Catalytic Performance, Characterization, and Mechanism Study of Fe2(SO4)3/TiO2 Catalyst for Selective Catalytic Reduction of NOx by Ammonia

Iron oxides supported on TiO 2 catalysts show good activity in selective catalytic reduction (SCR) of NOx by ammonia. In this work, Fe 2 (SO 4 ) 3 /TiO 2 and other catalysts containing iron and sulfates were prepared by the impregnation method, and their activities for SCR of NOx by ammonia were investigated. On Fe 2 (SO 4 ) 3 /TiO 2 catalyst, NOx conversion reached 98.0% in the temperature range of 350−450 °C, while yielding little N 2 O. Characterization results showed that α-Fe 2 O 3 and sulfates were mainly formed on the Fe 2 (SO 4 ) 3 /TiO 2 catalyst. Iron oxide catalysts with sulfates [e.g., Fe 2 (SO 4 ) 3 /TiO 2 ] caused more dispersed iron phase, and the sulfation effect might have mostly occurred on iron oxides but not TiO 2 . In contrast, Fe(NO 3 ) 3 precursor supported on TiO 2 without sulfates led to the Fe 2 O 3 particle products, which physically connected to the surface of TiO 2 and resulted in some agglomerations or heterogeneous distribution of Fe 2 O 3 particles. In addition, sulfates played an important role in the SCR reactions, which were responsible for strong Brönsted acid sites. The SCR reaction mechanism on Fe 2 (SO 4 ) 3 /TiO 2 might have taken place as follows: NH 3 was adsorbed onto the surface of Fe 2 (SO 4 ) 3 /TiO 2 and mainly formed NH 4 + on Brönsted acid sites. NO was oxidized to NO 2 by the oxygen in the reaction gas or on the iron oxide sites of the catalyst. Then, nitrates originated from NO 2 were generated on Fe 2 (SO 4 ) 3 /TiO 2 catalyst for NH 3 −SCR reaction. Finally, an active intermediate species like ammonium nitrite was formed, which eventually decomposed to gaseous nitrogen.