Recent advances in catalytic DeNO(X) science and technology

Abstract

The catalytic removal of nitrogen oxide (NOx) under lean-burn conditions is one of the most important targets in catalysis research. Some lean-NOx control technologies such as the direct decomposition of NOx, NOx storage-reduction (NSR), and selective catalytic reduction (SCR) using different reducing agents (diesel soot, NH3, or hydrocarbon) are described. The reaction mechanism of NSR, which is the most promising technology, together with some novel NSR catalysts is discussed. Some mechanisms of SCR of NOx by hydrocarbon (HC-SCR) were classified into two categories: one is the adsorption/dissociation mechanism, and the other is the oxidation-reduction mechanism. Based on the discussion of the reaction mechanism, the influence of some factors ( catalyst support, metal loading, calcination temperature, catalyst preparation method, oxygen, reducing agents, water, and sulfur) on the activity of HC-SCR catalyst is discussed. It seems that Ag/Al2O3 catalyst offers the most promising for SCR of NOx by hydrocarbon due to the exciting promotion effect of H-2. Plasma or microwave assisted zeolite-based catalyst may also lead to a new approach for HC-SCR of NOx. Combinatorial catalysis, which was developed recently for discovering the practical combined catalyst quickly, also was introduced. Finally, future research directions in the area of lean-NOx is proposed.