Boosting Ag/Al₂O₃ Catalytic Activity for NO_x 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 Ag_n^δ+ clusters as the dominant active species. Mechanistic studies reveal that Ag_n^δ+ clusters effectively accelerate the partial oxidation of C₃H₆ to reactive enolic species, which in turn trigger a new pathway for NO_x 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 NO_x 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.