Strikingly distinctive NH3-SCR behavior over Cu-SSZ-13 in the presence of NO2
Yulong Shan, Guangzhi He, Jinpeng Du, Yu Sun, Zhongqi Liu, Yu Fu, Fudong Liu, Xiaoyan Shi, Yunbo Yu, Hong He
Abstract
Abstract Commercial Cu-exchanged small-pore SSZ-13 (Cu-SSZ-13) zeolite catalysts are highly active for the standard selective catalytic reduction (SCR) of NO with NH 3 . However, their activity is unexpectedly inhibited in the presence of NO 2 at low temperatures. This is strikingly distinct from the NO 2 -accelerated NO x conversion over other typical SCR catalyst systems. Here, we combine kinetic experiments, in situ X-ray absorption spectroscopy, and density functional theory (DFT) calculations to obtain direct evidence that under reaction conditions, strong oxidation by NO 2 forces Cu ions to exist mainly as Cu II species (fw-Cu 2+ and NH 3 -solvated Cu II with high CNs), which impedes the mobility of Cu species. The SCR reaction occurring at these Cu II sites with weak mobility shows a higher energy barrier than that of the standard SCR reaction on dynamic binuclear sites. Moreover, the NO 2 -involved SCR reaction tends to occur at the Brønsted acid sites (BASs) rather than the Cu II sites. This work clearly explains the strikingly distinctive selective catalytic behavior in this zeolite system.