction of nitrogen oxides with hydrocarbons (HC-SCR). However, its practical implementation remains limited by insufficient catalytic performance. Herein, we present a novel strategy to fabricate a highly efficient Ag/TiO2/Al2O3 catalyst utilizing a functional TiO2-modified AlOOH precursor. The obtained catalyst demonstrates significantly enhanced catalytic activity, durability, and stability for C3H6-SCR across a broad temperature range compared to conventional Ag/Al2O3. The incorporation of TiO2 strengthens the Ag-support interaction through facilitating electron transfer from Ag to the TiO2/Al2O3 support, leading to the formation of highly dispersed Agnδ+ clusters as the dominant active species. Mechanistic studies reveal that Agnδ+ clusters effectively accelerate the partial oxidation of C3H6 to reactive enolic species, which in turn trigger a new pathway for NOx reduction via the formation of -CN intermediates. This change in reaction mechanism induced by TiO2 modification was also confirmed by a lower activation energy barrier for NOx reduction compared to that of Ag/Al2O3. By simultaneously optimizing both the density of active sites and their intrinsic reactivity, this approach delivers a substantial enhancement in C3H6-SCR performance, offering new insights into catalyst design for hydrocarbon-SCR applications.