Revealing the Dynamic Behavior of Active Sites on Acid-Functionalized CeO 2 Catalysts for NO x Reduction.

Unraveling the dynamics of the active sites upon CeO 2 -based catalysts in selective catalytic reduction of nitrogen oxides by ammonia (NH 3 -SCR) is challenging. In this work, we prepared tungsten-acidified and sulfated CeO 2 catalysts and used operando spectroscopy to reveal the dynamics of acid sites and redox sites on catalysts during NH 3 -SCR reaction. We found that both Lewis and Brønsted acid sites are needed to participate in the catalytic reaction. Notably, Brønsted acid sites are the main active sites after a tungsten-acidified or sulfated treatment, and the change of Brønsted acid sites significantly affects the NO x removal. Moreover, acid functionalization promotes the cerium species cycle between Ce 4+ and Ce 3+ for the NO x reduction. This work is critical to deeply understanding the natural properties of active sites, and it also provides new insights into the mechanism for NH 3 -SCR over CeO 2 -based catalysts.