An environmentally benign Cu–Ce–Ti oxide catalyst exhibited excellent NH₃-SCR activity, high N₂ selectivity and strong resistance against H₂O and SO₂ with a broad operation temperature window. The dual redox cycles (Cu²⁺ + Ce³⁺ ↔ Cu⁺ + Ce⁴⁺, Cu²⁺ + Ti³⁺ ↔ Cu⁺ + Ti⁴⁺) play key roles for the superior catalytic deNO_x performance.

Selective catalytic reduction of NO_x by hydrogen (H₂-SCR) in the presence of oxygen has received much attention as a potential technology for reducing NO_x emissions. A lot of research has been done in order to understand the reaction mechanism of H₂-SCR and some possible mechanisms have been proposed. These mechanisms can be classified into two categories: NO adsorption/dissociation mechanisms and oxidation–reduction mechanisms. Based on the discussion of the reaction mechanism, the influence of the nature of the noble metal, catalyst support, catalyst preparation method, promoters and reaction conditions (including the presence of H₂ and O₂, water, sulfur, CO and CO₂) on the catalytic performance of some H₂-SCR catalysts has been discussed. Finally, future research directions in the area of H₂-SCR have been proposed.

The redox cycle (Ce⁴⁺ + Fe²⁺ ↔ Ce³⁺ + Fe³⁺) over the Fe–Ce–Ti catalyst contributes to the activation of NO_x and NH₃ and thus the formation of reaction intermediates, leading to the high catalytic performance for the NH₃-SCR of NO_x.

Both the CO poisoning problem on the anode and the slow oxygen reduction reaction kinetics on the cathode lead to significantly decreased output power and energy utilization efficiency and remain main obstacles hindering commercialization of proton-exchange membrane fuel cells (PEMFCs). A promising means to mitigate CO poisoning and to improve the oxidation reduction reaction (ORR) activity is through the use of platinum alloy catalysts. This article reviews recent developments in Pt alloy catalyst utilization and addresses activity comparisons and the relationship between activity and structure characteristics. The mechanisms for improved CO-tolerance and ORR activity are also discussed. Finally, theoretical studies on Pt alloy catalysts are discussed briefly.